Friday, May 31, 2013

Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy


Rossini, A.J., et al., Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy. Acc. Chem. Res., 2013.


Many of the functions and applications of advanced materials result from their interfacial structures and properties. However, the difficulty in characterizing the surface structure of these materials at an atomic level can often slow their further development. Solid-state NMR can probe surface structure and complement established surface science techniques, but its low sensitivity often limits its application. Many materials have low surface areas and/or low concentrations of active/surface sites. Dynamic nuclear polarization (DNP) is one intriguing method to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude. In a DNP experiment, the large polarization of unpaired electrons is transferred to surrounding nuclei, which provides a maximum theoretical DNP enhancement of approximately 658 for 1H NMR. In this Account, we discuss the application of DNP to enhance surface NMR signals, an approach known as DNP surface enhanced NMR spectroscopy (DNP SENS). Enabling DNP for these systems requires bringing an exogeneous radical solution into contact with surfaces without diluting the sample. We proposed the incipient wetness impregnation technique (IWI), a well-known method in materials science, to impregnate porous and particulate materials with just enough radical containing solution to fill the porous volume. IWI offers several advantages: it is extremely simple, provides a uniform wetting of the surface, and does not increase the sample volume or substantially reduce the concentration of the sample. This Account describes the basic principles behind DNP SENS through results obtained for mesoporous and nanoparticulate samples impregnated with radical solutions. We also discuss the quantification of the overall sensitivity enhancements obtained with DNP SENS and compare that with ordinary room temperature NMR spectroscopy. We then review the development of radicals and solvents that give the best possible enhancements today. With the best polarizing mixtures, DNP SENS enhances sensitivity by a factor of up to 100, which decreases acquisition time by five orders of magnitude. Such enhancement enables the detailed and expedient atomic level characterization of the surfaces of complex materials at natural isotopic abundance and opens new avenues for NMR. To illustrate these improvements, we describe the successful application of DNP SENS to characterize hybrid materials, organometallic surface species, and metal-organic frameworks.

Wednesday, May 29, 2013

High Power Wideband Gyrotron Backward Wave Oscillator Operating towards the Terahertz Region


He, W., et al., High Power Wideband Gyrotron Backward Wave Oscillator Operating towards the Terahertz Region. Phys. Rev. Lett., 2013. 110(16): p. 165101.


Experimental results are presented of the first successful gyrotron backward wave oscillator (gyro-BWO) with continuous frequency tuning near the low-terahertz region. A helically corrugated interaction region was used to allow efficient interaction over a wide frequency band at the second harmonic of the electron cyclotron frequency without parasitic output. The gyro-BWO generated a maximum output power of 12 kW when driven by a 40 kV, 1.5 A, annular-shaped large-orbit electron beam and achieved a frequency tuning band of 88-102.5 GHz by adjusting the cavity magnetic field. The performance of the gyro-BWO is consistent with 3D particle-in-cell numerical simulations.

Friday, May 24, 2013

Liquid state DNP of water at 9.2 T: an experimental access to saturation

Neugebauer, P., et al., Liquid state DNP of water at 9.2 T: an experimental access to saturation. Phys Chem Chem Phys, 2013. 15(16): p. 6049-56.


We have performed liquid state ("Overhauser") Dynamic Nuclear Polarization (DNP) experiments at high magnetic field (9.2 T, corresponding to 260 GHz EPR and 400 MHz (1)H-NMR resonance frequency) on aqueous solutions of (14)N-TEMPOL nitroxide radicals. Integrated signal enhancements exceeding -80 were observed for the water protons at microwave superheated temperatures (160 degrees C) and still -14 at ambient temperatures (45 degrees C) relevant to biological applications. Different contributions contributing to the DNP enhancement such as saturation factor, leakage factor and sample temperature under microwave irradiation could be determined independently for a high spin concentration of 1 M, allowing the calculation of the coupling factors as a function of temperature and a quantitative comparison of this parameter with values derived from field dependent relaxation measurements or predictions from MD simulation.

Wednesday, May 22, 2013

Influence of deuteration in the glassing matrix on 13C dynamic nuclear polarization

Lumata, L., M.E. Merritt, and Z. Kovacs, Influence of deuteration in the glassing matrix on 13C dynamic nuclear polarization. Phys. Chem. Chem. Phys., 2013. 15(19): p. 7032-7035.


