Department of Chemistry, Duke University, Durham, North Carolina 27708-0346, USA.
J Chem Phys. 2009 Nov 14;131(18):181106. doi: 10.1063/1.3265861.
Fundamental optical and structural properties of melanins are not well understood due to their poor solubility characteristics and the chemical disorder present during biomolecular synthesis. We apply nonlinear transient absorption spectroscopy to quantify molar absorptivities for eumelanin and pheomelanin and thereby get an estimate for their average pigment sizes. We determine that pheomelanin exhibits a larger molar absorptivity at near IR wavelengths (750 nm), which may be extended to shorter wavelengths. Using the molar absorptivities, we estimate that melanin pigments contain approximately 46 and 28 monomer units for eumelanin and pheomelanin, respectively. This is considerably larger than the oligomeric species that have been recently proposed to account for the absorption spectrum of eumelanin and illustrates that larger pigments comprise a significant fraction of the pigment distribution.
由于黑色素的溶解度差和生物分子合成过程中存在化学无序性，其基本光学和结构性质还不太清楚。我们应用非线性瞬态吸收光谱技术来量化真黑色素和褐黑色素的摩尔消光系数，从而估算它们的平均色素大小。我们发现，褐黑色素在近红外波长（750nm）处表现出更大的摩尔消光系数，其吸收范围可能扩展到更短的波长。利用摩尔消光系数，我们估计真黑色素和褐黑色素的色素单元数分别约为 46 和 28。这明显大于最近提出的解释真黑色素吸收光谱的低聚物物种，表明较大的色素构成了色素分布的重要部分。
