The dissolution enthalpies of Gly-L-His and β-Ala-L-His in phosphate-buffered saline and in micellar solution (SDS + phosphate-buffered saline) are measured at pH = 7.4 and T = 298.15 K. The enthalpies of the interaction of peptides with SDS micelles are determined as the enthalpies of transfer of peptides from a buffer solution to a micellar buffer solution. The proportions of different ionic forms for both peptides in the solution are compared. Three ionic forms coexist in Gly-L-His solution at pH = 7.4, while in β-Ala-L-His solution, only two forms predominate. A higher proportion of zwitterions and a larger contribution of electrostatic forces are characteristic for the interaction of micelle with β-Ala-L-His. But a greater endothermic contribution of partial dehydration of more hydrophobic peptide equalizes its overall interaction enthalpy with the effect for Gly-L-His. The interaction of micelles with peptide ions is accompanied by compensation of the negative ζ-potential and compression of micelles.
