Time-resolved EPR study of the primary donor triplet in D1-D2-cyt b559 complexes of photosystem II: Temperature dependence of spin-lattice relaxation
- Leiden Univ. (Netherlands)
- Inst. of Soil Science and Photosynthesis, Pushchino (Russian Federation)
The temperature dependence of the EPR spectrum and kinetics of the primary donor triplet state {sup 3}P680 are measured with direct-detection CW EPR and electron spin echo (ESR) spectroscopy, respectively. The EPR spectrum was recorded up to 230 K; kinetics could be traced up to 70 K. The observed anisotropy of the temperature dependence of the EPR spectrum recorded within 1 {mu}s after a laser flash is explained by anisotropic spin relaxation in the precursor primary radical pair. The ESE-detected decay kinetics of the Z-canonical peak of {sup 3}P680 is close to its optical lifetime for T < 20 K but deviates strongly from the lifetime for T > 30 K, due to a rapid acceleration of spin relaxation with temperature. This relaxation is not caused by the presence of oxygen or the paramagnetic heme iron in the b559 cytochrome; it is attributed to slow triplet hopping in the P680 dimer itself. Comparison of the low-temperature kinetics with that of chlorophyll a in solution confirmed that the central Mg ion in the triplet-bearing Chl of {sup 3}P680 is pentacoordinated. 53 refs., 4 figs., 1 tab.
- OSTI ID:
- 223553
- Journal Information:
- Journal of Physical Chemistry, Vol. 100, Issue 6; Other Information: PBD: 8 Feb 1996
- Country of Publication:
- United States
- Language:
- English
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