The Experts below are selected from a list of 49119 Experts worldwide ranked by ideXlab platform
Jürgen M. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Heteronuclear relayed E.COSY revisited: Determination of 3J(Hα,Cγ) couplings in Asx and aromatic residues in proteins
Journal of Biomolecular NMR, 2000Co-Authors: Frank Löhr, Carlos Pérez, Rolf Köhler, Heinz Rüterjans, Jürgen M. SchmidtAbstract:Constant-time 3D heteronuclear relayed E.COSY [Schmidt et al. (1996) J. Biomol. NMR , 7 , 142–152], as based on generic 2D small-flip-angle HMQC-COSY [Schmidt et al. (1995) J. Biomol. NMR , 6 , 95–105], has been modified to allow for quantitative determination of heteronuclear three-bond ^3 J (H^α,C^γ) couplings. The method is applicable to amino acid spin topologies with carbons in the γ position which lack attached protons, i.e. to asparagine, aspartate, and aromatic residues in uniformly ^13C-enriched proteins. The pulse sequence critically exploits heteronuclear Triple-Quantum Coherence (HTQC) of CH_2 moieties involving geminal H^β proton pairs, taking advantage of improved multiple-quantum relaxation properties, at the same time avoiding scalar couplings between those spins involved in multiple-quantum Coherence, thus yielding E.COSY-type multiplets with a splitting structure that is simpler than with the original scheme. Numerical least-squares 2D line-shape simulation is used to extract ^3 J (H^α,C^γ) coupling constants which are of relevance to side-chain χ_1 dihedral-angle conformations in polypeptides. Methods are demonstrated with recombinant ^15N,^13C-enriched ribonuclease T1 and Desulfovibrio vulgaris flavodoxin with bound oxidized FMN.
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Heteronuclear relayed E.COSY revisited: determination of 3J(H(alpha),C(gamma)) couplings in Asx and aromatic residues in proteins.
Journal of biomolecular NMR, 2000Co-Authors: Frank Löhr, Carlos Pérez, Rolf Köhler, Heinz Rüterjans, Jürgen M. SchmidtAbstract:Constant-time 3D heteronuclear relayed E.COSY [Schmidt et al. (1996) J. Biomol. NMR, 7, 142–152], as based on generic 2D small-flip-angle HMQC-COSY [Schmidt et al. (1995) J. Biomol. NMR, 6, 95–105], has been modified to allow for quantitative determination of heteronuclear three-bond 3J(Hα,Cγ) couplings. The method is applicable to amino acid spin topologies with carbons in the γ position which lack attached protons, i.e. to asparagine, aspartate, and aromatic residues in uniformly 13C-enriched proteins. The pulse sequence critically exploits heteronuclear Triple-Quantum Coherence (HTQC) of CH2 moieties involving geminal Hβ proton pairs, taking advantage of improved multiple-quantum relaxation properties, at the same time avoiding scalar couplings between those spins involved in multiple-quantum Coherence, thus yielding E.COSY-type multiplets with a splitting structure that is simpler than with the original scheme. Numerical least-squares 2D line-shape simulation is used to extract 3J(Hα,Cγ) coupling constants which are of relevance to side-chain χ1 dihedral-angle conformations in polypeptides. Methods are demonstrated with recombinant 15N,13C-enriched ribonuclease T1 and Desulfovibrio vulgaris flavodoxin with bound oxidized FMN.
Alexander Pines - One of the best experts on this subject based on the ideXlab platform.
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theoretical studies of the spin dynamics of quadrupolar nuclei at rotational resonance conditions
Journal of Chemical Physics, 2002Co-Authors: Jamie D Walls, Alexander PinesAbstract:A theory of the spin dynamics of I=3/2 quadrupolar nuclei in the sudden-passage limit is discussed in relation to the recently observed rotational resonance (RR) effects on the excitation and conversion of Triple-Quantum Coherence in the FASTER multiple-quantum magic-angle spinning (MQMAS) experiments [T. Vosegaard, P. Florian, D. Massiot, and P. J. Grandinetti, J. Chem. Phys. 114, 4618 (2001)]. A novel interaction frame, which combines the quadrupolar interaction with the central transition radio frequency irradiation, is shown to be useful in understanding the complex spin dynamics at and away from RR conditions. Analytical expressions for the Hamiltonian obtained from bimodal Floquet theory are included in order to provide insight into the spin dynamics observed in the FASTER MQMAS experiments. Numerical simulations have been performed and were found to support the theoretical formalism.
