Crystal structure, solution properties and hydrolytic activity of an alkoxo-bridged dinuclear copper(ii) complex, as a ribonuclease model

Abstract

Crystal structures, solution properties and ribonuclease activity of copper(II) complexes of a binucleating, bis-pyridyl ligand (N,N′-bis(2-pyridylmethyl)-1,3-diaminopropan-2-ol, L) have been investigated. The single-crystal X-ray structure of the mononuclear complex [CuL(ClO₄)₂] (1) shows distorted octahedral geometry around the metal ion, with the four nitrogens of the ligand in the equatorial plane of copper(II). A μ-alkoxo-bridged dinuclear complex is formed in the presence of a two-fold metal excess. Despite the symmetrical ligand, the two metal ions in [Cu₂(LH₋₁)(DPP)(ClO₄)(CH₃OH)]ClO₄ (2, DPP = diphenyl phosphate) have distinct, distorted octahedral (Cu1) and square pyramidal (Cu2) geometry. Beside the alkoxo-oxygen, the phosphate group of DPP also bridges the two metal centers in 2 in a μ-1,3-bridging mode. The complexes formed in aqueous solution are likely to have analogous structures to 1 and 2. The dinuclear [Cu₂(LH₋₁)(OH)] complex efficiently promotes the hydrolysis/transesterification of both activated (2-hydroxypropyl p-nitrophenyl phosphate, hpnp) and non-activated, biological phosphodiesters (uridine-2′,3′-cyclic-monophosphate, cUMP and uridylyl-(3′,5′)-uridine, UpU). For example, a 2 mM solution of the dinuclear complex provides 5 orders of magnitude acceleration in the hydrolysis of cUMP. The proposed mechanisms include double Lewis-acid activation with intramolecular general base catalysis.