On the structure of human hair melanins from an infrared spectroscopy analysis of their interactions with Cu2+ ions.

Melanins were isolated from dark and red human hair and complexed with copper ions at various pH values in a complexing medium. IR spectra of melanins and their Cu2+-complexes for pellets with KBr were obtained. The IR spectra indicate that Cu2+ ions bound to melanins are fixed by different carboxyl and hydroxyl (phenolic and/or alcoholic) groups in the macromolecule. From these results it is concluded that, generally, melanin carboxyl groups are responsible for interactions of metal ions with the melanin molecule. Complexes of melanins isolated from dark and red human hair show structural differences when analysed by IR spectroscopy. Conclusions from these investigations assist in the differentiation of structures of analysed hair melanins. IR spectral analysis of melanin samples and their complexes suggest that melanin samples obtained from red hair may contain eumelanin.