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Interaction of sodium and potassium ions with the cis isomers of dicyclohexyl-18-crown-6 in nonaqueous media

100%

Wagner-Czauderna E. , Filipek S. , Kalinowski M. K.

tom Vol. 72, nr 10

2294-2302

The formation constants, K-s for 1:1 complexes of the cis-syn-cis and cis-anti-cis isomers of dicyclohexyl-18-crown-6 with sodium and potassium cations have been electrochemically determined in 10 nonaqueous (protic and aprotic) media. Linear correlations were obtained for log K-s with standard Gibbs transfer energies of the cation from water to a given solvent. The cis-anti-cis isomer was found to be a weaker complexer than the cis-syn-cis one and this was elucidated in terms of the ligand solvation. Energy-minimized structures of the ligands and complexes suuuounded by methanol and acetonitrile molecules were established by molecular dynamics computations.

Electrochemical reduction of p-chloronitrobenzene in dipolar aprotic solvents containing carboxylic acids

100%

Wagner-Czauderna E. , Orłowska E. , Kalinowski M. K.

1998

tom Vol. 72, nr 9

2127-2133

The effect of carboxylic acids of different strenght on polarographic behaviour of p-chloronitrobenzene in N, N-dimethylformamide has been investigated. In the presence of each acid a pre-wave appeared at a more positive potential than the original one, which was associated with the cathodic reduction of a hydrogen-bonded adduct, formed between the nitrocompound and the acid molecules in the double layer of the electrode. A linear correlation has been found between delta E-1/2 and pK(DMF/HA) (pK(DMF/HA) refers to the value of the pK-a measured in N, N-dimethylformamide, whereas delta E-1/2=E(pre-wave/1/2) - E(original wave/1/2)). Measurements in a solvent series in the presence of benzoic acid (BA) led to the correlation between delta E-1/2 and pK-BA (the symbol pK-BA denotes the value measured in a given solvent). The slopes of regression lines are discussed in terms of the double layer effect on the basicity of the -NO2 group.

Elektrody jonoselektywne w analizie specjacyjnej wapnia i magnezu w mleku

75%

Zdrodowska B. , Czerwinska K. , Raczynska A. , Bieganowski P. , Wagner-Czauderna E. , Lewenstam A. , Maj-Zurawska M.

Journal of Elementology

2008

tom 13

nr 3 Suppl.

67-68