Mechanistic Studies on the Oxidation of Short Peptides with Relevance to Hair Damage

The main purpose of this project was the mechanistic study of the aerobic oxidation of short peptides with relevance to hair protein damage. It is well-established that oxidation of biological matter leads to formation of intermediate hydroperoxides. It was hypothesised that accumulation and subsequent decomposition of hydroperoxides would lead to enhanced protein damage. This theory was tested in short peptides that were used as protein mimics. In Chapter 2 it was demonstrated that the combined damage of two insults (UV and heat) is greater than the sum of the two, thus confirming that the two insults act in synergy. Evidence for the role of intermediate hydroperoxides in the process were collected. In Chapter 3 the antioxidant effect of four catechol-based antioxidants derived from natural extracts was described. Protein damage in hair is known to occur via radical reactions. Antioxidants derived from natural sources have received attention in various industries as they have been shown to retard the oxidation of organic compounds. It was demonstrated that all four antioxidants offer significant protection against the HO•-mediated oxidation of two protected amino acids. By detecting degradation products formed on the antioxidants, reaction pathways were proposed to corroborate their antioxidant mechanism. Radical intermediates formed during protein oxidation are challenging to detect with the current detection methods, as their steady state concentration is usually too low. Recently, a new method for trapping and detecting radical intermediates was developed in our group, and this method was applied with success to many different areas of chemistry (e.g., atmospheric, synthetic). In Chapter 4, the scope of application of this method was further expanded. A great number of biological intermediate radicals (both C- and O-centred) generated via different oxidants, were successfully characterised. The exact identify of these radicals was further elucidated by well-established isotope-exchange experiments.