Distribution by Scientific Domains
Distribution within Chemistry

Kinds of NMR

  • CPMA nmr
  • extensive nmr
  • high-resolution nmr
  • ma nmr
  • multinuclear nmr
  • proton nmr
  • solid-state 13c nmr
  • solid-state nmr
  • solution nmr
  • spinning nmr
  • state nmr
  • two-dimensional nmr

  • Terms modified by NMR

  • nmr analysis
  • nmr approach
  • nmr assignment
  • nmr characterization
  • nmr chemical shift
  • nmr chemical shift assignment
  • nmr data
  • nmr diffusion measurement
  • nmr evidence
  • nmr experiment
  • nmr experiments.
  • nmr imaging
  • nmr investigation
  • nmr line
  • nmr measurement
  • nmr method
  • nmr methodology
  • nmr methods
  • nmr parameter
  • nmr probe
  • nmr property
  • nmr pulse sequence
  • nmr relaxation
  • nmr relaxation rate
  • nmr resonance
  • nmr result
  • nmr shift
  • nmr shows
  • nmr signal
  • nmr signal assignment
  • nmr solution structure
  • nmr spectral analysis
  • nmr spectral data
  • nmr spectral methods
  • nmr spectral studies
  • nmr spectrometer
  • nmr spectroscopic
  • nmr spectroscopic analysis
  • nmr spectroscopic data
  • nmr spectroscopic experiment
  • nmr spectroscopic investigation
  • nmr spectroscopic methods
  • nmr spectroscopic studies
  • nmr spectroscopic study
  • nmr spectroscopic techniques
  • nmr spectroscopy
  • nmr spectroscopy experiment
  • nmr spectrum
  • nmr spin
  • nmr structure
  • nmr structure determination
  • nmr studies
  • nmr study
  • nmr system
  • nmr technique
  • nmr techniques
  • nmr time-scale
  • nmr timescale
  • nmr titration
  • nmr titration experiment
  • nmr tube

  • Selected Abstracts

    Visualization of the distant dipolar field: A numerical study

    Stefan Kirsch
    Abstract The magnetization of liquid water in an external field generates an intrinsic magnetic field in the sample called the distant dipolar field (DDF). To visualize the spatial distribution of the DDF a numerical study was performed for the case of liquid,state 1H NMR at 7 T. 2D maps of the frequency offset caused by the DDF in pure water were calculated for homogenously magnetized spherical and cylindrical samples as well as for the case of a spatially modulated magnetization distribution occurring e.g., in CRAZED (Cosy Revamped by Asymmetric Z-Gradient Echo Detection) experiments. The calculation yielded DDF induced frequency offsets in the range of 0.58 Hz to 10.24 Hz inside the homogeneously magnetized cylinders, while DDF-induced frequency offsets ,10,5 Hz were obtained inside the sphere. The calculated frequency offsets were in good agreement with analytical results available for a sphere and an infinitely long cylinder. In the case of a spatially modulated magnetization distribution, DDF-induced frequency offsets with maximum values of +0.83 Hz were obtained inside the sphere. The presented 2D maps of the DDF-induced frequency offset have tutorial character and may help to visualize this phenomenon in a direct manner. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A:357,364, 2009. [source]

    The origins and present status of the radio wave controversy in NMR

    D.I. Hoult
    Abstract The origins, history, and present status of the controversy surrounding a quantum description of the NMR signal as being due to radio waves are traced. With the Principle of Relativity and Coulomb's Law as formal starting points and the minimum of mathematics needed for understanding, the derivation of a classical electromagnetic theory of signal reception is first given. The agreement between that classical theory and a recent NMR experiment is then presented, leading to proof that, except for the highest field imaging experiments, there is no significant contribution of radio waves to the signal. Attention is drawn to the very different properties of the near and far energy, momenta, and fields inherent in the derivation. The role of the Correspondence Principle in formulating a quantum description is then emphasized and it is shown that the standard NMR interpretation of Dicke's theory of coherent spontaneous emission,that the latter is responsible for the NMR signal,cannot be correct. Finally, the author speculates on some of the intriguing relationships found in the classical electrodynamics of NMR signal reception and attempts to relate them to a common quantum electrodynamic precept of near field interaction: that the free induction decay voltage present at the terminals of an open-circuit receiving coil is based on an exchange of virtual photons between the nuclei in a sample and the free electrons in a receiving coil. © 2009 Crown in the right of Canada. Concepts Magn Reson Part A 34A: 193,216, 2009. [source]

