Structure, equilibrium and ribonuclease activity of copper(II) and zinc(II) complexes formed with a dinucleating bis-imidazole ligand

Tamás Gajda, Roland Krämer, Attila Jancsó

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Abstract

The syntheses, crystal structures, solution equilibria and ribonuclease activity are reported for copper(II) and zinc(II) complexes of a new potentially dinucleating, bis-imidazole ligand N,N'-bis(5-methylimidazol-4- ylmethyl)-1,3-diaminopropan-2-ol (bimido). The zinc(II) ion in [Zn(bimido)Cl]NO3 is coordinated in a slightly distorted square pyramidal environment, with the four N atoms of bimido in the basal positions and the Cl- ion in the axial one. The two copper(II) ions in [Cu2(bimido(-1H)) (DPP)(ClO4)(CH3OH)]ClO4 · 1/2 H2O (DPP = diphenyl phosphate) are bridged by the deprotonated alkoxo group of bimido and by the phosphate group of DPP in a 1,3-bridging mode. Depending on the [M]/[L] ratio, the ML and M2L(-2H) species are present in solution in the neutral pH range, having analogous structures as described above for the crystalline complexes. The zinc(II)- bimido (2/1) system, in a 65% EtOH-H2O mixed solvent, shows an important increase of hydrolytic activity, parallel with the formation of the Zn2L(- 2H) species, with a sigmoidal pH-rate profile modelling both steps of RNA hydrolysis. The k(cat) value for the transesterification of 2-hydroxypropyl- p-nitrophenyl phosphate by Zn2L(-2H), determined from saturation kinetic measurements (T = 298 K), corresponds to a maximum rate acceleration (k(cat)/k(uncat)) of ca. 104. The observed pseudo-first order rate constant for the hydrolysis of uridine 2',3'-cyclic monophosphate, under nearly physiological conditions (T = 310 K, pH = 8, [Zn2L(-2H)] = 3.6 mM, k(obs) = 2.10-5 s-1) reflects a higher hydrolytic activity of Zn2L(-2H) towards this biologically relevant substrate (k(obs)/k(uncat) indicates ca. 104 fold rate acceleration). The proposed mechanisms include bifunctional Lewis-acid and general base catalysis.

Original languageEnglish
Pages (from-to)1635-1644
Number of pages10
JournalEuropean Journal of Inorganic Chemistry
Issue number7
DOIs
Publication statusPublished - Jan 1 2000

Keywords

  • Copper
  • Enzyme models
  • Hydrolyses
  • Phosphodiesters
  • Zinc

ASJC Scopus subject areas

  • Inorganic Chemistry

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