Interactions of some α-amino acids with tetra-n-alkylammonium bromides in aqueous medium at different temperatures

The densities and viscosities were measured for binary mixtures of 0.01 M aqueous tetramethylammonium bromide (TMAB) and tetraethylammonium bromide (TEAB) and ternary mixtures of glycine, dl-alanine and dl-valine (0.01 to 0.05 M) in 0.01 M-aqueous tetra-n-alkylammonium bromides at T = (298.15, 303.15, 308.15, and 313.15) K and at atmospheric pressure. The apparent molar volume, ϕv, was computed using the density data. The limiting apparent molar volume, ϕv∘ of amino acids and the slope, Sv∗ were obtained using the Masson’s equation. The transfer volume, ϕv∘(tr) of the amino acids and their side-chain contribution, ϕv∘(R) have also been determined. The viscosity data have been analyzed on the basis of the Jones–Dole equation, the viscosity A and B  -coefficients and free energy of activation of viscous flow, per mole of solvent, Δμ1∘# and solute, Δμ2∘# have been evaluated. Both ϕv∘ and Δμ2∘# vary linearly with increase in number of C atoms in the alkyl chain of the amino acids. This linearity is used to find the contribution of the zwitterionic end groups, (NH4+,COO-) and those of CH2 groups of side-chain to the ϕv∘ and Δμ2∘#. The variations of these parameters with concentration and temperature clearly suggests the role of alkyl cation on the solute–solvent interactions in aqueous medium. The structural influence of the large cations of quaternary ammonium salts upon solvent is also taken into consideration.