chapter 2. nuclear magnetic resonance spectroscopy

2 Nuclear Magnetic Resonance Spectroscopy

By G . A. WEBB

Department of Chemistry, University of Surrey, Guildford, GU2 5XH

1 Introduction It is an ineluctable fact that NMR acts as an alembic for many areas of molecular science. Evidence for this can be found in the expansion of the annual volume of literature relating to NMR spectroscopy. Consequently, the present report, in addition to being rather eclectic, follows the canon adopted in previous reports in this series.I4 The emphasis given here being in the direction of the more physical aspects of molecular investigations.

Annual accounts of all chemically related aspects of NMR appear in the Specialist Periodical Reports on NMR.’ These accounts provide extensive reference to the primary literature together with lists of books, reviews, and symposia proceedings which furnish a method of keeping in touch with the various developments in the NMR technique and its applications.

The present report, exceptis excipiendis, attempts to cover some of the more significant recent advances and to include a few key references. A glossary of abbreviations used is given on page 43.

2 Instrumental Aspects of NMR An attempt is made to concentrate on a few areas in which progress is being made. In particular those relating to pulse sequences, multi-dimensional NMR, and NMR imaging. A dictionary of concepts in NMR contains some interesting instrumental entries.6

A new book on 2D NMR has appeared which provides some explanations and practical guides for chemists in the processes of 2D NMR and in the analysis of the data produced.’ Some recent examples of Overhauser and exchange experiments are

‘ G. A. Webb, Annu. Rep. Prog. Chem., Sect. C, Phys. Chem., 1980, 77, 121. ‘ G. A. Webb, Annu. Rep. Prog. Chem., Sec,t. C , Phys. Chem., 1983, 80, 39. G. A. Webb, Annu. Rep. Prog. Chem., Seci. C, Pliys. Chem., 1985, 82, 3. G. A. Webb, Annu. Rep. Prog. Chem., Sect. C , Phys. Chem., 1988, 85, 3. ‘Nuclear Magnetic Resonance’, ed. G. A. Webb (Specialist Periodical Reports), The Royal Society of Chemistry, Cambridge 1990. Vol. 19; 1991, Vol. 20. S. W. Homans, ‘A Dictionary of Concepts in NMR’, Clarendon Press, Oxford, 1989.

VCH Publishers. ’ G. E. Martin and A. S. Zektzar, ‘2D NMR Methods for Establishing Molecular Connectivities’, 1988,

3

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25

. View Article Online / Journal Homepage / Table of Contents for this issue

http://dx.doi.org/10.1039/pc9908700003

http://pubs.rsc.org/en/journals/journal/PC

http://pubs.rsc.org/en/journals/journal/PC?issueid=PC1990_87_0

4 G . A . Webb

Figure 1 A tfamily tree’ showing how various pulse shaping functions (a) through (c) were used to

(Reproduced with permission from J . Magn. Reson., 1989, 85, 416) breed a new shaped selective pulse (f)

discussed in a book which gives a reasonably clear insight into the subject.’ Darwin’s ideas have been applied to magnetic resonance’ and have resulted in the production of a new shaped selective pulse as shown in Figure 1.

The basic principles of magnetic resonance imaging (MRI) have been reviewed and recent advances discussed in a number of High speed MRI methods have shown continued development. In particular FLASH (fast low angle shot)” and EPI (echo planar imaging)18 have attracted much attention.

’ D. Neuhaus and M. P. Williamson, “The NOE in Structural and Conformational Analysis’, 1989, VCH

lo J. M. Listerud, S. W. Sinton, and G. B. Drobny, A n d . Chem., 1989, 61, 23A. ‘ I J. M. S . Hutchinson and M. A. Foster, ‘Practical NMR Imaging’, 1987, IRL Press, Oxford. I * E. R. Andrew, Can. Assoc. Rdial J. , 1990, 41, 19. l 3 I . C. P. Smith, Clin. Biochem., 1989, 22, 69. l 4 B. Vaughan, Australas. Radiol., 1989, 33, 390. l 5 D. D. Browne, P. E. Ellsworth, and J. P. Hornack, J . Chem. Educ., 1989, 66, 647. l 6 R. H. Posteraro, R. A. Blinder, and R. J. Herfkens, Comput. Med. Imag. Graph., 1989, 13, 393.

Publishers. X. L. Wu and R. Freeman, J . Magn. Reson., 1989, 85, 414.

A. Haase, Magn. Reson. Med., 1990, 13, 77. R. J. Ordidge, A. Howseman, R. Coxon, R. Turner, B. Chapmen, P. Glover, M. Stehling, and P. Mansfield, Mugn. Reson. Men., 1989, 10, 227.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25

. View Article Online

http://dx.doi.org/10.1039/pc9908700003

Nuclear Magnetic Resonance Spectroscopy 5

Table 1 Refocused solvent suppression sequence Pulse No.

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

Flip angle" 7.09 5.26

- 7.61 - 53.75

53.75 7.6 1

- 5.26 - 7.09

5.53 6.03

- 11.70 - 34.26 - 72.46 - 138.57

138.57 72.46 34.26 1 1.70 - 6.03 - 5.53

Delay 0.183 0.158 0.198 0.191 0.198 0.158 0.183 A 0.174 0.37 1 0.183 0. I82 0.172 0.163 0.172 0.182 0.183 0.37 1 0.174 0.635 + A

"Flip angles of pulses are given in degrees, with 180" phase shifts denoted by negative angles.

+

0 250 500 750 1000 1250H,

Figure 2 Comparison between theoretical prediction (solid line) and observed absorption mode signal (+ ) for a doped chloroform sample with (upper trace) the sequence of Table 1 and (lower trace) the refocused JR sequence with T = 3 3 0 ~ s . Only positive offsets from resonance are shown; the excitation spectrum is antisymmetric about zero frequency. In both cases deviations from pure phase remained less than 10" through the range of offsets studied

(Reproduced with permission from J . Magn. Reson., 1989, 81, 643)

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

6 G. A . Webb

Pulse Sequences. - Efforts continue to be made to design satisfactory solvent suppression pulses. Computer generated least squares optimization has been used to derive pulse sequences giving a satisfactory excitation profile.'9320 The refocussed solvent suppression sequence used is given in Table 1.19 In Figure 2 a comparison is shown between the signal predicted as a function of offset and that measured experi- mentally for a 5 mm chloroform sample doped with tris-acetylacetonate. The upper trace relates to the sequence given in Table 1 and the lower trace to the refocussed jump return (JR) sequence. It is suggested that the main problem of binomial pulses is in the production of frequency dependent phase shifts which appear in the spectrum as lineshape distortions, baseline roll, and diminished resolution.2' A new family of hard pulses is introduced which combine spin locking and solvent frequency selec- tivity together with a non-selective hard pulse.22 The pulse schemes proposed are shown in Figure 3.22 The desired spectrum is produced by processing either the signal generated by scheme A or the difference signal between those generated by schemes A and B. The proposed solvent suppression sequence is demonstrated to provide (a) a pure absorption mode NMR spectrum, (b) good excitation spectra with efficient solvent signal suppression, (c) a variable flip angle, and (d) easy rf adjustment.

A composite binomial pulse sequence has been suggested for solvent suppression which gives minimal distortion in signal amplitude and phase.23 The procedure is based on the phase shifted JR pulse sequence using only hard pulses.

A solvent suppression procedure for incorporation into heteronuclear inverse experiments has been described.24 The method employs spin-lock purging pulses to suppress the water proton magnetization during the application of heteronuclear

Figure 3 Scheme of the dijerence technique for the solvent signal suppression involving solvent resonance presaturation. The signal delivering the j n a l spectrum is achieved by sub- tracting the signal generated by scheme (b) from the signal generated by scheme (a). G denotes t h e j e l d gradient pulse along the y axis (the axis of sample rotation). The frequency selective and ,frequency nonselective rf pulses are denoted by (s) and (ns) respectively. The typical time intervals used are, z = 1 ms, z2 = z ms, z3 = 1 ms, z4 = lops

(Reproduced with permission from J. Magn. Reson., 1989, 82, 266)

l 9 G. A. Morris. A. C. T. Silveston, and J. C. Waterton, J . Mugn. Reson., 1989, 81, 641. lo G. A. Morris, A. C. T. Silveston, and J . C . Waterton, J . Mugn. Reson., 1989, 82, 97. 21 Z. Starcuk, L. Pucek, R. Fiala, and Z . Starcuk, J . Mugn. Reson., 1988, 80, 344. -* Z. Starcuk, R. Fiala. F. Bartusek, and Z . Starcuk. J . Mcign. Reson., 1989, 82. 265. l3 A. L. Davies and S. Wimperis, J . Mugn. Rrson., 1989, 84, 620. 24 B. A. Messerle, G. Wider, G. Otting, C . Weber, and K. Wuthrich, J . Mugn. Reson., 1989, 85, 608.

77

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


Figure 4 (a) Soft pulse; a single weak pulse of duration T = 9At (b) A 10-pulse DANTE sequence with intervals of At (c) DANTE sequence of 9 pulses with initial andJInaI intervals of At12 s


pulses and thus requires neither solvent presaturation nor selective excitation. The water magnetization is randomized by the rf field inhomogeneity of the spin lock pulse while the magnetization of the X-bonded proton is retained.

A continuous sequence of pulses of differing flip angle and phase is known as a composite pulse. Composite pulses are often described as either broadbond or narrowbond with respect to the r.f. field strength. An account has been given of the production of both broadbond and narrowbond composite 90' excitation sequences.25 Refocussed chirped pulses for broadband excitation without phase distortion are useful when large bandwidths are encountered such as at very high applied magnetic fields or in the presence of paramagnetic centres.26

The DANTE pulse sequence has been compared to a single soft rectangular pulse of the same total duration and overall flip angle.27 A finely digitized DANTE sequence is indistinguishable from a soft pulse. However, errors may be produced by a coarsely digitized DANTE sequence which may result in positive displacement of the baseline together with an oscillatory contribution, These errors may be removed by a DANTE sequence in which the first and last pulses are halved in amplitude. This point is illustrated in Figure 4 where a rectangular soft pulse with various DANTE sequences is pre~ented.~' A double DANTE pulse scheme has been proposed for the simul- taneous selective excitation of two different frequencies.*' The requisite excitation frequency difference is produced by increasing the phase of the pulses, by regular steps, in one sequence while the phase of the second pulse sequence is held constant. A double DANTE pulse sequence28 is shown in Figure 5 and its application2' to the proton spectrum of 2,3-dibromopropanoic acid is given in Figure 6.

In the 2D INADEQUATE experiment, the effect of finite r.f. strength in a single pulse has been noted.29 Widespread use of this technique has been prevented by weak

'' S. Wimperis. J . Mugn. Reson.. 1990, 86, 46. 26 J. M . Bohlen, M. Rey, and G . Bodenhausen, J . Mugn. Reson., 1989, 84, 191. '' X. L. Wu, P. Xu, J. Friedrich, and R. Freeman, J . Mugn. Reson.. 1989. 81, 206.

H. Green, X. L. Wu. J. Friedrich. and R. Freeman, J . Mugn. Reson., 1989, 81, 646. 29 J. Lambert, H. J. Kuhn, and J. Buddrus, Angew. Chem., Int. Ed. Engf., 1989, 28, 738.

28

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

8

T I 2 d2 2/2

G. A . Webb

d2 d2

Figure 5 Double D A N T E pulse sequence with even numbered pulses rotating in phase. A pulse about the f X axis is represented by a zero phase angle. The fixed phase and rotating phase sequences are both about the + X axis oft = 0, the start of the data acquisition

(Reproduced with permission from J . Magn. Reson., 1989. , 81, 647)

intensity and amplitude distortion of signals at the double quantum frequencies. The replacement of single pulses by composite pulses, in the basic INADEQUATE sequence, can lead to a three fold sensitivity improvement together with attenuated amplitude distortion.

A new type of selective excitation sequence has been described which is based upon difference ~ p e c t r o s c o p y . ~ ~ ~ ~ ~ The given sequence does not require any pulse shaping in order to obtain a frequency domain excitation pattern. A revised range of r.f. pulse envelopes for selective inversion and in-phase excitation has been presented.32 Super-

I

Figure 6 Experimental test ofthe double-DANTE sequence on the proton spectrum of 2,3-dibromo acid (a). The two outer lines ofthe central multiplet have been excited in trace (b). The unwanted excitations are shown ampliJied ten .fold in trace (c)


30 X. Ping, X. L. Wu, and R. Freeman, J . Magn. Reson., 1989, 84, 198. 31 X. L. Wu, X. Ping, and R. Freeman, J . Magn. Reson., 1989, 83, 404. 32 L. Emsley and G . Bodenhausen, Chem. Phys. Lett., 1990, 165, 469.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


positions of three or four time shifted Gaussian pulses, with optimized width and peak amplitude, produce the envelope functions.

There is much interest in the use of spin decoupling in NMR experiments both for spectral simplification and for sensitivity enhancement. Two new homonuclear pulse sequences have been suggested which combine frequency band selective and nonselective pulses for spin decoupling in the first frequency domain of 2D correlation and cross relaxation spectra.33 Both methods rely on the use of the pulse sequence 9OSoft-1 80hard-r in order to refocus the magnetization.

The half Gaussian pulse is advantageous for semiselective excitation in that it does not create a significant amount of anti-phase component^.^^ This is a particular asset in experiments where the semi selective excitation pulse is followed by a mixing of in phase components.

A soft NOESY experiment has been used to observe NOE's between amide protons in proteins.35 Since the solvent signal is only minimally excited this procedure allows NOESY spectra to be recorded with short mixing times. In addition, cross peaks close to the diagonal are more readily detected by this procedure. Individual transition probabilities may also be determined from the soft NOESY e ~ p e r i m e n t . ~ ~

Structure determinations based upon NMR measurements often depend upon having reliable scalar coupling data. Some of the problems associated with the accurate determination of scalar couplings may be overcome by means of suitable pulse sequence^.^? An example is provided by the use of the 'HL"N HMQC pulse sequence with proton detection, the ensuing spectrum containing the homonuclear scalar coupling information for a protein. A successful comparison is made between the protein structure as determined from the scalar couplings and by X-ray d i f f ra~t ion .~~

Much conformational information is contained in long range heteronuclear spin couplings. These can be difficult to measure accurately in some cases although the use of stable isotope labelling techniques can be of assistance. Two techniques for measuring long range 15N--'H couplings have been described.39940 The soft H, C-COSY experiment, using selective excitation in the ' H domain, is suggested as a means of determining 3J (I3C--'H) value^.^' Two experiments are suggested, the soft H,C-COSY with selective pulses and the inverse soft H,C-COSY with a selective pulse on both ' H and I3C. A multiplet pattern is produced similar to that obtained from the E-COSY technique.

Gaussian shaped pulses have been used to excite carbonyl resonances in order to obtain long range carbonyl carbon-proton couplings.42 In another development some simple modifications have been proposed to the heteronuclear 2D J resolved experiment with a DEPT sequence which is followed by a semi selective spin inversion to improve ~ens i t iv i ty .~~ The technique appears to be favourable for the determination of long range I3C--'H couplings. 33 R. Bruschweiler, C. Griesinger, 0. W. Sorensen, and R. R. Ernst, J . Mugn. Reson., 1988, 78, 178. 34 H. Kessler, U. Anders, G. Gemmecker, and S. Steuernagel, J . Magn. Reson., 1989, 85, 1. 35 H. Oschkinat, G. M. Clore, and A. M. Gronenborn, J . Mugn. Reson., 1988, 78, 371. 36 H. Oschkinat and W. Bermel, J . Magn. Reson., 1989, 81, 220. '' L. E. Kay and A. Bax, J . Mugn. Reson., 1990, 86, 110. 38 L. E. Kay, B. Brooks, S. W. Sparks, D. A. Torchia, and A. Bax, J . Am. Chem. Soc., 1989, 111, 5488. 39 G. T. Montelione, M. E. Winkler, P. Ravenbiihler, and G . Wagner, J . Mugn. Reson., 1989, 82, 198. 40 G. T. Montelione and G. Wagner, J . Am. Chem. SOC., 1989, 111, 5474. 4' H. Kessler, U. Anders, and G. Gemmecker, J . Mugn. Reson., 1988, 78, 382. 42 W. Bermel, K. Wagner, and C. Griesinger, J . Magn. Reson., 1989, 83, 223. 43 D. Uhrin, T. Liptaj, H. Hricovini, and P. Capek, J . Mugn. Reson., 1989, 85, 137.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

10 G. A . Webb

A selective inverse correlation procedure with a selective X nucleus 90" pulse in a one dimensional inverse detection experiment has been described.4 The magnetization transfer pulse of the standard HMQC one dimensional experiment is replaced with a frequency selective Gaussian shaped pulse which transfers the X nucleus magnetization to the proton concerned.

