Chirality Control Of Supramolecular Gels From Amino Acid Derivatives By Achiral Factors

The field of supramolecular gels based on amino acid and their derivatives as building blocks has attracted great interests and witnessed great progress recently,due to their excellent biocompatibility,designable ability of molecules and respond to various external stimuli.Chirality is the basic features of amino acids(with the exception of glycine).More importantly,supramolecular chirality of these gels exhibits excellent stimuli-responsiveness,which can be modulated by external stimuli,due to the dynamic characteristics of the non-covalent interactions.Dynamic supramolecular chiral materials have potential value and significance in circularly polarized luminescence(CPL)materials,chiral recognition,biomedical materials and asymmetric catalysis.The research of controlled chirality of supramolecular gels through achiral factors provides novel thoughts and methods for the study of chiral scientific issues.Herein,the co-assembled systems composed of phenylalanine-glycine-based enantiomers and bipyridines are developed.The inversion of their supramolecular chirality can be triggered by stoichiometry.With regards to tuning the chirality of the nanostructures,a facile route is developed through the coordination interaction between metal ions and phenylalanine derived supramolecular hydrogelators.The coordination could lead to the inversion of supramolecular chirality by varying metal ions or gelator structures.Furthermore,the twist pitch and diameter of the chiral nanostructures could also be well-regulated with metal ions.Having control over the supramolecular chirality through multiexternal stimulators provides many possibilities in realizing functional chiral materials.Based on this idea,new alanine-based organogelators were designed and their self-assembled supramolecular chirality can be regulated by temperature,ultrasound,and even polarity of solvents.The contents and results of the thesis are as follows:1.Stoichiometry-controlled inversion of supramolecular chirality innanostructures co-assembled with bipyridines1)A new phenylalanine-glycine-based hydrogelators have been designed and synthesized,which can co-assemble with achiral bis(pyridinyl)derivatives to form hydrogels.2)It is found that the handedness of these chiral twists can be inverted by stoichiometry in co-assembled system,which was confirmed by a set of techniques including SEM,CD and VCD.3)To gain insight into the co-assembly mechanism of the hydrogels,FTIR,~1H NMR and XRD analysises were used.It was confirmed that the intermolecular hydrogen bonds and?-?stacking between the enantiomers and the achiral molecules are crucial factors for the inversion.2.Metal-ion-mediated supramolecular chirality of phenylalanine based hydrogels1)By changing the achiral substituent,phenylalanine-based hydrogelators have been designed and synthesized,which can self-assemble into hydrogels with different metal ions.2)Only changing metal ions could dramatically influence the overall chiral properties including the handedness,twist pitch and diameter of the supramolecular aggregates.Furthermore,the chirality of metal supramolecular aggregates could also be tuned by only changing achiral substituents rather than altering the inherent chirality of enantiomeric monomers.All these have been confirmed by SEM,CD and VCD.3)The results of FTIR and XRD suggested that the cooperative effect of intermolecular hydrogen bonding between the amide units and coordination interaction between the carbonyl groups and metal ions is proposed to account for the hierarchical nanostructure.3.Modulating supramolecular chirality in alanine derived assemblies by multiple external stimuli1)A new alanine-based organogelator was designed,which can form gels through heating-cooling and ultrasonication methods.2)SEM,CD and VCD confirm that the self-assembled supramolecular chirality can be regulated by temperature,ultrasound,and even polarity of solvents.3)The modulations are mainly due to the hydrogen bonds between gelators and solvent-gelator interactions,resulting in changes of the molecular arrangement and subsequent self-assembled nanostructures,which is confirmed by a set of techniques including FTIR,XRD and SC-XRD.