Friday, April 27, 2012

Shaped optimal control pulses for increased excitation bandwidth in EPR

Spindler, P.E., et al., Shaped optimal control pulses for increased excitation bandwidth in EPR. J. Magn. Reson., 2012. 218(0): p. 49-58.


A 1ns resolution pulse shaping unit has been developed for pulsed EPR spectroscopy to enable 14-bit amplitude and phase modulation. Shaped broadband excitation pulses designed using optimal control theory (OCT) have been tested with this device at X-band frequency (9GHz). FT-EPR experiments on organic radicals in solution have been performed with the new pulses, designed for uniform excitation over a significantly increased bandwidth compared to a classical rectangular π/2 pulse of the same B1 amplitude. The concept of a dead-time compensated prefocused pulse has been introduced to EPR with a self-refocusing of 200ns after the end of the pulse. Echo-like refocused signals have been recorded and compared to the performance of a classical Hahn-echo sequence. The impulse response function of the microwave setup has been measured and incorporated into the algorithm for designing OCT pulses, resulting in further significant improvements in performance. Experimental limitations and potential new applications of OCT pulses in EPR spectroscopy will be discussed.

Wednesday, April 25, 2012

Postdoc Position in PHIP - Nijmegen

*Post-doctoral position in the multidisciplinary Ultrasense NMR project: 

Development of para-hydrogen induced hyperpolarization **instrumentation and methodology for screening, biomarker research and/or molecular diagnostics.*** 

**UltraSense NMR is a large research and development programme (11 PhD and post-docs), granted by EFRO (EU) and GO, in cooperation between science and business. The project will be run by a consortium between Radboud University Nijmegen: Institute of Molecules and Materials, UMC St. Radboud, University of Twente and 3 knowledge companies: Future Chemistry, Spinnovation Analytical and NovioGendix. Goal of the project is to develop hyperpolarisation equipment and strategies based on both physical (DNP) and chemical principles, i.e. para-hydrogen induced hyperpolarisation (PHIP). With the ultrasensitive microfluidic and continuous flow technology and equipment, we will be developing new diagnostic services and a molecular diagnostic test for prostate cancer. In this research programme, multi-disciplined researchers (11 PhDs and post-docs), familiar with the field of physics, chemistry, biophysics, metabolic profiling, or molecular diagnostics will be working closely together in a development team responsible for generating diagnostic technologies of the future. For the above mentioned developments we are looking for enthusiastic PhD students and post-doctoral researchers who like to be part of a multidisciplinary team in an internationally oriented environment. 

PhD position -DNP/NMR- Solid State NMR Nijmegen

The department of Solid State NMR (group of Prof.dr. Arno Kentgens) is one of the partners of the so called "UltraSense NMR" project. 

*Large investment in UltraSense NMR for Analyses, screening and diagnostics.* 

**UltraSense NMR is a large research and development programme, sponsored by the EU and province, in cooperation between science and business. The project will be run by a large cooperation consortium between Radboud University Nijmegen: Institute of Molecules and Materials, UMC St. Radboud, University of Twente and 3 knowledge companies: Future Chemistry, Spinnovation Analytical and NovioGendix. 

Goal of the project is to develop hyperpolarisation equipment and strategies based on both physical (DNP) and chemical (pH2) principles. With the ultrasensitive microfluidic and continuous flow technology and equipment, we will be developing new diagnostic services and a molecular diagnostic test for prostate cancer. For this research programme we are looking for multidisciplined researchers, familiar with the field of physics, chemistry, biophysics, metabolic profiling, molecular diagnostics, who will be working closely togetherto generate a multidisciplinary research and development team responsible for generating the technology as well as the described prototype products. 

*VACANCIES* 

For the abovementioned developments we are looking for an enthusiastic PhD student who likes to be part of a multidisciplinary team in an internationally oriented environment:*. * 

* A PhD with experience in and enthusiasm for magnetic resonance. Knowledge of DNP is a benefit. The PhD will work on the development of optimized DNP technology allowing repetitive hyperpolarization with a focus on gaining both sensitivity and resolution in the context of metabolic profiling. 

For more information: http://www.ru.nl/physchem

If you're interested in this vacancy, please send an e-mail and cv to: m.dewith@science.ru.nl <mailto:m.dewith@science.ru.nl

-- 

Marian de With 
Radboud University 
Institute for Molecules and Materials 
Secretary for depts. of Biophysical Chemistry and Solid State NMR 
Tel. +31 24 3652678 
Fax +31 24 3652112 

Theory of the Overhauser effect in the pulsed mode of EPR pumping: exploiting the advantages of coherent electron spin motion

Nasibulov, E.A., et al., Theory of the Overhauser effect in the pulsed mode of EPR pumping: exploiting the advantages of coherent electron spin motion. Phys. Chem. Chem. Phys., 2012. 14(18): p. 6459-6468.


