Using time-of-flight secondary ion mass spectroscopy to investigate the reaction of alkylsulfate and alkylethoxysulfate surfactants with keratin

Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) was used to investigate the changes in keratin protein surface chemistry caused by the covalent bonding reactions of commercially available alkylsulfates and alkyl ethoxysulfates surfactants. Due to cystine and cysteine oxidation, plus regular shampooing, the surface chemistry of human hair is different from that of freshly scoured merino wool. Human hair can produce positive ions derived from the reaction of alkylsulfates and alkylethoxysulfates, commonly present in shampoos, with histidine and possibly lysine residues (with little evidence for cysteine thiol reaction). ToF-SIMS analysis of alkylsulfate treated keratin fibers confirmed the reaction of these surfactants with cysteine thiol, tyrosine phenolate, histidine imino, and possibly lysine amino residues. The reaction of alkylsulfates with keratin fiber surface nucleophiles is salutary since similar nucleophiles are present in skin proteins, enzymes, and DNA—which could reasonably be expected to undergo similar modification. In the case of skin, this reaction increases the surface hydrophobicity, which alters the skin biochemistry and microbiome. This results in suitable environmental conditions that could exacerbate existing afflictions such as dandruff, eczema, and mouth ulcers.