Nuclear Resonance Vibrational Spectroscopy (NRVS)

UNIVERSITY OF MICHIGANDEPARTMENT OF CHEMISTRY

The

LehnertGroup

Dr. Nicolai Lehnert

Nuclear Resonance Vibrational Spectroscopy (NRVS) Synchrotron-based vibrational technique Developed in the 1990’s First reported in 1970’s, but proper equipment was not

developed until later Combination of nuclear excitation and molecular

vibrations Uses the Mössbauer effect to excite the nucleus Measures inelastic scattering of the system Provides a complete set of bands that involve motion of

the probed nucleus

Mössbauer Spectroscopy: Energy Source

Mössbauer dominated by internal conversion

Source of gamma rays is a radioactive isotope of an element which decays into an excited state of the isotope under study

Returns to the ground state by the emission of a gamma ray or electron Mössbauer active

isotopes must have a meta-stable excited state

The relaxation to the ground state produces the gamma rays used in experiment

Mössbauer Spectroscopy

By moving the gamma ray source a change in energy of the emitted photons is achieved using the Doppler effect

When the energy of the modulated beam matches the difference in energy between the ground and first excited state of the absorber then the gamma rays are resonantly absorbed

Measures transmittance so peaks appear as a decrease in counts in the spectrum

Theory of NRVS NRVS measures inelastic scattering of the gamma rays

Selective for vibrations involving displacement of Mössbauer active nuclei No optical selection rules apply Yielding the complete set of motions involving probed

nucleus

The peaks seen are recoil-free resonance energies corresponding to vibrational quanta

Like Raman, NRVS is a very inefficient process, so an intense gamma ray source is needed

Nuclear Resonance Vibrational Spectroscopy (NRVS)

Undulator – synchrotron Only three 3rd generation

synchrotron’s in useFrance, USA, and Japan

Experimental Setup

Nuclear Resonance Vibrational Spectroscopy (NRVS)

‘Raman’ spectroscopy (inelastic scattering) on the Mössbauer line

NRVS Beamline

NRVS Theory: Sage, Sturhahn, Scheidt & coworkers, J. Phys. Condens. Matter 2001, 13, 7707

Refining the Incident Beam

Heat-load Monochromator Composed of 2 crystals

Silicon (France, Japan) Diamond (USA)

Has to be well cooled Beam is reduced to a few eV

High Resolution Monochromator Requires a separate crystal

for each nuclei Reduces the beam width to

around 1meV

NRVS Theory: Sage, Sturhahn, Scheidt & coworkers, J. Phys. Condens. Matter 2001, 13, 7707

Collection of Data

Beam grazes sample at only 6° Detector is located 90° from sample

Avoids the large amount of elastic scattering that comes off 180°from sample

Measures the amount of counts to hit the detector

NRVS Theory: Sage, Sturhahn, Scheidt & coworkers, J. Phys. Condens. Matter 2001, 13, 7707

Example of Raw Data

Software converts from raw intensity (photon count) to Vibrational Density of States (VDOS; see later)

VDOS data can be used to calculate sample temperature, analogous to Stokes/Antistokes ratio in Raman spectroscopy

Scheidt, Sage & coworkers, J. Inorg. Biochem. 2005, 99, 60-71.

Case Study: Ferrous Heme Nitrosyls NO binding to deoxy Mb/Hb

Effect of the distal hydrogen bond?

Compare to model complex NN

N

N

N

N

N

N

N

N

N

NN

NFe

NO

[Fe(TPP)(MI)(NO)]

Ferrous Heme-Nitrosyls

Vibrational Spectroscopy: isotope labeling Important vibrations:

• N-O stretching

• Fe-NO stretching

• Fe-N-O bending

Information about bond strengths, oxidation states, etc.

N. Lehnert, "Quantum Chemistry Centered Normal Coordinate Analysis (QCC-NCA): Application of NCA for the Simulation of the Vibrational Spectra of Large Molecules"; in: “Computational Inorganic and Bioinorganic Chemistry”; Solomon, E. I.; King, R. B.; Scott, R. A., Eds., The Encyclopedia of Inorganic Chemistry, John Wiley & Sons, Chichester, UK, 2009, 123-140

NRVS on [Fe(TPP)(MI)(NO)]

100 150 200 250 300 350 400 450 500 550 600 650 7000

200

400

600

800

1000

1200

1400

(Fe-N-O)

55142

9*

563

149

210

248 29

8 471

437

405

338

rela

tive

Inte

nsity

[cou

nts]

relative wavenumbers [cm-1]

N.A.I. 15N18O

[Fe(TPP)(MI)(NO)]

318

(Fe-NO)

NRVS raw data

Paulat, Berto, DeBeer George, Goodrich, Praneeth, Sulok & Lehnert, Inorg. Chem. 2008, 47, 11449

