Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

Abstract

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper(II) complexes, using the unsymmetrical ligands N',N',N-tris(2-pyridylmethyl)-N-(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L1) and N',N'-bis(2-pyridylmethyl)-N,N-(2-hydroxybenzyl)(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L2). The structures of the complexes [Cu(2)(L1)(μ-OAc)](ClO(4))(2)·(CH(3))(2)CHOH (1) and [Cu(2)(L2)(μ-OAc)](ClO(4))·H(2)O·(CH(3))(2)CHOH (2) were determined by X-ray crystallography. The complex [Cu(2)(L3)(μ-OAc)](2+) [3; L3 = N-(2-hydroxybenzyl)-N',N',N-tris(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. Inorg. Chim. Acta2005, 358, 1807-1822). Magnetic data show that the Cu(II) centers in 1 and 2 are antiferromagnetically coupled and that the difference in the exchange coupling J found for these complexes (J = -4.3 cm(-1) for 1 and J = -40.0 cm(-1) for 2) is a function of the Cu-O-Cu bridging angle. In addition, 1 and 2 were tested as catalysts in the oxidation of the model substrate 3,5-di-tert-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu(II)-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis(dinitrophenyl)phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu(II) center that contains the phenol group with tert-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (K(ass.) and k(cat.)) of 1 and 2 in comparison with that found for complex 3. In fact, complexes 1 and 2 show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity.

Synthesis, structure, magnetism, and hydrolase and catecholase activity of a new trinuclear copper(II) complex

“…NHE can be attributed to the couples Cu 2 II Cu I /Cu II Cu 2 I and Cu II Cu 2 I /3Cu 3 I , respectively. In fact, these values are in good agreement with the reduction potentials observed for dinuclear copper(II) complexes containing a l-alkoxo bridge and phenolate/pyridine ligands [7,9,10]. The electronic spectrum of 1 (Fig.…”

“…S4, the optimum pH is around 8.0 and sigmoidal fitting of the initial rate (V 0 ) versus pH curve in the pH range of 4.0-8.0 reveals a kinetic pK a value of $6.9, which can be attributed to the deprotonation of a Cu II -bound water molecule to generate the initiating nucleophile [9,25]. It is important to note that under these experimental conditions dissociation of the acetate bridge with replacement by two water molecules is expected, as previously reported in the literature [9]. Thus, the small decrease in reactivity at pH > 8.0 (see Fig.…”

“…The reactions were accompanied by monitoring the increase in the 2,4-dinitrophenolate characteristic absorption band at 400 nm (pH/e L mol À1 cm À1 = 3.5/2125; 4.0/3408; 4.5/7182; 5.0/10 078; 5.5/11 405; 6.0/ 12 004; 6.5-10.0/12 100) at 50°C for the hydrolase-like activity [18] and the formation of 3,5-di-tert-butylquinone (3,5-DTBQ) at 400 nm (e = 1900 M À1 cm À1 ) for the catecholase-like activity at 25°C. Less than 5% of the conversion of the substrate to the product was monitored and the data were treated using the initial rate method as previously described [9]. Synthesis of N,N 0 -(2-pyridylmethyl)-1,3-propanediamine-2-ol (2py): 4 mL of 2-pyridinecarboxaldehyde (40 mmol) in methanol was added slowly under continuous agitation, in an ice bath, to a solution containing 2.0 g (20 mmol) of 2-hydroxy-1,3-propanediamine in 30 mL of methanol.…”

“…While several enzymes displaying catalytic promiscuity have been the subject of recently reported investigations [6], there are few examples of synthetic analogues which exhibit such multifunctional activities [7][8][9][10][11].…”

Synthesis and characterization of mononuclear copper(II) complex of tetradentate N2S2 donor set and the study of DNA and bovine serum albumin binding

“…lated efforts to design and characterize copper complexes as models for providing better understanding of biological systems and for assisting in the development of new homogeneous catalysts for selective oxidation. Copper(II) complexes are effective for interaction and cleavage agents of DNA and hydrolysis catalysts [22][23][24]. Particularly, the coordination chemistry and reactivity of copper complexes involving nitrogen-sulfur donor ligands has received considerable attention as models [25][26][27][28][29].…”