Abstract
Early events of charge separation in reaction centers (RCs) of bacterial photosynthesis are modeled by kinetic equations with time-dependent rate constants. An illustrative case of regular motion along a “slow” coordinates leading to oscillations in the kinetics is examined. Different schemes of charge separation are investigated. A good fitting of experimental kinetics of native Rba. sphaeroides RCs is achieved in the five states model P*1BAHA↔P*2BAHA↔I↔P+HA↔P+BA with two excited states BAHA and BAHA and three charge separated states I, P+HA and P+BA (P is a primary electron donor, bacteriochlorophyll dimer, BA and HA are an electron acceptor, monomeric bacteriochlorophyll and bacteriopheophytin in active A-branch, respectively). In the model only the first excited state is directly populated by optical excitation. The emission of the two excited states is assumed to be at 905 and 940 nm, respectively. The intermediate state I is assumed to absorb at 1020 nm as well as the P+HA state. The model explains the deep oscillations in the kinetics of the stimulated emission and of the absorption. In the simpler schemes without the I state or with only one excited state the accordance with the experiment is achieved at unreal parameter values. A possible nature of the I and BAHA states and a possible incoherent nature of the oscillations are discussed.
Highlights
Events of charge separation in reaction centers (RCs) of bacterial photosynthesis are modeled by kinetic equations with time-dependent rate constants
A good fitting of experimental kinetics of native Rba. sphaeroides RCs is achieved in the five states model P*1BAHA ↔ P*2BAHA ↔ I ↔ P+ BA− HA
In reaction centers (RCs) of purple bacteria Rhodobacter (Rba.) sphaeroides primary charge separation consisted in electron is transferred from excited dimer of bacteriochlorophyll P* to monomeric bacteriochlorophyll BA within ~3 psec and from BA− to bacteriopheophytin HA within ~1 psec at room temperature
Summary
In reaction centers (RCs) of purple bacteria Rhodobacter (Rba.) sphaeroides primary charge separation consisted in electron is transferred from excited dimer of bacteriochlorophyll P* to monomeric bacteriochlorophyll BA within ~3 psec and from BA− to bacteriopheophytin HA within ~1 psec at room temperature (for reviews see [1,2]). In the present work the incoherent charge separation dynamics of native Rba. sphaeroides RCs is modeled by the kinetic equations with time-dependent rate constants. This approach is based on the Marcus theory [15]. According to Marcus theory [15], electron or energy transfer reaction occurs at the intersection of the potential energy surfaces of the initial and final states of the system. In harmonic approximation these surfaces are paraboloids shifted one from another: Uin = 1/2mω2x2 + 1/2MΩ2X2; Ufin = 1/2mω (x – x0)2 + 1/2MΩ2(X - X0)2 +. The incoherent dynamics of relative populations of these states was described by kinetic equations
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