    Toward portable nuclear magnetic resonance devices using atomic magnetometers

    Dindi Yu
    Abstract The motivation for developing alternative detection techniques for nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) is to overcome some of the limitations associated with high-field NMR/MRI instruments. The limitations include poor portability, cryogenic requirements, and high costs. To achieve this goal, a low magnetic field is preferred. Since the sensitivity of inductive detection for conventional NMR and MRI scales linearly with the magnetic field strength, it is not optimal for low-field detection. In this contribution, we describe the concept of using atomic magnetometers as an alternative detection method. Atomic magnetometers possess an ultrahigh sensitivity that is independent of the magnetic field strength, which makes them viable for low-field detection in NMR and MRI. We first introduce the principle of atomic magnetometry and follow this with a discussion of recent progress in the field. To compare the sensitivities of atomic magnetometers of diverse sizes, we define a signal-to-noise ratio for a fixed detection volume to normalize the sensitivity with regard to the cell size. We then focus on two coupling schemes for NMR and MRI detection using atomic magnetometers. Finally, we discuss the challenges involved in implementing this alternative detection technique for NMR and MRI. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A: 124,132, 2009. [source]

    Studying natural structural protein fibers by solid-state nuclear magnetic resonance

    Alexandre A. Arnold
    Abstract As a consequence of evolutionary pressure, various organisms have developed structural fibers displaying a range of exceptional mechanical properties adapted specifically to their functions. An understanding of these properties at the molecular level requires a detailed description of local structure, orientation with respect to the fiber and size of constitutive units, and dynamics on various timescales. The size and lack of long-range order in these protein systems constitute an important challenge to classical structural techniques such as high-resolution NMR and X-ray diffraction. Solid-state NMR overcomes these constraints and is uniquely suited to the study of these inherently disordered systems. Solid-state NMR experiments developed or applied to determine structure, orientation, and dynamics of these complex proteins will be reviewed and illustrated through examples of their applications to fibers such as spider and silkworm silks, collagen, elastin, and keratin. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A: 24,27, 2009. [source]

    NMR and the uncertainty principle: How to and how not to interpret homogeneous line broadening and pulse nonselectivity.

    IV. (Un?)certainty
    Abstract Following the treatments presented in Parts I, II, and III, I herein address the popular notion that the frequency of a monochromatic RF pulse as well as that of a monochromatic FID is "in effect" uncertain due to the (Heisenberg) Uncertainty Principle, which also manifests itself in the fact that the FT-spectrum of these temporal entities is spread over a nonzero frequency band. I will show that the frequency spread should not be interpreted as "in effect" meaning a range of physical driving RF fields in the former, and "spin frequencies" in the latter case. The fact that a shorter pulse or a more quickly decaying FID has a wider FT-spectrum is in fact solely due to the Fourier Uncertainty Principle, which is a less well known and easily misunderstood concept. A proper understanding of the Fourier Uncertainty Principle tells us that the FT-spectrum of a monochromatic pulse is not "broad" because of any "uncertainty" in the RF frequency, but because the spectrum profile carries all of the pulse's features (frequency, phase, amplitude, length, temporal location) coded into the complex amplitudes of the FT-spectrum's constituent eternal basis harmonic waves. A monochromatic RF pulse's capability to excite nonresonant magnetizations is in fact a purely classical off-resonance effect that has nothing to do with "uncertainty". Analogously, "Lorentzian lineshape" means exactly the same thing physically as "exponential decay," and all inferences as to the physical reasons for that decay must be based on independent assumptions or observations. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 373,404, 2008. [source]

    NMR and the uncertainty principle: How to and how not to interpret homogeneous line broadening and pulse nonselectivity.


