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. Author manuscript; available in PMC: 2012 Nov 17.
Published in final edited form as: J Phys Chem Lett. 2011 Nov 17;2(22):2906–2911. doi: 10.1021/jz2013215

Figure 4.

Figure 4

Molecular electrostatic potential mapped onto the electron density isosurface. The QM region is shown here for the reactant state with (a) a Mg2+ ion and (b) a Na+ ion at the catalytic position. In both panels, the scale is from −0.5 to 0.5 kT/e at 298 K. The dotted gray circle indicates the position of the metal ion in each case. These figures suggest that the Mg2+ ion at the catalytic site withdraws greater electron density from C75, making the residue more electron deficient and the transferring proton more acidic, as compared to the case of a Na+ ion at the catalytic site.