Friday, February 23, 2018

Optimal sample formulations for DNP SENS: The importance of radical-surface interactions #DNPNMR

Perras, F.A., et al., Optimal sample formulations for DNP SENS: The importance of radical-surface interactions. Current Opinion in Colloid & Interface Science, 2018. 33: p. 9-18.


The efficacy of dynamic nuclear polarization (DNP) surface-enhanced NMR spectroscopy (SENS) is reviewed for alumina, silica, and ordered mesoporous carbon (OMC) materials, with vastly different surface areas, as a function of the biradical concentration. Importantly, our studies show that the use of a “one-size-fits-all” biradical concentration should be avoided when performing DNP SENS experiments and instead an optimal concentration should be selected as appropriate for the type of material studied as well as its surface area. In general, materials with greater surface areas require higher radical concentrations for best possible DNP performance. This result is explained with the use of a thermodynamic model wherein radical-surface interactions are expected to lead to an increase in the local concentration of the polarizing agent at the surface. We also show, using plane-wave density functional theory calculations, that weak radical-surface interactions are the cause of the poor performance of DNP SENS for carbonaceous materials.

Wednesday, February 21, 2018

A quasi-optical and corrugated waveguide microwave transmission system for simultaneous dynamic nuclear polarization NMR on two separate 14.1 T spectrometers #DNPNMR

Gyrotrons typically generate much more microwave power than needed in a DNP-NMR experiment. This article describes a very nice way how to share the microwave power generated by a single gyrotron between two NMR experiments.


Dubroca, T., et al., A quasi-optical and corrugated waveguide microwave transmission system for simultaneous dynamic nuclear polarization NMR on two separate 14.1 T spectrometers. J. Magn. Reson., 2018.


Nuclear magnetic resonance (NMR) is an intrinsically insensitive technique, with Boltzmann distributions of nuclear spin states on the order of parts per million in conventional magnetic fields. To overcome this limitation, dynamic nuclear polarization (DNP) can be used to gain up to three orders of magnitude in signal enhancement, which can decrease experimental time by up to six orders of magnitude. In DNP experiments, nuclear spin polarization is enhanced by transferring the relatively larger electron polarization to NMR active nuclei via microwave irradiation. Here, we describe the design and performance of a quasi-optical system enabling the use of a single 395 GHz gyrotron microwave source to simultaneously perform DNP experiments on two different 14.1 T (1H 600 MHz) NMR spectrometers: one configured for magic angle spinning (MAS) solid state NMR; the other configured for solution state NMR experiments. In particular, we describe how the high power microwave beam is split, transmitted, and manipulated between the two spectrometers. A 13C enhancement of 128 is achieved via the cross effect for alanine, using the nitroxide biradical AMUPol, under MAS-DNP conditions at 110K, while a 31P enhancement of 160 is achieved via the Overhauser effect for triphenylphosphine using the monoradical BDPA under solution NMR conditions at room temperature. The latter result is the first demonstration of Overhauser DNP in the solution state at a field of 14.1 T (1H 600 MHz). Moreover these results have been produced with large sample volumes (∼100 µL, i.e. 3 mm diameter NMR tubes).

Tuesday, February 20, 2018

[NMR] AMPERE NMR SCHOOL 2018

Dear NMR Community, 

On behalf of the Organizing Committee it’s my great pleasure to invite you to attend the next AMPERE NMR School 2018, an annual event organized since earlier 90th in Zakopane under auspices of the Groupment AMPERE, will be organized from June 10 th to 16 th 2018 in Zakopane, Poland ( www. zakopane .pl). 

The traditional topics given in the School: 
· solid state and soft matter NMR
· NMR diffusometry and relaxometry
· application of NMR in biology and medicine
· magnetic resonance imaging and spectroscopy
· NMR and quantum information
· theoretical and experimental aspects of dynamic nuclear spin polarization
· NMR methodology and techniques.

The School is addressed to PhD students of various fields of physics, chemistry, biology and medicine and is focused on theoretical and experimental aspects of NMR methods and their applications. The lectures are expected to contain a basic (tutorial) introduction and the research of your interest. 

