Vibrational analysis of biliverdin dimethyl ester

Abstract

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 CCl 4 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. Soc. 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