Enthalpies of Transfer of Amino Acids from Water to Aqueous Cationic Surfactants Solutions at 298.15 K

Abstract

Enthalpies of solution of five amino acids, glycine, l-alanine, l-valine, l-serine, and l-threonine in aqueous solutions of three quarternary ammonium surfactants, [C n H2n+1(CH3)2NCH2CH2OH]Br (n = 12, 14, 16), have been measured at 298.15 K with a microcalorimeter. Enthalpies of transfer of amino acids from water to aqueous surfactant solutions have been derived. It has been observed that, at relatively low concentrations of the surfactant solutions, amino acids are still in the water phase and mainly interact with the hydrophilic head groups of the surfactant molecules. With an increase of the concentration of the surfactant solutions, the microenvironment of amino acids changes, and the molecules might insert into the micelles and interact with the hydrophobic tail groups of the surfactant molecules. The results are discussed in terms of a delicate balance of hydrophobic and hydrophilic interactions and differences in the molecular structure of amino acids.

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Surfactant–Amino Acid and Surfactant–Surfactant Interactions in Aqueous Medium: a Review

“…apparent molar volumes, ϕ v , partial molar volumes, ϕ 0 v , transfer volumes, ϕ 0 v;trans , Falkenhagen coefficients, A, Jones-Dole coefficients, B, free energies per mole of solute, Δμ 0≠ 1 , and per mole of solvent, Δμ 0≠ 2 , molar refraction, R D , and limiting molar conductivity, Λ 0 m , by using the experimental measured densities, ρ, viscosities, η, refractive indexes, n D , and specific conductivities, k, data of glycine (0.02-0.10 m) in 0.01 m aqueous SDS, CTAB and Tx-100 solutions at 298.15, 303.15, 308.15 and 313.15 K. The data from these parameters together with fluorescence were interpreted in terms of interactions prevailing in the system. Qiu et al [110] studied the quaternary ammonium surfactants, [C n H 2n+1 (CH3) 2 N CH 2 CH 2 OH]Br (n = 12, 14, 16), at 298.15 K with a micro-calorimeter. Enthalpies involved in transferring amino acids from water to aqueous surfactant solutions were investigated.…”