The mechanism of oxidation-reduction potential: The oxidation-reduction potential of cysteine and cystine.
The mechanism of oxidation-reduction potential: The oxidation-reduction potential of cysteine and cystine.
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DOI：
10.1042/bj0220669
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通讯作者：
E. Kendall;D. F. Loewen
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作者：
E. Kendall;D. F. Loewen
在最近的一篇论文中，Dixon[1927]讨论了还原电位的机制。他指出，可以用维兰关于氢从还原剂向氧化剂转移的理论来推导平衡方程。另一方面，Clark[1923]推导出了这些方程，他认为这种现象可能是由于电子转移，还原机制不一定涉及氢的实际转移。狄克逊的观点似乎使氧化还原现象的问题复杂化了，而不是简单化了。至于这个电位是由于氢的转移还是由于电子的转移，我们将不作讨论，但我们希望答复论文的另一部分，其中Dixon以半胱氨酸还原电位的机制为具体实例。他假设吸附在铂表面的氢来自三个来源：氢气、氢离子和从还原剂解离的氢。他假设，在还原剂和铂之间迅速达到平衡的情况下，铂表面的氢作为氢气扩散的部分是一个不重要的因素，但半胱氨酸的还原电位是由两个过程之间的动力学平衡的“稳定状态”决定的；氢从还原剂RC SH中解离，氢气从铂电极中扩散。假设“稳定状态”的机制迫使对目前的还原机制概念增加三个推论：(1)氢从铂电极上的扩散是如此重要，以至于它实际上决定了至少一种还原剂半胱氨酸的还原电位；(2)电极不仅记录了溶液的氧化还原电位，而且在金属电极表面建立了动力学平衡，确定了平衡电位；(3)半胱氨酸具有独特的还原能力
IN a recent paper Dixon [1927] has discussed the mechanism of the reduction potential. He points out that the theory of Wieland concerning the transfer of hydrogen from reductant to oxidant can beused to deduce the equilibrium equations. On the other hand these equations have been derived by Clark [1923], who assumes that the phenomenon may be due to electron transfer and that the reduction mechanism does not necessarily involve the actual transfer of hydrogen. The viewpoint of Dixon appears to have complicated rather than simplified the problem of oxidation-reduction phenomena. Whether the potential is due to transfer of hydrogen or electrons will not be discussed, but we wish to reply to another portion of the paper in which Dixon takes up as a specific instance the mechanism of the reduction potential of cysteine. He assumes that hydrogen whichis adsorbed on the surface of the platinum is derived from three sources: hydrogen gas, hydrogen ion and hydrogen dissociating from a reductant. He assumes that the portion of the hydrogen on the surface of the platinum diffusing awayas hydrogen gas is an unimportant factor in thosecases where prompt equilibrium is attained between the reductant and the platinum, but that the reduction potential of cysteine is determined by a" steady state" which is a kinetic equilibrium between two processes; dissociation of hydrogen from the reductant, RC SH, and the diffusion of hydrogen gas away from the platinum electrode. The mechanism suggested which postulates a" steady state" forces the addition of three corollaries to the present conception of the mechanism of reduction:(1) that diffusion of hydrogen away from the platinum electrode is of such importance that it actually determines the reduction potential of at least one reductant, cysteine;(2) that not merely does the electrode register the oxidation-reduction potential of the solution but that a kinetic equili-brium is established on the surface of the metal electrode which determines the equilibrium potential, and (3) that cysteine has unique reducing power