Monday, November 20, 2017

Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature 13C ODNP at Moderately Low Fields and Natural Abundance #DNPNMR


Dey, A., A. Banerjee, and N. Chandrakumar, Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature 13C ODNP at Moderately Low Fields and Natural Abundance. The Journal of Physical Chemistry B, 2017. 121(29): p. 7156-7162.


Overhauser dynamic nuclear polarization (ODNP) is investigated at a moderately low field (1.2 T) for natural abundance 13C NMR of small molecules in solution state at room temperature. It is shown that ODNP transferred from 1H to 13C by NMR coherence transfer is in general significantly more efficient than direct ODNP of 13C. Compared to direct 13C ODNP, we demonstrate over 4-fold higher 13C sensitivity (signal-to-noise ratio, SNR), achieved in one-eighth of the measurement time by transferred ODNP (t-ODNP). Compared to the 13C signal arising from Boltzmann equilibrium in a fixed measurement time, this is equivalent to about 1500-fold enhancement of 13C signal by t-ODNP, as against a direct 13C ODNP signal enhancement of about 45-fold, both at a moderate ESR saturation factor of about 0.25. This owes in part to the short polarization times characteristic of 1H. Typically, t-ODNP reflects the essentially uniform ODNP enhancements of all protons in a molecule. Although the purpose of this work is to establish the superiority of t-ODNP vis-a-vis direct 13C ODNP, a comparison is also made of the SNR in t-ODNP experiments with standard high resolution NMR as well. Finally, the potential of t-ODNP experiments for 2D heteronuclear correlation spectroscopy of small molecules is demonstrated in 2D 1H-13C HETCOR experiments at natural abundance, with decoupling in both dimensions.

Friday, November 17, 2017

High-resolution hyperpolarized in vivo metabolic 13C spectroscopy at low magnetic field (48.7mT) following murine tail-vein injection


Coffey, A.M., et al., High-resolution hyperpolarized in vivo metabolic 13C spectroscopy at low magnetic field (48.7mT) following murine tail-vein injection. J. Magn. Reson., 2017. 281(Supplement C): p. 246-252.


High-resolution 13C NMR spectroscopy of hyperpolarized succinate-1-13C-2,3-d2 is reported in vitro and in vivo using a clinical-scale, biplanar (80cm-gap) 48.7mT permanent magnet with a high homogeneity magnetic field. Non-localized 13C NMR spectra were recorded at 0.52MHz resonance frequency over the torso of a tumor-bearing mouse every 2s. Hyperpolarized 13C NMR signals with linewidths of ∼3Hz (corresponding to ∼6ppm) were recorded in vitro (2mL in a syringe) and in vivo (over a mouse torso). Comparison of the full width at half maximum (FWHM) for 13C NMR spectra acquired at 48.7mT and at 4.7T in a small-animal MRI scanner demonstrates a factor of ∼12 improvement for the 13C resonance linewidth attainable at 48.7mT compared to that at 4.7T in vitro. 13C hyperpolarized succinate-1-13C resonance linewidths in vivo are at least one order of magnitude narrower at 48.7mT compared to those observed in high-field (≥3T) studies employing HP contrast agents. The demonstrated high-resolution 13C in vivo spectroscopy could be useful for high-sensitivity spectroscopic studies involving monitoring HP agent uptake or detecting metabolism using HP contrast agents with sufficiently large 13C chemical shift differences.

Wednesday, November 15, 2017

Ramped-amplitude NOVEL #DNPNMR


Can, T.V., et al., Ramped-amplitude NOVEL. J. Chem. Phys., 2017. 146(15): p. 154204.


We present a pulsed dynamic nuclear polarization (DNP) study using a ramped-amplitude nuclear orientation via electron spin locking (RA-NOVEL) sequence that utilizes a fast arbitrary waveform generator (AWG) to modulate the microwave pulses together with samples doped with narrow-line radicals such as 1,3-bisdiphenylene-2-phenylallyl (BDPA), sulfonated-BDPA (SA-BDPA), and trityl- OX063. Similar to ramped-amplitude cross polarization in solid-state nuclear magnetic resonance, RA-NOVEL improves the DNP efficiency by a factor of up to 1.6 compared to constant-amplitude NOVEL (CA-NOVEL) but requires a longer mixing time. For example, at mix = 8 s, the DNP efficiency reaches a plateau at a ramp amplitude of 20 MHz for both SA-BDPA and trityl-OX063, regardless of the ramp profile (linear vs. tangent). At shorter mixing times (mix = 0.8 s), we found that the tangent ramp is superior to its linear counterpart and in both cases there exists an optimum ramp size and therefore ramp rate. Our results suggest that RA-NOVEL should be used instead of CA-NOVEL as long as the electronic spin lattice relaxation T1e is sufficiently long and/or the duty cycle of the microwave amplifier is not exceeded. To the best of our knowledge, this is the first example of a time domain DNP experiment that utilizes modulated microwave pulses. Our results also suggest that a precise modulation of the microwave pulses can play an important role in optimizing the efficiency of pulsed DNP experiments and an AWG is an elegant instrumental solution for this purpose.

Monday, November 13, 2017

Anisotropic longitudinal electronic relaxation affects DNP at cryogenic temperatures #DNPNMR

Anisotropic relaxation effects are well know and understood in EPR spectroscopy and have long served as measures to understand the motion (libration) of paramagnetic co-factors (quinones, nitroxide radicals etc.) in biological system. In this study the authors investigate the effect of anisotropic relaxation effects in DNP experiments.

