Bottari E, Festa M R
Dipartimento di Chimica, Università ;La Sapienza', P. le A. Moro 5, 00185 Roma, Italy.
Talanta. 1997 Oct;44(10):1705-18. doi: 10.1016/S0039-9140(97)00015-5.
The ability of cysteine to form complexes with cadmium(II) in aqueous solutions has been investigated at 25 degrees C and in constant ionic medium NaCl at two different concentrations, 1.00 and 3.00 mol l(-1). The presence of chloride ions was necessary to avoid the precipitation of cadmium(II). Two kinds of measurements were carried out. The electromotive force of galvanic cells containing glass and cadmium amalgam electrodes was measured as a function of cadmium and hydrogen ion concentrations in acid or moderately alkaline solutions in order to obtain the free concentration of cadmium(II) and hydrogen ions. The experimental data obtained in 1.00 mol l(-1) NaCl were explained by assuming the presence of CdHL and CdH(2)L(2), while those obtained in 3.00 mol l(-1) NaCl were accounted for with the formation of CdHL, CdH(2)L(2), CdH(3)L(3) and CdH(2)L(3). Moreover, polarographic measurements were carried out under the same experimental conditions but in alkaline solutions, and the formation of CdL(2) and CdL(3) was assumed from the shift of E(1/2) of cadmium(II) with an excess of cysteine. The stability constants of the assumed species were determined. Protonation constants of cysteine in 1.00 and 3.00 mol l(-1) NaCl have been also determined. A comparison with the behaviour of serine and alpha-aminopropanoate towards cadmium(II) is proposed.
在25℃以及两种不同浓度（1.00和3.00 mol·l⁻¹）的恒定离子介质氯化钠中，研究了半胱氨酸在水溶液中与镉（II）形成配合物的能力。氯离子的存在对于避免镉（II）沉淀是必要的。进行了两种测量。测量了含有玻璃电极和镉汞齐电极的原电池的电动势，作为酸或中等碱性溶液中镉和氢离子浓度的函数，以获得镉（II）和氢离子的自由浓度。在1.00 mol·l⁻¹氯化钠中获得的实验数据通过假设存在CdHL和CdH₂L₂来解释，而在3.00 mol·l⁻¹氯化钠中获得的数据则考虑了CdHL、CdH₂L₂、CdH₃L₃和CdH₂L₃的形成。此外，在相同实验条件下但在碱性溶液中进行了极谱测量，并根据过量半胱氨酸存在下镉（II）的E₁/₂位移假设形成了CdL₂和CdL₃。确定了假设物种的稳定常数。还测定了半胱氨酸在1.00和3.00 mol·l⁻¹氯化钠中的质子化常数。提出了与丝氨酸和α-氨基丙酸对镉（II）行为的比较。
