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Nuclear Polarization (nuclear + polarization)

Distribution by Scientific Domains
Medical Sciences54%
Chemistry36%

Kinds of Nuclear Polarization

  • dynamic nuclear polarization
    		•

    Selected Abstracts

    Scavenging Free Radicals To Preserve Enhancement and Extend Relaxation Times in NMR using Dynamic Nuclear Polarization,

    ANGEWANDTE CHEMIE, Issue 35 2010
    Pascal Miéville
    Länger leben dank Vitamin,C: N -Oxid-Radikale, die weithin zur dynamischen Kernpolarisation eingesetzt werden, können beim Auflösen durch Abfangreagentien wie Natriumascorbat (Vitamin,C) reduziert werden, wodurch Polarisierungsverluste während des Transfers vermieden und transversale wie longitudinale Relaxationszeiten in NMR-spektroskopischen Experimenten verlängert werden (siehe Bild). [source]

    Dynamic Nuclear Polarization with Polychlorotriphenylmethyl Radicals: Supramolecular Polarization-Transfer Effects,

    ANGEWANDTE CHEMIE, Issue 19 2010
    Cristina Gabellieri Dr.
    Positiv oder negativ: Polychlorierte Tritylradikale (siehe Struktur: C schwarz, Cl grün, Na grau, O rot) zeigten beim Einsatz in der dynamischen Kernpolarisation (DNP) einen neuen Transfermechanismus unter Beteiligung der quadrupolaren Chlorkerne. Die Beobachtung positiver oder negativer Verstärkungen für verschiedene Substrate spricht für einen supramolekularen Charakter des anfänglichen Polarisationstransfers. [source]

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

    CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2008
    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]

    Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.

    CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003

    Abstract Dynamic nuclear polarization of nuclear spins via the solid-state and thermal mixing effects is discussed. Continuous-wave S- and X-band microwave radiation have been employed to measure 13C signal enhancements and polarization times for 13C nuclei in a natural type Ib diamond as a function of magnetic field. It was found that thermal mixing plays an important role in the 13C signal enhancement because the central electron spin resonance (ESR) line width HL , H0,C/,e, resulting in flip-flip and flip-flop forbidden transitions taking place simultaneously. On the other hand, the 13C spin-lattice relaxation rate is determined to a large extent by the solid-state effect (forbidden transitions). 13C polarization rates have also been measured for a suite of natural diamonds. It is shown that the polarization rate is proportional to the paramagnetic impurity concentration, in agreement with the theory. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 36,43, 2003. [source]

    Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.

    CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003

    Abstract Dynamic nuclear polarization of nuclei by means of paramagnetic electron spin locking (Hartmann-Hahn cross-polarization between paramagnetic electrons and nuclei, or NOVEL) is discussed. The theory is demonstrated by experiments executed at 2.4 and 9.6 GHz on a natural type Ib diamond. It is shown that the 13C polarization rate is independent of the microwave frequency, in agreement with theory. NOVEL polarization takes place only while the spin-locking pulse is on. The rate at which the nuclei are polarized is proportional to the electron polarization in the rotating frame. Therefore, the length of the spin-locking pulse is limited by the value of T1,(e), and because T1,(e) , T1(e) for diamond the effective NOVEL polarization rate of 13C nuclei is usually relatively low. A comparison between the relative effectiveness of 13C polarization rates between NOVEL and the solid-state effect is made for high and low paramagnetic impurity concentrations. The dependence of the 13C polarization rate on the paramagnetic impurity concentration has been determined for a suite of natural diamonds. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 44,49, 2003. [source]

    Nuclear-Spin Polarization in Electron-Transfer Reactions of Amines

    HELVETICA CHIMICA ACTA, Issue 12 2006
    Heinz
    Abstract Chemically induced dynamic nuclear polarization (CIDNP) observed during electron transfer (ET) reactions of tertiary amines such as DABCO (1) or Et3N (2) with a wide range of electron acceptors support the involvement of amine radical-cations (e.g., 1.+ or 2.+) as key intermediates. Radical ions such as 2.+ may be deprotonated, generating neutral aminoalkyl radicals (e.g., 2.). When generated by reaction with an electron acceptor of energetically low triplet state such as naphthalene (1Naph*), the resulting pair 2.+/Naph., reacts mostly by reverse electron transfer (RET) from triplet pairs populating the naphthalene triplet state. [source]

    Electron spin resonance study of phosphorus-nitroxides from 1,3-additions of silicon-phosphorus reagents to nitrones