Techniques have been suggested for performing spin locking experiments on older NMR facilities. In one such approach only one rf source is used to perform rotating frame experiments. This is analogous to using the decoupler for all In another development a second rf circuit is electronically switched, very rapidly, to produce the rf field for solvent presaturation during spin locked experiment^.^^

With the continued development of new NMR techniques greater demands are placed on spectrometer performance. Instrumental imperfections have been considered and methods for determining pulse phase and amplitude reproducibility p r e ~ e n t e d . ~ ~ . ~ ~ Finite pulse intensity and the delay between excitation and acquisition are very common spectrometer imperfections which give rise to frequency dependent phase shifts. A recent proposal for dealing with the phase error is to employ a 90" pulse off-resonance which induces a phase error which is essentially a linear function of resonance offset over a wide range of f req~encies .~~ Consequently, the original phase error is compensated for by means of a 'reversed rotation pulse' [90° ( - X)]-' in place of a 90" (X) p ~ l s e . ~ '

Two closely related, sinusoidally modulated, rf pulses have been described which may compensate for bandwidth imperfections of composite pulses due to off- resonance effect^.".^' The time domain representations of the amplitude modulated rf pulses used are shown in Figure 7."

0.5 1

Time Time

Figure 7 Time domain representation of amplitude modulated rf pulses. Time scale is in units of 271. Over this time scale a pulse of amplitude 1 corresponds to a 271 pulse on resonance. (a) 90" point-to-point multfrequency pulse and associated squaredpulse. (b) 90" uniform propagator multfrequency pulse and associated squared pulse. (c) 180" point-to-point mult frequency pulse and associated squared pulse. (d) 180" uniform propagator multi- frequency pulse and associated squared pulse.


44 S. Berger, J . M a p . Reson., 1989, 81, 361. 45 G. Esposito, W. A. Gibbons, and R. Bazzo, J . Magn. Reson., 1988, 80, 523. 46 R. W. Dykstra and A. J . Wand, J . Magn. Reson., 1988, 79, 163. 47 G. A. Morris, J . Magn. Reson., 1988, 78, 281. 48 G. A. Morris, J . M a p . Reson., 1988, 80, 547. 49 R. Freeman, J. Friedrich, and X. L. Wu, J . Magn. Reson.. 1988, 79, 561. 50 D. B. Zax, G. Goelman, and S. Vega, J . M a p . Rcsson., 1988, 80, 375. 5' G. Goelman, S. Vega, and D. B. Zax. J . Magn. Reson., 1989, 81, 423.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

Nuclear Magnetic Resonance Spectroscopy 1 1

Multidimensional NMR. - A major restriction on the use of multidimensional NMR is the large amount of time required for data acquisition. For complicated molecules the 2D NMR data matrices become very large such that transformation times are enhanced and the time required for an experiment may become unacceptably long.

It has been suggested that multiple resonance techniques may be considered as an alternative to 2D NMR.52,53 In an attempt to reduce the data acquisition time required for a COSY spectrum a truncated COSY experiment has been suggested in which only a few F1 data points are collected.54 In order to reduce the amount of spectrometer time required for a given experiment Fourier analysis may be used to extract differing coherence transfer pathways from the same data ZQ, SQ, DQ, TQ, and 4Q,2D NMR spectra, with and without decoupling in the F, domain, may be reconstructed from a single time domain data set. This saves spectrometer time and permits the production of a series of complementary spectra under identical conditions.

A variety of rotating frame high resolution 2D NMR experiments are used for the study of molecular structure and dynamics. Magnetization transfer in the rotating frame may occur via scalar coupling, e.g. HOHAHA and TOCSY experiments or via dipole-dipole relaxation or chemical exchange, e.g. in the CAMELSPIN or ROESY experiments. Cases may occur where magnetization transfer by scalar, dipolar, or

n Al

I I I I 1 I i I I I I

5-4 5-0 4.6 4-2 3-8 3-4 PPM

Figure 8 Cross correlation in o, through the diagonal resonance of the A1 hydrogen for three phase sensitive 2D NMR experiments performed on the same 15% (wlv) heparin sample in 'H,O. For all of the experiments 128t, increments and 512t2 data points were recorded on a Varian VXR-500 Spectrometer. For each t, increment 32 were recorded leading to an experimental time of 6 h for each experiment. The rfjield strength was 8 KHz,for all pulses and the duration of the spin lock was 50 ms in each experiment. Cross peaks to the A1 diagonal peak are labeled. (a) HOHAHA with continuous wave spin lock. (b) HOHAHA with MLEV-17 spin lock. (c) Compensated HOHAHA using the pulse sequence shown in Figure 9 with m = 4, n = 6. This corresponds to 75 ms of spin lock ,follo~ied by 1 I .2 ms of laboratory frame cross relaxation


'* R. Freeman, J . Friedrich, and S. Davies, Mugn. Reson. Chem., 1988, 26, 903. 53 J. Friedrich, S. Davies, and R. Freeman, Mol. Phys., 1988, 64, 691. 54 L. McIntyre, X. L. Wu, and R. Freeman, J . Magn. Reson., 1990, 87. 194. 5 5 R. Ramachandran, P. Darba, and L. R. Brown, J . Magn. Reson., 1988, 81, 538.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

12 G. A . Webb

n times

Figure 9 Compensated HOHAHA pulse sequence. A 16 step phase cycle was used. This contains the following subcycles (a) suppression of odd quantum order terms after the second 90" pulse by concurrent (0", 180") cycling of 44 and +R; (b) suppression of axialpeaks by (0", 180") cycling of +2 and +4; and (c) suppression of undesired multiple quantum terms by (0", 90", 180°, 270") cycling of +4 and +R. The 180" pulse is a 90"-180"-90" composite. Quadrature in t, is obtained by recording a second experiment with the phases of +2 to $4 incremented by 90"


chemical exchange interactions proceed simultaneously. Thus, attempts have been made to select a particular mechanism of magnetization transfer in the rotating frame.

Techniques to eliminate cross relaxation contributions in HOHAHA and TOCSY experiments on macromolecules have been p r ~ p o s e d . ~ ~ , ~ ' Some HOHAHA spectra of heparin are shown in Figure 8. The compensated HOHAHA spectrum given in Figure 8(c) was obtained using the pulse sequence given in Figure 9.j6 The problem of scalar coupled and 'false' NOE cross peak suppression in CAMELSPIN experiments has also been c ~ n s i d e r e d . ~ ~ Additionally, a means of suppressing the HOHAHA mechanism has been reported such that ROESY spectra may be interpreted without ambiguity.

Selective excitation of a single, arbitrarily chosen, signal can be used to provide a means of subspectrum extraction to produce a simplified 2D COSY spectrum.59 Another approach to simplifying correlation spectra is to 'home in' on multiplets of interest using shaped pulses.60 In this way it is possible to apply selective inversion pulses to passive spins and thus to modify the multiplet structures and obtain coupling networks.

It is necessary to optimize the length of the isotropic mixing periods for the spin systems of interest in TOCSY experiments on amino acid and nucleic acid spin systems.61 A combined relayed NOESY and TOCSY set of experiments has been proposed.52 In the relayed NOESY component of the sequence, part of the mixing period acts as the acquisition time of the TOCSY experiment.

A proposal has been made for sorting out spin topologies,63 this involves combining the J modulated spin echo technique with both the TOCSY and the HMQC pulse sequences. A method for the automated elucidation of J connectivities in ' H NMR spectra has been proposed.64 The procedure consists of automation routines to link pattern recognition techniques used to locate cross peaks in 2D NMR spectra, with the determination of sequence specific resonance assignments from lists of NOE's and identified spin systems. An example of the application of this procedure is given in Figure lo.@

56 D. W. Bearden, S. Macura, and L. R. Brown, J . Magn. Reson., 1988, 80, 534. '' C. Griesinger, G. Otting, K. Wiithrich, and R. R. Ernst, J . Am. Chem. Sac., 1988, 110, 7870. '* J. Cavanagh and J. Keeler, J . Magn. Reson., 1988, 80, 186. 59 X. Ping, X. L. Wu, and R. Freeman, J . Magn. Reson., 199, 86, 426. 6o L. Emsley, P. Huber, and G. Bodenhausen, Angew. Chew., In(. Ed. Engl., 1990, 29, 517. 6' J. Cavanagh, W. J. Chazin, and M . Rance, J. Magn. Reson., 1990, 87, 110. 6i J. Cavanagh and M. Rance, J . Magn. Reson., 1990, 87, 408. 63 D. G. Davis, J . Mugn. Reson., 1989, 82, 640. 64 P. L. Weber, J . A. Malikayil, and L. Miiller, J . Magn. Reson., 1989, 82, 419.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


PPm PPm

Figure 10 Bottom: expanded region of the DQE-COSY spectrum of AL73 ubiquitin 8mM in 20mM ammonium acetate-d, bufler, pH 4.8, 90% H,O. Top: expanded region of DQF-RELAY spectrum. Both spectra were recorded at 50°C at 500 MHz proton frequency (Tm = 30ms in DQF-RELAY)


Due to the requirements of large amounts of spectrometer time, computing capa- bilities, and data storage space, 3D NMR methods have not yet become popular. Reviews have appeared which relate to the principles and the design of experimental techniques necessary for 3D NMR spectroscopy.65*66

In general, the dimensionality of a spectrum tends to increase with the complexity of the sample system being studied. Thus, reports of 4D NMR experiments have appeared for use on complicated biological system^.^^^^*

Heteronuclear 3D NM R experiments are composed of the corresponding heteronuclear MQ correlation experiment together with COSY, HOHAHA, or NOESY. The heteronuclear editing pulse may or s ~ c c e e d ~ * . ’ ~ the homonuclear magnetization transfer pulse sequence. This difference results in different information

b6 S. W. Fesik and E. R. P. Zuiderweg, Quart. Rev. Biophys., 1990, 23, 97. 6’ L. E. Kay, G. M. Clare, A. Bax, and A. Gronenborn, Science, 1990, 249, 41 1. 68 S. W. Fesik, H. L. Eaton, E. T. Olejniczak, and R. T. Gampe, J . Am. Chem. Soc., 1990, 112, 5370. 69 S. W. Fesik and E. R. P. Zuiderweg, J . Magn. Reson., 1988, 78, 588. 70 E. R. P. Zuiderweg and S . W. Fesik, Biochem., 1989, 28, 2387. 7’ S. W. Fesik, R. T. Gampe, E. R. P. Zuiderweg, W. E. Kohlbrenner, and D. Weigl, Biochem. Res.

’‘ D. Marian, L. E. Kay, S . W. Sparks, D. A. Torchia, and A. Bax, J . Am. Chem. Soc., 1989, 111, 1515.

C . Griesinger, 0. W. Sorensen, and R. R. Ernst, J . Magn. Reson., 1989, 84, 14. 65

Commun., 1989, 159, 842.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

14 G . A . Webb

Figure 11 An illustration of a 3D NMR spectrum (centre) with its three orthogonal projections (A, B, C ) . For two spin systems (shaded block and unshaded) with identicai amide- proton shift, cross peaks in each of the projections are connected by thin lines to the corresponding volume elements in the 3D experiment. The stippled and grey shaded cross peaks correspond to two other spin systems with identical nitrogen shifts, but diferent amide proton shifts


being represented on a given one of the three axes concerned. In the first case the signals of the X nucleus appear in the F1 dimension, the signals of the attached protons in F2, and the homonuclear coupled proton partners in F, . In the second case the same data sets appear in the F2, F,, and F, dimensions respectively.

The use of an automated 3D sorting process has been suggested as a way of analysing the various cross peaks in a 3D data set.73 An illustration of a 3D NMR spectrum and its three orthogonal projections is given in Figure 11 .73 The question of water signal suppression in 3D NMR systems, with rapidly exchanging amide protons, has been ~onsidered.'~ In another development a SUPERCOSY experiment has been devised to produce a 3D homonuclear J-resolved and correlated spectrum.75

NMR Imaging. -The educational aspects of NMR imaging have been presented in a number of publications. These include accounts of the basic principles and some app~ications.~~-"

A modified SENEX sequence, suitable for single or multi slice operation, has been used to map magnetic fields." By means of markers, produced by periodic non excitation of the spins, a method of assessing image quality and susceptibility effects has been developed.81 The timing protocol of the two pulse SENEX spin echo sequence is shown in Figure 12.*' The application of the sequence to a relexation phantom, containing vessels with different amounts of gadolinium DTPA, is shown in Figure 13.

It has been demonstrated that square excitation profiles of selective pulses are

73 P. L. Weber and L. Muller, J . Mugn. Reson., 1989, 81, 430. 74 H. Oschkinat, C. Ciesler, A. M. Gronenborn, and G. M. Clore, J . Mugn. Reson., 1989, 81, 212. 7 5 R. E. Hoffman and D. B. Davies, J . Mugn. Reson., 1988, 80, 377. 76 D. S. Browne, P. E. Ellsworth, and J. P. Harnack, J . Chem. Educ., 1989, 66, 647. 77 R. H. Posteraro, R. A. Blinder, and R. J. Herfkens, Computer. Med. Imug. Graph., 1989, 13, 393 78 V. J. Weedon, R. E. Wendt, and H. J. Jerosch, Mugn. Reson. Med. , 1989, 11, 114. 79 J. P. Chesick, J . Chem. Educ., 1989, 66, 283. 8o J. A. Malko and R. C. Nelson, Invest. Radio!., 1989, 24, 927. *' M. Braun, W. 1. Jung, 0. Lutz, and R. Oeschey, Z . Nururforsch, Ted A , 1988, 43, 291.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


Figure 12 Timing protocol of the whole two pulse SENEX spin echo sequence,for magnetic field

(Reproduced with permission from 2. Naturforsch., Teil A, 1988, 43, 292) imaging

Figure 13 Two pulse SENEX sequence applied to a relaxation phantom containing vessels with different amounts of GdDTPA. The characteristics of the frequency selective excitation are visible as contour plots superimposed on the NM R image. Clearly the image plus the magnetic field behaviour, changed by the object itself, can be recorded. Slice thickness 10 mm, matrix size: 256 x 256, measuring time 4.27 min, frequency difference between two dark structures: 32 Hz which corresponds to 0.5 ppm

(Reproduced with permission from Z . Naturforsch., Teil A , 1988, 43, 296)

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

16 G. A . Webb

Figure 14 Rapid FLASH NMR images (2.35T) as a function offrip angle. The transaxial cross sections of the forearm of a normal volunteer are recorded within a measuring time of about 4 s using TR = 30 ms and a spatial resolution of 128 x 256 complex data points (interpolated to 256'for display). The slice thickness is 5 mm. The frip angle increases ,from about 15" (a) to about 90" (f) in steps of 15"


important for high speed FLASH sequences.82 Both the approach to equilibrium and the saturation behaviour of the spin system are influenced by the excitation profile. The influence of flip angle on a FLASH image is shown for a cross section of a human forearm in Figure 14.82 The use of Gaussian pulses with 270" flip angle has been demonstrated to produce a non-linear phase error following e x ~ i t a t i o n . ~ ~ The self- refocussing thus produced could be useful in applications of magnetic resonance

82 W. Hiinicke, K . P. Merboldt, and J. Frahm, J . Mugn. Reson., 1988, 77, 64. L. Emsley and G. Bodenhausen, J. Mngn. Reson., 1989, 82, 21 1 .

