无规聚合物的电子性质：黑色素光谱的模拟
Electronic Properties of Random Polymers: Modelling Optical Spectra of Melanins
摘要：
黑色素是一组复杂的生物色素，广泛分布于从真菌到人类的所有物种中。在各种类型的黑色素中，人类黑色素，真黑素，是棕色或黑色的含氮色素，主要以其在人类皮肤中的光保护特性而闻名。我们进行了理论研究，旨在了解真黑素及其化学前体的吸收光谱。生物色素的结构定义不明确，尽管它被认为是由基于吲哚醌的交联杂聚物组成。作为真黑素结构的基本模型，我们选择了含有氢醌（HQ）和/或5，6-吲哚醌（IQ）和/或半醌（SQ）的五聚体，这些五聚体通常被列为结构黑素单体。真黑素低聚物已被构建为基本单体的随机组合物，并针对键合能量进行优化。在半经验中间忽略微分重叠（INDO）近似下计算了模型组件的吸收光谱。通过奇异聚合物的独立光谱求和，进一步得到真黑素的模型光谱。通过与实验数据的比较表明，INDO/CI方法能够很好地再现合成真黑素的实验光谱特征。
英文摘要：
Melanins are a group of complex pigments of biological origin, widely spread in all species from fungi to man. Among diverse types of melanins, the human melanins, eumelanins,are brown or black nitrogen-containing pigments, mostly known for their photoprotective properties in human skin. We have undertaken theoretical studies aimed to understand absorption spectra of eumelanins and their chemical precursors. The structure of the biopigment is poorly defined, although it is believed to be composed of cross-linked heteropolymers based on indolequinones. As a basic model of the eumelanin structure, we have chosen pentamers containing hydroquinones (HQ) and/or 5,6-indolequinones (IQ) and/or semiquinones (SQ) often listed as structural melanin monomers. The eumelanin oligomers have been constructed as random compositions of basic monomers and opitimized for the energy of bonding. Absorption spectra of model assemblies have been calculated within the semiempirical intermediate neglect of differential overlap (INDO) approximation. Model spectrum of eumelanin has been further obtained by sum of independent spectra of singular polymers. By comparison with experimental data it is shown that the INDO/CI method manages to reproduce well characteristic properties of experimental spectrum of synthetic eumelanins.
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