Interactions Of Perfluorinated Surfactant With Dipeptide In Aqueous Solution:Volumetric, Conductometric, And Spectroscopy Study

Perfluorinated surfactants are one of the most important special surfactants, which have the highest surface active among the known surfactants. The complex systems containing the surfactant and other compounds have been applied in many areas of industry and everyday life. The structure of small peptide is simple and small peptides are the fundamental part of proteins. The studies on the behavior of dipeptides in aqueous solution play an important role in understanding of thermodynamic stability of polypeptide and protein, as well as the degeneration of protein. In this paper, we selected dipeptide+perfluorinated surfactant+water ternary system as our studied system, and studied the interaction between perfluorinated surfactants and dipeptide.In this paper, the interactions between dipeptide and perfluorinated surfactants have been studied systematically by density, conductivity, fluorescence spectroscopy and UV absorbance spectroscopy. The major conclusions of the paper are as follows:1. The density of ternary systems of perfluorinated surfactants (sodium perfluorooctanoate (SPFO), perfluorobutane sulfonic acid potassium salt (PFBS), perfluorooctane sulfonic acid potassium salt (PFOS))+dipeptides (glycylglycine, glycyl-L-valine, glycyl-L-leucine, glycyl-L-glutamine, L-alanyl-L-glutamine)+water have been determined by using the specific gravity bottle. The apparent molar volumes (V2,φ), standard partial molar volumes (V2,φO), standard partial molar volumes of transfer from water to aqueous solutions of perfluorinated surfactants (△tVO), the hydration number (NH), partial molar expansibility, and Hepler’s constant of dipeptides have been calculated from density data.2. When the temperature and concentration of perfluorinated surfactants in aqueous solution were given, the values of standard partial molar volumes of transfer from water to aqueous solutions of perfluorinated surfactants are positive, and the values of V2,φO increase with the increasing temperature. The hydration number of dipeptides in aqueous perfluorinated surfactants solutions decreases with the increasing temperature. These suggest that ion-ion interactions and ion-dipeptide group interactions are the predominate interactions between dipeptide and perfluorinated surfactants. The increaseing temperature leads to the dehydrations of dipeptides. The peptides are structure-makers in aqueous perfluorinated surfactants solution. Standard partial molar volumes of dipeptides in aqueous PFBS and PFOS solutions increase with the increasing fluocarbon chains of the perfluorinated surfactants. The order of the interaction between PFBS/PFOS and dipeptides is:V(?)(PFOS)> V(?)(PFBS).3. The temperature, the concentration and structure of dipeptide in aqueous solution can affect the cmc values of SPFO. The addition of dipeptides decreases the cmc values of SPFO at a given temperature. The dipeptides with the long alkyl chains induce to the larger decrease in cmc of SPFO. The hydrophobic actions have the main effect on the interaction between the dipeptide and surfactants. The cmc of SPFO in dipeptides solutions decreased to a certain minimum and then increased with the temperature. From the result of thermodynamic functions, it is indicated that micelle formation is a thermodynamically favorable process. An enthalpy entropy compensation effect has been found.4. The data of steady-state fluorescence spectra implied that the addition of dipeptide in water can decreases the cmc values and the aggregation number of SPFO at a given temperature. This decrease is related to the length of alkyl chain of dipeptides. The longer the alkyl chain of dipeptides is, the small the cmc values, the aggregation number and micropolarity of SPFO are.5. The interaction constant of SPFO with dipeptide has been measured by UV method. The interaction between the SPFO and dipeptide is proportional to the length of alkyl chain of dipeptides.6. The conductivity of PFBS/PFOS has been determined in aqueous dipeptide solutions. The values of conductivity have been used to calculate the limited molar conductivity. The limited molar conductivity of PFBS/PFOS increase with the increasing of temperature. This maybe related to increase of transference number caused by the increasing temperature. On the other hand, the limited molar conductivity of PFBS/PFOS decrease with the the increasing concentration of the dipeptide, this caused by the viscosity of solvent and the presolvation of ions by peptide molecules.7. The structure of dipeptide and perfluorinated surfactants influences the interaction between them. The strength of the interaction is proportional to the length of alkyl chain of the two kinds of compounds. The order of the interactions between dipeptide and surfactant is glycylglycine<glycyl-L-valine<L-glycyl-L-leucine, glycyl-L-glutamine<L-alanyl-L-glutamine. The interaction of PFOS with dipeptide is larger than that of PFBS with dipeptides.