ELECTRON-TRANSFER REACTIONS ASSOCIATED WITH HOST GUEST COMPLEXATION - OXIDATION OF FERROCENECARBOXYLIC ACID IN THE PRESENCE OF BETA-CYCLODEXTRIN
ELECTRON-TRANSFER REACTIONS ASSOCIATED WITH HOST GUEST COMPLEXATION - OXIDATION OF FERROCENECARBOXYLIC ACID IN THE PRESENCE OF BETA-CYCLODEXTRIN
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DOI：
10.1021/ja00298a003
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发表时间：
1985-01-01
影响因子：
15
通讯作者：
KOBAYASHI, N
中科院分区：
文献类型：
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作者：
MATSUE, T;EVANS, DH;KOBAYASHI, N
在pH 9.2的水溶液中，以二茂铁为阴离子，用循环伏安法研究了3-环糊精（3-CD）存在下二茂铁甲酸的氧化反应。3-CD与FCA的结合通过UV-vis吸收光谱的变化和诱导圆二色性的出现来指示。后者的数据还表明，FCA'是由3-CD的配置与Cp-Fe-Cp轴平行的3-CD腔的轴络合。在慢扫描速率循环伏安法中，3-CD导致FCA氧化峰电流降低和峰电位正移。定量评价这些效应中的每一种，在20 ℃和Δ H =-2.8千卡/摩尔，Δ S = 5卡/（K-mol）下，给出FCA-3-CD的形成常数为2200 M-1。3-CD可检测到FCA的氧化形式的结合。快速扫描速率研究表明，包合复合物通过CE方案氧化，其中复合物首先解离为FCA”和3-CD，然后氧化游离FCA”。数据的定量评估给出2.1 X 104 s-1的解离速率常数，并且变温研究得到15 kcal/mol的解离活化焓。值得注意的是，在电极上没有检测到FCA ′-3-CD的直接氧化。环糊精（CD）是主体分子中最重要和最广泛研究的例子之一，它能够与各种客体形成包合物，通过将它们引入这些环状低聚糖的相对非极性空腔中。2.环糊精具有非常有趣的催化性质，已被用作水解酶的模型。以前的研究并没有强调环糊精对客体分子氧化还原反应的影响，但它作为有机电极反应修饰剂的研究越来越受到人们的关注。3已经发现，添加到溶液中或结合到电极表面的CD可以引起电有机合成的选择性的实质性有益变化。
The oxidation of ferrocenecarboxylic acid in the presence of 3-cyclodextrin (3-CD) has been investigated by cyclic voltammetry in pH 9.2 aqueoussolution in which the ferrocene is present as the anion, FCA". Binding ofFCA" by 3-CD is indicated by changes in the UV-vis absorption spectrum and the appearance of induced circular dichroism. The latter data also show that FCA'is complexed by 3-CD in a configuration with the Cp-Fe-Cp axis parallel to the axis of the 3-CD cavity. In slow scan rate cyclic voltammetry, 3-CD causes a decrease in the peak current and a positive shift in the peak potential for FCA" oxidation. Each of these effects was quantitatively evaluated, giving a formation constant for FCA"-3-CD of 2200 M" 1 at 20 C and AH=-2.8 kcal/mol, AS= 5 cal/(K-mol). Nobinding of the oxidized form of FCA" by 3-CD could be detected. Fast scan rate studies revealed that the inclusion complex is oxidized via a CE scheme inwhich the complex first dissociates to FCA" and 3-CD followed by oxidation of the free FCA". Quantitative evaluation of the data gave 2.1 X 104 s" 1 for the dissociation rate constant, and variable temperature studies yielded an activation enthalpy for dissociation of 15 kcal/mol. Significantly, no direct oxidation of FCA'-3-CD at the electrode could be detected. Possible explanations are discussed, and the significance of the present results to earlier electrochemical synthetic studies with cyclodextrins is highlighted.The cyclodextrins (CDs) are among the most important and widely studied examples of host molecules which are capable of forming inclusion complexes with a variety of guests byincorporating them within the relatively nonpolar cavity of these cyclic oligosaccharides. 2 The CDs have very interesting catalytic properties, and they havebeen used as models of hydrolytic en-zymes. Previous studies have not emphasized theeffect of CDs on the oxidation-reduction reactions of guest molecules, but there has been an increasing interest in their use as modifiers of organic electrode reactions. 3 It has been found that CDs, either added to solution or bound to the electrode surface, can cause substantial beneficial changes in the selectivity of electroorganic synthesis.