Protolytic equilibria in aqueous sodium deoxycholate solutions

Protolytic equilibria taking place in aqueous solutions of sodium deoxycholate (DCNa) have been studied at 25°C using 0.5M NaCl as ionic medium. Electromotive force measurements of a galvanic cell were carried out by means of a glass electrode.The reagent necessary to change the acidity of the solutions was produced in situ by supplying a constant small current.Solubility and acid constant of deoxycholic acid (HDC) have been determined for the chosen experimental conditions. Experimental data obtained in less acid solutions have been explained by assuming the presence of the species H(DC)₂. The relative stability constant has been determined. At higher deoxycholate concentration the presence of a polymeric micellar species has been assumed.

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Protolytische Gleichgewichte in wäßrigen Natriumdesoxycholat-Lösungen

Zusammenfassung Die Protonierung von Natrium-Desoxycholat (DCNa) in wäßrigen Lösungen mit 0.5M NaCl wurde bei 25°C mit Hilfe von E.M.K. Messungen mit einer Glaselektrode untersucht.Das notwendige Reagens für die Umwandlung der Säure in den untersuchten Lösungen wurde in situ durch einen konstanten schwachen Strom erzeugt.Löslichkeit und Dissoziationkonstante von Desoxycholsäure (HDC) wurden unter den gewählten experimentellen Bedingungen bestimmt. Die experimentellen Daten in schwach sauren Lösungen konnten mit der Annahme der Existenz von H(DC)₂ erklärt werden. Die entsprechende Konstante wurde bestimmt. Zur Erklärung der Daten in stärker konzentrierten Lösungen von Desoxycholat ist die Annahme einer polynuklearen Spezies nötig.

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Symbols H analytical excess of hydrogenions, if negative it corresponds to OH^–; - h free concentration of hydrogen ions; - A total concentration of deoxycholate; - a free concentration of deoxycholate; - K _a acid constant of deoxycholic acid (HDC) defined as follows: [HDC]K _a =ha; - _q,p stability constant of a speciesH _p (DC) _q defined as follows: [H _p (DC) _q ]= _q,p h ^p a ^q ; - C ⁰ solubility of HDC; - formation function representing the average number of H⁺ bonded to deoxycholate.     

Nanoelectrodes for intracellular measurements of reactive oxygen and nitrogen species in single living cells

Reactive oxygen and nitrogen species (ROS and RNS) play important roles in various physiological processes (e.g. phagocytosis) and pathological conditions (e.g. cancer). The primary ROS/RNS, viz., hydrogen peroxide, peroxynitrite ion, nitric oxide, and nitrite ion, can be oxidized at different electrode potentials and therefore detected and quantified by electroanalytical techniques. Nanometer-sized electrochemical probes are especially suitable for measuring ROS/RNS in single cells and cellular organelles. In this article, we survey recent advances in the localized measurements of ROS/RNS inside single cells and discuss several methodological issues, including optimization of nanoelectrode geometry, precise positioning of an electrochemical probe inside a cell, and interpretation of electroanalytical data.     

Antifungal activity of Mongolian medicinal plant extracts

Abstract

The in vitro antifungal activity of extracts obtained from 14 medicinal plants of the mongolian flora were investigated by measuring their minimal inhibitory concentration (MIC) against fungi cause of cutaneous diseases such as Candida species, dermatophytes and Malassezia furfur. Among the species examined, Stellaria dichotoma L., Scutellaria scordifolia L. Aquilegia sibirica Fisch. Et Schrenk. and Hyoscyamus niger L. extracts demonstrated antifungal activity against all studied fungi. In particular, S. scordifolia L. methanol extract, obtained at room temperature, showed the best activity against Candida spp., Malassezia furfur and dermatophytes with GMMIC₅₀ values of 22?µg/mL, 64?µg/mL and 32?µg/mL, respectively. The flavones, luteolin and apigenin, identified in S. scordifolia extracts, and rutin identified in S. dichotoma and Hyoscyamus niger L. extracts, could be responsible of the observed antifungal activity.     

Formation of volatile selenium species in synthetic seawater under light and dark experimental conditions

Experiments were performed in the laboratory on synthetic seawater spiked with different selenium species at trace levels to study the formation of volatile selenium compounds under dark or controlled simulated sunlight conditions. Spiking the reaction media with inorganic and organic selenium compounds demonstrated that several volatile selenium species could be formed under these simulated conditions. Selenoamino acids react to produce significant amounts of volatile selenium species in both light and dark conditions. Products formed include dimethyl selenide (DMSe), dimethyl selenyl sulphide (DMSeS) and dimethyl diselenide (DMDSe). Inorganic selenium oxyanions added to the synthetic reaction media did not form volatile species via abiotic reactions despite the presence of strong methylating agents. These results suggest that the formation of stable volatile species from bio‐organic selenium compounds can occur via abiotic reactions in the marine photic zone. Copyright © 2000 John Wiley & Sons, Ltd.