Spin-Correlated Radical Pairs as Quantum Sensors of Bidirectional ET Mechanisms in Photosystem I

Journal Article · Thu Sep 05 00:00:00 EDT 2019 · Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

DOI:https://doi.org/10.1021/acs.jpcb.9b06636· OSTI ID:1579911

Poluektov, Oleg G.; Niklas, Jens; Utschig, Lisa M.

Following light-generated electron transfer reactions in photosynthetic reaction center proteins, an entangled spin qubit (radical) pair is created. The exceptional sensitivity of entangled quantum spin states to weak magnetic interactions, structure, and local environments was used to monitor the directionality of electron transfer in Photosystem I (PSI). Electron paramagnetic resonance (EPR) spectra of radical pairs formed via each symmetric branch of cofactors, A or B, exhibit distinctive line shapes. By photochemical reduction and biochemical modification of PSI we created samples where the radical pair(s) from (1) only A branch, (2) only B branch, or (3) both A and B branches are detectable. These PSI samples were used to analyze the asymmetry of electron transfer as a function of temperature, freezing condition, and temperature cycling. The temperature dependency agrees with a dynamic model in which the conformational states of the protein regulate the directionality of electron transfer. High spectral resolution afforded by high-frequency (130 GHz) EPR, combined with extra resolution afforded by deuterated proteins, provides new mechanistic insight via structural and environmental sensitivity of the entangled electron spins of photogenerated radical pairs.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science - Office of Basic Energy Sciences - Chemical Sciences, Geosciences, and Biosciences Division
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1579911
• Journal Information: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Vol. 123, Issue 35
• Country of Publication: United States
• Language: English