Chiral Self-assembly Of Fmoc-tripeptides And Its Applications In Chiral Catalysis And Chiral Separation

Chiral self-assembly of peptides offers an appealing approach for creating chiral nanostructures,which has promising applications in the fields of biology and materials science.Although numerous self-assembled chiral materials have been designed,the precise control of their twisting tendency and their handedness is still a challenge.In this work,we are devoted to the study of the chiral self-assembly of short Fmoc-tripeptides.We designed a series of self-assembling tripeptides bearing different _L-amino acid sequences and explored the effects of amino acid sequence,concentration,solvent or pH on the chiral self-assembly of tripeptides.Furthermore,molecular dynamics simulations（MDs）were used to analyzed the possible mechanisms of self-assembly.Finally,we investigated the application of assembles in chiral catalysis and chiral separation.（1）We designed five pairs of Fmoc-tripeptides:Fmoc-Phe-Phe-X（Fmoc-FFX）and Fmoc-Phe-Trp-X（Fmoc-FWX）,X=His（H）,Arg（R）,Ser（S）,Glu（E）,Asp（D）.We investigated the self-assembly of these tripeptides at pH 6.0.The Fmoc-FWX（X=H,R,S,E or D）trend to form right-handed helices nanostructures while the Fmoc-FFX（X=H,R,S,E or D）trend to form left-handed helical nanostructures.The handedness of helical nanofibers was dictated by the aromatic side chains at the middle amino acid residues.Moreover,the width of the nanofibers indicating the scale of chiral amplification was determined by the charges of the terminal amino acid.（2）We investigated the chiral self-assembly of Fmoc-FWH and Fmoc-FFH with different concentrations and solvent.It was found that concentration has little effect on chiral self-assembly of Fmoc-FWH and Fmoc-FFH.However,solvent can cause the handedness inversion of Fmoc-FWH assembles.Furthermore,we investigated the self-assembly of five pairs of Fmoc-tripeptides in the presence of copper（II）ion(Cu²⁺).The formed tripeptide-Cu²⁺assembles can be used as chiral catalysis for Diels-Alder reaction between aza-chalcone and cyclopentadiene.Fmoc-FFD-Cu²⁺assembles catalyzed the asymmetric reaction with up to 99%yield and 31%ee.（3）We designed a novel tripeptide,Fmoc-Phe-Phe-Lys（Fmoc-FFK）.We investigated its self-assembling behavior at different pH.It was found that the Fmoc-FFK peptide self-assembled into right-handed helical ribbons at pH 2-3.Furthermore,with the increase of pH,lamellar structures formed by Fmoc-FFK assembles appeared in the alkaline environment.Finally,the Fmoc-FFK assembles can be used for the chiral separation ofα-methylbenzylamine enantiomers with up to 80.5%ee.