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