Department of Chemical Sciences, University of Naples "Federico II", I-80126 Naples, Italy.
Hair Care Products Research Laboratories, Kao Corporation, Tokyo 131-8501, Japan.
Int J Mol Sci. 2018 Jun 13;19(6):1753. doi: 10.3390/ijms19061753.
In the last decade, the late stages of melanin biosynthesis involving the oxidative polymerization of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) have been extensively investigated. Most of the information derived from a biomimetic approach in which the oxidation of melanogenic indoles was carried out under conditions mimicking those occurring in the biological environment. Characterization of the early oligomers allowed for drawing a structural picture of DHI and DHICA melanins, providing also an interpretative basis for the different properties exhibited by these pigments, e.g., the chromophore and the antioxidant ability. The improved knowledge has opened new perspectives toward the exploitation of the unique chemistry of melanins and its precursors in cosmetic and health care applications. A noticeable example is the development of an innovative hair dyeing system that is based on the marked ease of DHI to give rise to black melanin on air oxidation under slightly alkaline conditions. The advantage of this method for a step-wise coverage of gray hair with a natural shade pigmentation on repeated treatment with a DHI-based formulation with respect to traditional dyes is presented. A variant of DHICA melanin combining solubility in water-miscible organic solvents, an intense chromophore in the UltraViolet-A UV-A region, and a marked antioxidant potency was evaluated as an ingredient for cosmetic formulations.
在过去的十年中，涉及 5,6-二羟吲哚（DHI）和 5,6-二羟吲哚-2-羧酸（DHICA）氧化聚合的黑色素生物合成晚期阶段已经得到了广泛研究。这些信息主要来源于仿生学方法，其中在模拟生物环境中发生的条件下进行黑色素生成吲哚的氧化。对早期低聚物的特性分析可以描绘 DHI 和 DHICA 黑色素的结构，也为这些颜料表现出的不同性质提供了解释基础，例如生色团和抗氧化能力。这些改进的知识为在化妆品和医疗保健应用中利用黑色素及其前体的独特化学性质开辟了新的前景。一个显著的例子是一种创新的染发剂系统的开发，该系统基于 DHI 在微碱性条件下空气氧化时很容易产生黑色黑色素的特点。与传统染料相比，该方法在重复处理基于 DHI 的制剂时，以天然色调色素逐渐覆盖灰色头发具有优势。一种结合了水溶性有机溶剂中的溶解度、在紫外线-A（UV-A）区域中强烈的生色团和显著的抗氧化能力的 DHICA 黑色素变体被评估为化妆品制剂的成分。
