Studies on the diffusion coefficients of amino acids in aqueous solutions

The diffusion of amino acids in aqueous solution was investigated experimentally by a holographic interferometric technique where the real-time holographic interference fringes indicating the concentration profiles of the liquid were obtained by an automatic photographing and memorizing program. The reliability of the instrument was verified by the measurement of the diffusion coefficient of KCI and sucrose in aqueous solution at 298.15 K. Furthermore, the diffusion coefficients of glycine, L-alanine, L-valine, L-isoleucine, L-serine, L-threonine, and L-arginine in aqueous solution at 298.15 K were measured, and the affecting factors of molecular structure and polarity were analyzed and discussed. In addition, on the basis of the Gordon model of the diffusion coefficient in the literature, a new semiempirical model was proposed to predict the liquid diffusion coefficients of amino acids in aqueous solutions. The equation parameters were fitted by the experimental data of seven amino acids in this work and four in the literature.