Substituent effects of 3,5-disubstituted p-coumaryl alcohols on their oxidation using horseradish peroxidase-H2O2 as the oxidant
Substituent effects of 3,5-disubstituted p-coumaryl alcohols on their oxidation using horseradish peroxidase-H2O2 as the oxidant
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DOI：
10.1007/s10086-005-0702-2
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发表时间：
2005-01-01
影响因子：
2.9
通讯作者：
Tanahashi, M
中科院分区：
文献类型：
--
作者：
Kobayashi, T;Taguchi, H;Tanahashi, M
以辣根过氧化物酶(HRP)-H2O2为氧化剂，测定了三种单素醇（对香豆醇、松叶醇和新树醇）和八种类似物的消耗速率，并与循环伏安法测定的阳极峰电位进行了比较。3-单取代对香豆醇，即3-甲氧基-、3-乙氧基-、3-正丙氧基-和3-正丁氧基-对香豆醇的反应速率比对香豆醇快。这很可能是由于烷氧基的给电子作用。然而，随着烷氧基分子量的增加，反应速率逐渐降低。此外，t-丁氧基是一个非常大的取代基，尽管它的给电子作用与其他烷氧基几乎相同，但它的反应速率却大大降低。与3-单取代对香豆醇相比，3,5-二取代对香豆醇的反应速率非常低，尤其是3,5-二甲基对香豆醇。这些结果表明，在单脂醇接近HRP活性位点的过程中，有三个主要的阻碍因素。首先，从3-单烷氧基对香豆醇的实验结果来看，取代基的体积可以降低其氧化速率。其次，从3,5-二取代对香豆醇的结果来看，表明靠近血红素的氨基残基的局部空间位阻降低了氧化速率。第三，从3,5位疏水取代基的结果来看，我们认为血红素附近的亲水性会降低它们的氧化速率。
The consumption rates of three monolignols (p-coumaryl, coniferyl, and sinapyl alcohols) and eight analogues using horseradish peroxidase (HRP)-H2O2 as an oxidant were measured and compared with the anodic peak potentials thereof measured with cyclic voltammetry. 3-Monosubstituted p-coumaryl alcohols, i.e., 3-methoxy-, 3-ethoxy-, 3-n-propoxy-, and 3-n-butoxy-p-coumaryl alcohols, had faster reaction rates than p-coumaryl alcohol. This is most probably due to the electron-donating effect of alkoxyl groups. However, the reaction rates gradually decreased with an increase in the molecular weight of the alkoxyl groups. Furthermore, t-butoxyl group, which is a very bulky substituent, caused an extreme reduction in the reaction rate, even though its electron-donating effect was almost the same as that of other alkoxyl groups. The reaction rates of 3,5-disubstituted p-coumaryl alcohols, especially 3,5-dimethyl-p-coumaryl alcohol, were very low compared with 3-monosubstituted p-coumaryl alcohols. These results suggest that there are three main factors of hindrance during the approach of monolignols to the active site of HRP. First, from the results of 3-monoalkoxy-p-coumaryl alcohols, it was suggested that the volume of substituents could decrease their oxidation rates. Second, from the results of 3,5-disubstituted p-coumaryl alcohols, it was suggested that local steric hindrance by the amino residues quite near the heme decreased the oxidation rates. Third, from the results of the substrates with hydrophobic substituents at their 3,5-positions, we suggested that hydrophilicity near heme would decrease their oxidation rates.