Supramolecular complexes of transition-metal(II) ions for the hydrolysis of phosphate esters and of DNA

De novo design of a hydrolytic DNA cleavage agent, mono nitratobis(phen)cobalt(ii) aqua nitrate complex

Demonstration of DNA intercalation and hydrolytic cleavage by complex1.

Degradation of four organophosphorous pesticides catalyzed by chitosan-metal coordination complexes

Three types of chitosan with high (3.40 × 10(6)), medium (2.11 × 10(5)), and low (5.89 × 10(4)) molecular weights were chosen as ligands to synthesize chitosan magnesium, calcium, iron(III), and zinc coordination complexes. Degradation of four organophosphorous pesticides (dichlorvos, omethoate, dimethoate, and chlorpyrifos) by the above complexes in a heterogeneous system was studied using solid-phase extraction (SPE) and gas chromatography (GC). The degradation effect is related to the different types of chitosan, metal, and organophosphorus pesticides (OPs). Complexes of transition metals and the low molecular weight chitosan showed high hydrolytic activity. The chitosan-iron(III) complex was further used to study its catalytic kinetics on the hydrolysis of OPs. At pH 7.0 and 20 °C, the half-life of dichlorvos hydrolyzed by chitosan iron(III) was 52 h, whereas that of spontaneous dichlorvos hydrolysis was 105 h. The degradation ratio of omethoate and dimethoate increased to 38 and 52 %, respectively, which were 34 and 48 % higher than the control after 6 days at pH 7.0 and 20 °C. For all tested conditions, an increase of pH and temperature resulted in a higher degradation rate.

Hydrolytic Cleavage of DNA by a Ruthenium(II) Polypyridyl Complex

The complex [Ru(bpy)2(BPG)]Cl2 (1) containing hydrogen-bond donor (N-H atoms) and acceptor (O atoms) groups mediates hydrolytic cleavage of plasmid pBR322 DNA in an enzyme-like manner. The kinetic aspects of DNA cleavage under pseudo- and true-Michaelis-Menten conditions are detailed.

Kinetics and Mechanism of Hydrolysis of a Model Phosphate Diester by [Cu(Me3tacn)(OH2)2]2+ (Me3tacn = 1,4,7-Trimethyl-1,4,7-triazacyclononane)

The kinetics of hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) by [Cu(Me3tacn)(OH2)2]2+ has been studied by spectrophotometrical monitoring of the release of the p-nitrophenylate ion from BNPP. The reaction was followed for up to 8000 min at constant BNPP concentration (15 microM) and ionic strength (0.15 M) and variable concentration of complex (1.0-7.5 mM) and temperature (42.5-65.0 degrees C). Biphasic kinetic traces were observed, indicating that the complex promotes the cleavage of BNPP to NPP [(p-nitrophenyl)phosphate] and then cleavage of the latter to phosphate, the two processes differing in rate by 50-100-fold. Analysis of the more amenable cleavage of BNPP revealed that the rate of BNPP cleavage is among the highest measured for mononuclear copper(II) complexes and is slightly higher than that reported for the close analogue [Cu(iPr3tacn)(OH2)2]2+. Detailed analysis required the determination of the pKa for [Cu(Me3tacn)(OH2)2]2+ and the constant for the dimerization of the conjugate base to [(Me3tacn)Cu(OH)2Cu(Me3tacn)]2+ (Kdim). Thermodynamic parameters derived from spectrophotometric pH titration and the analysis of the kinetic data were in reasonable agreement. Second-order rate constants for cleavage of BNPP by [Cu(Me3tacn)(OH2)(OH)]+ and associated activation parameters were obtained from initial rate analysis (k = 0.065 M(-1) s(-1) at 50.0 degrees C, deltaH = 56+/-6 kJ mol(-1), deltaS = -95+/-18 J K(-1) mol(-1)) and biphasic kinetic analysis (k = 0.14 M(-1) s(-1) at 50.0 degrees C, deltaH = 55+/-6 kJ mol(-1), deltaS = -92+/-20 J K(-1) mol(-1)). The negative entropy of activation is consistent with a concerted mechanism with considerable associative character. The complex was found to catalyze the cleavage of BNPP with turnover rates of up to 1 per day. Although these turnover rates can be considered low from an application point of view, the ability of the complexes to catalyze phosphate ester cleavage is clearly demonstrated.

Double-strand hydrolysis of DNA by a magnesium(II) complex with diethylenetriamine

The development of artificial nucleases that hydrolyze DNA or RNA is of great interest in molecular biology, biotechnology, and medicine. We now report that a magnesium(II) complex of diethylenetriamine (Mg-dien) can effectively promote the double-stranded cleavage of plasmid DNA and the dideoxynucleotide dApdA under physiological conditions of pH and temperature. Experiments performed in the presence of hydrogen peroxide, radical scavengers, or under rigorously anaerobic conditions indicate that DNA cleavage mediated by Mg-dien occurs via a hydrolytic path. Mg-dien efficiently hydrolyzes supercoiled pBR322 DNA and the pseudo-first-order rate constant at 37 degrees C and pH 8.0 is estimated to be 1.60 h(-1). The dinucleotide dApdA hydrolysis, with Mg-dien at 170 microM, shows a rate enhancement factor of ca. 5 x 10(8). 1H and 31P(1H) NMR studies show that Mg-dien effectively hydrolyzes 5'-dAMP to give deoxyadenosine and inorganic phosphate. While Mg2+ has been found at the catalytic sites of many natural nucleases, Mg-dien appears to be the first synthetic Mg2+-containing system capable of hydrolyzing dideoxynucleotides and DNA and thus may provide a simple model system to assist mechanistic studies of naturally occurring nucleases.