Controlling interfacial electron-transfer kinetics of cytochrome c with mixed self-assembled monolayers
Controlling interfacial electron-transfer kinetics of cytochrome c with mixed self-assembled monolayers
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DOI：
10.1021/ja973417m
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发表时间：
1998-01-14
影响因子：
15
通讯作者：
Linderman, RJ
中科院分区：
文献类型：
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作者：
El Kasmi, A;Wallace, JM;Linderman, RJ
先前的工作已经确定，自组装单分子膜（SAMs）制备的COOH封端的烷硫醇（HS（CH 2）n-COOH）可以作为优良的金表面改性剂的固定化马细胞色素c（细胞色素c）在一个稳定的电活性状态。1，2从这些先前的研究中的一个重要发现是，对于组装使用链烷硫醇与n g 8的自组装膜，标准电子转移速率常数（ket）指数依赖于n和推测，因此，隧道距离。从这些细胞色素c实验中获得的隧道衰减因子（β）1.0-1.1/CH 2）与在SAM修饰的电极上从小分子电子转移（ET）研究中获得的基本相同3，我们最近已经建立了相同的定量依赖性的ET速率与距离的酿酒酵母（酵母）细胞色素c吸附在COOH SAM/Au衬底，即β）1.0-1.1/CH 2。[5]尽管预期有类似的β，但我们最初惊讶地发现，当在相同的SAM中进行比较时，酵母和马细胞色素c之间的ket存在很大差异。对于酵母细胞色素c，ket值为102-103小，尽管事实上，ET重组能量是相似的，为他们的三级结构和表面电荷分布。[7]可以肯定的是，这两种细胞色素具有实质性的氨基酸差异，确切地说，有40个氨基酸差异，这是解释这一结果的关键。突变研究正在进行中，以测试这方面的一些单位点假设，但这些结果不是本通讯的主题。我们在这里报告，细胞色素c的界面ET率可以增加，显着的酵母物种的情况下，通过改变SAM的结构。具体地，已经制备了混合单层，其中COOH-硫醇已经被稀释
Prior work has established that self-assembled monolayers (SAMs) prepared with COOH-terminated alkanethiols (HS (CH2) n-COOH) can serve as excellent gold surface modifiers for the immobilization of horse cytochrome c (cyt c) in a stable electroactive state. 1, 2 An important finding from these prior studies is that, for SAMs assembled using alkanethiols with n g 8, the standard electron-transfer rate constant (ket) depends exponentially on n and presumedly, therefore, on tunneling distance. The tunneling decay factor (β) 1.0-1.1/CH2) obtained from these cyt c experiments is essentially identical to that obtained from small molecule electron-transfer (ET) studies at SAM-modified electrodes3, 4 and is consistent with a through-bond tunneling mechanism.We have recently established the same quantitative dependence of ET rate vs distance for Saccharomyces cereVisiae (yeast) cyt c adsorbed on COOH SAM/Au substrates, ie, β) 1.0-1.1/CH2. 5 Although a similar β was expected, we were initially surprised to find large differences in ket between yeast and horse cyt c when compared at identical SAMs. For yeast cyt c, ket values were 102-103 smaller despite the fact that ET reorganization energies are similar for the two, 6 as are their tertiary structures and surface charge distributions. 7 For sure, these two cytochromes have substantial amino acid differences, 40 to be exact, 8 that hold the key to explaining this result. Mutagenesis studies are underway to test some single-site hypotheses in this regard, but these results are not the subject of the present communication. We report here that interfacial ET rates of cytochromes c can be increased, dramatically in the case of the yeast species, by altering the structure of the SAM. Specifically, mixed monolayers have been prepared in which the COOH-thiol has been diluted