The conference fee (450 Euro) includes full board, accommodation and the conference proceedings. We will be able to provide a financial support for the students you will recommend up to 200 Euro. More detailed information you will find on the conference website. 




With my best wishes

Stefan Jurga

……………………………………………………..
Prof. Stefan Jurga
Director
NanoBioMedical Centre
Adam Mickiewicz University
Ul. Umultowska 85
61-614 Poznań, Poland
Ph. +48 61 829 67 04

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[NMR] Open NMR Position at MPI Kohlenforschung in Mülheim an der Ruhr

A new position in the area NMR applied to catalysis research is now open in Mülheim an der Ruhr, Germany. Please distribute. (Basic German knowledge required ;)


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Christophe Farès, Ph.D.
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NMR Department/NMR Abteilung
Max-Planck Insitut für Kohlenforschung/ Max-Planck Insitute for Coal Research
Kaiser-Wilhelm Platz 1
45470 Mülheim an der Ruhr
Tel: +49 208 306 2130 
E-mail: fares [a] mpi-muelheim [.] mpg [.] de
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Monday, February 19, 2018

Sensitivity-enhanced detection of non-labile proton and carbon NMR spectra on water resonances #DNPNMR

Novakovic, M., et al., Sensitivity-enhanced detection of non-labile proton and carbon NMR spectra on water resonances. Phys. Chem. Chem. Phys., 2017. 20(1): p. 56-62.


Chemical exchange saturation transfer (CEST) experiments enhance the NMR signals of labile protons by continuously transferring these protons' saturation to an abundant solvent pool like water. The present study expands these principles by fusing into these experiments homonuclear isotropic mixing sequences, enabling the water-enhanced detection of non-exchangeable species. Further opportunities are opened by the addition of coupling-mediated heteronuclear polarization transfers, which then impose on the water resonance a saturation stemming from non-labile heteronuclear species like (13)C. To multiplex the ensuing experiments, these relayed approaches are combined with time-domain schemes involving multiple Ramsey-labeling experiments imparting the frequencies of the non-labile sites on the water resonance, via chemical exchange. (13)C and (1)H NMR spectra were detected in this fashion with about two-fold SNR amplification vis-a-vis conventionally detected spectroscopies. When combined with non-uniform sampling principles, this methodology thus becomes a sensitive alternative to detect non-exchangeable species in biomolecules. Still, multiple parameters including the scalar couplings and solvent exchange rates, will affect the efficiency and consequently the practicality of the overall experiment.

Friday, February 16, 2018

NMR Signal Quenching from Bound Biradical Affinity Reagents in DNP Samples #DNPNMR #NMR


Rogawski, R., et al., NMR Signal Quenching from Bound Biradical Affinity Reagents in DNP Samples. J Phys Chem B, 2017. 121(48): p. 10770-10781.


We characterize the effect of specifically bound biradicals on the NMR spectra of dihydrofolate reductase from E. coli. Dynamic nuclear polarization methods enhance the signal-to-noise of solid state NMR experiments by transferring polarization from unpaired electrons of biradicals to nuclei. There has been recent interest in colocalizing the paramagnetic polarizing agents with the analyte of interest through covalent or noncovalent specific interactions. This experimental approach broadens the scope of dynamic nuclear polarization methods by offering the possibility of selective signal enhancements and the potential to work in a broad range of environments. Paramagnetic compounds can have other effects on the NMR spectroscopy of nearby nuclei, including broadening of nuclear resonances due to the proximity of the paramagnetic agent. Understanding the distance dependence of these interactions is important for the success of the technique. Here we explore paramagnetic signal quenching due to a bound biradical, specifically a biradical-derivatized trimethoprim ligand of E. coli dihydrofolate reductase. Biradical-derivatized trimethoprim has nanomolar affinity for its target, and affords strong and selective signal enhancements in dynamic nuclear polarization experiments. In this work, we show that, although the trimethoprim fragment is well ordered, the biradical (TOTAPOL) moiety is disordered when bound to the protein. The distance dependence in bleaching of NMR signal intensity allows us to detect numerous NMR signals in the protein. We present the possibility that static disorder and electron spin diffusion play roles in this observation, among other contributions. The fact that the majority of signals are observed strengthens the case for the use of high affinity or covalent radicals in dynamic nuclear polarization solid state NMR enhancement.

