Ethyl Lauroyl Arginate, an Inherently Multicomponent Surfactant System

Area of Science:

• Food science and material science
• Surface chemistry and colloid science

Background:

• Ethyl lauroyl arginate (LAE) is a cationic surfactant used in food preservation and packaging.
• LAE can decompose via hydrolysis into Nα-lauroyl-l-arginine (LAS) and dodecanoic acid during storage.
• The surface activity mechanism of LAE and its decomposition products requires further investigation.

Purpose of the Study:

• To investigate the surface activity of ethyl lauroyl arginate (LAE) and its hydrolysis products.
• To elucidate the hydrolysis pathways and the formation of surface-active heterodimers.
• To understand the behavior of LAE at interfaces and in solution, particularly concerning its Critical Micelle Concentration (CMC).

Main Methods:

• Analysis of surface tension isotherms of LAE.
• Quantum mechanical density functional theory (DFT) computations to predict hydrolysis pathways.
• Molecular dynamics simulations to assess dimer stability.
• Application of surfactant mixture adsorption models.
• Measurement of surface dilational modulus using the oscillation drop method.

Main Results:

• DFT computations identified preferred hydrolysis paths for LAE.
• The formation of surface-active heterodimers (LAE-dodecanoate anion, LAE-LAS) was investigated.
• Molecular dynamics simulations confirmed the stability of these dimers through electrostatic interactions and hydrogen bonds.
• Experimental surface tension isotherms were successfully described using a surfactant mixture adsorption model.
• A diffusional transport mechanism governed the surface dilational modulus, with nonlinear responses observed near and above the CMC due to micelles and interfacial layer reorganization.

Conclusions:

• Hydrolysis of LAE leads to the formation of surface-active species that influence its overall behavior.
• The adsorption model for surfactant mixtures effectively describes the surface tension isotherms of LAE.
• The presence of micelles and interfacial layer reorganization significantly impacts the nonlinear surface tension response above the CMC.