Solvent effects on the resonance Raman spectra of bacteriochlorophyll a cation radical
| Main Authors: | Yasuhito, Misono, Ei‐ichi, Nishizawa, Leenawaty, Limantara, Yasushi, Koyama, Koichi, Itoh |
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| Format: | Article PeerReviewed |
| Terbitan: |
Elsevier BV
, 1995
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| Subjects: | |
| Online Access: |
http://eprints.upj.ac.id/id/eprint/76/ https://www.sciencedirect.com/science/article/abs/pii/000926149500237X |
Daftar Isi:
- Resonance Raman and electronic absorption spectra of bacteriochlorophyll a cation radical (BChl a•+) were recorded in 14 different kinds of solvents. The frequency of the ring-breathing Raman band of BChl a•+ was in the region of 1596−1599 cm-1 in solvents forming the pentacoordinated state in neutral bacteriochlorophyll a (BChl a), while it was in the region of 1584−1588 cm-1 in solvents forming the hexacoordinated state. BChl a•+ exhibited a key absorption band in the regions 546−554 and 557−563 nm in the above penta- and hexacoordinating solvents. Therefore, it has been concluded that the penta- and hexacoordinated states are retained even after conversion of BChl a into BChl a•+ (one-electron oxidation). Application of this rule to the case of 2-propanol solution showed transformation from the penta- to the hexacoordinated state upon one-electron oxidation in this particular solution. The coordination states of BChl a•+ could be correlated with the donor number (DN) and the Taft parameters, β and π*, of the solvent: The hexacoordinated state was formed in solvents with DN ≥ 18 or β > 0.5 showing higher electron-donating power, while the pentacoordinated state was formed in solvents with π* > 0.65 showing higher dielectric stabilization. Preferential solvation of a hexacoordinating solvent over a pentacoordinating solvent in their mixture (methanol/acetone or tetrahydrofuran/methylene chloride) was seen in both BChl a and BChl a•+, but the constant of preferential solvation was increased approximately 3 times by one-electron oxidation.