Improving the sensitivity and utility of pulseddipolar experiments in EPR at 94 GHz

Electron paramagnetic resonance spectroscopy;

Motion, Claire Louise ; Smith, Graham Murray ; Smith, Graham Murray

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Electron paramagnetic resonance spectroscopy;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/13969/ClaireMotionPhDThesis.pdf?sequence=2&isAllowed=y

来源: DR-NTU

【 摘 要 】

Pulsed dipolar spectroscopy (PDS) is an electron paramagnetic resonance (EPR) technique,used to conduct long range distance measurements in proteins in the nanometre range. Thisthesis presents a number of methodological and instrumental techniques to improve the sensitivity and utility of PDS experiments using a home-built high power pulsed spectrometer,HiPER, operating at 94 GHz. These include the implementation of phase-modulated composite pulses, which correct for imperfections arising due to inhomogeneity, and offer increasedexcitation bandwidth as well as experimental protocols such as annealing and glassing of samples. A theoretical study into the use of matched filtering to reduce echo noise during measurements, has predicted gains of up to a factor of 3 enhancement in signal-to-noise.Using such techniques we demonstrate sensitivity enhancements of more than 30 on PDSexperiments, between nitroxides and Fe centres, in haem-proteins, corresponding to a reduction in averaging time of almost 1,000, in comparison to standard commercial spectrometersoperating at X-band. The use of composite pulses in PDS experiments on nitroxide biradicalswere also investigated, including their limitations due to intramolecular effects. The thesisthen describes a single frequency dipolar modulation experiment, RIDME, and uses high fieldmeasurements to determine both the distance and relative orientation of a cobalt-nitroxidesystem, for the first time. Finally, a design study is conducted to implement frequency andamplitude modulated pulses on a spectrometer at 9/34 GHz to improve sensitivity.