Friday, December 30, 2016

Dissolution dynamic nuclear polarization–enhanced magnetic resonance spectroscopy and imaging: Chemical and biochemical reactions in nonequilibrium conditions #DNPNMR


Lee, Y., Dissolution dynamic nuclear polarization–enhanced magnetic resonance spectroscopy and imaging: Chemical and biochemical reactions in nonequilibrium conditions. Applied Spectroscopy Reviews, 2015. 51(3): p. 210-226.


Hyperpolarization techniques, in particular dissolution dynamic nuclear polarization (D-DNP), make a contribution to overcoming sensitivity limitations of magnetic resonance (MR) spectroscopy through signal enhancement, leading to the study of new fields of research in real time. Utilizing the large signal enhancement initially produced on small molecules, it has become possible to study systems with low gamma-nuclei, such as 13C, 15N, and 29Si. This review summarizes recent studies that have extended the applicability of D-DNP into various areas of research, especially for systems in nonequilibrium conditions that involve in vivo metabolic/molecular MR imaging for early stage disease diagnosis and real-time MR analysis of various chemical/biochemical reactions for kinetic and mechanistic studies. This review also deals with the theoretical aspects of DNP mechanisms and experimental arrangements of the dissolution setup.

Wednesday, December 28, 2016

Surface Binding of TOTAPOL Assists Structural Investigations of Amyloid Fibrils by Dynamic Nuclear Polarization NMR Spectroscopy #DNPNMR


Nagaraj, M., et al., Surface Binding of TOTAPOL Assists Structural Investigations of Amyloid Fibrils by Dynamic Nuclear Polarization NMR Spectroscopy. Chembiochem, 2016. 17(14): p. 1308-11.


Dynamic nuclear polarization (DNP) NMR can enhance sensitivity but often comes at the price of a substantial loss of resolution. Two major factors affect spectral quality: low-temperature heterogeneous line broadening and paramagnetic relaxation enhancement (PRE) effects. Investigations by NMR spectroscopy, isothermal titration calorimetry (ITC), and EPR revealed a new substantial affinity of TOTAPOL to amyloid surfaces, very similar to that shown by the fluorescent dye thioflavin-T (ThT). As a consequence, DNP spectra with remarkably good resolution and still reasonable enhancement could be obtained at very low TOTAPOL concentrations, typically 400 times lower than commonly employed. These spectra yielded several long-range constraints that were difficult to obtain without DNP. Our findings open up new strategies for structural studies with DNP NMR spectroscopy on amyloids that can bind the biradical with affinity similar to that shown towards ThT.

[NMR] Tenure-track NMR position at UCSD

From the Ampere Magnetic Resonance List



Tenure-track NMR position at UCSD

THE DEPARTMENT OF CHEMISTRY AND BIOCHEMISTRY within the Division of Physical Sciences at UC San Diego (http://chemistry.ucsd.edu/) invites applications for the position of tenure-track Assistant Professor in Chemistry & Biochemistry, broadly defined. Candidates with research interests in Biological, Materials, or Chemical NMR Spectroscopy are particularly encouraged to apply, especially experimentalists with a strong focus on addressing fundamental structural questions about macromolecules and supramolecular assemblies using the most up-to-date NMR methods. Applications to biomolecules and their complexes, novel materials and assemblies, nanoparticles, and surfaces and interfaces are all of interest. Candidates must have a Ph.D. in chemistry, biophysics or a closely related field and a demonstrated ability or potential for a recognized program of excellence in both teaching and research. All positions are subject to budget approval.

The Department of Chemistry and Biochemistry at UC San Diego is committed to academic excellence and diversity within the faculty, staff and student body. Successful candidates will be judged on research and teaching accomplishments, as well as on potential and/or demonstrated leadership in areas contributing to diversity, equity, and inclusion. Successful candidates will be expected to teach chemistry and/or biochemistry courses at both the graduate and undergraduate levels.

Candidates should submit online: Curriculum vitae with list of publications, reprints of up to five representative papers, a statement of teaching, and a personal statement that includes a summary of research plans. Additionally, a separate statement that addresses past and/or potential contributions to diversity, equity and inclusion should also be included in the application materials, see http://facultyequity.ucsd.edu/Faculty-Applicant-C2D-Info.asp.

Candidates should also provide the names and contact information for at least three references who can address the candidate’s research, teaching, and professional service.


Salary is commensurate with qualifications and based on University of California pay scale.

Review of applications will commence on February 1, 2017, and continue until the position is filled.

UCSD is an Affirmative Action/Equal Opportunity Employer with a strong institutional commitment to excellence through diversity.

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Friday, December 23, 2016

Atomistic Description of Reaction Intermediates for Supported Metathesis Catalysts Enabled by DNP SENS #DNPNMR


Ong, T.C., et al., Atomistic Description of Reaction Intermediates for Supported Metathesis Catalysts Enabled by DNP SENS. Angew Chem Int Ed Engl, 2016. 55(15): p. 4743-7.


