Spectroscopy and dynamics of reaction centers in electric and magnetic fields

Abstract

Two advances in Stark spectroscopy have opened new opportunities for probing more deeply into the spectroscopy and dynamics of bacterial RCs: higher order Stark (HOS) spectroscopy and vibrational Stark effect (VSE) spectroscopy. HOS experiments on RCs led to the discovery of an new type of Stark effect, which we call the resonance Stark effect [1]. An analysis of resonance Stark lineshapes provides information on the 1B ( BL+HL- reaction under conditions where it can not be observed by time-resolved spectroscopy because of much more rapid 1B ( P energy transfer. In contrast to kinetic measurements, the underlying parameters (driving force, electronic coupling etc.) that determine the rate can be determined. Changes in these parameters in different mutants suggest unusual correlations among these parameters. Development of VSE spectroscopy on an FTIR spectrometer [2] led to the possibility of studying the mixed-valence type electronic transition associated with P+ in the mid-IR. The conventional Stark effect for this band is quite small suggesting that the transition is largely delocalized in wild-type RCs, rather like the classical Creutz-Taube ion. In RCs where assembly with carotenoid is blocked, it is possible to study 3P formation and decay as was done extensively in the R26 strain. The temperature dependence of the 3P decay at high magnetic field has been used to investigate the energetics of primary charge separation in carotenoid-free mutants that perturb the P/P+, BL/BL-, and HL/HL- potentials