Computational studies of the Mn-4/Ca cluster in photosystem II

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Publication Details

Author list: Baituti B

Publisher: World Scientific Publishing

Place: SINGAPORE

Publication year: 2018

Journal: Journal of Theoretical and Computational Chemistry (0219-6336)

Journal acronym: J THEOR COMPUT CHEM

Volume number: 17

Issue number: 1

Number of pages: 19

ISSN: 0219-6336

eISSN: 1793-6888

Languages: English-Great Britain (EN-GB)

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Abstract

Computational chemistry with the data from more detailed X-ray diffraction (XRD) oxygen evolving complex (OEC) structure has been used extensively of late in exploring the mechanisms of water oxidation in the OEC. The study reported in this paper involves density functional theory (DFT) calculations to investigate whether the data are in agreement with the four manganese ions in the OEC, being organized as a '3+1' (trimer plus one) model [Gatt et al. Angewandte Chemie International Edition, 51, 12025-12028, 2012; Petrie et al. Chemistry - A European Journal, 21, 6780-6792, 2015; Terrett et al. Chemical Communications, 50, 3187-3190, 2014] or 'dimer of dimers' model. [Terrett et al. Journal of Inorganic Biochemistry, 162, 178-189, 2016]. The data analysis method used involves quantum chemical DFT calculations on relevant models of the OEC cluster. DFT calculations were performed using both the so-called 'open' and 'closed' forms [Terrett et al. Journal of Inorganic Biochemistry, 162, 178-189, 2016] of the S-2 OEC structure models with total spin (S-T) 1/2, 7/2, 9/2 and 15/2 within the Mn-III Mn-IV Mn-III Mn-III 'low' oxidation paradigm to examine exchange coupling within the OEC cluster. The results show that the J-coupling in the 'closed' form: J(23) = -23.4 cm(-1), J(13) = 43.66 cm(-1), J(12) = 126.1 cm(-1) and J(34) = 70-81.67 cm(-1). In the 'closed' form, J(12) and J(34) represent the two largest exchange interactions within the manganese cluster, whereas J(23) and J(13) are small and almost net cancel. The magnetic coupling between the four Mn ions is close to 'dimer of dimers', with both dimers anti-ferromagnetically coupled internally and with weak inter-dimer net coupling.

Keywords

computational chemistry, Density functional theory, electron paramagnetic resonance, oxygen evolving complex, photosystem II

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