A theoretical approach is proposed to describe Overhauser-type Dynamic Nuclear Polarization (DNP) for pulsed EPR pumping by application of a train of short pulses with a duration on the nanosecond time scale. We obtained an elegant general expression for the NMR enhancement provided by the DNP effect. The expression for the enhancement is similar to that known for cw-pumping except for the saturation factor, which is re-defined as the deviation of the electron spin magnetization from its equilibrium value averaged over the cycle of the pulse sequence. It is shown that one can achieve the maximal theoretically allowed NMR enhancement for pulsed pumping even when the duty cycle of pumping is low. This becomes possible because coherent motion of the electron spins in the B1-field is exploited, a key feature of the pulsed DNP experiment also enabling optimization of the achievable NMR enhancement. The dependence of the effect on the duty cycle, pulse duration and electron spin relaxation times has been studied in detail. Once the lines in the EPR spectrum are inhomogeneously broadened, higher DNP effects are expected in the pulsed pumping mode than in the cw-mode for the same total power of microwave irradiation. The theoretical results are in good agreement with experimental data obtained for the pumping frequencies of 300 MHz and 1.4 GHz.

Wednesday, April 18, 2012

THz Transmission Lines for DNP-NMR

A transmission line, linking the gyrotron (or solid-state) source to the NMR probe is an essential piece of THz instrumentation for DNP-NMR spectrometers. While quasi-optical transmission system have been used for setups using low-power solid-state sources, far more typical is the use of circular (corrugated) waveguides to deliver the THz power to the sample. Below is a list of two articles that have been published recently covering the topic of low-loss THz transmission lines for application in DNP-NMR spectroscopy:

Nanni, E., et al., Low-loss Transmission Lines for High-power Terahertz Radiation. J. Infrared Millim. Te., 2012: p. 1-20.

Bogdashov, A., et al., Transmission Line for 258 GHz Gyrotron DNP Spectrometry. J. Infrared Millim. Te., 2011. 32(6): p. 823-837.

Gunther Laukien Prize 2012 for DNP

The Gunther Laukien Prize for 2012 is awarded to Klaes Golman and Jan Henrik Ardenkjaer-Larsen for the conception, development, and application of dissolution-DNP NMR. This remarkable technique is capable of enhancing nuclear polarization by several orders of magnitude and provides access to a panacea for new spectacular applications that have been, so far, inconceivable because of a lack of signal strength. The method starts with Dynamic Nuclear Polarization (DNP) of the solidified sample at very low temperature in the presence of a radical, such as trityl, by microwave irradiation. Up to 65% 13C polarization can be achieved. Further information can be found here.

Gunther Laukien Prize 2012 for DNP

The Gunther Laukien Prize for 2012 is awarded to Klaes Golman and Jan Henrik Ardenkjaer-Larsen for the conception, development, and application of dissolution-DNP NMR. This remarkable technique is capable of enhancing nuclear polarization by several orders of magnitude and provides access to a panacea for new spectacular applications that have been, so far, inconceivable because of a lack of signal strength. The method starts with Dynamic Nuclear Polarization (DNP) of the solidified sample at very low temperature in the presence of a radical, such as trityl, by microwave irradiation. Up to 65% 13C polarization can be achieved. Further information can be found here.

Monday, April 16, 2012

1H Dynamic Nuclear Polarization Based on an Endogenous Radical

Maly, T., et al., 1H Dynamic Nuclear Polarization Based on an Endogenous Radical. Journal of Physical Chemistry B, 2012.


We demonstrate a 15-fold enhancement of solid-state NMR signals via dynamic nuclear polarization (DNP) based on a stable, naturally occurring radical in a protein: the flavin mononucleotide (FMN) semiquinone of flavodoxin. The linewidth of flavodoxin's EPR signal suggests that the dominant DNP mechanism is the solid effect, consistent with the field-dependent DNP enhancement profile. The magnitude of the enhancement as well as the bulk-polarization build-up time constant (tau<sub>B</sub>) with which it develops are dependent on the isotopic composition of the protein. Deuteration of the protein to 85 % increased the nuclear longitudinal relaxation time T<sub>1n</sub> and tau<sub>B</sub> by factors of five and seven, respectively. Slowed dissipation of polarization can explain the two-fold higher maximal enhancement than that obtained in proteated protein, based on the endogenous semiquinone. In contrast, the long tau_B of TOTAPOL-based DNP in non-glassy samples was not accompanied by a similarly important long T1n, and in this case the enhancement was greatly reduced. The low concentrations of radicals occurring naturally in biological systems limit the magnitude of DNP enhancement that is attainable by this means. However, our enhancement factors of up to 15 can nonetheless make an important difference to the feasibility of applying solid-state NMR to biochemical systems. We speculate that DNP based on endogenous radicals may facilitate MAS NMR characterization of biochemical complexes and even organelles, and could also serve as a source of additional structural and physiological information.

