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Morais AF, Radhakrishnan S, Arbiv G, Dom D, Duerinckx K, Chandran CV, Martens JA, Breynaert E. Noncontact In Situ Multidiagnostic NMR/Dielectric Spectroscopy. Anal Chem 2024; 96:5071-5077. [PMID: 38513052 DOI: 10.1021/acs.analchem.3c03007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/23/2024]
Abstract
Introduction of a dielectric material in a nuclear magnetic resonance (NMR) probe head modifies the frequency response of the probe circuit, a phenomenon revealed by detuning of the probe. For NMR spectroscopy, this detuning is corrected for by tuning and matching the probe head prior to the NMR measurement. The magnitude of the probe detuning, "the dielectric shift", provides direct access to the dielectric properties of the sample, enabling NMR spectrometers to simultaneously perform both dielectric and NMR spectroscopy. By measuring sample dielectric permittivity as a function of frequency, dielectric permittivity spectroscopy can be performed using the new methodology. As a proof of concept, this was evaluated on methanol, ethanol, 1-propanol, 1-pentanol, and 1-octanol using a commercial cross-polarization magic angle spinning (CPMAS) NMR probe head. The results accurately match the literature data collected by standard dielectric spectroscopy techniques. Subsequently, the method was also applied to investigate the solvent-surface interactions of water confined in the micropores of an MFI-type, hydrophilic zeolite with a Si/Al ratio of 11.5. In the micropores, water adsorbs to Bro̷nsted acid sites and defect sites, resulting in a drastically decreased dielectric permittivity of the nanoconfined water. Theoretical background for the new methodology is provided using an effective electric circuit model of a CPMAS probe head with a solenoid coil, describing the detuning resulting from the insertion of dielectric samples in the probe head.
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Affiliation(s)
- Alysson F Morais
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
| | - Sambhu Radhakrishnan
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
| | - Gavriel Arbiv
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- Center for Molecular Water Science (CMWS), Notkestraße 85, 22607 Hamburg, Germany
| | - Dirk Dom
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
| | - Karel Duerinckx
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
| | - C Vinod Chandran
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
| | - Johan A Martens
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
| | - Eric Breynaert
- Centre for Surface Chemistry and Catalysis - Characterization and Application Team (COK-KAT), Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- NMR for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F Box 2461, 3001 Heverlee, Belgium
- Center for Molecular Water Science (CMWS), Notkestraße 85, 22607 Hamburg, Germany
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De Man WL, Chandran CV, Wouters AGB, Radhakrishnan S, Martens JA, Breynaert E, Delcour JA. Hydration of Wheat Flour Water-Unextractable Cell Wall Material Enables Structural Analysis of Its Arabinoxylan by High-Resolution Solid-State 13C MAS NMR Spectroscopy. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2022; 70:10604-10610. [PMID: 35977412 DOI: 10.1021/acs.jafc.2c04087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
To enable its structural characterization by nuclear magnetic resonance (NMR) spectroscopy, the native structure of cereal water-unextractable arabinoxylan (WU-AX) is typically disrupted by alkali or enzymatic treatments. Here, WU-AX in the wheat flour unextractable cell wall material (UCWM) containing 40.9% ± 1.5 arabinoxylan with an arabinose-to-xylose ratio of 0.62 ± 0.04 was characterized by high-resolution solid-state NMR without disrupting its native structure. Hydration of the UCWM (1.7 mg H2O/mg UCWM) in combination with specific optimizations in the NMR methodology enabled analysis by solid-state 13C NMR with magic angle spinning and 1H high-power decoupling (13C HPDEC MAS NMR) which provided sufficiently high resolution to allow for carbon atom assignments. Spectral resonances of C-1 from arabinose and xylose residues of WU-AX were here assigned to the solid state. The proportions of un-, mono-, and di-substituted xyloses were 59.2, 19.5, and 21.2%, respectively. 13C HPDEC MAS NMR showed the presence of solid-state fractions with different mobilities in the UCWM. This study presents the first solid-state NMR spectrum of wheat WU-AX with sufficient resolution to enable assignment without prior WU-AX solubilization.
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Affiliation(s)
- Wannes L De Man
- Laboratory of Food Chemistry and Biochemistry (LFCB) and Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Kasteelpark Arenberg 23, B-3001Heverlee, Belgium
| | - C Vinod Chandran
- Centre for Surface Chemistry and Catalysis (COK-KAT), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
- X-ray/NMR Platform for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
| | - Arno G B Wouters
- Laboratory of Food Chemistry and Biochemistry (LFCB) and Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Kasteelpark Arenberg 23, B-3001Heverlee, Belgium
| | - Sambhu Radhakrishnan
- Centre for Surface Chemistry and Catalysis (COK-KAT), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
- X-ray/NMR Platform for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
| | - Johan A Martens
- Centre for Surface Chemistry and Catalysis (COK-KAT), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
- X-ray/NMR Platform for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
| | - Eric Breynaert
- Centre for Surface Chemistry and Catalysis (COK-KAT), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
- X-ray/NMR Platform for Convergence Research (NMRCoRe), KU Leuven, Celestijnenlaan 200F─box 2461, B-3001Heverlee, Belgium
| | - Jan A Delcour
- Laboratory of Food Chemistry and Biochemistry (LFCB) and Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Kasteelpark Arenberg 23, B-3001Heverlee, Belgium
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