Synthesis And Properties Of Novel Alkylbenzene Sulfonate And Alkyl Sulfate Gemini Surfactants And Their Interactions With Bovine Serum Albumin

Gemini surfactants are a novel class of surfactants, which could be considered as dimers or oligomers of conventional surfactants with single headgroup and single hydrophobic tail. Compared with conventional surfactants, Gemini surfactants show better surface activity and richer aggregation behaviors, and the structures of Gemini surfactants are also more adjustable than conventional surfactants. Owing to their excellent properties, Gemini surfactants have attracted worldwide attention in the field of colloid and surface science over the past decades. Anionic surfactants, especially alkylbenzene sulfonate and alkyl sulfate surfactants, have been widely used in the fields of industrial production and academic research. Design and synthesis of new types of alkylbenzene sulfonate and alkyl sulfate Gemini surfactants and study of the structure-performance relationship of these surfactants, have become an important part in the field of surfactant science.Surfactants and polymers are often used together in practical applications. Proteins are an important kind of biomacromolecules. Protein-surfactant systems are widely used in the fields of detergents industry, cosmetics, bioscience, pharmaceutics and food. Thus studies on interactions of proteins and surfactants become very important. In this paper, two types of anionic Gemini surfactants, i.e. the alkylbenzene sulfonate type and the alkyl sulfate type, have been synthesized, and their aurface active properties and the interactions with bovine serum albumin (BSA) have been studied. The main contents of the thesis are as follows:1. The synthesis and properties of Gemini surfactants and their interactions with BSA were briefly reviewed.2. Four alkylbenzene sulfonate gemini surfactants with different alkyl tail length were synthesized based on long chain alkyl carboxylic acid, aniline and1,6-hexamethylene diisocyanate. The structures of the products were confirmed by FT-IR,1H NMR and ESI-MS.3. Four alkyl sulfate Gemini surfactants with different spacer length were synthesized based on1-bromodecane, diethyl malonate and dibromoalkane. The structures of the products were confirmed by FT-IR,1H NMR and ESI-MS.4. The surface active and micellization properties of the alkylbenzene sulfonate Gemini surfactants were investigated by means of surface tension, electrical conductivity and fluorescence measurements. The results showed that the cmc of these compounds were one or two orders of magnitude lower than the corresponding monomeric surfactant. There was an initial decrease and then an increase in cmc with the increase of hydrophobic alkyl tail. Molar conductivity measurement revealed the existence of premicellar aggregates in solutions of Gemini IV. Fluorescence probing studies showed that the micropolarities of these Gemini micelles varied little with the increase in alkyl tail length. Performance properties of these surfactants were also studied; low foamability, foam stability and wetting ability but good lime soap dispersing ability were observed for these compounds, the emulsifying power of the Geminis was also better than that of sodium dodecylbenzene sulfonate.5. The surface active and micellization properties of the alkyl sulfate Gemini surfactants were investigated by means of surface tension, electrical conductivity and fluorescence measurements. The cmc values obtained by the conductivity method were considerably higher than those obtained by the surface tension method, and comparable with those obtained by the fluorescence probing method. Molar conductivity measurement revealed the existence of premicellar aggregates for these surfactants, the formation of premicellar aggregates may account for the discrepancy between the cmc obtained by these different methods. In these cases, the traditional cmc refer to the values obtained by the conductivity method. The cmc values of these Gemini surfactants decreased monotonously with the increase of spacer chain length from3to10. The foamability and wetting ability of alkyl sulfate Geminis were lower than those of SDS, but the foam stability, emulsifying power and lime soap dispersing ability were better than those of SDS.6. The interactions of alkylbenzene sulfonate Gemini surfactants with BSA were studied by means of fluorescence, UV-Vis absorption spectroscopy and circular dichroism (CD). Fluorescence probing studies revealed that the micropolarities of Gemini-BSA complexes showed little difference with the variation of alkyl tail length. The micropolarities of gemin-BSA complexes at high surfactant concentration range were close to those of free Gemini micelles. Synchronous fluorescence spectra displayed that Geminis mainly interacted with the tryptophan residues of BSA. BSA intrinsic fluorescence spectra illustrated that the addition of Gemini surfactants to BSA solution resulted in quenching of BSA fluorescence intensity. The quenching process contained a mixture of dynamic and static quenching. At low concentration range, the quenching constant demonstrated an initial increase and then a decrease with the increase in alky tail length, this is the result of two opposite factors, on the one hand, geminis with a shorter alkyl tail may be easier to approach the cavity and interact with the tryptophan residue in the cavity, on the other hand, geminis with a longer alkyl tail may interact stronger with BSA through hydrophobic interaction. CD experiment showed that changes in secondary structures occurred when Gemini surfactants were added to BSA, the a-helix content decreased and β-sheet content increased.7. The interactions of alkyl sulfate Gemini surfactants with BSA were studied by means of fluorescence, CD and dynamic light scattering (DLS). Fluorescence probing studies displayed that the micropolarities of Gemini-BSA complexes decreased with the increase of spacer carbon number n, and they were lower than those of the corresponding free Gemini micelles. BSA intrinsic and synchronous fluorescence spectra demonstrated that BSA probably went through an intermediate state upon denaturation by the addition of Gemini surfactant, and the intermediate has a stronger tendency to aggregate than native and partly denatured BSA. CD experiment showed that the alkyl sulfate Gemini surfactants played two opposite roles when interacted with BSA. At low Gemini/BSA molar ratios, Gemini surfactants could stabilize the secondary structure of BSA, while at higher molar ratios, Gemini mainly acted as denaturants. DLS experiment illustrated that the size of gemini-BSA complexes decreased with the increase in spacer chain length.The innovations of this work are as follows:1. Four alkylbenzene sulfonate Gemini surfactants with different alkyl tail length were synthesized. Their surface active and performance properties were investigated. This provides basic scientific data for theoretical research and application studies.2. Four alkyl sulfate Gemini surfactants with different spacer length were synthesized. Their surface active and performance properties were investigated. This research enriches the studies about the structure-performance relationships of Gemini surfactants and lays the foundations for practical applications.3. The interactions of alkyl sulfate Gemini surfactants with BSA were first studied. The influence of spacer length on the interactions was discussed. The possible mechanism of interaction was proposed based on multi-technique experimental results.