Complex formation between cystine and alkali-metal cations

Complex formation between cystine and lithium, sodium, and potassium ions was investigated by measuring the electromotive force (emf) of galvanic cells involving the glass electrode for hydrogen ion. All measurements were performed at 25±C and in 3.00—mol-dm¡3 N(CH3)4Cl, as a constant ionic medium. The solubility of cystine was increased by performing the measurements in acid and alkaline solutions. A series of measurements was made employing an ion-specific electrode for the sodium ion. Experimental data were explained by assuming the formation of species of the type ML and M2L, i.e., mononuclear in cystine and mono- and binuclear species in alkaline cations. The respective stability constants were determined.