The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Niels Chr Nielsen - One of the best experts on this subject based on the ideXlab platform.
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recoupling of native homonuclear dipolar couplings in magic angle spinning solid state nmr by the double oscillating Field Technique
Journal of Chemical Physics, 2010Co-Authors: Lasse Arnt Straaso, Niels Chr NielsenAbstract:A new solid-state NMR method, the double-oscillating Field Technique (DUO), that under magic-angle-spinning conditions produces an effective Hamiltonian proportional to the native high-Field homonuclear dipole-dipole coupling operator is presented. The method exploits one part of the radio frequency (rf) Field to recouple the dipolar coupling interaction with a relatively high scaling factor and to eliminate offset effects over a reasonable bandwidth while in the recoupling frame, the other part gives rise to a sufficiently large longitudinal component of the residual rf Field that averages nonsecular terms and in addition ensures stability toward rf inhomogeneity and rf miscalibration. The capability of the DUO experiment to mediate transfer of polarization is described theoretically and compared numerically and experimentally with finite pulse rf driven recoupling and experimentally with dipolar-assisted rotational resonance. Two-dimensional recoupling experiments were performed on antiparallel amyloid ...
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Triple oscillating Field Technique for accurate distance measurements by solid-state NMR.
The Journal of chemical physics, 2008Co-Authors: Navin Khaneja, Niels Chr NielsenAbstract:We present a new concept for homonuclear dipolar recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating Field Technique. We demonstrate this Technique as an efficient means to accomplish broadband dipolar recoupling of homonuclear spins, while decoupling heteronuclear dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it is possible to synthesize Ising interaction (2IzSz) Hamiltonians in homonuclear spin networks and thereby avoid dipolar truncation--a serious problem essentially all previous homonuclear dipolar recoupling experiments suffer from. Combination of this recoupling concept with rotor assisted dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly 13C labeled proteins through accurate measurement of 13C-13C internuclear distances. The concept is demonstrated experimentally by measurement of C alpha-C', C beta-C', and C gamma-C' internuclear distances in powder samples of the amino acids L-alanine and L-threonine.
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Triple oscillating Field Technique for accurate measurements of couplings in homonuclear spin systems
arXiv: Quantum Physics, 2007Co-Authors: Navin Khaneja, Niels Chr NielsenAbstract:We present a new concept for homonuclear dipolar recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating Field Technique. We demonstrate this Technique as an efficient means to accomplish broadband dipolar recoupling of homonuclear spins, while decoupling heteronuclear dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it possible to synthesize Ising interactions in homonuclear spin networks and thereby avoid dipolar truncation - a serious problem essentially all previous homonuclear dipolar recoupling experiments suffer from. Combination of this recoupling concept with rotor assisted dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly carbon labelled proteins through accurate measurement of {13}C-{13}C internuclear distances. The concept is demonstrated experimentally by measurement of C_alpha-C', C_\beta-C', and C_\gamma-C' internuclear distances in powder samples of the amino acids \textit{L}-alanine and \textit{L}-threonine.
N. Gautham - One of the best experts on this subject based on the ideXlab platform.
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A new peptide docking strategy using a mean Field Technique with mutually orthogonal Latin square sampling
Journal of Computer-Aided Molecular Design, 2008Co-Authors: P. Arun Prasad, N. GauthamAbstract:The theoretical prediction of the association of a flexible ligand with a protein receptor requires efficient sampling of the conformational space of the ligand. Several docking methodologies are currently available. We propose a new docking Technique that performs well at low computational cost. The method uses mutually orthogonal Latin squares to efficiently sample the docking space. A variant of the mean Field Technique is used to analyze this sample to arrive at the optimum. The method has been previously applied to explore the conformational space of peptides and identify structures with low values for the potential energy. Here we extend this method to simultaneously identify both the low energy conformation as well as a ‘high-scoring’ docking mode. Application of the method to 56 protein–peptide complexes, in which the length of the peptide ligand ranges from three to seven residues, and comparisons with Autodock 3.05, showed that the method works well.
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exploring conformational space using a mean Field Technique with mols sampling
Journal of Biosciences, 2007Co-Authors: Arun P Prasad, V Kanagasabai, Jothi Arunachalam, N. GauthamAbstract:The computational identification of all the low energy structures of a peptide given only its sequence is not an easy task even for small peptides, due to the multiple-minima problem and combinatorial explosion. We have developed an algorithm, called the MOLS Technique, that addresses this problem, and have applied it to a number of different aspects of the study of peptide and protein structure. Conformational studies of oligopeptides, including loop sequences in proteins have been carried out using this Technique. In general the calculations identified all the folds determined by previous studies, and in addition picked up other energetically favorable structures. The method was also used to map the energy surface of the peptides. In another application, we have combined the MOLS Technique, using it to generate a library of low energy structures of an oligopeptide, with a genetic algorithm to predict protein structures. The method has also been applied to explore the conformational space of loops in protein structures. Further, it has been applied to the problem of docking a ligand in its receptor site, with encouraging results.
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exploring the conformational space of protein loops using a mean Field Technique with mols sampling
Proteins, 2007Co-Authors: V Kanagasabai, Arun P Prasad, Jothi Arunachalam, N. GauthamAbstract:We have recently developed a computational Technique that uses mutually orthogonal Latin square sampling to explore the conformational space of oligopeptides in an exhaustive manner. In this article, we report its use to analyze the conformational spaces of 120 protein loop sequences in proteins, culled from the PDB, having the length ranging from 5 to 10 residues. The force Field used did not have any information regarding the sequences or structures that flanked the loop. The results of the analyses show that the native structure of the loop, as found in the PDB falls at one of the low energy points in the conformational landscape of the sequences. Thus, a large portion of the structural determinants of the loop may be considered intrinsic to the sequence, regardless of either adjacent sequences or structures, or the interactions that the atoms of the loop make with other residues in the protein or in neighboring proteins. Proteins 2007. © 2007 Wiley-Liss, Inc.
