The Study Of Conductivity And Spectroscopy On The Interaction Of Glycyl Dipeptide With Gemini-Surfactants In Aqueous Solution

Gemini surfactant is a new class of surfactant, and has the enhanced surface activity and unique solution properties. Small peptide, which has biochemical activities and variety, is a signal transmitter in cell communications and has significant influence on the aqueous system. They can also be used in drug production. Moreover, small peptide is an ideal model molecule of protein, which can more accurately reflect interaction of groups of the protein molecule with the surfactant because they have the similar chemical environment with the group of the protein. Therefore, the studies on the interactions between small peptide and Gemini surfactant can provide the theoretical basis and valuable information about the role of the presence of small peptides in the micellization process of surfactants, peptide's behavior as well as the insight into the conformational stability of peptide and proteins in surfactant solutions. The interactions between glycyl dipeptide and four Gemini surfactants have been investigated systematically by means of conductivity, fluorescence spectroscopy and UV-absorbance spectroscopy. The major contents and results are as follows:1. The conductivity at different temperatures, fluorescence and UV spectroscopy at room temperature of glycyl dipeptides (glycylglycine, glycyl-L-valine, and glycyl-L-leucine)-gemini surfactants-water ternary systems were determined. The data of conductivity were used to estimate the critical micelle concentration (CMC), degree of counterion binding and the thermodynamic parameters of micellization of surfactants in aqueous peptide solutions. The change of micropolarity produced by the interaction was monitored by the measurement of emission intensity ratio between the first and third bands (I1/I3) of pyrene fluorescence. The aggregation number of Gemini surfactants in water and water-dipeptides was calculated. The binding constant of the interaction between the Gemini surfactant and dipeptides were calculated by UV-spectrum date.2. The effect of temperature, the concentration and structure of dipeptides on the critical micelle concentration of Gemini surfactant in the presence of dipeptides has been investigated. The results showed that the critical micelle concentration (CMC) for Gemini surfactants (12-5-12,8-5-8 and 8-3-8) gradual decreases, then it increases significantly. A CMC minimum was observed for these surfactants. However the CMC for Gemini surfactants 12-3-12 increases with the increasing in the temperature. These results were caused by the different hydration of micelles with different shapes. At a given temperature, the CMC values of four Gemini surfactants decrease with the increase of dipeptides concentration. The micellization process was more favored with the longer alkyl chain of peptides.3. The critical micelle concentration was also influenced greatly by the structure of Gemini surfactants. The CMC of the surfactants with the same alkyl chain increase with the increasing of the spacer length. And the CMC of Gemini surfactants with the same space length and the different alkyl chain decrease with the increasing of the hydrophobic carbon atoms.4. According to the mass interaction model, the thermodynamic parameters of the micellization of the studied Gemini surfactants were calculated in water-dipeptide mixed media. It is found that the standard free energy of micellization was negative, which indicates the micelle formation is a thermodynamically favorable process. Both entropy and enthalpy of micellization decease with the increasing of the temperature, and the enthalpy-entropy compensation phenomena has been found in ternary solutions.5. The fluorescence spectroscopy of glycyl dipeptide-gemini surfactant-water systems were determined by using pyrene as a probe. The I1/I3 fluorescence vibronic ratio varies with surfactant concentration. The micropolarity of micellar was studied. The average aggregation number of micellization was measured by the steady state fluorescence quenching method. The micropolarity of pyrene in surfactant solution and the aggregation number of surfactant were decreased by addition of glycyl dipeptides. The glycyl dipeptide with longer alkyl chain will enhanced this trend.6. The binding reaction between the gemini surfactant and glycyl dipeptides was measured by UV spectrum. The equilibrium constant was calculated. The results showed that the binding constant increases with the increasing of the alkyl chain of dipeptide.