Models for proton-coupled electron transfer in photosystem II

Area of Science:

• Biochemistry
• Physical Chemistry
• Photosynthesis Research

Background:

• Proton-coupled electron transfer (PCET) is fundamental to biological processes like photosynthesis.
• Photosystem II (PS II) utilizes PCET for its oxidative functions, particularly during S-state transitions.
• Understanding PCET mechanisms is key to elucidating energy conversion in biological systems.

Purpose of the Study:

• To review recent studies on PCET model systems.
• To define and differentiate PCET from electron transfer (ET) and proton transfer (PT).
• To explore the role of PCET in the chemistry of photosystem II.

Main Methods:

• Investigated various PCET model systems in the laboratory.
• Defined PCET as a concerted transfer of an electron and a proton.
• Differentiated PCET into Hydrogen Atom Transfer (HAT) and other mechanisms.

Main Results:

• HAT reactions, a type of PCET, are well-predicted by thermochemistry and Marcus Theory.
• PCET models were developed for reactions involving phenols with pendent bases.
• Studies explored PCET mechanisms in photosystem II, including tyrosine Z radical oxidation of the manganese cluster.

Conclusions:

• PCET is a critical mechanism in the oxidative side of photosystem II.
• Model systems provide insights into the complex PCET steps in S-state transitions.
• Further research using model complexes like ruthenium-aquo is needed to fully understand OEC oxidation.