practical aspects schneider - tata institute of fundamental...
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Practical Aspects of Solid State NMR Experiments
Denis Schneider
International School on SS NMR, Jan. 4 – 8, 2010, Ooty, India
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Outline
• Practical aspects of solid state NMR experiments
• Magic angle adjustment
• Hartmann-Hahn adjustment (cross polarization)
• Decoupling
• CP throughout the periodic table
• What to consider for VT experiments
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Outline
• Practical aspects of solid state NMR experiments
• Magic angle adjustment
• Hartmann-Hahn adjustment (cross polarization)
• Decoupling
• CP throughout the periodic table
• What to consider for VT experiments
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Magic Angle Adjustment
• Requirements for the set-up sample:
• Sensitive to angle setting
• large interaction to be averaged by MAS
• narrow lines achievable
• more sensitive than samples of interest
• Easy to observe
• large signal
• at desired observe frequency
54.7°
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Magic Angle Adjustment
• Standard set-up sample (13C work):
• KBr with 79Br detection
• criterion: spinning side bands
• sensitive to magic angle due to approx. 100 kHzquadrupolar interaction
• narrow lines
• close to 13C frequency (75.16 MHz vs 75.43 MHz @ 300 MHz)
• good S/N on a single scan 54.7°
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Magic Angle Adjustment
-200400 200 0 ppm-16-14-12-10-8-6-4-20 ppm
setting the magic angle with KBr (79Br detection)spinning speed 5 kHz
angle grossly misset (by about 1 turn)x 16 x 8
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Magic Angle Adjustment
-200400 200 0 ppm-16-14-12-10-8-6-4-20 ppm
setting the magic angle with KBr (79Br detection)spinning speed 5 kHz
angle misset (by about 1/4 turn)x 16 x 8
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Magic Angle Adjustment
-200400 200 0 ppm-16-14-12-10-8-6-4-20 ppm
setting the magic angle with KBr (79Br detection)spinning speed 5 kHz
angle well set x 8x 16
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Outline
• Practical aspects of solid state NMR experiments
• Magic angle adjustment
• Hartmann-Hahn adjustment (cross polarization)
• Decoupling
• CP throughout the periodic table
• What to consider for VT experiments
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Cross Polarization – Basic Principles
I,0ω S,0ωS,1I,1 ωω =
laboratoryframe, I spin
laboratoryframe, S spin
rotatingframe
I,1II,1
0II,0
BB
γωγω
=
=
Hartmann-Hahn match: S,1SI,1I BB γγ =
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nucleus naturalabundance
max. enhancementfactor
13C 1.11 % 415N 0.37 % 1029Si 4.70 % 531P 100 % 2.5
Cross Polarization – What can beAchievedsignal enhancement by polarization transfer:
εγγ
+⋅1
1
S
I
faster repetition: recycle delay ~ 1.25 T1,1H
usually T1,1H << T1,13C (T1,15N …)
I
S
NN
=ε
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13C CP/MAS Set-up Using Glycine
CP/MAS spectrum of glycine (5 kHz spinning speed)
-20240 220 200 180 160 140 120 100 80 60 40 20 0 ppm
HOOHOOCC--CCHH22--NHNH22Carboxyl 13C:• sensitive HH match• easy to decouple• sensitive to angle 13Ca:
• broad HH match• high power decoupling
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Basic CP(/MAS) Pulse Sequence
90x
decoupling
contactaquire
1H
13C
contact
ν1,13-C = ν1,1-H
ν1=1/(4*τ90) is RF field
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Hartmann-Hahn Matching Profiles
MAS = 12500 Hz
75 70 65 60 55 50 45 40 35 30 25 kHz75 70 65 60 55 50 45 40 35 30 25 kHz
MAS = 2500 HzCH2 CH2
COCO
Ha-Ha-match Ha-Ha-match
Glycine 13C signal amplitudes as function of 1H RF field13C RF field constant at 45 kHzusing square pulses for CP
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Ramped (Variable Amplitude) Cross Polarization
90x
contactdecoupling
contactaquire
1H
13C
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Hartmann-Hahn Matching Profiles
MAS = 12500 Hz
75 70 65 60 55 50 45 40 35 30 25 kHz75 70 65 60 55 50 45 40 35 30 25 kHz
MAS = 2500 HzCH2 CH2
COCO
Ha-Ha-match Ha-Ha-match
Glycine 13C signal amplitudes as function of 1H RF field13C RF field constant at 45 kHzusing ramp pulse for CP from 100 % to 50 % amplitude
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Cross Polarization Dynamics
proton magnetization decays with T1ρ
cross polarization builds up with TIS
signal follows combined effect of buildup and decay
90
~ TIS
~ T1ρ
13C
1H
90° contact
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Cross Polarization Dynamics
best case: T1ρ >> TIS
worst case: T1ρ << TIS
1H
13C
1H
13C
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Cross Polarization Dynamics
• Contact time, practical considerations for 13C
• Short TIS (~500 µs): directly attached protons (-CH3, -CH2-, >CH-)
• Long TIS (>1 – 2 ms): quaternary carbons (>C<,-COO-, substituted aromatic systems, …), high mobility
• Short T1ρ: paramagnetic systems/impurities (e.g. in coal), high mobility
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Outline
• Practical aspects of solid state NMR experiments
• Magic angle adjustment
• Hartmann-Hahn adjustment (cross polarization)
• Decoupling
• CP throughout the periodic table
• What to consider for VT experiments
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Decoupling Methods
high power decoupling (CW)
ττdecdec
BB1,dec1,dec
TPPM decoupling (Two Pulse Phase Modulation)
ττdecdec
BB1,dec1,dec
ππ00
ππ11
55
ππ00
ππ11
55
……
and many more (XiX, SPINAL, π-pulse, etc.)
