Crystal structures, solution properties and ribonuclease activity of copper() complexes of a binucleating, bis-pyridyl ligand (N,NЈ-bis(2-pyridylmethyl)-1,3-diaminopropan-2-ol, L) have been investigated. The single-crystal X-ray structure of the mononuclear complex [CuL(ClO 4 ) 2 ] (1) shows distorted octahedral geometry around the metal ion, with the four nitrogens of the ligand in the equatorial plane of copper(). 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 [Cu 2 (LH Ϫ1 )(DPP)(ClO 4 )(CH 3 OH)]ClO 4 (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 [Cu 2 (LH Ϫ1 )(OH)] complex efficiently promotes the hydrolysis/transesterification of both activated (2-hydroxypropyl p-nitrophenyl phosphate, hpnp) and non-activated, biological phosphodiesters (uridine-2Ј,3Ј-cyclic-monophosphate, cUMP and uridylyl-(3Ј,5Ј)-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.

The solution chemical properties, superoxide dismutase and catecholase activity of the copper(ii)-Ac-His-His-Gly-His-OH (hhgh) complexes were studied to identify functional and structural models of copper-containing oxidases. The solution speciation was determined in the pH range 3-11 by two independent methods (potentiometry and pH-dependent EPR measurements). The results obtained by the two methods agree very well with each other and show the formation of differently protonated CuH(x)L complexes (where x= 2 ,1, 0, -1, -2, -3) in aqueous solution. The spectroscopic (UV-Vis, CD, EPR) data indicate that the coordination of the imidazole rings is a determinant factor in all these complexes. Amide coordinated complexes are dominant only above pH 8. This offers excellent possibilities for structural/functional modelling of copper(ii) containing metalloenzymes. Indeed, the {3N(im)} coordinated CuL species (pH = 6-7) has efficient superoxide dismutase-like activity. The {3N(im),OH(-)} coordinated CuH(-1)L possesses outstanding activity to catalyze the oxidation of 3,5-di-tert-butylcatechol (H(2)dtbc) by dioxygen in 86 wt% methanol-water, providing the first example that copper(ii)-peptide complexes are able to mimic copper containing oxidases.

The macro- and microprotonations of glycylglycylhistamine (GGHA) have been determined by combined potentiometric and 1H-NMR methods. The complexation of GGHA with Co(II), Ni(II), and Cu(II) has been studied by potentiometric, EPR, and 1H-NMR methods. In the pH range 3−11.2, more or less deprotonated monomeric complexes (MLH, ML, MLH- 1, MLH- 2, MLH- 3) formed in all systems. In the case of Ni(II) and Cu(II) at physiological pH, the MLH- 2 species is predominant with four nitrogen coordination sites (one amino, two peptide, and one imidazole-N3 nitrogens) in square planar arrangement. In Co(II) containing systems however, CoL is the predominant complex near pH 7 with a macrochelate coordination of terminal amino and imidazole nitrogens, while CoLH- 2 species forms at much higher pH. In accordance with NMR measurements, the formation of MLH- 3 species can be assigned to the further deprotonation of the N1-pyrrolic nitrogen in the imidazole ring without metal coordination. The formation constants determined were compared with those of the analogous histidine derivatives. Single-crystal X-ray analysis of CuLH- 2·3H2O verified the expected four nitrogen coordination in the equatorial plane of Cu(II).

The interaction of Cu(II) with the ligand tdci (1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol) was studied both in the solid state and in solution. The complexes that were formed were also tested for phosphoesterase activity. The pentanuclear complex [Cu(5)(tdciH(-2))(tdci)(2)(OH)(2)(NO(3))(2)](NO(3))(4).6H(2)O consists of two dinuclear units and one trinuclear unit, having two shared copper(II) ions. The metal centers within the pentanuclear structure have three distinct coordination environments. All five copper(II) ions are linked by hydroxo/alkoxo bridges forming a Cu(5)O(6) cage. The Cu-Cu separations of the bridged centers are between 2.916 and 3.782 A, while those of the nonbridged metal ions are 5.455-5.712 A. The solution equilibria in the Cu(II)-tdci system proved to be extremely complicated. Depending on the pH and metal-to-ligand ratio, several differently deprotonated mono-, di-, and trinuclear complexes are formed. Their presence in solution was supported by mass, CW, and pulse EPR spectroscopic study, too. In these complexes, the metal ions are presumed to occupy tridentate [O(ax),N(eq),O(ax)] coordination sites and the O-donors of tdci may serve as bridging units between two metal ions. Additionally, deprotonation of the metal-bound water molecules may occur. The dinuclear Cu(2)LH(-3) species, formed around pH 8.5, provides outstanding rate acceleration for the hydrolysis of the activated phosphodiester bis(4-nitrophenyl)phosphate (BNPP). The second-order rate constant of BNPP hydrolysis promoted by the dinuclear complex (T = 298 K) is 0.95 M(-1) s(-1), which is ca. 47600-fold higher than that of the hydroxide ion catalyzed hydrolysis (k(OH)). Its activity is selective for the phosphodiester, and the hydrolysis was proved to be catalytic. The proposed bifunctional mechanism of the hydrolysis includes double Lewis acid activation and intramolecular nucleophilic catalysis.