Interpretation of the resonance Raman spectra of linear tetrapyrroles based on DFT calculations

Raman spectra of linear methine-bridged tetrapyrroles in different conforma tional and protonation states were calculated on the basis of scaled force fields obtained by density functional theory. Results are reported for prot onated phycocyanobilin in the extended ZZZasa configuration, as it is found in C-phycocyanin of cyanobacteria. The calculated spectra are in good agre ement with experimental spectra of the protein-bound chromophore in the alp ha-subunit of C-phycocyanin and allow a plausible and consistent assignment of most of the observed resonance Raman bands in the region between 1000 a nd 1700 cm(-1). (C) 1999 Elsevier Science B.V. All rights reserved.