A DFT study of model complexes of zinc hydrolases and their inhibition by hydroxamic acids

DFT calculations carried out on zinc acetate and zinc hydroxamates using the Hartree-Fock and B3LYP methods with the 6-311+G* basis set give a series of stable pseudotetrahedral chelates (ZnL2) (L = OAc, FA, AA, NMeAA, GA, SA). Addition of a water molecule to these chelates gives the hydrates, ZnL2.H2O, which in all cases are energetically more stable than the corresponding chelate. Hydrates formed from O,O coordinated hydroxamate species with a five-membered chelate ring contain water molecules occupying vacant coordination sites of the zinc atom. In contrast, those formed from zinc chelates with four-membered chelate rings contain a water molecule inserted into the chelate ring to give a six-membered ring in which one hydrogen of the water molecule is H-bonded to an oxygen atom of the zinc chelate with the water oxygen strongly bonded to the zinc. A slight lengthening of the H-bonded O-H bond suggests incipient hydroxide activation of water by zinc. In contrast, the O,O bonded hydroxamates do not incorporate water into the chelate ring nor activate the water in accordance with the ability of hydroxamic acids to inhibit zinc containing metalloenzymes.