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Outline
• Practical aspects of solid state NMR experiments
• Magic angle adjustment
• Hartmann-Hahn adjustment (cross polarization)
• Decoupling
• CP throughout the periodic table
• What to consider for VT experiments
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Cross Polarization Throughout the Periodic Table
• Standard: I = ½ → S = ½
• Most frequent:
• I = 1H → S = 13C, 15N, 29Si, 31P
• Less common, but worthwhile:
• I = 1H → S = 77Se, 89Y, 113Cd, 119Sn, 129Xe, 195Pt, 199Hg, 207Pb
• Fluorinated materials:
• I = 19F → S = 13C, 15N, 29Si, 31P• Low γ nuclei (e.g. 15N): more X and/or less 1H power
• Quadrupolar nuclei: different story
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Cross Polarization Throughout the Periodic Table
• Experiment will be simple, if
• Natural abundance is high
• Larmor frequency is high
• CP can be used in case of spin ½ nuclei
• difficult, if TIS >> T1ρ, e.g. for low γ nuclei
• Spin I must be considered
• For spin > ½ selectivity and connectivity information is more importantthan gain in sensitivity
• Consider elements with several isotopes
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Cross Polarization Throughout the Periodic Table• Elements with several NMR aktive isotopes
• 6Li 7Li• 10B 11B• 14N 15N• 35Cl 37Cl• 39K 41K• 47Ti 49Ti• 50V 51V• 63Cu 65Cu• 69Ga 71Ga• 77Se 79Se• 79Br 81Br• 85Rb 87Rb• 95Mo 97Mo• 99Ru 101Ru• 101Rh 103Rh• 107Ag 109Ag• 111Cd 113Cd• 113In 115In• 115Sn 117Sn 119Sn
• 121Sb 123Sb• 123Te 125Te• 129Xe 131Xe• 135Ba 137Ba• 138La 139La• 147Sm 149Sm• 151Eu 153Eu• 155Gd 157Gd• 161Dy 163Dy• 171Yb 175Yb• 175Lu 176Lu• 177Hf 179Hf• 185Re 187Re• 187Os 189Os• 191Ir 193Ir• 199Hg 201Hg• 203Tl 205Tl
• Spin ½
• Spin n
• Spin n/2
• > 99 % natl. abundance• 9Be, 14N, 19F, 23Na• 27Al, 31P, 45Sc, 55Mn• 59Co, 75As, 89Y, 93Nb• 103Rh, 127I, 133Cs, 139La• 141Pr, 159Tb, 165Ho, 169Tm• 181Ta, 197Au, 209Bi
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Chart of all 29 X Nuclei with Spin ½
57Fe 187Os 13C 15N 29Si 77Se3He 115Sn
117Sn 119Sn123Te 125Te
< 10%
183W 111Cd 113Cd 171Yb 195Pt 199Hg 207Pb
129Xe50-10%
107Ag 109Ag203Tl 205Tl70-50%
89Y 103Rh 169Tm19F 31P100-70%
γN-15 > γXγC-13 ≥ γX ≥ γN-15γX > γC-13nucl.
