The aim of this research is to study the light phase of photosynthesis based on X-ray diffraction data from photosystems I and II (PS-I and PS-II), and the molecular structures of solar energy conversion and electron flow control systems.

Structural analysis of PS-II showed that the manganese cluster Mn₄O₅Ca(Н₂О)₄ is an electron generator, where solar energy breaks the chemical bonds of water, which is accompanied by H₂O₂ formation. Electrochemical oxidation of Н₂О₂ by Mn⁴⁺ ion leads to the formation of oxygen and two protons Н₂О₂-2е^-→О₂^↑+2Н⁺+23,5 kcal, while Mn4+ is reduced to Mn²⁺. Mn⁴⁺ regeneration occurs by donating 2 electrons to PS-I to NADPH·H.

Uncontrolled generation of electrons in chloroplasts leads to the appearance of free radicals that destroy cellular structures. In this regard, chloroplasts have protective mechanisms to remove excess electrons. X-ray diffraction studies of PS-I and PS-II showed that the active centers P680 and P700 have formed photoelectrolysis systems in which chlorophyll molecules act as electrodes (cathode and anode). Electronic circuits P680 and P700 close iron-sulfur trigger clusters that control the flow of electrons. Triggers switch electron flows to reduce NADPH·H or send excess electrons to electrolyzers to oxidize water at the anode: 2H₂O → O₂↑+ 4H⁺ + 4e^– and reduce protons at the cathode: 2H⁺ + 2e^- → ↑H₂.

Conclusions. Based on the results of X-ray diffraction studies of H₂O-plastoquinone oxidoreductase (PS-ΙΙ), the mechanism of electron generation of Mn₄O₅Ca(Н₂О)₄ is considered. Photoelectrolysis systems in the P680 PS-II and P700 PS-I structures have been identified and the principle of their operation is described. A natural molecular electronic device that controls and monitors the processes occurring in the ETC of the light phase of photosynthesis is considered.