A preliminary study of fungal melanin by infrared spectroscopy

Infrared spectra of melanin and methylated melanin have been interpreted to show the existence of carboxyl groups in two different environments in the melanin structure. In one, there are a small number of carboxyl groups with an absorption band at about 1700 cm−1; these are relatively free and are capable of interaction with alkali to produce carboxylate in the normal way. In the other environment, the carboxyl groups, absorbing at 1615 cm−1, are conjugated and strongly hydrogen bonded to presumably phenolic hydroxyl groups, and cannot be neutralized with alkali. They do, however, react with diazomethane, as do the free carboxyls, to produce methyl ester absorbing at 1728 cm−1. The significance of these conclusions for the survival of melanin in soil and its reactions therein, is briefly discussed.