Wednesday, May 30, 2012

Measurement of Arterial Input Function in Hyperpolarized 13C Studies

Marjańska, M., et al., Measurement of Arterial Input Function in Hyperpolarized 13C Studies. Appl. Magn. Reson.: p. 1-9.

Recently, hyperpolarized substrates generated through dynamic nuclear polarization have been introduced to study in vivo metabolism. Injection of hyperpolarized [1- 13 C] pyruvate, the most widely used substrate, allows detection of time courses of [1- 13 C] pyruvate and its metabolic products, such as [1- 13 C] lactate and 13 C-bicarbonate, in various organs. However, quantitative metabolic modeling of in vivo data to measure specific metabolic rates remains challenging without measuring the input function. In this study, we demonstrate that the input function of [1- 13 C] pyruvate can be measured in vivo in the rat carotid artery using an implantable coil.

Wednesday, May 23, 2012

Measurement and applications of dynamic nuclear polarization

I recently came across an old review article about Dynamic Nuclear Polarization from 1972 by Joseph Potenza. It is a very detailed review and I think it could be especially interesting for everyone who starts with DNP. A rare find in a journal that is (at least) not on my typical reading list.

J. Potenza, Advances in Molecular Relaxation Processes 4, 229-354 (1972)

Tuesday, May 22, 2012

COST summer school 2012 on Spin-Hyperpolarization

COST summer school 2012 on Spin-Hyperpolarization 

Lorentz Center, Leiden, The Netherlands, 29 Oct - 2 Nov 2012 
Organizers: Arno Kentgens & Joerg Matysik 

To strengthen and link European efforts on hyperpolarization, the COST Network EUROHyperPOL has been set up ( Annual summer schools presenting an overview and common grounds on the field will be organized. 

PhD students & young postdocs are now invited to apply. Maximum number of students is limited to 20. Please provide a short cv and statement of motivation via our Lorentz website. 

Participants of the network are especially encouraged to apply. Costs for workshop & accomodation (and possibly travel) will be covered. 

Deadline for application is June 11, 2012.

Friday, May 18, 2012

Developing DNP/Solid-State NMR Spectroscopy of Oriented Membranes

Salnikov, E., et al., Developing DNP/Solid-State NMR Spectroscopy of Oriented Membranes. Appl. Magn. Reson., 2012: p. 1-16.

Dynamic nuclear polarization (DNP)/solid-state nuclear magnetic resonance (NMR) spectroscopy bears great potential for the investigation of membrane-associated polypeptides which can often be produced only in small amounts and which need to be ‘diluted’ in lipid bilayer environments to adopt or maintain their functional structure. Here we present investigations using biradicals, such as TOTAPOL and bTbK, for solid-state NMR signal enhancement using DNP in the context of lipid membranes. By transferring polarization from electron to nuclear spins using microwave irradiation signal enhancement factors of up to 13 are obtained with TOTAPOL and up to 17 with bTbK. The possible reasons why these factors are below those obtained in glassy samples of bulk solvents (40–60 under similar conditions) are evaluated and discussed. In order to further ameliorate the enhancement factors the physico-chemical characteristics of TEMPOL, TOTAPOL, bTbK, and bCTbK, such as their partitioning between hydrophilic and hydrophobic solvents or their stability under different environmental conditions are presented. Finally, having provided proof-of-concept that DNP/solid-state NMR measurements can be performed with oriented membrane samples work in progress is presented on the development of a flat-coil probe for DNP/solid-state NMR experiments on oriented membranes.

Wednesday, May 16, 2012

Dynamic nuclear polarization of electron-beam irradiated polyethylene by pairs of alkyl free radicals

Kumada, T., Y. Noda, and N. Ishikawa, Dynamic nuclear polarization of electron-beam irradiated polyethylene by pairs of alkyl free radicals. J. Magn. Reson., 2012. 218(0): p. 59-65.

