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

Abstract

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 ∼300‐fold higher conductivity (of up to 0.12 mS cm−1 at 95 °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.

Self-assembly of water-filled molecular saddles to generate diverse morphologies and high proton conductivity

“…40 Furthermore, we have developed a helical scaffold based on the PDC framework that can exist in two distinct forms (yellow and orange) in polar and nonpolar solvents and also shows high SSPC (up to 1.2 × 10 −1 mS cm −1 at 95 °C and 95% RH). 41 Taking these explorations further, we aimed to create a novel compact macrocyclic system for efficient SSPC. The macrocycle named P2Mac (Fig.…”

Molecular clips with spatially proximal urea residues for efficient transmembrane co-transport of H+/Cl− ions

“…Previously, we reported anion binding-induced white light emission from PDC-based scaffolds 25 and also demonstrated their high solid-state proton conduction abilities. 26 Herein, we exploited the unique structural attributes of transporters 1a–1e to achieve efficient co-transport of H + /Cl − ions across lipid membranes.…”

“…The target molecules were readily synthesized in excellent yields by the reaction of precursor P2 26 with different commercially available phenyl isocyanate derivatives (Scheme 1). Compounds 1a and 1d have electron-withdrawing residues attached to the phenyl rings, while electron-donating residues are appended in molecules 1c and 1e .…”