No abstract

Four new cobalt(ii) complexes [Co(6-MeTPA)Cl]ClO4/PF6 (2/2a), [Co(6-Me2TPA)Cl]ClO4/PF6 (3/3a), [Co(BPQA)Cl]ClO4/PF6 (4/4a) and [Co(BQPA)Cl]ClO4/PF6 (5/5a) as well as [Co(TPA)Cl]ClO4 (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me2TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a-5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH3CN-H2O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H2O)](2+). The pKa values of the coordinated H2O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1-5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis-Menten kinetic conditions, the catalytic rate constants, kcat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the kcat value for complex 4 (6.02 h(-1)), where [Co(BPQA)(H2O)](2+) is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN3) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the kcat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)](+). The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(ii) center.

No abstract

No abstract

The reaction of 2‐chloro‐4,6‐bis(di‐2‐picolylamino)‐1,3,5‐triazine (bdpaTCl) with copper(II) perchlorate and copper(II) chloride afforded two dinuclear complexes [Cu2(μ‐bdpaTCl)(μ‐OH)2(H2O)0.5(ClO4)0.5](ClO4)1.5·(H2O)1.5 (1) and [Cu2(μ‐bdpaTCl)Cl4]·2CH3OH (2), respectively. These complexes were characterized by IR, UV/Vis, and EPR spectroscopy, single‐crystal X‐ray crystallography, and temperature dependence magnetic susceptibility measurements (2–300 K) as well as by electrochemical and molar conductivity measurements. In 1, each of the three N‐donor atoms of the binucleating bdpaTCl ligand coordinate to CuII ions, which are further bridged by two OH– anions in a distorted five‐coordinate geometry. In addition, each CuII ion forms a Cu–O semicoordinate bond with an aqua ligand or perchlorato anion. The Cu···Cu distance across the hydroxido bridges is 2.9698(11) Å. In 2, the bdpaTCl ligand acts as bis‐tridentate ligand connecting the two CuII ions, and the five‐coordinate geometry around each copper center is achieved by two terminal chloro ligands. Magnetic measurements revealed strong antiferromagnetic coupling in 1 (J = –311.2 cm–1) and very weak coupling in 2 (J = –2.4 cm–1). DNA cleavage by these two complexes has been investigated (pH = 7.0, 37 °C). Although the bridged dihydroxido complex 1 did not show any detectable cleavage for DNA, significant cleavage was observed with the tetrachloro complex 2. Under pseudo‐Michaelis–Menten kinetic conditions, the kinetic parameters kcat = 2.53 × 10–5 s–1 and KM = 1.44 × 10–4 M were determined for 2. The kcat value corresponds to a 2.5 × 106 fold rate enhancement over noncatalyzed DNA. Electrophoretic experiments conducted in the presence and absence of oxidative scavengers DMSO, KI, and NaN3, and radical promoter H2O2 provide evidence for the oxidative cleavage of DNA by hydroxy radicals and hydrogen peroxide species.