Electron Paramagnetic Resonance (EPR), otherwise known as Electron Spin Resonance (ESR), is a technique for understanding the local atomic environment of unpaired electrons in materials, often associated with the presence of free radicals or transition metal ions. These unpaired electrons often determine a materials key catalytic, enzymatic, optical, magnetic, electrical, chemical and physical properties and EPR provides the molecular understanding behind this functionality. In recent years pulse EPR techniques have come to the fore and can provide detail of tiny electron-electron or electron-nuclear couplings and their orientational dependence – even in disordered powder samples or glasses. Perhaps the most common pulse EPR technique used today is based on the DEER/PELDOR sequence, used in conjunction with site-directed spin labelling techniques for measuring long range distances in biomolecular systems.
Our group runs a modern commercial Bruker X-band/Q-band pulse EPR machine and a unique high power W-band pulse EPR machine known as HIPER, offering state of the art performance. These were both funded under the UK Basic Technology program and are used in a variety of applications - many based on DEER/PELDOR. Example applications are detailed here. Dr Hassane El Mkami is the applications manager for this program. Key EPR partners in this program were/are Dr David Keeble from Dundee Physics, Dr David Norman from Dundee Life Sciences, Prof Olav Schiemann (formerly at St Andrews, Biology, now at Bonn University), Dr Bela Bode recently appointed to St Andrews, Chemistry and Dr Janet Lovett (recently appointed to Edinburgh University).
A number of key mm-wave technology components offering state of the art performance were developed at St Andrews for the HIPER program, including feedhorns, isolators, switches, high performance optics and fast pulse technology and are detailed here. This was developed by a team of PDRAs, including Dr Paul Cruickshank, Dr Duncan Robertson, Dr David Bolton and Dr Robert Hunter. Another key partner on the technical program was Dr Richard Wylde from Thomas Keating Ltd, who is also an honourary member of staff at St Andrews University.
HIPER itself offers very high sensitivity for both cw and pulse EPR, combined with easy sample handling and large instantaneous bandwidths. In the context of DEER measurements HIPER can also give accurate orientational information from orientation-sensitive spin labels and a number of examples are given here.
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