Oxidation of 5-aminouracil with molecular oxygen in aqueous solution in the presence of copper(II) chloride

5-Aminouracil was found to form a six-coordinate copper(II) complex in aqueous solution and undergo oxidation to 5,5,6-trihydroxypyrimidine-2,4(1H,3H)-dione in the presence of molecular oxygen. A scheme was proposed for the fixation and activation of molecular oxygen on six-coordinate copper(II) complex with 5-aminouracil. The effect of the ligand structure on the rate of its oxidation with molecular oxygen in aqueous solution in the presence of copper(II) ions was shown.     

The role of copper(II) ions in the oxidation of 5-hydroxy-6-methyluracil in the ground and electronically excited states with molecular oxygen in aqueous solutions

A spectral fluorescence study of photoinduced reactions in aqueous solutions has been carried out in order to examine the mechanisms of the oxidation of 5-hydroxy-6-methyluracil (I) in the ground and electronically excited states by molecular oxygen in the presence of copper(II) chloride. It has been found that 5,5,6-trihydroxy-6-methylpyrimidine-2,4-dione (II) is formed upon the photolysis of I. The spectral parameters (λ_max) and the quantum yields (φ) of fluorescence (FL) of compounds I (φ = 8 × 10^–4; λ_max = 362 nm) and II (φ = 17 × 10^–4; λ_max = 306, 330 nm) have been determined. A reaction scheme was proposed, according to which the photooxidation of I occurs through the steps of the generation of the radical cation I ^?+ and the superoxide anion О ₂ ^?- with the subsequent formation of 5,5,6-trihydroxy-6-methylpyrimidine-2,4-dione. The catalytic and inhibitory effects of Cu(II) ions on the oxidation of 5-hydroxy-6-methyluracil in the ground and electronically excited states, respectively, by the oxygen radical anion О ₂ ^?- have been revealed.     

Experimental and quantum-chemical study of the mechanism of oxidation of 5-hydroxy-6-methyl-uracil by molecular oxygen in the presence of copper(II) ions

It has been discovered experimentally that 5,5,6-trihydroxy-6-methylpyrimidine-2,4-dione is formed on oxidizing 5-hydroxy-6-methyluracil with molecular oxygen in aqueous medium in the presence of copper(II) chloride. Ab initio and DFT calculations on the 6-31G* basis, both in the gas phase and allowing for solvent, showed that the process proceeds with the direct participation of an activated oxygen molecule on the complex CuCl₂·(5-hydroxy-6-methyluracil)2. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 586-593, April, 2009.     

A new synthesis of 5-hydroxy-6-methyluracil

Dehydration of 5,6-dihydro-5,6-dihydroxy-6-methyl- and 5,6-dihydro-5,6-dihydroxy-1,3,6-trimethyl-uracil in 0.4 M aqueous sulfuric acid gives 5-hydroxy-6-methyl- and 5-hydroxy-1,3,6-trimethyluracil in quantitative yields. Two possible mechanisms have been examined using the mPW1k/6-311+G(2df,2pd)//mPW1k/6-31+G(d,p) method for the transformation of methylated and non-methylated 5,6-dihydro-5,6-dihydroxy-6-methyluracils into the corresponding 5-hydroxy-6-methyluracils. The first is a hydride C5-C6 shift occurring in concert with the loss of a water molecule and formation of the corresponding protonated 5,6-dihydro-5-oxo-6-methyluracils. The second is an acid-catalyzed dehydration reaction to yield 5-hydroxy-6-methyluracils. The calculations demonstrated that the second pathway was energetically most favorable.     

Oxidation of bis[2-(2-pyridyl)benzimidazole]copper(II) by molecular oxygen in acetonitrile solution

Summary The complex bis[2-(2-pyridyl)benzimidazole]copper(I) perchlorate, [Cu(PBIM)₂]ClO₄, has been prepared and its oxidation with molecular oxygen in acetonitrile studied. Dependence of the rate constant, k₀, upon an excess of ligand was not observed. The rate constant for the oxidation of this complex was found to be 30 M^–2s^–1. The corresponding copper(II) compound behaves as a 11 electrolyte, commensurate with one of the complexed ligands losing a hydrogen.     

Oxidation of ferrocenes by copper(II) in aqueous acetonitrile: nitrate and chloride ion effects

The effect of nitrate and chloride ion on the rate of oxidation of ferrocene (Fc) and 1,1'-dimethylferrocene (DmFc) by Cu(II) has been studied in 95% and 80% acetonitrile/water solutions. The complex formation constants for Cu(II) with the same anions in the same media have been determined by spectrophotometry. Nitrate ion mildly inhibits the reaction, while chloride ion substantially increases the rate. The results have been analyzed in terms of the Marcus theory, and it is concluded that complexation increases the rate of self-exchange between the CuII(X)n and CuI(X)n species. In the case of nitrate, the latter effect is compensated for by a less favorable overall equilibrium constant, which results in mild inhibition.     