Obtaining detailed structural information of reaction intermediates remains a key challenge in heterogeneous catalysis because of the amorphous nature of the support and/or the support interface that prohibits the use of diffraction-based techniques. Combining isotopic labeling and dynamic nuclear polarization (DNP) increases the sensitivity of surface enhanced solid-state NMR spectroscopy (SENS) towards surface species in heterogeneous alkene metathesis catalysts; this in turn allows direct determination of the bond connectivity and measurement of the carbon-carbon bond distance in metallacycles, which are the cycloaddition intermediates in the alkene metathesis catalytic cycle. Furthermore, this approach makes possible the understanding of the slow initiation and deactivation steps in these heterogeneous metathesis catalysts.

Wednesday, December 21, 2016

Dynamic Nuclear Polarization and Other Magnetic Ideas at EPFL #DNPNMR


Bornet, A., et al., Dynamic Nuclear Polarization and Other Magnetic Ideas at EPFL. CHIMIA International Journal for Chemistry, 2012. 66(10): p. 734-740.


Although nuclear magnetic resonance (NMR) can provide a wealth of information, it often suffers from a lack of sensitivity. Dynamic Nuclear Polarization (DNP) provides a way to increase the polarization and hence the signal intensities in NMR spectra by transferring the favourable electron spin polarization of paramagnetic centres to the surrounding nuclear spins through appropriate microwave irradiation. In our group at EPFL, two complementary DNP techniques are under investigation: the combination of DNP with magic angle spinning at temperatures near 100 K ('MAS-DNP'), and the combination of DNP at 1.2 K with rapid heating followed by the transfer of the sample to a high-resolution magnet ('dissolution DNP'). Recent applications of MAS-DNP to surfaces, as well as new developments of magnetization transfer of 1H to 13C at 1.2 K prior to dissolution will illustrate the work performed in our group. A second part of the paper will give an overview of some 'non-enhanced' activities of our laboratory in liquid- and solid-state NMR.

Monday, December 19, 2016

Rational design of dinitroxide biradicals for efficient cross-effect dynamic nuclear polarization #DNPNMR


Kubicki, D.J., et al., Rational design of dinitroxide biradicals for efficient cross-effect dynamic nuclear polarization. Chem. Sci., 2016. 7(1): p. 550-558.


A series of 37 dinitroxide biradicals have been prepared and their performance studied as polarizing agents in cross-effect DNP NMR experiments at 9.4 T and 100 K in 1,1,2,2-tetrachloroethane (TCE). We observe that in this regime the DNP performance is strongly correlated with the substituents on the polarizing agents, and electron and nuclear spin relaxation times, with longer relaxation times leading to better enhancements. We also observe that deuteration of the radicals generally leads to better DNP enhancement but with longer build-up time. One of the new radicals introduced here provides the best performance obtained so far under these conditions.

Friday, December 16, 2016

Correction: Theory of solid effect and cross effect dynamic nuclear polarization with half-integer high-spin metal polarizing agents in rotating solids #DNPNMR


Corzilius, B., Correction: Theory of solid effect and cross effect dynamic nuclear polarization with half-integer high-spin metal polarizing agents in rotating solids. Phys. Chem. Chem. Phys., 2016. 18(42): p. 29643-29643.


Correction for 'Theory of solid effect and cross effect dynamic nuclear polarization with half-integer high-spin metal polarizing agents in rotating solids' by Bjorn Corzilius et al., Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/c6cp04621e.

Thursday, December 15, 2016

[NMR] Prestigous PhD fellowships

From the Ampere Magnetic Resonance List


URGENT !! Announcement of prestigious Fellowship for PhD candidates The Faculty of Science of Leiden University offers prestigious and competitive scholarships http://huygens.researchschool.nl/ for PhD candidates to work in interdisciplinary research projects within the Faculty of Sciences at Leiden University.

Candidates qualified to start a PhD program in 2017 and interested in a project that combines EPR with solution and solid state NMR to determine the mechanism of copper proteins should contact Huub de Groot (groot_h@lic.leidenuniv.nl).

If interested, or if you have any questions, please contact us as soon as possible, preferentially not later than Dec. 19th 2016.

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Wednesday, December 14, 2016

Microwave-gated dynamic nuclear polarization #DNPNMR


Bornet, A., et al., Microwave-gated dynamic nuclear polarization. Phys. Chem. Chem. Phys., 2016. 18(44): p. 30530-30535.


Dissolution dynamic nuclear polarization (D-DNP) has become a method of choice to enhance signals in nuclear magnetic resonance (NMR). Recently, we have proposed to combine cross-polarization (CP) with D-DNP to provide high polarization P(13C) in short build-up times. In this paper, we show that switching microwave irradiation off for a few hundreds of milliseconds prior to CP can significantly boost the efficiency. By implementing microwave gating, 13C polarizations on sodium [1-13C]acetate as high as 64% could be achieved with a polarization build-up time constant as short as 160 s. A polarization of P(13C) = 78% could even be reached for [13C]urea.

Monday, December 12, 2016

Trityl-based alkoxyamines as NMP controllers and spin-labels


Audran, G., et al., Trityl-based alkoxyamines as NMP controllers and spin-labels. Polym. Chem., 2016. 7(42): p. 6490-6499.


