¹⁷O Chemical Shifts in Water

How hydrogen bonding affects the ¹⁷O chemical shift in water is analyzed in depth in this work. It is found that the ¹⁷O chemical shift in water is sensitive to both hydrogen bond distance and the OH covalent bond length. The effects are greater when the water molecule is acting as an acceptor than when it is serving as a donor. Additivity is observed with multiple hydrogen bond partners. For these reasons, the hydrogen bond dependence can be summarized in terms of simple functions of the hydrogen bond distances. Successful prediction of chemical shifts in large clusters by using small model systems is demonstrated. With this outcome, it is shown that ¹⁷O chemical shifts of water in large systems can be estimated by simply considering the number and type of hydrogen bonds a water molecule is participating in and their respective hydrogen bond distances. Ab initio calculations have also been performed for the ¹⁷O shielding in water as a function of hydrogen bonding with dimethyl sulfoxide (DMSO), and with glycerol. In these cases, results likewise show that the dependence of the ¹⁷O chemical shift in water on hydrogen bonding is summarized by the hydrogen bond distance and whether water is acting as a donor or acceptor. Calculations suggest that in the presence of DMSO, ¹⁷O in water is likely deshielded while the opposite should be observed with glycerol.