UC Santa Barbara

Pulsed dipolar EPR spectroscopy offers the ability to measure distances between spin labels in the 1-8 nm distance range. The pulsed EPR technique DEER is particularly useful for highly disordered systems where x-ray crystallography and NMR cannot yet be applied. By modeling the dipolar coupling between two spin labels, we can obtain a distance distribution across the biomolecule. The main disadvantage of DEER is that it is common for experiments to require more than 24 hours of averaging to achieve reasonable signal to noise. In this work, we utilize the recent development of high-speed (>1GHz) DAC boards which now operate at high enough frequencies to offer significant performance increases to pulsed EPR experiments. By using shaped microwave pulses instead of rectangular pulses, one can demonstrate (1) dramatically increased excitation bandwidth, (2) increased selectivity of excitation, and (3) calibration of pulses for resonator bandwidth compensation. We demonstrate the performance improvement of arbitrarily shaped pulses for various pulsed EPR applications on a home-build AWG spectrometer as well as commercial spectrometers. In addition, we apply arbitrarily shaped pulses to study tau protein aggregation, which is involved in Alzheimer’s disease and particularly difficult to study because of its broad distance distribution and short spin-spin relaxation times. Other methods to offer signal to noise improvements to the DEER experiment including denoising and alternative methods for calculating the distance distribution are investigated.