Eugenijus Norkus

Deprotonation of β-cyclodextrin in alkaline solutions

Variable pH (13)C NMR and (1)H NMR spectroscopic studies of the beta-cyclodextrin (beta-CD) in alkaline aqueous solutions revealed that beta-CD does not deprotonate at pH<12.0. Further increase in solution pH results in the deprotonation of OH-groups adjacent to C-2 and C-3 carbon atoms of beta-CD glucopyranose units, whereas the deprotonation of OH-groups adjacent to C-6 carbon atoms is expressed less markedly. The pK(a) values for beta-CD OH-groups adjacent to C-2 and C-3 carbon atoms are rather close, pK(a1,2) being 13.5+/-0.2 (22.5 degrees C).

Stability of a Dinuclear Cu(II)–β-Cyclodextrin Complex

Cu(II) ions form a dinuclear complex with the tetraanion of β-cyclodextrin (CD4-) in alkaline solutions under conditions of metal ion excess. The spectrophotometric method of ligand displacement was used for the determination of the stability constant of this complex using EDTA and OH- ions as competitive ligands. The results obtained are in agreement with the 2:1 stoichiometry of the complex, namely Cu2CD, the logarithm of the stability constant being 39.2±0.2. This complex predominates in the pH range from 12.5 to 14.3 (3 M NaOH solution), transforming with the increase in alkalinity to

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 CoII concentration, pH and redox potential on an Au electrode. In most cases, the oxidation rate was proportional to the concentration of CoEn2+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 CoII 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.

Cu(II) Ion Complexation by Excess of β-cyclodextrin in Aqueous Alkaline Solutions

Polarographic investigations of Cu(II) complexation in aqueous alkaline solutions containing an excess of β-cyclodextrin (β-CD) show that the complex formation begins at pH > 11, the concentration of free (uncomplexed) Cu(II) ions being in the range from ca. 10-12 to ca. 10-19 M, depending on β-CD concentration and pH. The formation of copper(II) 1:1 hydroxy-complex with β-cyclodextrin anion (CD2-) was observed at pH 11–14. The logarithm of the stability constant of CuCD(OH)2-2 complex is 19.7 ± 0.2 (20 °C, ionic strength 1.0), the values of the molar extinction coefficient and of the diffusion coefficient of this complex are 50 M-1 cm-1 (λmax = 660 nm) and 1.0 × 10-6 cm2 s-1, respectively.

Kinetics of electroless copper deposition using cobalt(II)-ethylenediamine complex compounds as reducing agents

AbstractElectroless copper deposition using Co(II)-ethylenediamine (En) complexes as reducing agents was investigated in 0.4–1.2 M En solutions at 50 and 70 °C. There is a complicated dependence of the process rate on pH, En concentration and temperature. A copper deposition rate up to 6 μm h−1 (50–70 °C) in relatively stable solutions (pH ∼ 6) can be achieved. The stoichiometry of the Cu(II) reduction at pH 6–7 corresponds to the reaction:

Polarographic Determination of Formaldehyde According to the Anodic Oxidation Wave in Alkaline Solutions

{\text{Cu}}En_2^{2 + } + 2{\text{ Co}}En_2^{2 + } \xrightarrow{{{\text{Cu}}}}{\text{Cu + 2 Cu}}En_3^{3 + }

Influence of Ionic Strength and Cation Nature on the Deprotonation of Methanediol in Alkaline Solution

The correlation between the rate of the copper deposition on the catalytic surface and the concentration of the