Friday, June 28, 2013

Flexibility of ZIF-8 materials studied by 129 Xe NMR


Springuel, M.-A., et al., Flexibility of ZIF-8 materials studied by 129 Xe NMR. Chemical Communications, 2013.


Structural changes of porous hybrid inorganic-organic ZIF-8 compound has been explored by hyperpolarized 129Xe NMR of adsorbed xenon at various temperatures. Upon xenon adsorption at low temperature, the organic linkers undergo a reorientation leading to a stepwise increase in xenon adsorption and in chemical shift

Monday, June 24, 2013

Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids


Potapov, A., W.M. Yau, and R. Tycko, Dynamic nuclear polarization-enhanced (13)C NMR spectroscopy of static biological solids. J Magn Reson, 2013. 231(0): p. 5-14.


We explore the possibility of using dynamic nuclear polarization (DNP) to enhance signals in structural studies of biological solids by solid state NMR without sample spinning. Specifically, we use 2D (13)C-(13)C exchange spectroscopy to probe the peptide backbone torsion angles (varphi, psi) in a series of selectively (13)C-labeled 40-residue beta-amyloid (Abeta1-40) samples, in both fibrillar and non-fibrillar states. Experiments are carried out at 9.39T and 8K, using a static double-resonance NMR probe and low-power microwave irradiation at 264GHz. In frozen solutions of Abeta1-40 fibrils doped with DOTOPA-TEMPO, we observe DNP signal enhancement factors of 16-21. We show that the orientation- and frequency-dependent spin polarization exchange between sequential backbone carbonyl (13)C labels can be simulated accurately using a simple expression for the exchange rate, after experimentally determined homogeneous (13)C lineshapes are incorporated in the simulations. The experimental 2D (13)C-(13)C exchange spectra place constraints on the varphi and psi angles between the two carbonyl labels. Although the data are not sufficient to determine varphi and psi uniquely, the data do provide non-trivial constraints that could be included in structure calculations. With DNP at low temperatures, 2D (13)C-(13)C exchange spectra can be obtained from a 3.5mg sample of Abeta1-40 fibrils in 4h or less, despite the broad (13)C chemical shift anisotropy line shapes that are observed in static samples.

Friday, June 21, 2013

Bacteriopheophytin a in the active branch of the reaction center of rhodobacter sphaeroides is not disturbed by the protein matrix as shown by 13C photo-CIDNP MAS NMR


Sai Sankar Gupta, K.B., et al., Bacteriopheophytin a in the Active Branch of the Reaction Center of Rhodobacter sphaeroides Is Not Disturbed by the Protein Matrix as Shown by 13C Photo-CIDNP MAS NMR. The Journal of Physical Chemistry B, 2013. 117(12): p. 3287-3297.


The electronic structure of bacteriopheophytin a (BPhe a), the primary electron acceptor (PhiA) in photosynthetic reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides, is investigated by photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR spectroscopy at atomic resolution. By using various isotope labeling systems, introduced by adding different (13)C selectively labeled delta-aminolevulinic acid precursors in the growing medium of R. sphaeroides wild type (WT), we were able to extract light-induced (13)C NMR signals originating from the primary electron acceptor. The assignments are backed by theoretical calculations. By comparison of these chemical shifts to those obtained from monomeric BPhe a in solution, it is demonstrated that PhiA in the active branch appears to be electronically close to free bacteriopheophytin. Hence, there is little effect of the protein surrounding on the cofactor functionally which contributes with its standard redox potential to the electron transfer process that is asymmetric.

Thursday, June 20, 2013

Postdoctoral positions "high field μMAS-DNP- NMR” and “Rapid melt DNP"



Two postdoc positions for “DNP-enhanced NMR” both in the solid and liquid state are available immediately at the Solid State NMR group of the Institute of Molecules and Materials at the Radboud University of Nijmegen.

