Studies Of Metal Induced Fmoc-Amino Acid Supramolecular Hydrogels

Supramolecular self-assembly chemistry has made a breakthrough in the traditional research field of molecular chemistry based on covalent bonds.In this paper,single and multiple Fmoc-amino acids were taken as the research object,and the microstructure,mechanical strength and assembly mode of supramolecular hydrogels induced by metal ions were studied,and the possible assembly mechanism was proposed.Potential applications of supramolecular hydrogels are also explored.This thesis mainly includes three parts:In chapter 1,we briefly introduced the basic concepts of supramolecular chemistry and supramolecular assembly,several common supramolecular structures,and the properties and functional applications of supramolecular hydrogels based on aromatic amino acids and polypeptides.In the second chapter,the preparation and function of metal ion-induced Fmoc-alanine hydrogel were studied.Aryl polypeptides are a good self-assembling primitive molecule due to their ?-? stacking and hydrogen bonding.However,aryl amino acids are difficult to form stable aggregates through self-assembly due to the small number of hydrogen bond binding sites.We found that metal ions such as Cu2+ and Eu3+ could induce Fmoc-Ala to form hydrogel structure with stable properties,The microstructure of the gel was observed by SEM and TEM,the microstructure of the Cu2+-induced hydrogels was 0.5 ?m film structure,Eu3+-induced hydrogels are assembled into 50-300 nm in diameter of one-dimensional nano fibers,when two metal ions were mixed in equal proportions,the hydrogel assembly morphology was transformed into a cross-linked 3D network with an average diameter of about 20-100 nm.The mechanical strength of the three hydrogels was characterized by rheological test,and it was found that the three hydrogels were stable hydrogels with high mechanical strength,and the yield stress value exceeded 1000Pa.Based on infrared spectrum,ultraviolet spectrum and small Angle X ray scattering spectrum analysis,we put forward the possible mechanism of the hydrogel assembly.First,two Fmoc-Ala molecules formed overlapping antiparallel ?-? stacking of double-layer structure unit,after the metal ions and carboxylic acid coordination effect and hydrogen bonding interaction between the amide bond,the lamellar-like structure was formed.All these three kinds of supramolecular force generated one-dimensional nanometer fiber,and then continue assembled into flake or fiber network.Surprisingly,this supranolecular hydrogel system has a unique etching-response to molecules containing aromatic groups and amino groups.When different amino compounds or aromatic compounds are added into the gel,specific etching phenomena will occur in the gel,and the rate and morphology of dissolution are all different.It is believed that this unique guest-responsive hydrogels have potential applications in molecular recognition and pre-packaged materials.In chapter 3,the co-assembly behavior of metal ions and complex Fmoc-amino acids and the morphological control of the assembly were studied.We first studied the supramolecular assembly of Zn2+ with a single Fmoc-Ala or Fmoc-Val.Zn2+ and Fmoc-Ala were assembled into an unstable white gel,which would collapse in a short time to form a turbidity solution.Flaky aggregates of several microns could be observed under SEM and TEM.Zn2+ and Fmoc-Val can be assembled into a stable yellow gel within a certain concentration range,and the microstructure is a crosslinking network of about 20 nm fibers.Then we prepared Fmoc-Ala and Fmoc-Val into a mixed solution in a certain proportion,and then used Zn2+ to induce amino acids to form supramolecular aggregates.We found that it will be a transparent hydrogel when the two kinds of amino acid ratio is 1:1.Under scanning electron microscope,the microstructure of transparent hydrogel was observed as the co-existence of nano-fiber and nano-sphere.This indicates that the supramolecular assembly of complex Fmoc-amino acids and Zn2+ is different from that of single amino acid systems.Under the rheological test,we found that the stable hydrogels with different strength could be prepared by regulating the different proportions of the two amino acids.It is believed that this metal-induced hydrogel system based on complex Fmoc-amino acids can provide strong support for our understanding of multi-supramolecular assembly.