Structural Characteristics of a Fungal Melanin and a Soil Humic Acid

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Abstract
A melanin produced by Hendersonula toruloidea and a soil humic acid were characterized by a number of chemical (elemental and functional group analyses, carbohydrate content, amino acid, amino sugar, and NH3 analyses) and spectroscopic methods (IR and 13C NMR) before and after 6 M HCl hydrolysis. The following distinct differences were observed between the two materials: (i) phenolic components were prominent in the untreated and hydrolyzed melanins but not in the corresponding soil humic acids (HA); (ii) the melanin contained more complex unidentified N than did the soil HA; and (iii) following hot acid hydrolysis, the melanin was more aliphatic but considerably less aromatic than the soil HA. Hot acid hydrolysis, by removing practically all of the proteinaceous materials and carbohydrates from the two materials, made it possible to focus on the structural chemistry of the residual materials.