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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Probing the molecular and electronic structure of capsaicin: A spectroscopic and quantum mechanical study
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Probing the molecular and electronic structure of capsaicin: A spectroscopic and quantum mechanical study

机译：探测辣椒素的分子和电子结构：光谱和量子力学研究

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The conformational preferences of capsaicin were investigated by using the hybrid meta density functional theory (DFT) method MPWB1K. Its flexible, pendant side chain allows for a multitude of conformations only slightly different in energy. The distinctive vibrational features of the most stable conformers were characterized. To elucidate the most favorable reaction sites of capsaicin for radical scavenging, various homolytic bond-dissociation energies were also calculated. Of the possible radical intermediates, the allyl and benzyl radicals are energetically preferred. The filled and empty electronic structures of capsaicin were investigated by exploiting the photoelectron and electron-transmission spectra also of reference molecules and suitable quantum-mechanical calculations. On this basis, a reliable pattern of the vertical ionization energies and electron-attachment energies of capsaicin was proposed. The frontier pi molecular orbitals are concentrated over the vanillyl moiety, with a modest influence of the amidic-aliphatic chain. The (negative) first vertical electron affinity is predicted to be similar to that of benzene. The absorption spectrum of capsaicin and its change by conversion into a phenolic deprotonated anion (modest bathochromic displacement) or a phenoxyl neutral radical (from colorless to red) were interpreted with time-dependent DFT calculations. ESR measurements following chemical or electrochemical reduction of capsaicin did not lead to detection of the corresponding radical anion. The spectra show fragmentation of the original molecule and formation of a variety of radical species which are believed to have a semiquinonic structure.
机译：辣椒素的构象偏爱通过使用混合亚密度函数理论（DFT）方法MPWB1K进行了研究。其灵活的侧链侧链允许仅在能量上稍有不同的多种构象。表征了最稳定构象异构体的独特振动特征。为了阐明辣椒素最有利于自由基清除的反应位点，还计算了各种均质键解离能。在可能的自由基中间体中，烯丙基和苄基在能量上是优选的。通过利用参考分子的光电子和电子透射谱以及适当的量子力学计算，研究了辣椒素的填充和空电子结构。在此基础上，提出了辣椒素的垂直电离能和电子附着能的可靠模式。前沿的pi分子轨道集中在香草基部分上，并受到酰胺-脂族链的适度影响。预测（负）第一垂直电子亲和力与苯相似。辣椒素的吸收光谱及其通过转化为酚去质子化阴离子（适度的红移）或苯氧基中性基团（从无色到红色）的变化通过与时间相关的DFT计算来解释。辣椒素化学或电化学还原后的ESR测量未导致检测到相应的自由基阴离子。光谱显示原始分子的断裂和各种自由基物质的形成，据信这些自由基物质具有半醌结构。

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