    Abstract Following the treatments presented in Parts I and II, I herein discuss in more detail the popular notion that the frequency of a monochromatic RF pulse as well as that of a monochromatic FID is "in effect" uncertain due to the (Heisenberg) Uncertainty Principle, which also manifests itself in the fact that the FT-spectrum of these temporal entities is spread over a nonzero frequency band. In Part III, I continue my preliminary review of some further fundamental concepts, such as the Heisenberg and Fourier Uncertainty Principles, that are needed to understand whether or not the NMR linewidth and the RF excitation bandwidth have anything to do with "uncertainty". The article then culminates in re-addressing our Two NMR Problems in a more conscientious frame of mind by using a more refined formalism. The correct interpretation of these problems will be discussed in Part IV. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 302,325, 2008. [source]

    NMR studies of chiral organic compounds in non-isotropic phases

    Marek J. Potrzebowski
    Abstract In this article, new applications and perspectives of one- and two-dimensional NMR spectroscopy for study of chiral organic compounds in the non-isotropic phases (solid state and liquid crystals) are presented. The review is organized into five sections. In the first part, theoretical background and short introduction to solid state NMR are shown. The second part presents how NMR isotropic chemical shift can be used for distinguishing of racemates and enantiomers. In the third section, the power of the ODESSA pulse sequence for investigation of racemates, enantiomers and establishing of enantiomeric excess are discussed. The fourth part shows the application of analysis of principal elements of chemical shift tensors obtained by means of 2D NMR techniques for searching of absolute configuration and conformational changes in the solid state. The final part presents recent achievements of chiral liquid crystals NMR methodology for study of chiral compounds. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A:201,218, 2008. [source]

    The life of , and ,,A tutorial review of the ubiquitous use of these symbols in Zeeman and magnetic-resonance spectroscopy

    John Ashley Weil
    Abstract Certain concepts and symbolism as applied to electromagnetic radiation and especially the concept of photons are discussed and (perhaps) clarified. A useful summary of the properties of photons is provided, and the concept of polarization is discussed. In particular, the common usage in Zeeman and magnetic-resonance (EPR and NMR) spectroscopy of the symbols , and , is examined herein, both from the historical viewpoint and the scientific standpoint, and certain errors and fallacies are brought to attention. Brief reference to relevant recent work published on dynamic nuclear polarization and on pulse EPR is included. © 2008 Wiley Periodicals, Inc.Concepts Magn Reson Part A 32A: 134,142, 2008. [source]

    TROSY effects in MAS solid-state NMR

    Veniamin Chevelkov
    Abstract Use of transverse relaxation-optimized spectroscopy (TROSY) type techniques had a dramatic impact on the study of large proteins with a molecular weight >30kDa for solution-state NMR. In the solid-state, such an effect would not be expected a prior, as the investigated molecules are immobilized. However, local motions induce fluctuations of the local fields experienced by the nuclear spins and, this way, are effective for relaxation. We demonstrate that protein dynamics can significantly influence the resonance line width in ultra high resolution MAS (magic angle spinning) solid-state NMR experiments. Averaging of the 15NH,/, multiplet components as a consequence of 1H decoupling induces effective broadening of the 15N resonance. Application of TROSY type techniques that select only the narrow component of the multiplet pattern results in an increased resolution and, thus, will be of benefit for MAS solid-state NMR spectroscopy. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 143,156, 2008. [source]

    High-precision measurement of internuclear distances using solid-state NMR

    Jae-Seung Lee
    Abstract Today, nuclear magnetic resonance (NMR) is among the most efficient tools in structural studies. Measurement of interatomic distances is the most common way of determining high-resolution structures of molecules using NMR techniques. In this article, we describe NMR techniques for static powder samples, based on a two-dimensional single-echo scheme, enhanced with adiabatic cross-polarization. They can significantly increase the accuracy of measuring internuclear distances and turn NMR into a high-precision crystallographic technique, complementing the X-ray, and neutron-scattering methods. Experimental examples are presented for intramolecular CN and CC distances in ,-crystalline form of glycine. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 56,67, 2008. [source]

