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

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journal contribution
posted on 25.06.2015, 00:00 by Vladimir K. Michaelis, Eric G. Keeler, Ta-Chung Ong, Kimberley N. Craigen, Susanne Penzel, John E. C. Wren, Scott Kroeker, Robert G. Griffin
We demonstrate here that the 17O 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 17O 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 17O 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.