Search

Abstract  Aldimine 2,6-bis[(imino)methyl]pyridine iron(II) (1, 4, and 6) and cobalt(II) (3 and 5) complexes bearing bulky cycloaliphatic (bornyl and myrtanyl) or aromatic (naphthyl) terminal groups have been applied successfully, after activation with methyl aluminoxane (MAO), as catalysts for the polymerization of tert-butylacrylate. For comparison reasons, complex 2 that contains the ketimine ligand, 2,6-bis[(−)-cis-myrtanylimino)ethyl]pyridine (BMEP), has also been utilized. All studied complexes showed moderate polymerization activities, and they produced high molar mass syndiorich-atactic polymers. Surprisingly, the aldimine-based catalyst systems showed comparable activities compared with the corresponding ketimine complex (2), and they produced high molar mass polymers. In addition, complexes with bulky terminal cycloaliphatic substituents on the tridentate aldimine ligands showed higher polymerization activity compared with the aromatic ones (6). Polymerization activity and polymer molar masses are dependent on the ligand framework. [ABSTRACT FROM AUTHOR]

The DNA-cleavage properties of the two copper(ii) complexes, [Cu(mbpzbpy)Br2](H2O)2.5 (1) and [Cu(mpzbpya)Cl](CH3OH) (2), obtained from the ligands 6,6′-bis(3,5-dimethyl-N-pyrazolmethyl)-2,2′-bipyridine) (mbpzbpy) and 6′-(3,5-dimethyl-N–pyrazolmethyl)-2,2′-bipyridine-6-carboxylic acid) (Hmpzbpya), respectively, are reported. Upon coordination to CuII chloride in methanol, one arm of the ligand mbpzbpy is hydrolyzed to form mpzbpya. Under the same experimental conditions, the reaction of mbpzbpy with CuBr2 does not lead to ligand hydrolysis. The ligand mpzbpya is coordinated to a copper(ii) ion generating a CuN3OCl chromophore, resulting in a distorted square-pyramidal environment, whereas with the N4 mbpzbpy ligand, the CuII ion is four-coordinated in a distorted square planar geometry. Both complexes promote the oxidative DNA cleavage of ϕX174 phage DNA in the absence of reductant. The oxidative nature of the DNA cleavage reaction has been confirmed by religation and cell-transformation experiments. Studies using standard radical scavengers suggest the involvement of hydroxyl radicals in the oxidative cleavage of DNA. Although both compounds do convert form I (supercoiled) DNA to form II (nicked, relaxed form), only complex 1 is able to produce small amounts of form III (linearized DNA). This observation may be explained either by the attack of the copper(ii) complexes to only one single strand of DNA, or by a single cleavage event. Statistical analysis of relative DNA quantities present after the treatment with both copper(ii) complexes supports a random mode of DNA cleavage. [ABSTRACT FROM AUTHOR]