Modified Spin‐Echo Method for Measuring Nuclear Relaxation Times
TL;DR: In this article, a spin echo method adapted to the measurement of long nuclear relaxation times (T2) in liquids is described, and the pulse sequence is identical to the one proposed by Carr and Purcell, but the rf of the successive pulses is coherent, and a phase shift of 90° is introduced in the first pulse.
Abstract: A spin echo method adapted to the measurement of long nuclear relaxation times (T2) in liquids is described. The pulse sequence is identical to the one proposed by Carr and Purcell, but the rf of the successive pulses is coherent, and a phase shift of 90° is introduced in the first pulse. Very long T2 values can be measured without appreciable effect of diffusion.
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TL;DR: Corma et al. as mentioned in this paper used the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) on technology research (1996), to recognize the performance of zeolites as catalysts for oil refining and petrochemistry.
Abstract: It is possible to say that zeolites are the most widely used catalysts in industry They are crystalline microporous materials which have become extremely successful as catalysts for oil refining, petrochemistry, and organic synthesis in the production of fine and speciality chemicals, particularly when dealing with molecules having kinetic diameters below 10 A The reason for their success in catalysis is related to the following specific features of these materials:1 (1) They have very high surface area and adsorption capacity (2) The adsorption properties of the zeolites can be controlled, and they can be varied from hydrophobic to hydrophilic type materials (3) Active sites, such as acid sites for instance, can be generated in the framework and their strength and concentration can be tailored for a particular application (4) The sizes of their channels and cavities are in the range typical for many molecules of interest (5-12 A), and the strong electric fields2 existing in those micropores together with an electronic confinement of the guest molecules3 are responsible for a preactivation of the reactants (5) Their intricate channel structure allows the zeolites to present different types of shape selectivity, ie, product, reactant, and transition state, which can be used to direct a given catalytic reaction toward the desired product avoiding undesired side reactions (6) All of these properties of zeolites, which are of paramount importance in catalysis and make them attractive choices for the types of processes listed above, are ultimately dependent on the thermal and hydrothermal stability of these materials In the case of zeolites, they can be activated to produce very stable materials not just resistant to heat and steam but also to chemical attacks Avelino Corma Canos was born in Moncofar, Spain, in 1951 He studied chemistry at the Universidad de Valencia (1967−1973) and received his PhD at the Universidad Complutense de Madrid in 1976 He became director of the Instituto de Tecnologia Quimica (UPV-CSIC) at the Universidad Politecnica de Valencia in 1990 His current research field is zeolites as catalysts, covering aspects of synthesis, characterization and reactivity in acid−base and redox catalysis A Corma has written about 250 articles on these subjects in international journals, three books, and a number of reviews and book chapters He is a member of the Editorial Board of Zeolites, Catalysis Review Science and Engineering, Catalysis Letters, Applied Catalysis, Journal of Molecular Catalysis, Research Trends, CaTTech, and Journal of the Chemical Society, Chemical Communications A Corma is coauthor of 20 patents, five of them being for commercial applications He has been awarded with the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) 2373 Chem Rev 1997, 97, 2373−2419
5,290 citations
TL;DR: Overall, higher order parameters were not found in the peptide-bound form, indicating that on average, picosecond-time-scale disorder is not reduced upon binding peptide, and the relaxation data of the SH2-phosphopeptide complex were fit with fewer exchange terms than the uncomplexed form.
Abstract: The backbone dynamics of the C-terminal SH2 domain of phospholipase C gamma 1 have been investigated. Two forms of the domain were studied, one in complex with a high-affinity binding peptide derived from the platelet-derived growth factor receptor and the other in the absence of this peptide. 2-D 1H-15N NMR methods, employing pulsed field gradients, were used to determine steady-state 1H-15N NOE values and T1 and T2 15N relaxation times. Backbone dynamics were characterized by the overall correlation time (tau m), order parameters (S2), effective correlation times for internal motions (tau e), and, if required, terms to account for motions on a microsecond-to-millisecond-time scale. An extended two-time-scale formalism was used for residues having relaxation data and that could not be fit adequately using a single-time-scale formalism. The overall correlation times of the uncomplexed and complexed forms of SH2 were found to be 9.2 and 6.5 ns, respectively, suggesting that the uncomplexed form is in a monomer-dimer equilibrium. This was subsequently confirmed by hydrodynamic measurements. Analysis of order parameters reveals that residues in the so-called phosphotyrosine-binding loop exhibited higher than average disorder in both forms of SH2. Although localized differences in order parameters were observed between the uncomplexed and complexed forms of SH2, overall, higher order parameters were not found in the peptide-bound form, indicating that on average, picosecond-time-scale disorder is not reduced upon binding peptide. The relaxation data of the SH2-phosphopeptide complex were fit with fewer exchange terms than the uncomplexed form. This may reflect the monomer-dimer equilibrium that exists in the uncomplexed form or may indicate that the complexed form has lower conformational flexibility on a microsecond-to-millisecond-time scale.
