The ESR signals in silk fibroin and wool keratin under both the effect of UV-irradiation and without any external effects and the formation of free radicals

Abstract

ESR studies have been done on natural and UV-irradiated silk fibroins and wool keratins at the temperature range of −196°C to 20°C. The intensities of ESR signals obtained from the irradiated samples at −196°C remarkably increase with respect to those of natural samples. While the signals mainly consist of triplet peaks at −196°C, a doublet arises around the room temperatures. For the first time, at room temperature without any external effect the complicated ESR spectra of fibrous proteins (wool keratin and silk fibroin) whose components are as follows have been observed: (1) (for white wool keratin) a central doublet with ΔHm=1.1mT and g=2.0075; ΔHm=5mT and g=2.1911; (2) a wide peak with ΔHm≈66mT and g≈2.1575; (3) the ‘sulfur’ peak given in the literature with ΔHm=2.2mT and g=2.0218; (4) the signal with ΔHm=0.6mT and g=2.0065, and for silk fibroin, (a) a very wide signal with ΔHm≈70mT and g≈2.084; (b) a very sharp signal with ΔHm≈1.1mT and g≈2.01; and (c) relatively narrower signal with ΔHm≈5mT and g≈2.336.It has been shown by recombination kinetic method that 30–50% of the free radicals formed by UV-irradiation do not undergo recombination up to 220°C and 150°C for silk fibroin and wool keratin, respectively, even they keep their concentration constant for long period of time (weeks, months, even longer). In this article, considering above-mentioned results, the mechanism of signals observed in natural wool keratin and silk fibroin without any external effects is examined.We can briefly explain the role of the subject of the article, by considering fibrous proteins and some applications of the reactions by free radical occurring in these proteins under the effects of different factors in medicine and biology and the important role of oxidation and the other kinds of degradations on these processes, as well as the significant applications of ESR investigations on comprehending the processes by free radical.