Tuesday, November 6, 2018 - 3:45pm
Event Date Details:
Light refreshments served at 3:30 seminar begins at 3:45 and lasts one hour, including questions.
This presentation will selectively cover closely related sets of experiments that employ time domain and continuous wave (CW) dynamic nuclear polarization (DNP) experiments, magic angle spinning (MAS) NMR, and the application of these techniques to structural determination of amyloid fibrils from Aβ and membrane proteins.
High field dynamic nuclear polarization (DNP) experiments utilizing subterahertz microwaves (~150-600 GHz) are now well established as a routine means to enhance nuclear spin polarization and sensitivity in MAS NMR experiments. Specifically, irradiation of electron-nuclear transitions transfers the large electron polarization from the polarization agent to nuclear spins via the Overhauser effect (OE), the cross effect (CE) and/or the solid effect (SE). However, the field/frequency dependence of the CE and SE enhancements scale as ω_0I^(-n), where n=1-2, leading to attenuated enhancements in experiments at 14.1 and 18.8 T. Accordingly, we have initiated time domain DNP in order to circumvent the field dependence of CW DNP. We show that spin locking the electrons and matching the NOVEL condition serves as an effective approach to time domain DNP, and that the spin lock can be modulated to increase the efficiency of the polarization transfer. In addition, a significant reduction in the power required to perform pulsed DNP is achieved by using the integrated solid effect and sweeping the microwave frequency with an AWG. Finally, we report a new low power approach -- Time Optimized Pulsed DNP (TOP DNP) – that utilizes pulses at ω_0S synchronized with ω_0I, the nuclear Larmor frequency, to efficiently perform polarization transfer. Time permitting applications to Aβ_(1-42)and bR will be presented.
November 2, 2018 - 10:28am