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


imaging to investigations of particular slices. In another development, it has been shown that soft 270” pulses are useful for minimizing phase roll.84

A variation of the EPI procedure has been reported which removes the need for good gradient waveform^.^^ An improved image contrast in neurological studies has been obtained by the inclusion of an inversion pulse in the EPI technique.86 However, this also produces a time penalty. Magnetic field inhomogeneity and resolution problems in EPI have been considered in the light of ‘zoom’ imaging of an easily skimmed localized volume by means of STEAM-EP1.87 The established stimulated echo technique has enabled single shot localization and 0.5 mm resolution of chosen areas of a cat brain of 4.7T.

The quantification of lipid levels in tissue has been achieved by means of the relative dephasing of the water and lipid signals.88 Chemical shift artefacts, due mainly to the displaced lipid image, may be removed via deconvolution of the NMR spectrum of the sample.*’ Unfortunately, the success of the method appears to depend upon all of the resonances having the same spatial distribution. Thus its applications to clinical problems are likely to be limited.

Various clinical and animal imaging studies require the observation of more than one nucleus without disturbing the subject. This situation may now be achieved by the improved design and versatility of radiofrequency coils. Such developments include slotted tube r e s o n a t o r ~ , ~ ~ ~ ” solenoidal r e s o n a t o r ~ , ~ ~ 23Na/1H double tuned probe^,'^ a quadrature tuned set of ”P birdcage coils coupled to a ’H Alderman-Grant and low inductance 23Na/31P cylindrical window probes for studies of the developing heart.95

By applying a field gradient, which is incremental for successive free induction decays, a slice selection procedure has been developed for solid^.'^ This method has the advantage that the applied field amplitude need only be of the order of the linewidth, although the gradients may correspond to offsets which are much larger. A variant of refocussed gradient imaging has been reported in which the direction of the effective Hamiltonian is periodically reversed. This has the effect of removing the influences of homonuclear dipolar coupling and inhomogeneous broadening, without detracting from the imaging capability of the applied field gradients.97

In another recent development, switched array coils are used to allow the operator to make a choice between enhanced signal-to-noise ratio and field of view. The modus operand involves using suitable switches to select the current path within a conductor array, thus a large sample area may be covered by electronically shifting the sensitive

84 F. Loaiza, M. A. McCoy, S. L. Hammes, and W. S. Warren, J . Mugn. Reson., 1988, 77, 173. 85 D. A. Feinberg, R. Turner, P. D. Jakob, and M. Von Kienlin, Magn. Reson. Men., 1990, 13, 162. 86 M. K. Stehling, R. J. Ordidge, R. Coxon, and R. Mansfield, Magn. Reson. Med., 1990, 13, 514.

*’ A. Leroy-Willig, 1. Idy-Peretti, and A. M. Laval-Jeautet, J . Med. Nucl. Bioplijs., 1988, 12, 49. 89 D. G. Cory, A. M. Reichwein, and W. S. Veeman, J . Mugn. Reson., 1988, 80, 259. 90 R. Griitter, C. Bosch, M . Muri, E. Martin, and K. Wutrich, Mugn. Reson. Med., 1990, 15, 128. 9’ E. J. Nijhof, Mugn. Reson. fmag., 1990, 8, 345. 92 D. Bollan, M. C. Graham, S . Miodownik, and J. A. Koutcher, Magn. Reson. Imag., 1989, 7, 155. 93 S. J. Blackband, L. Constantinidis, K. A. McGovern, and J. S. Schoniger, J . Mugn. Reson., 1989,82, 139. 94 K. Derby, J. Tropp, and C . Hawryszko, J . Magn. Reson., 1990, 86. 645. 95 G. J. Kast, S. E. Anderson, G. B. Matison, and C. B. Conboy, J . Mugn. Reson., 1989, 82, 238. 96 M. Conti, F. Borsa, and A. Rigamonti, J . Magn. Reson., 1988, 79, 21. 9’ J. B. Miller and A. N. Garroway, J . Magn. Reson., 1989, 82, 529.

R. Turner, M. Von Kienlin, C. T. Moonen, and P. C. Van ZijI, Mugn. Reson. Med., 1990, 14, 401. 87

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

G . A . Webb

region.98 The use of implanted coils for NMR microscopy has produced increases in signal-to-noise ratio by up to ten times when compared with whole body imaging coils for small animals.99 An implanted coil has been inductively coupled to an external birdcage coil to permit the observation of renal pathology in a rat.'00

NMR images of polymers have been produced by the application of well developed techniques for line narrowing, e.g. MAS, multipulse sequences, and deconvolution procedures."' In another development, a microscopic study of polymer dynamics has been achieved by the use of pulsed field gradient sequences.Io2

3 NMR of Solid Materials In line with p r e v i o ~ s ~ . ~ thoughts this section includes a mention of NMR studies on living systems. Both NMR imaging and high resolution NMR reports are covered. In addition reports are included which deal with high resolution NMR investigations on more chemically familiar solids.

High Resolution NMR of Solids. - A number of general reviews of this very interesting area of NMR have appeared.lo2~lo6 Other reviews have dealt with industrial applications of 13C CP/MAS NMR,"' applications to inorganic systems,Io8 the uses of NMR in the study of solid state ultra slow motion by one and two dimensional spectroscopy,' I * and pharmaceutical conformation and polymorphism."3

Many of the reported developments in solid state NMR techniques involve modifications to known procedures. Reviews have appeared of diffusion measurements by NMR and some of their applications of solid^."^."^ The dynamic angle spinning (DAS) and double rotation (DOR) experiments have been primarily considered for producing high resolution spectra from second order quadrupole broadened signals. However, it appears that these techniques may be more generally applicable to the removal of broadening from other second order effects. ' I 6

It has been demonstrated that IH homonuclear decoupling conditions can lead to an improvement in the detection of 15N and I3C signals."' Multipulse sequences, e.g.

98 H. Requardt, J. Offermann, and P. Erhard, Magn. Reson. Med., 1990, 13, 385. 99 T. H. Farmer, G. P. Cofer, and G . A. Johnson, Invest. Radial., 1990, 25, 552. '00 T. H. Farmer, G. A. Johnson, G. P. Cofer, R. R. Moronpot, D. Dixon, and L. W. Hedlund, Magn. Reson.

lo ' D. G. Corey, A. M. Reichwein, J. W. M. Van Os, and W. S. Veeman, Polymer Prepr., 1988, 29, 92. Io2 P. T. Callaghan and Y. Xia, Polym. Prepr., 1988, 29, 102. I o 3 L. W. Jelinski and W. T. Melchior, 'NMR Spectroscopy Techniques'. Dekker, New York, 1987, p. 253. Io4 B. F. Chmelka and A. Pines, Science, 1989, 24, 7 I .

B. Wrackmeyer, Chem. Unserer Zei f , 1988, 22, 100. Io6 E. R. Andrew, NATO ASI Ser., Ser. C., 1988, 278, 31. I o 7 M. E. A. Cudby, Anal. Appl. Spectrosc., 1988, p. 331. Io8 N. J. Clayden, Chem. Scr., 1988, 28, 21 1 . Io9 N. J. Clayden, NATO AS1 Ser.. Ser. C., 1988, 228, 49. ' l o S. Aime, NATO AS1 Ser., Ser. C., 1988, 228, 65. I " R. G. Griffin, K. Beshah, R. Ebelhauser. T. H. Huang, E. T. Olejniczak, D. M. Rice, D. J. Siminovitch,

and R. J. Wittebort, NATO ASI Ser., Ser. C., 1988, 228, 81 . ' I 2 B. Bliimich, A. Hagemeyer, K. Schmidt-Rohy, and H. W. Spies, Ber. Bunsenges. Phys. Chem., 1989,93,

1189. ' I 3 H . Y. Aboul-Enein, Spectroscopy (Eugene, Oreg.), 1990. 5, 32. ' I 4 J. Karger, H. Pfeifer, and W. Heink, A h . Magn. Reson., 1988, 12, 1. 'I5 A. V. Chadwick, Int. Rev. Phys. Chem., 1988, 7 , 251. ' I 6 K . T. Miiller, B. Q, Sun, G. C . Chingas, J. W. Zwanziger, T. Terao, and A. Pines, .I. Magn. Reson., 1990,

' I 7 A. Bielecki, A. C. Kolbert, and M. H. Levitt, Chem. Phys. Letf. , 1989, 155, 341.

Med., 1989, 10, 310.

86, 470.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


Figure 15 IRCP spectral separation of the two components of POM. Spectrum (b) is the crystalline component and (a) is the amorphous one. The phase of spectrum (a) is inverted from the sense of spectrum (b)

(Reproduced with permission from Macromolecules, 1989, 22, 16 1 3)

BR-24, which facilitate ' H observation may not provide acceptable decoupled "C signals. However, the use of Lee-Goldburg decoupling leads to appreciable signal enhancement. "'3 I l 8

Several developments of cross polarization (CP) have appeared and been, in the main, applied to I3C NMR. CP followed by CP inversion has been used by several workers, an example being its application to differentiating between the amorphous and crystalline components of polymer I3C NMR spectra."' The inversion recovery cross polarization (TRCP) sequence has been applied to poly(oxymethy1ene) POM in order to distinguish between its two components, as shown in Figure 15.'19 A modified version of CP includes the presence of a delay between the proton 90' preparation pulse and the spin locking."' For biological systems, this has the effect that only the water magnetization does not dephase. Consequently, the solvent to solid magnetization transfer is monitored by the CP generated signal. The pulse sequence used to detect proton exchange between the liquid and immobile phases of a hydrated

c

D E C O ~ n.2 1 CP ' H 1 m m

'% CP

Figure 16 Pulse sequence employed to detect proton exchange between liquid and immobile phases

(Reproduced with permission from J . Am. Chem. Soc., 1988, 110, 7222)

' I 8 M . Lee and W. I . Goldburg, Phvs. Rev., A , 1965, 140, 1261. 'I9 D. G. Corey and W. M. Ritchey, Macromolecules, 1989, 22, 161 1 .

in a hydrated bacteriorhodopsin sample

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

20 G. A . Webb

n z = lmsec

I i I

CHEMICAL SHIFT Figure 17 Top, standard CP/MAS "N spectrum of bacteriorhodopsin obtained by using the pulse

sequence shown in Figure 16 with a value for t of 0.OpS and with the IT pulse omitted. Bottom, spectrum of the same sample with the same pulse sequence but with a IT pulse and a t value of 1 ms; note the absence of the nonexchanging peptide resonances

(Reproduced with permission from J . Am. Soc., 1988, 110, 7222)

bacteriorhodopsin sample is given in Figure 16."' The corresponding CP/MAS spectra taken with different values of z are presented in Figure 17.12'.

Solution methods for rf calibration have been applied to I3C CP/MAS measurements.12' Results have been presented for "C subspectral editing, on the basis of the numbers of attached protons, by using multiple pulse decoupling. A double 13C echo sequence has been employed for selective editing of CH,, units of camphor.'*' A series of papers has appeared which examines the details of the spin locked CP proce~s .~*~- l '~ In spite of its widespread usage i t appears that some aspects of this process are still not fully understood.

The possibility of I3C spectral editing has been proposed on the basis of a difference in CH, CP inversion rates.'29 Applications to polymer and coal 13C spectra have been reported. In another de~e lopmen t , ' ~~ pulse sequences have been proposed for the

G . S. Harbison, J. E. Roberts, J. Herzfeld, and R. G. Griffin, J . Am. Chem. Soc., 1988, 110, 7221. ' * I N. C . Nielsen, H. Bildsne, H. J. Jakobsen, and 0. W. Sorensen, J . Magn. Reson., 1988, 79, 554. '22 P. Tekely, J. Brondeau, A. Retournard, and D. Canet, Magn. Reson. Chem., 1989, 27, 696.

124 S. Zhang and X. Wu, Chem. Phys. Lett., 1989, 156, 333. '25 X . Wu, X. Xie, and X. Wu, Chem. Phys. Lett., 1989, 162, 325.

X. Wu and S. Zhang, Chem. Phjs. Lett., 1989, 156, 79.

X. Wu, S. Zhang, and X. Wu, Chem. Phys. Letf., 1989, 162, 321. S. Zhang, X. Wu, H. Zhang, and X. Wu, Chem. P h p . Let[., 1990, 165, 465.

I * * S. Zhang, X. Wu. and M. Mehring, Chem. Phys. Let[., 1990, 166, 92. P. Tekely and J. J. Delpuech, Fuel, 1989, 68, 947.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


measurement of proton T2 and interphase spin diffusion behaviour from the signal obtained following CP transfer to I3C. However, it has been claimed that the proposed pulse sequences lead to incorrect estimates for mobile regions since CP becomes increasingly inefficient as the value of the proton T, increase^.'^' This point has been illustrated by means of a zeolite sample containing adsorbed acetone with a restricted mobility.

2D solid state NMR spectroscopy has found a number of applications. 13C/'H chemical shift correlations and I3C ~hift/ '~C--'H dipolar coupling correlations, obtained using proton multiple pulse decoupling, have been reported. 132 Applications include those to fossil fuels'33 and to matrix isolated reaction intermediate^.'^^ Similar procedures have been used for the structural analysis of 15N labelled fragments in g rad i~ id in . '~~ Two reviews have appeared of applications of 2D NMR methods to polymers, with particular reference to slow polymer m o t i ~ n . ' ~ ~ ' ' ~ ' It has been reported that there are advantages in obtaining 2D NMR spectra of solids under fast spinning at an angle not corresponding to MAS, rather than under static condition^.'^^

Progress has been made in the use of 2D methods for establishing zeolite framework connectivity. Initially, an 80% enriched, in 29Si, zeolite sample was used,'39 more recently it has been demonstrated that suitable data are available in comparable times from natural abundance samples of ZSM-12 and IcZ-~. '~ ' . '~ '

Methods for obtaining chemical shift/dipolar 2D NMR spectra have been con- ~ i d e r e d . ' ~ ~ - ' ~ ~ A I3C spectrum, taken on a sample spinning not at the magic angle, of calcium formate is shown to have an asymmetric dipolar coupling, apparently due to small amplitude motions of the formate ions.142 Other 2D procedures have been used to provide correlations between single crystal o r i en ta t ion~ '~~ and between l3C/I5N shifts and l3C/I4N overtone f req~encies . '~~

In recent years much attention has turned to the fruitful area of solid state NMR studies on quadrupolar nuclei. Solid state deuterium NMR attracts attention as a possible means of characterizing motion in biological and synthetic macromolecules. A quadruple echo sequence has been described which employs composite pulses to

I3O P. Tekely, D. Canet, and J. J . Delpuech, Mol. Phys., 1989, 67, 81. 1 3 ' D. Schulze, H. Ernst, D. Fenzke, W. Meiler, and H. Pfeifer, J . Phys. Chem., 1990, 94, 3499. 13* G. G. Webb and K. W. Zilm, J. Am. Chem. Sac., 1989, 11 1, 2455. 133 K. W. Zilm and G. G. Webb, Fuel, 1988, 67, 707. 134 K. W. Zilm, R. A. Merrill, G. G. Webb, M. M. Greenberg, and J. A. Benson, J . Am. Chem. Sor., 1989,

135 P. V. Lo Grasso, L. K. Nicholson, and T. A. Cross, J . Am. Chem. Soc., 1989, 111, 1910. 136 H. W. Spies, Macromol. Chem., Macromol. Symp., 1989, 26, 197. 13' B. Bliimich and H . W. Spies, Angew. Chem., 1989, 100, 1716. 138 B. Bliimich and A. Hagemeyer, Chem. Phys. Lett., 1989, 161, 55. 139 C. A. Fyfe, H. Gies, and Y . Feng, J . Am. Chem. SOC., 1989, 111, 7702. I4O C. A. Fyfe, H. Gies, Y. Feng, and G. T. Kokotailo, Nature, 1989, 341, 223. 14' C. A. Fyfe, Y . Feng, H. Gies, H. Grondey, and G. T. Kokotailo, J . Am. Chem. Sor., 1990, 112, 3264. '42 T. Nakai, J. Ashida, and T. Terao, Mof. Phys., 1989, 67, 839. 143 A. C . Kolbert, D. P. Raleigh, M. H. Levitt, and R. G . Griffin, J . Chem. Phys., 1989, 90, 679.

