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首页> 外文期刊>Journal of Applied Polymer Science >AN ESR STUDY OF THE SILICA-INDUCED AUTOCONDENSATION OF POLYFLAVONOID TANNINS
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AN ESR STUDY OF THE SILICA-INDUCED AUTOCONDENSATION OF POLYFLAVONOID TANNINS

机译：二氧化硅诱导聚乙烯黄单宁自缩的ESR研究

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摘要

Radical mechanisms of silica-induced polyflavonoid tannin autocondensation and hardening through alkaline pyran ring cleavage are shown to be important, especially at different levels according to the reaction conditions and type of tannin. For prodelphinidin tannins, radical mechanisms are shown to be more important than are ionic ones even under mild alkaline reaction conditions. For procyanidin tannins, radical mechanisms appear to be of little or no importance under mild alkaline reaction conditions, but acquire more importance at more alkaline pHs, a result confirmed also with a (+)-catechin monomer as a model compound. Under the latter conditions, the radical mechanism of pyran ring cleavage inverts the relative importance of the interflavonoid bond cleavage and pyran ring opening for procyanidins. Relative intensities of phenoxide radical and radical anion ESR signals indicate that pyran ring opening and autocondensation are rapid under alkaline conditions. (C) 1996 John Wiley & Sons, Inc. [References: 37]
机译：二氧化硅诱导的聚类黄酮单宁的自动缩合和通过碱性吡喃环断裂硬化的自由基机理很重要，尤其是根据反应条件和单宁类型的不同而不同。对于原卟啉单宁，即使在温和的碱性反应条件下，自由基机理也比离子机理更重要。对于原花青素单宁，自由基机制在温和的碱性反应条件下似乎很少或没有任何作用，但在更多的碱性pH值下则更为重要，这一结果也证实了（+）-儿茶素单体作为模型化合物。在后一种条件下，吡喃环裂解的自由基机理颠倒了黄酮类键间裂解和吡喃环开环对原花青素的相对重要性。酚盐自由基和自由基阴离子ESR信号的相对强度表明吡喃环在碱性条件下开环和自动缩合迅速。 （C）1996 John Wiley＆Sons，Inc. [参考：37]

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