Spectroscopy and Photoreactivity of Trichochromes: Molecular Components of Pheomelanins†
Spectroscopy and Photoreactivity of Trichochromes: Molecular Components of Pheomelanins†
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DOI：
10.1562/2005-06-17-ra-578
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发表时间：
2006-01
期刊：
影响因子：
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通讯作者：
J. Simon;M. Goldsmith;L. Hong;V. Kempf;Laura E L McGuckin;T. Ye;Gérard Zuber
中科院分区：
文献类型：
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作者：
J. Simon;M. Goldsmith;L. Hong;V. Kempf;Laura E L McGuckin;T. Ye;Gérard Zuber
黑色素是一类存在于褐黑素（红色黑色素）中而不存在于真黑素（黑色黑色素）中的小分子。在此，检测了脱羧色素F（TF）和脱羧色素C（dTC）。这两种染料的特征在于由一个可见的吸收带，这被证明是顺式和反式异构体的重叠过渡的结果。的吸收光谱的dTC的温度依赖性表明的烯醇和酮形式的分子之间的平衡的额外存在。这些结论是支持这些异构体的基态能量使用连续溶剂化模型。近红外发射测量无法检测到1O2的光生产物，而自旋捕获实验显示O2·−的形成。DNA切口分析也揭示了低水平的光诱导的dTC有氧活性，这表明光生O2·−的量子效率至多为5 × 10−6。这些结果是一致的泵浦探测光学实验，揭示了有效的和几乎完全的基态恢复在几皮秒的激发。这两种染料都是1O2的有效猝灭剂，表现出与维生素C相当的双分子速率常数。这些结果表明，铬可以起到保护作用的褐黑素色素。
Abstract The trichochromes are a class of small molecules present in pheomelanin (the red melanin) and absent in eumelanin (the black melanin). Herein trichochrome F (TF) and decarboxytrichochrome C (dTC) are examined. Both trichochromes are characterized by a visible absorption band, which is shown to be the result of overlapping transitions of the cis and trans isomers. The temperature dependence of the absorption spectrum of dTC suggests the additional presence of equilibrium between the enol and keto forms of the molecule. These conclusions are supported by ground-state energies of these isomers obtained using a continuum solvation model. Near-infrared emission measurements were not able to detect photoproduction of 1O2, and spin-trapping experiments revealed formation of O2·−. DNA nicking assays also revealed a low level of light-induced aerobic activity of dTC, suggesting a quantum efficiency of at most 5 × 10−6 for the photogeneration of O2·−. These results are consistent with pump-probe optical experiments, which reveal efficient and nearly complete ground-state recovery within a few picoseconds of excitation. Both trichochromes are efficient quenchers of 1O2, exhibiting a bimolecular rate constant comparable with vitamin C. These results suggest that trichochromes could serve a protective role in pheomelanin pigments.