Lawrie Kirsten J, Meredith Paul, McGeary Ross P
School of Molecular and Microbial Sciences, University of Queensland, Brisbane, Queensland, Australia.
Photochem Photobiol. 2008 May-Jun;84(3):632-8. doi: 10.1111/j.1751-1097.2007.00295.x. Epub 2008 Feb 11.
The isolation, structure determination and chemical characterization of eumelanins has been plagued by their very low solubility in organic solvents. To gain insights into the structure and reactivity of these unusual and important biologic macromolecules and to pave the way for their use in electronics, we have prepared soluble melanins via the synthesis of monomeric precursors containing lipophilic substituents. Two such monomers derived from 5,6-dihydroxyindole-2-carboxylic acid (DHICA) were prepared, namely the benzyl and octyl ester derivatives. Both benzyl and octyl ester monomers were oxidatively polymerized to yield dark, melanin-like pigments. These polymerization processes were followed by UV-visible, fluorescence and NMR spectroscopy. These studies showed that the polymerizations proceeded by cross-linking at the 4- and 7-positions of the indole nucleus and led to highly heterogeneous polymeric products. Incorporation of a lipophilic benzyl or octyl group resulted in enhanced solubility of the pigments in a wide range of organic solvents. The UV-visible spectra of the organically soluble synthetic melanins were essentially identical to that of natural eumelanin.
真黑素在有机溶剂中的溶解度极低，这一直困扰着其分离、结构测定及化学表征。为深入了解这些特殊且重要的生物大分子的结构与反应活性，并为其在电子学领域的应用铺平道路，我们通过合成含亲脂性取代基的单体前体来制备可溶性黑素。制备了两种源自5,6 - 二羟基吲哚 - 2 - 羧酸（DHICA）的此类单体，即苄酯和辛酯衍生物。苄酯和辛酯单体均通过氧化聚合生成深色的、类似黑素的色素。这些聚合过程通过紫外 - 可见光谱、荧光光谱和核磁共振光谱进行跟踪。这些研究表明，聚合反应是通过吲哚核的4位和7位交联进行的，并导致形成高度不均一的聚合物产物。引入亲脂性苄基或辛基使色素在多种有机溶剂中的溶解度增强。有机可溶性合成黑素的紫外 - 可见光谱与天然真黑素的基本相同。