Cyclo(L-histidyl-L-histidyl)copper(II) complexes in aqueous solution

Summary The structure of the copper(II) complex cation with HISH₂ [HISH₂ = cyclo(L-histidyl-L-histidyl)] was determined from molecular weight data and n.m.r. and c.d. spectra in aqueous solution. Two HISH₂ moieties ligate to coppervia two nitrogen atoms of the imidazole rings giving rise to two 13-membered chelate rings in solution, a situation seen previously in the crystal.     

Oxidation of cobalt(II) with air oxygen in aqueous ethylenediamine solutions

Oxidation of aqueous Co(NO₃)₂–ethylenediamine (En) solutions with air oxygen was investigated at 20 °C and pH 5.2–7.0, with and without mechanical stirring, by measuring the Co^II concentration, pH and redox potential on an Au electrode. In most cases, the oxidation rate was proportional to the concentration of CoEn ²⁺ _n (n = 2, 3) complexes, and the influence of the solution pH on the rate of reaction was accounted for by the pH dependence of the Co^II complex distribution. It was found that sulphate inhibits and bromide accelerates the oxidation process. Possible oxidation routes are discussed. The oxidation process is limited to some extent by O₂ transport from the air to the bulk solution.     

Oxidation of 3-hydroxyflavones in the presence of copper(I) and copper(II) chlorides

The reactions of 3-hydroxyflavones with dioxygen in the presence of CuCl and CuCl₂ have been studied. 2-Benzoyl-2-hydroxy-3(2H)-benzofuranone (2) was formed along with 2-hydroxybenzil (4), salicylic acid (5), benzoic acid (6), coumaronedione (8) and the depside (11). A copper(II) flavonolate complex has been also isolated.     

Thermodynamics of copper(II) dicarboxylate coordination in aqueous solution

Summary The association of H⁺ and Cu²⁺ with malonate, maleate, succinate and phthalate ions has been investigated both potentiometrically and calorimetrically at 25° and I = 0.1 mol dm^–3 (NaClO₄).The structures of the complexes existing in aqueous solution are proposed on the basis of thermodynamic data.     

Oxidation of 5-Hydroxy-6-methyluracil in Alkaline Aqueous Solutions

Russian Journal of General Chemistry - 5-Hydroxy-6-methyluracil was found to be oxidized by molecular oxygen in an alkaline aqueous solution. The effect of temperature, concentration of alkali and...     

Oxidation of hydrogen chloride with hydrogen peroxide in aqueous solution

Evolution of chlorine into the gas phase upon mixing of aqueous solutions of hydrogen chloride and hydrogen peroxide was studied. The threshold hydrogen chloride concentration corresponding to the onset of the chlorine evolution was determined.     

Complex formation equilibria of L-Amino-Acid amides with copper(II) in aqueous solution

Protonation and Cu(II) complexation equilibria of L -phenyhilaninamide, N²-methyl-L-phenylalaninamide, N², N²-dimethyl-L-phenylalaninamide, L -valinamide, and L -prolinamide have been studied by potentiometry in aqueous solution. The formation constants of the species observed, CuL²⁺, CuL, CuLH, CuL₂H and CuL₂H_?2, are discussed in relation to the structures of the ligands. Possible structures of bisamidato complexes are proposed on the ground of VIS and CD spectra. Since Cu(II) complexes of the present ligands (pH range 6–8) perform chiral resolution of dansyl- and unmodified amino acids in HPLC (reversed phase), it is relevant for the investigation of the resolution mechanism to know which are the species potentially involved in the recognition process.     

Activation of molecular oxygen on copper(II) complexes of 5-hydroxy and 5-aminoorotic acids

The fixation and activation of molecular oxygen on copper(II) complexes with 5-hydroxy and 5-aminoorotic acids, leading to oxidation of the ligand.     

Potentiometric behaviour of the copper electrode in aqueous copper(II) perchlorate solutions containing sodium chloride

It is demonstrated that the copper metal electrode corrodes in the presence of copper(II) ions in solution. A model based on mass balance can properly describe the experimental results. In the presence of copper(II) ions the copper electrode responds to copper(I), indicating that the electrode potential corresponds to a mixed potential.     

On the complex formation of copper(ii) chloride with 6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline

Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1321–1322, July, 1993.     

Oxidation of aqueous solutions of cobalt(II) in the presence of some aminoacids

Summary The complexes between cobalt(III) and aminoacids such as glutamine, asparagine, glutamic acid, aspartic acid and proline were studied.Cobalt(III)-aminoacid systems were investigated by spectrophotometry after oxidizing the cobalt(II) complexes by sodium peroxide. The variation of the absorption spectra shows the pH dependence of the process and it is clear that the formation of the complexes occurs through oxo-intermediates.Complexation ratios, molar absorptivity values and the concentration quotients at equilibrium were determined at pH 2.2 to avoid the formation of binuclear dioxygen-cobalt complexes.     

Dimethyl sulfoxide structuring in the presence of aqueous manganese(II) sulfate solution

Mixing of an aqueous MnSO₄ solution with liquid dimethyl sulfoxide leads to gelation and loss of fluidity of the mixture.