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Stannous fluoride (SnF₂) is an effective fluoride source and antimicrobial agent that is widely used in commercial toothpaste formulations. The antimicrobial activity of SnF₂is partly attributed to the presence of Sn(II) ions. However, it is challenging to directly determine the Sn speciation and oxidation state within commercially available toothpaste products due to the low weight loading of SnF₂(0.454 wt% SnF₂, 0.34 wt% Sn) and the amorphous, semi-solid nature of the toothpaste. Here, we show that dynamic nuclear polarization (DNP) enables¹¹⁹Sn solid-state NMR experiments that can probe the Sn speciation within commercially available toothpaste. Solid-state NMR experiments on SnF₂and SnF₄show that ¹⁹F isotropic chemical shift and¹¹⁹Sn chemical shift anisotropy (CSA) are highly sensitive to the Sn oxidation state. DNP-enhanced¹¹⁹Sn magic-angle turning (MAT) 2D NMR spectra of toothpastes resolve Sn(II) and Sn(IV) by their¹¹⁹Sn chemical shift tensor parameters. Fits of DNP-enhanced 1D¹H → ¹¹⁹Sn solid-state NMR spectra allow the populations of Sn(II) and Sn(IV) within the toothpastes to be estimated. This analysis reveals that three of the four commercially available toothpastes contained at least 80% Sn(II), whereas one of the toothpaste contained a significantly higher amount of Sn(IV).

 

Gamma alumina (γ-Al2O3) is widely used as a catalyst and catalytic support due to its high specific surface area and porosity. However, synthesis of γ-Al2O3 nanocrystals is often a complicated process requiring high temperatures or additional post-synthetic steps. Here, we report a single-step synthesis of size-controlled and monodisperse, facetted γ-Al2O3 nanocrystals in an inductively coupled nonthermal plasma reactor using trimethylaluminum and oxygen as precursors. Under optimized conditions, we observed phase-pure, cuboctahedral γ-Al2O3 nanocrystals with defined surface facets. Nuclear magnetic resonance studies revealed that nanocrystal surfaces are populated with AlO6, AlO5 and AlO4 units with clusters of hydroxyl groups. Nanocrystal size tuning was achieved by varying the total reactor pressure yielding particles as small as 3.5 nm, below the predicted thermodynamic stability limit for γ-Al2O3.

 

Boron oxide/hydroxide supported on oxidized activated carbon (B/OAC) was shown to be an inexpensive catalyst for the oxidative dehydrogenation (ODH) of propane that offers activity and selectivity comparable to boron nitride. Here, we obtain an atomistic picture of the boron oxide/hydroxide layer in B/OAC by using 35.2 T 11B and 17O solid-state NMR experiments. NMR spectra measured at 35.2 T resolve the boron and oxygen sites due to narrowing of the central-transition powder patterns. A 35.2 T 2D 11B{17O} dipolar heteronuclear correlation NMR spectrum revealed the structural connectivity between boron and oxygen atoms. The approach outlined here should be generally applicable to determine atomistic structures of heterogeneous catalysts containing quadrupolar nuclei.