A. C. Kolbert, H. J. M. De Groot, and R. G. Griffin, J. Magn. Reson., 1989, 85, 60. ' 45 M. H. Sherwood, D. W. Alderman, and D. M . Grant, J . Magn. Reson., 1989, 84, 4466. 146 K . V. Ramanathan and S. J. Opella, J . Magn. Reson., 1990, 86, 227.

111, 1533.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

22 G. A . Webb

. . ' 54.7, ; 901 a

* s : (sin(Qltl) sin(Q2t2)) 9OY 51.7-*

(b) cos(R1t1) COS(Q2t2) sin(Rltl) sin(Q2t2) 1 Fourier transformation (t2) I Fourier transformation (f2)

cos( R1 t 1 )' /2[A2+ + A T +,i (D2+ + Dz-)] sin( Q1 tl)' /2 [ D2+-D2--i (A2+-A2-)] I Zero imaginary part 1 Zero real part

s i n (R1 t 1 ) '12 ( A2+-A;) 1 Fourier transformation (tl) I Fourier transformation (tl) f Take real part I Take real part

Cos(R1t1)1/2 (A2++A2-)

/4(Al++Al-)(A2++AZ) -' /4( A1+-A I-) (A2+-A;) L o - - - - - J

'/2(Al+ A*+ + A,- A27

Figure 18 Schemes of the pulse sequence (a) and the 2D Fourier transformation (b) for pure absorption mode 2D deuteron spectra. The pulse sequences contain also the echoes created by the last two pulses (detection sequences) in order to illustrate the refocussing character of the fourth pulse. The symbols A and D indicate absorptive and dispersive lineshapes

(Reproduced with permission from J. M a p . Reson., 1988, 79, 271)

reduce distortion arising from the finite length of real pulse^.'^' Quadrupole nutation spectroscopy has been considered by various groups of ~ o r k e r s . ' ~ ~ - ' ' ~

In another development, a spin echo train has been used, with over sampled acquisition, running through the pulse sequence as a means of determining the degree of homogeneity of quadrupole broadened signal^.'^^^'^^ The spectrum produced consists of a comb of sharp peaks which roughly follow the original powder pattern envelope. As the t values become progressively shorter the echoes merge and the train approaches the spin locking sequence.

Deuteron 2D exchange NMR experiments have been used to study slow molecular motions in polycrystalline and amorphous solids.'55 Schemes for the pulse sequences

14' G . Li, D. Wang, and X. Wu, Rev. Sci. Instrum., 1988, 59, 569. 14* A. Samosan and E. Lippman, J . Mugn. Reson., 1988, 79, 255. 149 A. Samosan, E.up. Tech. Phys., 1988, 36, 273.

P. P. Man, J . Magn. Reson., 1988, 77, 148. I5 l P. P. Man, J. Klinowski, A. Trahiner, H. Zanni, and P. Papon, Chem. Phys. Lett., 1988, 151, 143. ' 5 2 G. Engelhardt, J. C. Buhl, J. Felsche, and H. Forster, Chem. Phys. Leti., 1988, 153, 332.

IS4 S. Bank, J. F. Bank, and P. D. Ellis, J . Phy.7. Chem., 1989, 93, 4847. J. T. Cheng and P. D. Ellis, J . Phys. Chem., 1989, 93, 2549.

C. Schmidt, B. Bliimich, and H. W. Spiess, J. Mugn. Reson., 1988, 79, 269.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


Figure 19 Experimental 2D exchange spectra of dimethyl sulphone of 3 10 K obtained by means of the pulse sequence and Fourier transformations shown in Figure 18. ( a ) cosine spectrum, (b) sine spectrum, (c) absorption mode spectrum


Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

24 G. A . Webb

and for the 2D Fourier transformation of pure absorption mode 2D deuterium spectra are shown in Figure 18.155Some experimental 2D exchange spectra obtained using these pulse sequences, of diemthylsulphone at 310 K, are given in Figure 19.'"

The problem of second order broadening in MAS spectra of quadrupolar nuclei has been addressed by means of novel sample spinning schemes. Dynamic angle spinning (DAS) introduces a time dependence of the spinner axis such that the second order interaction is n a r r 0 ~ e d . I ~ ~ An alternative, but equivalent approach, is double rotation (DOR) in which a 5 mm rotor containing the sample spins inside a 20 mm rotor. The former being inclined at 30.6" to the outer spinner axis which remains at the magic angle.

In other developments, involving solid state NMR spectra of quadrupolar nuclei, computer optimized composite 90" pulses have been used for broadband excitation and inversion of deuterium powder Simulations have been presented of the outer transition MAS sideband patterns for spin 3 and 3 n~c le i . "~ 14N overtones have been observed by indirect detectionI6' and 27Al signal intensities have been quantified.

Relative CP inefficiency at high spinning speeds may be overcome by stopping the rotor during the contact time. This procedure has been described as stop-and-go (STAG) spinning.I6' In this experiment the spinner drive gas is switched by the pulse programmer. Experimental details and some applications of CRAMPS (combined rotation and multi pulse sequences) have been r e ~ i e w e d . ' ~ ~ . ~ ~ Applications reported include those for polymers and fossil fuels. The characterization of super slow motions, of the order of a few Hz or less, and ordering in synthetic polymers has been examined by means of rotor synchronized I3C 2D NMR experiment^.'^^.'^^ Some Applications of High Resolution Solid State NMR Studies. - A general review of the applications of NMR to organometallic chemistry has appea~ed'~' which includes reference to solid state studies. Phosphide bridged iron, ruthenium, and osmium carbonyl complexes have been studied by means of 31P CPMAS,'68 which has revealed some metal-phosphorus-metal bond angles. A complete multinuclear NMR study of the six-membered ring dimethyltin chalcogenide trimers (Me, SnX), , where X = S, Se, Te, has been r e ~ 0 r t e d . I ~ ~ The sulphide and selenide trimers, together with diphenyltin sulphide cyclic trimer, di-t-butyltin sulphide cyclic dimer, and monomeric tricyclohexyltin sulphide and triphenyltin oxide, have been studied separately. I7O

Tin-tin coupling via a chalcogen atom (0, Se, Te) has been studied for forty-six

A. Llor and J. Virlet, Chem. Phys. Let[., 1988, 152, 248.

D. P. Raleigh, E. T. Olejniczak, and R. G. Griffin, J. Mugn. Reson., 1989, 81, 455. H. J. Jakobsen, J. Skibsted, H. Bildsoe, and N. C. Nielsen, J . Mugn. Reson., 1989, 85, 173.

P. P. Man, R. Couty, and J. Fraissard, J . Mugn. Reson., 1990, 86, 613.

157 A. Samoson, E. Lippmaa, and A. Pines, Mol. Phys., 1988, 65, 1013.

I6O A. N. Garroway and J . B. Miller, J . Magn. Reson., 189, 82, 591.

1 6 * R. C. Zeigler, R. A. Wind, and G. E. Maciel, J . Mugn. Reson., 1988, 79, 299. 163 C. E. Bronnimann, B. L. Hawkins, M. Zhang, and G. E. Maciel, Anal. Chem., 1988, 60, 1743. '64 P. Jackson and R. K. Harris, Mugn. Reson. Chem., 1988, 26, 1003. 16' Y . Yang, A. Hagemeyer, B. Blumich, and H. W. Speiss, Chem. Phys. L e f f . , 1988, 150, 1. 166 Y. Yang, A. Hagemeyer, and H. W. Spiess, Mucromolecules, 1989, 22, 1004. '67 B. E. Mann, Adv. Orgunomet. Chem., 1988, 28, 397.

'69 I . D. Gay, C. H. W. Jones, and R. D. Sharma, J . Mugn. Reson., 1989, 84, 501. A. J. Carty, C. A. Fyfe, M. Lettinga, S. Johnson, and L. H. Randall, Inorg. Chem., 1989, 28, 4120.

R. K. Harris and A. Sebald, Mugn. Reson. Chem., 1989, 27, 81.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


organo tin compound^.'^' Some correlations with Sn-X-Sn bond angles are reported. The application of high resolution solid state NMR to conductors and superconductors has been reviewed.'72

29Si and 27A1 MAS NMR continue to find widespread applications, particularly in the area of zeolite catalyst r e ~ e a r c h . ' ~ ~ ' ' ~ ~ A number of reviews have appeared of the application of NMR to zeolite chara~terization.'~~-'~~ The relationship between 29Si shielding and molecular structure has been the source of much New catalyst types formed by surface reaction with A12C16 have been characterized by means of solid state 27Al NMR studies."'

The use of 29Si NMR data to provide structural information on silica glasses has been r e~ iewed . "~ - '~~ A high field (1 1.7427 and high speed MAS 27Al NMR procedure has been used to study clay mineral^.'^' Data on twenty five clay samples are reported. The octahedral and tetrahedral sites are quantitatively differentiated. The observed trends in the shielding of the tetrahedral sites and in the nuclear quadrupole couplings are accounted for by distortions caused by progressive aluminium substitution. 29Si and 27Al MAS data have been used to study the cation exchange of substituted tobermorites.Is6 In another account, the 29Si shielding tensor for a single crystal of amethyst is r ep~r t ed . "~

Reviews have appeared of the characterization of the void structure of zeolites by means of xenon gas adsorption and '29Xe NMR ~ t u d i e s . ' ~ ~ , ' ~ ~ It has also been demonstrated that '29Xe NMR can be used to study the guest metal cluster particles in zeolites, e.g. platinum in zeolite Y.190

Several reports have appeared of the applications of NMR to kaolinite chemistry. These include accounts of thermal d e h y d r ~ x y l a t i o n ' ~ ' ~ ' ~ ~ alkali leaching processes leading to zeolite formation'93 and a quantification of the crystallinity changes brought about by mechanical grinding.'94

Reviews have appeared of the use of spectroscopic methods for the study of

171 T. P. Lockhart, H. Puff, W. Schuh, H. Reuter, and T. N. Mitchell, J. Orgunomet. Chem., 1989, 366, 61. I7l A. Vainrub, I. Heinmaa, A. Allan, S. Vija, and E. Lippmaa, Muter. Sci., 1988, 14, 89.

174 J. Klinowski, Ann. Rev. Muter. Sci., 1988, 18, 189. 175 G . Engelhardt, TrAc . Trends Anal. Chem., 1989, 8, 343.

177 B. Norden and U. Edlund, Kem. Tielskr., 1989, 101, 129. 1 7 * J. M. Thomas and D. E. W. Vaughan, J. Phys. Chem. Solid, 1989, 50, 449. 179 B. L. Sherriff and H. D. Grundy, Nature, 1989, 332, 819.

'*' E. E. Getty and R. S. Drago, Inorg. Chem., 1990, 29, 1186. I*' A. R. Grimmer, Exp. Tech. Phys., 1988, 36, 315.

R. Dupree, Exp. Tech. Phys., 1988, 36, 31 5. R. F. Pettifer, R. Dupree, I. Farnon, and U. Sternberg, J . Non-Cryst. Solids, 1988, 106, 408. D. E. Woessner, Am. Mineral., 1989, 74, 203. S. Kamarneni and M. Tsuji, J. Am. Cerum. Soc., 1989, 72, 1668.

J. B. Nagy and E. G . Derouane, ACS Symp. Ser., 1988, 368, 2.

J. Klinowski, Colloids Surf., 1989, 36, 133.

J. M. Newson, M. T. Melchior, and R. A. Beyerlein, Mafer. Res. SOC. Symp. Proc., 1988, 111, 125.

I R 7 D. R. Spearing and J. F. Stebbins, Am. Mineru/., 1989, 74, 956. 18' J. Fraissard, Z . Phys. Chem., (Leipzig), 1988, 269 657.

I9O B. F. Chmelka, R. Ryoo, S. B. Liu, L. C. Menorval, C. J. Radke, E. E. Petersen, and A. Pines, J. Am.

19' R. C. T. Slade and T. W. Davies, Colloids Surf., 1989, 36, 119. 192 B. Jalajakumori, K. G. K. Warrier, and K. G. Satyanarayana, J . Muter. Sci., 1989, 24, 2653. 193 A. Madoni, A. Aznar, J. Sanz, and J. M. Serratosa, J. Phys. Chem., 1990, 94, 760. 194 H. Kodama, L. S. Kotlyar, and J. A. Ripmeester, Claps Cluy Miner., 1989, 37, 364.

J. Fraissard and T. Ito, Zeolites, 1988, 8, 350.

Chem. SOC., 1988, 110, 4465.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

26 G. A . Webb

geological and inorganic Thermal solid state reactions of phosphate fluoride salt mixtures have been studied with the assistance of 31P MAS to monitor the reaction progress and to identify the product phase^.'^^.'^^

The use of I3C CP MAS studies for the determination of the structures of metal complexes include some on complexes of titanium2003201 and cobalt.202 A MAS study of the quadrupolar nuclei 27Al, 69Ga, 7'Ga, ",In, and "'In has appeared for a complete family of binary group 111-V semiconductors.203 The linewidths range from 0. I7 KHz to 14.7 KHz at 11.7T and are found to be controlled by spin-spin exchange and second-order quadrupole broadening. A shielding range in excess of 2500 ppm is found in a 29Si MAS NMR study on twenty five transition metal ~ilicides.~'~ As a consequence of this large range, mixed phases are readily detected. A 23Na MAS NMR study of fi and p" sodium/potassium gallates has led to characterization of the cation site.205

Single crystal 14N NMR measurements have been r e p ~ r t e d . ~ ' ~ . ~ ' ~ For solid solutions of [Me,N],CuBr,C14-, , inhomogeneous linebroadening was used to determine the extent of disorder206 while centro symmetric unit cells have been demonstrated for AgNO, , Ba(N0,)2, and Pb(N03)2 .*'' NMR Imaging. -Chemical shift imaging (CSI) continues to attract much attention. An example being the use of perfluorooctylbromide as an oxygen carrier to provide an imaging route to the vascular system by means of IYF NMR.208 A study in mice employs a chemical shift selective driven equilibrium projection imaging sequences.209 At relatively low doses of the perfluorocarbon, less than 10 g Kg-' , contrast enhancement of the liver and spleen is reported.

In clinical studies using 'H CSI it is usually important to eliminate either the fat or the water signal. Suppression of the fat signal is required in order to improve dynamic range when observing joints such as the knee.210-212 Fat imaging, both in and around the heart, has been reported213 and a warning has been presented that the fat shift can produce poor differentiation between structures and may simulate aortic d i s~ec t ion .~ '~

195 L. L. Jackson, D. M. McKown, J. E. Taggart, P. J. Lamothe, and F. E. Lichte, Anal. Chem., 1989, 61,

'96 J. F. Stebbins and I. Farnon, Science, 1989, 245, 257. 19' D. Ehrt and C. Jager, Z . Phys. Chem. (Munich), 1989, 162, 97. I y 8 C. Jager and D. Ehrt, Z . Phys. Chern. (Munich), 1989, 162, 109. '99 D. Ehrt and C. Jiiger, Z . Phys. Chem. (Munich), 1989, 165, 55. 'O0 S. Doeuff, Y. Dromzee, F. Taulelle, and C. Sanchez, Inorg. Chem., 1989, 28, 4439.

