Department of Chemistry, Chemical Engineering and Materials, University of L'Aquila, Via Vetoio, I-67100, Coppito, L'Aquila, Italy.
J Mass Spectrom. 2012 Jan;47(1):49-53. doi: 10.1002/jms.2025.
New trends in material science and nanotechnologies have spurred growing interest in eumelanins black insoluble biopolymers derived by tyrosinase-catalysed oxidation of tyrosine via 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA). Efficient antioxidant and photoprotective actions, associated with peculiar optoelectronic properties, are recognised as prominent functions of eumelanin macromolecules within the human and mammalian pigmentary system, making them unique candidates for the realisation of innovative bio-inspired functional soft materials, with structure-based physical-chemical properties. An unprecedented breakthrough into the mechanism of synthetic eumelanin buildup has derived from a detailed investigation of the oxidative polymerization of DHI and its N-methyl derivative (NMDHI) by linear and reflectron matrix-assisted laser/desorption ionization mass spectrometry. Regular collections of oligomers of increasing masses, spanning the entire m/z ranges up to 5000 Da (>30-mer) and 8000 Da (> 50-mer) for the two building blocks, respectively, were disclosed. It is the first time that the in vitro polymerisation of dihydroxyindoles to form synthetic eumelanins is explored up to its high mass limits, giving at the same time information on the polymerisation mode, whether it follows a stepwise pattern (being this the conclusion in our case) or a staking sequencing of small-sized entities. It also highlighted the influence of the N-methyl substituent on the polymerization process; this opens the way to the production of N-functionalized, synthetic eumelanin-inspired soft materials, for possible future technological applications.
新的材料科学和纳米技术趋势激发了人们对真黑素的日益浓厚的兴趣，真黑素是通过酪氨酸酶催化酪氨酸氧化生成的不溶性生物聚合物，其前体为 5,6-二羟基吲哚（DHI）及其 2-羧酸（DHICA）。真黑素大分子在人类和哺乳动物色素系统中具有有效的抗氧化和光保护作用，以及独特的光电特性，被认为是其主要功能，使它们成为实现具有结构基物理化学性质的创新仿生功能软材料的独特候选材料。通过对 DHI 和其 N-甲基衍生物（NMDHI）的氧化聚合进行线性和反射矩阵辅助激光/解吸电离质谱的详细研究，人们对合成真黑素形成的机制取得了前所未有的突破。分别对两种构建块进行了常规的高聚合度寡聚物的收集，其质量范围涵盖整个 m/z 范围，直至 5000 Da（> 30 聚体）和 8000 Da（> 50 聚体）。这是首次探索体外二羟基吲哚聚合形成合成真黑素的高质量极限，同时还提供了关于聚合模式的信息，即是否遵循逐步模式（这是我们的结论）还是小尺寸实体的堆叠序列。它还强调了 N-甲基取代基对聚合过程的影响；这为生产 N-功能化、合成真黑素启发的软材料开辟了道路，可能为未来的技术应用提供了可能。
