Keeler Eric G, Michaelis Vladimir K, Griffin Robert G
Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
J Phys Chem B. 2016 Aug 18;120(32):7851-8. doi: 10.1021/acs.jpcb.6b05755. Epub 2016 Aug 9.
The structure and dynamics of the bound water in barium chlorate monohydrate were studied with (17)O nuclear magnetic resonance (NMR) spectroscopy in samples that are stationary and spinning at the magic-angle in magnetic fields ranging from 14.1 to 21.1 T. (17)O NMR parameters of the water were determined, and the effects of torsional oscillations of the water molecule on the (17)O quadrupolar coupling constant (CQ) were delineated with variable temperature MAS NMR. With decreasing temperature and reduction of the librational motion, we observe an increase in the experimentally measured CQ explaining the discrepancy between experiments and predictions from density functional theory. In addition, at low temperatures and in the absence of (1)H decoupling, we observe a well-resolved (1)H-(17)O dipole splitting in the spectra, which provides information on the structure of the H2O molecule. The splitting arises because of the homogeneous nature of the coupling between the two (1)H-(17)O dipoles and the (1)H-(1)H dipole.
利用¹⁷O核磁共振（NMR）光谱，在14.1至21.1 T磁场中处于静止和魔角旋转状态的一水合氯酸钡样品中，研究了其结合水的结构和动力学。测定了水的¹⁷O NMR参数，并用变温MAS NMR描绘了水分子扭转振荡对¹⁷O四极耦合常数（CQ）的影响。随着温度降低和振动运动减少，我们观察到实验测量的CQ增加，这解释了实验与密度泛函理论预测之间的差异。此外，在低温且不存在¹H去耦的情况下，我们在光谱中观察到了分辨良好的¹H - ¹⁷O偶极分裂，这提供了有关H₂O分子结构的信息。这种分裂是由于两个¹H - ¹⁷O偶极与¹H - ¹H偶极之间耦合的均匀性质引起的。
