Structural Insights into Bound Water in Crystalline Amino Acids: Experimental and Theoretical 17O NMR

We demonstrate here that the O-17 NMR properties of bound water in a series of amino acids and dipeptides can be determined with a combination of nonspinning and magic-angle spinning experiments using a range of magnetic field strengths from 9.4 to 21.1 T. Furthermore, we propose a 170 chemical shift fingerprint region for bound water molecules in biological solids that is well outside the previously determined ranges for carbonyl; Carboxylic, and hydroxyl oxygens, thereby offering the ability to resolve multiple 170 environments using rapid one-dimensional NMR techniques. Finally, we compare our experimental data against quantum chemical calculations using GIPAW and hybrid-DFT, finding intriguing discrepancies between the electric field gradients calculated from structures determined by X-ray and neutron diffraction.