Supramolecular Helical Fluid Columns from Self‐Assembly of Homomeric Dipeptides

• Published in: Chemistry : a European journal 2008-11, Vol.14 (33), p.10462-10471
• Main Authors: Yelamaggad, Channabasaveshwar V., Shanker, Govindaswamy, Rao, R. V. Ramana, Rao, Doddamane S. Shankar, Prasad, Subbarao Krishna, Babu, Vommina V. Suresh
• Format: Article
• Language: English
• Subjects: amino acids; Calorimetry, Differential Scanning; Circular Dichroism; Dipeptides - chemistry; gelation; hydrogen bonds; liquid crystals; Microscopy, Electron, Scanning; Models, Chemical; Molecular Structure; peptides; Phase Transition; Spectrophotometry; Spectrophotometry, Infrared; Temperature; X-Ray Diffraction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200801607

Herein, we demonstrate that with the widespread theme of residue patterning and stereochemical restraints of self‐complimenting proteinogenic amino acids, a new and rich class of homomeric dipeptides exhibiting two‐dimensional fluid aggregates with hierarchical ordering can be obtained. In particular, a simple way of achieving a class of functional dipeptides, wherein the first and the second residues chosen are L‐/D‐alanines and L‐/D‐leucines, has been accomplished. The supramolecules synthesized can be regarded as intermediates between polycatenars and taper‐shaped amphiphiles because they possess two lipophilic segments interlinked by a peptide unit (spacer). Two pairs of enantiomers and their respective diastereomers derived from these amino acids are evidenced to self‐organize into a helical columnar phase through hydrogen bonding by means of FTIR, UV/Vis, and chiroptical circular dichroism (CD) spectral analyses as well as by optical, calorimetric, electrical switching, and X‐ray studies. The CD and X‐ray studies have revealed that the form chirality (handedness) and the magnitude of out‐of‐plane fluctuations of the lattice planes of the fluid supramolecular columnar structures are solely directed by the stereochemistry encoded in the spacer. Of special significance, the less frequently found oblique helical columnar phase formed by a pair of enantiomers derived from L‐/D‐alanines, unlike those derived from other amino acids, exhibit ferroelectric behavior; the measured spontaneous polarization is as high as 440 nC cm−2. Besides, all these supramolecules form stable organogels in ethanol and the CD and SEM studies on a representative gel suggest the presence of helical structures. Helical fluid columns: Hexacatenar homomeric dipeptides, the first of their kind, self‐assemble into novel supramolecular helical fluid columns (see figure). Of special significance, a pair of enantiomers derived from L/D‐alanine exhibit ferroelectric behavior with high spontaneous polarization values. Additionally, all these supramolecules form stable organogels (in ethanol) comprising helical fibers.