Supramolecular Organic Gels And Micro/nanostructures Self-assembled From Aromatic Amide Building Blocks

Aromatic amide derivatives are one of the most widely used building blocks in the construction of self-assembled nanomaterials.?-? stacking and hydrogen bond interactions play a vital role in the self-assembly process.The aromatic plane of aromatic amide derivatives is the main group of forming ?-? stacking interactions.Complementary hydrogen bonds are one of the most important non-covalent interactions and have been widely used in the construction of micro/nanostructures.Generally speaking,N-H acting as the hydrogen bond donor and C=O acting as the hydrogen bond receptor,provide a strong(about 2.0 A)and directional complementary hydrogen bond interaction in the arnide groups of aromatic amide derivatives.Aromatic amide derivatives have been used to prepare micro/nanostructures of various dimensions and scales via their strong intermolecular interactions.By rational design,assemblies from aromatic amide derivatives are endowed with a variety of functions,showing great potential in the application of stimulation-responsive materials,photoelectric materials and biomaterials,which have attracted people's continuous attention.In this thesis,a series of organic small molecule building blocks based on aromatic amide derivatives are designed and synthesized,which demonstrat good performance in constructing various self-assembled micro/nanostructures.In particular,the self-assembled organic supramolecular gels,controllable hierarchical self-assembled behavior and morphological transformation from organic building blocks are investigated in depth.Then the formation mechanism and molecular arrangement modes of these supramolecular structures are discussed and summarized.In addition,we also explore the applications of these supramolecular assemblies in intelligent material design,oil-containing water treatment and other fields.This thesis mainly includes the following four parts:1.IntroductionIn this chapter,we mainly introduce the background and basis of this thesis,and briefly introduce the concept of supramolecular self-assembly.Noncovalent bond interactions including hydrogen bonding,aromatic stacking,hydrophobic,host and guest,ionic bond and other common interactions involved in the self-assembly are introduced.Several morphologies of supramolecular micro/nanostructures,including supramolecular vesicles,micelles and nanoparticles,and nanotubes are demonstrated.The basic concept,classification,formation mechanism and applications of supramolecular gels are summarized.In this part,we also introduce some important progress in the construction of supramolecular gels from typical aromatic amides such as amino acid derivative gelators and cholesterol derivative gelators.Finally,The applications of supramolecular functional materials in biomedicine,information technology and environmental science are briefly summarized at the end of this chapter.2.Design of arylserine-based organic gels and its application in purification of oily waterWith the continuous increase of oil-containing water discharge and marine oil pollution,the environment and ecological system are suffering irreversible damage.Separation and recovery of water and oil biphasic systems has always been a major challenge.PSOGs,derived from LMOGs,can selectively gelate oil in the oil-water biphasic system,which are easy to be collected and recovered.However,in the practical application,problems such as poor selectivity,long gelation time and poor recovery performance are the great challenges in developing new high efficiency gelators.To solve this problem,we have designed a series of Fmoc-amino acid derivatives and studied their gelation abilities on a series of petroleum products.Among them,serine-based compounds show excellent gel performance for petroleum products,while gels from alanine-based compounds are unstable for petroleum products,and phenylalanine-based compounds could not gel petroleum products.Since the Fmoc-amino acid derivatives with different substituents exhibit different assembly properties,we also have investigated the formation mechanism and molecular arrangement modes of these three kinds of assemblies.In addition,serine-based gelators show good selectivity for gelling oil in water.We have explored the influence of solvent system,oil type,critical gelator concentration,gelation time and inorganic salt solution in the gel system.Further studies on the variation of serine-based gelators demonstrate a considerable structure-function relationship between oil gelation performance and the molecular structure.The gelation time and mechanical strength both showed the dependence on the alkyl chain length.The ability of removal and recovery of treated oil is an important factor for practical application of gelators,and the fact that gels could be hydrolyzed by acid or pyrolysis