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New developments in the calculation of metalloporphyrin Raman spectra via density functional theory
Author(s) -
Spiro Thomas G.,
Kozlowski Pawel M.,
Zgierski Marek Z.
Publication year - 1998
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/(sici)1097-4555(199810/11)29:10/11<869::aid-jrs331>3.0.co;2-t
Subject(s) - density functional theory , raman spectroscopy , chemistry , wavenumber , dipole , molecular physics , excited state , porphyrin , ground state , normal mode , molecular vibration , bond length , distortion (music) , computational chemistry , atomic physics , vibration , crystallography , materials science , physics , optics , photochemistry , optoelectronics , organic chemistry , quantum mechanics , cmos , crystal structure , amplifier
The recent development of density functional theory (DFT) makes itpossible to calculate accurately metalloporphyrin structures andpotential surfaces. This is illustrated for nickel porphine, thevibrations of which are reliably assigned from extensive spectroscopicstudies. With a minimal set of scaling factors, the DFT force fieldreproduces the experimental wavenumbers to higher accuracy than thebest available empirical force field. Moreover, the calculatedintensities are in good accord with experiment, including thesurprisingly large off‐resonant Raman intensities of non‐totallysymmetric ( B 1 g ) modes. DFT alsopredicts a slight ruffling distortion of the porphyrin, and accuratelyreproduces the IR intensity of a distortion‐induced out‐of‐plane mode.In the case of iron porphine, DFT correctly predicts anintermediate‐spin( 3 A 2 g ) ground state,with short Fe—N bonds, and a high‐spin( 5 A 1 g ) excited statewith a planar geometry but an expanded porphyrin core. When the Fe isdisplaced from the plane, the potential rises faster for the 3 A 2 g than the 5 A 1 g state, whichbecomes the ground state beyond a 0.4 Å displacement. The domingmode is predicted to be at 71 cm ‐1 , close to the 75cm ‐1 wavenumber determined from coherent reaction dynamicsin myoglobin. The vibrational wavenumbers of CO bound to heme arecorrectly calculated, and the potential for distorting the CO awayfrom the heme normal is found to be surprisingly soft. Also, thetransition dipole for the CO stretching mode is calculated to lagsignificantly behind the CO bond vector, thereby resolving an apparentdiscrepancy between crystallography and polarized IR spectroscopy withregard to the CO geometry in its adduct with myoglobin. Finally, theDFT force field was used successfully in conjunction with INDOcalculations of the excited states, to reproduce resonance Ramanintensities for NiP, both for Soret and Q ‐band resonances.These results give promise for developing a quantitative modelingcapability for heme protein vibrational spectra. Copyright © 1998 JohnWiley & Sons, Ltd.