Exploring the effects of selected essential amino acids on the self-association of sodium dodecyl sulphate at different temperatures

Abstract

Sodium dodecyl sulphate (SDS) has well established biological applications in the determination of molecular weights and structure determination of proteins, peptides etc. Due to these reasons, the study of SDS interactions with essential amino acids (AAs) can be valuable as they can diversify the use of SDS in applications of importance in biology and drug delivery designs etc. The aggregation process of SDS and its detailed physiochemical properties in aqueous system, in the presence and absence of three essential amino acids L-Threonine (THR), DL- Methionine (MET) and L-Phenylalanine (PHE), is studied in a temperature range of 293 K-323 K using conductivities, surface tension (γ), particle size and zetapotential measurements using dynamic light scattering (DLS) technique. From conductivity measurements, critical micelle concentration (CMC), counterion binding (β) and thermodynamic parameters such as standard free energy change of micellization (ΔGmo), standard enthalpy change of micellization (ΔHmo), standard entropy change of micellization (ΔSmo) etc., are calculated. The surface properties and interfacial parameters of SDS systems are studied using surface tensiometery. Results established that the presence of amino acids (AAs) reduced the CMC of SDS. The electrostatic interaction of AAs with charged micellar surface were also observed. The micellization process of SDS was found thermodynamically feasible in the aqueous amino acid (AAA) system. From the surface tension data, interfacial parameters such as Гmax, Amin,pC20 , and surface effectiveness of SDS in aqueous and AAA system have been calculated and compared. It was revealed that surface adsorption and rearrangement of SDS molecular ion at their micellar concentration at air/liquid interface are significantly affected by AA addition. Hydrodynamic diameter (Dh) and zetapotential (ζ) of aqueous SDS solution helped to check the effect of amino acid additives on the colloidal size and stability of SDS aggregates. The results from different techniques were consistent to establish the feasibility of SDS micellization process in aqueous as well as aqueous AA solution.