ACETAZOLAMIDE BINDING TO ZINC(II), COBALT(II) AND COPPER(II) MODEL COMPLEXES OF CARBONIC-ANHYDRASE

New zinc(II), cobalt(II) and copper(II) complexes with is[2-(1-methylb enzimidazol-2-yl)ethyl]nitromethane (L) have been prepared. The tris(b enzimidazole) donors provided by the ligand simulate the environment o f the zinc(II) site of carbonic anhydrase. The structural properties o f the complexes deduced on the basis of their spectroscopic characteri stics correlate with those of the metal derivatives of the enzyme, at least in the solid state, while the alkyl chains connecting the donor groups of L allow a more flexible co-ordination environment of the met al sites in solution, with the adoption of five-co-ordinate structures . The complexes bind the inhibitor acetazolamide 5-(aminosulfonyl)-1,3 ,4-thiadiazol-2-yl]acetamide} in its monoanionic form through the depr otonated sulfonamide group and these ternary complexes model the carbo nic anhydrase-acetazolamide adduct recently characterized by X-ray cry stallography. In the case of copper(II) it was impossible to isolate t he pure ternary complex, probably because of the ease of formation of a dinuclear Cu(II)-L-OH- complex under the reaction conditions, but th e related ternary complexes with acetazolamide and diethylene- or dipr opylene-triamine were readily obtained.