DNA phosphodiester bond hydrolysis mediated by Cu(II) and Zn(II) complexes of 1,3,5,-triamino-cyclohexane derivatives.

The hydrolytic activity of the 1,3,5-triaminocyclohexane derivatives TACH, TACI and TMCA complexed to Zn(II) and Cu(II) towards a model phosphoric ester and plasmid DNA has been evaluated by means of spectroscopic and gel-electrophoresis techniques. At conditions close to physiological, a prominent cleavage effect mediated by the nature of the ligand and metal ion was generally observed. TACI complexes are the most active in relaxing supercoiled DNA, the effect being explained by the affinity of the hydroxylated ligand for the nucleic acid. As indicated by the dependence of cleavage efficiency upon pH, Zn(II)-complexes act by a purely hydrolytic mechanism. In the case of Cu(II)-complexes, although hydrolysis should be prominent, involvement of an oxidative pathway cannot be completely ruled out.

A highly sensitive method for the analysis of nitrite ions by capillary zone electrophoresis using water-soluble aminophenylporphyrin derivative as chromogenic reagent.

The water soluble 5-p-aminophenyl)-10,15,20-tris(p-sulfonatophenyl) porphyrin, 4, acts as an extremely efficient chromogenic reagent for the detection of very low amounts of nitrites. The amino group of porphyrin 4 reacts smoothly with nitrite in acidic conditions 0.2 M HCl) producing the corresponding diazo-porphyrin derivative which is stable and does not show any appreciable hydrolysis to phenol within 6 h. The reaction is carried out in the presence of 25 mM heptakis-(2,6-di-O-methyl)-beta-cyclodextrin that prevents precipitation of the protonated form of porphyrins 4 or 5 due to the formation of strong inclusion complexes. The capillary zone electrophoresis of the diazoporphyrin and amino-porphyrin mixture shows severe peak tailing. However, symmetrical peaks can be obtained by adding 5 mM beta-cyclodextrin to the background electrolyte (20 mM phosphate buffer, pH 7.0). Calibration curve for nitrite analysis is linear up to 0.25 mM nitrite and the detection limit (at a signal-to-noise ratio of 3) has been estimated to be a 1 microM (50 ppb) of nitrite concentration in aqueous solutions.

Capillary electrophoresis behavior of water-soluble anionic porphyrins in the presence of beta-cyclodextrin and its O-methylated derivatives.

The electrophoretic behavior of water-soluble anionic porphyrins, such as meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP), meso-tetrakis(4-sulfonatophenyl) porphyrin (TSPP) and its zinc(II) and copper(II) complexes (ZnTSPP and CuTSPP, respectively) has been studied by capillary zone electrophoresis using fused-silica capillaries. The selectivity of the separation is strongly dependent on the type and concentration of betacyclodextrin (betaCD) or the O-methylated derivatives added to the background electrolyte. CuTSPP and TSPP can be separated using a pH 2.5 aqueous sodium phosphate buffer in the presence of 1 mM betaCD. Resolution is poorer or absent employing alkylated betaCDs, such as the heptakis (2,6-di-O-methyl)-beta-cyclodextrin or the heptakis(2,3,6-triO-methyl)-beta-cyclodextrin, as additives. On the other hand, separation of TSPP from its copper and zinc complexes has been achieved using a pH 7.0 aqueous sodium phosphate buffer, in the presence of 0.75 mM betaCD and 20% dimethyl sulfoxide (DMSO) as organic modifier. Under such conditions, the calibration curve for quantitative analysis of copper(II) was obtained. A rationale for the observed behavior will be presented and discussed on the basis of binding and protonation equilibria and a simple mathematical model.

Synthesis, characterization, and supramolecular properties of a hydrophilic porphyrin--beta-cyclodextrin conjugate.

Reductive amination of 6-deoxy-6-formyl-beta-cyclodextrin with 5-(p-aminophenyl)-10,15,20-tris(p-sulfonatophenyl)porphyrin in the presence of an excess of sodium cyanoborohydride affords the hydrophilic cyclodextrin-porphyrin conjugate 3 in 23% yield. The structure of 3 was confirmed by NMR spectroscopy and mass spectrometry techniques. Compound 3 showed a marked tendency to dimerize in aqueous conditions via the formation of intermolecular porphyrin-cyclodextrin inclusion complexes and/or through electrostatic interactions. Information on the structure of these aggregates has been obtained by the use of circular dichroism and UV-vis spectroscopy. Aggregation can be avoided by the use of heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM beta CD) that forms a 1:1 inclusion complex with compound 3.

Exploiting the Self-Assembly Strategy for the Design of Selective Cu(II) Ion Chemosensors.

Simply by mixing in water, a liphophilic dipeptide (L), a surfactant (S), and a fluorophore (F) self-assemble to give a sensor able to detect Cu(II) ions (see scheme). Despite the ease of construction, the sensor displays high selectivity and a low detection limit for the target ion. This new modular approach to sensing devices allows easy variations of the components, making optimization of the system very simple and fast.