Grieco Christopher, Kohl Forrest R, Hanes Alex T, Kohler Bern
Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio, 43210, USA.
Nat Commun. 2020 Sep 11;11(1):4569. doi: 10.1038/s41467-020-18393-w.
Eumelanin is a brown-black biological pigment with sunscreen and radical scavenging functions important to numerous organisms. Eumelanin is also a promising redox-active material for energy conversion and storage, but the chemical structures present in this heterogeneous pigment remain unknown, limiting understanding of the properties of its light-responsive subunits. Here, we introduce an ultrafast vibrational fingerprinting approach for probing the structure and interactions of chromophores in heterogeneous materials like eumelanin. Specifically, transient vibrational spectra in the double-bond stretching region are recorded for subsets of electronic chromophores photoselected by an ultrafast excitation pulse tuned through the UV-visible spectrum. All subsets show a common vibrational fingerprint, indicating that the diverse electronic absorbers in eumelanin, regardless of transition energy, contain the same distribution of IR-active functional groups. Aggregation of chromophores diverse in oxidation state is the key structural property underlying the universal, ultrafast deactivation behavior of eumelanin in response to photoexcitation with any wavelength.
真黑素是一种棕黑色生物色素，具有防晒和清除自由基的功能，对许多生物体都很重要。真黑素也是一种很有前景的用于能量转换和存储的氧化还原活性材料，但其化学结构存在于这种非均质色素中，仍然未知，这限制了人们对其光响应亚基性质的理解。在这里，我们引入了一种超快振动指纹图谱方法，用于探测真黑素等非均质材料中发色团的结构和相互作用。具体来说，通过在紫外可见光谱范围内调谐的超快激发脉冲对电子发色团子集进行光选，记录双键拉伸区域的瞬态振动光谱。所有子集都显示出共同的振动指纹，这表明真黑素中不同的电子吸收体，无论跃迁能量如何，都含有相同分布的红外活性官能团。氧化态不同的发色团聚集是真黑素在受到任何波长的光激发时普遍超快失活行为的关键结构特性。