provides the possibility for the recovery of the treated oil in actual oil spill.These gels exhibit potential applications in an effective treatment of marine oil spills and oily wastewater from daily life and industry.3.Solvent-tuned micro/nanostructures assembled from modified octadecylcarbamate with an anthracen moietyThe formation and transformation of molecular self-assembly structures under weak intermolecular interactions are important.The construction of micro/nano-structures with controllable scale,dimension and morphology is of special importance for the preparation of high-performance nanomaterials.As an important part of the self-assembly system,solvent environment plays a crucial role in regulating the self-assembly process.Therefore,it is significant to understand the organization mechanism of complex systems to regulate noncovalent interactions by regulating solvents to facilitate the evolution of self-assembly to optimized supramolecular structures.In this chapter,we synthesize an A-9-YMOC building block.Due to the rigid anthracyl,amide ester group and long alkyl chain,providing ?-? stacking,hydrogen bond interactions and van der Waals force in the molecule,A-9-YMOC has a very good self-assembly performance.It its the simple molecular structure and obvious intermolecular interaction make possible to study the influence of solvents on self-assembly process.In this chapter,we mainly studies the self-assembly ability of A-9-YMOC molecule to form ordered micro/nanostructure and the influence of solvents with different polarity on the self-assembly behavior.We have found that the solute-solvent interactions in different polar solvents can subtly alter the molecular arrangement patterns and thus affect the self-assembled nanostructures.The ?-?stacking interactions in polar solvents direct the self-assembly process,and the aggregates possess a morphology of nano-flower structures.In non-polar solvents,hydrogen bond interactions direct the self-assembly process and the aggregates with a nano-fiber morphology.We have put forward ?-induced solvents and hydrogen bond induced solvents,and proposed different molecular arrangement patterns in different supramolecular structures by infrared spectrum,fluorescence spectrum and X-ray powder diffraction.This work provides a theoretical basis for the design and preparation of functional aggregates from organic small molecules and the regulation of micro/nanostructures in terms of interactions between solvents.4.Gel transformation with supramolecular chirality regulation based on an Fmoc-amino acid building blockChiralities or chiral micro/nanostructures are ubiquitous in various biological systems.Among them,controlling of chiral amplification in the self-assembly process of chiral compounds is particularly important in the evolution of life and supramolecular materials.Self-assembled micro/nanostructures in the gel phase can be regulated by chiral or achiral molecules,which may bring about significant changes in gel performance.On the basis of reasonable design of supramolecular gelators,a large number of functional materials have been prepared.Amphiphilic molecules based on Fmoc amino acids have been proved as attractive building blocks with biocompatibility.In order to regulate supramolecular chiralities and investigate its effect on gel performance,Fmoc-L-Asn-OH is used as the model molecule in this chapter,and its self-assembly behavior in good/poor solvent system(DMSO/H2O)has been studied.By controlling the solvent environment,we achieve the transformation of gel-precipitation-gel,including the transformation of morphologies,supramolecular chiralities and gel properties during the self-assembly process.In this process,the proportion of water has a significant influence on the formation and properties of the gel.Fmoc-L-Asn-OH molecules can form gels in DMSO/H2O mixed solvents with high water fraction or low water fraction,and their morphologies are flat nanofibers and nanotwist fibers,respectively.The latter gel possess the appearance of supramolecular chirality.However,in solvents with moderate fraction of water,the formation of gel is replaced by precipitated aggregates with nanosheets morphology.Further mechanism studies show that the ?-? stacking interactions between aromatic Fmoc groups and the hydrogen bond interaction between amide groups play an important role in the self-assembly process of the gels,and the kinetics and thermodynamics controll the formation of the two gels,respectively.In addition,the two gels exhibit different thermal stabilities and mechanical properties.The gels have higher thermal stability and lower mechanical properties in the system with less water fraction.This work provides a new method for the regulation of chiral gels with multi-morphological aggregates via self-assembly,and has potential applications in the field of intelligent material design.