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A TDDFT investigation of the Photosystem II reaction center: Insights into the precursors to charge separation. | LitMetric

A TDDFT investigation of the Photosystem II reaction center: Insights into the precursors to charge separation.

Proc Natl Acad Sci U S A

Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, W12 0BZ London, United Kingdom;

Published: August 2020

AI Article Synopsis

  • Photosystem II (PS II) is essential for photosynthesis as it captures solar energy and drives the process of charge separation across the thylakoid membrane, crucial for water oxidation.
  • This study uses advanced time-dependent density functional theory (TDDFT) to model the structure of PS II's reaction center, revealing how specific chromophores and adjacent amino acids affect chlorophyll absorption and the resulting electronic states.
  • The findings reveal important molecular orbital interactions involved in the excited states leading to charge separation, and highlight TDDFT's potential for enhancing our understanding of both natural and artificial photosynthetic systems.

Article Abstract

Photosystem II (PS II) captures solar energy and directs charge separation (CS) across the thylakoid membrane during photosynthesis. The highly oxidizing, charge-separated state generated within its reaction center (RC) drives water oxidation. Spectroscopic studies on PS II RCs are difficult to interpret due to large spectral congestion, necessitating modeling to elucidate key spectral features. Herein, we present results from time-dependent density functional theory (TDDFT) calculations on the largest PS II RC model reported to date. This model explicitly includes six RC chromophores and both the chlorin phytol chains and the amino acid residues <6 Å from the pigments' porphyrin ring centers. Comparing our wild-type model results with calculations on mutant D1-His-198-Ala and D2-His-197-Ala RCs, our simulated absorption-difference spectra reproduce experimentally observed shifts in known chlorophyll absorption bands, demonstrating the predictive capabilities of this model. We find that inclusion of both nearby residues and phytol chains is necessary to reproduce this behavior. Our calculations provide a unique opportunity to observe the molecular orbitals that contribute to the excited states that are precursors to CS. Strikingly, we observe two high oscillator strength, low-lying states, in which molecular orbitals are delocalized over Chl and Phe as well as one weaker oscillator strength state with molecular orbitals delocalized over the P chlorophylls. Both these configurations are a match for previously identified exciton-charge transfer states (ChlPhe)* and (PP)*. Our results demonstrate the power of TDDFT as a tool, for studies of natural photosynthesis, or indeed future studies of artificial photosynthetic complexes.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7443915PMC
http://dx.doi.org/10.1073/pnas.1922158117DOI Listing

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