The Experts below are selected from a list of 56988 Experts worldwide ranked by ideXlab platform
Geoffrey Bodenhausen - One of the best experts on this subject based on the ideXlab platform.
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Double Cross Polarization for the indirect detection of nitrogen-14 nuclei in magic angle spinning NMR spectroscopy
Journal of Chemical Physics, 2017Co-Authors: Diego Carnevale, Geoffrey BodenhausenAbstract:Nitrogen-14 NMR spectra at fast magic-angle spinning rates can be acquired indirectly by means of two-dimensional techniques based on double Cross Polarization transfer 1H → 14N →1H. Experimental evidence is given for polycrystalline samples of glycine, l-histidine, and the dipeptide Ala-Gly. Either one-bond or long-range correlations can be favored by choosing the length of the Cross Polarization contact pulses. Longer contact pulses allow the detection of unprotonated nitrogen sites. In contrast to earlier methods that exploited second-order quadrupolar/dipolar Cross-terms, Cross Polarization operates in the manner of the method of Hartmann and Hahn, even for 14N quadrupolar couplings up to 4 MHz. Simulations explain why amorphous samples tend to give rise to featureless spectra because the 14N quadrupolar interactions may vary dramatically with the lattice environment. The experiments are straightforward to set up and are shown to be effective for different nitrogen environments and robust with respect to the rf-field strengths and to the 14N carrier frequency during Cross Polarization. The efficiency of indirect detection of 14N nuclei by double Cross Polarization is shown to be similar to that of isotopically enriched 13C nuclei.
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double Cross Polarization for the indirect detection of nitrogen 14 nuclei in magic angle spinning nmr spectroscopy
Journal of Chemical Physics, 2017Co-Authors: Diego Carnevale, Xiao Ji, Geoffrey BodenhausenAbstract:Nitrogen-14 NMR spectra at fast magic-angle spinning rates can be acquired indirectly by means of two-dimensional techniques based on double Cross Polarization transfer 1H → 14N →1H. Experimental evidence is given for polycrystalline samples of glycine, l-histidine, and the dipeptide Ala-Gly. Either one-bond or long-range correlations can be favored by choosing the length of the Cross Polarization contact pulses. Longer contact pulses allow the detection of unprotonated nitrogen sites. In contrast to earlier methods that exploited second-order quadrupolar/dipolar Cross-terms, Cross Polarization operates in the manner of the method of Hartmann and Hahn, even for 14N quadrupolar couplings up to 4 MHz. Simulations explain why amorphous samples tend to give rise to featureless spectra because the 14N quadrupolar interactions may vary dramatically with the lattice environment. The experiments are straightforward to set up and are shown to be effective for different nitrogen environments and robust with respect...
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Cross Polarization from 1h to quadrupolar 6li nuclei for dissolution dnp
Physical Chemistry Chemical Physics, 2014Co-Authors: Angel Perez J Linde, Aurélien Bornet, Sami Jannin, Roberto Melzi, Jonas Milani, Basile Vuichoud, Geoffrey BodenhausenAbstract:Cross Polarization from protons to quadrupolar 6Li nuclei is combined with dynamic nuclear Polarization of protons at 1.2 K and 6.7 T using TEMPOL as a polarizing agent followed by rapid dissolution. Compared to direct 6Li DNP without Cross-Polarization, a higher nuclear spin Polarization P(6Li) can be obtained in a shorter time. A double resonance 1H–6Li probe was designed that is equipped for Longitudinally Detected Electron Spin Resonance.
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Boosting Dissolution Dynamic Nuclear Polarization by Cross Polarization
Journal of Physical Chemistry Letters, 2013Co-Authors: Aurélien Bornet, Sami Jannin, Roberto Melzi, Angel J. Perez Linde, Patrick Hautle, Ben Brandt, Geoffrey BodenhausenAbstract:The efficiency of dissolution dynamic nuclear Polarization can be boosted by Hartmann-Hahn Cross Polarization at temperatures near 1.2 K. This enables high throughput of hyperpolarized solutions with substantial gains in buildup times and Polarization levels. During dissolution and transport, the C-13 nuclear spin Polarization P(C-13) merely decreases from 45 to 40%.
