Thursday, January 26, 2012

The Effect of Sample Age and Neutron Radiation to Dynamic Nuclear Polarization Parameters in Some Asphaltene Suspensions

Ovalioglu, H., The Effect of Sample Age and Neutron Radiation to Dynamic Nuclear Polarization Parameters in Some Asphaltene Suspensions. Journal of Dispersion Science and Technology, 2011. 32(10): p. 1470-1476.


Nuclear magnetic resonance and the Overhauser effect type dynamic nuclear polarization experiments were performed to study suspensions of asphaltene in the xylene isomers at a low magnetic field of 1.44mT at room temperature. Intermolecular spin-spin interactions occur between nuclear spins of hydrogen in the solvent medium and the free electron spins in the asphaltene micelles. The samples were prepared in three different asphaltene concentrations at vacuum. The samples were waited for four years and dynamic nuclear polarization parameters were found via dynamic nuclear polarization experiments performed again. Thus, it was investigated the effect of sample age to dynamic nuclear polarization parameters. In addition, the medium concentrations of each sample were exposed to radiation for 48 hours and neutron radiation effects to the dynamic nuclear polarization parameters were investigated. The results are discussed.



Spin tagging for hyperpolarized 13C metabolic studies

Chen, A.P., R.E. Hurd, and C.H. Cunningham, Spin tagging for hyperpolarized 13C metabolic studies. J. Magn. Reson., 2012. 214(0): p. 319-323.


In studies utilizing pre-polarized 13C substrates to investigate metabolic activities in vivo, the metabolite signals observed in a region or a voxel contains a mixture of intracellular and extracellular components. This extracellular component arriving via perfusion may confound the measurements of metabolic flux or exchange rates. But if spin tagging is performed on the magnetization of the substrate, it may be possible to measure the signals of the metabolic products in the intracellular space that were derived from the tagged substrate spins locally. In this study, a spin tagging pulse sequence designed for acquiring data from spatially tagged longitudinal magnetization in hyperpolarized 13C metabolic studies was presented and tested. Using a spectral–spatial RF pulse during the tagging preparation enabled the observation of metabolite signals derived exclusively from the tagged substrate in vivo.

A multi-sample 94GHz dissolution dynamic-nuclear-polarization system

Batel, M., et al., A multi-sample 94GHz dissolution dynamic-nuclear-polarization system. J. Magn. Reson., 2012. 214(0): p. 166-174.


We describe the design and initial performance results of a multi-sample dissolution dynamic-nuclear-polarization (DNP) polarizer based on a Helium-temperature NMR cryostat for use in a wide-bore NMR magnet with a room-temperature bore. The system is designed to accommodate up to six samples in a revolver-style sample changer that allows changing samples at liquid-Helium temperature and at pressures ranging from ambient pressure down to 1mbar. The multi-sample setup is motivated by the desire to do repetitive in vivo measurements and to characterize the DNP process by investigating samples of different chemical composition. The system can be loaded with up to six samples simultaneously to reduce sample loading and unloading. Therefore, series of experiments can be carried out faster and more reliably. The DNP probe contains an oversized microwave cavity and includes EPR and NMR capabilities for monitoring the DNP process. In the solid state, DNP enhancements corresponding to ~45% polarization for [1-13C]pyruvic acid with a trityl radical have been measured. In the initial liquid-state acquisition experiments described here, the polarization was found to be ~13%, corresponding to an enhancement factor exceeding 16,000 relative to thermal polarization at 9.4T and ambient temperature.

Theoretical aspects of dynamic nuclear polarization in the solid state - The cross effect

Hovav, Y., A. Feintuch, and S. Vega, Theoretical aspects of dynamic nuclear polarization in the solid state - The cross effect. J. Magn. Reson., 2012. 214(0): p. 29-41.

http://dx.doi.org/10.1016/j.jmr.2011.09.047

In recent years Dynamic Nuclear Polarization (DNP) signal enhancement techniques have become an important and integral part of modern NMR and MRI spectroscopy. The DNP mechanisms transferring polarization from unpaired electrons to the nuclei in the sample is accomplished by microwave (MW) irradiation. For solid samples a distinction is made between three main enhancement processes: Solid Effect (SE), Cross Effect (CE) and Thermal Mixing (TM) DNP.

Three-field NMR to preserve hyperpolarized proton magnetization as long-lived states in moderate magnetic fields

Bornet, A.l., S. Jannin, and G. Bodenhausen, Three-field NMR to preserve hyperpolarized proton magnetization as long-lived states in moderate magnetic fields. Chem. Phys. Lett., 2011. 512(4–6): p. 151-154.


