Sashima, Tokutake and Limantara, Leenawaty and Koyama, Yasushi (2000) Changes in Carbon-Carbon and Carbon-Nitrogen Stretching Force Constants in the Macrocycles of Bacteriochlorophyll a and Bacteriopheophytin a upon Triplet and Singlet Excitation: Resonance Raman Spectroscopy and Normal Coordinate Analysis of the Unlabelled and Totally 15N-, 13C- and 2H-labelled Species. Journal of Physical Chemistry, 104 (34). pp. 8308-8320.
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The Raman spectra of bacteriochlorophyll a and bacteriopheophytin a in the S0, T1, and S1 states were recorded for the unlabeled species and the totally-labeled species with the 15N, 13C, and 2H isotopes, and an empirical normal-coordinate analysis of the Raman data was performed to establish the assignments of Raman lines in the 1650−1200 cm-1 region and to determine the stretching force constants of the carbon−carbon and the carbon−nitrogen bonds within the macrocycle. By the use of the stretching force constants as a scale, changes in bond order upon triplet and singlet excitation were characterized in both BChl a and BPhe a as follows. (a) For BChla, upon triplet excitation, the carbon−carbon bonds in the methine bridge (Ca−Cm) and those in the pyrrole rings I and III (Ca−Cb and Cb−Cb) decrease in bond order, whereas the carbon−nitrogen bonds in all the pyrrole rings (Ca−N) and the carbon−carbon bonds in rings II and IV (Ca‘−Cb‘) increase in bond order. Upon singlet excitation, the Cb−Cb bonds substantially increase in bond order at the expense of decrease in the bond orders of the Ca−Cm and Ca−Cbbonds; the Ca‘−Cb‘ and the Ca−N bonds also increase in bond order as in the case of triplet excitation. (b) For BPhe a, upon triplet excitation, changes in bond order similar to those in the case of BChl a take place. Upon singlet excitation, the Cb−Cb bonds drastically increase in bond order at the expense of decrease in the bond orders of the Ca−Cm, Ca−Cb, and Ca−N bonds. Change in the stretching force constant of each bond, upon singlet or triplet excitation, varies in magnitude depending on its location in the macrocycle, a fact which suggests that the HOMO and the LUMO are not completely delocalized. Possible relevance of this result to the pigment arrangements in the bacterial photoreaction center is discussed
| Item Type: | Artikel |
|---|---|
| Subjects: | Q Science > QD Chemistry |
| Divisions: | Fakultas Teknologi dan Desain > Teknik Sipil |
| Depositing User: | Admin Repository |
| Date Deposited: | 15 Apr 2020 10:19 |
| Last Modified: | 03 Jun 2022 02:46 |
| URI: | http://eprints.upj.ac.id/id/eprint/84 |
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