Recently, new applications of trityl-nitroxide biradicals were proposed. In the present study, attachment of a trityl radical to alkoxyamines was performed for the first time. The rate constants kd of C-ON bond homolysis in these alkoxyamines were measured and found to be similar to those for alkoxyamines without a trityl moiety. The electron paramagnetic resonance (EPR) spectra of the products of alkoxyamine homolysis (trityl-TEMPO and trityl-SG1 biradicals) were recorded, and the corresponding exchange interactions were estimated. The decomposition of trityl-alkoxyamines showed more than an 80% yield of biradicals, meaning that the C-ON bond homolysis is the main reaction. The suitability of these labelled initiators/controllers for polymerisation was exemplified by means of a successful nitroxide-mediated polymerisation (NMP) of styrene. Thus, this is the first report of a spin-labelled alkoxyamine suitable for NMP.

Friday, December 9, 2016

Diffusion-mediated 129Xe gas depolarization in magnetic field gradients during continuous-flow optical pumping


Burant, A. and R.T. Branca, Diffusion-mediated 129Xe gas depolarization in magnetic field gradients during continuous-flow optical pumping. J Magn Reson, 2016. 273: p. 124-129.


The production of large volumes of highly polarized noble gases like helium and xenon is vital to applications of magnetic resonance imaging and spectroscopy with hyperpolarized (HP) gas in humans. In the past ten years, 129Xe has become the gas of choice due to its lower cost, higher availability, relatively high tissue solubility, and wide range of chemical shift values. Though near unity levels of xenon polarization have been achieved in-cell using stopped-flow Spin Exchange Optical Pumping (SEOP), these levels are currently unmatched by continuous-flow SEOP methods. Among the various mechanisms that cause xenon relaxation, such as persistent and transient xenon dimers, wall collisions, and interactions with oxygen, relaxation due to diffusion in magnetic field gradients, caused by rapidly changing magnetic field strength and direction, is often ignored. However, during continuous-flow SEOP production, magnetic field gradients may not have a negligible contribution, especially considering that this methodology requires the combined use of magnets with very different characteristics (low field for spin exchange optical pumping and high field for the reduction of xenon depolarization in the solid state during the freeze out phase) that, when placed together, inevitably create magnetic field gradients along the gas-flow-path. Here, a combination of finite element analysis and Monte Carlo simulations is used to determine the effect of such magnetic field gradients on xenon gas polarization with applications to a specific, continuous-flow hyperpolarization system.

Monday, December 5, 2016

High-Resolution Two-Field Nuclear Magnetic Resonance Spectroscopy


Cousin, S.F., et al., High-Resolution Two-Field Nuclear Magnetic Resonance Spectroscopy. Phys. Chem. Chem. Phys., 2016.


Nuclear Magnetic Resonance (NMR) is a ubiquitous branch of spectroscopy that can explore matter on the scale of the atom. Significant improvements in sensitivity and resolution have been driven by a steady increase of static magnetic field strengths. However, some properties of nuclei may be more favourable at low magnetic fields. For example, line-broadening due to chemical shift anisotropy increases sharply at higher magnetic fields. Here, we present a two-field NMR spectrometer that permits the application of rf-pulses and acquisition of NMR signals in two magnetic centres. Our prototype operates at 14.1 T and 0.33 T. The main features of this system are demonstrated by novel NMR experiments that correlate zero-quantum coherences at low magnetic field with single quantum coherences at high magnetic field, so that high resolution can be achieved in both dimensions, despite a ca. 10 ppm inhomogeneity of the low field centre. Two-field NMR spectroscopy offers the possibility to circumvent the limits of high magnetic fields, while benefiting from their exceptional sensitivity and resolution. This approach opens new avenues for NMR above 1 GHz.

Friday, December 2, 2016

Nuclear spin-lattice relaxation in nitroxide spin-label EPR


Marsh, D., Nuclear spin-lattice relaxation in nitroxide spin-label EPR. J Magn Reson, 2016. 272: p. 166-171.


Nuclear relaxation is a sensitive monitor of rotational dynamics in spin-label EPR. It also contributes competing saturation transfer pathways in T1-exchange spectroscopy, and the determination of paramagnetic relaxation enhancement in site-directed spin labelling. A survey shows that the definition of nitrogen nuclear relaxation rate Wn commonly used in the CW-EPR literature for 14N-nitroxyl spin labels is inconsistent with that currently adopted in time-resolved EPR measurements of saturation recovery. Redefinition of the normalised 14N spin-lattice relaxation rate, b=Wn/(2We), preserves the expressions used for CW-EPR, whilst rendering them consistent with expressions for saturation recovery rates in pulsed EPR. Furthermore, values routinely quoted for nuclear relaxation times that are deduced from EPR spectral diffusion rates in 14N-nitroxyl spin labels do not accord with conventional analysis of spin-lattice relaxation in this three-level system. Expressions for CW-saturation EPR with the revised definitions are summarised. Data on nitrogen nuclear spin-lattice relaxation times are compiled according to the three-level scheme for 14N-relaxation: T1n=1/Wn. Results are compared and contrasted with those for the two-level 15N-nitroxide system.