Solid-state cross-polarization magic angle spinning 13C and 15N NMR characterization of Sepia melanin, Sepia melanin free acid and Human hair melanin in comparison with several model compounds
Solid-state cross-polarization magic angle spinning 13C and 15N NMR characterization of Sepia melanin, Sepia melanin free acid and Human hair melanin in comparison with several model compounds
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DOI：
10.1002/mrc.1193
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发表时间：
2003-06-01
影响因子：
2
通讯作者：
Bowers, CR
中科院分区：
文献类型：
--
作者：
Adhyaru, BB;Akhmedov, NG;Bowers, CR
本文报道了三种天然黑色素固体：乌贼黑色素、乌贼黑色素游离酸（MFA）和人发黑色素的高分辨C-13和N-15交叉极化魔角旋转（CP/MAS）NMR谱。用核磁共振法对人发黑色素的官能团进行表征是迄今为止的第一次，本文报道的C-13 CP/MAS核磁共振谱显示化学不等价位点的分辨率提高。观察到的固体黑色素样品的光谱区域可以被分配到假定的结构单元的聚合物链的乌贼MFA来自溶液状态的NMR研究。为了帮助在光谱中的官能团的归属，固态CP/MAS NMR光谱与高分辨率C-13和N-15 CP/MAS光谱的四个模型化合物，L-多巴，多巴胺，2-甲氧羰基-3-乙氧羰基-4-甲基吡咯和乙基5，6-二甲氧基吲哚-2-羧酸酯进行了比较。为了进一步帮助质子化和非质子化碳原子的分配，对黑色素样品进行CP接触时间依赖性和非季碳抑制（NQS）实验。黑色素样品的N-15 CP/MAS光谱证实了在黑色素聚合物链中存在吲哚和吡咯单元。在所有黑色素样品中观察到的NMR峰相对较宽，推测是由于自由基的存在。电子自旋共振（ESR）数据显示，所有三种黑色素样品都含有局部自由基（g = 2.007），其中乌贼黑色素含有比人发黑色素高10倍的自由基密度。版权所有（C）2003约翰威利父子有限公司。
This paper presents the high-resolution C-13 and N-15 cross-polarization magic angle spinning (CP/MAS) NMR spectra of three natural melanin solids: Sepia officinalis melanin, Sepia officinalis melanin free acid (MFA) and Human hair melanin. The functional group characterization of Human hair melanin by NMR is the first to date and the C-13 CP/MAS NMR spectra reported here show improved resolution of chemically inequivalent sites. The observed spectral regions of the solid melanin samples can be assigned to the postulated structural unit of the polymer chain of Sepia MFA derived from solution-state NMR studies. To assist in the assignment of functional groups in the spectra, the solid-state CP/MAS NMR spectra are compared with high-resolution C-13 and N-15 CP/MAS spectra of four model compounds, L-dopa, dopamine, 2-methoxycarbonyl-3-ethoxycarbonyl-4-methylpyrrole and ethyl 5,6-dimethoxyindole-2-carboxylate. To aid further in the assignment of protonated and non-protonated carbon atoms, CP contact time dependence and non-quaternary carbon suppression (NQS) experiments were performed on the melanin samples. The N-15 CP/MAS spectra of the melanin samples confirm the presence of indole and pyrrole units in the melanin polymer chain. The NMR peaks observed in all of the melanin samples are relatively broad, presumably owing to the presence of free radicals. Electron spin resonance (ESR) data shows that all three melanin samples contain localized free radicals (g = 2.007), with the Sepia melanin containing a 10-fold higher free radical density than Human hair melanin. Copyright (C) 2003 John Wiley Sons, Ltd.