This communication describes a three-field experiment where inequivalent scalar coupled spin pairs are hyperpolarized at 3.35T and 1.2K by dynamic nuclear polarization (DNP), rapidly transferred to high field (7T) to prepare a suitable initial condition that is converted adiabatically into a long-lived state (LLS) by shuttling to a 'low' magnetic field (2mT - 7T). Even without applying any rf irradiation to sustain the LLS, it has a lifetime TLLS>>T1 in low fields. Finally, the sample is shuttled back to high field for observation under high-resolution conditions.

The effect of 13 C enrichment in the glassing matrix on dynamic nuclear polarization of [1- 13 C]pyruvate

Lloyd, L., et al., The effect of 13 C enrichment in the glassing matrix on dynamic nuclear polarization of [1- 13 C]pyruvate. Physics in Medicine and Biology, 2011. 56(5): p. N85-N92.


Dimethyl sulfoxide (DMSO) can effectively form a glassy matrix necessary for dynamic nuclear polarization (DNP) experiments. We tested the effects of 13C enrichment in DMSO on DNP of [1- 13 C]pyruvate doped with trityl radical OX063Me. We found that the polarization build-up time τ of pyruvate in 13 C-labeled DMSO glassing solution is twice as fast as the unenriched DMSO while the nuclear magnetic resonance enhancement was unchanged. This indicates that 13 C-13 C spin diffusion is a limiting factor in the kinetics of DNP in this system, but it has a minimal effect on the absolute value of polarization achievable for the target.

Sunday, January 22, 2012

On the accuracy of the state space restriction approximation for spin dynamics simulations

Karabanov, A., et al., On the accuracy of the state space restriction approximation for spin dynamics simulations. J. Chem. Phys., 2011. 135(8): p. 084106-8.


We present an algebraic foundation for the state space restriction approximation in spin dynamics simulations and derive applicability criteria as well as minimal basis set requirements for practically encountered simulation tasks. The results are illustrated with nuclear magnetic resonance (NMR), electron spin resonance (ESR), dynamic nuclear polarization (DNP), and spin chemistry simulations. It is demonstrated that state space restriction yields accurate results in systems where the time scale of spin relaxation processes approximately matches the time scale of the experiment. Rigorous error bounds and basis set requirements are derived.

Wednesday, January 18, 2012

Site-Specific Hydration Dynamics in the Nonpolar Core of a Molten Globule by Dynamic Nuclear Polarization of Water

Armstrong, B.D., et al., Site-Specific Hydration Dynamics in the Nonpolar Core of a Molten Globule by Dynamic Nuclear Polarization of Water. J. Am. Chem. Soc., 2011. 133(15): p. 5987-5995.


Water-protein interactions play a direct role in protein folding. The chain collapse that accompanies protein folding involves extrusion of water from the nonpolar core. For many proteins, including apomyoglobin (apoMb), hydrophobic interactions drive an initial collapse to an intermediate state before folding to the final structure. However, the debate continues as to whether the core of the collapsed intermediate state is hydrated and, if so, what the dynamic nature of this water is.

Solution NMR of Polypeptides Hyperpolarized by Dynamic Nuclear Polarization

Ragavan, M., et al., Solution NMR of Polypeptides Hyperpolarized by Dynamic Nuclear Polarization. Analytical Chemistry, 2011. 83(15): p. 6054-6059.


Hyperpolarization of nuclear spins through techniques such as dynamic nuclear polarization (DNP) can greatly increase the signal-to-noise ratio in NMR measurements, thus eliminating the need for signal averaging. This enables the study of many dynamic processes which would otherwise not be amenable to study by NMR spectroscopy. A report of solid- to liquid-state DNP of a short peptide, bacitracin A, as well as of a full-length protein, L23, is presented here. The polypeptides are hyperpolarized at low temperature and dissolved for NMR signal acquisition in the liquid state in mixtures of organic solvent and water.

Tuesday, January 17, 2012

Localized in vivo hyperpolarization transfer sequences

Mishkovsky, M., et al., Localized in vivo hyperpolarization transfer sequences. Magnetic Resonance in Medicine, 2011: p. n/a-n/a.


In vivo localized and fully adiabatic homonuclear and heteronuclear polarization transfer experiments were designed and performed in the rat brain at 9.4 T after infusion of hyperpolarized sodium [1,2-13C2] and sodium [1-13C] acetate. The method presented herein leads to highly enhanced in vivo detection of short-T113C as well as attached protons. This indirect detection scheme allows for probing additional molecular sites in hyperpolarized substrates and their metabolites and can thus lead to improved spectral resolution such as in the case of 13C-acetate metabolism.