The solid NMR group at the Radboud University specializes in developing innovative technology to perform NMR spectroscopy on very small samples volumes both in the solid and in the liquid state. In the solid phase one can obtain ultrahigh proton decoupling fields (above 1 MHz RF field strength) improving the resolution to a few Hz at 20 T. Using on-chip NMR detection in a microfluidic environment we aim to resolve for example reaction pathways that are too fast for normal NMR. In this context we have started several new projects to improve the sensitivity by implementation of Dynamic Nuclear Polarization methods.

In collaboration with Agilent technologies and Bridge12 Technologies we are developing a solid state DNP setup at 600 MHz. The aim here is to combine the mMAS technology with DNP. The small sample size may allow lower temperatures and much higher microwave B1 field strengths.

Monday, June 17, 2013

Achievement of high nuclear spin polarization using lanthanides as low-temperature NMR relaxation agents


Peat, D.T., et al., Achievement of high nuclear spin polarization using lanthanides as low-temperature NMR relaxation agents. Phys. Chem. Chem. Phys., 2013. 15(20): p. 7586-7591.


Many approaches are now available for achieving high levels of nuclear spin polarization. One of these methods is based on the notion that as the temperature is reduced, the equilibrium nuclear polarization will increase, according to the Boltzmann distribution. The main problem with this approach is the length of time it may take to approach thermal equilibrium at low temperatures, since nuclear relaxation times (characterized by the spin-lattice relaxation time T1) can become very long. Here, we show, by means of relaxation time measurements of frozen solutions, that selected lanthanide ions, in the form of their chelates with DTPA, can act as effective relaxation agents at low temperatures. Differential effects are seen with the different lanthanides that were tested, holmium and dysprosium showing highest relaxivity, while gadolinium is ineffective at temperatures of 20 K and below. These observations are consistent with the known electron-spin relaxation time characteristics of these lanthanides. The maximum relaxivity occurs at around 10 K for Ho-DTPA and 20 K for Dy-DTPA. Moreover, these two agents show only modest relaxivity at room temperature, and can thus be regarded as relaxation switches. We conclude that these agents can speed up solid state NMR experiments by reducing the T1 values of the relevant nuclei, and hence increasing the rate at which data can be acquired. They could also be of value in the context of a simple low-cost method of achieving several-hundred-fold improvements in polarization for experiments in which samples are pre-polarized at low temperatures, then rewarmed and dissolved immediately prior to analysis.

Wednesday, June 12, 2013

Towards Structure Determination of Self-Assembled Peptides Using Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy


Takahashi, H., et al., Towards Structure Determination of Self-Assembled Peptides Using Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy. Angew. Chem. Int. Ed., 2013: p. n/a-n/a.


Supra-sensitivity: Dynamic nuclear polarization (DNP) enhanced solid-state NMR spectroscopy was performed on self-assembled peptide nanotubes. This approach yields significant experimental time savings (about five orders of magnitude; see picture) and was used to exemplify the feasibility of supramolecular structural studies of organic nanoassemblies at an atomic scale using DNP-enhanced solid-state NMR spectroscopy.

Monday, June 10, 2013

Electron spin resonance studies of trityl OX063 at a concentration optimal for DNP


Lumata, L., et al., Electron spin resonance studies of trityl OX063 at a concentration optimal for DNP. Phys. Chem. Chem. Phys., 2013. 15(24): p. 9800-9807.


