Wednesday, June 20, 2018

A table-top PXI based low-field spectrometer for solution dynamic nuclear polarization #DNPNMR #ODNP

Biller, Joshua R., Karl F. Stupic, and J. Moreland. “A Table-Top PXI Based Low-Field Spectrometer for Solution Dynamic Nuclear Polarization.” Magnetic Resonance in Chemistry 56, no. 3 (2017): 153–63.

We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of 1H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alderman–Grant resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced 1H signal at 288 kHz was constructed with Litz wire. The largest observed 1H enhancements (ε) at 6.7 mT for 14N-CTPO radical in air saturated aqueous solution was ε 65. A concentration dependence of the enhancement is observed, with maximum ε at 5.5 mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3 mM sample. At high incident powers (42 W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi-frequency DNP work, depending on available main magnets and selection of the “plug and play” arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards.

Monday, June 18, 2018

DNP sensitivity of 19F-NMR signals in hexafluorobenzene depending on polarizing agent type #DNPNMR #ODNP

Peksoz, Ahmet. “DNP Sensitivity of 19F-NMR Signals in Hexafluorobenzene Depending on Polarizing Agent Type.” Magnetic Resonance in Chemistry 54, no. 9 (2016): 748–52. 

Low field dynamic nuclear polarization or low field magnetic double resonance technique enables enhanced nuclear magnetic resonance signals to be detected without increasing the strength of the polarizing field. The study reports that the dynamic nuclear polarization of 19F nuclei in hexafluorobenzene solutions doped with nitroxide, BDPA, MC800 asphaltene and MC30 asphaltene free radicals at 15 G. The 19F nuclei in all solutions gave positive DNP enhancements changing between 3.42 and 189.54, corresponding to predominantly scalar interactions with the unpaired electrons in the radicals. DNP sensitivity of 19F nuclei in hexafluorobenzene was observed to be changed significantly depending on the radical type. Nitroxide was found to have the best DNP performance among the polarizing agents. Copyright © 2016 John Wiley & Sons, Ltd.

Friday, June 15, 2018

13C dynamic nuclear polarization using isotopically enriched 4-oxo-TEMPO free radicals #DNPNMR

Niedbalski, Peter, Christopher Parish, Andhika Kiswandhi, and Lloyd Lumata. “13C Dynamic Nuclear Polarization Using Isotopically Enriched 4-Oxo-TEMPO Free Radicals.” Magnetic Resonance in Chemistry 54, no. 12 (2016): 962–67.

The nitroxide-based free radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) is a widely used polarizing agent in NMR signal amplification via dissolution dynamic nuclear polarization (DNP). In this study, we have thoroughly investigated the effects of 15N and/or 2H isotopic labeling of 4-oxo-TEMPO free radical on 13C DNP of 3 M [1-13C] sodium acetate samples in 1 : 1 v/v glycerol : water at 3.35 T and 1.2 K. Four variants of this free radical were used for 13C DNP: 4-oxo-TEMPO, 4-oxo-TEMPO-15N, 4-oxo-TEMPO-d16 and 4-oxo-TEMPO-15N,d16. Our results indicate that, despite the striking differences seen in the electron spin resonance (ESR) spectral features, the 13C DNP efficiency of these 15N and/or 2H-enriched 4-oxo-TEMPO free radicals are relatively the same compared with 13C DNP performance of the regular 4-oxo-TEMPO. Furthermore, when fully deuterated glassing solvents were used, the 13C DNP signals of these samples all doubled in the same manner, and the 13C polarization buildup was faster by a factor of 2 for all samples. The data here suggest that the hyperfine coupling contributions of these isotopically enriched 4-oxo-TEMPO free radicals have negligible effects on the 13C DNP efficiency at 3.35 T and 1.2 K. These results are discussed in light of the spin temperature model of DNP. Copyright © 2016 John Wiley & Sons, Ltd.

Wednesday, June 13, 2018

ESR line width and line shape dependence of Overhauser-enhanced magnetic resonance imaging #DNPNMR

Meenakumari, V., Hideo Utsumi, A. Jawahar, and A. Milton Franklin Benial. “ESR Line Width and Line Shape Dependence of Overhauser-Enhanced Magnetic Resonance Imaging.” Magnetic Resonance in Chemistry 54, no. 11 (2016): 874–79.

