Aggregation-Induced Chirality: Twist and Stacking Handedness of the Biphenylene Groups of n-C₁₂H₂₅O-BP-CO-Ala-Ala Dipeptides

Abstract

In mixtures of water and dimethyl sulfoxide, 4'-(n-dodecyloxy)-1,1'-biphenyl-4-carbonyl Ala-Ala dipeptides can self-assemble into tubular structures that are formed by coiled nanoribbons. The twist and stacking handedness of biphenylene groups were studied using circular dichroism and confirmed by theoretical chemical calculations. The handedness of the coiled nanoribbons and the stacking handedness of biphenylene groups are controlled by the chirality of alanine at the C-terminus, whereas the twist handedness of biphenylene groups is determined by the chirality of alanine at the N-terminus. H NMR spectra indicated that the hydrogen bond formed by the N-H group of alanine at the N-terminus plays an important role in the formation of organic self-assemblies. On the basis of small-angle X-ray scattering characterization, a dimer structure was proposed to form through the terminal COOH groups.

Synthesis and Properties of New Alkyl Alanine Dipeptides Based on Difluoroboron β‐diketonates

“…The FE‐SEM images indicate that the handedness of the self‐assemblies is controlled by the chirality of the alanine near the alkyl chain. Such observation of handedness is quite similar to the previous report …”

“…In the field‐emission scanning electron microscopy (FE‐SEM) images (Figure ), all of the four dipeptide derivatives 4 could self‐assemble into twisted nanoribbons in methanol. Unlike the compounds with linkage of a biphenyl group and alanine dipeptides in our previous studies, no nano‐ or micro‐tubes was observed. The handedness of nanoribbons for (L, L)‐ 4 and (L, D)‐ 4 is left (Figure , a and b), while that of nanoribbons for (D, L)‐ 4 and (D, D)‐ 4 is right (Figure , c and d).…”

“…As the temperature decreased to 25 °C, two protons were observed at 8.43 and 7.96 ppm (Figure ). The chemical shifts move downfield at 25 °C, indicating the formation of hydrogen bonding among the molecules , . Similar results are found for (L, L)‐ 4 , (L, D)‐ 4 and (D, L)‐ 4 (Figure S7).…”

“…As shown in Scheme , the β ‐diketone ligand 1 was synthesized by Claisen condensation with NaH, and the difluoroboron complex 2 was achieved with BF 3 · OEt 2 with previously described method . Similar to those procedures reported in the literature,, the four dipeptides C 10 H 21 CO‐Ala‐Ala‐OH ( 3 ) were prepared starting from the manual solid phase peptide synthesis (SPPS) procedure, using the corresponding Fmoc‐protected alanine dipeptide and 2‐chlorotrityl chloride resin. After the removal of Fmoc‐ group, the N ‐terminal of the dipeptides was coupled with undecylic acid (C 10 H 21 COOH) in the presence of DIEA using O‐(benzotriazol‐1‐yl)‐N,N,N′,N′‐tetramethyluronium hexafluorophosphate/1‐hydroxybenzotriazole (HBTU/HOBt) as coupling reagents.…”

Effect of Stereochemistry on Chirality and Gelation Properties of Supramolecular Self‐Assemblies

“…The above SEM results clearly indicated that the supramolecular chirality was solely determined by the chirality of the amino acid adjacent to the benzene core, irrespective of the absolute configuration of the terminal amino acid. This finding was contradictory to some previous reports that the supramolecular chirality was dictated by the C‐terminal chirality, which was called “C‐terminal rule.” [46–48] In fact, the gelators in those systems were amphiphilic molecules and upon self‐assembly the C‐terminal hydrophilic head group residues were located on the surface of the self‐assembled aggregates. It could be anticipated that terminal noncovalent interactions among gelators or solvents play a profound effect on controlling the supramolecular morphology and handedness [16] .…”