We have performed temperature-dependent electron spin resonance (ESR) measurements of the stable free radical trityl OX063, an efficient polarizing agent for dissolution dynamic nuclear polarization (DNP), at the optimum DNP concentration (15 mM). We have found that (i) when compared to the W-band electron spin-lattice relaxation rate T1e-1 of other free radicals used in DNP at the same concentration, trityl OX063 has slower T1e-1 than BDPA and 4-oxo-TEMPO. At T > 20 K, the T1e-1vs. T data of trityl OX063 appears to follow a power law dependence close to the Raman process prediction whereas at T < 10 K, electronic relaxation slows and approaches the direct process behaviour. (ii) Gd3+ doping, a factor known to enhance DNP, of trityl OX063 samples measured at W-band resulted in monotonic increases of T1e-1 especially at temperatures below 20-40 K while the ESR lineshapes remained essentially unchanged. (iii) The high frequency ESR spectrum can be fitted with an axial g-tensor with a slight g-anisotropy: gx = gy = 2.00319(3) and gz = 2.00258(3). Although the ESR linewidth D monotonically increases with field, the temperature-dependent T1e-1 is almost unchanged as the ESR frequency is increased from 9.5 GHz to 95 GHz, but becomes faster at 240 GHz and 336 GHz. The ESR properties of trityl OX063 reported here may provide insights into the efficiency of DNP of low-[gamma] nuclei performed at various magnetic fields, from 0.35 T to 12 T.

Friday, June 7, 2013

High Frequency Dynamic Nuclear Polarization


Ni, Q.Z., et al., High Frequency Dynamic Nuclear Polarization. Acc Chem Res, 2013.


During the three decades 1980-2010, magic angle spinning (MAS) NMR developed into the method of choice to examine many chemical, physical, and biological problems. In particular, a variety of dipolar recoupling methods to measure distances and torsion angles can now constrain molecular structures to high resolution. However, applications are often limited by the low sensitivity of the experiments, due in large part to the necessity of observing spectra of low-gamma nuclei such as the I = 1/2 species 13C or 15N. The difficulty is still greater when quadrupolar nuclei, such as 17O or 27Al, are involved. This problem has stimulated efforts to increase the sensitivity of MAS experiments. A particularly powerful approach is dynamic nuclear polarization (DNP) which takes advantage of the higher equilibrium polarization of electrons (which conventionally manifests in the great sensitivity advantage of EPR over NMR). In DNP, the sample is doped with a stable paramagnetic polarizing agent and irradiated with microwaves to transfer the high polarization in the electron spin reservoir to the nuclei of interest. The idea was first explored by Overhauser and Slichter in 1953. However, these experiments were carried out on static samples, at magnetic fields that are low by current standards. To be implemented in contemporary MAS NMR experiments, DNP requires microwave sources operating in the subterahertz regime, roughly 150-660 GHz, and cryogenic MAS probes. In addition, improvements were required in the polarizing agents, because the high concentrations of conventional radicals that are required to produce significant enhancements compromise spectral resolution. In the last two decades, scientific and technical advances have addressed these problems and brought DNP to the point where it is achieving wide applicability. These advances include the development of high frequency gyrotron microwave sources operating in the subterahertz frequency range. In addition, low temperature MAS probes were developed that permit in situ microwave irradiation of the samples. And, finally, biradical polarizing agents were developed that increased the efficiency of DNP experiments by factors of approximately 4 at considerably lower paramagnet concentrations. Collectively, these developments have made it possible to apply DNP on a routine basis to a number of different scientific endeavors, most prominently in the biological and material sciences. This Account reviews these developments, including the primary mechanisms used to transfer polarization in high frequency DNP, and the current choice of microwave sources and biradical polarizing agents. In addition, we illustrate the utility of the technique with a description of applications to membrane and amyloid proteins that emphasizes the unique structural information that is available in these two cases.

Wednesday, June 5, 2013

4th International DNP Symposium

Dear Colleague

The 4th International DNP Symposium (www.DNPsymposium.org), Copenhagen, Denmark, Aug 28-31, 2013, is in less than three months.

The registration has been extended to July 31 or until capacity (200). There are only a few seats left, so secure your registration if you wish to participate.

Likewise, we have extended the abstract submission deadline to allow “late submissions” until July 31. If you missed the original deadline we encourage you to submit your work.

We have received a high number of quality abstracts that will be reviewed during June, and a preliminary program will be posted by the end of June. I am sure we will have a fantastic meeting. Further practical information about the meeting will be posted on the webpage in the coming weeks.

