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334492 
Journal Article 
The reduction of L-cystine hydrochloride at lead using static and rotating disc electrodes 
Ralph, TR; Hitchman, ML; Millington, JP; Walsh, FC 
2005 
1 
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry
ISSN: 0022-0728 
583 
2 
260-272 
The reduction of the disulphide, L-cystine hydrochloride to the L-cysteine hydrochloride thiol, in 0.1 mol dm[sub]-3[/sub] HCl at 298 K, has been studied at pre-treated, circular, 0.50 cm[sub]2[/sub] lead disc electrodes using steady state linear sweep voltammetry, non-steady state voltammetry and controlled potential coulometry. The diffusion coefficient for i.-cystine hydrochloride was approximately 4.8 x 10[sub]-10[/sub] m[sub]2[/sub] s ' from the three techniques. Reduction of the disulphide was irreversible and hydrogen evolution occurred as a competitive reaction at approximately-1.35V vs. SCE. Analysis of the mixed control kinetics, using a Koutecky-Levich approach, allowed the relative roles of charge transfer and mass transport to be resolved. Anomalously high Tafel slopes, of typically -183 mV, were observed due to disulphide adsorption. The charge transfer kinetics are consistent with the first electron gain being rate determining while reaction orders are +1 with respect to both the disulphide and proton concentrations. The mechanism of i.-cystine hydrochloride reduction has been critically discussed. (English) 
Amino acid electrosynthesis: Charge transfer control: Controlled potential coulometry; Koutecky. Levich equation; L-cystine hydrochloride; L-cysteine hydrochloride; Lead electrodes; Mass transport control; Rotating disc electrode; Voltammetry; Constante vitesse; Paramètre cinétique; Transfert masse; Transfert électron; Mécanisme réaction; Plomb; Electrode disque tournant; Cystine; Aminoacide soufré; Disulfure organique; Réduction chimique; Réaction électrode; Réaction électrochimique; Etude expérimentale; Rate constant; Kinetic parameter; Mass transfer; Electron transfer; Reaction mechanism; Lead; Rotating disk electrode; Sulfur containing aminoacid; Organic disulfide; Chemical reduction; Electrode reaction; Electrochemical reaction; Experimental study; Constante velocidad; Parámetro cinético; Transferencia masa; Transferencia electrón; Mecanismo reacción; Plomo; Electrodo disco giratorio; Cistina; Aminoácido azufrado; Disulfuro orgánico; Reducción química; Reacción electrodo; Reacción electroquímica; Estudio experimental