Theoretical investigations on water oxidation mechanism in both natural and artificial photosynthesis
Title: Theoretical investigations on water oxidation mechanism in both natural and artificial photosynthesis
SNIC Project: SNIC 2020/5-70
Project Type: SNIC Medium Compute
Principal Investigator: Licheng Sun <>
Affiliation: Kungliga Tekniska högskolan
Duration: 2020-01-31 – 2021-02-01
Classification: 10407


The high-resolution crystal structures of the oxygen-evolving complex (OEC) of photosystem II (PSII) in its (meta)stable S0, S1, S2, S3 states have recently been resolved (Kern et al, Nature, 2018, 563, 421-425; Suga et al, Science, 2019, 336, 334-338). This provides a good structural basis as the starting point for computer simulations to uncover the most important O-O bond formation step taking place in the transient S4 state which is experimentally hard to capture. So far there have been quite a few hypotheses regarding the mechanism of O-O bond formation, however, there are obvious drawbacks regarding the spectroscopic consistency, kinetic measurements, energetic possibility, etc. Inspired by the active Mn(VII)-oxo species in electrochemical water oxidation in the artificial system, we proposed a novel mechanism of O-O bond formation in PSII. The new points lie in charge rearrangement within the OEC cluster during the S3-S4 transition and Mn(VII)-induced O-O bond formation in the S4 state (Zhang and Sun, Dalton Trans., 2018, 47,14381-14387; Zhang and Sun, ChemSusChem, 2019,12, 3401-3404). This new proposal can match the latest X-ray observation, kinetic data in time-resolved spectroscopies and substrate water exchange experiments. Scientists in this area are becoming aware of its conceptual importance and practical feasibility. Thanks to the NSC computational support in the past year, we found the theoretical support to the key O-O bond formation and a manuscript is now submitted to the journal Proc. Natl. Acad. Sci. As an ongoing but potentially more challenging project for the preceding charge and structural rearrangement involving multiple steps of proton and electron transfer and coordination transformation, we need more CPU resources to find more theoretical evidences for this promising proposal. Given the large model size and the strong electron correlations in the OEC, SCF convergence speed would demand much CPU resources. Besides the natural system of PSII, we are going to do some quantum chemical calculations on artificial systems on water splitting as well, such as Ru-bda, Co-based water clusters, BiVO4, etc, in order to shed light on the mechanisms and help synthesize man made water oxidation catalysts. Consequently, we sincerely apply for this Medium allocation in NSC and look forward to your approval.