I would like to draw your attention to the training school “Acquisition strategies for hyperpolarized spin systems: spatial, spectral and temporal” (www.esmrmb.org) in Copenhagen that precedes the symposium.

All the best, and hoping to see you in Copenhagen in August.

The Organizing Committee

Lise Vejby Søgaard
Lars G. Hanson
Susanne Mossin
Sebastian Meier
Charlotte Held Gotfredsen
Mathilde H. Lerche
Niels Chr Nielsen
Jan Henrik Ardenkjaer-Larsen

Jan Henrik Ardenkjær-Larsen 
Adjunct Professor 
DTU Electrical Engineering 

Technical University of Denmark 
Department of Electrical Engineering 
Ørsteds Plads 
Building 349, Room 106 
DK - 2800 Kgs. Lyngby 
Denmark 

Direct +45 4540272775 

Postdoctoral position "DNP-enhanced bio solid-state NMR"

A postdoc position for “DNP-enhanced solid-state NMR” will be available from September 2013 at the Helmholtz center Jülich/ Heinrich Heine-Universität Düsseldorf.

One of the most demanding challenges of biomolecular NMR spectroscopy is the inherently low sensitivity. Signal enhancement by DNP is therefore a promising alternative to gain insights into systems which otherwise could not be investigated. We will exploit the technique to obtain structural information on complex systems (protein aggregates, and membrane proteins in lipid bilayers) which otherwise would be inaccessible to structural investigations. Further, the possibilities of this technique for selective enhancement will be exploited.

The candidate should hold a PhD in Physics or Chemistry or a related field. Basic knowledge and experience in solid-state NMR or EPR spectroscopy as well as a strong interest in physics and structural biology is a prerequisite. Experience with DNP is highly desirable. The applicant should be highly motivated, open for new approaches and techniques, and able to tackle demanding challenges. As most of the systems involve collaborations with other research groups, good communication skills are required.

The biomolecular NMR center of the Heinrich-Heine University of Düsseldorf at the Helmholtz Research Center Jülich (Forschungszentrum Jülich) offers an exciting and stimulating research environment. State-of-the art solid-state NMR spectrometers operating at 600 and 800 MHz are already available, a 600 MHz DNP spectrometer will be installed in September of 2013, and the installation of an 800 with DNP is scheduled for 2014.

The position will be available for 2 years with the possibility of extension.

Please send a CV and the names and addresses of three references to Henrike Heise (h.heise@fz-juelich.de) until June 22nd.

Group homepage:

Announcement of the DFG:

Best regards,
Henrike Heise

-- 
Prof. Dr. Henrike Heise 
Heinrich-Heine-Universitaet Duesseldorf 
Institut fuer Physikalische Biologie 
40225 Duesseldorf 

ICS-6 / Structural Biochemistry 
Forschungszentrum Jülich 
D-52425 Jülich, Germany 
Tel.: +49 2461 61-4658 
Fax: +49 2461 61-2023 


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Forschungszentrum Juelich GmbH
52425 Juelich
Sitz der Gesellschaft: Juelich
Eingetragen im Handelsregister des Amtsgerichts Dueren Nr. HR B 3498
Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher
Geschaeftsfuehrung: Prof. Dr. Achim Bachem (Vorsitzender),
Karsten Beneke (stellv. Vorsitzender), Prof. Dr.-Ing. Harald Bolt,
Prof. Dr. Sebastian M. Schmidt

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Tuesday, June 4, 2013

Open position: Post Doc specialist in MM and SUB-MMW technologies (M/F)

EPFL/LPMN and SWISSto12 SA ( http://swissto12.ch ) are now opening a position for Research and Development activities focused on Terahertz Technologies. The project funded by CTI/KTI aims at developing a new family of Planar Probes for Dynamic Nuclear Polarization Enhanced Nuclear Magnetic Resonance. 

