L-Cystine is the natural least soluble of the naturally occurring amino acids. Its solubility is a function of the hydrogen ion concentration depending on its protonation. This paper presents an investigation on properties of L-Cystine in a constant ionic medium of NaCl at different concentrations (3.00. 2.00, 1.00. 0.500, 0.150 mol dm(-3)) and at 25 degreesC. In such experimental conditions, solubility and its changes as a function of hydrogen ion concentration were determined. Protonation of cystine was studied in acid and basic solution, by measuring the electromotive force of galvanic cell involving a glass electrode. Four protonation constants for L-cystine were determined in all the selected concentrations of ionic medium. The different values obtained for the constants in ionic medium of different concentration could be explained both with the variation of activity coefficients or with the complex formation between L-Cystine and sodium ions. Variations of solubility for different concentration of NaCl were observed as well. (C) 2002 Elsevier Science B.V. All rights reserved.
Protonation equilibria and solubility of L-cystine / F., Apruzzese; Bottari, Emilio Giovanni; Festa, Maria Rosa. - In: TALANTA. - ISSN 0039-9140. - STAMPA. - 56:(2002), pp. 459-467. [10.1016/S0039-9140(01)00570-7]
Protonation equilibria and solubility of L-cystine.
BOTTARI, Emilio Giovanni;FESTA, Maria Rosa
2002
Abstract
L-Cystine is the natural least soluble of the naturally occurring amino acids. Its solubility is a function of the hydrogen ion concentration depending on its protonation. This paper presents an investigation on properties of L-Cystine in a constant ionic medium of NaCl at different concentrations (3.00. 2.00, 1.00. 0.500, 0.150 mol dm(-3)) and at 25 degreesC. In such experimental conditions, solubility and its changes as a function of hydrogen ion concentration were determined. Protonation of cystine was studied in acid and basic solution, by measuring the electromotive force of galvanic cell involving a glass electrode. Four protonation constants for L-cystine were determined in all the selected concentrations of ionic medium. The different values obtained for the constants in ionic medium of different concentration could be explained both with the variation of activity coefficients or with the complex formation between L-Cystine and sodium ions. Variations of solubility for different concentration of NaCl were observed as well. (C) 2002 Elsevier Science B.V. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
