Assignment of bacteriochlorophyll a ligation state from absorption and resonance raman spectra

Journal Article · Wed Nov 11 04:00:00 EST 1987 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00257a016· OSTI ID:6981634

Callahan, P M; Cotton, T M

Absorption and Soret excitation resonance Raman (RR) spectra have been obtained for a series of coordination forms on monomeric bacteriochlorophyll a (BChl a). Strong and moderate intensity bands are observed in the RR spectrum at 1609 and 1530 cm/sup -1/ for five-coordinate species, which shift to 1595 and 1512 cm/sup -1/, respectively, in the six-coordinate form. These coordination-sensitive vibrations are independent of the nature of the axial ligand and are suggested to have significant C/sub a/ C/sub m/ character, while several other less intense coordination-sensitive bands at 1463, 1444, and 1375 cm/sup -1/ are considered to arise from C/sub b/C/sub b/ and C/sub a/N stretching vibrations. These coordination-sensitive RR bands were used to determine BChl a ligation state in the solvents used, and structure correlations based on absorption maxima have been developed. The Q/sub x/ absorption band position is sensitive not only to BChl a Mg/sup 2 +/ coordination number but also to the nature of the axial ligand, i.e., oxygen, sulfur, or nitrogen. Q/sub x/ maxima are observed at 570, 575-580, and 582 nm for five-coordinate oxygen, sulfur, and nitrogen ligands, respectively, and at 590-595 and 605-612 nm, for six-coordinate oxygen and nitrogen species, respectively. The Q/sub y/ absorption maximum is insensitive to coordination number changes but is dependent on the nature of the axial ligand: 770 nm for oxygen ligand(s) and 775 nm for nitrogen ligand(s). A similar series of absorption and Soret excitation RR spectra were obtained for the demetalated form of BChl a, BPheo a.

• Research Organization: Univ. of Nebraska, Lincoln (USA)
• OSTI ID: 6981634
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 109:23; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
ABSORPTION SPECTRA
ABSORPTION SPECTROSCOPY
CARBOXYLIC ACIDS
CHLOROPHYLL
DATA
ELEMENTS
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
LASER SPECTROSCOPY
LIGANDS
MONOMERS
NITROGEN
NONMETALS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PROTEINS
RAMAN SPECTRA
RAMAN SPECTROSCOPY
SPECTRA
SPECTROSCOPY