Intermolecular [pi]-Electron Perturbations Generate Extrinsic Visible Contributions to Eumelanin Black Chromophore in Model Polymers with Interrupted Interring Conjugation

The key structural factors underlying the unique black chromophore of eumelanin biopolymers have so far defied elucidation. Capitalizing on the ability of 1% polyvinylalcohol (PVA) to prevent pigment precipitation during melanogenesis in vitro, we have investigated the visible chromophore properties...

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Bibliographic Details
Published inPhotochemistry and photobiology Vol. 89; no. 2; p. 314
Main Authors Ascione, Laura, Pezzella, Alessandro, Ambrogi, Veronica, Carfagna, Cosimo, d'Ischia, Marco
Format Journal Article
LanguageEnglish
Published Lawrence Blackwell Publishing Ltd 01.03.2013
Subjects
Biopolymers
Electrons
Molecular chemistry
Photochemistry
Pigments
Polyvinyl alcohol
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Summary:The key structural factors underlying the unique black chromophore of eumelanin biopolymers have so far defied elucidation. Capitalizing on the ability of 1% polyvinylalcohol (PVA) to prevent pigment precipitation during melanogenesis in vitro, we have investigated the visible chromophore properties of soluble eumelanin-like polymers produced by biomimetic oxidation of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic (DHICA) in 1% PVA-containing buffer at pH 7. Upon dilution DHI-eumelanin solutions exhibited almost linear visible absorbance changes, whereas DHICA-eumelanin displayed a remarkable deviation from linearity in simple buffer, but not in PVA-containing buffer. It is suggested that in DHICA polymers, exhibiting repeated interruptions of interring conjugation due to lack of planar conformations, the black chromophore is not due to an overlap of static entities defined intrinsically by the conjugation length across the carbon frame, but results largely from aggregation-related intermolecular perturbations of the ...-electron systems which are extrinsic in character. (ProQuest: ... denotes formulae/symbols omitted.)
ISSN:0031-8655
1751-1097