| Imidazolium surfactants are a new generation of amphiphilic molecules. For l-alkyl-3-methylimidazolium bromine, it is ionic liquid at room temperature when its alkyl chain is shorter. It has specific properties such as no significant vapor pressures, nonflammability, no kindling point and high stableness. Therefore, it has attracted much attention on chemical separation, organic synthesis, nano materials, solar cell and so on. But when alkyl chain is longer, it can be seen as a cationic surfactant. Compared with quaternary ammonium surfactant, imidazolium surfactant has the higher surface activity, and it has been widely used in many areas.The imidazolium Gemini surfactant has prominent advantages, because it owns the properties of traditional Gemini surfactant and single-chain imidazolium surfactant. The study on its aggregation behavior and the interaction with biomacromolecules would be very important in the food, cosmetics and pharmaceutical industries. In this thesis, a series of imidazolium Gemini surfactants with different hydrophobic chain and spacer length are synthesized, and their aggregation behavior in solution and on solid surface have been studied. Besides, the interactions between imidazolium Gemini surfactant and proteins (gelatin and BSA) have been investigated. This thesis is divided into six parts.In the first section, the properties and synthesized methods of Gemini surfactant, the study progress on the interaction between surfactant and protein, and the importance of study on Gemini surfactant and protein are summarized.In the second section, a series of imidazolium Gemini surfactants with different hydrophobic chain and spacer length are synthesized, and their molecular structures are characterized by 1HNMR, LC-MS and elemental analysis. The results prove that these surfactants all are objective products.In the third section, the surface activity and micellization properties of the gemini imidazolium surfactants are investigated by means of surface tension, electrical conductivity and fluorescence measurements. The results show that the Gemini surfactant with shorter spacer has the higher surface activity. Compared with micellization, the adsorption at the air/aqueous interface for Gemini surfactant with shorter spacer is easier. For the Gemini surfactant with longer hydrophobic chain, it has the higher efficiency and lower effectiveness for lowering the surface tension. The hydrophilic group of imidazolium Gemini surfactant opposes micellization, while the methylene unit of the hydrophobic group favors micellization, and the contribution of methylene unit in Gemini surfactant to the micellization is higher than that of its corresponding monomer. The degree of counterion binding to micelle decreases with increasing temperature, suggesting that the micelle would be smaller in size at higher temperature. The micellization of [C12-2-C12im]Br2, [C12-4-C12im]Br2, [C10-4-C10im]Br2and [C14-4-C14im]Br2 are entropy driven; For [C12-6-C12im]Br2, it is enthalpy-driven at low temperature, and entropy-driven at high temperature. The fluorescence measurements show that the micropolarity of micelles increases and aggregation numbers decreases with increasing the spacer length, but hydrophobic chain length does not has obviously effect on the micropolarity, and the aggregation numbers increase with increasing the hydrophobic chain length.In the fourth section, The aggregation of imidazolium Gemini surfactant [C12-4-C12im]Br2 on silicon wafer, which is compared with its monomer [C12mim]Br, have been studied by AFM, contact angle, IR and computer simulation. For [C12-4-C12im]Br2, with increasing the concentration, the surfactants aggregation experience an evolving course from no aggregates to circular islands, then to semi-continuous islands, and finally the whole silica surface is nearly covered with the surfactant aggregates in a bilayer structure. No matter what kind of aggregates exist, the height values all keep at about 3.0nm and close to the bilayer thickness. But for its corresponding monomer [C12mim]Br, the layer numbers are increasing with the increase of surfactant concentration and finally the molecules form the multilayer structure. The contact angles results indicate the adsorbed surfactant molecules could be thought to distribute randomly on the silica surface with hydrophobic tails facing the air below the CSAC. But above the CSAC, the [C12-4-C12im]Br2 aggregates exist with the hydrophilic head groups facing the air. While for [C12mim]Br, with increasing its concentration, the hydrophobic chains and hydrophilic head groups face the air by turns. The IR spectra suggests the methylene chain of [C12-4-C12im]Br2 is less ordered packing than [C12mim]Br inside the aggregates at 5.0cmc, and this may be the one reason to determine the larger contact angle of [C12-4-C12im]Br2 than that of [C12mim]Br.In the fifth section, Circular dichroism (CD), fluorescence and UV-vis absorption methods have been used to investigate the interactions between bovine serum albumin (BSA) and a series of imidazolium gemini surfactants. For comparison, the quaternary ammonium salt-type gemini surfactant and their corresponding monomers have been also selected. The results show that the micropolariry (I1/I3) of BSA solution in the presence of gemini surfactant with a shorter spacer or with a longer hydrophobic chain is lower. Compared with quaternary ammonium gemini surfactant, micropolarity of BSA solution in the presence of imidazolium gemini surfactant is higher. But for [C12mim]Br/BSA and DTAB/BSA, their micropolarities are nearly the same when the surfactants binding on BSA reach saturation. The imidazolium gemini surfactant with a shorter spacer or with a longer hydrophobic chain has a larger effect on BSA unfolding, and they have the stronger ability than quaternary ammonium surfactants and its corresponding monomer binding with BSA. This can be confirmed by the circular dichroism and fluorescence spectra measurements. The synchronous fluorescence spectra show that the surfactants mainly interact with tryptophan residues of BSA. Fluorescence quenching of BSA by the surfactants are the static quenching procedures.In the sixth section, the surface properties of gelatin solutions without and with imidazolium gemini surfactants have been investigated via surface shear and dilational rheology as well as surface tension measurements. Both the surface shear and dilational rheological properties show that the strength of gelatin film is enhanced in the presence of 0.005 mmol/L [C12-4-C12im]Br2, and the storage modulus is larger than loss modulus for gelatin/[C12-4-C12im]Br2, indicating it is an elastic film. With increasing the concentration of imidazolium gemini surfactant, the dilational modulus increases firstly and then passes through a maximum value. This is because the gelatin chains can interact with surfactant molecules through electrostatic and hydrophobic interaction at low surfactant concentration, and then form the cross-linked network structure. But after that, at higher surfactant concentration, the surfactant molecules begin to disrupt the network structure and result in the decrease of dilational modulus. The structure of the gemini surfactant has great effect on the interfacial viscoelastic modulus of gelatin, it is found that the gelatin film in the presence of imidazolium gemini surfactant with longer hydrophobic chain or longer spacer reveals the larger strength. Although the surface tension of gelatin/surfactant mixed solution is identical to that of the pure surfactant solution at high surfactant concentration, the dilational modulus shows that the surfactant molecules are unable to fully replace gelatin molecules from the air/water surface.
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