Category Archives: 9 GHz ODNP

Chemical-shift-resolved (1)(9)F NMR spectroscopy between 13.5 and 135 MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy

George, C. and N. Chandrakumar, Chemical-shift-resolved (1)(9)F NMR spectroscopy between 13.5 and 135 MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy. Angew Chem Int Ed Engl, 2014. 53(32): p. 8441-4.

https://www.ncbi.nlm.nih.gov/pubmed/24962142

Overhauser-DNP-enhanced homonuclear 2D (19)F correlation spectroscopy with diagonal suppression is presented for small molecules in the solution state at moderate fields. Multi-frequency, multi-radical studies demonstrate that these relatively low-field experiments may be operated with sensitivity rivalling that of standard 200-1000 MHz NMR spectroscopy. Structural information is accessible without a sensitivity penalty, and diagonal suppressed 2D NMR correlations emerge despite the general lack of multiplet resolution in the 1D ODNP spectra. This powerful general approach avoids the rather stiff excitation, detection, and other special requirements of high-field (19)F NMR spectroscopy.

Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence #DNPNMR

Nasibulov, E.A., et al., Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence. JETP Letters, 2016. 103(9): p. 582-587.

http://dx.doi.org/10.1134/S0021364016090113

A general theoretical approach to pulsed Overhauser-type dynamic nuclear polarization (DNP) is presented. Dynamic nuclear polarization is a powerful method to create non-thermal polarization of nuclear spins, thereby enhancing their nuclear magnetic resonance signals. The theory presented can treat pulsed microwave irradiation of electron paramagnetic resonance transitions for periodic pulse sequences of general composition. Dynamic nuclear polarization enhancement is analyzed in detail as a function of the microwave pulse length for rectangular pulses and pulses with finite rise time. Characteristic oscillations of the DNP enhancement are found when the pulse-length is stepwise increased, originating from coherent motion of the electron spins driven by the pulses. Experimental low-field DNP data are in very good agreement with this theoretical approach.

A compact X-Band resonator for DNP-enhanced Fast-Field-Cycling NMR #DNPNMR

Neudert, O., C. Mattea, and S. Stapf, A compact X-Band resonator for DNP-enhanced Fast-Field-Cycling NMR. J Magn Reson, 2016. 271: p. 7-14.

https://www.ncbi.nlm.nih.gov/pubmed/27526396

A new probehead was developed enabling Dynamic Nuclear Polarization (DNP)-enhanced Fast-Field-Cycling relaxometry at 340mT polarization field strength. It is based on a dielectric cavity resonator operating in the TM110 mode at 9.5GHz, which is suitable for both transverse and axial magnet geometries with a bore access of at least 20mm. The probehead includes a planar radio frequency coil for NMR detection and is compatible with standard 3mm NMR tubes. The resonator was assessed in terms of the microwave conversion factor and microwave-induced sample heating effects. Due to the compact size of the cavity, appreciable microwave magnetic field strengths were observed even with only moderate quality factors. Exemplary DNP experiments at 9.5GHz and 2.0GHz microwave frequency are compared for three different viscous samples, demonstrating the advantage of DNP at 9.5GHz for such systems. This new probehead enables new applications of DNP-enhanced Fast-Field-Cycling relaxometry of viscous and solid systems.

Hydration Dynamics of a Peripheral Membrane Protein #DNPNMR

Fisette, O., et al., Hydration Dynamics of a Peripheral Membrane Protein. J Am Chem Soc, 2016. 138(36): p. 11526-35.

https://www.ncbi.nlm.nih.gov/pubmed/27548572

Water dynamics in the hydration shell of the peripheral membrane protein annexin B12 were studied using MD simulations and Overhauser DNP-enhanced NMR. We show that retardation of water motions near phospholipid bilayers is extended by the presence of a membrane-bound protein, up to around 10 A above that protein. Near the membrane surface, electrostatic interactions with the lipid head groups strongly slow down water dynamics, whereas protein-induced water retardation is weaker and dominates only at distances beyond 10 A from the membrane surface. The results can be understood from a simple model based on additive contributions from the membrane and the protein to the activation free energy barriers of water diffusion next to the biomolecular surfaces. Furthermore, analysis of the intermolecular vibrations of the water network reveals that retarded water motions near the membrane shift the vibrational modes to higher frequencies, which we used to identify an entropy gradient from the membrane surface toward the bulk water. Our results have implications for processes that take place at lipid membrane surfaces, including molecular recognition, binding, and protein-protein interactions.

Hydration Dynamics of a Peripheral Membrane Protein #DNPNMR

Fisette, O., et al., Hydration Dynamics of a Peripheral Membrane Protein. J. Am. Chem. Soc., 2016. 138(36): p. 11526-11535.

http://dx.doi.org/10.1021/jacs.6b07005

Water dynamics in the hydration shell of the peripheral membrane protein annexin B12 were studied using MD simulations and Overhauser DNP-enhanced NMR. We show that retardation of water motions near phospholipid bilayers is extended by the presence of a membrane-bound protein, up to around 10 Å above that protein. Near the membrane surface, electrostatic interactions with the lipid head groups strongly slow down water dynamics, whereas protein-induced water retardation is weaker and dominates only at distances beyond 10 Å from the membrane surface. The results can be understood from a simple model based on additive contributions from the membrane and the protein to the activation free energy barriers of water diffusion next to the biomolecular surfaces. Furthermore, analysis of the intermolecular vibrations of the water network reveals that retarded water motions near the membrane shift the vibrational modes to higher frequencies, which we used to identify an entropy gradient from the membrane surface toward the bulk water. Our results have implications for processes that take place at lipid membrane surfaces, including molecular recognition, binding, and protein–protein interactions.