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multiple quantum magic angle spinning and dynamic angle spinning nmr spectroscopy of quadrupolar nuclei
Solid State Nuclear Magnetic Resonance, 1997Co-Authors: S H Wang, Zhi Xu, Jay H Baltisberger, L M Bull, Jonathan F Stebbins, Alexander PinesAbstract:Abstract Several aspects of the Multiple-Quantum Magic-Angle Spinning (MQMAS) technique (L. Frydman and J.S. Harwood, J. Am. Chem. Soc., 117 (1995) 5367) are compared with Dynamic-Angle Spinning (DAS). Examples of MQMAS spectra are shown for I = 3 2 nuclei with C Q up to 3.6 MHz, and for 27 Al ( I = 5 2 ) with C Q up to 10 MHz. The MQMAS linewidth is largely independent of the magnitude of the homonuclear dipolar interaction, while the spinning sideband manifold is similar to that observed in DAS experiments. MQMAS is technically simple and routinely useful for studying nuclei with short spin-lattice relaxation times, but care must be taken in its use for quantitative studies as the excitation of the Triple-Quantum Coherence is not uniform. In this regard, MQMAS is most useful for samples with small quadrupolar coupling constants. In the specific case of 17 O, DAS would give spectra with excellent resolution in comparison to MQMAS. The different advantages of DAS and MQMAS make them useful complementary techniques in many cases. Two additional methods are also presented for extracting the chemical shift anisotropy (CSA) directly for quadrupolar nuclei using the multiple-quantum scheme.
Gil Navon - One of the best experts on this subject based on the ideXlab platform.
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Complete elimination of the extracellular 23Na NMR signal in triple quantum filtered spectra of rat hearts in the presence of shift reagents.
Magnetic resonance in medicine, 1993Co-Authors: Gil NavonAbstract:A method is suggested whereby the shifted extracellular triple quantum filtered 23Na signal of an isolated organ is completely eliminated. The method is based on the long relaxation time of the triple quantum Coherence and on its fast evolution rate. When the carrier frequency is set on top of the intracellular sodium signal and the time interval between the last two pulses to (12 delta nu)-1 (delta nu is the frequency difference between the intracellular and the extracellular signals), a complete elimination of the extracellular 23Na signal is achieved. The method is demonstrated for isolated rat hearts and the quantification of intracellular sodium using triple quantum filtered spectroscopy is discussed.
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Nuclear magnetic resonance line shapes of double and triple quantum Coherences of spin 3/2 nuclei
The Journal of Chemical Physics, 1991Co-Authors: Uzi Eliav, Gil NavonAbstract:Nuclear magnetic resonance (NMR) line shapes of double and triple quantum Coherences were calculated for spin 3/2 nuclei over a wide range of reorientation times. It is shown that for slow rotating molecules the dynamic shifts of all the Coherences are a result of adiabatic averaging of the powder spectra. Line shapes are shown to be single Lorentzians far beyond the range of rotational motion, where Redfield’s theory is valid. Analytical expressions for linewidths and dynamic shifts are given for the whole range of motion for which the line shape is Lorentzian. It is suggested that the high ratio between the dynamic shift and the linewidth for the triple quantum Coherence can make it possible to distinguish between sodium nuclei in environments with different rotational mobility and quadrupole interactions.
Malcolm H. Levitt - One of the best experts on this subject based on the ideXlab platform.
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Signal enhancement in the Triple-Quantum magic-angle spinning NMR of spins-3/2 in solids: the FAM-RIACT-FAM sequence.
Journal of magnetic resonance (San Diego Calif. : 1997), 2002Co-Authors: Perunthiruthy K. Madhu, Malcolm H. LevittAbstract:We achieve a significant signal enhancement for the Triple-Quantum magic-angle spinning NMR of a spin-3/2 system, by using an amplitude-modulated radiofrequency field, followed by a selective 90° pulse and a phase-shifted strong rf field, for the Triple-Quantum excitation, and an amplitude-modulated radiofrequency field for the conversion of Triple-Quantum Coherence to observable single-quantum Coherence. The experiment is demonstrated on the Rb-87 NMR of polycrystalline rubidium nitrate.
