The relative proportion of 5,6-dihydroxyindole (DHI) versus 5,6-dihydroxyindole-2-carboxylic acid (DHICA) units in Sepia melanin and their degree of structural integrity were assessed by an integrated approach involving quantitative determination of pyrrole-2,3-dicarboxylic acid (PDCA) and pyrrole-2,3,5-tricarboxylic acid (PTCA), specific degradation products of DHI- and DHICA-derived units; carboxyl content; rate of ferricyanide consumption; and absorption spectrum. Analyses of both intact and surfactant-solubilised pigment samples, in comparison with synthetic DHI and DHICA melanins, revealed that Sepia melanin consists of a mixture of oligomeric structures incorporating over 75% of DHICA-derived units and only 20% of DHI-derived units, occurring for the most part in an irreversibly degraded form, possibly as pyrrolecarboxylic acids.
An integrated approach to the structure of Sepia Melanin. Evidence for a high proportion of degraded 5,6-dihydroxyindole-2-carboxylic acid units in the pigment backbone
M. D'ISCHIA;
1997
Abstract
The relative proportion of 5,6-dihydroxyindole (DHI) versus 5,6-dihydroxyindole-2-carboxylic acid (DHICA) units in Sepia melanin and their degree of structural integrity were assessed by an integrated approach involving quantitative determination of pyrrole-2,3-dicarboxylic acid (PDCA) and pyrrole-2,3,5-tricarboxylic acid (PTCA), specific degradation products of DHI- and DHICA-derived units; carboxyl content; rate of ferricyanide consumption; and absorption spectrum. Analyses of both intact and surfactant-solubilised pigment samples, in comparison with synthetic DHI and DHICA melanins, revealed that Sepia melanin consists of a mixture of oligomeric structures incorporating over 75% of DHICA-derived units and only 20% of DHI-derived units, occurring for the most part in an irreversibly degraded form, possibly as pyrrolecarboxylic acids.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
