Volumetric, Conductometric, And Spectroscopy Study On The Interaction Of Dipeptide With1-octyl-3-methylimidazolium Ionic Liquid In Aqueous Solution

The imidazolium-based ionic liquids (IBILs) are widely applied in industrialproduction and the various areas of life due to its unique physicochemical properties.Small peptides generally composed of two or three amino acids, and their simplestructure is the activity function basis of protein. The study on the interactionsbetween small peptide and imidazoles ionic liquid is of great significance. We havesystematically studied the density and conductivity of ternary system whichcomposed of imidazolium-based ionic liquids (IBILs)[C8mim]X (X=Cl, Br,[CH3COO],[CF3COO])+dipeptide(glygly, glyval, glyleu, glyglu, alaglu)+water.The aggressive number of ionic liquid and the nature of the binding reaction internary system were measured by using the static fluorescence quenching technologyand ultraviolet-visible spectrometry, respectively. The main conclusions of the paperis as follows:1. The electrical conductivity of ternary system was measured. It is found thatthe critical micelle concentration of [C8mim]X in aqueous dipeptide solution isinfluenced by the type of ionic liquid and dipeptide, temperature and theconcentration of dipeptide. In aqueous dipeptide solution, the critical micelleconcentration of [C8mim] X gradual decreases to a certain minimum, then it increaseswith the temperature increasing. At a certain temperature the critical micelleconcentration of [C8mim]X decreases gradually with the increase of dipeptideconcentration. In different dipeptide aqueous solution, critical micelle concentrationof [C8mim]X gradually reduce with the increases of dipeptide alkyl chain length.2. According to mass action model, thermodynamic parameters of micellizationof [C8mim]X in aqueous dipeptide solutions have been calculated. It showed that thestandard Gibbs free energy of [C8mim]X was negative. The micelle formation ofionic liquids [C8mim]X is a thermodynamically spontaneously process. The enthalpyand entropy decreases with the increase of temperature. At the low temperature themicellar process is an entropy driven process, however it is an enthalpy drivenprocess at high temperature. The enthalpy-entropy compensation effect is remarkable. 3. The density of the dipeptide under four temperatures in differentconcentrations ionic liquid solution was measured by using the specific gravity bottle.Some volume parameters have been calculated. It is found that the standard partialmolar volume of dipeptide in [C8mim]X aqueous solution is larger than that in waterat the same temperature. With the increase of temperature standard partial molarvolumes of transfer of dipeptide from water to [C8mim]X-dipeptide solution ispositive and gradually increase. It suggests that it has stronger interactions of thecharged groups and polar group of dipeptide with ionic liquid. The hydration numberdecreases with the rise of temperature in aqueous [C8mim]X solution, which suggeststhat the increase of temperature can cause dehydration of dipeptide.4. The chart of the ratio of the first and third vibration peak intensity I1/I3ofpyrene fluorescence spectrum in the ternary system versus concentration of[C8mim]X and the aggregation number of [C8mim]X were obtained by fluorescencespectrometry. From the spectral data, it is found that the aggregation number of[C8mim]X is smaller in aqueous dipeptide solution than that in aqueous solution andthe degree of reduction is less with the increase of the length of alkyl chain ofdipeptide. The micropolarity of the ionic liquid [C8mim]X is hydrophobic.5. From the results of UV-vis absorption spectra, the binding constant betweenthe dipeptide and ionic liquid [C8mim]X was calculated. It is found that theinteraction between them is gradually increase with increasing dipeptide alkyl chainlength...