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Vibrational analysis of biliverdin dimethyl ester
Zitatschlüssel ISI:A1993MH56300009
Autor Smit, K and Matysik, J and Hildebrandt, P and Mark, F
Seiten 11887-11900
Jahr 1993
ISSN 0022-3654
Adresse 1155 16TH ST, NW, WASHINGTON, DC 20036
Journal J. Phys. Chem.
Jahrgang 97
Nummer 46
Monat NOV 18
Zusammenfassung The Fourier-transform resonance Raman and infrared spectra of biliverdin dimethyl ester and the isotopomer deuterated at the pyrrole nitrogens were measured in the solid state and in CCl4 solution. A vibrational analysis of the spectra is presented. The force field was obtained on the basis of the semiempirical AM1 method by a two-step procedure. First, scaled AM1 force fields for fragments of the tetrapyrrole system were developed according to Pulay's scaling method (Pulay, P.; Fogarasi, G.; Pongor, G.; Boggs, J. E.; Vargha, A. J. Am. Chem. Sec. 1983, 105, 7037). These force fields were checked against those from ab-initio Hartree-Fock calculations. The scaling factors optimized for the fragments were used as initial parameters for the vibrational analysis of biliverdin dimethyl ester. They were refined in the second step by using both the frequencies and the infrared and resonance Raman intensities as criteria. The resonance Raman intensities were estimated according to the model introduced by Peticolas and co-workers (Peticolas, W. L.; Strommen, D. P.; Lakshminarayanan, V. J. Chem. Phys. 1980, 73, 4185). The accuracy of the normal mode analysis was better than 20 cm(-1) which along with the evaluated intensities allowed for a unique assignment of most of the observed bands. It was found that most of the vibrational modes are localized in the individual pyrrole rings and the adjacent methine bridges.
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