Saturday, April 14, 2012

Rigid Orthogonal Bis-TEMPO Biradicals with Improved Solubility for Dynamic Nuclear Polarization


Dane, E.L., et al., Rigid Orthogonal Bis-TEMPO Biradicals with Improved Solubility for Dynamic Nuclear Polarization. The Journal of Organic Chemistry, 2012. 77(4): p. 1789-1797.


The synthesis and characterization of oxidized bis-thioketal-trispiro dinitroxide biradicals that orient the nitroxides in a rigid, approximately orthogonal geometry are reported. The biradicals show better performance as polarizing agents in dynamic nuclear polarization (DNP) NMR experiments as compared to biradicals lacking the constrained geometry. In addition, the biradicals display improved solubility in aqueous media due to the presence of polar sulfoxides. The results suggest that the orientation of the radicals is not dramatically affected by the oxidation state of the sulfur atoms in the biradical, and we conclude that a biradical polarizing agent containing a mixture of oxidation states can be used for improved solubility without a loss in performance.

Thursday, April 12, 2012

Electron Spin Density Distribution in the Special Pair Triplet of Rhodobacter sphaeroides R26 Revealed by Magnetic Field Dependence of the Solid-State Photo-CIDNP Effect

Thamarath, S.S., et al., Electron Spin Density Distribution in the Special Pair Triplet of Rhodobacter sphaeroides R26 Revealed by Magnetic Field Dependence of the Solid-State Photo-CIDNP Effect. J. Am. Chem. Soc., 2012. 134(13): p. 5921-5930.


Photo-CIDNP (photochemically induced dynamic nuclear polarization) can be observed in frozen and quinone-blocked photosynthetic reaction centers (RCs) as modification of magic-angle spinning (MAS) NMR signal intensity under illumination. Studying the carotenoidless mutant strain R26 of Rhodobacter sphaeroides, we demonstrate by experiment and theory that contributions to the nuclear spin polarization from the three-spin mixing and differential decay mechanism can be separated from polarization generated by the radical pair mechanism, which is partially maintained due to differential relaxation (DR) in the singlet and triplet branch. At a magnetic field of 1.4 T, the latter contribution leads to dramatic signal enhancement of about 80 000 and dominates over the two other mechanisms. The DR mechanism encodes information on the spin density distribution in the donor triplet state. Relative peak intensities in the photo-CIDNP spectra provide a critical test for triplet spin densities computed for different model chemistries and conformations. The unpaired electrons are distributed almost evenly over the two moieties of the special pair of bacteriochlorophylls, with only slight excess in the L branch.

Bridge12 at ENC

are you attending this years 53rd ENC conference held at the Intercontinental Hotel in Miami, Florida from April 15th to 20th 2012? If yes, we would like to meet you.

Our team members Jagadishwar Sirigiri and Thorsten Maly will be at ENC to discuss our latest innovations in gyrotron technology for DNP-enhanced NMR spectroscopy (DNP-NMR). Please let us know in advance if you’d like to meet up, or simply pull us aside at the conference. We are looking forward to this exciting event to discuss how we can help you push the boundaries of nuclear magnetic research.

Also, please take a moment and stop by at our poster (number 171). We will present preliminary results of our first prototype operating at 395 GHz for 600 MHz DNP-NMR spectroscopy.

Tuesday, April 10, 2012

Development of DNP-Enhanced High-Resolution Solid-State NMR System for the Characterization of the Surface Structure of Polymer Materials

Horii, F., et al., Development of DNP-Enhanced High-Resolution Solid-State NMR System for the Characterization of the Surface Structure of Polymer Materials. J. Infrared Millim. Te., 2012: p. 1-10.


