Mapping Hydrogens in Hydrous Materials

doi:10.1021/acs.jpcc.3c00277

2023-05-02

PRE

DOI：10.1021/acs.jpcc.3c00277

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摘要

En 中文

Hydrous materials such as clays, cements, hydroxyapatite, and metal hydroxides have been known and extensively used since antiquity. However, experimental elucidation of hydrogen in hydrous materials remains challenging due to the intrinsic insensitivity, limited accessibility, sample damage, or poor spectral resolution of many characterization methods. 1H solid-state NMR spectroscopy has evolved into an ideal site-specific characterization tool of hydrogen-containing materials, but its current application in hydrous materials is hampered by the low resolution of 1H NMR spectra in the solid state due to the presence of intense dipolar coupling networks and a narrow 1H chemical shift range. Herein, a significant advance in the characterization of hydrogens in hydrous materials is reported. A combination of magic-angle spinning (MAS) NMR, moderate 2H substitution, and high magnetic fields has unlocked the capacity of identifying many chemically similar while crystallographically distinct hydrogen sites in a prototypical hydrous material Y4(OH)10Br2 center dot 3H2O (LYH-Br) by 1D 1H solid-state NMR experiments. 1H NMR peaks were first tentatively assigned in accordance with the density functional theory (DFT) calculation results, and the assignment was further refined by 2D 1H-89Y heteronuclear correlation (HETCOR) and 1H-1H double quantum (DQ) MAS NMR data. The order of 1H chemical shift (delta iso) values provides valuable information on the relative strength of hydrogen bond for ten hydroxide hydrogen sites. The power of very high spectral resolution is further described by observing all triple-quantum (TQ) coherences in the 2D 1H-1H TQ MAS NMR spectrum, in which all spatial proximities among three hydrogen sites are resolved. This demonstration of the very high spectral resolution obtained in 1D and 2D 1H solid-state NMR experiments illustrates how scientists in various communities can now study the multiple hydrous species of hydrous materials and obtain previously inaccessible fine structural information.

Keyword:

SOLID-STATE NMR

LAYERED DOUBLE HYDROXIDES

RESOLUTION H-1-NMR SPECTROSCOPY

PERDEUTERATED PROTEINS

RESONANCE-ABSORPTION

GADOLINIUM HYDROXIDE

H-1

CRYSTALLINE

NANOSHEETS

SPECTRA