Second-Sphere Effects in Dinuclear FeIIIZnII Hydrolase Biomimetics: Tuning Binding and Reactivity Properties.

Herein, we report the synthesis and characterization of two dinuclear FeIIIZnII complexes [FeIIIZnIILP1] (1) and [FeIIIZnIILP2] (2), in which LP1 and LP2 are conjugated systems containing one and two pyrene groups, respectively, connected via the diamine -HN(CH2)4NH- spacer to the well-known N5O2-donor H2L ligand (H2L = 2-bis{[(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxybenzyl)(2-pyridylmethyl)]aminomethyl}-4-methylphenol). The complex [FeIIIZnIIL1] (3), in which H2L was modified to H2L1, with a carbonyl group attached to the terminal phenol group, was included in this study for comparison purposes.1 Both complexes 1 and 2 were satisfactorily characterized in the solid state and in solution. Extended X-ray absorption fine structure data for 1 and 3 in an acetonitrile solution show that the multiply bridged structure seen in the solid state of 3 is retained in solution. Potentiometric and UV-vis titration of 1 and 2 show that electrostatic interaction between the protonated amino groups and coordinated water molecules significantly decreases the pKa of the iron(III)-bound water compared to those of 3. On the other hand, catalytic activity studies using 1 and 2 in the hydrolysis of the activated substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) resulted in a significant increase in the association of the substrate (Kass ≅ 1/KM) compared to that of 3 because of electrostatic and hydrophobic interactions between BDNPP and the side-chain diaminopyrene of the ligands H2LP1 and H2LP2. In addition, the introduction of the pyrene motifs in 1 and 2 enhanced their activity toward DNA and as effective antitumor drugs, although the biochemical mechanism of the latter effect is currently under investigation. These complexes represent interesting examples of how to promote an increase in the activity of traditional artificial metal nucleases by introducing second-coordination-sphere effects.

Targeting an Artificial Metal Nuclease to DNA by a Simple Chemical Modification and Its Drastic Effect on Catalysis.

A novel metal complex was synthesized containing a purine derived ligand in order to increase its binding to DNA. We observed a huge increase in nuclease activity and, quite interestingly, an improvement on DNA sequence selectivity. A potential site of specific cleavage in the presence of a reductant in the reaction medium is suggested. We were able to synthesize a novel metal nuclease with improved activity on DNA, and with sequence specificity when exposed to a coreactant, this opens up new possibilities to create site specific and redox status modulated artificial nucleases.

Self-assembled monolayer of nickel(II) complex and thiol on gold electrode for the determination of catechin.

Self-assembled monolayers of a nickel(II) complex and 3-mercaptopropionic acid on a gold electrode were obtained for determination of catechin by square wave voltammetry. The complex [Ni(II)L] with L=[N-(methyl)-N'-(2-pyridylmethyl)-N,N'-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-1,3-propanediamine[nickel(II)] was synthesized and characterized by (1)H NMR, IR, and electronic spectroscopies and electrochemical methods. The optimized conditions obtained for the electrodes were 0.1 mol L(-1) phosphate buffer solution (pH 7.0), frequency of 80.0 Hz, pulse amplitude of 60.0 mV and scan increment of 10.0 mV. Under these optimum conditions, the resultant peak current on square wave voltammograms increases linearly with the concentration of catechin in the range of 3.31 x 10(-6) to 2.53 x 10(-5)mol L(-1) with detection limits of 8.26 x 10(-7)mol L(-1). The relative standard deviation for a solution containing 1.61 x 10(-5)mol L(-1) catechin solution was 2.45% for eight successive assays. The lifetime of the Ni(II) complex-SAM-Au electrode was investigated through testing every day over 4 weeks. The results showed apparent loss of activity after 20 days. The results obtained for catechin in green tea samples using the proposed sensor and those obtained by electrophoresis are in agreement at the 95% confidence level.