Time-resolved magnetic field effect on triplet formation in photosynthetic reaction centers of Rhodopseudomonas sphaeroides R-26.

The primary events in bacterial photosynthesis have been studied since it became possible [l] to isolate reaction centers of photosynthetic bacteria, e.g., of Rhodopseudomonas sphaeroides. Within <lO ps [2,3] after excitation of bacteriochlorophyll to its first excited singlet state, the radical pair state PF is formed consisting of a bacteriochlorophyll dimer cation (Bdhl); and a bacteriopheophytin anion, BPh[4] . Then, within 200 ps, the electron is further transferred to an ubiquinone nonheme iron complex. However, if this pathway is blocked, either by prereducing the ubiquinone chemically [5] or by its, elimination [6,7] , the lifetime of PF increases to -10 ns [S] . The radical pair PF decays to form either the state PR, i.e., the lowest excited triplet of the system 3(BChl)2, or the ground states bf the bacteriochlorophyll dimer and the bacteriopheophytin (see the kinetic scheme in fig.1):