natl.abundance
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Cross Polarization of “Standard” Nuclei
002relative attenuation 1H [dB]
656355RF field [kHz]
30-2relative attenuation X [dB]
150200500X power at CP match [≈W]
16210040Larmor frequency [MHz]
31P13C15Nnucleus
15N 13C 31Pfrequency
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Cross Polarization of “Exotic” Nuclei
15N 13C 31P
57Fe 89Y 199Hg 29Si 113Cd 125Te 119Sn
frequency
002relative attenuation 1H [dB]
656355RF field [kHz]
30-2relative attenuation X [dB]
150200500X power at CP match [≈W]
16210040Larmor frequency [MHz]
31P13C15Nnucleus
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Some Reference Compounds forCP Set-up
nucleus sample shift (ppm) relative to contact (ms)
recycle (s) frequency (MHz) rel. to 200
remarks
15N glycine, enriched -345 CH3NO2 5 10 20.280213 natl. abundance: visible in 1 scan
29Si Q8M8 12.4 (t) TMS 5 10 39.758361 easy but expensive
-110 (o)
31P (NH4)H2PO4 0 H3PO4 1 4 81.013812 anything will do
77Se H2SeO3 Se(Me)2 3 4 38.217585 1 scan, but poisonous easy, narrow
(NH4)2SeO4 -1040.2 38.128907
89Y Y(NO3)3*H2O -53.2 sol. in H2O 10 10 9.807451 visible after 1 scan FT
113Cd Cd(NO3)*4H2O -100 1m Cd(ClO4)2 15 8 44.381609
119Sn Sn(cyclohexyl)4 -97.35 Sn(Me)4 1 20 74.639360 easy, 1 scan
129Xe Xe at 40b in hydroquinone clathrate, 3 hours
222 Xe in air 30 5 55.333703 Xe in air is visible overnight (single pulse)
199Hg Hg(OAc)2 -2487 Hg(Me)2 5 10 35.765352 16 scans, 125 kHz, 4K points (lots of sidebands)
-2493
207Pb Pb(phe)4 41.861650 1 scan, poisonous, no good set-up
Pb(p-tol)4 -148.8 Pb(Me)4 5 12 41.863710 better, but also poisonous, 1 scan
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Outline
• Practical aspects of solid state NMR experiments
• Magic angle adjustment
• Hartmann-Hahn adjustment (cross polarization)
• Decoupling
• CP throughout the periodic table
• What to consider for VT experiments
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Variable temperature in MAS
• experimental aspects
• probe design
• high temperature experiments
• low temperature experiments
• rotors and caps
• temperature determination
• undesired temperature changes
• challenges and problems
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Variable temperature - demands
• In general
• stable temperature (during experiment)
• small temperature gradient
• protection of probe, shim system, magnet
• temperature calibration
• MAS in particular
• stable spinning during cooling or heating
• stable spinning at high and low temperature
• temperature calibration
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VT ranges of WB MAS probes
Exception: 1.3 mm and 2.5 mm probes: -30°C ↔ +70°C
VTN : Variable Temperature Normal (BN-Stator)WVT : Wide Variable Temperature (MgO-Stator)DVT : Direct Variable Temperature (BN-Stator)
VTNVTN
+150+150°°CC +300+300°°CC
WVTWVT
--140140°°CC
DVTDVT
TT
+120+120°°CC--8080°°CC--120120°°CC
2020°°CC+700+700°°CC+400+400°°CC
MASCAT (7mm)MASCAT (7mm)
LTMASLTMAS
LASERMAS (7mm)LASERMAS (7mm)
SB MASSB MAS
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MAS probe design
VTN/WVT
variable temperature via bearinggas
DVT
variable temperature via separate (direct) gas
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Arrangement of thermocouples
TC 2: regulation (regul)
TC 1: control (read)
PH MAS DVT 600 WB BL4 (H8724)
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heaterheaterconnectorconnector
heaterheater
bearingbearing gas gas plus VT gasplus VT gas
thermocouplethermocouple((Cu/ConstCu/Const))
spinningspinning rate rate sensorsensor electronicselectronics
drivedrive gasgas
frameframe flushingflushingVTNVTN
VTN + WVTVTN + WVT
all all typestypes
Variable temperature
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thermocouplethermocouple 1 (gas 1 (gas exhaustexhaust))
thermocouplethermocouple 2 (VT gas 2 (VT gas inputinput))
VT gas VT gas onlyonly
bearingbearing gasgas
drivedrive gasgas
WVTWVT
DVTDVT
DVTDVT
bearingbearing gasgasplus VT gasplus VT gas
Variable temperature
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Low temperature
Moderately low: BCU-05 cooling unitHR- and MAS-Version (pressure)cools gas stream typically by 65 Ktemperature range: approx. -15°C to +50°C
Low temperature: BCU-X cooling unitHR- and MAS-Version (pressure)cools gas stream typically by 100 Ktemperature range: approx. -50°C to +50°C
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Low temperature
really low: heat exchangerMAS version for VTN, WVT, DVTHR version for DVTcooling down of heat exchanger only underdry N2 gas
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Low temperature
LT-MAS system: 100K
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High temperature
Laser MAS system
diode Laser
7mm MAS probe
up to 700°C
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Rotor caps
ZrOZrO22 MacorMacor BNBN KelKel--FF VespelVespel
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Rotor caps
Kel-F (polymer): ambient temperature ± , (cold: shrinks, hot: deforms), easy pull-out
BN (ceramic): high and low temperature, mechanicallydamageable (glue in, if necessary)
Macor (ceramic): high and low temperature, mechanicallyweak (glue in, if necessary)
ZrO2 (ceramic): high and low temperature, mechanicallyrobust, easy pull-out,not cheap ...
