Friday, May 26, 2017

Nuclear-Electron Overhauser Effect in MC800 Liquid Asphalt Solutions


Yet another application (although not new) for Overhauser DNP at 9 GHz. 





Firat, Y.E., H. Yildirim, and A. Peksoz, Nuclear-Electron Overhauser Effect in MC800 Liquid Asphalt Solutions. Journal of Dispersion Science and Technology, 2015. 37(9): p. 1349-1359.


Experimental results on the extrapolated ultimate enhancement factors of o-, m-, and p-xylene protons at 1.53 mT are obtained for MC800 asphalt solutions. The ultimate enhancement factors are found such as ?26.9, ?25.7, and ?11.7 for o-, m-, and p-xylene, respectively. These results show that the solvent proton Overhauser effect cannot reach the extrapolated enhancement of ?330 in the extreme narrowing case because of occurrence of small scalar interactions in addition to the dipole?dipole interactions between solvent protons and asphalt electrons. The ortho, meta, and para positions of the ?CH3 group change the nature of the interactions. The nuclear magnetic resonance (NMR) signal enhancements exhibit a sensitive behavior depending on the chemical environment differing from isomer to isomer. The solvation or association of asphalt in xylene isomers at room temperature is revealed. Quantum chemical calculations for the xylene isomers with the electronic and optical properties; absorption wavelengths, excitation energy, atomic charges, dipole moment and frontier molecular orbital energies, molecular electrostatic potential; are carried out using the density functional theory (DFT) method (B3LYP) with the 6-311G(d,p) basis set by the standard Gaussian 09 software package program. The relative importance of scalar and translational dipolar interaction parameters determined in dynamic nuclear polarization experiments is explained by the electronic structure of HOMO?LUMO of the xylene isomers.

Wednesday, May 24, 2017

High field hyperpolarization-EXSY experiment for fast determination of dissociation rates in SABRE complexes


Hermkens, N.K.J., et al., High field hyperpolarization-EXSY experiment for fast determination of dissociation rates in SABRE complexes. J. Magn. Reson., 2017. 276: p. 122-127.


SABRE (Signal Amplification By Reversible Exchange) is a nuclear spin hyperpolarization technique based on the reversible concurrent binding of small molecules and para-hydrogen (p-H2) to an iridium metal complex in solution. At low magnetic field, spontaneous conversion of p-H2 spin order to enhanced longitudinal magnetization of the nuclear spins of the other ligands occurs. Subsequent complex dissociation results in hyperpolarized substrate molecules in solution. The lifetime of this complex plays a crucial role in attained SABRE NMR signal enhancements. Depending on the ligands, vastly different dissociation rates have been previously measured using EXSY or selective inversion experiments. However, both these approaches are generally time-consuming due to the long recycle delays (up to 2 min) necessary to reach thermal equilibrium for the nuclear spins of interest. In the cases of dilute solutions, signal averaging aggravates the problem, further extending the experimental time. Here, a new approach is proposed based on coherent hyperpolarization transfer to substrate protons in asymmetric complexes at high magnetic field. We have previously shown that such asymmetric complexes are important for application of SABRE to dilute substrates. Our results demonstrate that a series of high sensitivity EXSY spectra can be collected in a short experimental time thanks to the NMR signal enhancement and much shorter recycle delay.

Monday, May 22, 2017

Molecular dynamics-based selectivity for Fast-Field-Cycling relaxometry by Overhauser and solid effect dynamic nuclear polarization #DNPNMR


Neudert, O., C. Mattea, and S. Stapf, Molecular dynamics-based selectivity for Fast-Field-Cycling relaxometry by Overhauser and solid effect dynamic nuclear polarization. J. Magn. Reson., 2017. 276: p. 113-121.


In the last decade nuclear spin hyperpolarization methods, especially Dynamic Nuclear Polarization (DNP), have provided unprecedented possibilities for various NMR techniques by increasing the sensitivity by several orders of magnitude. Recently, in-situ DNP-enhanced Fast Field Cycling (FFC) relaxometry was shown to provide appreciable NMR signal enhancements in liquids and viscous systems. In this work, a measurement protocol for DNP-enhanced NMR studies is introduced which enables the selective detection of nuclear spin hyperpolarized by either Overhauser effect or solid effect DNP. Based on field-cycled DNP and relaxation studies it is shown that these methods allow for the independent measurement of polymer and solvent nuclear spins in a concentrated solution of high molecular weight polybutadiene in benzene doped with α,γ-bisdiphenylene-β-phenylallyl radical. Appreciable NMR signal enhancements of about 10-fold were obtained for both constituents. Moreover, qualitative information about the dynamics of the radical and solvent was obtained. Selective DNP-enhanced FFC relaxometry is applied for the measurement of the 1H nuclear magnetic relaxation dispersion of both constituents with improved precision. The introduced method is expected to greatly facilitate NMR studies of complex systems with multiple overlapping signal contributions that cannot be distinguished by standard methods.