Replacement of protons by deuterons in the glassing solvents led to 2-3-fold improvement of the (13)C dynamic nuclear polarization (DNP) solid-state NMR signal for samples doped with large electron spin resonance (ESR) linewidth free radicals galvinoxyl, DPPH, and 4-oxo-TEMPO. Meanwhile, the reverse effect is observed for (13)C DNP using small ESR linewidth free radicals BDPA and trityl OX063.


Monday, May 20, 2013

Fundamental Aspects of Parahydrogen Enhanced Low-Field Nuclear Magnetic Resonance

Colell, J., et al., Fundamental Aspects of Parahydrogen Enhanced Low-Field Nuclear Magnetic Resonance. Phys. Rev. Lett., 2013. 110(13): p. 137602.


We report new phenomena in low-field ^{1}H nuclear magnetic resonance (NMR) spectroscopy using parahydrogen induced polarization (PHIP), enabling determination of chemical shift differences, deltanu, and the scalar coupling constant J. NMR experiments performed with thermal polarization in millitesla magnetic fields do not allow the determination of scalar coupling constants for homonuclear coupled spins in the inverse weak coupling regime (deltanu<J). We show here that low-field PHIP experiments in the inverse weak coupling regime enable the precise determination of deltanu and J. Furthermore we experimentally prove that observed splittings are related to deltanu in a nonlinear way. Naturally abundant ^{13}C and ^{29}Si isotopes lead to heteronuclear J-coupled ^{1}H-multiplet lines with amplitudes significantly enhanced compared to the amplitudes for thermally prepolarized spins. PHIP-enhanced NMR in the millitesla regime allows us to measure characteristic NMR parameters in a single scan using samples containing rare spins in natural abundance.


Friday, May 17, 2013

Applications of dynamic nuclear polarization to the study of reactions and reagents in organic and biomolecular chemistry

Hilty, C. and S. Bowen, Applications of dynamic nuclear polarization to the study of reactions and reagents in organic and biomolecular chemistry. Organic & Biomolecular Chemistry, 2010. 8(15): p. 3361-3365.


Nuclear Magnetic Resonance (NMR) is an important spectroscopic tool for the identification and structural characterization of molecules in chemistry and biochemistry. The most significant limitation of NMR compared to other spectroscopies is its relatively low sensitivity, which thus often requires long measurement times or large amounts of sample. A way of increasing sensitivity of single scan NMR spectra by several orders of magnitude is through hyperpolarization of nuclear spins. Dynamic nuclear polarization allows hyperpolarization of most spins in small molecules encountered in chemistry and biochemistry. NMR spectra of small amounts of samples from natural source, or from chemical synthesis can readily be acquired. Perhaps more interestingly, the availability of the entire hyperpolarized NMR signal in one single scan allows the measurement of transient processes in real time, if applied together with a stopped-flow technique. Through observation of chemical shift, different reactant and product species can be distinguished, and kinetics and mechanisms, for example in enzyme catalyzed reactions, can be elucidated. Real-time hyperpolarization-enhanced NMR is uniquely amenable to correlating atomic positions not only through space, but also over time between reactant and product species. Such correlations carry mechanistic information about a reaction, and can prove reaction pathways. Applications of this technique are emerging in different areas of chemistry concerned with rapid reactions, including not only enzymatic processes, but also chemical catalysis and protein folding.

Wednesday, May 15, 2013

One hundred fold overall sensitivity enhancements for Silicon-29 NMR spectroscopy of surfaces by dynamic nuclear polarization with CPMG acquisition

Rossini, A.J., et al., One hundred fold overall sensitivity enhancements for Silicon-29 NMR spectroscopy of surfaces by dynamic nuclear polarization with CPMG acquisition. Chemical Science, 2012. 3(1): p. 108-115.


