The interactions of glycyl dipeptides (glycylglycine, glycyl-L-valine and glycyl-L-leucine) with sodium
caprylate (NaC8) in aqueous solution have been investigated by a combination of density, conductivity
and fluorescence methods. Apparent molar volumes (V2,/), standard partial molar volumes (V
2;/), and
standard partial molar volumes of transfer from water to aqueous NaC8 solutions (DtVo) are evaluated
using density data. The limiting molar conductivity of sodium caprylate (Ko) and its anion contribution
koðC
8 Þ, as well as the Stokes’ radii of caprylate anion in aqueous glycyl dipeptide solutions have been calculated
using conductivity data. Pyrene fluorescence spectra were used to estimate the critical micellar
concentration (ccmc) of NaC8 in aqueous dipeptide solutions. The analysis shows that the interactions
of sodium caprylate with charged and polar groups of glycyl dipeptides are dominating over the sodium
caprylate-non-polar group interactions over the entire concentration range of sodium caprylate. From the
volumetric data, it is suggested that the glycyl dipeptides are solubilized in the palisade layer of sodium
caprylate micelles. The decrease in Ko values of sodium caprylate with an increase in dipeptide concentration
is attributed to the interaction of sodium caprylate with the dipeptides and increasing viscosity of
solvent. The addition of dipeptide in water decreases the ccmc of NaC8. The interactions of glycyl dipeptides
with sodium caprylate increase with the increase in the size of side chain of carboxylate anions
and of glycyl dipeptides.