Role of side-chain and chirality of the amino acids on the supramolecular assemblies of dipeptides

The supramolecular self-association of alternating L/L and L/D amino acid-containing dipeptides, Boc-LIle-L-Phe-OMe (1), Boc-L-Ile-d-Phe-OMe (2), Boc-L-Ile-L-Phg-OMe (3 , Phg = phenylglycine), and Boc-LIle-d-Phg-OMe (4) have been investigated. The presence of extra methylene (-CH2-) group on the sidechain of C-terminal Phe-of 1 causes a significant deviation of molecular arrangements from that of 3 . While the molecules in 1 self-assemble to form a single helix-like architecture, the molecules in 3 selfassociate around a water molecule to form a cylinder-like structure in the crystalline state. Alternatively, the observed supramolecular arrangements of 2 and 4 are similar, but deviate from that of 1 and 3 , due to chirality difference. Peptides 2 and 4 exhibit a discontinued double helix-like structure in the crystalline state. While 1 and 3 self-associate to form helical ribbon-like and nano tube-like structures, respectively, both 2 and 4 form nano rod-like structures in solution. (C) 2020 Elsevier B.V. All rights reserved.