Ivan Kron

The ionic product of water in highly-concentrated aqueous electrolyte solutions

SummaryThe ionic product of water,

Improved apparatus and procedures for isopiestic studies at elevated temperatures

K_w = [H^ + ][OH^ - ] = 10^{ - pK_w }

Effect of selected dimethylaminochalcones on some mitochondrial activities

, has been determined in aqueous NaCl (0.5–5.0M), KCl (3.0M), NaNO3 (3.0 and 5.0M), and KNO3 (2.5M) at 25 °C from high-precision potentiometric titrations carried out in cells with liquid junction using either glass or hydrogen electrodes. Measurements ofKw provide a set of self-consistent data that can be used in the estimation of activity coefficient changes and liquid junction potentials in the study of extremely concentrated electrolyte solutions. Where comparison is possible, results obtained by hydrogen electrode measurements are in excellent agreement (ca ± 0.005 inpKw) with other reliable experimental values and the predictions of thePitzer activity-coefficient model. The glass electrode results are, as expected, routinely lower (by 0.03–0.05pKw units), owing to interference by Na+ ions. This effect virtually disappears in solutions of potassium salts. Comparison of the experimental results with thePitzer predictions shows that knowledge of the ternary interaction parameters is essential to account for specific ionic effects in the concentration dependence ofpKw.ZusammenfassungDas Ionenprodukt des Wassers,

(E)-2-Benzylidenecyclanones: Part VI. Solvent effect on the UV and fluorescence properties of some chalcones and their cyclic analogues. Interaction of 4-dimethylaminochalcones with bovine and human serum albumin: a UV–vis study

K_w = [H^ + ][OH^ - ] = 10^{ - pK_w }

Antioxidant properties of phenols against superoxide radicals

, wurde in wässerigen Lösungen von NaCl (0.5–5.0M), KCl (3.0M), NaNO3 (3.0 and 5.0M) und KNO3 (2.5M) bei 25 °C gemessen. Dazu wurden potentiometrische Titrationen unter Verwendung von Glas- oder Wasserstoffelektroden in Zellen mit Überführung durchgeführt. Mit diesenpKw-Werten kann man Änderungen der Aktivitätskoeffizienten in hochkonzentrierten Elektrolytlösungen ermitteln sowie Diffusionspotentiale abschätzen. Die mit Wasserstoffelektroden erhaltenenpKw-Werte stimmen mit verläßlichen Literaturdaten innerhalb vonca. ± 0.005 überein. Bei Messungen mit Glaselektroden führt der Na+-Fehler zu um 0.03–0.05 kleinerenpKw-Werten. Dieser Effekt wurde in Kaliumsalzlösungen nicht beobachtet. Der Vergleich der experimentellen Resultate mit Voraussagen desPitzer-Modells unterstreicht die Bedeutung ternärer Wechselwirkungsparameter für die exakte Berechnung des Ionenproduktes.

(E)-2-Benzylidenecycloalkanones XII.* Kinetic Measurement of Bovine and Human Serum Albumine Interaction with Selected Chalcones and Their Cyclic Chalcone Analogues by UV Spectrophotometry

UV–Vis spectrophotometry was used to determine acid dissociation constant (pKa) values of the natural flavonoids phloretin, phlorizin, naringenin, and naringin, as well as 4′-hydroxychalcone, 4′-(dimethylamino)chalcone, and their cyclic analogues. Comparison of the results with those previously reported for the natural flavonoids showed the applied method is a relatively straightforward and easy-to-perform technique for the determination of pKa values of compounds with relatively low solubility. Comparative analysis of the pKa values of the synthetic chalcones showed a strong correlation between the degree of conjugation and the acid strength of the respective compounds with different geometry. Our results provide further evidence that modification of the three-dimensional structure of open-chain bioactive compounds is the method of choice to modify not only their stereochemistry but also their physicochemical properties.Graphical abstract