202 Y. Yamamoto, E. Toyota, and S. Shimokawa, Bull. Chem. SOC. Japan., 1989, 62, 2717. '03 0. H. Han, H. K. C. Timken, and E. Oldfield, J. Chem. Phgs., 1988, 89, 6046. 204 T. M. Duncan and D. M. Hamilton, J. Muter. Res., 1988, 3 , 943. *05 H. Ikawa, K. Shima, and K. Urobe, Chem. Lett., 1988, 613. *06 0. Liechti and R. Kind, J . Magn. Reson., 1989, 85, 480. *07 R. A. Santos, P. Tang, W. J . Chien, S. Kwan, and G. S. Harbison, J. Phys. Chem., 1990, 94, 2717. *Ox D. M. Long, R. F. Mattrey, R. A. Long, A. R. Burgon, W. C. Herrick, and D. F. Shellhawer, Biomater.,

209 D. M. Freeman, H. H. Muller, R. E. Hurd, and S . W. Young, Magn. Reson. Imag., 1988, 6, 61. 'I" E. M. Harned, D. G. Mitchell, D. L. Burk, S. Vinitski, and M. D. Rifkin, Magn. Reson. Imag., 1990, 8,

' I ' D. Checkley, D. Johnstone, K. Taylor, and J . C. Waterton, Magn. Reson. Med.. 1989, 11, 221. 'I' S. Tatterman, S. L. Weiss, J. Szumowski, R. W. Katzberg, J. P. Hornak, H. M. Proskin, and J . Eisen, J.

' I 3 J. S. Kriegshauser, P. R. Julsrud, and J. T. Lund, Am. J. Roentgenol., 1990, 155, 259. * I 4 C. S. Loton, G. B. Cranney, M. Doyle, and G. M. Pohost, Am. J. Roentgenof., 1989, 152, 361.

109R.

T. Enokida and R. Hirohashi, Nippon Kagaku Kaishi, 1990, 21 1.

Artif. Cells, Artif. Organs, 1988, 16, 411.

27.

Comput. Assist. Tomogr., 1989, 13, 473.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


Quantitative proton CSI procedures have been presented for the separation of water and fat images in conventional magnetic resonance imaging s t ~ d i e s . ~ ' ~ . ~ ' ~ Other proposed techniques for differentiating between fat and water include fast imaging,217*2'8 cyclic gradient2I9 and multiple delay technique^.^^'-^^^

31P images of the human brain at 1.5 T have been produced by 4D CSI sequences employing pulsed field gradients.224 Phosphocreatine to ATP ratios of I : 15 are reported and the absolute concentration of ATP is estimated to be 3 mM. 'IP FLASH NMR imaging has been reported.225 By means of this procedure a 32 x 32 image of a rat at 3.4T has been obtained, requiring an imaging time of 1.5 minutes. Extensive shimming is found to produce significant improvements in the "P CSI of brain and calf muscle samples.226

CSI using loB and "B has been r e p ~ r t e d . ~ ~ ' . ' ~ ~ It is suggested that images of both boron isotopes may be used for NMR studies on tumours and the measurement of pharmaco kine tics in conjunction with radio therapy.

Biomedical applications of 23Na CSI have recently been reviewed.229 A surface coil study on unexposed kidney has produced both clearly defined 23Na NMR images and 3D data sets with a 1.5 mm3 voxel resolution.230 Other 23Na images reported include those from human brains2" and the vitreous body in eye disorders.232

A discussion has been presented of the properties required of an ideal magnetic resonance contrast agent.233 As a prerequisite to understanding the mechanism of relaxation it is stressed that field dependent measurements are highly desirable.234 It is suggested that the field cycling method is the most appropriate means for determining relaxation profiles over the normal imaging range of 0.02 to 1.5T.

The first contrast reagent approved for MRI studies was Gd DTPA. After more than a year of clinic usage its suitability has been the subject of review.235.236 In general ' Is W. P. Aue, F. Lazeyras, and F. Ternier, J . Mugn. Reson., 1988, 77, 160. ' I 6 H. W. Park, Y. H. Kim, and Z . H. Cho, Muggn. Reson. Men., 1988, 7, 340. 2 1 7 P. Webb, D. Spielman, and A. Macovski. Mugn. Reson. Med. , 1989, 12, 306. 2 1 8 D. N. Guilfoyle, A. Blamire, B. Chapman, R. J. Ordidge, and P. Mansfield, Mugn. Reson. Med. , 1989,

219 D. B. Tweig, Mug. Reson. Med. , 1989, 12, 64. 220 S. Vinitski, D. G . Mitchell, J. Szumowski, D. L. Burk, and M. D. Rijkin, Mugn. Reson. [mug., 1990, 8,

221 E. Hiltbrand and P. Santago, f f e l v . Phys. Actu, 1989, 62, 254. 22' C. C . Lodes, J. P. Felmee, R. L. Ehman, C. M. Schgal, J. F. Greenleaf, G. H. Glover, and J . E. Grass.

223 S. C . R. Williams, M. A. Horsfield, and L. D. Hall, Radiology, 1989, 173, 249. 224 P. A. Bottomley, H. C. Charles, P. B. Romer, D. Flamig, H. Engeseth, W. A. Edelstein, a n d 0 . M. Miiller,

225 A. Haase, D. Leibfritz, and W. Werk, Mugn. Reson. Med. , 1988, 7, 358. '*' J. Trapp, K. A. Derby, C. Hawryszko, S. Sugiura, and H. Yamagata, J . Mugn. Reson., 1989, 85, 244. 227 G. W. Kabalka, P. Bendel, M. Davis, D. N. Slatkin, and P. L. Micca, Basic Life Sci., 1989, 50, 243. 228 T. L. Richards, K. M. Bradshaw, D. M. Freeman, C. H. Solak, and P. R. Gavin, Struhlenther Onkol.,

229 Y. Seo and M. Maeda, Iguku no Ayumi, 1989, 148, 331. 230 S. D. Wolff, J. Eng, B. A. Berkowitz, S. James, and R. S. Balaban, Am. J . Physiol., 1990, 258, 1125. 2 3 1 S. S. Winkler, D. M. Thomasson, K. Sherwood, and W. H . Perman, J . Comput. Assist. Tomogr., 1989,

232 S. J. Kohler, N. H. Kolodny, D. J. D'Amico, S. Balasubramanian, P. Mainardi, and E. S. Gragoudas,

233 G . A. Wolf, Invest. Radio/., 1988, 23 (suppl. I) , S249. 234 R. N. Miiller, L. Van der Elst, P. A. Rinck, P. Vallet, F. Marton, H. Rischer, A. Roch, and Y. Haverbeke,

Invest. Rudiol., 1988, 23 (Suppl. I ) , S229. 235 G . M. Bydder, Br. Hosp. Med. , 1990, 43, 149. 236 G. L. Wolf, Radiology, 1989, 172, 709.

10, 282.

131.

J . Comput. Assist. Tomogr., 1989, 13, 855.

Mugn. Reson. Med. , 1988, 7, 319.

1989, 165, 179.

13, 561.

J . Mugn. Reson., 1989, 82, 505.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

28 G. A . Webb

the situation seems to be promising for further usage of Gd DTPA. Hematoporphyrin- Mn has been assessed as a possible contrast agent for t ~ m 0 u r . s . ~ ~ ~ It is reported that this compound accumulates mainly in the kidneys with smaller amounts being found in the liver and heart. By means of this agent, good contrast images of tumours in Fl hybrid mice have been obtained. However, it appears to be a rather toxic agent and this may limit its applications.

It is claimed that iron based superparamagnetic particles would be suitable for NMR imaging contrast agents for the liver.238*239 Ferric pyrophosphate has been used in studies on pigs and is found to localize in the ischaemic and necrotic muscle cells at the periphery of the infarct.240

The search for successful delivery and targeting methods for imaging contrast agents continues. 2,2,6,6-tetramethyl piperidine-N-oxyl-4-trimethylammonium, which is a nitroxide free radical, has been encapsulated in liposomes and incubated with mouse thymus bone marrow cells.24* It is found that the phosphatidylserine/phosphatidylcholine liposomes interact with the plasma membrane, whereas the phosphatidylserine/ distearoylphosphatidylcholine/diperlmitoyl phosphatidylcholine liposomes are primarily taken up by endocytosis. Such nitroxide free radicals contained within liposomes may modulate the water relaxation rates.242

High Resolution NMR of Living Systems. -This area of NMR spectroscopy has been the subject of a number of reviews covering topics ranging from isolated cells to man.243-247 Reviews have also appeared which cover enzyme mechanism248 and in vivo enzyme kinetics.249 A report has appeared of a means of producing NMR surface coils using computer aided design programs, graphics laser printers, and a photoresistive etching process.25o It is claimed that the coils produced are of a high precision and repro- ducability. Control of the sample depth of excitation is available by means of recent single surface coil localization techniques. These also appear to permit shimming on the region of interest and eliminate surface artefacts from the 90" contour reg i~n .~" Another method of disposing of surface signals uses aqueous dysprosium chloride close to the surface This method has been applied to the measurement of NMR spectra in human heart and liver. A 31P NMR spectrum of a human heart produced by the surface gradient method is shown in Figure 20.252

237 P. Poulet, M. Ouzafe, J. Steibel, Y. Maury, and J. Charnbron, NATO, ASI Ser., Ser. H , 1988, 15, 97. 238 P. Van Hecke, G. Marchal, E. Decrop, and A. L. Baert, Invest. Radiol., 1989, 24, 397. 239 U. Schroder and G. Nyberg, PCT Int. Appl., W089103675, 1989. 240 A. H. Maurer, L. C. Knight, and J. A. Siegel, US 4867963, 1989. 24' H. C. Chan, R. L. Magin, and H. M. Swartz, Magn. Reson. Med. , 1988, 8, 160. 242 C. Bacic, M. R. Niesman, H. F. Bennett, R. L. Magin, and H. M. Schwartz, Magn. Reson. Med. , 1988,

243 W. P. Aue, New Methods Drug Res., 1988, 2, 66. 244 E. D. Becker, Biosci. Rep., 1988, 8, 509. 245 J. L. Bock, Am. J. Clin. Pathol., 1989, 91 (Suppl. I) , S19. 246 P. Boesinger, Phys. Sci., 1988, T23, 3 12. 247 'Annals of the New York Academy of Sciences', 1987, Volume 598, 537pp. 248 A. E. Scott, Proc. Third Int. Conc Chem. Biotechnol. Biol. Act. Nat. Prod., 1987, 1, 117. 249 K. M. Brindle, Prog. N M R SpecItrosc., 1988, 20, 257. 250 T. W. M. Fan and R. M. Higashi, Anal. Chem., 1989, 61, 636. 25' J. W. Pan, H. P. Hetherington, J. R. Hamm, D. L. Rothman, and R. G. Schulrnan, J . Magn. Reson., 1989,

252 C. R. Malloy, R. A. Lange, D. L. Klein, F. M. Jeffrey, R. M. Peshock, J. T. Willerson, and R. L. Nunnally,

6, 445.

81, 608.

J . Magn. Reson., 1988, 80, 364.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

Nuclear Magnetic Resonance Spectroscopy 29 PCr

l " " " ' ~ ~ ~ " " ~ ' " ' " ~ " 1 20 10 0 -10 -20 -30

Figure 20 3'P NMR spectrum of a human heart using the surface gradient method. Acquisition parameters are, pulse duration 600 ps, 200 scans, pulse delay 4.2 s, total acquisition time, 14 min.


Y - L I P

P

PCr

0 mA

194 mA

h 77 mA 135 mA

287 mA 390 mA

0, 0 2 pulse m - i - . - 7 (02'201)

G radi e nt

Figure 21 Magnetic gradient and rf pulse timing diagram and representative 3' P NMR spectra of rat in vivo. A phase cycled Hahn spin-echo sequence was employed with 0, = 30ps, 0, = 60 ps, 7 = 1 ms, pulse repetition period 3 s and 160 scans per spectrum for 8 min total acquisition time. The phase of the gradient is alternated during the second z period. Resonances are assigned as phosphomonoesters (PME) inorganic phosphate (Pi) phosphodiesters (PDE), phosphocreatine (Pcr) and y , a and B phosphate of ATP. The surface gradient current is given below each spectrum in milliamperes


Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

G. A . Webb

Electrically generated surface field gradients have also been proposed as a means of suppressing surface signals.253 Use of the full echo evolution period is obtained by reversing the gradient direction. It is switched off during acquisition to prevent line broadening from partial penetration into deep lying regions. Figure 21 shows the magnetic gradient and rf pulse timing diagram together with some representative 31P NMR spectra of rat in v ~ v o . ’ ~ ~

A review has appeared of recent applications of proton NMR spectroscopy in the study of metabolic pa thophy~io logy .~~~ Renal metabolites have been studied by means of 2D homocorrelated proton spectroscopy.255 The intensity of the water signal is reduced by means of a low power selective pulse during the preparation time, in addition a spin echo during the detection period is used to suppress the fat resonances.

An extensive review has appeared of the uses of 13C NMR in the study of metabolic regulation.2s6 This includes an account of isotopomer analysis and an appendix detailing the I3C chemical shifts of common metabolic intermediates. An account has been presented of the use of polarization transfer to enhance I3C NMR in vivo signals.257

A new range of 19F NMR based pH indicators have been described.258 These are based upon fluorine substituted aniline derivatives and have single resonances with pK, values ranging from 1 to 7 and pH sensitivities from 2 to 7 ppm per pH unit. The distribution of trifluoroacetate ion has been suggested as a sensitive probe of membrane potential.’” The cell volume is simultaneously measured by using the neutral analogue trifluoracetamide. In both cases the intra- and extra-cellular resonances are resolved, the intra-cellular signal being deshielded by about 0.2 ppm.

Cells. - Reviews have appeared relating to the NMR spectroscopy of sodium in intact cells260 and of the proton NMR of human erythrocytes.26’ 31P relaxation times of 2,3-diphosphoglycerate (2,3-DPG) have been reported for living erythrocytes.262 The data are found to be pH dependent due to a modification of the binding of 2,3-DPG to haemoglobin. In uremic erythrocytes increased 31P relaxation rates are observed which are not accounted for on the basis of a simple change in pH. Phosphate levels are found to be increased by two and half times in the red cells of a patient with hyperactive pyruvate kinase t r i o ~ e . ~ ~ ’ A four fold increase in the 2,3-DPG level is also no ted.263

Methorobacterium bryantii and Methorospirillum hungatei are shown to be capable of N, fixation, by ‘’N NMR studies to give soluble amino acids, insoluble cell protein, and other macromolecules.264 The 31P chemical shift of inorganic phosphate has been

253 W. Chen and J. H. Ackerman, J . Magn. Reson., 1989, 82, 655. 254 0. A. C . Petroff, Comp. Biochem. Physiol. Comp. Biochem., B, 1988, 90, 249. 255 B. A. Berkowitz, S. D. Wolff, and R. S . Balaban, J . Magn. Reson., 1988, 79, 547. 256 R. E. London, Prog. N M R Specrrosc., 1988, 20, 337. 257 D. G. Norris, N. Schuff, and D. Liebfritz, J . Magn. Reson., 1988, 78, 362. 258 C. J. Deutsch and J. S. Taylor, Biophys. J . , 1989, 55, 799. 259 R. E. London and S. A. Gabel, Biochemistry, 1989, 28, 2378. 260 R. Gupta and L. A. Jelicks, Indian J . Chcm., Sect. A , 1988, 27, 829. 26‘

262 J. P. Manti, P. Gallic, A. Munisasco, and A. Cervat, Biochim. Biophys. Acra, 1989, 1010, 210. 263 R. Ouwerkerk, C. J. A. Van Echteld, G. E. J. Stoal, and G. Rijksen, Blood, 1988, 72, 1224.

D. L. Rabenstein, K . K. Millis, and E. J. Straws, Anal. Chem., 1988, 60, 1380A.

N. Belay, R. Sparling, B. S. Choi, M . Roberts, J. E. Roberts, and L. Daniels, Biochim. Biophys. Acta, 1988, 97, 233.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


used to determine intracellular pH of cultured Chinese hamster ovary fibroblasts.265 Good agreement with the results of a weak acid partitioning experiment is found over the pH range 6.8 to 7.7 but slightly more acidic values are indicated by the weak acid method in the range 6.0 to 6.8.

