Anion radicals of bacteriochlorophylls c, d, and e. Likely electron acceptors in the primary photochemistry of green and brown photosynthetic bacteria

Theoretical Calculations of Photosynthetic Pigments

“…The anion radicals show sizeable spin density at the C1 and C5 positions (the relative magnitudes of the observed hfcs are -1 : 2 for Chl derivatives and 1 : 1 for BChl derivatives), the meso positions, and two nitrogens (NII and NIV). PPP calculations on Chl a-and Pheo a- , the Chlorobium chlorophyll BChl d-and its pheophytin (Fajer et al, 1983), BChl a-and BPh a- (Fajer et a / . , 1977b), and BChl b-and BPh b- (Davis et ul., 1979a) reproduced these features including the correct relative magnitudes for the C1 and C5 positions.…”

“…Since then, they have been extensively applied to photosynthetic pigments. Unpaired spin density distributions have been published for pyroChl a- , Chl aand Pheo a- (Forman et al, 1981), the Chlorobium chlorophylls-BChls c-, d-, eand their respective pheophytins (Fajer et al, 1983), BChls a -, 6and BPhs a -, b- (Davis et al, 1979a), and BChl g- . Because they are relatively fast and inexpensive, IEH calculations have been especially useful in modelling the effects of changes in structure (Fajer et al, 1983) and of interactions with the environment (Forman et al, 1981).…”

“…Unpaired spin density distributions have been published for pyroChl a- , Chl aand Pheo a- (Forman et al, 1981), the Chlorobium chlorophylls-BChls c-, d-, eand their respective pheophytins (Fajer et al, 1983), BChls a -, 6and BPhs a -, b- (Davis et al, 1979a), and BChl g- . Because they are relatively fast and inexpensive, IEH calculations have been especially useful in modelling the effects of changes in structure (Fajer et al, 1983) and of interactions with the environment (Forman et al, 1981). The calculated unpaired spin densities at the C1 and C5 positions of (B)Chls and (B)Phs are sensitive to the orientation of C2 vinyl or acetyl substituents: rolling the vinyl or acetyl into plane increases the C1 spin density and decreases the C5.…”

“…1 for the structures. ?Abbreviations used: acetyl (Ac); methyl (Me); ethyl (Et); n-propyl (n-Pr); iso-butyl $Fajer et al (1983). PBrockmann and Lipinski (1983) (i-Bu); neo-pentyl (neo-Pen); carbomethoxy (C02Me); 1-hydroxethyl (HOEt).…”

Electron transport in green photosynthetic bacteria

“…However, further work indicated that P840 r can still be formed even when the --550 mV Fe-S center is reduced, suggesting that even earlier electron acceptors are present. Spectral and ESR studies have suggested that these acceptors are BChl a and BPh c [22,58,89,98]. Nanosecond (ns) and picosecond (ps) flash kinetic experiments indicate that BPh c serves as the first electron acceptor.…”