3 MM EPR INVESTIGATION OF THE PRIMARY DONOR CATION RADICAL P865+. IN SINGLE-CRYSTALS OF RHODOBACTER-SPHAEROIDES R-26 REACTION CENTERS

The EPR g-factor rotation pattern of the primary donor cation radical P865+. in the x-y plane of illuminated reaction center single crystals of Rb. sphaeroides R-26 near room temperature was measured at 3 mm wavelength (W-band, 95 GHz). In contrast to earlier X-band (9.5 GHz) EPR experiments, the two magnetically inequivalent sites of the four reaction centers per unit cell were well resolved. P865+. in frozen reaction center solution was also measured by 3 mm EPR. The analysis of both the frozen-solution spectrum and the single-crystal rotation pattern yields the principal values of the g-tensor and the phase angle between the two magnetically inequivalent sites in the x-y plane.