A Unique Discrete Tetranuclear Cu鈥测€揅u(N-N)2Cu鈥揅u鈥?Copper(II) Complex, Built from a 渭3-1,2,4-Triazolato-渭-carboxylato Ligand, as an Effective DNA Cleavage Agent
文摘
The title compound, characterized by means of an X-ray structure analysis, represents an easy example of a noncatena 鈥? + 2 + 1鈥?tetranuclear copper(II) 渭3-triazolate compound. [Cu4(atc)2(dien)4(ClO4)2](ClO4)2路2H2O (1), where H2atc = 5-amino-l,2,4-triazole-3-carboxylic acid and dien = diethylenetriamine = 1,4,7-triazaheptane, contains two copper atoms linked by a double diazinic bridge, each of which is further connected to a third and fourth copper atom (Cu鈥? through the triply bridging triazolato ring and the bidentate carboxylato group of the atc2鈥?/sup> ligands. The copper鈥揷opper distances within the tetranuclear unit are Cu鈥揅u = 4.059 脜, Cu鈥揅u鈥?= 5.686 and 6.370 脜, and Cu鈥测€揅u鈥?= 11.373 脜. The compound self-assembles into a tridimensional hydrogen-bonded network to generate a MOF. 1 exhibits antiferromagnetic behavior with g = 2.10(1), J = 鈭?4.1(2) cm鈥? and j = 鈭?.50(3) cm鈥?, where J is the coupling constant of the central Cu鈥揅u pair and j the coupling constant of the two Cu鈥揅u鈥?(Cucentral鈥揅upheripheral) pairs, as defined by H = 鈭?i>JS2S2a 鈥?j (S1S2 + S2aS1a). Complex 1 has been tested as nuclease mimic. It shows good binding propensity to calf thymus DNA, with a binding constant value of 6.20 脳 106 M鈥? (Kapp) and 螖Tm = 18.3 掳C. Moreover, the compound displays efficient oxidative cleavage of pUC18 DNA, even at low concentration, in the presence of a mild reducing agent (ascorbate), with a rate constant for the conversion of supercoiled to nicked DNA (kobs) of 0.126 min鈥?. The good reactivity of 1 toward DNA is explained from the electrostatic interactions of the cationic species produced in solution.