Characterization of complexation of uracil with peptides through its volumetric properties in buffer saline solution at different temperatures

Densities of mixtures of uracil (Ura) with glycyl-glycine (GlyGly) and glycyl-phenylalanine (GlyPhe) in a buffered saline (pH 7.4) were measured at T=(288.15, 293.15, 298.15, 303.15, 308.15 and 313.15) K using the density meter DMA 5000 M (Anton Paar). The apparent molar volumes, limiting apparent molar volumes at infinite dilution and their derivatives with respect to temperature have been evaluated. Interactions of uracil (Ura) with glycylpeptides (GlyGly, GlyPhe, GlyTyr, GlyGlu) were studied with using review volumetric properties obtained early for Ura in GlyTyr and GlyGlu buffered solutions. The effect of concentration, ionic state and hydrophobicity of reagents on the Ura volume properties were discussed. The results indicate the complex formation between Ura and glycylpeptides with 1:1 stoichiometry. It was shown that the complexation of uracil with the glycylpeptides is accompanied by the positive changes of molar volume of Ura. The positive values of Hepler parameter indicate an increase in the ordering of the solvent in the environment of uracil with the addition of peptides. Uracil acts as a structure maker and its structure-making ability increases in series: Ura < GlyPhe < GlyGly < GlyGlu < GlyTyr.