Vespel (polymer): high speed and temperature, easypull-out
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spinner diameter
-140°C ... +300°CBoron nitrid
-140°C ... +300°CZirconia, Macor
-10°C ... +50°CKel-F7 mm
-140°C ... +300°C
-140°C ... +300°C
Zirconia
Boron nitrid
-10°C ... +50°C
-30°C ... +70°C
Kel-F
Vespel4 mm
-140°C ... +300°CZirconia
-10°C ... +50°C
-30°C ... +70°C
Kel-F
Vespel3.2 mm
-30°C ... +70°CVespel1.3 mm and 2.5 mm
temperature rangematerial of rotor cap
Spinner Caps: Materials / Applic. Ranges
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VT gas
N2 from boil-off device:dry, oil freelow pressure fluctuationinert
! Caution !! Look after fresh air !
! O2 warning system where required !
Compressed gas from compressor:pay attention to dew point and oil content (0.0 %)condensation of O2 at low temperaturerisc of oxidation at high temperaturepressure fluctuation
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Probe and magnet protection
transfer tube
shimsystem “frame cooling“
NO ice nor heat at O-rings!
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Probe and magnet protection
flush gas (ambient temperature) forshimsystemprobehead (“frame cooling“)transfertube
critical parameters:high temperature: shim coils: T ≤ 70 °Clow temperature: shim coils: T > 0 °Clow temperature: in case of icing of O-rings risc of leakage of vacuum and quench!
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Undesired temperature effects
coolingJoule-Thompson-effect when bearing gas expands(depends on bearing pressure)
heatingfrictional heating in the bearingsdepends on bearing pressure and flowimportant to consider at fast spinning
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Slow heating and cooling!
For heating and cooling consider thermal burdenon probe
using a ramp of 6 to 10 degrees per minute is recommended
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Change temperature via ramp (1)
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Change temperature via ramp (2)
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Challenges and problems
rotor crashunbalance when sample meltspushing out of rotor caps due to
degassing, loss of crystal water, decompositionmoving material (plastic crystals, fatty acids)extreme thermal expansion
solution:reduce volume (insert-plugs, CRAMPS rotor)glue cap inuse top CRAMPS plug
no sample ejectreason: moist air is absorbed via the transfer tube
and condensation in low temperature experimentssolution: flush gas trough “insert“-tube
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Variable temperature: literature
• Chemical shift thermometer:
• 207Pb-MAS using Pb(NO3)2:A.Bielecki and D.P. Burum: Temperature Dependence of 207Pb MAS Spectra of Solid Lead Nitrate. An Accurate, Sensitive Thermometer for Variable-Temperature MAS; J.Magn.Reson. A116, 215-220 (1995)
• 119Sn-MAS using Sm2Sn2O7:B. Langer, I. Schnell, H.W. Spiess and A.-R. Grimmer: Temperature Calibration under Ultrafast MAS Conditions, J.Magn.Reson. 138, 182-186 (1999)
• 79Br-MAS using KBr:Measurement of sample temperatures under Magic-angle spinning from the chemical shift and spin-lattice relaxation rate of 79Br in KBr powder, J.Magn.Reson. – in Press
• Fix points with liquid to solid or solid to solid phase transition:
• J.F. Haw, R.A. Crook and R.C. Crosby: Solid-Solid Phase Transition for Temperature Calibration in Magic-Angle Spinning, J.Magn.Reson. 66, 551-554 (1986)
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