Vibrational Density of States (VDOS)

63

1

2,Fe )~~(e)~(

N

D

(total VDOS)

63

1

2

,Fe )~~(e)~(N

k kD

(VDOS in direction k; k = x, y, z)

Calculation of VDOS from NRVS raw intensity:

Factors e : amount of iron motion in a normaI mode specific property of a vibration:

2Fe

i

2ii

2FeFe2

Feerm

rm

Sage, Sturhahn, Scheidt & coworkers, J. Phys. Condens. Matter 2001, 13, 7707

100 150 200 250 300 350 400 450 500 550 600 650 7000.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

eFe2 = 0.06

eFe2 = 0.126

203

429

551

56314

9

209

248

297

318

338

405

472

437

VDO

S (c

m)

rel. wavenumbers (cm-1)

[57Fe(TPP)(MI)(14N16O)] [57Fe(TPP)(MI)(15N18O)]

• Integrated VDOS intensity is proportional to the amount of iron motion in a normal mode • Can be simulated using normal coordinate analysis!

EXP:

48.0]437[e]563[e

2Fe

2Fe

Vibrational Density of States (VDOS)

Paulat, Berto, DeBeer George, Goodrich, Praneeth, Sulok & Lehnert, Inorg. Chem. 2008, 47, 11449

Vibrational Analysis (NCA) Simulation of Data using Normal Coordinate Analysis

(with some help from DFT: QCC-NCA method)

100 150 200 250 300 350 400 450 500 550 600 650 7000.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040total Intensity

Experiment (powder) QCC-NCA: total intensity

563

149

210

248

297

318

338

405

472

437

[Fe(TPP)(MI)(NO)]

VDO

S[c

m]

rel. wavenumbers [cm-1]

QCC-NCA: Praneeth, Näther, Peters & Lehnert, Inorg. Chem. 2006, 45, 2795

Assignment

Lehnert, Sage, Silvernail, Scheidt, Alp, Sturhahn & Zhao, Inorg. Chem. 2010, 49, 7197

Or a bit more dynamic… The Fe-N-O bending mode

(563 cm-1)

The Fe-NO stretching mode(437 cm-1)

Summary [Fe(TPP)(MI)(NO)] models hydrogen-bond free Mb mutants!

1600 1605 1610 1615 1620 1625 1630 1635 1640 1645 1650540

542

544

546

548

550

552

554

556

558

560

562

564

566

568

570

[Fe(TPP)(MI)(NO)]

V68T

V68A

V68G

H64L

H64IH64VH64A

H64G

H64Q

ip(F

e-N

-O) [

cm-1]

(N-O) [cm-1]

wt

Similar Fe-NO stretching frequency in wt Mb(II)-NO and [Fe(TPP)(MI)(NO)] indicates weak effect of H-bond on Fe-NO bond!

Shift in N-O stretching frequency is due to polarization of the /* orbitals of NO

Data from: Coyle, Vogel, Rush III, Kozlowski, Williams, Spiro, Dou, Ikeda-Saito, Olson & Zgierski, Biochemistry 2003, 42, 4896

Lehnert, Sage, Silvernail, Scheidt, Alp, Sturhahn & Zhao, Inorg. Chem. 2010, 49, 7197

One Electron Oxidation

100 150 200 250 300 350 400 450 500 550 600 650 7000

100

200

300

400

500

600

571

581

455

407

323

286

236

118

[Fe(TPP)(MI)(NO)](BF4)N

RVS

Inte

nsity

[cou

nts]

relative wavenumbers [cm-1]

N.A.I. 15N18O

NRVS on [Fe(TPP)(MI)(NO)](BF4) – the analogous ferric complex

V. K. K. Praneeth, F. Paulat, T. C. Berto, S. DeBeer George, C. Näther, C. D. Sulok, N. Lehnert, J. Am. Chem. Soc. 2008, 130, 15288

NRVS on [Fe(TPP)(MI)(NO)](BF4)

400 450 500 550 600 6500.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

e2Fe=0.311

554

547

540

586

407

455

571

578

N.A.I. 15N18O

[Fe(TPP)(MI)(NO)](BF4)

VDO

S [c

m]

rel. wavenumbers [cm-1]

e2Fe=0.225 35.1

]O)-N(Fe[e]NO)ν(Fe[e

lb2Fe

2Fe

EXP:(Fe-NO) (Fe-N-O)

Fe-NO stretch shifts to 578 cm-1

(with natural abundance Fe: 580 cm-1)

V. K. K. Praneeth, F. Paulat, T. C. Berto, S. DeBeer George, C. Näther, C. D. Sulok, N. Lehnert, J. Am. Chem. Soc. 2008, 130, 15288