Chlorophyll a triplet-state ESR in frozen phosphatidylcholine vesicles

Journal Article · Thu May 19 00:00:00 EDT 1988 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100321a016· OSTI ID:6884656

Hiromitsu, I; Kevan, L

Photoexcited chlorophyll a (Chla) triplet state in rapidly frozen egg phosphatidylcholine (EPC) vesicles is investigated at 77 K by electron spin resonance (ESR) spectroscopy using light intensity modulation. The electron spin polarization (ESP) intensity is stronger for 0.2 mM Chla than for 1.0 mM Chla. The absolute values of the zero field splitting parameter, D, are 283 (+/-1) x 10/sup -4/ and 276 (+/-2) x 10/sup -4/ cm/sup -1/, and the average depopulation rates of the triplet state are 0.671 +/- 0.052 and 1.054 +/- 0.036 ms/sup -1/ for 0.2 mM Chla and 1.0 mM Chla, respectively. This difference can be consistently attributed to faster triplet-state migration between adjacent Chla's at the higher 1.0 mM Chla concentration. A characteristic migration time of 2.6 ms is obtained. The ESP pattern of the Chla triplet state in the frozen EPC vesicles resembles that in polycrystals more than that in glasses. This suggests that the local environment around Chla in the vesicles is more structured than in glasses.

• Research Organization: Univ. of Houston, TX (USA)
• OSTI ID: 6884656
• Journal Information: J. Phys. Chem.; (United States), Vol. 92:10
• Country of Publication: United States
• Language: English

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