ESR study of hair and melanin-keratin mixtures - the effects of temperature and light

Synopsis The ESR spectrum of hair presents a symmetrical absorption band with the same characteristics as pure melanin (g= 2.0030; deltaH= 5 G). Between 250 degrees K and 490 degrees K, the intensity of the signal increases as for pure melanin. This variation may be explained by a change in the moisture content of hair as function of the temperature. Below 250 degrees K, in a frozen medium, melanin-water interactions remain constant and the number of radicals is no longer a function of temperature. Under exposure to light of hair, melanin-derived radicals were formed. Stable and short-lived radicals were observed at lambda > 345 nm; only unstable radicals were formed at lambda > 450 nm. At shorter wavelengths (lambda > 280 nm), a new asymmetric signal (g= 2.0065H= 20 G) appeared on UV exposure of black, grey or white hair; this signal was attributed to radicals formed in the direct excitation of keratin amino acids.