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low temperature Cross Polarization in view of enhancing dissolution dynamic nuclear Polarization in nmr
Chemical Physics Letters, 2011Co-Authors: Sami Jannin, Aurélien Bornet, Sonia Colombo, Geoffrey BodenhausenAbstract:Dynamic Nuclear Polarization (DNP) induced by saturation of ESR transitions of TEMPO at 1.2 K and 3.35 T is characterized by build-up rates that are typically 5 times faster for protons than for the carboxylic carbon-13 in acetate. We show that Cross Polarization from protons to carbon-13 allows one to achieve a Polarization P(C-13) >20% in less than 10 min, twice as much as has been previously reported, in one-fifth of the time. This should open the way to an unprecedented improvement in the efficiency of dissolution DNP. (C) 2011 Elsevier B.V. All rights reserved.
J Granholm - One of the best experts on this subject based on the ideXlab platform.
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dual Polarization stacked microstrip patch antenna array with very low Cross Polarization
IEEE Transactions on Antennas and Propagation, 2001Co-Authors: J Granholm, Kim WoeldersAbstract:This paper describes the development and performance of a wideband dual linear Polarization microstrip antenna array used in the Danish high-resolution airborne multifrequency polarimetric synthetic aperture radar, EMISAR. The antenna was designed for an operating frequency of 1.25 GHz/spl plusmn/50 MHz and was built as an array of 8/spl times/2 probe-fed stacked microstrip patches. The feeding network is constructed in microstrip and is capable of handling 6 kW of peak input-power at an altitude of 45000 ft (unpressurized). The impedance bandwidth (return loss better than -14 dB) of the antenna is 10%, the isolation between the horizontal and the vertical ports of the array is 50 dB and the Cross-Polarization suppression is 40 dB. A new design principle for simultaneously achieving very low Cross-Polarization and low side lobes in dual linear Polarization antenna arrays has been applied.
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Cross Polarization and sidelobe suppression in dual linear Polarization antenna arrays
IEEE Transactions on Antennas and Propagation, 1997Co-Authors: K Woelder, J GranholmAbstract:In recent years, there has been an increasing interest in dual linear Polarization antennas for various purposes, e.g. polarimetric synthetic aperture radar (SAR) imaging. A key design goal for dual Polarization antennas is to obtain a high Cross-Polarization suppression. When using standard techniques for improving the Cross-Polarization suppression in dual linear Polarization antenna arrays undesired sidelobes appear. This paper describes the properties of some known Cross-Polarization suppression methods and presents a new method for obtaining high Cross-Polarization suppression and simultaneously avoiding undesired sidelobes.
Sharon E Ashbrook - One of the best experts on this subject based on the ideXlab platform.
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multiple quantum Cross Polarization and two dimensional mqmas nmr of quadrupolar nuclei
Journal of Magnetic Resonance, 2000Co-Authors: Sharon E Ashbrook, Stephen WimperisAbstract:Abstract Cross-Polarization from 1H to the multiple-quantum coherences of a quadrupolar nucleus is used in combination with the two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR experiment in order to extract high-resolution CPMAS NMR spectra. The technique is demonstrated on 23Na (S = 3 2 ), 17O, 27Al (both S = 5 2 ), and 45Sc (S = 7 2 ) nuclei, showing the applicability of multiple-quantum Cross-Polarization to systems with differing spin quantum number, gyromagnetic ratio, and relative nuclide abundance. The utility of this two-dimensional MAS NMR experiment for spectral editing and site-specific measurement of Cross-Polarization intensities is demonstrated. The possibility of direct Cross-Polarization to higher order multiple-quantum coherences is also considered and three-, five-, and seven-quantum Cross-polarized 45Sc MAS NMR spectra are presented.
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multiple quantum Cross Polarization in mas nmr of quadrupolar nuclei
Chemical Physics Letters, 1998Co-Authors: Sharon E Ashbrook, Steven P Brown, Stephen WimperisAbstract:Abstract Using 27 Al ( I =5/2) NMR of aluminium acetylacetonate, we show that it is possible to Cross-polarize from a spin I =1/2 nucleus ( 1 H ) directly to the central triple-quantum transition of a half-integer quadrupolar nucleus ( 27 Al ) in a powdered sample under MAS conditions. The optimum conditions for this multiple-quantum Cross-Polarization (MQCP) are investigated experimentally and compared with existing theoretical results. The new technique is applied to the recently introduced two-dimensional MQMAS experiment for recording high-resolution NMR spectra of half-integer quadrupolar nuclei.