    Generalized treatment of NMR spectra for rapid chemical reactions

    Matthew D. Christianson
    Abstract Application of NMR spectroscopy to fast irreversible reactions (t1/2 < 0.7 s) has been hampered by limitations in instrumentation and general methods for modeling the complicated spectra that result. Analytical descriptions of nuclear spin dynamics during fast reactions, first solved by Ernst and coworkers, are limited to first-order reaction kinetics. We demonstrate that numeric methods enable simulation of NMR spectra for fast reactions having any form of rate law. Simulated stopped-flow NMR spectra are presented for a variety of common kinetic scenarios including reversible and irreversible reactions of first and second-order, multistep reactions, and catalytic transformations. The simulations demonstrate that a wealth of mechanistic information, including reaction rates, rate laws, and the existence of intermediates, is imbedded in a single NMR spectrum. The sensitivity of modern NMR instrumentation along with robust methods for simulating and fitting kinetic parameters of fast reactions make stopped-flow NMR an attractive method for kinetic studies of fast chemical reactions. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 165,183, 2007. [source]

    A pulse programmer for nuclear magnetic resonance spectrometers

    C.C. Odebrecht
    Abstract A pulse programmer (PP) designed to control a nuclear magnetic resonance (NMR) spectrometer is reported on. The heart of the PP is a computer programmable logic device (CPDL) that provides flexibility to the design and, at the same time, reduces the number of electronics components needed and the dimensions of the printed circuit board. The PP works as follow: first, a pulse sequence defined by a set of instructions is loaded into the RAM memory of the PP. Then, when the process is started, the instructions are, one by one, read, decoded, and executed. Four types of instructions (functions) were defined: PRINT A, PRINT B, WAIT, and STOP. PRINT A and PRINT B change the status of the output channels A and B, respectively, WAIT generates a time delay, and STOP terminates the sequence. The output ports A and B have 14 channels each, and the shortest pulse and resolution are both 200 ns. The design of the PP is versatile, and new functions can be added through software without modifying the printed circuit board. To control the PP from a personal computer, a program named PulseJr was developed. It contains a graphical user interface (GUI) and pulse sequences can be drawn on the monitor screen with the mouse of the computer. Once the pulse sequence is sketched, clicking a button the program compiles the pulse sequence, generates the set of instructions, loads them into the RAM memory of the PP, and starts the pulse sequence. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 127,131, 2007. [source]

    The hydrogen atom, revisited: Parallel-field magnetic resonance,

    John A. Weil
    Abstract Consideration of the magnetic resonance spectroscopy of the free hydrogen atom (1H0) reveals that, in addition to the well-known transitions (EPR and NMR) occurring between the four spin states when the excitation magnetic field B1 is perpendicular to the static external field B, there exists a combination line (simultaneous electronic and nuclear spin flips) when B1 , B, which becomes strong under some circumstances. The latter phenomenon is focused on and discussed herein, in some detail. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 331,336, 2006 [source]

    NMR in photo-induced chemical exchange systems.

    -dipyridyl)ethene photoisomerization kinetics, Double-resonance inverse fractional population transfer application for investigation of
    Abstract The analytical expression describing the dynamics of nuclear magnetization with the use of double-resonance NMR by the procedure of inverse fractional population transfer in requirements of photo-induced chemical exchange (PICE) is obtained in this article. Laser-induced (, = 308 nm) photoisomerization of 1,2-(2,2,-dipyridyl)ethene was studied by NMR and UV absorption spectroscopy under irreversible and photostationary conditions. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 337,346, 2006 [source]

    NMR in photoinduced chemical exchange systems: Theoretical basis of double-resonance inverse fractional population transfer