Tissues. - Reviews have appeared relating to the application of NMR to the study of parasite metabolism in the general case266 and in the particular case of Fasciola hepatica.267 A major phosphoglycide contributor has been found in the larval stage of the tape worm Tueniu crossiceps.268

The metabolism of [I-'3C]-glucose by two species of silkworm, Bornbyx mori and Philosamiu Cynthia ricini has been The label is found to be incorporated into glucose 1 -phosphate, glucose 6-phosphate, and trihalose. Two days after the [ 1 -13C]-glucose was administered, labelled alanine, glycine, serine, urea, glycogen, trihalose, and glycerol are clearly detectable in the Bornbyx larvae. A number of phosphorylated metabolites have been found by 3 1 P NMR studies of the Bombyx larvae.

NMR has shown that the accumulation of glycerol is one of the adaptive responses to cold in the arctic caterpillar of the long-lived moth Gynaephora groenlandi~a.~'~ The production of [13C]-glycerol in this organism over the temperature range - 30°C to + 30°C has been shown by means of in vivo time lapse [l-'3C]-glucose experiments.271

on the uses of 31P NMR studies of cardiac and skeletal muscle energetic^,^^'.'^^ and on the application of 'P NMR to the study of neonatal disorder^.'^^

Reviews have appeared of the application of NMR to ocular

4 Nuclear Relaxation Processes Various aspects of nuclear relaxation have been covered in a number of books and review^.^^^-*^' The dynamic behaviour of small molecules has been an area of recent interest in conjunction with liquid-state NMR relaxation data. Reviews of this field have appeared.'s2-284

265 R. Galzalez-Mendez, G. M. Hahn, N. G. Wade-Jardetzky, and 0. Jardetzky, M a p . Reson. Med., 1988,

266 W. J. O'Sullivan, M. R. Edwards, and R. S. Norton, Parasitol. Today, 1989, 5, 79. X' P. M. Matthews and T. E . Mansour, UCLA S y n p . Cell. Biol., 1987, 60, 477.

S. N. Thompson, E. G. Platzer, and R. W. K. Lee, J . Parasitol., 1988, 74, 194. 269 T. Asakura, Y. Kawaguchi, M. Demurd, and M. Osanai, Insect Biochem., 1988, 18, 531.

0. Kukal, J. G. Duman, and A. S . Serionni, J . Comp. Ph~~siol., B, 1989, 158, 661. 0. Kukal, A. S. Serionni, and J. G. Duman, J . Comp. Physiol., B, 1989, 158, 175.

6, 373.

26X

270

27 I

272 H. M. Cheng, Med. Sci. Res, 1988, 16, 441. 273 A. Rossi, Arch. Int. Physiol. Biochim. A., 1988, 96, 393. 274 M. J . Dawson, Adv. Exp. Med. Biol., 1988, 226, 433.

"' R. E. Wasylishen in 'NMR Spectroscopic Techniques', ed. C. Dybowski and R. Lichter, Dekker, New D. P. Younkin, Mead Johnson Symp. Perinat. Div. Med., 1987, 25, 19.

York, 1987. R. Kitamaru, 'Nuclear Magnetic Resonance', Elsevier, Amsterdam, 1990. D. Neuhaus and M. Williamson, 'The Nuclear Overhauser Effect in Structural and Conformational Analysis', VCH Verlag, Weinheim, 1989.

M. Munowitz, 'Coherence and NMR', John Wiley, New York, 1988.

1990, Volume 22, p. 308.

275

277 ?7R

279 R. Freeman, 'A Handbook of NMR', Longmans, London, 1987.

28' J. Kowalewski, 'Annual Reports on NMR Spectroscopy', ed. G. A. Webb, Academic Press, London,

?" M. Zeidler, Electrochim. Acta, 1988. 33, 1195. 2x3 P. J. Bray, S. J. Gravins, D. H. Hintenlang, and R. V . Mulkern, Magn. Reson. Rev., 1988, 13, 263. 2x4 A. Doelle and T. Blum, Prog. N M R Spectrosc., 1988, 21, 175.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

32 G . A . Webb

Pure Liquids and Solutions. - Molecular motions in pure liquids and non-electrolyte solutions have been widely ~ t u d i e d . ~ ~ ~ , ~ ~ ' Multinuclear NMR studies of CH3CN and CHCl, in their binary mixtures have been used to study the effect of intermolecular re~r ien ta t ion . '~~ .~~ ' The reorientational dynamics of CH,CN in water-prepared mixtures2s9 and of pyrrole dissolved in acetonitrile, tetrachloroethylene, and N,N- dimethyl a ~ e t a m i d e ~ ~ ' have been monitored by means of I4N relaxation measurements. A similar characterization of trichloroethane has been performed by using a combination of 35Cl and 13C relaxation data in conjunction with a Raman band shape

Beyond the extreme narrowing limit relaxation dispersion can be observed, several reports have appeared of molecular motions in liquids within this regime. Such studies on simple molecular liquids require supercooling while more complicated liquids, such as 2-ethylhexyl cyclohexane carbonate and the model lubricant 2-ethylhexyl benzoate, exist beyond the extreme narrowing limit at around room t e m p e r a t ~ r e . ~ ~ ~ . ' ~ ,

The various motions of flexible modules continue to attract the attention of I3C relaxation time measurements. Such data have been used in a study of the rotational dynamics of hydrocarbon chains attached to b e n ~ o p h e n o n e . ~ ~ ~ The anisotropic and internal motions of morphine and related molecules in aqueous solutions have been investigated as part of a study on the molecular factors determining drug-receptor interactions.295 The molecular motions of CHF2Cl over a wide range of temperature and pressure have been discussed in the light of multinuclear relaxation data.296

Experiments on some glass forming molecular liquids have shown that at about 20 K above the calorimetric glass transition temperature the deuterium spin-lattice relaxation becomes non-exponential while H relaxation remains strictly mono- exponential, thus 'H spin-lattice relaxation may provide a signature of the glassy state.297 It has been proposed that the motional behaviour of deuteriated hexamethyl- benzene, employed as a guest molecule, may be used to obtain information on the structure of organic glasses.298 A corresponding states concept has been proposed for the dynamics of supercooled l i q ~ i d s . ~ ~ ~ * ~ ' '

The I9F relaxation of hexafluorobenzene appears to be controlled by CSA. A comparison of the I3C and I9F relaxation results for C6F6 has been made in a study of anisotropic re~rientation.~"

Molecular motions in plastic crystalline rotator phases and in the corresponding

28s J. Jonas, Ber. Bunsenges. Phys. Chem., 1990, 94, 325. 2x6 E. W. Lang, W. Fink, H. Radkowitsch, and D. Girlich, Ber. Bunsenges. Phys. Chem., 1990, 94, 342. 287 H. Kovdcs, J. Kowalewski, A. Maliniak, and P. Stilbs, J. Phys. Chem., 1989, 93, 962.

289 H. Kovacs, J. Kowalewski, and A. Maliniak, Chem. Phys. Lett., 1988, 152, 427. 290 H. M. Ratajczak and J. A. Ladd, J. Mol. Liq., 1989, 40, 135. 29' S. P. Wang and M. Schwartz, J. Phys. Chem., 1990, 94, 2702. 292 N. A. Walker, D. M. Lamb, S. T. Adamy, and J. Jonas, J . Phys. Chem., 1988, 92, 3675. 293 J. Jonas, S. T. Adamy, P. J. Grandinetti, Y. Masuda, S. J. Morris, D. M. Campbell, and Y. Li, J. Phys.

294 P. Dais, Mugn. Reson. Chem., 1989, 27, 61. 295 A. Grassi, B. Perly, and G. Pappalardo, Chem. Phys., 1989, 130, 335. 296 J. M. Vardag and H. D. Ludemann, Chem. Phys., 1988, 128, 527.

298 B. Jansen-Glow, E. Roessler, M. Taupitz, and H. M. Vieth, J . Chem. Phys., 1989, 90, 6858. 299 E. Roessler, Ber. Bunsenges. Phys. Chem., 1990, 94, 392. 'O0 E. Roessler, J. Chem. Phys., 1990, 92, 3725. 30' M. A. Suhm and H. Weingirtner, Chem. Phys. Lert., 1989, 159, 193.

J. Kowalewski and E. Berggren, Magn. Reson. Chem., 1989, 27, 386.

Chem., 1990, 94, 1157.

W. Schnauss, F. Fujara, K. Hartmann, and H. Silescu, Chem. Phys. Lett., 1990. 166, 381. 297

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


liquids have been compared by means of NMR measurements on pi~aldehyde,~'~ t-butyl chloride, t-butyl nitride, and t-butyl iodide.303 Some of the less common nuclei are now being widely used in molecular reorientation studies. An example being that of 33S, which appears frequently in reports of studies in this area.304-306

Electrolyte Solutions. - Aqueous electrolyte solutions have been the source of attention for many relaxation studies. Aqueous zinc chloride solutions have been subjected to 'H, 'H, and 170 relaxation rneas~rernents.~'~ From the results, estimates have been obtained of the 0-H separation and of the 'H and "0 nuclear quadrupole coupling constants. These are found to differ significantly from the corresponding values for pure water. Anisotropic reorientation is claimed for the water molecules in these solutions.

The pressure, temperature, and concentration dependence of molecular motions in aqueous solutions of various potassium and caesium halides,308 and in aqueous solutions of sodium chloride and iodide,309 as well as lithium ~hloride,~" have been reported.

Water exchange with a series of 12 paramagnetic lanthanide ions has been studied by means of relaxation data.3" The results obtained indicate that each ion has nine water molecules coordinated to it. In aqueous solutions of polyatomic ions, relaxation measurements have been reported for the central nuclei of several ions, for example the nitrate,312 a l ~ m i n a t e , ~ ' ~ tetracyanoplatinate, and hexacyanoplatinate

Intermolecular relaxation has been used to study ion association in aqueous electrolyte solutions by observing the relaxation of the fluoride ion produced by the protons in neighbouring tetramethylammonium The dynamic processes occurring in silicate solutions, possibly containing anions, have been studied by means of I7O and 29Si NMR measurements. An investigation has been aimed at detecting the presence of polymeric silicate A study on ion pairing in alkali silicate solutions has shown that silicon exchange is influenced by the presence of alkali metal

The quadrupolar relaxations of the magnesium and chloride ions in aqueous MgCI, solutions at infinite dilution319 and at finite ion concentration^^^' have been reported. The data are interpreted in terms of a modification of the electrostatic theory

ions,317, 318

'02 S. Mooibroek. R. E. Wasylishen, J. B. McDonald, C . I . Ratcliffe, and J. A. Ripmeester, Can. J . Chem.,

303 D. W. Aksnes, K. Ramstadt, and 0. P. Bjoerlykke, Magn. Reson. Chem., 1988, 26, 1086. '04 A. A. M. Ali, R. K. Harris, and P. S. Belton, Magn. Reson. Chem., 1990, 28, 318. 305 M. J. Collins, C. I . Ratcliffe, and J. A. Ripmeester, J . Phys. Chem., 1989, 93, 7495. '06 D. C. French and D. S . Crumrine, J . Magn. Reson., 1989, 84, 548. '07 J. R. C. Van der Maarel, J . Magn. Reson., 1989, 81, 92. '08 W. Fink, H. Radkowitsch, and E. W. Lang, Z. Naturforsch., Teil A. 1988, 43, 538. '09 W. Fink, H. Radkowitsch, and E. W. Lang, Chem. Phys., 1988, 124, 239.

E. W. Lang and F. X . Prielmeier, Ber. Bunsenges. Phjs . Chem., 1988, 92, 71 7. 3 1 ' C. Cossy, L. Helm, and A. E. Merbach, Inorg. Chem., 1988, 27, 1973. 3 1 2 A. Adachi, H. Kiyoyama, M. Nokahara, Y. Masuda. H. Yamatera, A. Shimizu. and T. Taniguchi, J .

3 1 3 J. W. Akitt, W. Gessner, and M. Weinberger, Mugn. Reson. Chem., 1988, 26, 1047. 314 R. E. Wasylishen and J. F. Britten, Magn. Reson. Chem., 1988, 26, 1075. 'I5 K. J. Miiller and H. G. Hertz, Chem. Scripta, 1989, 29, 277. ' I 6 S. D. Kinrade and T. W. Swaddle, Inorg. Chem., 1988, 27, 4259. ' I 7 A. V. McCormick, A. T. Bell, and C. J. Radke, J . Phys. Chem., 1989, 93, 1733. 3 1 8 A. V. McCormick, A. T. Bell. and C. J. Radke, J . Phys. Chem., 1989, 93, 1737. ' I9 R. P. W. J. Struis, J. de Bleijser, and J. C. Leyte, J. Phys. Chem., 1989, 93, 7932. '*O R. P. W. J. Struis, J. de Bleijser, and J. C . Leyte. J . Phys. Chem.. 1989, 93, 7943.

1988, 66, 734.

310

Chem. Phys., 1989, 90, 392.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

34 G . A . Webb

proposed by Hertz.321s322 Other papers have covered work on the exchange of water with the lanthanide ions from terbium to thulium323 and the oligomerization reactions of vanadate ions.324

Several NMR studies on the structure and dynamics of non-aqueous electrolyte solutions have been reported. The reorientation of the ammonium ion in several solvents has been studied by means of I5N relaxation times and NOE data.325 A range of reorientational correlation times from 0.46 to 20ps has been observed. The rotational diffusion and segemental motions of the tetraoctylammonium ion in a variety of solvents have been subjected to a 13C relaxation

The slowing down of the translational and rotational molecular motions of DMSO by added alkali halides has been Valuable information has been obtained on the coupling of the rotational and translational molecular motions in such systems.

The selective solvation of metal ions in mixed solvents can be readily investigated by NMR techniques. For example, 27Al NMR provides an insight into the solvation of A13+ in mixed solvent^.'^^-^^^ The 27Al chemical shift difference in water-DMF mixtures is too small to provide separated signals for species with mixed coordination. However, the changes in the 27Al line widths are found to be dependent upon the solvent composition, suggesting a selective solvation process. In the case of AI3+ in mixed acetone-water-perchloric acid solutions, evidence has been reported for selective ionic h y d r a t i ~ n . ~ ~ '

In further ion-solvent interaction studies, 7Li+ relaxation has been recorded in 4 -b~ ty ro lac tone~~~ and sulphuryl '39La and 35Cl NMR have been used to study the structures of La(C10,)3 and La(N03)3 solutions in water-acetone mixtures.334

A review has appeared of metal ion NMR studies of ion binding.335 23Na NMR is a useful means of following the reactions which generate Na- ions in crown ethers.336 The conformation of crown ethers and conformational variations during alkali complexation have been studied by 13C spin lattice time relaxation and NOE data.337-339 In another development, it has been proposed that self diffusion measurements may be used to determine complex formation constants of crown ether complexes.340

32' H. G. Hertz, Ber. Bunsenges. Phys. Chem., 1973, 77, 531. 322 H. Weingirtner and H. G. Hertz, Ber. Bunsenges. Phys. Chem., 1977, 81, 1204. 323 C. Cossy, L. Helm, and A. E. Merbach, fnorg. Chern., 1989. 28, 2699. 324 D. C. Cram, C. D. Rithner, and L. A. Theisen, J . Am. Chem. SOC., 1990, 112, 2901. 325 C . L. Perrin and R. K . Gipe, Science, 1987, 238, 1393. 32h F. Coletta, A. Ferrarini, and P. L. Nordio, Chem. Phys., 1988, 123, 397. 327 A. Sacco, M . Carbonara, and M. Holz, J . Chem. Soc., Faruduy Trans. I , 1989, 85, 1257. 328 E. Hallas, H. H. Emons, M. Seidler, and B. Thomas. Magn. Reson. Chem., 1989, 27, 307. 329 H. H. Emons, M. Seidler, B. Thomas, and A. Parzel. Z . Anorg. Allg. Chem., 1988, 558, 231. 330 H. H. Emons, M. Seidler, B. Thomas, and E. Hallas, Z . Anorg. Aflg. Chem., 1988, 566, 169. 33' J. M. Garrison and A. L. Crumbliss, Inorg. Chem., 1988, 27, 3058. 3 3 2 A. I . Mishustin, Zh. Fiz. Khim., 1989, 63, 828. 333 A. I. Mishustin, V. A. Mozalevskaya, and V. P. Ponkratov, Zh. Fiz. Khim., 1989, 63, 1345. 334 A. Fratiello, V. Kubo-Anderson, T. Bolinger, C. Cordero, B. DeMenit, T. Flores, and R. D. Perrigon,

335 C. Johansson and T. Drakenberg, 'Annual Reports on NMR Spectroscopy', ed. G. A. Webb, Academic

336 P. P. Edwards, A. S. Ellaboudy, D. M. Holton, and N. C. Pyper, Mol. Phys., 1990, 69, 206. 337 E. Kleinpeter, S. Stoss, M. Gabler, and W. Schroth, Magn. Reson. Chem., 1989, 27, 676. 338 G. X. He, T. Imato, N. Ishibashi, S. Shinkai, and T. Matsuda, Bull. Chem. Soc. Japan. 1990, 63, 401. 339 G. W. Buchanan, R. A. Kirby, and K . Bourque, Can. J . Chern., 1989, 67, 449. 340 M. Geringer and H. Sterk, Magn. Reson. Chem., 1989. 27, 1148.

