Category Archives: 17O

Natural Abundance 17 O DNP NMR Provides Precise O-H Distances and Insights into the Bronsted Acidity of Heterogeneous Catalysts #DNPNMR

Perras, F.A., et al., Natural Abundance 17 O DNP NMR Provides Precise O-H Distances and Insights into the Bronsted Acidity of Heterogeneous Catalysts. Angew Chem Int Ed Engl, 2017. 56(31): p. 9165-9169.

https://www.ncbi.nlm.nih.gov/pubmed/28499071

Heterogeneous Bronsted acid catalysts are tremendously important in industry, particularly in catalytic cracking processes. Here we show that these Bronsted acid sites can be directly observed at natural abundance by 17 O DNP surface-enhanced NMR spectroscopy (SENS). We additionally show that the O-H bond length in these catalysts can be measured with sub-picometer precision, to enable a direct structural gauge of the lability of protons in a given material, which is correlated with the pH of the zero point of charge of the material. Experiments performed on materials impregnated with pyridine also allow for the direct detection of intermolecular hydrogen bonding interactions through the lengthening of O-H bonds.

Oxygen-17 dynamic nuclear polarisation enhanced solid-state NMR spectroscopy at 18.8 T #DNPNMR

Brownbill, N.J., et al., Oxygen-17 dynamic nuclear polarisation enhanced solid-state NMR spectroscopy at 18.8 T. Chem Commun (Camb), 2017. 53(17): p. 2563-2566.

https://www.ncbi.nlm.nih.gov/pubmed/28184389

We report 17O dynamic nuclear polarisation (DNP) enhanced solid-state NMR experiments at 18.8 T. Several formulations were investigated on the Mg(OH)2 compound. A signal enhancement factor of 17 could be obtained when the solid particles were incorporated into a glassy o-terphenyl matrix doped with BDPA using the Overhauser polarisation transfer scheme whilst the cross effect mechanism enabled by TEKPol yielded a slightly lower enhancement but more time efficient data acquisition.

Surface-selective direct 17O DNP NMR of CeO2 nanoparticles #DNPNMR

Michael A. Hope et. al, Chem. Commun., 2017,53, 2142-2145 

http://pubs.rsc.org/en/Content/ArticleLanding/2017/CC/C6CC10145C

Surface-selective direct 17O DNP has been demonstrated for the first time on CeO2nanoparticles, for which the first three layers can be distinguished with high selectivity. Polarisation build-up curves show that the polarisation of the (sub-)surface sites builds up faster than the bulk, accounting for the remarkable surface selectivity.

Natural Abundance (17)O DNP Two-Dimensional and Surface-Enhanced NMR Spectroscopy

Perras, F.A., T. Kobayashi, and M. Pruski, Natural Abundance (17)O DNP Two-Dimensional and Surface-Enhanced NMR Spectroscopy. J Am Chem Soc, 2015. 137(26): p. 8336-9.

http://www.ncbi.nlm.nih.gov/pubmed/26098846

Due to its extremely low natural abundance and quadrupolar nature, the (17)O nuclide is very rarely used for spectroscopic investigation of solids by NMR without isotope enrichment. Additionally, the applicability of dynamic nuclear polarization (DNP), which leads to sensitivity enhancements of 2 orders of magnitude, to (17)O is wrought with challenges due to the lack of spin diffusion and low polarization transfer efficiency from (1)H. Here, we demonstrate new DNP-based measurements that extend (17)O solid-state NMR beyond its current capabilities. The use of the PRESTO technique instead of conventional (1)H-(17)O cross-polarization greatly improves the sensitivity and enables the facile measurement of undistorted line shapes and two-dimensional (1)H-(17)O HETCOR NMR spectra as well as accurate internuclear distance measurements at natural abundance. This was applied for distinguishing hydrogen-bonded and lone (17)O sites on the surface of silica gel; the one-dimensional spectrum of which could not be used to extract such detail. Lastly, this greatly enhanced sensitivity has enabled, for the first time, the detection of surface hydroxyl sites on mesoporous silica at natural abundance, thereby extending the concept of DNP surface-enhanced NMR spectroscopy to the (17)O nuclide.

Dynamic nuclear polarization of (17)o: direct polarization

Michaelis, V.K., et al., Dynamic nuclear polarization of (17)o: direct polarization. J Phys Chem B, 2013. 117(48): p. 14894-906.

http://www.ncbi.nlm.nih.gov/pubmed/24195759

Dynamic nuclear polarization of (17)O was studied using four different polarizing agents: the biradical TOTAPOL and the monoradicals trityl and SA-BDPA, as well as a mixture of the latter two. Field profiles, DNP mechanisms, and enhancements were measured to better understand and optimize directly polarizing this low-gamma quadrupolar nucleus using both mono- and biradical polarizing agents. Enhancements were recorded at <88 K and were >100 using the trityl (OX063) radical and <10 with the other polarizing agents. The >10 000-fold savings in acquisition time enabled a series of biologically relevant small molecules to be studied with small sample sizes and the measurement of various quadrupolar parameters. The results are discussed with comparison to room temperature studies and GIPAW quantum chemical calculations. These experimental results illustrate the strength of high field DNP and the importance of radical selection for studying low-gamma nuclei.

Dynamic Nuclear Polarization Enhanced Natural Abundance 17O Spectroscopy

Blanc, F., et al., Dynamic Nuclear Polarization Enhanced Natural Abundance 17O Spectroscopy. J. Am. Chem. Soc., 2013. 135(8): p. 2975-2978.

http://dx.doi.org/10.1021/ja4004377

We show that natural abundance oxygen-17 NMR of solids could be obtained in minutes at a moderate magnetic field strength by using dynamic nuclear polarization (DNP). Electron spin polarization could be transferred either directly to 17O spins or indirectly via 1H spins in inorganic oxides and hydroxides using an oxygen-free solution containing a biradical polarization agent (bTbK). The results open up a powerful method for rapidly acquiring high signal-to-noise ratio solid-state NMR spectra of 17O nuclear spins and to probe sites on or near the surface, without the need for isotope labeling.

Dynamic Nuclear Polarization Enhanced Natural Abundance 17O Spectroscopy

Blanc, F., et al., Dynamic Nuclear Polarization Enhanced Natural Abundance 17O Spectroscopy. J. Am. Chem. Soc., 2013. 135(8): p. 2975-2978.

http://dx.doi.org/10.1021/ja4004377

We show that natural abundance oxygen-17 NMR of solids could be obtained in minutes at a moderate magnetic field strength by using dynamic nuclear polarization (DNP). Electron spin polarization could be transferred either directly to 17O spins or indirectly via 1H spins in inorganic oxides and hydroxides using an oxygen-free solution containing a biradical polarization agent (bTbK). The results open up a powerful method for rapidly acquiring high signal-to-noise ratio solid-state NMR spectra of 17O nuclear spins and to probe sites on or near the surface, without the need for isotope labeling.

Have a question?

If you have questions about our instrumentation or how we can help you, please contact us.