pKa of zinc-bound water and nucleophilicity of hydroxo-containing species. Ab initio calculations on models for zinc enzymes

Ab initio Hartree-Fock calculations have been performed on a series of zinc complexes containing a coordinated water molecule in order to understand the factors governing the pK a of the coordinated water and the nucleophilicity of the Zn-OH and Zn-OH 2 groups. The systems investigated include Zn(NH 3 ) n OH 2 2+ (n=3-5), Zn(NH 3 ) 2 (OCOH)OH 2 + , Zn(NH 3 ) 2 (SCH 3 )OH 2 + , Zn-(NH 3 )(SCH 3 ) 2 OH 2 , and their deprotonated partners. The order of nucleophilicity for the various compounds is presented, as well as the order of acidity of the aqua complexes