Navin Khaneja - One of the best experts on this subject based on the ideXlab platform.
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Triple oscillating Field Technique for accurate distance measurements by solid-state NMR.
The Journal of chemical physics, 2008Co-Authors: Navin Khaneja, Niels Chr NielsenAbstract:We present a new concept for homonuclear dipolar recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating Field Technique. We demonstrate this Technique as an efficient means to accomplish broadband dipolar recoupling of homonuclear spins, while decoupling heteronuclear dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it is possible to synthesize Ising interaction (2IzSz) Hamiltonians in homonuclear spin networks and thereby avoid dipolar truncation--a serious problem essentially all previous homonuclear dipolar recoupling experiments suffer from. Combination of this recoupling concept with rotor assisted dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly 13C labeled proteins through accurate measurement of 13C-13C internuclear distances. The concept is demonstrated experimentally by measurement of C alpha-C', C beta-C', and C gamma-C' internuclear distances in powder samples of the amino acids L-alanine and L-threonine.
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Triple oscillating Field Technique for accurate measurements of couplings in homonuclear spin systems
arXiv: Quantum Physics, 2007Co-Authors: Navin Khaneja, Niels Chr NielsenAbstract:We present a new concept for homonuclear dipolar recoupling in magic-angle-spinning (MAS) solid-state NMR experiments which avoids the problem of dipolar truncation. This is accomplished through the introduction of a new NMR pulse sequence design principle: the triple oscillating Field Technique. We demonstrate this Technique as an efficient means to accomplish broadband dipolar recoupling of homonuclear spins, while decoupling heteronuclear dipolar couplings and anisotropic chemicals shifts and retaining influence from isotropic chemical shifts. In this manner, it possible to synthesize Ising interactions in homonuclear spin networks and thereby avoid dipolar truncation - a serious problem essentially all previous homonuclear dipolar recoupling experiments suffer from. Combination of this recoupling concept with rotor assisted dipolar refocusing enables easy readout of internuclear distances through comparison with analytical Fresnel curves. This forms the basis for a new class of solid-state NMR experiments with potential for structure analysis of uniformly carbon labelled proteins through accurate measurement of {13}C-{13}C internuclear distances. The concept is demonstrated experimentally by measurement of C_alpha-C', C_\beta-C', and C_\gamma-C' internuclear distances in powder samples of the amino acids \textit{L}-alanine and \textit{L}-threonine.
L. Segen - One of the best experts on this subject based on the ideXlab platform.
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Measurement of g factors of excited states in radioactive beams by the transient Field Technique: 132Te
Physics Letters B, 2008Co-Authors: N. Benczer-koller, G.j. Kumbartzki, G. Gürdal, C.j. Gross, A.e. Stuchbery, B. Krieger, R. Hatarik, P. O'malley, S. Pain, L. SegenAbstract:AbstractThe g factor of the 21+ state in 13252Te, E(21+)=0.9739 MeV, τ=2.6 ps, was measured by the transient Field Technique applied to a radioactive beam. The development of an experimental approach necessary for work in radioactive beam environments is described. The result g=0.28(15) agrees with the previous measurement by the recoil-in-vacuum Technique, but here the sign of the g factor is measured as well
J De Wyngaert - One of the best experts on this subject based on the ideXlab platform.
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su gg t 487 Field in Field Technique to reduce high dose regions in the treatment of the axillary and supraclavicular lymph nodes
Medical Physics, 2008Co-Authors: R Stevenson, G Jozsef, C Hitchen, J De WyngaertAbstract:Purpose: To eliminate the 10–30% excess dose in the standard parallel opposed beam treatment of the axillary and supraclavicular lymph nodes to decrease related skin toxicity. Method and Materials: In a Field‐in‐Field Technique a new Field was added to the supraclavicular (SCLAV) Field with the projection of the posterior axillary boost (PAB) Field blocked out. With appropriate weighting of the 3 Fields equal (prescription) doses can be delivered to 3 cm under both the blocked and unblocked part of the SCLAV and to the midplane under the PAB Field. The weightings can be obtained by solving a simple linear equation system (e.g. in Excel). The Field‐in‐Field Technique was planned with Eclipse treatment planning system on 12 patient CT scans and compared to the standard two beam arrangement. Film measurements were made on phantom to evaluate the match of the Field‐in‐Field with the PAB Field at a depth of 3 cm and at the skin surface. In addition, plans were calculated in phantoms to study the relationship of the weighting and the separation. Results: The prescription requirements, similar coverage to the standard Technique, and minimal excess dose were all achieved with the proposed Technique. The average maximum dose for the 12 sample CT scans decreased from 119.8% as treated to 107.9%. The match between the proposed SCLAV Field‐in‐Field and PAB Field used was good and would be clinically acceptable. Conclusion: The proposed Field‐in‐Field Technique provides more uniform coverage for the treatment of the supraclavicular/axillary region in the treatment of breast cancer. Since the third Field is only a rearrangement of the MLCs in the supraclavicular Field, it does not add much to either the planning or the treatment time.