Stephen Wimperis - One of the best experts on this subject based on the ideXlab platform.
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multiple quantum Cross Polarization and two dimensional mqmas nmr of quadrupolar nuclei
Journal of Magnetic Resonance, 2000Co-Authors: Sharon E Ashbrook, Stephen WimperisAbstract:Abstract Cross-Polarization from 1H to the multiple-quantum coherences of a quadrupolar nucleus is used in combination with the two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR experiment in order to extract high-resolution CPMAS NMR spectra. The technique is demonstrated on 23Na (S = 3 2 ), 17O, 27Al (both S = 5 2 ), and 45Sc (S = 7 2 ) nuclei, showing the applicability of multiple-quantum Cross-Polarization to systems with differing spin quantum number, gyromagnetic ratio, and relative nuclide abundance. The utility of this two-dimensional MAS NMR experiment for spectral editing and site-specific measurement of Cross-Polarization intensities is demonstrated. The possibility of direct Cross-Polarization to higher order multiple-quantum coherences is also considered and three-, five-, and seven-quantum Cross-polarized 45Sc MAS NMR spectra are presented.
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multiple quantum Cross Polarization in mas nmr of quadrupolar nuclei
Chemical Physics Letters, 1998Co-Authors: Sharon E Ashbrook, Steven P Brown, Stephen WimperisAbstract:Abstract Using 27 Al ( I =5/2) NMR of aluminium acetylacetonate, we show that it is possible to Cross-polarize from a spin I =1/2 nucleus ( 1 H ) directly to the central triple-quantum transition of a half-integer quadrupolar nucleus ( 27 Al ) in a powdered sample under MAS conditions. The optimum conditions for this multiple-quantum Cross-Polarization (MQCP) are investigated experimentally and compared with existing theoretical results. The new technique is applied to the recently introduced two-dimensional MQMAS experiment for recording high-resolution NMR spectra of half-integer quadrupolar nuclei.
Aurélien Bornet - One of the best experts on this subject based on the ideXlab platform.
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Cross Polarization from 1h to quadrupolar 6li nuclei for dissolution dnp
Physical Chemistry Chemical Physics, 2014Co-Authors: Angel Perez J Linde, Aurélien Bornet, Sami Jannin, Roberto Melzi, Jonas Milani, Basile Vuichoud, Geoffrey BodenhausenAbstract:Cross Polarization from protons to quadrupolar 6Li nuclei is combined with dynamic nuclear Polarization of protons at 1.2 K and 6.7 T using TEMPOL as a polarizing agent followed by rapid dissolution. Compared to direct 6Li DNP without Cross-Polarization, a higher nuclear spin Polarization P(6Li) can be obtained in a shorter time. A double resonance 1H–6Li probe was designed that is equipped for Longitudinally Detected Electron Spin Resonance.
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Boosting Dissolution Dynamic Nuclear Polarization by Cross Polarization
Journal of Physical Chemistry Letters, 2013Co-Authors: Aurélien Bornet, Sami Jannin, Roberto Melzi, Angel J. Perez Linde, Patrick Hautle, Ben Brandt, Geoffrey BodenhausenAbstract:The efficiency of dissolution dynamic nuclear Polarization can be boosted by Hartmann-Hahn Cross Polarization at temperatures near 1.2 K. This enables high throughput of hyperpolarized solutions with substantial gains in buildup times and Polarization levels. During dissolution and transport, the C-13 nuclear spin Polarization P(C-13) merely decreases from 45 to 40%.
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low temperature Cross Polarization in view of enhancing dissolution dynamic nuclear Polarization in nmr
Chemical Physics Letters, 2011Co-Authors: Sami Jannin, Aurélien Bornet, Sonia Colombo, Geoffrey BodenhausenAbstract:Dynamic Nuclear Polarization (DNP) induced by saturation of ESR transitions of TEMPO at 1.2 K and 3.35 T is characterized by build-up rates that are typically 5 times faster for protons than for the carboxylic carbon-13 in acetate. We show that Cross Polarization from protons to carbon-13 allows one to achieve a Polarization P(C-13) >20% in less than 10 min, twice as much as has been previously reported, in one-fifth of the time. This should open the way to an unprecedented improvement in the efficiency of dissolution DNP. (C) 2011 Elsevier B.V. All rights reserved.