ИСТИНА

Electron transfer (ET) in the photosynthetic reaction centers (RC) is one of the key steps of energy conversion during photosynthesis. An important question for the modeling of ET is to determine which intermediate states participate in this process. One of the steps in the whole ET process in RC of Rba. Sphaeroides is the transfer between quinone molecules. These molecules are separated by a large distance. Thus, a question if it is a direct transfer arises. Alternatively Fe ion, which is located between these quinones, can participate in this ET step. The scope of the current research was to determine the prerequisites of the electron transfer between these molecules and to get the energy of the elec-tronic states participating in the process and couplings between them. The molecular mechanics force fields which fit the quantum chemistry calculations for ubiquinone and its anion in vacuum were obtained. The molecular dynamical simulations were performed for RC enclosed in DMPC lipid bilayer. The dynamics was carried out for the three states of the system: 1) With both neutral quinones. 2) With neutral quinone QB and anion QA−. 3) With anion QB− and neutral QA. Two stable conformations were detected for the last case. The structures of the quinones and Fe ion with its ligands were picked out from this conformations for the further calculations. The CI method, which is applicable in the case of the non-orthogonal localized orbitals (LOCI) was developed previously by our lab team. This method in particular gives the opportunity to calculate small parts of the large system by standard techniques of well known QC packages with subsequent reunion and CI calculation. The CASSCF calculations of separated parts (each quinone and Fe ion with its protein environment) were performed for two structures mentioned above. On the next step the LOCI calculations were performed. The couplings and energy levels of the full system was obtained. The results of CASSCF computa-tion of the full system were used for the comparative analysis.