We compared dynamic nuclear polarization (DNP) behavior of electron-beam irradiated polyethylene (e-PE) with that of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-doped polystyrene (T-PS). Growth and decay rates of nuclear polarization Pn of e-PE increased linearly with increasing concentration Ce of free radicals, whereas those of T-PS increased with square of Ce. From these results, we suggest that the pair of alkyl radicals produced by the radiolysis, –CH2–CH2–CH2– → –CH2–CH–CH2– + H, and the subsequent hydrogen abstraction reaction, H + –CH2–CH2–CH2– → H2 + –CH2–CH–CH2– in e-PE plays an important role on DNP by the cross effect, whereas T-PS is polarized by a pair of unspecified TEMPO radicals accidentally located nearby. We propose that higher Pn would be expected by optimizing the inter-radical distance within the pair in e-PE and other irradiated samples.

Monday, May 14, 2012

Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states

Haag, M., et al., Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states. Nucl. Instrum. Methods Phys. Res., Sect. A, 2012. 678(0): p. 91-97.

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks. The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ∼ 0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.

Saturday, May 12, 2012

Dynamic polarization of 13C nuclei in solid 13C labeled pyruvic acid

Meyer, W., et al., Dynamic polarization of 13C nuclei in solid 13C labeled pyruvic acid. Nucl. Instrum. Methods Phys. Res., Sect. A, 2011. 631(1): p. 1-5.

Dynamic nuclear polarization (DNP) has proved to be one of the most effective methods to increase the nuclear spin polarization in inorganic as well as organic materials since several decades. In combination with methods to rapidly dissolve the polarized solid sample it is possible to obtain a solution of molecules containing hyperpolarized nuclei. This has enabled new applications in Nuclear Magnetic Resonance (NMR) spectroscopy as well as medical applications in Magnetic Resonance Imaging (MRI). We studied the dynamic nuclear 13C polarization in solid [1-13C] pyruvic acid doped with the trityl radical AH 111 501 at different temperatures and magnetic fields. The measurements were performed in a 4He evaporation refrigerator operated inside a superconducting solenoid system. Working points at temperatures between 900 and 1350 mK have been adjusted and the polarization measurements have been performed at magnetic fields of 2.5, 3.5 and 5 T, respectively. This set of measurements allows to draw a clear picture of the temperature and magnetic field dependency of the 13C polarization within the given range. The highest polarization measured was 74.7% at a temperature of 900 mK in a magnetic field of 5 T.

Thursday, May 10, 2012

In Memory of Albert W. Overhauser (1925–2011)

Slichter, C., In Memory of Albert W. Overhauser (1925–2011). Appl. Magn. Reson.: p. 1-4.

Sunday, May 6, 2012

Application of Continuously Frequency-Tunable 0.4 THz Gyrotron to Dynamic Nuclear Polarization for 600 MHz Solid-State NMR

Matsuki, Y., et al., Application of Continuously Frequency-Tunable 0.4 THz Gyrotron to Dynamic Nuclear Polarization for 600 MHz Solid-State NMR. J. Infrared Millim. Te.: p. 1-11.

In this paper we present results that demonstrate the utility of a continuously frequency-tunable 0.4 THz-gyrotron in a dynamic nuclear polarization (DNP)-enhanced solid-state NMR (SSNMR) spectroscopy at one of the highest magnetic fields, B 0 = 14.1 T (600 MHz for 1 H Larmor frequency). Our gyrotron called FU CW VI generates sub-mm wave at a frequency near 0.4 THz with an output power of 4–25 W and a tunability over a range of more than 1 GHz by sweeping the magnetic field at the gyrotron cavity. We observed overall down shifting of the central frequency by up to ~1 GHz at high radiation duty factors and beam current, presumably due to the cavity thermal expansion by a heating, but the tunable range was not significantly changed. The frequency tunability facilitated the optimization of the DNP resonance condition without time-consuming field-sweep of the high-resolution NMR magnet, and enabled us to observe substantial enhancement of the SSNMR signal ( ε DNP = 12 at 90 K).

Friday, May 4, 2012

Dynamic Nuclear Polarization in Solids: The Birth and Development of the Many-Particle Concept

Atsarkin, V. and A. Kessenikh, Dynamic Nuclear Polarization in Solids: The Birth and Development of the Many-Particle Concept. Appl. Magn. Reson.: p. 1-13.

A brief review is presented on historical aspects of the dynamic nuclear polarization (DNP) research in 1960–1970s of the last century. Much attention is given to development of the many-particle approach, from pioneering studies of the 3-spin electron–nuclear cross effect to development of spin-temperature concept and thermal mixing mechanism of DNP in solids. Applicability of different models to modern DNP data is briefly discussed.