Friday, May 19, 2017

T1 - Dynamic Nuclear Polarization Signal Enhancement with High-Affinity Biradical Tags #DNPNMR

Rivkah Rogawski, Ivan V. Sergeyev, Yongjun Li, M. Francesca Ottaviani, Virginia Cornish, and Ann E. McDermott The Journal of Physical Chemistry B 2017 121 (6), 1169-1175


Dynamic nuclear polarization is an emerging technique for sensitizing solid-state NMR experiments by transferring polarization from electrons to nuclei. Stable biradicals, the polarization source for the cross effect mechanism, are typically codissolved at millimolar concentrations with proteins of interest. Here we describe the high-affinity biradical tag TMP-T, created by covalently linking trimethoprim, a nanomolar affinity ligand of dihydrofolate reductase (DHFR), to the biradical polarizing agent TOTAPOL. With TMP-T bound to DHFR, large enhancements of the protein spectrum are observed, comparable to when TOTAPOL is codissolved with the protein. In contrast to TOTAPOL, the tight binding TMP-T can be added stoichiometrically at radical concentrations orders of magnitude lower than in previously described preparations. Benefits of the reduced radical concentration include reduced spectral bleaching, reduced chemical perturbation of the sample, and the ability to selectively enhance signals for the protein of interest.

Thursday, May 18, 2017

[NMR] Postdoc in biomolecular SSNMR - protein aggregation & protein-lipid interactions


Postdoctoral position in biological MAS ssNMR

The Van der Wel lab is looking for a postdoc candidate with a background in NMR, preferably solid-state NMR, to join our research effort focused on protein aggregation and protein-lipid interactions. More information on our research and recent publications can be found below and on our website at http://www.vanderwellab.org

Potentially interested parties are encouraged to email any questions and/or (informal) inquiries to vanderwel@pitt.edu

Patrick van der Wel
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Research topics: 

The researcher is expected to join the Van der Wel lab to contribute to our NIH-funded research. One focus in the lab is the use of MAS NMR to study amyloid structure and protein aggregation with a particular focus on polyglutamine-expanded proteins implicated in Huntington’s Disease. Another key focus is on the study by ssNMR of membrane structure and dynamics, as well as protein-lipid interactions, in particular in context of mitochondrial apoptosis, which has important implications for neurodegenerative disease and cancer research. 

Selected recent publications: (online access here )

  • Mandal et al. (2015) Structural Changes and Proapoptotic Peroxidase Activity of Cardiolipin-Bound Mitochondrial Cytochrome c. Biophys. J., 109(9), 1873–84.
  • Hoop et al. (2016) Huntingtin exon 1 fibrils feature an interdigitated β-hairpin-based polyglutamine core. PNAS, 113(6), 1546–51. 
  • Merg et al. (2016) Peptide-Directed Assembly of Single-Helical Gold Nanoparticle Superstructures Exhibiting Intense Chiroptical Activity. JACS, 138(41), 13655–63. 
  • Boatz et al. (2017) Cataract-associated P23T γD-crystallin retains a native-like fold in amorphous-looking aggregates formed at physiological pH. Nat Commun, 8, 15137. 

Location/Resources:

Our facility houses wide-bore 600MHz and 750MHz Bruker ssNMR spectrometers outfitted with 4-, 3.2-, 1.9-, and 1.3-mm CP/MAS as well as static ssNMR probes. Additional facilities include state-of-the-art EM, X-ray and solution NMR instrumentation, with the latter including 700, 800, and 900 MHz spectrometers. Excellent resources are available for protein production, biophysical and computational studies. The lab is housed in the interdisciplinary Dept of Structural Biology, one of the basic science departments of the University of Pittsburgh School of Medicine in Pittsburgh, Pennsylvania (USA). 

Application/More Information.

For more detailed information on these projects, links to related publications, and other information please visit the lab website at http://www.vanderwellab.org. To apply, or to obtain more information, please contact Patrick van der Wel by email at vanderwel@pitt.edu. Applications are expected to include a cover letter (or “cover email”) explaining specific research interests, a CV, and the names and contact information for three reference writers.

