溶剂、pH值和分子大小在关键真黑素结构单元激发态失活中的作用：对黑色素色素光稳定性的影响。

Role of solvent, pH, and molecular size in excited-state deactivation of key eumelanin building blocks: implications for melanin pigment photostability.

作者信息

Gauden M, Pezzella A, Panzella L, Neves-Petersen M T, Skovsen E, Petersen S B, Mullen K M, Napolitano A, d'Ischia M, Sundström V

机构信息

Department of Chemical Physics, Lund University, Box 124, S 22100 Lund, Sweden.

出版信息

J Am Chem Soc. 2008 Dec 17;130(50):17038-43. doi: 10.1021/ja806345q.

DOI:10.1021/ja806345q

PMID:19007162

Abstract

Ultrafast time-resolved fluorescence spectroscopy has been used to investigate the excited-state dynamics of the basic eumelanin building block 5,6-dihydroxyindole-2-carboxylic acid (DHICA), its acetylated, methylated, and carboxylic ester derivatives, and two oligomers, a dimer and a trimer in the O-acetylated forms. The results show that (1) excited-state decays are faster for the trimer relative to the monomer; (2) for parent DHICA, excited-state lifetimes are much shorter in aqueous acidic medium (380 ps) as compared to organic solvent (acetonitrile, 2.6 ns); and (3) variation of fluorescence spectra and excited-state dynamics can be understood as a result of excited-state intramolecular proton transfer (ESIPT). The dependence on the DHICA oligomer size of the excited-state deactivation and its ESIPT mechanism provides important insight into the photostability and the photoprotective function of eumelanin. Mechanistic analogies with the corresponding processes in DNA and other biomolecules are recognized.

摘要

超快时间分辨荧光光谱已被用于研究基本真黑素结构单元5,6 - 二羟基吲哚 - 2 - 羧酸（DHICA）、其乙酰化、甲基化和羧酸酯衍生物以及两种低聚物（O - 乙酰化形式的二聚体和三聚体）的激发态动力学。结果表明：（1）相对于单体，三聚体的激发态衰减更快；（2）对于母体DHICA，与有机溶剂（乙腈，2.6 ns）相比，在水性酸性介质中激发态寿命要短得多（380 ps）；（3）荧光光谱和激发态动力学的变化可理解为激发态分子内质子转移（ESIPT）的结果。激发态失活对DHICA低聚物大小的依赖性及其ESIPT机制为真黑素的光稳定性和光保护功能提供了重要见解。认识到与DNA和其他生物分子中相应过程的机制类比。