Spectral properties of chlorines and electron transfer with their participation in the photosynthetic reaction center of photosystem II

Structural factors that provide localization of excited states and determine the properties of primary donor and acceptor of electron in the reaction center of photosystem II (PSII RC) are studied. The results of calculations using stationary and time-dependent density functional theory indicate an important role of protein environments of chlorophylls P A , P B , B A , and B B and pheophytins H A and H B in the area with a radius of no greater than ≤10 Å in the formation of excitonic states of PSII RC. When the neighboring elements are taken into account, the wavelength of long-wavelength Q y transition of chlorophyll molecules is varied by about 10 nm. The effect is less developed for pheophytin molecules (Δλ ≅ 2 nm). The following elements strongly affect energy of the transition: His A198 and His D197 amino-acid residues that serve as ligands of magnesium atoms affect P A and P B , respectively; Met A183 affects P A ; Met A172 and Met D198 affect B A ; water molecules that are located above the planes of the B A and B B macrocycles form H bonds with carbonyl groups; and phytol chains of P A and P B affect B A , B B , H A , and H B . The analysis of excitonic states, mutual positions of molecular orbitals of electron donors and acceptors, and matrix elements of electron transfer reaction shows that (i) charge separation between B A and H A and P B and B A is possible in the active A branch of cofactors of PSII RC and (ii) electron transfer is blocked at the B B - H B fragment in inactive B branch of PSII RC.