Effect of sodium chloride on the behaviour of the lactose in aqueous solution studied from diffusion experiments and molecular dynamics simulations

Abstract

Ternary mutual diffusion coefficients (D11, D22, D12 and D21) measured by the Taylor dispersion method are reported for aqueous solutions of (NaCl + lactose) at 298.15 K and NaCl concentrations up to 1.00 mol dm−3. The coupled diffusion of NaCl (1) and lactose (2) is significant, as indicated by the large negative cross-diffusion coefficients. In this sense, from the values of these cross-diffusion coefficients a counter-transport of 0.4 mol of NaCl per mol of diffusing lactose is inferred, whereas only 0.02 mol of lactose could be counter-transported by one diffusing mole of NaCl. The main diffusion coefficient data are compared with the binary ones of both pure solutes in water and discussed on the basis of Onsager-Fuoss and Pikal models. From these data and by performing molecular dynamics simulations, it is possible to obtain a better understanding of the effect of sodium chloride on the transport of lactose in aqueous solutions, as well as to assume the importance of the Na+-lactose short-range interaction, competing with the coulomb long-range interaction between the sodium and chloride ions, especially at low concentration of NaCl.