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Zn−O 2 H 3 −Zn: a Coordination Mode of the Hydrolytic Zinc−Aqua Function and a Possible Structural Motif for Oligozinc Enzymes

1996; American Chemical Society; Volume: 118; Issue: 39 Linguagem: Inglês

10.1021/ja960629v

1943-2984

Michael Ruf, K. H. Weis, Heinrich Vahrenkamp,

Enzyme Structure and Function

Reactions of the pyrazolylborates KTp' with Zn(ClO4)2 and KOH in a 2:2:1 ratio yield the complexes [Tp'2Zn2O2H3]ClO4 (1) for Tp' = hydrotris(3-R-5-methylpyrazolyl)borate with R = p-isopropylphenyl (a), 3-pyridyl (b), and 3-(6-methyl)pyridyl (c). Their structure determinations have revealed a Zn-OH-H···OH-Zn array (i.e., a bridging H3O2- ligand) in the dinuclear complex cations. The zinc ions in complex 1a are in a distorted tetrahedral ZnN3O environment, and those in 1b and 1c are in a distorted trigonal bipyramidal ZnN4O environment due to additional coordination of one pyridyl nitrogen from the opposing Tp' ligand. In 1b, one Zn-OH function is involved in a hydrogen bridge to a cocrystallized methanol molecule. The complexes represent a mode of stabilization for the zinc−aqua function in the cationic Tp'Zn-OH2 species, and they are intermediates in the formation of the stable Tp'Zn-OH complexes. It is suggested that the Zn-O2H3-Zn unit is present as a structural and possibly functional motif in oligozinc enzymes like phospholipase C or P1 nuclease.