Copper(II) complexes of a new N-picolylated bis benzimidazolyl diamide ligand: Synthesis, crystal structure and catechol oxidase studies

Aerial Oxidation of Phenol/Catechol in the Presence of Catalytic Amounts of [(Cl)2Mn(RCOOET)], RCOOET= Ethyl-5-Methyl-1-(((6-Methyl-3-Nitropyridin-2-yl)Amino)Methyl)-1H-Pyrazole-3-Carboxylate

In this work, we report on the catalytic activity of a manganese complex [(Cl)2Mn(RCOOET)], where RCOOET is ethyl-5-methyl-1-(((6-methyl-3-nitropyridin-2-yl)amino)methyl)-1H-pyrazole-3-carboxylate, in the oxidation of phenol or catechol by atmospheric oxygen to form o-quinone. The [(Cl)2Mn(RCOOET)] catalyzes the oxidation of catechol at a rate of 3.74 µmol L−1 min−1 in tetrahydrofuran (THF), in a similar manner to catecholase or tyrosinase.

Copper(II) complexes as catalyst for the aerobic oxidation of o-phenylenediamine to 2,3-diaminophenazine

Two new mononuclear copper(II) complexes [Cu (L) (NO3)2] (1) and [Cu (L) Br2] (2) where (L=bis(1-(pyridin-2-ylmethyl)-benzimidazol-2-ylmethyl)ether) are synthesized and characterized by single-crystal X-ray diffraction analysis, elemental analysis, UV-Visible, IR spectroscopy, EPR and cyclic voltammetry. The complexes exhibit different coordination structures; the E1/2 value of the complex (1) is found to be relatively more cathodic than that of complex (2). X-band EPR spectra at low temperature in DMF supports a tetragonally distorted complex (1) while complex (2) shows three different g values suggesting a rhombic geometry. These complexes were utilized as a catalyst for the aerobic oxidation of o-phenylenediamine to 2,3-diaminophenazine assisted by molecular oxygen. The initial rate of reaction is dependent on the concentration of Cu(II) complex as well as substrate, and was found to be higher for the nitrate bound complex, while presence of acetate anion acts as a mild inhibitor of the reaction, as it is likely to pick up protons generated during the course of reaction. The inhibition suggests that the generated protons are further required in another important catalytic step.

A water soluble copper(ii) complex as a HSO4− ion selective turn-on fluorescent sensor applicable in living cell imaging

A water soluble non-fluorescent biofriendly cell permeable structurally characterised copper(ii) complex (1) selectively senses HSO₄⁻ ions as low as 3.18 × 10⁻⁷ M in water : DMSO (9 : 1, v/v) HEPES buffer at biological pH.

Iron(III) complexes of bis (benzimidazol-2-yl) methyl) thiophene-2,5-dicarboxamide: synthesis, spectral and oxidation of o-phenylenediamine

Iron(III) complexes of a potentially pentadentate ligand N(2), N(5)-bis ((1H-benzo [d] imidazol-2-yl) methyl) thiophene-2,5-dicarboxamide are synthesized with an exogenous anion X=Cl(-), NO(3)(-). Mössbauer and EPR spectroscopy indicates axially distorted complexes. These complexes were utilized for the oxidation of o-phenylenediamine to 2,3-diaminophenazine in presence of H(2)O(2). The initial rate of reaction is dependent on the concentration of o-phenylenediamine as well as the iron(III) complex. Rates of reaction were found to be at least five times higher for the Cl(-) bound complex. The effect of an added anion like acetate, azide and citrate is found to inhibit the rate of reaction. This suggests that one of the factors affecting the rate determining step is the binding of these anions on a vacant site at the iron(III) centre. The oxidation of o-phenylenediamine to 2,3-diaminophenazine is reminiscent of the functioning of horse radish peroxidase.