Towards the development of a novel bioinspired functional material: synthesis and characterization of hybrid TiO2/DHICA-melanin nanoparticles.

A large number of recent literature data focus on modification/modulation of surface chemistry of inorganic materials in order to improve their functional properties. Melanins, a wide class of natural pigments, are recently emerging as a powerful organic component for developing bioinspired active material for a large number of applications from organoelectronics to bioactive compounds. Here we report the use of the approach referred as "chimie douce", involving in situ formation of the hybrids through reactions of precursors under mild conditions, to prepare novel hybrid functional architectures based on eumelanin like 5,6 dihydroxyindole-2-carboxylic acid (DHICA) polymer and TiO2.

π-Electron manipulation of the 5,6-dihydroxyindole/quinone system by 3-alkynylation: mild acid-mediated entry to (cross)-conjugated scaffolds and paradigms for medium-tunable chromophores.

5,6-Dihydroxyindole-based systems engender increasing interest for the design and implementation of new functional aromatic scaffolds and eumelanin-like materials with tailored absorption and electronic properties. However, studies aimed at elucidating the influence of external π-conjugating groups on the redox properties and acid-induced reactivity of these highly oxidizable indolic platforms are lacking. We report herein the synthesis (as acetyl derivatives) and chemical/quantum chemical characterization of the first π-extended 5,6-dihydroxyindole derivatives, 3-ethynyl-5,6-dihydroxyindole (1) and 3,3'-(1,2-ethynediyl)bis-5,6-dihydroxyindole (2), in order to understand whether and how β extension of the enamine-like pyrrole sector affects the absorption properties, redox behavior, and protonation equilibria at both the o-diphenol and quinone levels.

First synthetic entry to the trimer stage of 5,6-dihydroxyindole polymerization: ortho-alkynylaniline-based access to the missing 2,7':2',7''-triindole.

5,6-Dihydroxyindole oligomers are valuable synthetic targets for the structural characterization of eumelanin biopolymers as well as for the realization of bioinspired functional materials. An ortho-alkynylaniline-based strategy allowed the first access to a trimer, the missing 5,5',5'',6,6',6''-hexaacetoxy-2,7':2',7''-triindole, and its detection as a minor intermediate en route from 5,6-dihydroxyindole to eumelanin-like polymers.

Efficient synthesis of 5,6-dihydroxyindole dimers, key eumelanin building blocks, by a unified o-ethynylaniline-based strategy for the construction of 2-linked biindolyl scaffolds.

A unified convenient strategy for the synthesis of 5,6-dihydroxyindole-derived 2,7'-, 2,2'-, and 2,3'-biindolyls is reported, which is based on proper manipulation of key o-ethynylaniline precursors. By the same methodology 5,6-diacetoxy-7-iodoindole can also be obtained in good yield.

Chemistry of nitrated lipids: remarkable instability of 9-nitrolinoleic acid in neutral aqueous medium and a novel nitronitrate ester product by concurrent autoxidation/nitric oxide-release pathways.

Despite the mounting interest in nitrolinoleic acids and related nitrated polyunsaturated fatty acids as a novel class of bioactive signaling lipids, their chemistry and metabolic fate have remained poorly elucidated. Herein, we report an expedient nitroselenenylation/oxidation route to 9-nitrolinoleic acid (1) and 10-nitrolinoleic acid (2), which enabled comparative product studies under physiologically relevant conditions. Under biomimetic conditions, 1 decayed at an unusually fast rate to give the hydroxy-, keto-, and nitronitrate ester derivatives 3, 4, and 5 as main products, identified by ESI-MS and 2D NMR spectroscopy, including (1)H, (15)N HMBC experiments on the (15)N-labeled derivatives.