Unleashing the Potential of ¹⁷O NMR Spectroscopy Using Mechanochemistry

Abstract

17O NMR spectroscopy has been the subject of vivid interest in recent years, because there is increasing evidence that it can provide unique insight into the structure and reactivity of many molecules and materials. However, due to the very poor natural abundance of oxygen‐17, 17O labeling is generally a prerequisite. This is a real obstacle for most research groups, because of the high costs and/or strong experimental constraints of the most frequently used 17O‐labeling schemes. Here, we show for the first time that mechanosynthesis offers unique opportunities for enriching in 17O a variety of organic and inorganic precursors of synthetic interest. The protocols are fast, user‐friendly, and low‐cost, which makes them highly attractive for a broad research community, and their suitability for 17O solid‐state NMR applications is demonstrated.

Direct 17O Isotopic Labeling of Oxides Using Mechanochemistry

“…We first focused on improving the labeling strategy that we had previously proposed for enriching calcium oxide. 18 More specifically, in order to avoid the initial equilibration step ( Scheme 1 ) and to achieve a better enrichment level of the intermediate hydroxide, we started from the non-labeled oxide CaO and hydrolyzed it by mechanochemistry to produce Ca(*OH) 2 ( Scheme 2 ). The idea here is that all of the 17 O labels introduced as H 2 *O during the LAG step react with CaO to form the 17 O-enriched hydroxide.…”

“…In both cases, mechanochemistry techniques like ball-milling (BM) have been shown to be particularly attractive. 7 , 18 …”

Probing O–H Bonding through Proton Detected1H–17O Double Resonance Solid-State NMR Spectroscopy

“…Notably, with small diameter 1.3 mm rotors these experiments require only a few mg of material and moderate 17 One challenge associated with 17 O SSNMR spectroscopy is that labeling can be time intensive and expensive; however, mechanochemistry methods have shown promise to improve the efficiency, cost, and ease of 17 O labeling. 31 With respect to the cost of 17 O-enriched samples, fast MAS rotors are beneficial because they typically require less than 10 mg of material.…”

“…The most common approach to improving the sensitivity of 17 O NMR experiments is isotopic enrichment of oxygen-17, for which a variety of methods have been successfully demonstrated. 3,[27][28][29][30][31] More recently, it has been demonstrated that with the large NMR sensitivity enhancements provided by high-field dynamic nuclear polarization (DNP), [32][33][34] natural isotopic abundance 17 O NMR experiments can be performed on inorganic materials. 19, 23-24, 26, 35-36 The resolution of 17 O SSNMR spectra is most often improved either by utilizing selective 17 O labeling schemes, 37 working at the highest possible magnetic field strengths, 12,25,[38][39] or using multiple quantum magic angle spinning (MQMAS).…”

17O solid-state NMR spectroscopy of A2B2O7oxides: quantitative isotopic enrichment and spectral acquisition?

“…These often include the reduction or removal of water from a synthesis ( e.g. , the use of dry gel conversion reactions, 10 , 11 steaming procedures, 11 , 12 ionothermal synthesis 13 or mechanochemistry 14 ). However, for many oxides, enrichment is typically carried out post synthesis, by heating in 17 O 2 gas, 2 , 5 , 7 although the literature often provides little information about why the times and temperatures used were chosen, or on the eventual enrichment level achieved (although this can be very difficult to determine accurately).…”