Studies On The Short ?-helical Peptides Assembly For Selective Capture Enantiomers

Short peptides that self-assemble into nanostructures are of enormous interest for biological,medical,and biotechnological applications because the design of model peptides exhibiting a high tendency for self-assembled structure formation proved to be an ideal target for mimicking biological activities of proteins.The formation of well-defined peptide assemblies depends critically not only on their amino acid sequence but also on their folded secondary structure.Such assemblies include tubules from cyclic peptides,porous cages from three-armed peptides,nanofibers from sequence-controlled short peptides,vesicles from linear block co-peptides,toroids from cyclic block co-peptides,and nanosheets from collagen mimic short peptides.However,the formation of nanostructures by the self-assembly of such short peptides is mostly based on a ?-sheet arrangement of peptide motifs because the folding of short peptides into an ?-helical structure is accompanied by large entropic cost related to the folding of short peptide chains.Stabilizing the folded forms of short ?-peptides is thus prerequisite for the peptide chains to assemble into desired nanostructures.Methods achieved to stabilize ?-helical structures include covalent bridging amino acid side chains,metal chelates,helix nucleation,and molecular crowding.In addition,to these strategies,cyclization of peptides was also proved to be an efficient approach to stabilizing an ?-helical structure through reducing conformational entropic penalty associated with chain folding.We have demonstrated that macrocyclization of the linear peptide precursors with a random coil conformation enforces the peptide chains to adopt an ?-helical structure.The resulting helical peptides self-assemble into undulated nanofibers through 1-dimensional stacking of elementary micelles.We have also shown that cyclization of short peptides through a ?-sheet linker induces an ?-helical conformation through aggregation of the ?-sheet peptides.However,most of the short ?-peptides are far from dynamic conformational switching between random coil and helical states which are essential for generating switchable peptide nanostructures because the helical conformation is stabilized by covalent or non-covalent bond stitching incompatible with dynamic motion.Therefore,the challenging target in peptide assembly based on ?-helical peptides is how to confer dynamic switching functions with their conformations.Considering that the structural transformations of proteins originate from the conformational change of the peptide chains,the design of short ?-helical peptides that exhibit high tendencies for medium-induced conformational changes is anticipated to be an ideal target for the construction of dynamic peptide nanostructures.To address this challenge,we considered that lateral grafting of a short ?-helical peptide with oligoether dendrons would drive a random coil conformation to fold into an ?-helical structure which,in turn,self-assembles into well-defined peptide nanostructures due to thermal dehydration of oligoether chains.The thermal dehydration of oligoether side chains would enforce random coil peptide backbones to adopt a helical conformation through enhanced hydrophobic interactions between oligoether side chains and peptide backbones to minimize water influence on ?-helical peptide hydrogen bonds.Furthermore,the lateral grafting would drive the induced ?-helical peptides to align parallel to the 2-dimensional plane to form anisotropic membrane structures with helical voids between the helical peptide chains.There are three chapters in this paper.The chapter 1 and chapter 2 have published in the J.Am.Chem.Soc.2016.The chapter 1 and chapter 2 are focused on the function of dynamic switching of ?-helical peptide with their conformations.The chapter 3 is the work which we are focused on now.In the chapter 1,we introduce how to confer reversible switching between random coil and ?-helical structure We thought if we synthesis the peptide grafting with oligoether dendrons,the thermal dehydration of oligoether side chains would enforce random coil peptide backbones to adopt a helical conformation through enhanced hydrophobic interactions between oligoether side chains and peptide backbones to minimize water influence on ?-helical peptide hydrogen bonds.In the chapter 2,we show the reversible ?-peptide nanodisks and vesicles based on flat membrane assembly of ?-helical peptides that undergo reversible switching between assembly and disassembly states triggered by a thermal switch.The self-assembled structures consist of the lateral association of rod-like ?-helical peptides which allow the assembly to function as an enantioselective membrane.In particular,the hollow vesicles can spontaneously capture a racemic mixture through the self-formation of membrane walls in response to a thermal signal and enantioselectively release racemic molecules through preferential diffusion across the vesicular walls.In the chapter 3,we show some work which we fcous on new.The main purpose is how to confer the higher ee value with the ?-helical enantioselective membrane,and show the possibly of chiral reaction with this enantioselective membranes.