    S.P. Babailov
    Abstract The analytical expression describing dynamics of the nuclear magnetization with the use of double-resonance NMR in the transfer of inverse fractional population under photoinduced chemical exchange is obtained. An experimental procedure for the definition of effective rate constants and quantum yield of responses is considered. The technical approach created allows for planning experimental strategies for the study of photoinduced chemical exchange in any solvable substances. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 299,305, 2006 [source]

    Structural information from quadrupolar nuclei in solid state NMR

    Sharon E. Ashbrook
    Abstract Solid-state NMR has become the method of choice for determining details of molecular-level structure in heterogeneous systems. Though spin-1/2 nuclei still form the core of most such studies, quadrupolar nuclei are increasingly being used. This review assesses what is currently possible, from achieving high-resolution spectra for quadrupolar nuclei (a prerequisite for most structure determination work), to forming correlation spectra which give qualitative details of spatial proximity of nuclei and the determination of internuclear distances, between quadrupolar spins and quadrupolar and spin-1/2 nuclei. Examples are given of each method discussed, and the advantages and disadvantages of the various experiments for different possible applications are assessed. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 183,248, 2006. [source]

    How accurately can parameters from exponential models be estimated?

    A Bayesian view
    Abstract Estimating the amplitudes and decay rate constants of exponentially decaying signals is an important problem in NMR. Understanding how the uncertainty in the parameter estimates depends on the data acquisition parameters and on the "true" but unknown values of the exponential signal parameters is an important step in designing experiments and determining the amount and quality of the data that must be gathered to make good parameter estimates. In this article, Bayesian probability theory is applied to this problem. Explicit relationships between the data acquisition parameters and the "true" but unknown exponential signal parameters are derived for the cases of data containing one and two exponential signal components. Because uniform prior probabilities are purposely employed, the results are broadly applicable to experimental parameter estimation. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 27A: 73,83, 2005 [source]

    Dynamic study of cerebral bioenergetics and brain function using in vivo multinuclear MRS approaches

    Wei Chen
    Abstract One of the greatest merits of nuclear magnetic resonance (NMR) methodology used in biomedical research and clinical settings is its capability of measuring various physiological parameters in vivo. Besides MR imaging (MRI), which has been routinely applied to obtain vital information in living organs at normal and diseased states, in vivo MR spectroscopy (MRS) provides an invaluable tool for determining metabolites, chemical reaction rates, bioenergetics, and their dynamic changes in the human and animals noninvasively. These MRS capabilities are further enhanced at high/ultrahigh magnetic fields because of significant gain in NMR detection sensitivity and improvement in the spectral resolution. Recent progress has shown that in vivo MRS holds great promise in many biomedical research areas,in particular, brain research. This article provides a broad review of (i) in vivo multinuclear MRS approaches, (ii) advanced MRS methodologies, and (iii) MRS applications for determining cerebral metabolism as well as bioenergetics at resting brain state and their dynamic changes in response to brain activation. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 27A: 84-121, 2005 [source]

    NMR methods for studying membrane-active antimicrobial peptides

    Erik Strandberg
    Abstract NMR is a versatile tool for studying interactions between antimicrobial peptides and lipid membranes. Different approaches using both liquid state and solid state NMR are outlined here, with an emphasis on solid state NMR methods, to study the structures of antimicrobial peptides in lipid bilayers as well as the effect of these peptides on model membranes. Different NMR techniques for observing both peptides and lipids are explained, including 2H, 13C, 15N, and 19F labels, or natural abundance 1H, 13C, or 31P. Previous studies in the field are extensively reviewed in easily accessible tables. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 23A: 89,120, 2004. [source]

    NMR studies of surfactants

    Olle Söderman
    Abstract Surfactant molecules are amphipathic and posses complicated solution chemistry and self-assembly properties. In addition to being of enormous practical significance, the physical characterization of surfactant systems presents a rich area of condensed matter physics. This article focuses on the application and interpretation of the commonly used NMR approaches for probing these systems. In particular, the use of NMR relaxation, diffusometry and, more briefly, electrophoretic NMR to determine characteristics such as micellar size and structure, ion-binding and solubilization are considered. The application of these NMR techniques is illustrated by a number of pertinent examples. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 23A:, 121,135, 2004. [source]

