The Research Of Conductivity And Fluorescence Spectroscopy Of The Dipeptide-Surfactants Interaction In Aqueous Solution

The molecular ordered assemble systems with the size and the interfacial properties have a very important application value in materials science and daily-use chemical industry. It is very significative to study the physical and chemical properties of bio-active substances in the molecular ordered assemble systems and explore the essence of the phenomenon of life when micro-emulsion, micelles and other molecular organized assemblies were used as an ideal system for simulating the bio-reaction in the body. Peptide is a biological active substance and the fragment of the protein. They are important molecules due to their wide application in drug production and their roles as signal transmitters in cell communications. Moreover, small peptides have been widely used as a protein model compound recently in the studies of the thermodynamic properties of protein because they contain more complex structure and more component of protein than amino acids. The systematic study of peptide-surfactant interactions can provide valuable information about peptide's behavior and insight into the conformational stability of proteins in surfactant solutions. Such investigation can also obtain the information about the role of the presence of peptides in the micellization process.In this paper, the interaction between dipeptides and surfactant has been studied systematically by conductometry and fluorescence spectroscopy. The major contents and results are as follows:1.In this study, conductivity and fluorescence data for the dipeptide-SDS-water systems were determined at different temperatures. Electrical conductivity was used to estimate the critical micellar 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 surfactants in water and water+dipeptides was determined.2.The critical micellar concentration of the studied surfactants in aqueous dipeptides solutions was influenced by temperature, concentration and structure of dipeptides. At a given temperature, the cmc values of surfactants decrease with the increase of dipeptide concentration. Longer alkyl chain of peptides is markedly effective in promoting the micellar formation. The variation of cmc with temperatures appears to follow a curve concave downward with a minimum at a certain temperature. The observed phenomena reflects the effect of temperature on a gradual dehydration of the hydration around the hydration chain, promoting micelle formation, and partial dehydration of the hydrophilic hydration, leading to an increase in repulsion between polar head groups.3.The concentration of dipeptide and temperature have the cocperative effect on the degree of counterion binding. The degree of counterion binding decreases with increase in the temperature and the concentration of dipeptides.4. The free energy of micellization is negative, which indicatives that micelle formation is a thermodynamically favorable process. Standard enthalpy of micellization is found to be positive at lower temperature and it becomes negative at higher temperature. And positive entropy of micellization was observed. The weak temperature dependence of standard Gibbs free energy of micellization reflects an enthalpy-entropy compensation effect. The interactions between dipeptides and surfactants are influenced by the structure and style of surfactants. The order of the interactions between dipeptide and surfactant is SDS>SAS>DTAB.5.The decrease in I1/I3 ratio of pyrene in SDS solution by addition of dipeptides indicates that the micelle polarity is affected by dipeptides. The aggregation number and cmc of surfactant decrease when the dipeptide was added into the aqueous surfactant solution.6. The alkyl chain length of the dipeptides influences the cmc, the degree of counterion binding,I1/I3 ratio and the aggregation number of surfactant. The marked reduction in cmc as well as I1/I3 ratio and the larger values of the degree of counterion binding as well as the aggregation number were observed with the increase in size of the alkyl chain length of the dipeptides.