Effects of hydroxyl groups on binary diffusion coefficients of α-amino acids in dilute aqueous solutions

Binary diffusion coefficients, D12, of α-amino acids with hydroxyl groups, e.g., serine, threonine, allothreonine and homoserine, in dilute aqueous solutions were measured at six different temperatures from 293.2 to 333.2 K by the Taylor dispersion method. The determined D12 values of serine and threonine at 298.2 K were in good agreement with the published data, whereas no data for allothreonine and homoserine is available in the literature. The D12 values for each amino acid were well represented with the Stokes–Einstein equation by adjusting the molecular diameter. The D12 values for amino acids containing hydroxyl groups, except for homoserine, were lower by approximately 5%, on the basis of the same solute molar volume, than those from the corresponding amino acids without hydroxyl groups.