1 H/ 17 O Chemical Shift Waves in Carboxyl-Bridged Hydrogen Bond Networks in Organic Solids.

We report solid-state 1 H and 17 O NMR results for four 17 O-labeled organic compounds each containing an extensive carboxyl-bridged hydrogen bond (CBHB) network in the crystal lattice: tetrabutylammonium hydrogen di-[ 17 O 2 ]salicylate ( 1 ), [ 17 O 4 ]quinolinic acid ( 2 ), [ 17 O 4 ]dinicotinic acid ( 3 ), and [ 17 O 2 ]Gly/[ 17 O 2 ]Gly·HCl cocrystal ( 4 ). The 1 H isotropic chemical shifts found for protons involved in different CBHB networks are between 8.2 and 20.5 ppm, which reflect very different hydrogen-bonding environments. Similarly, the 17 O isotropic chemical shifts found for the carboxylate oxygen atoms in CBHB networks, spanning a large range between 166 and 341 ppm, are also remarkably sensitive to the hydrogen-bonding environments. We introduced a simple graphical representation in which 1 H and 17 O chemical shifts are displayed along the H and O atomic chains that form the CBHB network. In such a depiction, because wavy patterns are often observed, we refer to these wavy patterns as 1 H/ 17 O chemical shift waves. Typical patterns of 1 H/ 17 O chemical shift waves in CBHB networks are discussed. The reported 1 H and 17 O NMR parameters for the CBHB network models examined in this study can serve as benchmarks to aid in spectral interpretation for CBHB networks in proteins.