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[NMR] Postdoctoral position in structural biology of membrane remodeling



POSTDOCTORAL POSITION AVAILABLE
STRUCTURAL BIOLOGY OF MEMBRANE REMODELING

A NIH-funded postdoctoral position is available immediately in the Ramachandran Lab at Case Western Reserve University (CWRU) to study the structural aspects of protein-mediated membrane remodeling during endocytic and mitochondrial membrane fission. This position involves extensive collaboration with the lab of Patrick van der Wel at the University of Pittsburgh. The position requires a Ph.D. in biochemistry or biophysics with a focus on structural biology or membrane biophysics (NMR or ssNMR, preferably). This position will provide an excellent opportunity to learn and apply a wide array of structural and biophysical techniques to explore protein function on a model membrane surface. The Ramachandran laboratory also employs a host of cutting-edge spectroscopic approaches including FRET, fluorescence correlation spectroscopy (FCS) and fluorescence lifetime imaging (FLIM) to explore protein-protein and protein-membrane interactions in membrane remodeling and fission, both in vitro and in vivo. The Ramachandran and Van der Wel labs and the facilities at CWRU and University of Pittsburgh are equipped with state-of-the-art instrumentation for both biophysical techniques and structural biology, as well as for protein purification, characterization and membrane reconstitution.

Requirements: Applicants must be highly motivated and must have demonstrated experience (i.e. relevant publications) in protein biochemistry and structural biology. The candidate should have a strong conceptual and experimental background in biochemistry and biophysics, as well as in the mechanistic dissection of structure-function relationships in proteins; he/she should be independent, proactive, hardworking and productive; only candidates that have first-author publications (or articles in press) will be considered. Candidates must have completed their PhD at the time of appointment. Salary will commensurate with experience and will adhere to current NIH guidelines. Interested candidates should submit their CV, reprints of selected publications, three reference letters (directly from referees), and a cover letter summarizing their experience, long-term goals, and estimated start date directly to Rajesh Ramachandran at rxr275@case.edu.

Relevant Publications, please visit our webpage:

Van der Wel lab: http://www.vanderwellab.org

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[NMR] Position as Research Engineer / Lab Manager for the magnetic resonance lab @ IPF Dresden


Position as Research Engineer / Lab Manager for the magnetic resonance lab @ IPF Dresden

At the Institute of Physical Chemistry and Polymer Physics, Department Polyelectrolytes and Dispersions, at the 

Leibniz-Institut für Polymerforschung is an opening for a Research Engineer / Lab Manager for the magnetic resonance laboratory. 

We are looking for a motivated, skillful person, who is willing to learn about novel technolgies and is closely collaborating with the PI's. The research engineer will be responsible for ensuring the operation of the laboratory and the various spectrometers (high-field NMR, low-field NMR and X-band EPR), perform routine experiments and sample preparation and support in simulations. Ensuring the smooth operation of the lab includes trouble shooting and modification of experimental setups. Skills in electronics and computing are desirable.

Qualification: MSc/Diploma in Physical Technology or equivalent
Duration: initially for two years

The Leibniz-Institut für Polymerforschung Dresden e.V. (IPF) is one of the largest polymer research facilities in Germany. As an institute of the Leibniz Association, the IPF is committed to carrying out application-oriented basic research. The focus of activities at the IPF is directed toward the advancement of basic scientific knowledge for the development of functional polymer materials and polymer materials with new or improved characteristics. Leading scientists of the IPF are at the same time appointed professors at the Technische Universität Dresden (TUD). Since 2011 the TUD has been one of the excellence universities in Germany. The IPF offers a stimulating working atmosphere for outstanding interdisciplinary research in one of the most beautiful cities of Germany. 

Dresden, the capital of Saxony, possesses an extraordinarily high density of research facilities which have made Dresden a leading research site, particularly in the fields of material research, microelectronics, and biotechnology. 

Applications including motivation letter, CV, should be submitted by e-mail as a single PDF document to the Department of Human Resources (with the No. 063-2017):

Leibniz-Institut für Polymerforschung Dresden e.V.
Frau Susanne Otto
Leiterin Personal und Soziales
Hohe Straße 6
01069 Dresden

Queries about the lab and the research project should be directed by e-mail to:
Ulrich Scheler Scheler@ipfdd.de .

Job offer (in German)

Best regards,
Ulrich Scheler

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Dr. Ulrich Scheler
Leibniz-Institut für Polymerforschung Dresden e.V.
Hohe Strasse 6
D-01069 Dresden, Germany
phone +49 351 4658 275
fax +49 351 4658 231
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