| Stable supramolecular gels are formed by self-assembly of Low molecular mass organic gelator(sLMOG)through the non-covalent bond, such as intermolecular hydrogen bonding,π-πinteraction, hydrophobic interaction, electrostatic interaction and van der Waals force. The low molecules compounds with chiral structure used as a gelator will self-assemble to form a unique supramolecular helical structure, and generate supramolecular chirality. Therefore, circular dichroism spectroscopy can be used to investigate the supramolecular self-assembly process of the chiral structure. Molecularly imprinted supramolecular polymer materials were prepared by self-assembly of chiral gelators in polymerized solvent, then the supramolecular aggregates were removed by extraction, leaving the chiral channels in the polymer matrix, which was helpful for improving the molecular recognition capacity of chiral substrate.This thesis is consisted of several sections as the following:(1)A series of sorbitol-based gelators with chiral structures(DBS,MDBS, DMDBS) were used as gelators. Their self-assembly and disassembly behaviors in different solvents were investigated by using varying temperature circular dichroism technique (CD). The results showed that the chiral characteristics of the gelators in the self-assembly and disassembly process is different. There were enhanced CD signals observed as the time changed because of self-assembly. It was also found that the CD signals of three gelators were decreased with an increase of temperature during the process of disassembly. There is a distinct turning point in a certain range of temperature, which is correspond with sol-gel phase transition temperature, suggesting that the disassembly of gelator aggregates occurred. The dynamics of self-assembly of three gelators were also investigated by CD. These results suggest that self-assembly ability of gelators with chiral structure should be prejudged based on their CD spectra. Thus, the optimized geometries and molecular dipole moment were calculated by utilizing the Spartan program package and density functional theory. The formation mechanism of helical aggregates may involve the ordered stack of benzylidene chromophores. Theπ-πstack of benzylidene groups may enhance polarizable capacity of the molecules, resulting in an increase of molecular dipole moment and enhanced CD signals. The polarity of the solvent also affected the CD spectral in the self-assembly process because of the interaction between gelators and solvents.(2)Under the action of surfactant, the solvent mixtures containing monomerβ-Hydroxyethyl methacrylate(HEMA), photoinitiator and crosslinker and a chiral gelator, N-stearine-N′-steryl-L-Phenylalanine(Bis18-L-Phe),were firstly dispersed into the aqueous suspension, then gelatinized into supramolecular gel droplets. Herein gelator was also used as a chiral template. Subsequently, the suspension was polymerized by UV irradiation to yield novel polymerized supramolecular organogel particles. After extraction of the aggregates of Bis18-L-Phe gelator with ethanol, imprinted supramolecular organogel particles were obtained. The average diameter of these particles was found to be about 240 ?m. DSC and SEM analysis of the imprinted supramolecular organogel particles showed that, after subsequent extraction by ethanol, bis-18-Phe aggregates acting as template are removed from the polymer matrices and the corresponding complementary imprinted cavities matched to the chiral structure of guest molecules. The imprinted particles were loaded as a stationary phase into a column and L- and D-phenylalanine racemic mixtures were used as the mobile phase. The circular dichroism(CD)and optical rotation of the racemic mixtures that flowed through the column indicated that the imprinted supramolecular organogel particles exhibited distinct selective adsorption for L-phenylalanine.(3)The solvent mixtures containingβ-hydroxyethyl methacrylate ( HEMA), methylacrylic acid (MAA), crosslinker (PEGDMA-200),polymerizable gelator N-octadecyl maleamic acid (ODMA)and template molecule Boc-L-Phe were firstly dispersed into the aqueous suspension, then gelatinized into supramolecular gel droplets under the action of surfactant. Subsequently, the suspension was polymerized by UV irradiation to yield novel polymerized supramolecular organogel particles. After extraction of the template molecule Boc-L-Phe with ethanol, imprinted supramolecular organogel particles were obtained. The imprinted particles were loaded as a stationary phase into a column and L- and D-phenylalanine racemic mixtures were used as the mobile phase. It was observed that the chiral separation for L-, D-phenylalanine racemic mixture of the imprinted polymer microspheres by UV-Vis spectrophotometry and optical rotation. The different adsorption capacity of D- and L-Phenylalanine on MIPs with different concentration of templates molecular,different concentration of ODMA,different mass of crosslinking agent were investied , respectively. We found that the polymerization of ODMA fixed and could not be extracted, leaving only the template molecules cavity in the polymer matrix,which excluded the impact of the destruction of gel in the extraction process. The aggregates of ODMA provided three-dimensional network structure enhances the rigidity of imprinted polymer, improving the efficiency of adsorption to a certain extent.
|
PDF Full Text Request