Abstract

Melanins are natural pigments distributed in living organisms and they are responsible for pigmentation of surface structure. In the present work, gel exclusion chromatography, spectrophotometric, and dielectric relaxation techniques were used to characterize DOPA melanin before and after irradiation with ⁶⁰Co gamma rays in the range of 5 to 50 Gy. The results show that the studied melanin is composed of two structural groups. The extinction absorption coefficient and relative permittivity and conductivity of melanin sample increased after irradiation with gamma rays and were dose dependent in manner. These increases were attributed to the formation of melanin aggregation and crosslinks which result from the growing number of the formed free radicals by radiation. It was concluded from the results that melanin goes through some structural changes after irradiation with the gamma doses demonstrated. Further studies were recommended to investigate and evaluate whether these changes could affect its efficiency as a radio protector against gamma radiation.

Key words: Melanin structure, gamma irradiation, gel chromatography absorption spectra, relative permittivity and conductivity.