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Excitation of carbon-13 triple quantum Coherence in magic-angle-spinning NMR
Chemical Physics Letters, 1998Co-Authors: Mattias Edén, Malcolm H. LevittAbstract:AbstractWe excite triple quantum Coherence between carbon-13 nuclei in magic-angle-spinning solid state NMR, using a C7pulse sequence applied to transverse 13 C-magnetization. Experimental results on a powder of 98% labelled 13 C L -alanine 3 are in good agreement with analytical solutions and exact numerical simulations. We achieve a Triple-Quantum filteringefficiency of around 8% for the central site in the three-spin topology.q1998 Elsevier Science B.V. All rights reserved. 1. IntroductionMultiple quantum Coherence MQC is used ex-.tensively in NMR for suppressing natural abundancesignals 1–3 , enhancing spectral resolution 1,2,4 ,wx w xdetermining the size of spin clusters 2 , determiningwxdipole–dipole couplings 1,2 , selecting couplingwxtopologies 2,5 and measuring molecular torsionalwxangles 6–11 .wxIn the solid state NMR of powders, multiple-quantum spectroscopy is often combined withmagic-angle-spinning MAS , in which the sample is.rotated rapidly about an axis subtending an angle ofarctan 2 with respect to the static field. Magic-an-
Frank Löhr - One of the best experts on this subject based on the ideXlab platform.
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Heteronuclear relayed E.COSY revisited: Determination of 3J(Hα,Cγ) couplings in Asx and aromatic residues in proteins
Journal of Biomolecular NMR, 2000Co-Authors: Frank Löhr, Carlos Pérez, Rolf Köhler, Heinz Rüterjans, Jürgen M. SchmidtAbstract:Constant-time 3D heteronuclear relayed E.COSY [Schmidt et al. (1996) J. Biomol. NMR , 7 , 142–152], as based on generic 2D small-flip-angle HMQC-COSY [Schmidt et al. (1995) J. Biomol. NMR , 6 , 95–105], has been modified to allow for quantitative determination of heteronuclear three-bond ^3 J (H^α,C^γ) couplings. The method is applicable to amino acid spin topologies with carbons in the γ position which lack attached protons, i.e. to asparagine, aspartate, and aromatic residues in uniformly ^13C-enriched proteins. The pulse sequence critically exploits heteronuclear Triple-Quantum Coherence (HTQC) of CH_2 moieties involving geminal H^β proton pairs, taking advantage of improved multiple-quantum relaxation properties, at the same time avoiding scalar couplings between those spins involved in multiple-quantum Coherence, thus yielding E.COSY-type multiplets with a splitting structure that is simpler than with the original scheme. Numerical least-squares 2D line-shape simulation is used to extract ^3 J (H^α,C^γ) coupling constants which are of relevance to side-chain χ_1 dihedral-angle conformations in polypeptides. Methods are demonstrated with recombinant ^15N,^13C-enriched ribonuclease T1 and Desulfovibrio vulgaris flavodoxin with bound oxidized FMN.
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Heteronuclear relayed E.COSY revisited: determination of 3J(H(alpha),C(gamma)) couplings in Asx and aromatic residues in proteins.
Journal of biomolecular NMR, 2000Co-Authors: Frank Löhr, Carlos Pérez, Rolf Köhler, Heinz Rüterjans, Jürgen M. SchmidtAbstract:Constant-time 3D heteronuclear relayed E.COSY [Schmidt et al. (1996) J. Biomol. NMR, 7, 142–152], as based on generic 2D small-flip-angle HMQC-COSY [Schmidt et al. (1995) J. Biomol. NMR, 6, 95–105], has been modified to allow for quantitative determination of heteronuclear three-bond 3J(Hα,Cγ) couplings. The method is applicable to amino acid spin topologies with carbons in the γ position which lack attached protons, i.e. to asparagine, aspartate, and aromatic residues in uniformly 13C-enriched proteins. The pulse sequence critically exploits heteronuclear Triple-Quantum Coherence (HTQC) of CH2 moieties involving geminal Hβ proton pairs, taking advantage of improved multiple-quantum relaxation properties, at the same time avoiding scalar couplings between those spins involved in multiple-quantum Coherence, thus yielding E.COSY-type multiplets with a splitting structure that is simpler than with the original scheme. Numerical least-squares 2D line-shape simulation is used to extract 3J(Hα,Cγ) coupling constants which are of relevance to side-chain χ1 dihedral-angle conformations in polypeptides. Methods are demonstrated with recombinant 15N,13C-enriched ribonuclease T1 and Desulfovibrio vulgaris flavodoxin with bound oxidized FMN.
