The Experts below are selected from a list of 2454 Experts worldwide ranked by ideXlab platform
Jean-paul Amoureux - One of the best experts on this subject based on the ideXlab platform.
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improving the resolution in proton detected through space Heteronuclear multiple quantum Correlation nmr spectroscopy
Journal of Magnetic Resonance, 2014Co-Authors: Bingwen Hu, Jean-paul Amoureux, Olivier Lafon, Frédérique Pourpoint, Julien Trebosc, Qun Chen, Ming ShenAbstract:Abstract Connectivities and proximities between protons and low-gamma nuclei can be probed in solid-state NMR spectroscopy using two-dimensional (2D) proton-detected Heteronuclear Correlation, through Heteronuclear Multiple Quantum Correlation (HMQC) pulse sequence. The indirect detection via protons dramatically enhances the sensitivity. However, the spectra are often broadened along the indirect F 1 dimension by the decay of Heteronuclear Multiple-Quantum coherences under the strong 1 H– 1 H dipolar couplings. This work presents a systematic comparison of the performances of various decoupling schemes during the indirect t 1 evolution period of dipolar-mediated HMQC ( D -HMQC) experiment. We demonstrate that 1 H– 1 H dipolar decoupling sequences during t 1 , such as symmetry-based schemes, phase-modulated Lee–Goldburg (PMLG) and Decoupling Using Mind-Boggling Optimization (DUMBO), provide better resolution than continuous wave 1 H irradiation. We also report that high resolution requires the preservation of 1 H isotropic chemical shifts during the decoupling sequences. When observing indirectly broad spectra presenting numerous spinning sidebands, the D -HMQC sequence must be fully rotor-synchronized owing to the rotor-synchronized indirect sampling and dipolar recoupling sequence employed. In this case, we propose a solution to reduce artefact sidebands caused by the modulation of window delays before and after the decoupling application during the t 1 period. Moreover, we show that 1 H– 1 H dipolar decoupling sequence using Smooth Amplitude Modulation (SAM) minimizes the t 1 -noise. The performances of the various decoupling schemes are assessed via numerical simulations and compared to 2D 1 H–{ 13 C} D -HMQC experiments on [U– 13 C]– L -histidine⋅HCl⋅H 2 O at various magnetic fields and Magic Angle spinning (MAS) frequencies. Great resolution and sensitivity enhancements resulting from decoupling during t 1 period enable the detection of Heteronuclear Correlation between aliphatic protons and ammonium 14 N sites in L -histidine⋅HCl⋅H 2 O.
Andrew B Lowe - One of the best experts on this subject based on the ideXlab platform.
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a 2 naphthalen 2 yl phenyl rhodium i complex formed by a proposed intramolecular 1 4 ortho to ortho rh metal atom migration and its efficacy as an initiator in the controlled stereospecific polymerisation of phenylacetylene
Dalton Transactions, 2019Co-Authors: Nicholas Sheng Long Tan, Gareth L Nealon, Jason M Lynam, Alexandre N Sobolev, Matthew R Rowles, Mark I Ogden, Massimiliano Massi, Andrew B LoweAbstract:The synthesis of a novel Rh(I)-aryl complex is detailed and its ability to serve as an initiator in the stereospecific polymerisation of phenylacetylene evaluated. Targeting the Rh(I) species, (2-phenylnaphthalen-1-yl)rhodium(I)(2,5-norbornadiene)tris(para-fluorophenylphosphine), Rh(nbd)(P(4-FC6H4)3)(2-PhNapth), following recrystallization we obtained the isomeric (2-(naphthalen-2-yl)phenyl)rhodium(I) complex, Rh(nbd)(P(4-FC6H4)3)(2-NapthPh), as determined by X-ray single-crystal structure analysis, and confirmed by X-ray powder diffraction. The isolation of the latter species was proposed to occur from the target (2-PhNapth) derivative via an intramolecular 1,4-Rh atom migration. This supposition was supported by density functional theory (DFT) calculations that indicated the isolated (2-NapthPh) derivative has lower energy (−19 kJ mol−1) than the targeted complex. The structure of the isolated (2-NapthPh) species was confirmed by multinuclear NMR spectroscopy including 2D 31P–103Rh{1H, 103Rh}, Heteronuclear Multiple-Quantum Correlation (HMQC) experiments; however, NMR analysis indicated the presence of a second, minor species in solution in an approximate 1 : 4 ratio with the 2-NapthPh complex. The minor species was identified as a second structural isomer, the 3-phenylnaphthyl derivative, proposed to be formed under a dynamic equilibrium with the 2-NapthPh derivative via a second 1,4-Rh atom migration. DFT calculations indicate that this 1,4-migration proceeds through a low-energy pathway involved in the oxidative addition of a C–H bond to Rh followed by a reductive elimination with the distribution of the products being thermodynamically controlled. The recrystallized Rh(nbd)(P(4-FC6H4)3)(2-NapthPh) complex was subsequently evaluated as an initiator in the polymerisation of phenylacetylene (PA); gratifyingly, the Rh(I) species was an active initiating species with the pseudo-first-order kinetic and molecular weight evolution vs time plots both linear implying a controlled polymerisation while yielding (co)polymers with low dispersities (Đ = Mw/Mn typically ≤1.25) and high cis-transoidal stereoregularity (>95%). Typical initiation efficiencies, while not quantitative (as judged by size exclusion chromatography), were nonetheless high at ca. 0.8. The presence of the minor 3-phenylnaphthyl species when in solution is proposed to be the cause of the observed non-quantitative initiation.
