•Designed as a molecular switching unit.•Controlled by acid or base.•Stimuli responsive supramolecular can be designed based upon our amide devices.Nuclear magnetic resonance (NMR) studies of acid-induced conformational switching (trans/cis isomerization) of N,N-diarylamides bearing a pyridine moiety indicated that the trans/cis conformational preference of these amides is dependent on the relative π-electron densities of the two N-aromatic parts, and can be controlled by protonation or deprotonation of pyridine.

We have investigated acid- and base-induced conformational alterations of N-aryl-N-troponyl amides containing an electron-donating group on the phenyl ring. NMR spectral studies indicated that the E/Z conformational preferences of these amides can be reversibly controlled by pH-dependent protonation or deprotonation of the tropolone moiety. Thus, these compounds have potential applications as acid/base-controllable molecular switches.

Amide oligomers composed of pyridine-2-carboxamide as the repeating unit were synthesized in a stepwise manner and their structures were examined by means of 1H NMR, NOE measurements, and DFT calculations. All the synthesized oligomers adopted a folded conformation, but became partially unfolded at the C-terminal upon addition of acid. A characteristic long-range hydrogen bond, which stabilizes local folding, was present in oligomers with a long main chain.