| Surfactant molecules contain hydrophilic polar groups and hydrophobic chains. In aqueous solutions, after the saturated adsorbtion at the air/water interface, they can self-assemble into diverse aggregates such as spherical micelles, rod-like micelles, worm-like micelles, vesicles, liquid crystallines and so on. Surfactant aggregates have wide-ranging applications as drug delivery, selective membranes, and microreactors depending on their structural properties. Surfactants show rich aggregation behaviors according to their molecular structures and the additives. Most researchers focus on the kinds and structures of aggregates formed by surfactants. However, the phase behavior studies based on the specific molecular structures of surfactants and organic additives are seldom concerned.The aggregation behavior of carboxyl substances and their salts are the main thesis to be investigated in the present paper. We mainly focused on the phase behaviors of mixtures formed by four kinds of carboxyl substances with nonionic surfactants/lecithin in aqueous solutions to summarize the aggregation rules based on the molecular structures.Chapter Ⅰ is a brief introduction of the research background. The concepts of the aggregation behaviors of carboxyl substances and their salts in aqueous solutions were discussed. At the end of this part, the object and scientific significance of this doctoral dissertation are alsopointed out.In chapter Ⅱ, the effects of hydrophobic chains and metal ions on the self-assembly behavior of metal-coordinated surfactant systems were studied. The aggregation behavior of metal-ligand coordination systems is strongly affected by the comprehensive equilibrium between metal-coordination and hydrophobic interaction. Several properties of metal-ligand complexes formed by Mn+-surfactants and CnDMAO can be identified, ⅰ) CnDMAO with longer chains are more favorable to form vesicle bilayers; ⅱ) Bilayers are more likely to form in the presence of fluorocarbon chains than in the presence of corresponding hydrocarbon ones and the Lα phase formed by fluorocarbon chains has a higher viscoelasticity than that formed by hydrocarbon chains; ⅲ) Branched chains are more favorable for the formation of bilayers than linear chains of the same component. The bilayers formed by branched chains are more flexible than those formed by linear chains and the Lα phase exhibits very weak viscoelasticity; ⅳ) The La phase forms more easily in the presence of metal ions with higher coordinated capability, and the viscoelasticity of the Lα phase is affected by the coordinated capability. Based on these results, we can construct an Lα phase with anticipative properties by choosing surfactants with appropriate structures.In chapter Ⅲ, we investigated how bio-peptides curve membrane bilayers of nonbio-amphiphiles. Different membrane bilayers can be tightly controlled due to the different membrane compositions such as lipids, proteins, etc., which result in the changes of physical properties of membrane bilayers and the membrane deformation (lamellar structures to budding, bending and fusion). On the basis of our experimental observations and the calculation of the curvature of membrane bilayers, one can be convinced of the bending membrane bilayers of lipids due to the specific structures of peptide molecules, in which peptide molecules have the same way to bend membrane bilayers of synthesized amphiphiles. For the structural transition of lamellar bilayers observed from the mixtures of GSSG and C18DMAO in water, the variation of curvature energies with different values must be of0and the order kBT. Three factors can control the bending of membrane bilayers:ⅰ) peptide (protein) molecules anchoring to membrane bilayers; ⅱ) steric pressure produced by peptide molecules; ⅲ) much more compact packing of amphiphile hydrophobic chains, and it is similar to "lipid rafts". Combining both previous studies and our observations and calculations, we propose the assembly bilayer changes should be based on the specific structure of peptides and amphiphiles (bio-or synthesized). The assembly rules between peptides and amphiphiles should be generalized in order to enlarge understandings on living and be applied in people’s lives.In chapter IV, we investigated aggregation behaviors induced by the chiral-OH group in the steroid skeletons of different desoxycholic acids. CDC is chenodeoxycholic acid, UDC is ursodeoxycholic acid and C12E4is C12H25(OCH2CH2)4OH. The-OH and-COOH groups in the bile acids participated to form hydrogen bonds. The location and orientation of the different-OH groups led to the formation of different hydrogen bonds. However, due to the orientation and saturation of hydrogen bonding, the chirality of different bile acids molecules induced the formation of different aggregates. For CDC/C12E4/H2O system, at low CDC concentration, with C12E4concentration increasing, vesicles are the main aggregates. When C12E4concentration is fixed, with CDC concentration increasing, the transition from vesicles to stacked lamellar structures can be observed. At very high CDC concentrations, the stacked lamellar structures transform to vesicles with the increase in C12E4concentration. The reasons might be that, at low CDC concentrations, the H+ions dissociate from CDC molecules combine with O atom of C12E4through the electrostatic interaction, which inhibits the undulation of the bilayers formed by C12E4, so it is easy to form vesicles. When CDC concentration increases, the volumes of hydrophobic chains become larger, which induce the increase of the packing parameter P, and the aggregation transfers to stacked lamellar structures. For UDC/C12E4/H2O system, the-OH group at the middle of the steroid skeletons has different chirality to that of CDC. At low UDC concentrations, with the increase in C12E4concentrations, the aggregates formed are mainly vesicles, which is similar to CDC/C12E4/H2O system. When C12E4concentrations are high, the orientation of the-OH groups induces the coexistence of vesicles and lamellar structures. At very high UDC concentrations, with C12E4concentrations increasing, the bilayers transform to gels composed of sheets. The results of SEM, SAXS and rheological measurements indicate that the sheets are formed through the connection of polar groups with each other..In chapter V, the aggregation behaviors of OA/PC/H2O and UA/PC/H2O systems were investigated. The L1/Lα and Lα phases were used to study the drug activities. OA is oleanolic acid, UA is ursolic acid, and PC is lecithin. The drug activities were found dependent on time and concentration, and the time dependence is stronger for UA system. The effect of drug activities of the two-phase is weak. When the concentrations of OA and UA are1mmol·L-1, the aqueous solutions show high viscoelasticity became of the similar molecular structures of OA and UA to cholesterol, for which perhaps the formation of "lipid rafts" stabilizes the vesicle bilayers. However, when the concentrations of OA and UA reach10mmol·L-1, the viscoelasticity of aqueous solutions decreases. We attribute it to the loose packing of molecules in bilayers with the increase in OA and UA concentrations. |
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