Direct detection of hydrogen bonds in supramolecular systems using ¹H-¹⁵N Heteronuclear multiple quantum coherence spectroscopy

Hydrogen-bonded supramolecular systems are usually characterized in solution through analysis of NMR data such as complexation-induced shifts and nuclear Overhauser effects (nOe). Routine direct detection of hydrogen bonding particularly in multicomponent mixtures, even with the aid of 2D NMR experiments for full assignment, is more challenging. We describe an elementary rapid ¹H-¹⁵N HMQC NMR experiment which addresses these challenges without the need for complex pulse sequences. Under readily accessible conditions (243/263 K, 50 mM solutions) and natural ¹⁵N abundance, unambiguous assignment of ¹⁵N resonances facilitates direct detection of intra- and intermolecular hydrogen bonds in mechanically interlocked structures and quadruply hydrogen-bonded dimers-of dialkylaminoureidopyrimidinones, ureidopyrimidinones, and diamidonaphthyridines-in single or multicomponent mixtures to establish tautomeric configuration, conformation, and, to resolve self-sorted speciation.