Solid-State 17O NMR Study of α-D-Glucose: Exploring New Frontiers in Isotopic Labeling, Sensitivity Enhancement, and NMR Crystallography

We report synthesis and solid-state 17O NMR characterization of α-D-glucose for which all six oxygen atoms are site-specifically 17O-labeled. Solid-state 17O NMR spectra were recorded for α-D-glucose/NaCl/H2O (2/1/1) cocrystals under...

Semi-Rigid (Aminomethyl) Piperidine-Based Pentadentate Ligands for Mn(II) Complexation

Two pentadentate ligands built on the 2-aminomethylpiperidine structure and bearing two tertiary amino and three oxygen donors (three carboxylates in the case of AMPTA and two carboxylates and one phenolate for AMPDA-HB) were developed for Mn(II) complexation. Equilibrium studies on the ligands and the Mn(II) complexes were carried out using pH potentiometry, 1H-NMR spectroscopy and UV-vis spectrophotometry. The Mn complexes that were formed by the two ligands were more stable than the Mn complexes of other pentadentate ligands but with a lower pMn than Mn(EDTA) and Mn(CDTA) (pMn for Mn(AMPTA) = 7.89 and for Mn(AMPDA-HB) = 7.07). 1H and 17O-NMR relaxometric studies showed that the two Mn-complexes were q = 1 with a relaxivity value of 3.3 mM−1 s−1 for Mn(AMPTA) and 3.4 mM−1 s−1 for Mn(AMPDA-HB) at 20 MHz and 298 K. Finally, the geometries of the two complexes were optimized at the DFT level, finding an octahedral coordination environment around the Mn2+ ion, and MD simulations were performed to monitor the distance between the Mn2+ ion and the oxygen of the coordinated water molecule to estimate its residence time, which was in good agreement with that determined using the 17O NMR data.

Imidazole-Based Ionic Liquids with BF4 as the Counterion Perform Outstanding Abilities in Both Inhibiting Clay Swelling and Lowing Water Cluster Size

Promoting fluid transportation in porous media has important applications in energy, pedology, bioscience, etc. For this purpose, one effective way is to prevent swelling through surface modification; however, it is far from enough in real cases, such as ultra-low permeability reservoirs and tight oils. In this study, we considered the comprehensive effects of inhibiting clay swelling, flocculation performance, reducing water clusters and interfacial tension and developed a series of imidazole-based tetrafluoroborate ionic liquids (ILs) with different lengths of alkyl chains. Through measurements of anti-swelling rates, XRD, SEM, 17O NMR, molecular dynamics simulation, zeta potential, flocculation evaluation, interfacial tension and a core flooding experiment based on ultra-low permeability reservoirs, the relationships between the molecular structure and physicochemical properties of ILs have been revealed. Interestingly, one of the selected ILs, imidazole-based tetrafluoroborate ILs (C8-OMImBF4), shows excellent performance, which is helpful to design an effective strategy in promoting fluid transportation in narrow spaces.

Labeling and Probing the Silica Surface Using Mechanochemistry and 17O NMR Spectroscopy

In recent years, there has been increasing interest in developing cost-efficient, fast, and user-friendly ¹⁷O enrichment protocols to help understand the structure and reactivity of materials using ¹⁷O NMR. Here, we show for the first time how ball milling (BM) can be used to selectively and efficiently enrich the surface of fumed silica, which is widely used at the industrial scale. Short milling times (up to 15 min) allowed modulation of the enrichment level (up to ca. 5%) without significantly changing the nature of the material. High-precision ¹⁷O-compositions were measured at different milling times using LG-SIMS. High-resolution ¹⁷O NMR analyses (including at 35.2 T) allowed clear identification of the signals from siloxane (Si-O-Si) and silanols (Si-OH), while DNP analyses, performed using direct ¹⁷O polarization and indirect ¹⁷O{¹H} CP excitation, agreed with selectivelabeling of the surface. Information on the distribution of Si-OH environments at the surface was obtained from 2D ¹H-¹⁷O D-HMQC correlations. Finally, the surface-labeled silica was reacted with titania and using ¹⁷O DNP, their common interface was probed and Si-O-Ti bonds identified.

Labeling and Probing the Silica Surface Using Mechanochemistry and 17O NMR Spectroscopy

In recent years, there has been increasing interest in developing cost-efficient, fast, and user-friendly ¹⁷O enrichment protocols to help understand the structure and reactivity of materials using ¹⁷O NMR. Here, we show for the first time how ball milling (BM) can be used to selectively and efficiently enrich the surface of fumed silica, which is widely used at the industrial scale. Short milling times (up to 15 min) allowed modulation of the enrichment level (up to ca. 5%) without significantly changing the nature of the material. High-precision ¹⁷O-compositions were measured at different milling times using LG-SIMS. High-resolution ¹⁷O NMR analyses (including at 35.2 T) allowed clear identification of the signals from siloxane (Si-O-Si) and silanols (Si-OH), while DNP analyses, performed using direct ¹⁷O polarization and indirect ¹⁷O{¹H} CP excitation, agreed with selectivelabeling of the surface. Information on the distribution of Si-OH environments at the surface was obtained from 2D ¹H-¹⁷O D-HMQC correlations. Finally, the surface-labeled silica was reacted with titania and using ¹⁷O DNP, their common interface was probed and Si-O-Ti bonds identified.

17O NMR spectroscopy of crystalline microporous materials

Cost-effective and atom-efficient isotopic enrichment enables 17O NMR spectroscopy of microporous materials to be used to probe local structure and disorder and to explore chemical reactivity.