Intermolecular π-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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Published in | Photochemistry and photobiology Vol. 89; no. 2; pp. 314 - 318 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
United States
Blackwell Publishing Ltd
01.03.2013
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Subjects | |
Online Access | Get full text |
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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 π‐electron systems which are extrinsic in character.
DHICA units enhance aggregation‐dependent contributions to Eumelanin black color. |
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Bibliography: | Italian Ministry of University (MIUR) istex:988605012E7799BFF70AAC842A59B4459AA3037E ark:/67375/WNG-5NM0VB07-B ArticleID:PHP12003 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0031-8655 1751-1097 |
DOI: | 10.1111/php.12003 |