    Geometric algebra and transition-selective implementations of the controlled-NOT gate

    Timothy F. Havel
    Geometric algebra provides a complete set of simple rules for the manipulation of product operator expressions at a symbolic level, without any explicit use of matrices. This approach can be used not only to describe the state and evolution of a spin system, but also to derive the effective Hamiltonian and associated propagator in full generality. In this article, we illustrate the use of geometric algebra via a detailed analysis of transition-selective implementations of the controlled-NOT gate, which plays a key role in NMR-based quantum information processing. In the appendices, we show how one can also use geometric algebra to derive tight bounds on the magnitudes of the errors associated with these implementations of the controlled-NOT. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part A 23A: 49,62, 2004 [source]

    Setting up 13C CP/MAS experiments

    R.E. Taylor
    Abstract The 13C cross-polarization (CP) technique combined with magic angle spinning (MAS) has become one of the more commonly performed solid-state nuclear magnetic resonance (NMR) experiments. The basics of initially setting up the experiment are given and used to illustrate such NMR phenomena as rotational echoes, homogeneous and inhomogeneous interactions, continuous wave 1H decoupling, and coupling of quadrupolar 14N nuclei to 13C nuclei. The polarization transfer from the protons to the carbons is described briefly with the usual thermodynamic and quantum mechanical models. The setup and use of the experiment for routine analyses are discussed. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 22A: 37,49, 2004. [source]

    Nuclear magnetic resonance data processing.

    MestRe-C: A software package for desktop computers
    Abstract Magnetic Resonance Companion (MestRe-C) is a software package that offers state-of-the-art facilities for data processing, visualization, and analysis of high-resolution nuclear magnetic resonance (NMR) data, combined with a robust, user-friendly graphical interface that fully exploits the power and flexibility of the Windows platform. The program provides a variety of conversion facilities for most NMR spectrometer formats and includes all the conventional processing, displaying, and plotting capabilities of an NMR program, as well as more advanced processing techniques. A brief review of the basic concepts of NMR data processing is included also. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 80,96, 2003. [source]

    Thermal relaxation and coherence dynamics of spin 3/2.


    Abstract The relaxation dynamics of the spin 3/2 density operator in the presence of fluctuating and static quadrupolar interactions is reviewed. The nuclear magnetic resonance (NMR) line shapes are analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. Pulse sequences optimized for the elimination of line broadening due to an inhomogeneous static quadrupolar interaction and for the detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part II, the dynamics of spin 3/2 in the presence of a (pulsed) radio frequency (RF) field is reviewed. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 97,116, 2003. [source]

    Using pulsed gradient spin echo NMR for chemical mixture analysis: How to obtain optimum results

    Brian Antalek
    Abstract Pulsed gradient spin echo NMR is a powerful technique for measuring diffusion coefficients. When coupled with appropriate data processing schemes, the technique becomes an exceptionally valuable tool for mixture analysis, the separation of which is based on the molecular size. Extremely fine differentiation may be possible in the diffusion dimension but only with high-quality data. For fully resolved resonances, components with diffusion coefficients that differ by less than 2% may be distinguished in mixtures. For highly overlapped resonances, the resolved spectra of pure components with diffusion coefficients that differ by less than 30% may be obtained. In order to achieve the best possible data quality one must be aware of the primary sources of artifacts and incorporate the necessary means to alleviate them. The origin of these artifacts are described, along with the methods necessary to observe them. Practical solutions are presented. Examples are shown that demonstrate the effects of the artifacts on the acquired data set. Many mixture analysis problems may be addressed with conventional high resolution pulsed field gradient probe technology delivering less than 0.5 T m,1 (50 G cm,1). © 2002 Wiley Periodicals, Inc. Concepts Magn Reson 14: 225,258, 2002. [source]

