Effect of temperature on the interactions of glycyl dipeptides with sodium perfluorooctanoate in aqueous solution: Volumetric, conductometric, and spectroscopic study

The interactions of glycyl dipeptides (glyglycine, glycyl-l-valine and glycyl-l-leucine) with sodium perfluorooctanoate (SPFO) in aqueous solutions have been investigated by means of density, conductivity, fluorescence spectroscopy, and UV–vis spectroscopy. The standard partial molar volume (V2,ϕ∘V2,ϕ∘), standard partial molar volume of transfer for dipeptide from water to aqueous SPFO solutions (ΔtVo), partial molar expansibility (Eϕ∘Eϕ∘) and Hepler’s constant have been calculated from density data. Electrical conductivity was used to estimate the critical micellar concentration (ccmc) and the thermodynamic parameters of micellization of SPFO in aqueous glycyl dipeptide solutions. Effects of temperature and hydrocarbon chain length of the glycyl dipeptides on the volumetric properties of dipeptides and critical micelle concentration (ccmc) of SPFO were examined. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interactions of SPFO with glycyl dipeptides, and the aggregation behaviour of SPFO. From the results of UV-vis absorption spectra, the binding constant between dipeptide and SPFO above the ccmc was determined.

► The values of V2,ϕ° and ΔtV° are positive.
► The interactions of SPFO with charged polar groups of glycyl dipeptides dominate.
► Addition of glycyl dipeptide in water decreases the ccmc and the aggregation number of SPFO.
► Thermodynamic parameters of micellization of SPFO have been obtained.
► The affinity between dipeptide and SPFO micelle increases with the increase in the length of alkyl chain of peptides.