Related Experiment Video
Updated: Jul 5, 2026

Methods to Inhibit Bacterial Pyomelanin Production and Determine the Corresponding Increase in Sensitivity to Oxidative Stress
Published on: August 31, 2015
The "benzothiazine" chromophore of pheomelanins: a reassessment
Alessandra Napolitano1, Maria De Lucia, Lucia Panzella
1Department of Organic Chemistry and Biochemistry, University of Naples Federico II Complesso Universitario, Monte S. Angelo, Naples, Italy. alesnapo@unina.it
Abstract:
The characteristic absorption and photochemical properties of pheomelanins are generally attributed to "benzothiazine" structural units derived biogenetically from 5-S-cysteinyldopa. This notion, however, conveys little or no information about the structural chromophores responsible for the photoreactivity of pheomelanins. At pH 7.4, natural and synthetic pheomelanins show a defined maximum around 305 nm, which is not affected by reductive treatment with sodium borohydride, and a monotonic decrease in the absorption in the range 350-550 nm. These features are not compatible with a significant proportion of structural units related to 2H-1,4-benzothiazine and 2H-1,4-benzothiazine-3-carboxylic acid, the early borohydride-reducible pheomelanin precursors featuring absorption maxima above 340 nm. Rather, these features would better accommodate a contribution by the nonreducible 3-oxo-3,4-dihydrobenzothiazine (lambdamax 299 nm) and benzothiazole (lambdamax 303 nm) structural motifs, which are generated in the later stages of pheomelanogenesis in vitro. This conclusion is supported by a detailed liquid chromatography/UV and mass spectrometry monitoring of the species formed in the oxidative conversion of 5-S-cysteinyldopa to pheomelanin, and would point to a critical reassessment of the commonly reported "benzothiazine" chromophore in terms of more specific and substantiated structural units, like those formed during the later stages of pheomelanin synthesis in vitro.
Related Concept Videos
Pigmentation
Melanin occurs in two primary forms: eumelanin that provides black and brown pigment and pheomelanin that provides red color. Dark-skinned individuals produce more melanin than those with pale...
NMR Spectroscopy of Benzene Derivatives
Physical Properties of Amines
Changes in Skin Color: Clinical Perspectives
Albinism
Albinism is a genetic disorder that affects (completely or partially) the coloring of skin, hair, and eyes. The defect is primarily...
Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
Photoreceptors and Visual Pathways