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2004
    Dr D. Lawrence Haire
    Abstract This article explores a new, convenient route to ,-phosphorus nitroxides. Specifically, the reaction sequence involves the novel 1,3-addition of trimethylsilyl phosphites (e.g. diethyl) or trimethylsilyl phosphines (e.g. diphenyl) to aldo-nitrones [e.g. ,-phenyl-N- tert -butylnitrone (PBN) or 5,5-dimethyl-l-pyrroline-N-oxide (DMPO)] or keto-nitrones [e.g. 2-ethyl-5,5-dimethyl-1 pyrroline-N-oxide (2-Et-DMPO) or 2-phenyl-5,5-dimethyl-l-pyrroline-N-oxide (2-Ph-DMPO)] to form ,-phosphityl- or ,-phosphinyl-O-silylhydroxylamines. Acidic hydrolysis provides the corresponding hydroxylamines that are easily oxidized to the title ,-phosphorus-nitroxides. ESR spectroscopic analysis revealed some very large ,-phosphorus hyperfine splittings (i.e. in excess of 5 mT). For this reason and their remarkable stability (persistence) some of these nitroxides show promise as integral components in new, improved weak-field dynamic nuclear polarization (DNP) magnetometers. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Hyperpolarized 13C magnetic resonance detection of carboxypeptidase G2 activity

    MAGNETIC RESONANCE IN MEDICINE, Issue 5 2009
    Yann Jamin
    Abstract Carboxypeptidase G2 (CPG2) is a bacterial enzyme that is currently employed in a range of targeted cancer chemotherapy strategies such as gene-directed enzyme prodrug therapy (GDEPT). Employing dynamic nuclear polarization (DNP) and natural abundance 13C magnetic resonance spectroscopy (MRS), we observed the CPG2-mediated conversion of a novel hyperpolarized reporter probe 3,5-difluorobenzoyl-L-glutamic acid (3,5-DFBGlu) to 3,5-difluorobenzoic acid (3,5-DFBA) and L-glutamic acid (L-Glu) in vitro. Isotopic labeling of the relevant nuclei with 13C in 3,5-DFBGlu or related substrates will yield a further factor of 100 increase in the signal-to-noise. We discuss the feasibility of translating these experiments to generate metabolic images of CPG2 activity in vivo. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source]

    Application of subsecond spiral chemical shift imaging to real-time multislice metabolic imaging of the rat in vivo after injection of hyperpolarized 13C1 -pyruvate

    MAGNETIC RESONANCE IN MEDICINE, Issue 3 2009
    Dirk Mayer
    Abstract Dynamic nuclear polarization can create hyperpolarized compounds with MR signal-to-noise ratio enhancements on the order of 10,000-fold. Both exogenous and normally occurring endogenous compounds can be polarized, and their initial concentration and downstream metabolic products can be assessed using MR spectroscopy. Given the transient nature of the hyperpolarized signal enhancement, fast imaging techniques are a critical requirement for real-time metabolic imaging. We report on the development of an ultrafast, multislice, spiral chemical shift imaging sequence, with subsecond acquisition time, achieved on a clinical MR scanner. The technique was used for dynamic metabolic imaging in rats, with measurement of time-resolved spatial distributions of hyperpolarized 13C1 -pyruvate and metabolic products 13C1 -lactate and 13C1 -alanine, with a temporal resolution of as fast as 1 s. Metabolic imaging revealed different signal time courses in liver from kidney. These results demonstrate the feasibility of real-time, hyperpolarized metabolic imaging and highlight its potential in assessing organ-specific kinetic parameters. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source]

    Assessment of tumor oxygenation by electron paramagnetic resonance: principles and applications

    NMR IN BIOMEDICINE, Issue 5 2004
    Bernard Gallez
    Abstract This review paper attempts to provide an overview of the principles and techniques that are often termed electron paramagnetic resonance (EPR) oximetry. The paper discusses the potential of such methods and illustrates they have been successfully applied to measure oxygen tension, an essential parameter of the tumor microenvironment. To help the reader understand the motivation for carrying out these measurements, the importance of tumor hypoxia is first discussed: the basic issues of why a tumor is hypoxic, why these hypoxic microenvironments promote processes driving malignant progression and why hypoxia dramatically influences the response of tumors to cytotoxic treatments will be explained. The different methods that have been used to estimate the oxygenation in tumors will be reviewed. To introduce the basics of EPR oximetry, the specificity of in vivo EPR will be discussed by comparing this technique with NMR and MRI. The different types of paramagnetic oxygen sensors will be presented, as well as the methods for recording the information (EPR spectroscopy, EPR imaging, dynamic nuclear polarization). Several applications of EPR for characterizing tumor oxygenation will be illustrated, with a special emphasis on pharmacological interventions that modulate the tumor microenvironment. Finally, the challenges for transposing the method into the clinic will also be discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Photo-CIDNP Study of the Interaction of Tyrosine with Nifedipine.

    PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2004
    An Attempt to Model the Binding Between Calcium Receptor, Calcium Antagonist Nifedipine
    This article proposes a new approach to the modeling of the molecular-level mechanism of ligand-receptor interaction for Ca2+ receptor binding site. Chemically induced dynamic nuclear polarization (CIDNP) technique has been used to unravel fine details of the reaction in the model system composed of one of the known Ca2+ antagonist drugs, nifedipine (NF), and isolated amino acid residuals (e.g. tyrosine [Tyr]) of Ca2+ receptor binding site. It has been conclusively demonstrated that the reaction between NF and Tyr resulting in the oxidation product,nitroso form of NF,obeys the radical mechanism. CIDNP data in combination with the results of mathematical modeling of the structures of ligandreceptor complexes have allowed to propose the mechanism of the interaction of NF with Ca2+ receptor binding site. [source]