Supramolecular helix and β-sheet through self-assembly of two isomeric tetrapeptides in crystals and formation of filaments and ribbons in the solid state

Abstract

Single crystal X-ray diffraction studies show that the β-turn structure of tetrapeptide I, Boc-Gly-Phe-Aib-Leu-OMe (Aib: α-amino isobutyric acid) self-assembles to a supramolecular helix through intermolecular hydrogen bonding along the crystallographic a axis. By contrast the β-turn structure of an isomeric tetrapeptide II, Boc-Gly-Leu-Aib-Phe-OMe self-assembles to a supramolecular β-sheet-like structure via a two-dimensional (a, b axis) intermolecular hydrogen bonding network and π-π interactions. FT-IR studies of the peptides revealed that both of them form intermolecularly hydrogen bonded supramolecular structures in the solid state. Field emission scanning electron micrographs (FE-SEM) of the dried fibrous materials of the peptides show different morphologies, non-twisted filaments in case of peptide I and non-twisted filaments and ribbon-like structures in case of peptide II.

Keywords:

• self-assembly
• supramolecular helix
• supramolecular β-sheet
• peptides
• filaments
• ribbon

Acknowledgements

A. Dutta is grateful to the CSIR, New Delhi for offering her a Junior Research Fellowship (JRF) and A. Dutt to UGC, New Delhi for offering her a Senior Research Fellowship (SRF). The financial assistance of University of Calcutta is acknowledged. We thank EPSRC and the University of Reading, UK for funds for Oxford Diffraction X-Calibur CCD diffractometer.