[NMR] PhD position at the CNRS/University of Marseille #DNPNMR


ERC-funded PhD position is available in Marseille on the structural investigation of functional organic materials by DNP and NMR

Project title: “Structural investigation of polymorphic organic powders at natural isotopic abundance”

A 3-year PhD position is available at the CNRS/University of Aix-Marseille on the development of new experimental and theoretical approaches in dynamic nuclear polarization (DNP) NMR for the structural investigation of functional organic powders at natural isotopic abundance.

Context: Functional organic materials have been successfully used as active components in many applications, going from light emitters to optical devices, flexible photovoltaic devices, printed electronic inks, molecular machines, pigments, pharmaceuticals, etc. Such compounds can be used to produce low-cost, easily manufacturable, and lightweight materials that can replace traditional inorganic functional materials in energy-related applications (e.g. as semiconductors in solar cells or light emitter diodes), bringing significant economic and practical benefits. Moreover, they can be easily chemically modified to respond to specific application requirements (e.g. as active principle ingredients in pharmacy). In view of obtaining new functional materials with tailored properties, the true challenge in this field is the ability to establish a clear two-way relationship between the structure and the properties of the functional material in its end-use solid form. Because, in their end-use form, materials for the mentioned applications generally form particles with nanometer to micrometer-size dimensions, the main actual limitation to the rational development of new functional materials is the lack of a widely applicable methodology able to characterize fully and unambiguously the structure of functional organic powders lacking long-range order. 

Aim and job description: The aim of the thesis is to devise new analytical routes for accessing ab initio the structure of polymorphic organic microcrystalline powders at natural isotopic abundance through a combination of DNP NMR experiments and computational methods. The selected candidate will actively develop and optimize new NMR experiments for accessing dipolar and scalar couplings on functional materials for energy or pharmaceutical applications at natural isotopic abundance. The candidate will also use first principle calculations of NMR observables (in collaboration with the University of Oxford), as well as analytical (Mathematica, MatLab) or numerical (SIMPSON) simulations to help interpretation of experimental data.

Practical details: The PhD project will be performed at the Institut de Chimie Radicalaire (ICR UMR7273). Located in the south of France in Marseille, ICR is internationally recognized for its double expertise in i) the development of new DNP approaches for the characterization of organic solids and ii) the synthesis of radical species currently used as the most effective polarizing agents for solid DNP. Through the analytical facility Spectropole, ICR has access to a vast range of instrumentation for X-ray diffraction, mass spectrometry, IR, elemental analysis, as well as several NMR spectrometers for liquids and solids with fields ranging from 300 to 600 MHz. Notably, the candidate will access two 400 MHz wide-bore NMR spectrometers equipped with the latest hardware and numerous solid-state probes for spinning speeds up to 60 kHz. 

The PhD studentship will be funded by a European contract (ERC Starting grant, STRUCTURE project, G. Mollica) for a duration of 3 years, starting October 1st 2018. In the framework of ongoing collaborations, the candidate will be in contact with researchers from other European groups. He/she is expected to communicate the results of his/her work at international conferences.



Profile: The candidate should have a Master degree in Chemistry or Physics. Previous experience in NMR spectroscopy and/or computational methods is an advantage. Skills in organic chemistry are not required, but experience with crystallization procedures will be a plus. He/she is expected to be a motivated, imaginative, independent hard worker, with an interest in understanding fundamental aspects of NMR and polymorphism. He/she should have no issues with mobility and demonstrate excellent communication skills in English (knowledge of French is not required).

Application procedure: The candidate should send a motivation letter, at least two names for recommendation, CV (with list of publications and communications) and Master grades (with ranking) to:


&

Stephane Viel s.viel@univ-amu.fr

Application deadline: 15th March 2018.
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(EURAXESS Job Offer id: 279201)
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