Volumetric, Conductometric, And Spectroscopy Study Of Glycyl Dipeptide With Imidazolium Ionic Liquids In Aqueous Solution

As a special surfactant, imidazolium ionic liquids [Cnmim]Br are widely used in various fields of industrial production and life. Small peptides which have smaller structure of biological fragment play an irreplaceable role in chemistry, medicine, biology, food and other industries and they are composed of peptides and proteins. Because of the unique biological activity of small dipeptides, we can study the micellization behavior of surfactant in the solution of small peptides, polypeptides, proteins and the role of small dipeptides in the process of micellization through the research on the interactions of small dipeptides and imidazolium ionic liquid [Cnmim]Br. This research has a great significance. In this paper, the conductivity, volumetric, fluorescence spectroscopy and UV absorption spectroscopy method are used to study the interactions of imidazolium ionic liquids [Cnmim]Br (n=10,12,14) with glycyl dipeptide in aqueous solutions. The main contents and results are as follows:1. The conductivities of three imidazolium ionic liquids [Cnmim]Br in aqueous solution of dipeptides (glycyl-glycine, glycyl-L-valine, glycyl-L-Leucine) at six temperatures were measured by conductivity method.2. The results showed that the critical micelle concentration (CMC) of the imidazolium ionic liquid [Cnmim]Br in the aqueous dipeptide solutions is affected by the concentration of dipeptide, temperature, as well as the species of the dipeitide and ionic liquid. In a certain solution of dipeptide, the CMC value of the imidazolium ionic liquid surfactant [Cnmim]Br gradual decreases, then it increases with the increasing of temperature. At the same temperature, the CMC value gradually decreases with the increase in the concentration of the dipeptide, and the alkyl chain length of the dipeptide and ionic liquid.3. Thermodynamic parameters of micellization of [Cnmim]Br in aqueous glycyl dipeptide solutions have been obtained by applying the mass action model. The data showed that the micelle behavior is the spontaneous. The micellization process is entropy driven process at the low temperature, but it is enthalpy driven at the high temperature. Moreover, the enthalpy-entropy compensation effect is observed.4. The density of the dipeptide (glycylglycine, glycyl-L-valine, glycyl acyl-Z-leucine) is measured in0.05,0.10mol·kg-1solution of [Cnmim]Br at four different temperatures by using the specific gravity bottle. Various volume parameters were calculated by using the density data.5. When the concentration of [Cnmim]Br is constant, at the same temperature, standard partial molar volumes of dipeptide is larger than the corresponding values in water. Standard partial molar volumes of transfer from water to [Cnmim]Br is positive, and gradually increases as the temperature increases. This is due to the larger interactions of ion-ion and ion-polar group than ion-nonpolar and nonpolar-nonpolar group of dipeptide and [Cnmim]Br. The hydration numbers decrease as the temperature increases, which suggests that the increase of temperature can cause dehydration of dipeptide.6. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interactions of [Cnmim]Br with glycyl dipeptides, and the aggregation behaviour of [Cnmim]Br. The I1/I3ratio of pyrene in solution and the aggregation number of [Cnmim]Br were decreased by addition of glycyl dipeptides. The micropolarity of the microenvironment and aggregation number of [Cnmim]Br decrease with the increase of the chain length of the dipeptides. However, the degree of reduction of the aggregation number is less. The interactions between dipeptide and [Cnmim]Br make microenvironment of [Cnmim]Br more hydrophobic.7. From the results of UV-vis absorption spectra, the binding constant between dipeptide and [Cnmim]Br was determined. The result shows that the strength of the affinity between dipeptide and [Cnmim]Br micelle increases with the increase in the length of alkyl chain of peptides.