Time Domain and High Frequency DNP Experiments
Date:
Lecture / Seminar
Time: 09:30-10:30
Location: Gerhard M.J. Schmidt Lecture Hall
Lecturer: Prof. Robert G. Griffin
Organizer: Clore Institute for High-Field Magnetic Resonance Imaging and Spectroscopy
Details: Dept. Chemistry, MIT
Abstract: Dynamic nuclear polarization (DNP) has become an invaluable tool to enhance sens ... Read more Dynamic nuclear polarization (DNP) has become an invaluable tool to enhance sensitivity of
magic angle spinning (MAS) NMR, enabling the study of biomolecules and materials which are
otherwise intractable. In this presentation we explore some new aspects of time domain DNP
experiments and their applications.
One of the main thrusts of DNP was to provide increased sensitivity for MAS spectroscopy of
membrane and amyloid protein experiments. A problem frequently encountered in these
experiments is the broadened resonances that occur at low temperatures when motion is quenched.
In some cases it is clear that the proteins are homogeneously broadened, and therefore that higher
Zeeman fields and faster spinning is required to recall the resolution. We show this is the case for
MAS DNP spectra of Ab1-42 amyloid fibrils where the resolution at 100 K is identical to that at room
temperature. Furthermore, we compare the sensitivity of DNP and 1H detected experiments and find
that DNP, even with a modest ℇ=22, is ~x6.5 times more sensitive.
We have also investigated the frequency swept-integrated solid effect (FS-ISE) and two recently
discovered variants – the stretched solid effect (SSE) and the adiabatic solid effect (ASE). We find
that the latter two experiments can give up to a factor of ~2 larger enhancement than the FS-ISE.
The SSE and ASE experiments should function well at high fields.
Finally, we discuss two new instrumental advances. First, a frequency swept microwave source
that permits facile investigation of field profiles. It circumvents the need for a B0 sweep coil and the
compromise of field homogeneity and loss of helium associated with such studies. This
instrumentation has permitted us to elucidate the polarization transfer mechanism of the Overhauser
effect, and also revealed interesting additional couplings (ripples) in field profiles of cross effect
polarizing agents. Second, to improve the spinning frequency in DNP experiments, we have
developed MAS rotors laser machined from single crystal diamonds. Diamond rotors should permit
higher spinning frequencies, improved microwave penetration, and sample cooling.Close abstract