Dynamic nuclear polarization (DNP) 29Si solid-state NMR spectra of a hybrid mesoporous silica material impregnated with aqueous biradical solutions have been acquired with cross-polarization (CP) and cross-polarization Carr-Purcell Meiboom-Gill (CP/CPMG) pulse sequences. The integrated intensities (II) and signal to noise ratios (S/N) of the 29Si solid-state NMR spectra are monitored in order to measure the DNP enhancement factors (?Si CP) as well as the overall sensitivity enhancement ([capital Sigma]Si CP) available from the combination of DNP and CPMG acquisition. Here, , where [small theta]Si is a factor which quantifies reduction of the NMR signal by paramagnetic effects (quenching) and [small kappa] is the square root of the ratio of nuclear longitudinal relaxation times of the dry material and material impregnated with radical solution. It is found that [capital Sigma]Si CP is always substantially lower than the measured value of ?Si CP due to paramagnetic effects which reduce the II of the 29Si CP solid-state NMR spectra at high biradical concentrations. In this system, it is observed that the sample preparation which provides optimal DNP signal enhancement does not provide optimal overall signal enhancement. Notably, optimal signal enhancements are obtained for CPMG acquisition of the 29Si solid-state NMR spectra when lower radical concentrations are employed due to slower transverse relaxation rates. To the best of our knowledge this is the first study which seeks to quantify the overall sensitivity enhancements available from DNP solid-state NMR experiments.

Monday, May 13, 2013

Postdoc position in Warwick doing ENDOR-DNP

The Magnetic Resonance Group in the Physics Department at the University of Warwick invites applications for a post-doctoral research fellow to work on the EPSRC-funded project "ENDOR-DNP". In addition to dynamic nuclear polarization (DNP), the group has a broad research program from high-field EPR to solid-state NMR. 

Friday, May 10, 2013

Open PhD Position in the Field of Membrane Protein Biophysics in Frankfurt/M, Germany

The Glaubitz lab is looking for a new PhD student to join our team working on transport proteins. The PhD project is concerned with the functional understanding of ATP driven efflux pumps (ABC transporters). It involves solid-state NMR and DNP as well as membrane protein biochemistry and is well connected via collaboration with complementary methods such as EPR or single molecule fluorescence spectroscopy. The successful candidate should hold a degree (MSc) in biochemistry/chemistry/biophysics or related subjects. Some previous biochemical wet lab experiences will be helpful. We offer an exciting research project and very good research infrastructure including high field solid-state NMR (850 and 600 MHz) and DNP spectrometers. The lab is part of the Frankfurt Centre for Biomolecular Magnetic Resonance (BMRZ), the research network “Transport across membranes “ and the Cluster of Excellence “Macromolecular Complexes”. The lab is located at the Riedberg Campus of the Goethe University Frankfurt, which is a hotspot for membrane protein research, structural biology and magnetic resonance spectroscopy. 

Applications shall be addressed to Clemens Glaubitz (glaubitz@em.uni-frankfurt.de). Informal pre-application enquiries are welcome. Formal applications should include a CV, a brief summary of the Diploma/Master thesis project, copies of degree certificates and names of two professors who could be contacted for a reference. Please combine all documents into one single PDF. 

----------------------------------------------------- 
Clemens Glaubitz, D.Phil 
University Professor 
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Goethe University Frankfurt 
Institute of Biophysical Chemistry & 
Centre for Biomolecular Magnetic Resonance 
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Postal Address: 
Institute for Biophysical Chemistry 
Goethe University Frankfurt 
Max von Laue Str. 9 
60438 Frankfurt 
Germany 
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Office: Biocenter, N202, Room 006 
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Tel: +49+69+798-29927 
Fax:+49+69+798-29929 
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Administrative Assistance 
Simone Kobylka 
Office: Biocenter, N202, Room 007 
Tel: +49+69+798-29928 
Fax:+49+69+798-29929 
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Wednesday, May 8, 2013

4th International DNP Symposium: ONE week to registration deadline

Dear Colleagues

We are now one week away from registration deadline for the 4th International DNP Symposium (www.DNPsymposium.org), Copenhagen, Denmark, Aug 28-31, 2013: Registration closes May 15. 

The preliminary program is posted along with the invited speakers list. The invited speakers are also abstract reviewers, and a blinded peer-reviewed process is applied for acceptance of the remaining oral presentations and posters. This way we aim to build a scientific program of the highest quality by transparent and fair selection. Abstract submission closes June 1, but is already open for submission. 



All the best, 
The Organizing Committee 


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

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NMR web database: 

Monday, May 6, 2013

The interplay between the solid effect and the cross effect mechanisms in solid state 13C DNP at 95 GHz using trityl radicals

Banerjee, D., et al., The interplay between the solid effect and the cross effect mechanisms in solid state 13C DNP at 95&#xa0;GHz using trityl radicals. J. Magn. Reson., 2013. 230(0): p. 212-219.