2,064 citations
TL;DR: Based on the principles of echo imaging, a method is proposed to acquire sufficient data for a 256 × 256 image in from 2 to 40s, and the signal amplitudes of structures with long T2 are nearly the same as those in a conventional 2D FT experiment.
Abstract: Based on the principles of echo imaging, we present a method to acquire sufficient data for a 256 X 256 image in from 2 to 40 s. The image contrast is dominated by the transverse relaxation time T2. Sampling all projections for 2D FT image reconstruction in one (or a few) echo trains leads to image artifacts due to the different T2 weighting of the echo. These artifacts cannot be described by a simple smearing out of the image in the phase direction. Proper distribution of the phase-encoding steps on the echoes can be used to minimize artifacts and even lead to resolution enhancement. In spite of the short data acquisition times, the signal amplitudes of structures with long T2 are nearly the same as those in a conventional 2D FT experiment. Our method, therefore, is an ideal screening technique for lesions with long T2.
2,051 citations
TL;DR: The main NMR spectroscopic applications in modern metabolic research are summarized, and detailed protocols for biofluid and tissue sample collection and preparation are provided, including the extraction of polar and lipophilic metabolites from tissues.
Abstract: Metabolic profiling, metabolomic and metabonomic studies mainly involve the multicomponent analysis of biological fluids, tissue and cell extracts using NMR spectroscopy and/or mass spectrometry (MS). We summarize the main NMR spectroscopic applications in modern metabolic research, and provide detailed protocols for biofluid (urine, serum/plasma) and tissue sample collection and preparation, including the extraction of polar and lipophilic metabolites from tissues. 1H NMR spectroscopic techniques such as standard 1D spectroscopy, relaxation-edited, diffusion-edited and 2D J-resolved pulse sequences are widely used at the analysis stage to monitor different groups of metabolites and are described here. They are often followed by more detailed statistical analysis or additional 2D NMR analysis for biomarker discovery. The standard acquisition time per sample is 4-5 min for a simple 1D spectrum, and both preparation and analysis can be automated to allow application to high-throughput screening for clinical diagnostic and toxicological studies, as well as molecular phenotyping and functional genomics.
1,808 citations
TL;DR: The use of novel two-dimensional nuclear magnetic resonance (NMR) pulse sequences to provide insight into protein dynamics is described, suggesting that there is no correlation between these rapid small amplitude motions and secondary structure for S. Nase.
Abstract: This paper describes the use of novel two-dimensional nuclear magnetic resonance (NMR) pulse sequences to provide insight into protein dynamics. The sequences developed permit the measurement of the relaxation properties of individual nuclei in macromolecules, thereby providing a powerful experimental approach to the study of local protein mobility. For isotopically labeled macromolecules, the sequences enable measurements of heteronuclear nuclear Overhauser effects (NOE) and spin-lattice (T1) and spin-spin (T2) 15N or 13C relaxation times with a sensitivity similar to those of many homonuclear 1H experiments. Because T1 values and heteronuclear NOEs are sensitive to high-frequency motions (10(8)-10(12) s-1) while T2 values are also a function of much slower processes, it is possible to explore dynamic events occurring over a large time scale. We have applied these techniques to investigate the backbone dynamics of the protein staphylococcal nuclease (S. Nase) complexed with thymidine 3',5'-bisphosphate (pdTp) and Ca2+ and labeled uniformly with 15N. T1, T2, and NOE values were obtained for over 100 assigned backbone amide nitrogens in the protein. Values of the order parameter (S), characterizing the extent of rapid 1H-15N bond motions, have been determined. These results suggest that there is no correlation between these rapid small amplitude motions and secondary structure for S. Nase. In contrast, 15N line widths suggest a possible correlation between secondary structure and motions on the millisecond time scale. In particular, the loop region between residues 42 and 56 appears to be considerably more flexible on this slow time scale than the rest of the protein.
1,760 citations
Cites methods from "Modified Spin‐Echo Method for Measu..."
...By use of the well-known Carr-Purcell-Meiboom4ill (CPMG) pulse train (Carr & Purcell, 1954; Meiboom & Gill, 1958) during the transverse relaxation time T in the sequence of Figure 1 b, these effects are substantially reduced....
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References
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TL;DR: In this paper, the effect of diffusion on free precession in nuclear resonance has been studied, and a new scheme for measuring the transverse relaxation time is described, which largely circumvents the diffusion effect.
