Prof. Akio OHTA
Study of the Antioxidative Properties of Several Green
Surfactants Originated by Amino Acid and their Synergistic Effect
N-Acyl amino acid surfactants, which are anionic amino acid-type surfactants, are very valuable because of their biodegradability and low toxicity. Amino acids have been known for their AOX activity and can be extensively used to prepare surfactants having low toxicity and biodegradability. The uses of amino acid-type surfactants were diverse such as anti-ageing, antimicrobial, and AOX in food, cosmetic and pharmaceutical industries. But there is almost no reporting which emphasis on the AOX properties of amino acid-type surfactants having good water solubility. Our aim was to introduce amino acid-based green surfactants as antioxidants which are of low-toxicity, highly soluble and comparatively safer than conventional antioxidants. In this study, we found excellent solubility of the lauroyl cysteine (C12-Cys) and lauroyl methionine (C12-Met) in both water and other conventional non-polar solvents. Later, the AOX property of the materials was checked at pre-micellar and micellar condition. Density functional theory (DFT) calculation was utilized to understand the mechanism and kinetics of the AOX processes of both the surfactants. Cysteine tends to form dimer molecule in the solution; hence we investigated any dimer formation of C12-Cys and checked any effect of this phenomena on its AOX activity at pre-micellar and micellar states and the synergistic effect with other previously developed aromatic amino acid-based surfactants: lauroyl histidine (C12-His), lauroyl tyrosine (C12-Tyr), and lauroyl tryptophan (C12-Trp).