Dynamic nuclear polarization system output volume reduction using inert fluids

Peterson, E.T., et al., Dynamic nuclear polarization system output volume reduction using inert fluids. Journal of Magnetic Resonance Imaging, 2011. 33(4): p. 1003-1008.


Purpose: To present a method for significantly increasing the concentration of a hyperpolarized compound produced by a commercial dynamic nuclear polarization (DNP) polarizer, enabling the polarization process to be more suitable for preclinical applications.
Materials and Methods: Using a HyperSense DNP polarizer, we investigated the combined use of perfluorocarbon and water to warm and dissolve the hyperpolarized material from the polarization temperature of 1.4K to produce material at temperatures suitable for injection.
Results: By replacing 75% of the water in the dissolution volume with a chemically and biologically inert liquid that is immiscible with water, the injection volume can be reduced 4-fold. Rapid separation of the water and perfluorocarbon mixture enables the aqueous layer containing polarized material to be easily and rapidly collected.
Conclusion: The approach provides a significantly increased concentration of compound in a volume for injection that is more appropriate for small animal studies. This is demonstrated for 13C-labeled pyruvic acid and 13C-labeled succinate, but may be applied to the majority of nuclei and compounds hyperpolarized by the DNP method. J. Magn. Reson. Imaging 2011;33:1003–1008. © 2011 Wiley-Liss, Inc.



Fractional Spin-Labeling of Polymers for Enhancing NMR Sensitivity by Solvent-Free Dynamic Nuclear Polarization

Vitzthum, V., et al., Fractional Spin-Labeling of Polymers for Enhancing NMR Sensitivity by Solvent-Free Dynamic Nuclear Polarization. ChemPhysChem, 2011. 12(16): p. 2929-2932.

http://dx.doi.org/10.1002/cphc.201100630

Decapeptides are partly covalently labeled with a polarizing agent to enhance NMR signals by dynamic nuclear polarization (DNP). DNP under magic angle spinning conditions at T=100 K was performed directly on these molecules in the absence of any solvent.

BDPA: An Efficient Polarizing Agent for Fast Dissolution Dynamic Nuclear Polarization NMR Spectroscopy

Lumata, L., et al., BDPA: An Efficient Polarizing Agent for Fast Dissolution Dynamic Nuclear Polarization NMR Spectroscopy. Chemistry – A European Journal, 2011. 17(39): p. 10825-10827.

http://dx.doi.org/10.1002/chem.201102037

Teaching an old free radical new tricks: The stable free radical 1,3-bisdiphenylene-2-phenylallyl (BDPA) is an efficient polarizing agent in the dissolution dynamic nuclear polarization (DNP) of a variety of hydrophilic and hydrophobic compounds, such as tetramethylallene or [15N]choline. In addition, BDPA can be easily removed from the hyperpolarized solution by a simple mechanical filtration, when water is used for dissolution.

Thursday, January 12, 2012

Dynamic Nuclear Polarization: New Methodology and Applications

Sze, K., et al., Dynamic Nuclear Polarization: New Methodology and Applications. 2011: p. 1-28.


One way to overcome the intrinsically low sensitivity of Nuclear Magnetic Resonance spectroscopy is to enhance the signal by dynamic nuclear polarization (DNP), where the polarization of high-gyromagnetic ratio (γ) electrons is transferred to the surrounding nuclei using microwave (MW) irradiation. Recent developments in DNP instrumentations and applications have shown that DNP is one of the most effective methods to increase the nuclear spin polarization in inorganic, organic, and biological materials. It is possible to obtain a solution of molecules containing hyperpolarized nuclei in combination with methods to dissolve rapidly the polarized solid sample. In this chapter, a brief introduction on a theoretical basis and some of new DNP applications in NMR spectroscopy as well as medical applications in Magnetic Resonance Imaging (MRI) are described.

Dynamic Nuclear Hyperpolarization in Liquids

Günther, U., Dynamic Nuclear Hyperpolarization in Liquids. 2011: p. 1-47.


Nuclear magnetic resonance (NMR) spectroscopy is a broadly used analytical method with major applications in chemistry, biochemistry and medicine. Key applications include structural analysis of small molecules, metabolites, larger biomolecules such as proteins, RNA and DNA, and applications in material science. Magnetic resonance imaging (MRI), which is based on the same physical principles, is extensively used in medical diagnostics and represents the most widespread application of NMR. However, NMR is fundamentally limited in sensitivity and this has always restricted its applicability. Hyperpolarization techniques such as dynamic nuclear polarization (DNP) have become a major field of research and development because they hold the promise of increasing the sensitivity of NMR by several orders of magnitude. Such sensitivity enhancements could significantly broaden NMR applications, combining its unique structural information with much higher sensitivity. Unfortunately, there is no single implementation of DNP that would be suitable for a broader range of typical NMR applications. Experimental conditions often circumscribe areas of possible applications. Nevertheless, recent developments point towards experimental protocols providing solutions for specific applications of NMR. This review summarizes the concepts behind DNP in the light of recent developments and potential applications.

