“Fifty Shades” of Black and Red or How Carboxyl Groups Fine Tune Eumelanin and Pheomelanin Properties

Recent advances in the chemistry of melanins have begun to disclose a number of important structure-property-function relationships of crucial relevance to the biological role of human pigments, including skin (photo) protection and UV-susceptibility. Even slight variations in the monomer composition of black eumelanins and red pheomelanins have been shown to determine significant differences in light absorption, antioxidant, paramagnetic and redox behavior, particle morphology, surface properties, metal chelation and resistance to photo-oxidative wear-and-tear. These variations are primarily governed by the extent of decarboxylation at critical branching points of the eumelanin and pheomelanin pathways, namely the rearrangement of dopachrome to 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and the rearrangement of 5-S-cysteinyldopa o-quinoneimine to 1,4-benzothiazine (BTZ) and its 3-carboxylic acid (BTZCA). In eumelanins, the DHICA-to-DHI ratio markedly affects the overall antioxidant and paramagnetic properties of the resulting pigments. In particular, a higher content in DHICA decreases visible light absorption and paramagnetic response relative to DHI-based melanins, but markedly enhances antioxidant properties. In pheomelanins, likewise, BTZCA-related units, prevalently formed in the presence of zinc ions, appear to confer pronounced visible and ultraviolet A (UVA) absorption features, accounting for light-dependent reactive oxygen species (ROS) production, whereas non-carboxylated benzothiazine intermediates seem to be more effective in inducing ROS production by redox cycling mechanisms in the dark. The possible biological and functional significance of carboxyl retention in the eumelanin and pheomelanin pathways is discussed.     

美白剂的发展现状及其黑色素抑制机理的研究进展

鉴于黑色素抑制剂在美白型化妆品中的不断开发、应用,使得对近年来的黑色素抑制剂的发展状况作一综述显向尤为必要;在黑色素形成机理研究的基础上,从亚细胞结构层次上对黑色素的抑制机理作一综述,最后,为黑色素抑制剂在化妆品等领域的研究、开发提出未来发展思路。     

天然黑色素的研究进展

阐述了关于天然黑色素的性质、提取纯化的方法、资源及主要应用领域的研究进展。     

On the structure of macromolecules obtained by oxidative polymerization of polyhydroxyphenols and quinones

The chemical structure of synthetic humic acid or synthetic melanin, obtained by oxidative polymerization of hydroquinone or para-benzoquinone in alkali solutions was determined by means of elemental analysis, ¹H NMR, electronic and FTIR spectroscopies, and by high temperature zinc dust treatment. The shiny black material obtained was proved to be a poly(hydroxyhydro-quinone-co-hydroxybenzoquinone) having the monomeric units connected at the ortho position and hence having a poly(ortho-phenylene) backbone instead of the other possible structure with a poly(para-phenylene) backbone. The chemical similarity between this synthetic humic acid and natural humic acids and natural melanins is discussed. © 1998 SCI.     

曲酸衍生物的制备及在化妆品上的应用

综述了皮肤美白剂的发展现状，介绍了若干曲酸衍生物及其性能和制法，并对皮肤黑色素的形成及美白机理作了简述。     

Studies in vivo by electron spin resonance of free radical mechanisms implicated in UV-induced skin photocarcinogenesis

Solar ultraviolet radiation (UVR) is implicated in many types of skin damage, such as photodermatoses, photoageing, erythema, pigmentation, skin cancer etc. Free radicals and reactive oxygen species are considered to play an important role in cutaneous photocarcinogenesis. But skin is endowed with photoprotective agents, namely melanins and antioxidant enzymatic and non-enzymatic mechanisms. In this study we describe the in vivo electron spin resonance (ESR) signals of melanins after UVR exposure, using skin specimens of various types of mice, which were taken from different parts of their bodies. The ESR signals were used as a model for testing the antioxidant properties of butylated hydroxyanisole, tocopherol acetate, and octyl p -methoxycinnamate with butyl methoxy dibenzoyl methane and superoxide dismutase (SOD). Additional UVB radiation was applied to the skin samples in situ (in the cavity of the ESR spectrometer). Suppression of ESR signals of melanins was observed in all cases.
Etudes in vivo par resonance paramagnetique electronique, après exposition au rayonnement UV, des méchanismes radicalans impliqués a la photocarcinogénèse cutanée