Modeling water exchange on monomeric and dimeric Mn centers |
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| Authors: | Email author" target="_blank">Marcus?LundbergEmail author Margareta R A?Blomberg Per E M?Siegbahn |
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| Institution: | (1) Department of Physics, Astronomy and Biotechnology, Stockholm University, Stockholm Center for Physics, 106 91 Stockholm, Sweden |
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| Abstract: | Water exchange on Mn centers in proteins has been modeled with density functional theory using the B3LYP functional. The reaction barrier for dissociative water exchange on MnIV(H2O)2(OH)4] is only 9.6 kcal mol–1, corresponding to a rate of 6×105 s–1. It has also been investigated how modifications of the model complex change the exchange rate. Three cases of water exchange on Mn dimers have been modeled. The reaction barrier for dissociative exchange of a terminal water ligand on (H2O)2(OH)2MnIV( -O)2MnIV(H2O)2(OH)2] is 8.6 kcal mol–1, while the bridging oxo group exchange with a ring-opening mechanism has a barrier of 19.2 kcal mol–1. These results are intended for interpretations of measurements of water exchange for the oxygen evolving complex of photosystem II. Finally, a tautomerization mechanism for exchange of a terminal oxyl radical has been modeled for the synthetic O2 catalyst (terpy)(H2O)MnIV(-O)2MnIV(O )(terpy)]3+ (terpy=2,2 :6,2 -terpyridine). The calculated reaction barrier is 14.7 kcal mol–1.Contribution to the Björn Roos Honorary Issue |
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| Keywords: | Water exchange – Manganese – Dimers – Density functional theory |
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