Direct Probing of the Free-Energy Penalty for Helix Reversals and Chiral Mismatches in Chiral Supramolecular Polymers

Abstract

The amplification of chirality, where a small imbalance in a chiral constituent is propagated into a strong optical purity, can occur in the spontaneous formation of helical 1-D stacks of molecules stabilized by hydrogen bonding, also known as supramolecular polymers. We have extended a statistical model by van Gestel et al. describing the highly nonlinear relationship between supramolecular helicity and enantiomeric excess for mixtures of enantiomers (the majority-rules effect) and quantitatively account for how this affects the thermodynamic stability of the assemblies. Our method allows for a direct comparison with experimental data, providing an unambiguous determination of the key parameters of the model (i.e., the mismatch and the helix reversal penalties). We demonstrate the successful application of this model to calorimetry data for bis-urea-based helical nanotubes, showing that reversals in the handedness of these nanotubes are not all that rare even though the helix reversal penalty is fairly large. By contrast, the mismatch penalty we obtain is small, implying that a large proportion of enantiomers are present in tube fractions not of their preferred handedness.

Emergence of Homochiral Benzene-1,3,5-tricarboxamide Helical Assemblies and Catalysts upon Addition of an Achiral Monomer

“…In comparison to previously reported BTA mixtures, the better chirality amplification properties observed in the present system are likely related to its higher HRP value (Table ). , BTA helices embedding a-BTA exhibit a similar extent of amplification of chirality in comparison to triphenylamine trisamide and bisurea , based assemblies, which is well substantiated by their remarkably close energetic parameters.…”

Controlling Mirror Symmetry Breaking and Network Formation in Liquid Crystalline Cubic, Isotropic Liquid and Crystalline Phases of Benzil‐Based Polycatenars

“…Chirality synchronization of the local helical structure by network formation, suppressing helix reversal defects, [63] appears to be the key feature required for mirror symmetry breaking of polycatenar mesogens in the liquid, LC and soft crystalline states. The helical networks, developing in the Iso 1 /Iso 1 [ * ] and Cub bi Ia d / I 23 [ * ] phases, can obviously be retained after crystallization of the aromatic cores in the optically isotropic crystalline mesophases of compounds 3/ 2 Y n , where the polyaromatic cores and parts of the alkyl chains assume a crystalline packing in the networks and the disordered segments of the alkyl chains fill the remaining space.…”

“…Chiralitys ynchronization of the local helical structure by network formation, suppressing helix reversal defects, [63] appears to be the key feature required for mirror symmetry breaking of polycatenar mesogensi nt he liquid,L Ca nd soft crystalline states. The helical networks, developing in the Iso 1 /Iso 1…”

Impact of Molecular Size and Shape on the Supramolecular Co‐Assembly of Chiral Tricarboxamides: A Comparative Study

“…[17,18] The balance between MMP and the enthalpy gain experienced by the system upon the formation of the correspondings upramolecular polymer bias the final helical outcome of the co-assembly.I mportantly,d espite the interesti ne lucidating the energetic parameters to design efficient chiral co-assemblies and the large number of supramolecular polymers exhibitingc hiral amplification, very few reports quantify the helical reversal penalty (HRP) and/orM MP parameters. [17][18][19] Indeed, examples in which self-assembling units with similar shape and identical noncovalent forces operating in the supramolecular copolymerization are compared in terms of chiral amplification are very scarce. In fact, to the best of our knowledge,t his comparative study has only been developed for 1,3,5-benzenetricarboxamides (BTAs) and oligo(phenylenee thynylene) tricarboxamides (OPE-TAs) ( Figure 1).…”