Electron spin resonance and Overhauser-enhanced magnetic resonance imaging studies were carried out for various concentrations of 14N-labeled 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl in pure water. Overhauser-enhancement factor attains maxima in the range of 2.5–3 mm concentration. The leakage factor showed an asymptotic increase with increasing agent concentration. The coupling parameter showed the interaction between the electron and nuclear spins to be mainly dipolar in origin. The electron spin resonance parameters, such as the line width, line shape and g-factor, were determined. The line width analysis confirms that the line broadening is proportional to the agent concentration, and also the agent concentration is optimized in the range of 2.5–3 mm. The line shape analysis shows that the observed electron spin resonance line shape is a Voigt line shape, in which the Lorentzian component is dominant. The contribution of Lorentzian component was estimated using the winsim package. The Lorentzian component of the resonance line attains maxima in the range of 2.5–3 mm concentration. Therefore, this study reveals that the agent concentration, line width and Lorentzian component are the important factors in determining the Overhauser-enhancement factor. Hence, the agent concentration was optimized as 2.5–3 mm for in vivo/in vitro electron spin resonance imaging and Overhauser-enhanced magnetic resonance imaging phantom studies. Copyright © 2016 John Wiley & Sons, Ltd.

Monday, June 11, 2018

Co-acquisition of hyperpolarised 13C and 15N NMR spectra #DNPNMR

Already I bit older bit still worth to read.

Day, Iain J., John C. Mitchell, Martin J. Snowden, and Adrian L. Davis. “Co-Acquisition of Hyperpolarised 13C and 15N NMR Spectra.” Magnetic Resonance in Chemistry 45, no. 12 (2007): 1018–21.

Recent developments in dynamic nuclear polarisation now allow significant enhancements to be generated in the cryo solid state and transferred to the liquid state for detection at high resolution. We demonstrate that the Ardenkjaer–Larsen method can be extended by taking advantage of the properties of the trityl radicals used. It is possible to hyperpolarise 13C and 15N simultaneously in the solid state, and to maintain these hyperpolarisations through rapid dissolution into the liquid state. We demonstrate the almost simultaneous measurement of hyperpolarised 13C and hyperpolarised 15N NMR spectra. The prospects for further improvement of the method using contemporary technology are also discussed. Copyright © 2007 John Wiley & Sons, Ltd.

Friday, June 8, 2018

Perspectives on hyperpolarised solution-state magnetic resonance in chemistry #DNPNMR

Dumez, Jean-Nicolas. “Perspectives on Hyperpolarised Solution-State Magnetic Resonance in Chemistry.” Magnetic Resonance in Chemistry 55, no. 1 (2016): 38–46. 

This perspective article reviews some of the recent developments in the field of hyperpolarisation, with a focus on solution-state NMR spectroscopy of small molecules. Two techniques are considered in more detail, dissolution dynamic nuclear polarisation (D-DNP) and signal amplification by reversible exchange (SABRE). Some of the opportunities and challenges for applications of hyperpolarised solution-state magnetic resonance in chemistry are discussed. 

Wednesday, June 6, 2018

Nanodiamond as a New Hyperpolarizing Agent and Its 13C MRS #DNPNMR

Dutta, Prasanta, Gary V. Martinez, and Robert J. Gillies. “Nanodiamond as a New Hyperpolarizing Agent and Its 13C MRS.” The Journal of Physical Chemistry Letters 5, no. 3 (February 6, 2014): 597–600.

In this work, we have hyperpolarized carbonaceous nanoparticles (D ≈ 10 nm), that is, “nanodiamonds”, with 1.1% 13C (natural abundance) using dynamic nuclear polarization (DNP). The polarization buildup curve showed a signal enhancement with relative intensity up to 4700 at 1.4 K and 100 mW microwave power. 13C magnetic resonance spectra (MRS) were obtained from the sample at 7 T, and the signal decayed with a T1 of 55 ± 3s. Notably, polarization was possible in the absence of added radical, consistent with previous results showing endogenous unpaired electrons in natural nanodiamonds. These likely contribute to the shorter T1’s compared to those of highly pure diamond. Despite the relatively short T1, these observations suggest that natural nanodiamonds may be useful for in vivo applications.