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. Author manuscript; available in PMC: 2009 Feb 1.
Published in final edited form as: Coord Chem Rev. 2008 Feb;252(3-4):395–415. doi: 10.1016/j.ccr.2007.09.006

Figure 9.

Figure 9

DFT-QM/MM energy profiles, as a function of the coordination bond lengths between substrate water molecules attached to Ca2+ (red) and the dangling Mn3+ (black), for the OEC of PSII in the S1 (dash) and S2 (solid) states [18]. ESP ionic charges are indicated in parenthesis (q). The energy barriers are 21.2, 16.6, 8.4 and 7.9 kcal mol−1, for water exchange from Ca2+(S1), Ca2+(S2), Mn3+(S2) and Mn3+(S1), respectively.