Synthesis and characterization of melanin in DMSO

• Published in: Journal of molecular structure Vol. 1047; pp. 102 - 108
• Main Authors: Bronze-Uhle, Erika S., Batagin-Neto, Augusto, Xavier, Pedro H.P., Fernandes, Nicole I., de Azevedo, Eduardo R., Graeff, Carlos F.O.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.09.2013
• Subjects: air; Biomaterial; Carbon; Derivatives; dimethyl sulfoxide; Infrared spectroscopy; L-dopa; Melanin; nuclear magnetic resonance spectroscopy; Organic synthesis; Oxidation; sodium hydroxide; Solubility; Spectroscopy methods; Structural characterization; Sulfonates; Synthesis; water; Organic synthesis; Spectroscopy methods; Biomaterial; Structural characterization; Solubility
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2013.04.061

[Display omitted] •Study on the structural characteristics of melanin synthesized in water and DMSO.•Sulphonate groups (SO2CH3) in the monomeric structure of d-melanin.•Sulphonate groups render the compound soluble in DMSO.•The synthetic method has been widely cited in literature.•The structure was not understood until this structural study. Recently soluble melanin derivatives have been obtained by a synthetic procedure carried out in DMSO (D-melanin). In this work a comparative study of the structural characteristics of synthetic melanin derivatives obtained by oxidation of L-DOPA in H2O and DMSO are presented. To this end, Fourier-transform infrared spectroscopy as well as proton and carbon nuclear magnetic resonance techniques has been employed. In addition, aging effects have been investigated for D-melanin. The results suggest that sulfonate groups (–SO2CH3) from the oxidation of DMSO, are incorporated into melanin, which confers protection to the phenolic hydroxyl group present in its structure. The solubility of D-melanin in DMSO is attributed to the presence of these groups. When D-melanin is left in air for long time periods, the sulfonate groups leave the structure, and an insoluble compound is obtained. NaOH and water have been used, in order to accelerate the release of the sulfonate groups attached to D-melanin, thereby corroborating the proposed structure and the synthesis mechanism.