To find more about anisotropic relaxation effects studied by EPR take a look at the work by Sergei Dzuba or the Eatons:


Weber, E.M.M., et al., Anisotropic longitudinal electronic relaxation affects DNP at cryogenic temperatures. Phys. Chem. Chem. Phys., 2017. 19(24): p. 16087-16094.


We report the observation of anisotropic longitudinal electronic relaxation in nitroxide radicals under typical dynamic nuclear polarization conditions. This anisotropy affects the efficiency of dynamic nuclear polarization at cryogenic temperatures of 4 K and high magnetic fields of 6.7 T. Under our experimental conditions, the electron paramagnetic resonance spectrum of nitroxides such as TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl) is only partly averaged by electronic spectral diffusion, so that the relaxation times T1e([small omega]) vary across the spectrum. We demonstrate how the anisotropy of T1e([small omega]) can be taken into account in simple DNP models.

Friday, November 10, 2017

Natural Abundance 17 O DNP NMR Provides Precise O-H Distances and Insights into the Bronsted Acidity of Heterogeneous Catalysts #DNPNMR


Perras, F.A., et al., Natural Abundance 17 O DNP NMR Provides Precise O-H Distances and Insights into the Bronsted Acidity of Heterogeneous Catalysts. Angew Chem Int Ed Engl, 2017. 56(31): p. 9165-9169.

https://www.ncbi.nlm.nih.gov/pubmed/28499071

Heterogeneous Bronsted acid catalysts are tremendously important in industry, particularly in catalytic cracking processes. Here we show that these Bronsted acid sites can be directly observed at natural abundance by 17 O DNP surface-enhanced NMR spectroscopy (SENS). We additionally show that the O-H bond length in these catalysts can be measured with sub-picometer precision, to enable a direct structural gauge of the lability of protons in a given material, which is correlated with the pH of the zero point of charge of the material. Experiments performed on materials impregnated with pyridine also allow for the direct detection of intermolecular hydrogen bonding interactions through the lengthening of O-H bonds.

Research Faculty I, 12 Month Salaried (NHMFL) #DNPNMR

Research Faculty I, 12 Month Salaried (NHMFL)

For more information follow this link: Faculty Position

Research Faculty I, 12 Month Salaried (NHMFL)

Job ID
42607

Location
Tallahassee, FL

Full/Part Time
Full-Time

Regular/Temporary
Regular

Apply On Or Before
12/13/2017

Department
National High Magnetic Field Laboratory (NHMFL)

Responsibilities
This position will be part of a major initiative involving Dynamic Nuclear Polarization (DNP) including magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectroscopy. Position will be focused primarily on, but not limited to the operation of the MAS-DNP NMR spectrometer. The research faculty is expected to develop independent and collaborative research in chemical, biological, and material applications of DNP as well as DNP instrumentation and technology. They will work within a team of faculty and engineers through the NMR, EMR and AMRIS programs and in collaboration with users of the NHMFL facilities. A Bruker 600MHz DNP system equipping a 600MHz field-sweepable wide-bore magnet had been installed and is fully operational.

Qualifications
Ph.D. in Chemistry, Physics, Biology, or a related discipline. Experience in DNP and NMR (or EPR).

Expert knowledge in both experimental and theoretical fields in NMR spectroscopy and DNP.
Knowledge of Linux-based computer systems and networks, as it is the operating system of the spectrometer and requires collaborative research with users in various areas locally and remotely.
Computer simulation skills, which are indispensable in interpreting the spectra at the DNP and NMR domains.

Preferred
Electron paramagentic resonance (EPR) spectroscopy.

Contact Info
For additional information, please contact Bettina Roberson at roberson@magnet.fsu.edu.

Pay Plan
This is a Faculty position.

Criminal Background Check
This position requires successful completion of a criminal history background check.

How To Apply
If qualified and interested in a specific job opening as advertised, apply to Florida State University at https://jobs.fsu.edu. If you are a current FSU employee, apply via myFSU > Self Service.

Applicants are required to complete the online application with all applicable information. Applications must include all work history up to ten years, and education details even if attaching a resume.

Equal Employment Opportunity
An Equal Opportunity/Access/Affirmative Action/Pro Disabled & Veteran Employer.

FSU's Equal Opportunity Statement can be viewed at: http://www.hr.fsu.edu/PDF/Publications/diversity/EEO_Statement.pdf

Wednesday, November 8, 2017

In Silico Design of DNP Polarizing Agents: Can Current Dinitroxides Be Improved? #DNPNMR


Perras, F.A., A. Sadow, and M. Pruski, In Silico Design of DNP Polarizing Agents: Can Current Dinitroxides Be Improved? ChemPhysChem, 2017. 18(16): p. 2279-2287.


Numerical calculations of enhancement factors offered by dynamic nuclear polarization in solids under magic angle spinning (DNP-MAS) were performed to determine the optimal EPR parameters for a dinitroxide polarizing agent. We found that the DNP performance of a biradical is more tolerant to the relative orientation of the two nitroxide moieties than previously thought. Generally, any condition in which the gyy tensor components of both radicals are perpendicular to one another is expected to have near-optimal DNP performance. Our results highlight the important role of the exchange coupling, which can lessen the sensitivity of DNP performance to the inter-radical distance, but also lead to lower enhancements when the number of atoms in the linker becomes less than three. Lastly, the calculations showed that the electron T1e value should be near 500 mus to yield optimal performance. Importantly, the newest polarizing agents already feature all of the qualities of the optimal polarizing agent, leaving little room for further improvement. Further research into DNP polarizing agents should then target non-nitroxide radicals, as well as improvements in sample formulations to advance high-temperature DNP and limit quenching and reactivity.