An application containing a CV, a motivation letter, two reference letters and a copy of your diplomas and grades can be sent by mail at: jean-philippe.ansermet@epfl.ch

Contract : with EPFL/LPMN, can be extended up to 3 years. 

Nuclear Magnetic Resonance (NMR) is a widespread tool used for research in Chemistry, Physics and Biology. NMR Spectroscopy performances are greatly enhanced by Dynamic Nuclear Polarization (DNP). This technique involves irradiating samples with terahertz waves in order to excite the electron spin resonance. An innovative DNP-NMR probe based on a planar geometry has been recently patented by EPFL and CNR(I). Among other unprecedented features, this new piece of instrumentation (the probe) will allow the study of biological samples at room temperature.

SWISSto12 is a private start-up company, spin-off of the Swiss Federal Institute of Technology in Lausanne, (EPFL). It aims at becoming a leading supplier of components and systems for Terahertz (THz) signal transmission. SWISSto12 holds exclusive licenses for patent applications owned by the EPFL, of which the company founders are the inventors. These patent applications cover manufacturing techniques that are the first ones to enable the production of efficient THz signal transmission components over the full THz frequency range.

The strategic market position of SWISSto12 can only be developed and sustained through a strong and continuous R&D effort, allowing it to stay in tune with the latest developments. This effort is currently distributed over different projects aiming at reducing production costs, increasing product performances, seeking new solutions for THz signal transmission, as well as developing new products in the domain of Terahertz transmission and probing. Through collaborations with various companies and research institutions around the world SWISSto12 interacts with the key stakeholders for the development of future THz systems and components.

Tasks :

· Design and Numerical characterization of the probe.
· Cold Tests on Sub-Components on a brand-new THz lab at LPMN
· Probe Assembly
· Experimental Validation.
· Gyrotron DNP experiments for benchmark and training with an existing saddle-coil probe
· Interface with industrial partners and research institutions for R&D projects and collaborations.

Profile required for this position:

· A PhD in physics, electrical engineering or electronics covering research on applied electromagnetism, or demonstrated equivalent experience;
· Proven experience in laboratory tests and instrumentation development at a scientific R&D level;
· Proven ability to perform high-level analytical calculations and simulations using scientific software applications like Comsol, Mathlab, Mathematica or equivalent;
· Experience with supporting software applications for equipment design or laboratory tests, e.g. SolidWorks, Labview etc. is considered an advantage;
· Innovative approach towards cutting edge R&D in electromagnetism;
· Autonomous and proactive working style;
· Communicating effectively, excellent relational skills and ability to work in a team;
· Languages: Fluent in English and possibly in French,.
· Ability to coordinate working groups with different professional and cultural backgrounds.

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Monday, June 3, 2013

Can metal ion complexes be used as polarizing agents for solution DNP? A theoretical discussion


Luchinat, C., G. Parigi, and E. Ravera, Can metal ion complexes be used as polarizing agents for solution DNP? A theoretical discussion. J. Biomol. NMR, 2013: p. 1-11.


Dynamic nuclear polarization (DNP) can be used to dramatically increase the NMR signal intensities in solutions and solids. DNP is usually performed using nitroxide radicals as polarizing agents, characterized by sharp EPR lines, fast rotation, fast diffusion, and favorable distribution of the unpaired electron. These features make the nitroxide radicals ideally suited for solution DNP. Here, we report some theoretical considerations on the different behavior of some inorganic compounds with respect to nitroxide radicals. The relaxation profiles of slow relaxing paramagnetic metal aqua ions [copper(II), manganese(II), gadolinium(III) and oxovanadium(IV)] and complexes have been re-analyzed according to the standard theory for dipolar and contact relaxation, in order to estimate the coupling factor responsible for the maximum DNP enhancement that can be achieved in solution and its dependence on field, temperature and relative importance of outer-sphere versus inner-sphere relaxation.