Category Archives: X-Band ODNP

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.

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.

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

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.

X-Band DNP Hyperpolarization of Viscous Liquids and Polymer Melts

Neudert, O., et al., X-Band DNP Hyperpolarization of Viscous Liquids and Polymer Melts. Macromol Rapid Commun, 2015. 36(10): p. 885-9.

http://www.ncbi.nlm.nih.gov/pubmed/25757144

NMR studies of synthetic polymers and biomacromolecules, which provide insight into the conformation and dynamics of these materials, can benefit strongly from the increased sensitivity offered by dynamic nuclear polarization (DNP) and other hyperpolarizing methods. In this study (1) H DNP nuclear spin hyperpolarization of two polybutadiene samples, representing a supercooled liquid and an entangled polymer melt, is demonstrated at 0.35 T magnetic field strength and at temperatures between -80 and +50 degrees C. Electron spin polarization transfer from the alpha,gamma-bisdiphenylene-beta-phenylallyl radical to the sample nuclei is achieved by the Overhauser and solid effect. DNP signal enhancements are studied, varying the electron spin resonance offset, microwave power, and sample temperature. The influence of spin relaxation times, line widths, and molecular dynamics are discussed. The results show promising, up to 15-fold NMR signal enhancements using noncryogenic temperatures and an inexpensive setup that is less technically demanding than current high-field DNP setups.

Have a question?

If you have questions about our instrumentation or how we can help you, please contact us.