Effect of the electrostatic interaction on the redox reaction of positively charged cytochrome C adsorbed on the negatively charged surfaces of acid-terminated alkanethiol monolayers on a Au(111) electrode.
Effect of the electrostatic interaction on the redox reaction of positively charged cytochrome C adsorbed on the negatively charged surfaces of acid-terminated alkanethiol monolayers on a Au(111) electrode.
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DOI：
10.1021/la047992x
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发表时间：
2005-02
期刊：
影响因子：
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通讯作者：
S. Imabayashi;Takahiro Mita;T. Kakiuchi
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文献类型：
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作者：
S. Imabayashi;Takahiro Mita;T. Kakiuchi
用循环伏安法和电位调制紫外可见光谱比较了细胞色素c(Cytc)在2-巯基乙磺酸(MES)/2-巯基乙醇(MEL)混合自组装膜(SAM)上的电化学性质，并与MES、MEL和巯基丙酸(MPA)的单组分自组装膜的电化学性质进行了比较。吸附在Mpa自组装膜上的电子转移速率常数k(Et)从1450+/-210 S(-1)下降到890+/-100 S(-1)。而在100+/-15 S(-1)时，细胞色素c在MES自组装膜上的k(Et)值与pH无关。这些事实表明，SAM表面的大负电荷密度减缓了Cytc和电极之间的ET。表面电荷密度对表面电活性Cytc，Gamma(E)也有影响，随着pH从7增加到9，其电活性由10.0+/-1.0下降到5.3+/-1.1pmol·cm(-2)。同样，当MES的表面摩尔分数超过0.5时，吸附在MES/MEL混合自组装膜上的Cytc的k(Et)从90 0+/-30 0 S(-1)急剧下降到1 1 0 S(-1)，这表明存在一个负的表面电荷阈值，超过这个阈值，Cytc的Et速率显著降低.在高负电荷密度下，自组装膜上k(Et)的降低可能是由于强静电力将吸附的Cytc限制在不利于Et反应的方向。
The electrochemical properties of cytochrome c (cyt c) adsorbed on mixed self-assembled monolayers (SAMs) of 2-mercaptoethanesulfonate (MES)/2-mercaptoethanol (MEL) are compared with those on single-component SAMs of MES, MEL, and mercaptopropionic acid (MPA), using cyclic voltammetry and potential-modulated UV-vis reflectance spectroscopy. The rate constant of electron transfer (ET), k(et), of cyt c adsorbed on the SAM of MPA decreases from 1450 +/- 210 s(-1) at pH 7 to 890 +/- 100 s(-1) at pH 9. In contrast, the value of k(et) of cyt c on the SAM of MES is pH-independent at 100 +/- 15 s(-1). Those facts suggest that a large negative charge density on the SAM surface slows down the ET between cyt c and the electrode. The surface charge density of the SAM affects also the amount of electroactive cyt c, Gamma(e), which decreases from 10.0 +/- 1.0 to 5.3 +/- 1.1 pmol cm(-2) with increasing pH from 7 to 9 on the SAM of MPA. Similarly, the k(et) of cyt c adsorbed on the mixed SAMs of MES/MEL sharply decreases from 900 +/- 300 s(-1) to 110 s(-1) as the surface mole fraction of MES increases beyond 0.5, suggesting the presence of a negative surface charge threshold beyond which the rate of ET of cyt c is dramatically lowered. The decrease in the k(et) on the SAMs at high negative charge densities probably results from the confinement of adsorbed cyt c by the strong electrostatic force to an orientation that is not optimal for the ET reaction.