Spin dynamics in a spin-correlated radical pair of photosystem I. Pulsed time-resolved EPR at high magnetic field.
Spin-dynamics of the spin-correlated radical pair (SCRP) P{sub 700}{sup +}A{sub 1A}{sup -} in the photosystem I (PSI) reaction center protein have been investigated with high-frequency (HF), time-resolved EPR spectroscopy. The superior spectral resolution of HF EPR enables spin-dynamics for both the donor and acceptor radicals in the pair to be monitored independently. Decay constants of each spin were measured as a function of temperature and compared to data obtained at X-band EPR. Relaxation times, T{sub 1}, and decay rates, k{sub S}, are the same at both X- and D-band magnetic fields. The spin-dynamics within the radical pair were determined from theoretical simulation of experimental time-resolved HF EPR spectra. At low temperatures, T < 60 K, the decay of the SCRP from the singlet state, k{sub S}, is the predominant process, while at high temperatures, T > 130 K, the T{sub 1} relaxation is much faster than k{sub S}. The recombination rate k{sub S} was observed to decrease as the temperature is increased. These EPR spectral results are in agreement with previously reported optical measurements of P{sub 700}{sup +}A{sub 1}{sup -} radical pair recombination.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 962884
- Report Number(s):
- ANL/CSE/JA-63960; TRN: US200916%%412
- Journal Information:
- PCCP, Vol. 11, Issue 31 ; 2009; ISSN 1463-9076
- Country of Publication:
- United States
- Language:
- ENGLISH
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