Friday, December 15, 2017

Uniform field loop-gap resonator and rectangular TEU02 for aqueous sample EPR at 94GHz


Sidabras, J.W., et al., Uniform field loop-gap resonator and rectangular TEU02 for aqueous sample EPR at 94GHz. J. Magn. Reson., 2017. 282(Supplement C): p. 129-135.


In this work we present the design and implementation of two uniform-field resonators: a seven-loop–six-gap loop-gap resonator (LGR) and a rectangular TEU02 cavity resonator. Each resonator has uniform-field-producing end-sections. These resonators have been designed for electron paramagnetic resonance (EPR) of aqueous samples at 94GHz. The LGR geometry employs low-loss Rexolite end-sections to improve the field homogeneity over a 3mm sample region-of-interest from near-cosine distribution to 90% uniform. The LGR was designed to accommodate large degassable Polytetrafluorethylen (PTFE) tubes (0.81mm O.D.; 0.25mm I.D.) for aqueous samples. Additionally, field modulation slots are designed for uniform 100kHz field modulation incident at the sample. Experiments using a point sample of lithium phthalocyanine (LiPC) were performed to measure both the uniformity of the microwave magnetic field and 100kHz field modulation, and confirm simulations. The rectangular TEU02 cavity resonator employs over-sized end-sections with sample shielding to provide an 87% uniform field for a 0.1×2×6mm3 sample geometry. An evanescent slotted window was designed for light access to irradiate 90% of the sample volume. A novel dual-slot iris was used to minimize microwave magnetic field perturbations and maintain cross-sectional uniformity. Practical EPR experiments using the application of light irradiated rose bengal (4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein) were performed in the TEU02 cavity. The implementation of these geometries providing a practical designs for uniform field resonators that continue resonator advancements towards quantitative EPR spectroscopy.

Wednesday, December 13, 2017

Perspectives on paramagnetic NMR from a life sciences infrastructure


Ravera, E., G. Parigi, and C. Luchinat, Perspectives on paramagnetic NMR from a life sciences infrastructure. J Magn Reson, 2017. 282(Supplement C): p. 154-169.


The effects arising in NMR spectroscopy because of the presence of unpaired electrons, collectively referred to as "paramagnetic NMR" have attracted increasing attention over the last decades. From the standpoint of the structural and mechanistic biology, paramagnetic NMR provides long range restraints that can be used to assess the accuracy of crystal structures in solution and to improve them by simultaneous refinements through NMR and X-ray data. These restraints also provide information on structure rearrangements and conformational variability in biomolecular systems. Theoretical improvements in quantum chemistry calculations can nowadays allow for accurate calculations of the paramagnetic data from a molecular structural model, thus providing a tool to refine the metal coordination environment by matching the paramagnetic effects observed far away from the metal. Furthermore, the availability of an improved technology (higher fields and faster magic angle spinning) has promoted paramagnetic NMR applications in the fast-growing area of biomolecular solid-state NMR. Major improvements in dynamic nuclear polarization have been recently achieved, especially through the exploitation of the Overhauser effect occurring through the contact-driven relaxation mechanism: the very large enhancement of the (13)C signal observed in a variety of liquid organic compounds at high fields is expected to open up new perspectives for applications of solution NMR.

Monday, December 11, 2017

Real-Time Analysis of Folding upon Binding of a Disordered Protein by Using Dissolution DNP NMR Spectroscopy #DNPNMR


Ragavan, M., et al., Real-Time Analysis of Folding upon Binding of a Disordered Protein by Using Dissolution DNP NMR Spectroscopy. Angew Chem Int Ed Engl, 2017. 56(25): p. 7070-7073.


The kinase inhibitory domain of the cell cycle regulatory protein p27(Kip1) (p27) was nuclear spin hyperpolarized using dissolution dynamic nuclear polarization (D-DNP). While intrinsically disordered in isolation, p27 adopts secondary structural motifs, including an alpha-helical structure, upon binding to cyclin-dependent kinase 2 (Cdk2)/cyclin A. The sensitivity gains obtained with hyperpolarization enable the real-time observation of (13) C NMR signals during p27 folding upon binding to Cdk2/cyclin A on a time scale of several seconds. Time-dependent intensity changes are dependent on the extent of folding and binding, as manifested in differential spin relaxation. The analysis of signal decay rates suggests the existence of a partially folded p27 intermediate during the timescale of the D-DNP NMR experiment.

Friday, December 8, 2017

In Situ Characterization of Pharmaceutical Formulations by Dynamic Nuclear Polarization Enhanced MAS NMR #DNPNMR


Ni, Q.Z., et al., In Situ Characterization of Pharmaceutical Formulations by Dynamic Nuclear Polarization Enhanced MAS NMR. The Journal of Physical Chemistry B, 2017. 121(34): p. 8132-8141.