Abstract: Nuclear resonance techniques involving free precession are examined, and, in particular, a convenient variation of Hahn's spin-echo method is described. This variation employs a combination of pulses of different intensity or duration ("90-degree" and "180-degree" pulses). Measurements of the transverse relaxation time ${T}_{2}$ in fluids are often severely compromised by molecular diffusion. Hahn's analysis of the effect of diffusion is reformulated and extended, and a new scheme for measuring ${T}_{2}$ is described which, as predicted by the extended theory, largely circumvents the diffusion effect. On the other hand, the free precession technique, applied in a different way, permits a direct measurement of the molecular self-diffusion constant in suitable fluids. A measurement of the self-diffusion constant of water at 25\ifmmode^\circ\else\textdegree\fi{}C is described which yields $D=2.5(\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ ${\mathrm{cm}}^{2}$/sec, in good agreement with previous determinations. An analysis of the effect of convection on free precession is also given. A null method for measuring the longitudinal relaxation time ${T}_{1}$, based on the unequal-pulse technique, is described.
5,630 citations
TL;DR: In this paper, the thermal relaxation time can be directly found by observing the dependence of initial amplitude on the time between pulses, and the spin-spin time constant can be found from the rate of decay even in the presence of normally disturbing inhomogeneity in magnetic field.
Abstract: Transient nutations of the resultant nuclear magnetic moment vector are set up by applying radiofrequency power in the form of pulses in the neighborhood of resonance ($\ensuremath{\omega}=\ensuremath{\gamma}{H}_{0}$). The nutations have an initial amplitude depending on the state of magnetization at the start of a pulse and on the proximity to resonance, and are damped by spin-spin and spin-lattice interaction. The thermal relaxation time can be directly found by observing the dependence of initial amplitude on the time between pulses. The spin-spin time constant ${T}_{2}$ can be found from the rate of decay even in the presence of normally disturbing inhomogeneity in magnetic field. Sensitivity is in many cases comparable to that obtained in the modulation method with narrow band amplifiers. The fast response due to the relatively wide band widths used can be applied to a rapid search for unknown resonances. The effects observed are in qualitative accord with predictions based on the Bloch theory.
602 citations
TL;DR: In this article, the use of a rotating coordinate system to solve magnetic resonance problems is described, where the effective field is reduced by the Larmor field appropriate to the rotational frequency.
Abstract: The use of a rotating coordinate system to solve magnetic resonance problems is described. On a coordinate system rotating with the applied rotating magnetic field the effective field is reduced by the Larmor field appropriate to the rotational frequency. However, on such a coordinate system problems can more readily be solved since there is no time variation of the field. The solution in a stationary frame of reference is then obtained by a transformation from the rotating to the stationary frame. This procedure is equally valid in classical and in quantum-mechanical problems. The method is applied both to the molecular beam magnetic resonance method and to resonance absorption and nuclear induction experiments.
370 citations
01 Apr 1950
TL;DR: In this article, different approximations for the shapes and sizes of nuclear induction signals are derived for various limiting cases, depending on whether the passage of Hz is adiabatic or extremely non-adiabatic (very weak radio-frequency field) and whether the relaxation times are shorter or longer than the period of the sweep of Hz.
Abstract: Equations of motion, previously derived by Bloch (1946), for the nuclear magnetic moment in a nuclear induction experiment are applied to the steady state reached when the strong magnetic field Hz is swept sinusoidally about its resonance value. Different approximations for the shapes and sizes of nuclear induction signals are derived for various limiting cases, depending (a) whether the passage of Hz is ` adiabatic ' or ` extremely non-adiabatic ' (very weak radio-frequency field) and (b) whether the relaxation times are shorter or longer than the period of the sweep of Hz. It is found that quite large signals may be induced by even a very weak radio-frequency field if the relaxation times are very long.
16 citations
TL;DR: Torrey has proposed and used a method in which long relaxation times T2 can be studied in the presence of an inhomogeneous magnetic field, and the observation of his phenomenon depends on maintaining the magnetic field at resonance, and is quite unrelated to the ‘wiggles’ experiments.
Abstract: IT is well known1 that when a nuclear magnetic resonance signal is obtained in a rapidly rising magnetic field, the nuclei continue processing after resonance is passed. Their precessional frequency increases with the magnetic field, and while doing so forms beats with the exciting radio-frequency. These beats appear as ‘wiggles’ after passing the main resonance. In a perfectly homogeneous field, these wiggles die away exponentially at a rate determined by the relaxation time T22. T2 is related to the natural line-width by the relation T2 = 1/γΔH, where ΔH is the line-width and γ the gyromagnetic ratio of the nuclei being used. If the magnetic field is inhomogeneous by more than ΔH over the sample volume, say by ΔH, then the rate of decay of the wiggles is generally believed to be determined by the time, ∼1/γΔH. This has proved a limitation in the measurement of transverse relaxation times T2 ≫ 10−3 sec., as for such measurements a magnetic field inhomogeneity of ≲ 0.003 gauss is required; and, hitherto, this requirement has not been satisfied. Torrey3 has proposed and used a method in which long relaxation times T2 can be studied in the presence of an inhomogeneous magnetic field. The observation of his phenomenon depends on maintaining the magnetic field at resonance, and is quite unrelated to the ‘wiggles’ experiments.
6 citations