Water accessibility in a membrane-inserting peptide comparing Overhauser DNP and pulse EPR methods

Segawa, T.F., et al., Water accessibility in a membrane-inserting peptide comparing Overhauser DNP and pulse EPR methods. J Chem Phys, 2016. 144(19): p. 194201.

http://www.ncbi.nlm.nih.gov/pubmed/27208942

Water accessibility is a key parameter for the understanding of the structure of biomolecules, especially membrane proteins. Several experimental techniques based on the combination of electron paramagnetic resonance (EPR) spectroscopy with site-directed spin labeling are currently available. Among those, we compare relaxation time measurements and electron spin echo envelope modulation (ESEEM) experiments using pulse EPR with Overhauser dynamic nuclear polarization (DNP) at X-band frequency and a magnetic field of 0.33 T. Overhauser DNP transfers the electron spin polarization to nuclear spins via cross-relaxation. The change in the intensity of the (1)H NMR spectrum of H2O at a Larmor frequency of 14 MHz under a continuous-wave microwave irradiation of the nitroxide spin label contains information on the water accessibility of the labeled site. As a model system for a membrane protein, we use the hydrophobic alpha-helical peptide WALP23 in unilamellar liposomes of DOPC. Water accessibility measurements with all techniques are conducted for eight peptides with different spin label positions and low radical concentrations (10-20 muM). Consistently in all experiments, the water accessibility appears to be very low, even for labels positioned near the end of the helix. The best profile is obtained by Overhauser DNP, which is the only technique that succeeds in discriminating neighboring positions in WALP23. Since the concentration of the spin-labeled peptides varied, we normalized the DNP parameter , being the relative change of the NMR intensity, by the electron spin concentration, which was determined from a continuous-wave EPR spectrum.

A peripheral component interconnect express-based scalable and highly integrated pulsed spectrometer for solution state dynamic nuclear polarization #DNPNMR

He, Y., et al., A peripheral component interconnect express-based scalable and highly integrated pulsed spectrometer for solution state dynamic nuclear polarization. Rev Sci Instrum, 2015. 86(8): p. 083101.

http://www.ncbi.nlm.nih.gov/pubmed/26329168

High sensitivity, high data rates, fast pulses, and accurate synchronization all represent challenges for modern nuclear magnetic resonance spectrometers, which make any expansion or adaptation of these devices to new techniques and experiments difficult. Here, we present a Peripheral Component Interconnect Express (PCIe)-based highly integrated distributed digital architecture pulsed spectrometer that is implemented with electron and nucleus double resonances and is scalable specifically for broad dynamic nuclear polarization (DNP) enhancement applications, including DNP-magnetic resonance spectroscopy/imaging (DNP-MRS/MRI). The distributed modularized architecture can implement more transceiver channels flexibly to meet a variety of MRS/MRI instrumentation needs. The proposed PCIe bus with high data rates can significantly improve data transmission efficiency and communication reliability and allow precise control of pulse sequences. An external high speed double data rate memory chip is used to store acquired data and pulse sequence elements, which greatly accelerates the execution of the pulse sequence, reduces the TR (time of repetition) interval, and improves the accuracy of TR in imaging sequences. Using clock phase-shift technology, we can produce digital pulses accurately with high timing resolution of 1 ns and narrow widths of 4 ns to control the microwave pulses required by pulsed DNP and ensure overall system synchronization. The proposed spectrometer is proved to be both feasible and reliable by observation of a maximum signal enhancement factor of approximately -170 for (1)H, and a high quality water image was successfully obtained by DNP-enhanced spin-echo (1)H MRI at 0.35 T.

Multiscale computational modeling of (13)C DNP in liquids #DNPNMR

Kucuk, S.E. and D. Sezer, Multiscale computational modeling of (13)C DNP in liquids. Phys Chem Chem Phys, 2016. 18(14): p. 9353-7.

http://www.ncbi.nlm.nih.gov/pubmed/27001446

Dynamic nuclear polarization (DNP) enables the substantial enhancement of the NMR signal intensity in liquids. While proton DNP is dominated by the dipolar interaction between the electron and nuclear spins, the Fermi contact (scalar) interaction is equally important for heavier nuclei. The impossibility to predict the magnitude and field dependence of the scalar contribution hampers the application of high-field DNP to nuclei other than (1)H. We demonstrate that molecular dynamics (MD) simulations followed by density functional calculations of the Fermi contacts along the MD trajectory lead to quantitative agreement with the DNP coupling factors of the methyl and carbonyl carbons of acetone in water at 0.35 T. Thus, the accurate calculation of scalar-dominated DNP enhancement at a desired magnetic field is demonstrated for the first time. For liquid chloroform at fields above 9 T, our methodology predicts direct (13)C DNP enhancements that are two orders of magnitude larger than those of (1)H.

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