Ming Shen - One of the best experts on this subject based on the ideXlab platform.
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improving the resolution in proton detected through space Heteronuclear multiple quantum Correlation nmr spectroscopy
Journal of Magnetic Resonance, 2014Co-Authors: Bingwen Hu, Jean-paul Amoureux, Olivier Lafon, Frédérique Pourpoint, Julien Trebosc, Qun Chen, Ming ShenAbstract:Abstract Connectivities and proximities between protons and low-gamma nuclei can be probed in solid-state NMR spectroscopy using two-dimensional (2D) proton-detected Heteronuclear Correlation, through Heteronuclear Multiple Quantum Correlation (HMQC) pulse sequence. The indirect detection via protons dramatically enhances the sensitivity. However, the spectra are often broadened along the indirect F 1 dimension by the decay of Heteronuclear Multiple-Quantum coherences under the strong 1 H– 1 H dipolar couplings. This work presents a systematic comparison of the performances of various decoupling schemes during the indirect t 1 evolution period of dipolar-mediated HMQC ( D -HMQC) experiment. We demonstrate that 1 H– 1 H dipolar decoupling sequences during t 1 , such as symmetry-based schemes, phase-modulated Lee–Goldburg (PMLG) and Decoupling Using Mind-Boggling Optimization (DUMBO), provide better resolution than continuous wave 1 H irradiation. We also report that high resolution requires the preservation of 1 H isotropic chemical shifts during the decoupling sequences. When observing indirectly broad spectra presenting numerous spinning sidebands, the D -HMQC sequence must be fully rotor-synchronized owing to the rotor-synchronized indirect sampling and dipolar recoupling sequence employed. In this case, we propose a solution to reduce artefact sidebands caused by the modulation of window delays before and after the decoupling application during the t 1 period. Moreover, we show that 1 H– 1 H dipolar decoupling sequence using Smooth Amplitude Modulation (SAM) minimizes the t 1 -noise. The performances of the various decoupling schemes are assessed via numerical simulations and compared to 2D 1 H–{ 13 C} D -HMQC experiments on [U– 13 C]– L -histidine⋅HCl⋅H 2 O at various magnetic fields and Magic Angle spinning (MAS) frequencies. Great resolution and sensitivity enhancements resulting from decoupling during t 1 period enable the detection of Heteronuclear Correlation between aliphatic protons and ammonium 14 N sites in L -histidine⋅HCl⋅H 2 O.
Qun Chen - One of the best experts on this subject based on the ideXlab platform.
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population transfer hmqc for half integer quadrupolar nuclei
Journal of Chemical Physics, 2015Co-Authors: Qiang Wang, Bingwen Hu, Olivier Lafon, Ningdong Feng, Yixuan Li, Julien Trebosc, Jun Xu, Qun ChenAbstract:This work presents a detailed analysis of a recently proposed nuclear magnetic resonance method [Wang et al., Chem. Commun. 49(59), 6653-6655 (2013)] for accelerating Heteronuclear coherence transfers involving half-integer spin quadrupolar nuclei by manipulating their satellite transitions. This method, called Population Transfer Heteronuclear Multiple Quantum Correlation (PT-HMQC), is investigated in details by combining theoretical analyses, numerical simulations, and experimental investigations. We find that compared to instant inversion or instant saturation, continuous saturation is the most practical strategy to accelerate coherence transfers on half-integer quadrupolar nuclei. We further demonstrate that this strategy is efficient to enhance the sensitivity of J-mediated Heteronuclear Correlation experiments between two half-integer quadrupolar isotopes (e.g., Al-27-O-17). In this case, the build-up is strongly affected by relaxation for small T-2' and J coupling values, and shortening the mixing time makes a huge signal enhancement. Moreover, this concept of population transfer can also be applied to dipolar-mediated HMQC experiments. Indeed, on the AlPO4-14 sample, one still observes experimentally a 2-fold shortening of the optimum mixing time albeit with no significant signal gain in the P-31-{Al-27} experiments. (C) 2015 AIP Publishing LLC.