A principal advantage of magic angle spinning (MAS) NMR spectroscopy lies in its ability to determine molecular structure in a noninvasive and quantitative manner. Accordingly, MAS should be widely applicable to studies of the structure of active pharmaceutical ingredients (API) and formulations. However, the low sensitivity encountered in spectroscopy of natural abundance APIs present at low concentration has limited the success of MAS experiments. Dynamic nuclear polarization (DNP) enhances NMR sensitivity and can be used to circumvent this problem provided that suitable paramagnetic polarizing agent can be incorporated into the system without altering the integrity of solid dosages. Here, we demonstrate that DNP polarizing agents can be added in situ during the preparation of amorphous solid dispersions (ASDs) via spray drying and hot-melt extrusion so that ASDs can be examined during drug development. Specifically, the dependence of DNP enhancement on sample composition, radical concentration, relaxation properties of the API and excipients, types of polarizing agents and proton density, has been thoroughly investigated. Optimal enhancement values are obtained from ASDs containing 1% w/w radical concentration. Both polarizing agents TOTAPOL and AMUPol provided reasonable enhancements. Partial deuteration of the excipient produced 3× higher enhancement values. With these parameters, an ASD containing posaconazole and vinyl acetate yields a 32-fold enhancement which presumably results in a reduction of NMR measurement time by ∼1000. This boost in signal intensity enables the full assignment of the natural abundance pharmaceutical formulation through multidimensional correlation experiments.

Wednesday, December 6, 2017

A sub-Kelvin cryogen-free EPR system


This article has nothing to do with DNP. However, the article nicely describes an impressive piece of isntrumentation to reach very low temperatures.


Melhuish, S.J., et al., A sub-Kelvin cryogen-free EPR system. J. Magn. Reson., 2017. 282(Supplement C): p. 83-88.


We present an EPR instrument built for operation at Q band below 1K. Our cryogen-free Dewar integrates with a commercial electro-magnet and bridge. A description of the cryogenic and RF systems is given, along with the adaptations to the standard EPR experiment for operation at sub-Kelvin temperatures. As a first experiment, the EPR spectra of powdered Cr12O9(OH)3(O2CCMe3)15 were measured. The sub-Kelvin EPR spectra agree well with predictions, and the performance of the sub-Kelvin system at 5K is compared to that of a commercial spectrometer.

Tuesday, December 5, 2017

[NMR] HYP18 meeting, Southampton Sep 2-5, 2018 #DNPNMR

This is advance notice of an international meeting on hyperpolarization, HYP18, which will be held in Southampton, UK on Sep 2-5, 2018

The program will cover a wide range of hyperpolarization techniques and their applications, including DNP in both liquids and solids, parahydrogen-based techniques, optical pumping, quantum rotor polarization, and other methods. We hope that the meeting will promote comparison, discussion, and cross-fertilisation between the different techniques. 

Confirmed speakers include:

Stephan Appelt, Aachen, Germany
Peter Blümler, Mainz, Germany
Kevin Brindle, Cambridge, UK
Arnaud Comment, Cambridge, UK
Bob Griffin, MIT, USA
Meghan Halse, York, UK
Sami Jannin, Lyon, France
Fedor Jelezko, Ulm, Germany
John Kurhanewicz, San Francisco, USA
Mathilde Lerche, Copenhagen, Denmark
Anne Lesage, Lyon, France
Gaël de Paëpe, Grenoble, France
Marek Pruski, Iowa, USA
Leif Schröder, Berlin, Germany
Thomas Theis, North Carolina, USA

Registration will open in january. 
So bookmark the link: www.southampton.ac.uk/hyp18
and pencil the dates in your diaries!

Malcolm Levitt and Giuseppe Pileio

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HYP18
Hyperpolarized Magnetic Resonance
Southampton UK, Sep 2-5 2018
——————————————————
Prof Malcolm Levitt
School of Chemistry
Room 27:2026
University of Southampton
Southampton SO17 1BJ
England.
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Monday, December 4, 2017

Photo-induced radical polarization and liquid-state dynamic nuclear polarization with fullerene nitroxide derivatives

DNP without microwave radiation? A very interesting approach.


Liu, G., et al., Photo-induced radical polarization and liquid-state dynamic nuclear polarization with fullerene nitroxide derivatives. Phys. Chem. Chem. Phys., 2017.


We report on radical polarization and optically-driven liquid DNP with nitroxide radicals functionalized by photoexcitable fullerene derivatives. Pulse laser excitation of the fullerene moiety leads to a transient nitroxide radical polarization that is one order of magnitude larger than at Boltzmann equilibrium. Life time of radical polarization increases with size of the fullerene derivative and correlates with the electronic spin lattice relaxation time T1e. Overhauser NMR signal enhancements of toluene solvent protons were observed under steady-state illumination, which replaced microwave irradiation.