Bioinspired Design of an Uncharged Ambipolar Helical Scaffold To Achieve Efficient Solid-State Proton Conduction

This work demonstrates highly efficient solid-state proton conduction in helical organic scaffolds inspired by the biomolecule gramicidin A. The scaffold, 1, derived from a pyridine-2,6-dicarboxamide (PDC) residue adopts a helical conformation that is stabilized by a network of strong bifurcated intramolecular H-bonds between the polar residues that align the inner (concave) face of the molecule, while the aromatic units in 1 are oriented outwards. As a result, the helix attains an ambipolar nature just like gramicidin A. Two different solid forms of 1 could be isolated: a yellow solid from high-polarity solvents and an orange solid from low-polarity solvents. Single-crystal X-ray diffraction (SCXRD) studies showed that in the former, molecules of 1 are stacked in a homochiral fashion, while in the latter heterochiral stacks of 1 were present. The yellow form exhibited an almost similar to 300-fold higher conductivity (of up to 0.12 mS cm(-1) at 95 degrees C and 95 % relative humidity) than the orange form as a result of closer intermolecular proximity and lower activation energy of 0.098 eV, thus indicating a Grotthus mechanism of proton transport. This study establishes the key role of bioinspired design and controlled stereo-organization of such discrete uncharged organic molecules in achieving efficient solid-state proton conduction.

Automated summary

This work demonstrates highly efficient solid-state proton conduction in helical organic scaffolds inspired by the biomolecule gramicidin A. The helix attains an ambipolar nature just like gramicidin A, and the yellow form of the scaffold exhibits a significantly higher conductivity than the orange form. The study highlights the importance of bioinspired design and controlled stereo-organization in achieving efficient solid-state proton conduction.