FT-IR and near-infrared FT-Raman study of aggregation of bacteriochlorophyll c in solutions: evidence for involvement of the ester group in the aggregation.
Ultraviolet-visible (UV-Vis) absorption, Fourier-transform infrared (FT-IR), and near-infrared (NIR)-excited FT-Raman spectra have been measured for bacteriochlorophyll c (BChl-c) in acetone, tetrahydrofuran (THF), pyridine-d5, carbon disulfide (CS2), and water-saturated carbon tetrachloride (CCl4) to investigate its aggregation in vitro. The UV-Vis absorption spectra can be classified into two groups. Group I (acetone, THF, and pyridine-d5 solutions) gives a spectrum with a Qy band around 665 nm while group II (CS2 and water-saturated CCl4 solutions) shows a spectrum typical of BChl-c aggregates with a broader red-shifted Qy band. All the NIR-FT-Raman spectra, which are preresonant with the Qy band, are very close to those of chlorophyll a (Chl-a) measured in the corresponding solutions. Bands due to a C = O stretching mode of free and strongly hydrogen-bonded 13(1)-keto carbonyl groups appear near 1685 and 1645 cm-1, respectively. In contrast to the FT-Raman spectra, FT-IR spectra of the pyridine-d5 solution and group II are largely different from those of Chl-a in the corresponding solutions, suggesting that BChl-c forms quite different types of aggregates. It is clear from the IR spectra that the ester carbonyl group plays an important role in the aggregation for the pyridine-d5 and group II solutions. Of particular note is that bands due to C = O stretching modes of the ester group are observed at 1733, 1719, and 1705 cm-1 in the spectrum of BChl-c in water-saturated CCl4.(ABSTRACT TRUNCATED AT 250 WORDS)
Sato
H
H
Department of Chemistry, School of Science, Kwansei-Gakuin University, Nishinomiya, Japan.
Uehara
K
K
Ishii
T
T
Ozaki
Y
Y
D001419:Bacteria; D001426:Bacterial Proteins / Q000737:chemistry*; D001429:Bacteriochlorophylls; D004952:Esters; D008958:Models, Molecular; D008968:Molecular Conformation; D010316:Particle Size; D012996:Solutions / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D004952:Esters; D012996:Solutions; C002084:bacteriochlorophyll c