A dynamic nuclear polarization (DNP)-enhanced cross-polarization/magic-angle spinning (DNP/CP/MAS) NMR system has been developed by combining a 200 MHz Chemagnetics CMX-200 spectrometer operating at 4.7 T with a high-power 131.5 GHz Gyrotron FU CW IV. The 30 W sub-THz wave generated in a long pulse TE41 mode with a frequency of 5 Hz was successfully transmitted to the modified Doty Scientific low-temperature CP/MAS probe through copper smooth-wall circular waveguides. Since serious RF noises on NMR signals by arcing in the electric circuit of the probe and undesired sample heating were induced by the continuous sub-THz wave pulse irradiation with higher powers, the on-off sub-THz wave pulse irradiation synchronized with the NMR detection was developed and the appropriate setting of the irradiation time and the cooling time corresponding to the non-irradiation time was found to be very effective for the suppression of the arcing and the sample heating. The attainable maximum DNP enhancement was more than 30 folds for C1 13 C-enriched D -glucose dissolved in the frozen medium containing mono-radical 4-amino-TEMPO. The first DNP/CP/MAS 13 C NMR spectra of poly(methyl methacrylate) (PMMA) sub-micron particles were obtained at the dispersed state in the same frozen medium, indicating that DNP-enhanced 1 H spins effectively diffuse from the medium to the PMMA particles through their surface and are detected as high-resolution 13 C spectra in the surficial region to which the 1 H spins reach. On the basis of these results, the possibility of the DNP/CP/MAS NMR characterization of the surface structure of nanomaterials including polymer materials was discussed.

Sunday, April 8, 2012

Low-loss Transmission Lines for High-power Terahertz Radiation

Nanni, E., et al., Low-loss Transmission Lines for High-power Terahertz Radiation. J. Infrared Millim. Te., 2012: p. 1-20.


Applications of high-power Terahertz (THz) sources require low-loss transmission lines to minimize loss, prevent overheating and preserve the purity of the transmission mode. Concepts for THz transmission lines are reviewed with special emphasis on overmoded, metallic, corrugated transmission lines. Using the fundamental HE 11 mode, these transmission lines have been successfully implemented with very low-loss at high average power levels on plasma heating experiments and THz dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments. Loss in these lines occurs directly, due to ohmic loss in the fundamental mode, and indirectly, due to mode conversion into high order modes whose ohmic loss increases as the square of the mode index. An analytic expression is derived for ohmic loss in the modes of a corrugated, metallic waveguide, including loss on both the waveguide inner surfaces and grooves. Simulations of loss with the numerical code HFSS are in good agreement with the analytic expression. Experimental tests were conducted to determine the loss of the HE 11 mode in a 19 mm diameter, helically-tapped, three meter long brass waveguide with a design frequency of 330 GHz. The measured loss at 250 GHz was 0.029 ± 0.009 dB/m using a vector network analyzer approach and 0.047 ± 0.01 dB/m using a radiometer. The experimental results are in reasonable agreement with theory. These values of loss, amounting to about 1% or less per meter, are acceptable for the DNP NMR application. Loss in a practical transmission line may be much higher than the loss calculated for the HE 11 mode due to mode conversion to higher order modes caused by waveguide imperfections or miter bends.



Thursday, April 5, 2012

Transmission Line for 258 GHz Gyrotron DNP Spectrometry

Bogdashov, A., et al., Transmission Line for 258 GHz Gyrotron DNP Spectrometry. J. Infrared Millim. Te., 2011. 32(6): p. 823-837.


We describe the design and test results of the transmission line for liquid-state (LS) and solid-state (SS) DNP spectrometers with the second-harmonic 258.6 GHz gyrotron at the Institute of the Biophysical Chemistry Center of Goethe University (Frankfurt). The 13-meter line includes a mode converter, HE11 waveguides, 4 mitre bends, a variable polarizer-attenuator, directional couplers, a water-flow calorimeter and a mechanical switch. A microwave power of about 15 W was obtained in the pure HE11 mode at the spectrometer inputs.



Monday, April 2, 2012

Liquid state Dynamic Nuclear Polarization probe with Fabry–Perot resonator at 9.2 T

Denysenkov, V. and T. Prisner, Liquid state Dynamic Nuclear Polarization probe with Fabry–Perot resonator at 9.2 T. J. Magn. Reson., 2012. 217(0): p. 1-5.


Recent achievements in liquid state DNP at high magnetic fields showing significant enhancements on aqueous solutions have initiated strong interest in possible applications of this method to biomolecular research. However, in situ DNP of biomolecules at ambient temperatures is a challenging task due to high microwave losses leading to excessive sample heating. To avoid such heating the sample volume has to be reduced strongly to keep it away from the electric component of the microwave field. A helical double resonance structure, used for the first demonstrations of the applicability of Overhauser DNP to aqueous solutions at high magnetic fields (9.2 T), restricted the sample size to a very small volume of 2 nl. Together with a poor spectral resolution this resulted in small overall signal amplitude, hampering observations of biomolecules. Here we present a new type of the double resonance structure for liquid-state DNP which consists of a Fabry–Perot resonator for the microwave excitation and a stripline resonator for the NMR detection. This new double resonance structure (260&#xa0;GHz/400&#xa0;MHz) offers a 30-fold increase in aqueous sample volume (80 nl) with respect to the helical probe and exhibits improved NMR sensitivity and linewidth.