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Identification of Partially Degraded Oligomers of 5,6‐Dihydroxyindole‐2‐carboxylic Acid in Sepia Melanin by Matrix‐assisted Laser Desorption/Ionization Mass Spectrometry
Author(s) -
Pezzella Alessandro,
Napolitano Alessandra,
d'Ischia Marco,
Prota Giuseppe,
Seraglia Roberta,
Traldi Pietro
Publication year - 1997
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/(sici)1097-0231(19970228)11:4<368::aid-rcm859>3.0.co;2-e
Subject(s) - chemistry , mass spectrometry , soft laser desorption , desorption , carboxylic acid , ionization , matrix assisted laser desorption/ionization , chromatography , matrix assisted laser desorption electrospray ionization , matrix (chemical analysis) , atmospheric pressure laser ionization , analytical chemistry (journal) , electron ionization , organic chemistry , adsorption , ion
Despite extensive efforts over more than half a century, the direct structural investigation of natural melanins has, so far, been largely unsuccessful, because of the adverse physical and chemical properties of these pigments. In the present study, we applied matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) to the direct analysis of fresh melanin samples from the cuttlefish Sepia officinalis , and succeeded in identifying clearly distinct patterns of low molecular weight ionic species, ranging from 450 to 1200 Da. Detailed analysis of the molecular weights and mass differences between the major species, aided by comparison with MALDI‐MS spectra of synthetic melanins, allowed formulation of the major components as oligomers of 5,6‐dihydroxyindole‐2‐carboxylic acid partially degraded by peroxidative fission of the o ‐diphenol moieties with concomitant decarboxylation and oxygenation reactions. These results provide the first direct insight into the structure of Sepia melanin and confirm the unique value of MALDI‐MS techniques for the investigation of highly complex and heterogeneous polymers such as melanins. © 1997 John Wiley & Sons, Ltd.