The 13C solid state Dynamic Nuclear Polarization (DNP) mechanism using trityl radicals (OX63) as polarizers was investigated in the temperature range of 10–60 K. The solutions used were 6 M 13C urea in DMSO/H2O (50% v/v) with 15 mM and 30 mM OX63. The measurements were carried out at ∼3.5 T, which corresponds to Larmor frequencies of 95 GHz and 36 MHz for the OX63 and the 13C nuclei, respectively. Measurements of the 13C signal intensity as a function of the microwave (MW) irradiation frequency yielded 13C DNP spectra with temperature dependent lineshapes for both samples. The maximum enhancement for the 30 mM sample was reached at 40 K, while that of the 15 mM sample at 20–30 K. Furthermore, the lineshapes observed showed that both the cross effect (CE) and the solid effect (SE) DNP mechanisms are active in this temperature range and that their relative contribution is temperature dependent. Simulations of the spectra with the relative contributions of the CE and SE mechanisms as a fit parameter revealed that for both samples the CE contribution decreases with decreasing temperature while the SE contribution increases. In addition, for the 15 mM sample the contributions of the two mechanisms are comparable from 20 K to 60 K while for the 30 mM the CE dominates in this range, as expected from the higher concentration. The steep decrease of the CE contribution towards low temperatures is however unexpected. The temperature dependence of the OX63 longitudinal relaxation, DNP buildup times and 13C spin lattice relaxation times did not reveal any obvious correlation with the DNP temperature dependence. A similar behavior of the CE and SE mechanism was observed for 1H DNP with the nitroxide radical TEMPOL as a polarizer. This suggests that this effect is a general phenomenon involving a temperature dependent competition between the CE and SE mechanisms, the source of which is, however, still unknown.



Friday, May 3, 2013

TEMPOL as a polarizing agent for dynamic nuclear polarization of aqueous solutions

Gafurov, M., TEMPOL as a polarizing agent for dynamic nuclear polarization of aqueous solutions. Magn. Reson. Solids., 2013. 15: p. 13103.


High-resolution proton NMR (400 MHz) and multifrequency EPR (9 - 260 GHz) characterization of aqueous solutions of the nitroxyl radical TEMPOL in the temperature range (10 - 40) °C is performed for the liquid-state DNP. Characteristic features of the in-situ DNP observations at high frequencies are presented. Optimal conditions (concentration, temperature, position of the microwave pumping, repetition/build-up time for the DNP experiments) are extracted. The results are compared with the DNP experiments, molecular dynamic calculations, saturation models, and classical models of translational and rotational diffusion. Perspectives for using TEMPOL as polarizing agent in even higher magnetic fields are discussed.



Wednesday, May 1, 2013

Dynamic Nuclear Polarization Key Topic At 54th ENC Conference


Dynamic Nuclear Polarization Key Topic At 54th ENC Conference

It was great to see many familiar faces at this year’s ENC Conference in beautiful Asilomar. For those who couldn’t make it this year, I’d like to summarize some key takeaways:
  • Dynamic Nuclear Polarization a dominant theme: Almost two entire parallel sessions were dedicated to Dynamic Nuclear Polarization. Lectures were given by David Doty, Sudheer Jawla, Melanie Rosay, Song-I Han, Maja Cassidy, Sami Jannin, Gunnar Jeschke, Kent Thurber and Joshua Wand.
  • DNP NMR applied to biosolids and material science: Continuing last year’s trend, many posters were dedicated to DNP NMR applications to biosolids and material science. It’s encouraging to see more focus on real-world problems rather than on instrumentation, thanks to the increasing availability of off-the-shelf DNP instruments.
  • Novel approach to using reverse micelles in DNP NMR: My personal highlight was the talk by Joshua Wand, who presented a novel approach to using reverse micelles for solution state DNP NMR spectroscopy. The basic idea is to encapsulate a protein dissolved in an organic solvent with a low dielectric constant, with the polarizing agent present inside the micelle. Such samples are largely transparent to the THz radiation and thereby avoid significant heating during the DNP process. Kathleen Valentine’s poster provided additional information. This very interesting approach definitely has the potential to address some of the problems that solution-state DNP currently faces such as sample heating due to irradiation of the sample with THz radiation.
  • Laukien Prize awarded to Clare Grey: Congratulations to Clare Grey for receiving this years Laukien Prize for her accomplishments in studying battery materials using solid-state NMR spectroscopy.
I hope you enjoyed the 54th ENC as much as I did. I hope to see you all again in Boston next year.