Speciation 98: Abstracts

Model compounds mimicking the main features of active sites have long been used to characterize better the relation between structure and function of a large number of (metallo)proteins. In this respect, many imidazole-containing ligands have been studied from co-ordination chemical point of view. The equilibrium and structural properties of copper(II) and zinc(II) complexes of N,N`-di-L-histidylethane-1,2-diamine (dhen) and those of the strongly related histamine have been characterized by pH-metric and spectroscopic (UV-VIS, CD, ESR and NMR) methods. In both M/L = 1/1 and 1/2 dhen systems a dimeric M<sub>2</sub>L<sub>2</sub> species is dominant near the physiological pH, having bis(histamine-like) 2N<sub>im</sub>, 2NH<sub>2</sub> co-ordination. The MLH<sub>-2</sub> complex, also formed in both systems above pH 10, has different structures with the two metal ions. A hydroxo mixed-ligand-complex is formed in the case of zinc(II), while the base-consuming processes are assigned to metal-promoted deprotonation of amide nitrogens in the copper(II) system. Between these two dominant species (pH=7-10) tetrameric complexes are formed in each case with the participations of imidazole N<sup>1</sup>(pyrrolic) nitrogen in the co-ordination. The presence of imidazole moiety in the active centre is often related to hydrolytic reactions, even in the absence of metal ions. The catalytic activity of the zinc(II)-containing systems towards the hydrolysis of uridine 2`,3`-cyclic monophosphate as nuclease model has been examined. The zinc(II)-histamine complexes efficiently catalyse the hydrolysis. This activity is nearly equal to that of the Zn<sup>II</sup>-[12]aneN<sub>3</sub> complex, measured under similar conditions, which is known as the most active zinc(II)-containing accelerator of 2`,3`-cUMP hydrolysis reported up to date.

Acknowledgement: The authors are thankful to the NSRF for financial support (Project No. OTKA F014954).

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