Studies related to the chemistry of melanins. Part X. Quantitative assessment of different types of units present in dopa-melanin

Abstract

(±)-3,4-Dihydroxyphenyl[carboxy-¹⁴C]alanine was converted into melanin, which was oxidised to give pyrrole-2,3,5-tricarboxylic acid, and also decarboxylated. The specific activities of the precursor, the melanin, the acid, the decarboxylated melanin, and the carbon dioxide evolved during the decarboxylation were compared. From the results it was possible to assess approximately the fractions of the polymer units which are (a) uncyclised amino-acid units, (b) carboxylated indole and indoline units, and (c) carboxylated pyrrole units. From the results of methylation experiments the relative proportions of units in the quinonoid and phenolic states were deduced.