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() 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.

New Cu(II) complexes with polydentate chelating Schiff base ligands: Synthesis, structures, characterisations and biochemical activity studies

“…In the spectra of the complexes, the bands of the azomethine chromophore n − π * transition are shifted to lower frequencies indicating that the imine nitrogen atom is involved in coordination to the metal ion [25]. The UV absorption bands observed at 385, 388 and 395 nm for complexes 1, 2 and 3, respectively can be attributed to the ligand to Cu(II) charge transfer transition (LMCT) [26,27]. Those very weak low-intensity absorption bands associated with d − d transitions at 670, 675 and 676 nm may be assigned for to a Cu(II) d-d transition [26][27][28][29] for 1, 2 and 3, respectively and support the five-coordinated geometry around copper(II) ions with the CuN 4 chromophoric group.…”

Designer ligands. part 15. synthesis and characterisation of novel Mn(lI), Ni(II) and Zn(II) complexes of 1,10-phenanthroline-derived ligands.

“…[1][2][3][4] Mononuclear manganese centres have been found in the oxygen evolving center (OEC) of photosystem II (PS-II) 5 and in numerous enzymes, 6 including the superoxide dismutase, Mn-SOD, 7 and Mn-dioxygenase. 8 Dinuclear manganese centres, on the other hand, have been found in various metalloenzymes, 14 including catalase, 9-11 Mn-ribonucleotide reductase 12 and arginase.…”

A novel 1,3,5-triaminocyclohexane-based tripodal ligand forms a unique tetra(pyrazolate)-bridged tricopper(ii) core: solution equilibrium, structure and catecholase activity

“…[4][5][6][7][8][9][10][11] On the other hand, a great number of low molecular weight enzyme models studied also emphasized the importance of the adequate and preorganized structure around the metal ions, which is trivially present in enzymes. Although a large number of metal complexes formed with linear/acyclic ligands were reported to possess important catalytic activity, [4][5][6]12,13 tripodal compounds may have several advantages over the linear ones, such as the preorganized structure, higher metal binding ability and facial coordination. 14 Tripodal ligands, such as cis,cis-1,3,5-triaminocyclohexane (tach) and related compounds (1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) and its N-methylated derivatives), are versatile ligands with several unique coordination properties.…”