J. Soln. Chem., 1989, 18, 313.

Press, London, 1990, Vol. 22, p. 1.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


The quadrupolar relaxation of 23Na+, ”Rb’, and 36Cl has been studied in aqueous, non-aqueous, and mixed electrolyte solutions in the presence of electric fields as large as 40Vcm-I. It is found that the relaxation rates may be variously unaffected, increased, or decreased by the presence of the electric field.341 Those changes which do occur are usually less than twenty per cent. It seems likely that at least two different effects, operating in opposite directions, may be responsible for this behaviour. Polymer Solutions and Melts. - A dynamic rotational-rotational isomeric state model has been applied to a study of chemical structure and local dynamics in dilute polymer solutions.342 In another investigation, the effect of chain stiffness on nuclear relaxation in melts has been

A report on polyisoprene shows that IH relaxation data may be analysed to give information on chain motion in the melt and in solution.344 The relation between light scattering and ’ H relaxation results has been investigated for poly(methy1meth- acrylate) and polystyrene.345 13C relaxation and NOE data have been analysed for some chlorolefin copolymers on the basis of a conformation jump

Gases. - Frequency, the SR interaction is responsible for producing nuclear relaxation in the gaseous phase. Since the correlation function for SR interactions contains mixed orientation-angular momentum terms it is possible to obtain data on cross sections for the angular momentum vector. This approach has been adopted for tetrafluoromethane where T, measurements yield such cross section inf~rmat ion .~~’

F relaxation has also been studied for UF6 where it is found that a 235U-’9F scalar interaction also contributes to the relaxation rate.’48

Gaseous state H relaxation measurements have been reported for f ~ r a n ’ ~ ~ and benzene,3s0 together with some 13C data in the latter case. It is found that the SR interaction is the predominant source of nuclear relaxation in both cases. A similar approach has been used in a study of the ring inversion of 1,3,5-trimethylhexahydro- 1,3,5-triazine.’”

19

5 Theoretical Aspects of NMR Parameters The past two years have witnessed further advances in the theoretical interpretation of nuclear shielding, spin-spin coupling and spin relaxation. The most significant improvements in our understanding of these parameters come from advanced calculations of nuclear shielding. Nuclear Shielding. - Ab initio calculations of nuclear shielding have been reviewed.’52 It remains generally true that satisfactory calculations of shielding data require large basis sets and, in many cases, the inclusion of electron correlation. Thus, ab initio

34’ R. E. S. Hofmann and M . Holz, Ckem. Phys. Lett., 1987, 142, 492. 342 L. Bahor, B. Erman, and L. Monnerie, Polym. Commun., 1988, 29, 349. 343 R. Guyonnet and J. P. Cohen-Addad, Macromolecules. 1989, 22, 135. 344 M. Kopf, G. Schnur, and R. Kimmich, J. Pofym. Sci., Part A. Polym. Chem., 1988, 26, 319. 345 F. Tabak, J. Mol. Liq., 1988, 39, 137.

H. Bergmann and K. Schlothauer, Acta Polym., 1988, 39, 694. 347 C. J. Jameson and A. K. Jameson, J . Chem. Phys., 1988, 89, 866. 348 D. E. Demco, M. Bogdan, P. Fitori, F. Balibanu, and A. Darabant, Rev. Roum. Phys., 1988, 33, 509. 349 B. E. Weiss-Lopez, E. D. Winegar, and N. S . True, J . Phj..~. Chem., 1988, 92, 4052. 350 M. M. Falkendt, B. E. Weiss-Lopez, and N. S . True, J . P h p . Chem., 1988, 92, 4859.

346

C. €3. LeMaster, C. L. LeMaster, M. Tafazzoli, C. Suarez, and N. S. True, J. Phys. Chem., 1988,92, 5933. D. B. Chesnut, ‘Annual Reports on NMR Spectroscopy’, ed. G. A. Webb, Academic Press, London, 1989, Volume 21. p. 5 1 .

352

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

36 G . A . Webb

calculations tend to be limited to molecules containing not more than about ten heavy (C, N, 0) atoms. An attempt to extend calculations of this quality to larger molecules involves the use of locally dense basis sets for the resonant atom of interest and attenuated sets on other atoms.353 Unfortunately, for atoms such as N, 0, and F, where standard basis sets do not provide good agreement with experiment, use of the attenuated sets provides no significant improvement. However, the use of the locally dense basis sets is successful for application to carbon and suggests that carbon chemical shifts are mostly dependent upon the local basis set.

A similar view is available from the IGLO and LORG methods of calculation. These successful variants of the coupled Hartree-Fock procedure (CHF) have been compared in the same notation.354 The IGLO and LORG procedures reduce the gauge dependence in a finite basis set calculation by using local origins. Usually the local origins are taken to be the centroids of the occupied localized molecular orbitals. Essentially equivalent results are produced by the IGLO and LORG methods for calculations of carbon and fluorine shielding tens01-s.~~~

As an aid in the display of the anisotropy of the symmetric part of the shielding tensor, and in the elucidation of the antisymmetric part, it has been proposed that the shielding tensor may be satisfactorily analysed in terms of the components of the shielding response vector, T.355 Where T is defined as the shielding field per unit applied magnetic field. It is reported that specifically distorted double bonds can lead to large antisymmetric components in the shielding of the atoms concerned for example in diazirine.

The shielding response parallel to the applied magnetic field is given by TB and a plot of the in-plane contours of TB for the carbon atoms in pyridine is given in Figure 22,356 where the solid contours indicate an increased shielding response and the dashed lines a decreased response relative to the bare nucleus.356 The enhancement of the paramagnetic shielding components of the ortho and para carbons, relative to the meta position, is rationalized by a large, in-plane, magnetic moment from the nitrogen n -+ n* excitation. Figure 23 shows a similar plot of TB for the nitrogen shielding in pyrazine. Again the most shielded component is perpendicular to the ring.

In a few cases, e.g. NNO and NZ, the use of local origins and large basis sets still do not produce calculated results which are within experimental error. This implies the need for a higher level of theory such as that provided by the second order polarization propagator approximation (SOPPA).357 The SOPPA calculated value for the average nitrogen shielding of N, is - 72.2 ppm compared with an experimental value of -61.6ppm and about - 1 lOppm for previous calculations. This is an encouraging result and indicates the possible use of SOPPA for future shielding calculations, beyond the CHF limit as already experienced for spin-spin couplings.

The standard CHF approach has been applied to calculating the shieldings of all of the nuclei in the CX and XCY molecules, where X, Y = 0, S, and Se.358 In general, good agreement is found with the available experimental results. Comparison with the

3s3 D. B. Chesnut and K . D. Moore, J . Comp. Chem., 1989, 10, 648. 354 J. C. Facelli, D. M. Grant, T. D. Bouman, and A. E. Hansen, J. Comp. Chem., 1990, 11, 32. 355 A. E. Hansen and T. D. Bouman, J. Chew. Phq’s., 1989, 91, 3552. 356 T. D. Bouman and A. E. Hansen, Int. J . Quant. Chem., 1989, 23, 381. ”’ J. Oddershede and J . Geertsen, J. Chem. Phys., 1990, 92, 6036. 35R J. Jokisaari, P. Lazzeretti, and P. Pyykko, Chem. Phys., 1988. 123, 339.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


H

Figure 22 Plot of the in plane contours of T, for the three magnetically distinct carbon atoms in

(Reproduced with permission from Int . J. Quant. Chem., 1989, 23, 391) pyridine

results of semi-empirical REX calculations provides an estimate of relativistic influences.358 The average 33S shielding of SF4 has been the subject of calculations.

The CHF result is 2 9 2 . 7 ~ p m , ~ ~ ~ while that produced by the IGLO procedure is 128.7 Unfortunately, there is no experimental result available for comparison purposes. CHF calculations of some Ti, Mo, and Sn shieldings have been reported using basis

sets of double zeta q ~ a l i t y . ~ ~ ' - ~ ~ ~ A triple zeta basis set has been used in some LORG calculations of Mo shielding in small complexes.364 A comparison of the CHF and

H \

C

Figure 23 Plot of the T, function for the "N shielding in pyrazine (Reproduced with permission from Int. J . Quant. Chem., 1989, 23, 393)

359 J . A. Tossell and P. Lazzeretti, J . Chem. Phys., 1988, 88, 7251. 360 M. Schindler, J. Chem. Phys., 1988, 88, 7638.

H. Nakatsuji and T. Nakao, Chem. Phys. Lett., 1990, 167, 571. H. Nakatsuji and M . Sugimoto, horg . Chem., 1990, 29, 1221.

363 H. Nakatsuji, T. Inoue, and T. Nakao, Chem. Phq's. Let t . , 1990, 167, 1 1 1. 364 J. E. Combariza, J. H. Enemark, M. Barfield, and J . C. Facelli, J . Am. Chem. SOC., 1989, 111 , 7619.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

38 G. A . Webb

0 1000 2000 3000 Theoretical Value (pprn)

Figure 24 Comparison between theory and experiments for the 95Mo shifts of various molybdenum

(Reproduced with permission from Inorg. Chem., 1990, 29, 1222) complexes

LORG results for the Mo ~ h i e l d i n g s ~ ~ ~ . ~ ~ indicates that the CHF data are in better agreement with the experimental results. The results of the CHF calculations of Mo shieldings are compared with the corresponding experimental values for some molybdenum complexes in Figure 24.362 In general the LORG and CHF calculated Mo shieldings differ by 300-900ppm, an absolute shieldings scale is required to examine these differences.

The gauge included atomic orbitals (GIAO) procedure has been applied to the calculation of the silicon shielding tensors of 28 silicon compounds.365 The 6-31 G* basis set results fairly well reproduce the 29Si shielding trends in the series SiH, F4-n. However, the absolute shieldings differ from experiment by about 50 ppm. The results of IGLO calculations of silicon chemical shifts appear to be more satisfactory even though the 6-31 G* basis set is not adequate for shielding calculations.366

The largest molecule to date, for which ab initio calculations of nuclear shielding have appeared, seems to be c60.367 It is found that the calculated carbon shielding decreases as the basis set increases in size. The largest basis set used being 6-31 G*. It is estimated that the effect of the C60 cage on the magnetic shielding of an atom placed at the centre would be an increase of 7ppm.

Semiempirical methods are still employed in the calculations of shielding for heavy nuclei, e.g. 195Pt, or 207Pb, o r for first and second row nuclei in very large molecules. 207 Pb shieldings in the halides, PbF,, PbCl,, PbBr,, PbI,, and PbFCl have been calculated using the ground state electronic structure and a p~eudo-potent ia l .~~~ Reasonable agreement with experiment is reported.

The MIND0/3 semiempirical procedure associated with GIAO calculations of I3C shieldings, has been revisited.369 As reported earlier, the calculations produce vacant molecular orbital energies which are too In the recent approach, this short-

365 J. R. Van Wazer, C. s. Ewig, and R. Ditchfield, J . Pliys. Chem.. 1989, 93, 222. U. Fleischer, M. Schindler, and W. Kutzelnigg. J . Chem. Phys.. 1987, 86, 6337.

367 P. W. Fowler, P. Lazzeretti, and R. Zanasi, Chem. Phys. Lett., 1990, 165, 79. 36x M. Nizam, M. Allavena, Y. Bouteiller, B. H. Suits, and D. White, J . Magn. Reson., 1989, 82, 441.

370 M. Jallai-Heravi and G. A. Webb, Org. Magn. Reson., 1979, 12, 174.

366

D. B. Chesnut and C. Zhang, J. Comp. Clzem., 1988, 9, 416. 369

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


coming is dealt with by introducing parameters in the shielding calculation which reduce the calculated paramagnetic shielding component and correct the ground state electron distribution. For a series of hydrocarbons the agreement with observed 13C shieldings is reasonable.

The INDO-CS method has been used in a discussion of the 13C chemical shifts of a molecule chemisorbed on zeolites.37’ The INDO-CS results are in reasonable agreement with experiment, and some IGLO data, for all carbons with the exception of one bearing a formal positive charge. INDO-GIAO calculations have also been used to account for the unusual 13C shieldings found in bicyclic molecules with a strained framework. 372

Evidently X-alpha calculations of nuclear shielding are not very promising. Some recent results for the I3C shieldings in the series CH,-,F, and for 19F in H F and F2 support this The calculated 13C shielding range is 16.5 ppm compared with the observed range of 122 ppm.

Calculated charge densities appear to provide an account of the relative shieldings of the four nitrogens in dibenzo[ 1.3a.4.6aItetraza~entalene~~~ and for the eleven nitrogen atoms in some purine and adenine derivative^.^"

Both specific and non-specific solvent effects on nitrogen shieldings have been reported for cyano groups,376 methyl nitrate, methyl is~thiocyanate ,~~~ and pyridine N - o ~ i d e . ~ ~ * In all cases INDO/S parameterized SOS shielding calculations using the solvation model have been reported as giving a satisfactory account of non-specific interactions. The results for pyridine N-oxide are similar to those found for pyridine where proton donation from solvent-to-solute appears to be the major factor in determining the sensitivity of the nitrogen shielding to solvent variation. In the case of alkyl cyanides, hydrogen bonding and non-specific effects appear to influence the nitrogen shielding to a similar extent.

CNDO calculations are reported for a study of the dependence of the anisotropy, on the Si-0 bond length, of the 29Si shielding tensor in the [SiO4I4- anion.379 It is of interest that a careful comparison of the IGLO and LORG methods and their shielding results reveal that early, semiempirical, ideas of nuclear shielding are fairly a c c ~ r a t e . ~ ~ ~ ’ ~ ~ ~ Namely that significant shielding contributions arise mainly from localized orbitals directly attached to the nuclei of interest. In passing along a series of molecules the diamagnetic contributions to the shielding are found to be almost constant, further, they do not contribute to the shielding anisotropy to any appreciable extent. Consequently, variations in the paramagnetic shielding component, from the localized orbitals, control the observed chemical shift differences.

