Abstract
Amino acid-based surfactants, which have an amino acid residue as a hydrophilic moiety, are widely used for shampoo formulation because of high detergency and low irritancy. However, it's not easy to develop shampoo with ideal foam volume as well as elasticity by using amino acidbased surfactants as a main detergent. So we decided to synthesize a new surfactant, an N-Acyl-N-(2-hydroxyethyl)-β-alanine amino acid-type surfactant (HEA) with a hydroxy group in amino acid residue, and this surface chemical and its physicochemical properties in aqueous solution were investigated. HEA showed unique interfacial behavior around CMC. However, it was not clear that this behavior is due to the hydroxy group. So we used NMR measurement to compare it with an N-acyl-N-methyl-β-alanine amino acid-type surfactant (LMA) without a hydroxy group to understand its behavior in the aqueous solution of HEA. According to the result of NOESY (NMR using the Nuclear Overhauser Effect (NOE)) at 1 mmol/L, inter-molecular correlation was observed between the hydroxyethyl group and lauroyl group of HEA. On the other hand, it was not observed in LMA. The results suggested that formation of hydrogen bonds affect the unique behavior of the HEA solution. HEA was superior to LMA in terms of foam volume, fineness, elasticity and stability. These performances of HEA are thought to result from the formation of hydrogen bonds by having a hydroxyl group on amino acid residue. HEA is a useful detergent for shampoo formulation, and the shampoo with HEA has excellent foam performance.
