Solvent effects on the resonance Raman and electronic absorption spectra of bacteriochlorophyll a cation radical

Journal Article · Thu Feb 08 04:00:00 EST 1996 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/jp952295m· OSTI ID:219696

Misono, Yasuhito; Itoh, Koichi ^[1]; Limanatara, Leenawaty; Koyama, Yasushi ^[2]

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1. Waseda Univ., Tokyo (Japan)
2. Kwansei Gakuin Univ., Nishinomiya (Japan)

Resonance Raman and electronic absorption spectra of bacteriocholrophyll a cation radical (BChl a{sup .+}) were recorded in 14 different kinds of solvents. The frequency of the ring-breathing Raman band of BChl a{sup .+} was in the region of 1596-1599 cm{sup -1} in solvents forming the pentacoordinated state in neutral bacteriochlorophyll a (BChl a), while it was in the region of 1584-1588 cm{sup -1} in solvents forming the hexacoordinated state. BChl a{sup .+} exhibited a key absorption band in the regions 546-554 and 557-563 nm in the above penta- and hexa-coordinating solvents. Therefore, it has been concluded that the penta- and hexa-coordinated states are retained even after conversion of BChl a into BChl a{sup .+} (one-electron oxidization). Application of this rule to the case of 2-propanol solution showed transformation from the penta- to the hexa-coordinated state upon one-electron oxidation in this particular solution. The coordination states of BChl a{sup .+} could be correlated with the donor number(DN) and the Taft parameters, {Beta} and {pi}{sup *}, of the solvent: The hexacoordinated state was formed in solvents with DN >= 18 or {Beta} > 0.5 showing higher electron donating power, while the pentacoordinated state was formed in solvents with {pi}{sup *} > 0.65 showing higher dielectric stabilization. 27 refs., 8 figs., 3 tabs.

• OSTI ID: 219696
• Journal Information: Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 6 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
55 BIOLOGY AND MEDICINE
BASIC STUDIES
ABSORPTION SPECTRA
CATIONS
CHLOROPHYLL
MOLECULAR STRUCTURE
PHOTOSYNTHESIS
PHOTOSYNTHETIC REACTION CENTERS
PROTEINS
RADICALS
RAMAN SPECTRA
SOLVATION
SOLVENTS