371 V. G. Malkin, V. V. Chesnokov, E. Paukstis, and G. M. Zhidomirov, J. Am. Chem. SOL.., 1990, 112, 666. 372 C. F. Wilcox and R. Gleiter, J . Org. Chem., 1989, 54, 2688. 373 K. Friedrich, G. Grossmann, and G. Seifert, Z. Chem., 1988, 28, 156. 374 M. Witanowski, J. Sitkowski, W. Sicinska, S. Biernat, and G. A. Webb, Magn. Reson. Chem., 1989, 27,

88. T. Zeegers-Huyskens, Bull. SOC. Chim. Berg., 1988, 97, 23. 375

37h M. Witanowski, W. Sicinska, and G. A. Webb, Magn. Reson. Chem., 1989, 27, 380. ’” M. Witanowski, J. Sitkowski, S. Biernat, L. V. Sudha, and G. A. Webb, Magn. Reson. Chem., 1987, 25,

378 M. Witanowski, W. Sicinska, S. Biernat. and G. A. Webb, J . Magn. Reson., 1989, 83, 351. 379 C . Vogel, R. Wolff, and R. Radeglia, Z. PIiys. Chem. (Leipzig), 1989, 270, 1073.

K. A. K. Ebraheem and G. A. Webb, Prog. N M R Spectrosc., 1977, I t , 149. 381 I . Ando and G. A. Webb, ‘Theory of NMR Parameters’, Academic Press, London, 1983.

725.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

40 G. A . Webb

Spin-Spin Coupling. - During recent years the number of publications dealing with calculations of spin-spin couplings appears to have declined. This is particularly the case for ab initio calculations. The reasons for this are not too clear, especially when the unpredictability of the relative sizes of the various contributions to spin-spin coupling interactions is borne in mind.

A thorough ab initio investigation of 'J for BH and AIH has appeared.382 Three approximations to the polarization propagator were used, namely coupled Hartree- Fock (CHF), or the first order polarization propagator approximation, (SOPPA), and the coupled cluster singles and doubles polarization propagator approximation (CCSDPPA). The extent of electronic correlation included in the calculations increases from CHF to SOPPA to CCSDPPA. For BH the calculated results are 65.77 Hz (CHF), 59.67 Hz (SOPPA), and 5 1.39 Hz (CSDPPA); the corresponding results for AIH being - 17.88 Hz, 0.33 Hz and 10.01 Hz. It is found that both couplings are controlled by the contact interaction. Regrettably, there appear to be no experimental results available for comparison purposes. Ab initio spin-spin coupling calculations have been reported by CH2X2 where X = H, CH,, or F.383 A major interest being the dependence of the two bond couplings on the valance angle 8. It is found that 'J(H-H) increases linearly with 8, 'J(C-C) is independent of 6, and 'J(F7F) decreases rapidly with an increase in 8.

An area suitable for theoretical investigations is that of 'H--'H exchange coupling which has been proposed as a likely explanation of some unusually large 'J('H--'H)

The full spin-spin coupling tensors of the series CX, CX,, and XCY where X, Y = 0 or Te have been calculated by means of the REX procedure.3s8 It is found that the reduced scalar coupling becomes increasingly negative in value as X becomes heavier. The same approach has been used to obtain the anisotropy ratio A'J(C-Se)/ A*J(Se-Se) for CS2. A value of about 0.2 is reported.386

The non-contact contributions to spin-spin couplings, derived from semiempirical calculations, may be analysed in terms of localized molecular orbitals (LMO)387. The scheme used provides contributions from localized orbitals using the polarization propagator approach (CLOPPA). The scheme has been applied to two diseleno substituted alkenyls and it is shown that the in plane Se CJ lone pair of electrons make the most important contribution to 2J(Se-Se).388

A study of the effect of substituents of 'J(13C-13C) in substituted acetylenes389 and e thylene~~~ ' has been performed by means of INDO calculations at the RPA level of approximation. It is found that, in all cases studied, the couplings are very dependent upon the electronegativity of the attached substituents. The largest couplings being found for fluorinated molecules.

data.384.385

382 G. E. Scuseria, J. Geertsen, and J . Oddershede, J . Chem. Phjs., 1989, 90, 2338. 383 M. Klessinger and P. Bolte, J . Mol. Struct., 1988, 169, 119. 384 D. H. Jones, J. A. Labinger, and D. P. Weterkamp, J . Am. Chem. Soc., 1989, 111, 3087. 385 K. W. Zilm, D. H. Heinekey, J . M. Millar, N. G. Payne, and P. Demou, J . Am. Chem. Soc., 1989, 111,

386 A. Pulkkinen and J. Jokisaari, J. M a p . Reson., 1989, 85, 388. 387 A. C. Diz, M. C . Ruiz de Azua, C. G. Giribet, and R. H . Contreras, fnt. J . Quunt. Chem., 1990, 37, 663. 388 C. N. Cavasatto, C. G. Giribet, M. C. Ruiz de Azua, R. H. Contreras, and J. E. Perez, J . Magn. Reson.,

389 K. Kamienska-Trela, Z. Biedrzycka, R. Machinek, and W. Luttke, Bull. Pol. Acud. Sci., Chem., 1988,36,

390 K. Kamienska-Trela and Z . Biedrzycka, Bull. Pol. Acud. Sci., Chem., 1988, 36, 285.

3088.

1990, 87, 209.

105.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003


For some transoid homoallylic compounds, values of 'J('H--'H) across a C=C double bond have been reported."' INDO-RPA calculations predict the angular dependence of 5J('H--1H) satifactorily but fail to account for the observation that the 'J,.,, coupling is larger than the corresponding trans coupling. Some similar INDO- RPA calculations have been applied to 4J('H--1H) data for cy~ lopen tanone .~~~ The correct signs are found for the cis and trans couplings. However, the calculated magnitudes are too small. Another application of INDO-RPA calculations has been in the search for a Karplus type of relation for the angular variation of 3J('3C-1H) in some a-substituted pro pane^.^^^

The hindered rotor model is frequently used to determine rotation barriers for internal molecular motions. This is based upon a knowledge o f J a s a function of some dihedral angles. In the case of the "J('H-'H), n = 4-7, couplings of some methyl styrenes, as a function of the twist angle about the exocyclic C-C bond, the values calculated by the INDO-FPT procedure appear to be larger than those found experi- mentally.394 This seems to be due to an overestimate of the n and 0-n contributions to J . In the case of V(13C-13C), n = 3-5, as a function of the angle by which the SCH3 group is bent out of the benzene plane, satisfactory agreement with experiment is found for 23 thioanisole derivative^.^'^ Spin Relaxation. -Theoretical aspects of nuclear spin relaxation have been covered in various reviews.396-399 A quantum mechanical account of the basis of relaxation theory has appeared in a recent

Normally, the Wangsness, Bloch, Redfield (WBR) approach, employing density matrix theory, is used to describe spin rela~ation.~" A more generalized formulation of the WBR theory has been presented402 which uses the Liouville space formalism to derive the relevant relaxation equations. This approach has recently been extended to include scalar coupling relaxation, which results in a simpler version of a general theory of scalar coupling of the first kind.403

A topological approach has been developed for interpreting intramolecular dipolar I3C relaxation times.404 Topographic axes are defined, their number and location depending upon the molecular structure. As an illustration, the dipolar 13C relaxation in toluene is considered.

A theory has been presented for zero field NMR line shapes of spin systems undergoing Brownian reorientation.405407 Although mainly of interest for zero field

'" M. Barfield, R. 3. Spear, and S . Sternhell. Aust. J . Chem., 1989, 42, 659. 392 M. P. Golache, A. L. Esteban, and E. Diaz, Anafes Quim., Ser. A , 1988, 84, 316.

394 T. Schaefer, R. Sebastian, and G. H. Penner, Can. J . Chem., 1988, 66, 584. 39s T. Schaefer and G. H. Penner, Can. J . Chem., 1988, 66, 1229. 396 C. Rudowicz, Magn. Reson. Rev., 1987, 13, 1 . '" A. Abragam, Proc. Roy. Soc., A , 1987, 412, 255. 398 A. D. Bain, Prog. N M R Spectrosc., 1988, 20, 295. 39y D. Canet, Prog. NMR Spectrosc., 1989, 21, 237. 400 M. Goldman, 'Quantum Description of High Resolution NMR in Liquids', Oxford University Press,

40' A. G. Redfield, Adv. Magn. Reson., 1965, 1, 1 . 402 S. Szymanski, A. M. Gryff-Keller, and G. Binsch, J . Magn. Reson., 1986, 68, 399. 403 S. Szymanski and G. Binsch, J . Magn. Reson., 1989, 81, 104. 404 P. Born and T. Bluhm, J. Magn. Reson., 1989, 83, 494. 40s Y . A. Serebrennikov, Chem. Phys., 1987, 112, 253. 406 Y . A. Serebrennikov, M. I . Majitov, and Z . M. Muldakhmetov, Chem. Phys., 1988, 121, 307. 407 Y. A. Serebrennikov, Chem. Phys. Lett., 1987, 137, 183.

A. A. Van Beuzekom, F. A. A. M. de Leeuw, and C. Altona, Magn. Reson. Chem., 1990, 28, 68. 393

1988.

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

42 G . A . Webb

NMR studies of powders, the theory may also be applied to viscous liquids. Cal- culated line shapes are presented for systems of two homonuclear or heteronuclear spins with I = 4 coupled by a dipolar interaction. The case of one spin with I > 4 is also considered. An extension of this work includes a discussion of spin-lattice relaxation in zero magnetic field induced by molecular reorientation^.^" The stochastic Liouville approach is used to account for spin-lattice relaxation in molecules undergoing Markovian reorientations.

A model has been presented for the relaxation of simple flexible molecules in solution.409 Brownian motion is considered between different conformations which correspond to local minima of the energy surface. The overall tumbling is assumed to be unaffected by jumping between the conformations. The relaxation of 2-fluorobutane is considered as an example.

Where low applied magnetic fields or slow motion occurs the difference in the Zeeman frequencies of two spins may become comparable to the signal widths such that the spins are strongly correlated. A theory for dynamic line shapes of such strongly correlated two spin systems has been presented!1° In another development, line shapes produced by the dipolar interaction of two almost identical spins, undergoing slow motion, have been disc~ssed.~"

Outside the extreme narrowing region the relaxation of I 2 $ nuclei is non exponential. The consequences of this have been studied in various quarters. The effects of higher rank multipoles I 2 3, on the line shapes of I = 3, 5 , and 4 nuclei have been analy~ed.~" In another study, the relaxation of an I = 3 system in a non zero average electric field gradient has been considered together with its detection by non selective inversion recovery and multiple quantum experiment^.^'^

When high spin nuclei are involved in exchange processes complications may occur if one of the sites gives rise to relaxation outside the extreme narrowing region. This situation may frequently arise for exchange between a bound site and a free site in the bulk s o l ~ t i o n . ~ ' ~ * ~ ' ~

Cross relaxation between different interactions can produce interference terms which affect relaxation. A case in point being the interference term between the CSA and the dipolar interactions. Such terms may produce differential line broadening (DLB).4'6 A theory of DLB has been produced for coupled spin systems and molecular aggregates characterized by fast internal motions and slow overall A good example of this type of interaction is produced by the 'H coupled I3C multiplets of methyl groups.

A general analysis has been presented of the effects of non exponential transverse relaxation during the free precession periods of 2D NMR experiment^.^'^ The resulting cross peaks could give rise to assignment problems. 4ox Y . A. Serebrennikov and M. I. Mazhitov, Chem. Phys. Let[., 1989, 157, 462. 409 M. Baldo and A. Grassi, Magn. Reson. Chem., 1989, 27, 533. 410 N. P. Benetis, D. J. Schnejder, and J. H. Freed, J . Magn. Reson., 1989, 85, 275. 4 1 1 F. A. L. Anet and D. J. O'Leary, J . Magn. Reson., 1990, 86, 358. 412 L. Einarsson and P. 0. Westlund, J . Magn. Reson., 1988, 79, 54. 4 ' 3 J. R. C. Van der Maarel, Chem. Phys. Le f t . , 1989, 155, 288. 414 U. Elliov, A. Baram, and G. Navon, J . Chem. Phys., 1988, 89, 5584.

P. 0. Westlund and H . Wennerstrom, J. Magn. Reson., 1989, 81, 68. 4'6 T. C. Farrar and I. C . Locker, J . Chem. Phys.. 1987, 87, 3281. 4 1 7 L. P. Hwang, P. L. Wang, and T. C. Wong, J . P h j ~ . Chem., 1988, 92, 4753. 4 ' 8 T. C. Wong, P. L. Wang, D. M . Duh, and L. P. Hwang, J. Pliys. Clrenr., 1989, 93, 1295. 4'9 S. Wimperis and G. Bodenhausen, Mol. Phys., 1989, 66, 897.

415

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

Nuclear Magnetic Resonance Spectroscopy

Glossary of Abbreviations

43

AQ BIRD cc CCPPA CCSDPPA

CHESS C H F COSY CP CPMG CRAMPS CSA CSI DAS D D DEPT DLB DOR 2,3 DPG DQ D G F DTPA ECOSY EHT EOM EPI EXSY FID FLASH FPT GIAO HMQ HOHAHA HRPA IDESS IGLO INADEQUATE INDO INDO/S INEPT IPPPA IRCP ISIS J R LMO LORG MAS MBPT MEM M I N D 0

CH-COSY

MQ MQC MQF M RI NMR

Acquire Bilinear Rotation Decoupling Coupled Cluster Coupled Cluster Polarization Propagator Approximation Coupled Cluster Singles and Doubles Polarization Propagator Approximation Carbon-Hydrogen Correlation Spectroscopy Chemical Shift Selection Coupled Hartree-Fock Molecular Orbital Calculations Correlation Spectroscopy Cross Polarization Carr-Purcell Pulse Sequence with Meiboom Gill Modification Combined Rotation and Multipulse Sequences Chemical Shielding Anisotropy Chemical Shift Imaging Dynamic Angle Spinning Dipole-Dipole Contribution to Nuclear Relaxation Process Distortionless Enhancement by Polarization Transfer Differential Line Broadening Double Rotation 2,3-Diphosphoglycerate Double Quantum Double Quantum Filter Diethylene Triamine Pentacetic Acid Exclusive Correlation Spectroscopy Extended Huckel Molecular Orbital Theory Equations of Motion Echo Planar Imaging Exchange Spectroscopy Free Induction Decay Fast Low Angle Shot Finite Perturbation Theory Gauge Included Atomic Orbitals Heteronuclear Multi-Quantum Homonuclear Hartman-Hahu Higher Random Phase Approximation Improved Depth Selective Single Surface Coil Spectroscopy Individual Gauge for Different Localized Orbitals Incredible Natural Abundance Double Quantum Transfer Experiment Intermediate Neglect of Differential Overlap Molecular Orbital Calculations Intermediate Neglect of Differential Overlap Calculations for Spectroscopy Insensitive Nuclei Enhanced by Polarization Transfer Inner Projection of the Polarization Transfer Inversion Recovery Cross Polarization Image Selected Zn vivo Spectroscopy Jump Return Localized Molecular Orbitals Local Origin Magic Angle Sample Spinning Many Body Perturbation Theory Maximum Entropy Method Modified Intermediate Neglect of Differential Overlap Multiple Quantum Multiple Quantum Coherence Multiple Quantum Filter Magnetic Resonance Imaging Nuclear Magnetic Resonance

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

44 G. A . Webb

NOE NOESY PFG POM REX ROESY RPA SOPPA sos SQ TOCSY TQ WBR ZQ ZQC

Nuclear Overhauser Enhancement Nuclear Overhauser Enhancement Spectroscopy Pulsed Field Gradient Poly(Oxymethy1ene) Relativistically Extended Huckel Molecular Orbital Theory Rotating Frame Overhauser Enhancement Spectroscopy Random Phase Approximation Second Order Polarization Propagator Approach Sum-Over-States Single Quantum Total Correlation Spectroscopy Triple Quantum Wangsness Block Redfield Zero Quantum Zero Quantum Coherence

Publ

ishe

d on

01

Janu

ary

1990

. Dow

nloa

ded

by U

nive

rsity

of

Cal

ifor

nia

- Sa

nta

Cru

z on

29/

10/2

014

06:4

9:25


http://dx.doi.org/10.1039/pc9908700003

chapter 2. nuclear magnetic resonance spectroscopy

Documents