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*₁B_AH_A↔P*₂B_AH_A↔I↔P⁺H_A↔P⁺B_A with two excited states B_AH_A and B_AH_A and three charge separated states I, P⁺H_A and P⁺B_A (P is a primary electron donor, bacteriochlorophyll dimer, B_A and H_A 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⁺H_A 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 B_AH_A states and a possible incoherent nature of the oscillations are discussed.

A novel impedimetric biosensor was fabricated for total cholesterol sensing based on platinum nanoparticle and polypyrrole multilayer nanocomposite electrode. The Pt nanoparticles (PtNP) electrochemically deposited between two polypyrrole layers on indium tin oxide (ITO) glass plates (PtNP/PPY/ITO) have offered high-electroactive surface area and favourable microenvironment for immobilization of cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) resulting in enhanced electron transfer between the enzyme system and the electrode. Impedimetric response studies of the ChEt-ChOx/PtNP/ITO nanobioelectrode exhibit improved linearity (2.5 × 10^-4 to 6.5 × 10-³ M/l), low detection limit (2.5 × 10^-4 M/l), fast response time (25 s), high sensitivity (196 Ω/mM/cm^-2) and a low value of the Michaelis-Menten constant (Km, 0.2 M/l) with a regression coefficient of 0.997.