Next Article in Journal
Vitamin D in Pain Management
Next Article in Special Issue
Melanin-Based Functional Materials
Previous Article in Journal
Molecular Aspects of Circadian Pharmacology and Relevance for Cancer Chronotherapy
Previous Article in Special Issue
The Supramolecular Buildup of Eumelanin: Structures, Mechanisms, Controllability
Article Menu
Issue 10 (October) cover image

Export Article

Open AccessArticle
Int. J. Mol. Sci. 2017, 18(10), 2169; https://doi.org/10.3390/ijms18102169

Replacing Nitrogen by Sulfur: From Structurally Disordered Eumelanins to Regioregular Thiomelanin Polymers

1
Department of Chemical Sciences, University of Naples “Federico II”, Via Cintia 4, 80126 Naples, Italy
2
Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra, Spain
3
Department de Química, Universitat Autònoma de Barcelona (UAB), Campus UAB, 08193 Bellaterra, Spain
*
Authors to whom correspondence should be addressed.
Received: 19 September 2017 / Revised: 11 October 2017 / Accepted: 13 October 2017 / Published: 17 October 2017
(This article belongs to the Special Issue Melanin Based Functional Materials)
Full-Text   |   PDF [2868 KB, uploaded 18 October 2017]   |  

Abstract

The oxidative polymerization of 5,6-dihydroxybenzothiophene (DHBT), the sulfur analog of the key eumelanin building block 5,6-dihydroxyindole (DHI), was investigated to probe the role of nitrogen in eumelanin build-up and properties. Unlike DHI, which gives a typical black insoluble eumelanin polymer on oxidation, DHBT is converted to a grayish amorphous solid (referred to as thiomelanin) with visible absorption and electron paramagnetic resonance properties different from those of DHI melanin. Mass spectrometry experiments revealed gradational mixtures of oligomers up to the decamer level. Quite unexpectedly, nuclear magnetic resonance (NMR) analysis of the early oligomer fractions indicated linear, 4-, and 7-linked structures in marked contrast with DHI, which gives highly complex mixtures of partially degraded oligomers. Density functional theory (DFT) calculations supported the tendency of DHBT to couple via the 4- and 7-positions. These results uncover the role of nitrogen as a major determinant of the structural diversity generated by the polymerization of DHI, and point to replacement by sulfur as a viable entry to regioregular eumelanin-type materials for potential applications for surface functionalization by dip coating. View Full-Text
Keywords: eumelanin; polydopamine; bioinspired polymers; bioinspired coatings; thiomelanin eumelanin; polydopamine; bioinspired polymers; bioinspired coatings; thiomelanin
Figures

Graphical abstract

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

Supplementary material

SciFeed

Share & Cite This Article

MDPI and ACS Style

Iacomino, M.; Mancebo-Aracil, J.; Guardingo, M.; Martín, R.; D’Errico, G.; Perfetti, M.; Manini, P.; Crescenzi, O.; Busqué, F.; Napolitano, A.; d’Ischia, M.; Sedó, J.; Ruiz-Molina, D. Replacing Nitrogen by Sulfur: From Structurally Disordered Eumelanins to Regioregular Thiomelanin Polymers. Int. J. Mol. Sci. 2017, 18, 2169.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Int. J. Mol. Sci. EISSN 1422-0067 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top