Dynamic nuclear polarization: Yesterday, today, and tomorrow

Atsarkin, V.A., Dynamic nuclear polarization: Yesterday, today, and tomorrow. Journal of Physics: Conference Series, 2011. 324(1): p. 012003.


A review is given of the history and basic principles of dynamic nuclear polarization (DNP) in condensed matter, starting from the Overhauser pioneering work and up to the modern applications in chemistry and medicine. Different physical mechanisms of DNP, such as the Overhauser effect, solid effect, electron-nuclear cross relaxation, and thermal mixing are considered. Further prospects of the DNP techniques for future are discussed.

Wednesday, January 11, 2012

Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy of Functionalized Metal–Organic Frameworks

Rossini, A.J., et al., Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy of Functionalized Metal–Organic Frameworks. Angewandte Chemie, 2012. 124(1): p. 127-131


Dynamic nuclear polarization (DNP) is applied to enhance the signal of solid-state NMR spectra of metal–organic framework (MOF) materials. The signal enhancement enables the acquisition of high-quality 1D 13C solid-state NMR spectra, 2D 1H–13C dipolar HETCOR and 1D 15N solid-state NMR spectra with natural isotopic abundance in experiment times on the order of minutes. MW=microwaves.

Monday, January 9, 2012

Solid effect dynamic nuclear polarization and polarization pathways

Smith, A. A.; Corzilius, B.; Barnes, A. B.; Maly, T.; Griffin, R. G. J. Chem. Phys. 2012, 136, 015101.


Using dynamic nuclear polarization (DNP)/nuclear magnetic resonance instrumentation that utilizes a microwave cavity and a balanced rf circuit, we observe a solid effect DNP enhancement of 94 at 5 T and 80 K using trityl radical as the polarizing agent. Because the buildup rate of the solid effect increases with microwave field strength, we obtain a sensitivity gain of 128. The data suggest that higher microwave field strengths would lead to further improvements in sensitivity. In addition, the observation of microwave field dependent enhancements permits us to draw conclusions about the path that polarization takes during the DNP process.

Friday, January 6, 2012

Dynamic nuclear polarization at 9T using a novel 250 Gyrotron microwave source

Griffin, R. G. J. Magn. Reson. 2011, 213, 410


In the 1990's we initiated development of high frequency gyrotron microwave sources with the goal of performing dynamic nuclear polarization at magnetic fields (~5-23T) used in contemporary NMR experiments. This article describes the motivation for these efforts and the developments that led to the operation of a gyrotron source for DNP operating at 250 GHz. We also mention results obtained with this instrument that would have been otherwise impossible absent the increased sensitivity. Finally, we describe recent efforts that have extended DNP to 460 GHz and 700 MHz 1H frequencies.

Probing Porosity and Pore Interconnectivity in Self-Assembled TiO2-Graphene Hybrid Nanostructures Using Hyperpolarized 129Xe NMR

Wang, L.-Q.; Wang, D.; Liu, J.; Exarhos, G. J. The Journal of Physical Chemistry C 2011.


Hyperpolarized (HP) 129Xe NMR was used to probe the porosity and interconnectivity of pores in self-assembled hybrid TiO2-graphene nanostructures. We have demonstrated that HP 129Xe NMR is a powerful technique in probing any changes in porosity and interconnectivity of the pores caused by the addition of a small amount of functionalized graphene sheets (FGSs) (1% weight percent) into the network of mesoporous TiO2. To obtain the information on the changes in porosity and interconnectivity of the pores caused by the addition of a small amount of FGSs, a comparative study has been carried out by acquiring HP 129Xe NMR spectra under identical experimental conditions for both pure mesoporous TiO2 and hybrid TiO2-FGSs. The HP 129Xe NMR results from our comparative study suggest that TiO2 and graphene are mixed uniformly on the nanoscale and the resulting hybrid nanostructure has better channel connectivity between different domains, enhancing the transport property for Li-insertion/extraction.

Thursday, January 5, 2012

A Life in NMR: Interview with Regina Schuck, VP and General Manager of Agilent Research Products Division

Agilent Research Products Division vice president and general manager, Regina Schuck talks about her experiences of a lifetime spent in NMR, including the most significant recent developments, the current challenges and a glimpse into the NMR of the future.

You can find the complete interview by following this link: http://bit.ly/z5VR69