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improving the resolution in proton detected through space Heteronuclear multiple quantum Correlation nmr spectroscopy
Journal of Magnetic Resonance, 2014Co-Authors: Bingwen Hu, Jean-paul Amoureux, Olivier Lafon, Frédérique Pourpoint, Julien Trebosc, Qun Chen, Ming ShenAbstract:Abstract Connectivities and proximities between protons and low-gamma nuclei can be probed in solid-state NMR spectroscopy using two-dimensional (2D) proton-detected Heteronuclear Correlation, through Heteronuclear Multiple Quantum Correlation (HMQC) pulse sequence. The indirect detection via protons dramatically enhances the sensitivity. However, the spectra are often broadened along the indirect F 1 dimension by the decay of Heteronuclear Multiple-Quantum coherences under the strong 1 H– 1 H dipolar couplings. This work presents a systematic comparison of the performances of various decoupling schemes during the indirect t 1 evolution period of dipolar-mediated HMQC ( D -HMQC) experiment. We demonstrate that 1 H– 1 H dipolar decoupling sequences during t 1 , such as symmetry-based schemes, phase-modulated Lee–Goldburg (PMLG) and Decoupling Using Mind-Boggling Optimization (DUMBO), provide better resolution than continuous wave 1 H irradiation. We also report that high resolution requires the preservation of 1 H isotropic chemical shifts during the decoupling sequences. When observing indirectly broad spectra presenting numerous spinning sidebands, the D -HMQC sequence must be fully rotor-synchronized owing to the rotor-synchronized indirect sampling and dipolar recoupling sequence employed. In this case, we propose a solution to reduce artefact sidebands caused by the modulation of window delays before and after the decoupling application during the t 1 period. Moreover, we show that 1 H– 1 H dipolar decoupling sequence using Smooth Amplitude Modulation (SAM) minimizes the t 1 -noise. The performances of the various decoupling schemes are assessed via numerical simulations and compared to 2D 1 H–{ 13 C} D -HMQC experiments on [U– 13 C]– L -histidine⋅HCl⋅H 2 O at various magnetic fields and Magic Angle spinning (MAS) frequencies. Great resolution and sensitivity enhancements resulting from decoupling during t 1 period enable the detection of Heteronuclear Correlation between aliphatic protons and ammonium 14 N sites in L -histidine⋅HCl⋅H 2 O.
Nicholas Sheng Long Tan - One of the best experts on this subject based on the ideXlab platform.
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a 2 naphthalen 2 yl phenyl rhodium i complex formed by a proposed intramolecular 1 4 ortho to ortho rh metal atom migration and its efficacy as an initiator in the controlled stereospecific polymerisation of phenylacetylene
Dalton Transactions, 2019Co-Authors: Nicholas Sheng Long Tan, Gareth L Nealon, Jason M Lynam, Alexandre N Sobolev, Matthew R Rowles, Mark I Ogden, Massimiliano Massi, Andrew B LoweAbstract:The synthesis of a novel Rh(I)-aryl complex is detailed and its ability to serve as an initiator in the stereospecific polymerisation of phenylacetylene evaluated. Targeting the Rh(I) species, (2-phenylnaphthalen-1-yl)rhodium(I)(2,5-norbornadiene)tris(para-fluorophenylphosphine), Rh(nbd)(P(4-FC6H4)3)(2-PhNapth), following recrystallization we obtained the isomeric (2-(naphthalen-2-yl)phenyl)rhodium(I) complex, Rh(nbd)(P(4-FC6H4)3)(2-NapthPh), as determined by X-ray single-crystal structure analysis, and confirmed by X-ray powder diffraction. The isolation of the latter species was proposed to occur from the target (2-PhNapth) derivative via an intramolecular 1,4-Rh atom migration. This supposition was supported by density functional theory (DFT) calculations that indicated the isolated (2-NapthPh) derivative has lower energy (−19 kJ mol−1) than the targeted complex. The structure of the isolated (2-NapthPh) species was confirmed by multinuclear NMR spectroscopy including 2D 31P–103Rh{1H, 103Rh}, Heteronuclear Multiple-Quantum Correlation (HMQC) experiments; however, NMR analysis indicated the presence of a second, minor species in solution in an approximate 1 : 4 ratio with the 2-NapthPh complex. The minor species was identified as a second structural isomer, the 3-phenylnaphthyl derivative, proposed to be formed under a dynamic equilibrium with the 2-NapthPh derivative via a second 1,4-Rh atom migration. DFT calculations indicate that this 1,4-migration proceeds through a low-energy pathway involved in the oxidative addition of a C–H bond to Rh followed by a reductive elimination with the distribution of the products being thermodynamically controlled. The recrystallized Rh(nbd)(P(4-FC6H4)3)(2-NapthPh) complex was subsequently evaluated as an initiator in the polymerisation of phenylacetylene (PA); gratifyingly, the Rh(I) species was an active initiating species with the pseudo-first-order kinetic and molecular weight evolution vs time plots both linear implying a controlled polymerisation while yielding (co)polymers with low dispersities (Đ = Mw/Mn typically ≤1.25) and high cis-transoidal stereoregularity (>95%). Typical initiation efficiencies, while not quantitative (as judged by size exclusion chromatography), were nonetheless high at ca. 0.8. The presence of the minor 3-phenylnaphthyl species when in solution is proposed to be the cause of the observed non-quantitative initiation.