    NMR of peptides and proteins in oriented membranes

    Francesca M. Marassi
    Abstract Solid-state NMR spectroscopy is used to determine the structures of membrane peptides and proteins in lipid bilayers. The methodology for membrane protein structure determination using solid-state NMR of oriented lipid bilayer samples is outlined. Recent developments in recombinant bacterial expression systems for the preparation of isotopically labeled membrane proteins, pulse sequences for high-resolution spectroscopy, and structural indices that guide the structure assembly process greatly extend the capabilities of the technique. © 2002 Wiley Periodicals, Inc. Concepts in Magn Reson 14, 212,224, 2002. [source]

    Los Alamos NMR well logging project

    Jasper A. Jackson
    First page of article [source]

    Solenoidal microcoil design,Part II: Optimizing winding parameters for maximum signal-to-noise performance

    Kevin R. Minard
    Abstract In high-field proton NMR, the signal-to-noise ratio (SNR) achieved with a close-fitting solenoidal microcoil is adversely affected by radio frequency (RF) losses in the coil, its leads, the capacitor used to tune it, and finally, the sample. In Part II, a rigorous description of these various losses is presented, and their severity is related to the details of coil design. Results not only provide a rational basis for defining a microcoil's optimal wire diameter and the number of turns, but also for evaluating how the SNR varies with coil size and NMR frequency in high-field proton NMR studies involving either conducting or non-conducting samples. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 190,210, 2001 [source]

    FS01.3 Disperse (yes), orange (yes), 3 (no): what do we test in textile dye dermatitis?

    CONTACT DERMATITIS, Issue 3 2004
    Christophe J Le Coz
    Introduction:, Patients sensitized to para-phenylenediamine (PPD) have a high degree of patch test reactivity to Disperse Orange 3 (DO3), and a lesser one to Disperse Red 1 and Red 17. Two successive patients positive to PPD, Disperse Red 1 and 17, negative to DO3 were real eye-openers for our considerations about purity of our current allergen DO3. Materials and methods:, We realized comparative thin-layer chromatography (TLC), with DO3 from Chemotechnique®(DO3-Chem) and Trolab®(both extracted from petrolatum), and "pure" DO3 from two chemical providers. TLC clearly indicated that DO3-Chem was not DO3. HPLC analysis with pure DO3 from Chemotechnique® and comparison of structures by NMR with samples of DO3, revealed that DO3-Chem was Disperse Orange 31 (DO31). In addition, signals through the GERDA network allowed the collection of test materials and observations. Among other members, only 2 used DO3-Chem (from 2 different batches) that was DO31 too, according to TLC Results: According to their data, they observed no or a lower reactivity to DO3 than expected (4 patients DO3-Chem + among 23 PPD+ e.g.). Finally, the error was proved to be due to the provider of the dye to Chemotechnique®, who likely deleted the 1 of Disperse Orange 31 on his packaging. Discussion:, Chemical structure of DO31 indicates a possible in vivo hydrolysis into nitroaniline and a second compound, a substituted PPD derivative that clearly does not frequently react in PPD positive patients. Like drugs, patch tests are submitted to post-commercialization controls. In addition to allergens providers who should enhance their quality controls, dermato-allergologists have to be vigilant, and must active networks when they observe a rare bird. [source]

    Synthesis and characterization of tetraprolinium silicotungstic acid tetra-hydrate, a new organic-inorganic hybrid based on polyoxometallates

    M. H. Alizadeh
    Abstract A new solvated polyoxometallate bearing an amino acid, (I), has been prepared for the first time by the reaction of 0.16 mmol ,-H4SiW12O40.15H2O with 0.78 mmol of L-proline in hydrochloric acid at pH 3. The structure of (I) was substantially characterized by some physical approaches, such as elemental analysis, infrared spectroscopy, and 1H-NMR. Our findings proved that (I) could be formulated as [L-C5H10NO2]4[SiW12O40].4H2O. It is believed that the electrostatic attractions and hydrogen bonding between tungstosilisic acid and the prolinium cation affected the structure of (I). It is evident that the polyoxometallates moieties were arranged in good order to form large holes in the structural backbone. These cavities were occupied by the prolinium cations and water molecules. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]