Cryogen-Free Arbitrary Waveform EPR for Structural Biology and Biophysics

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This equipment upgrade will enhance a large number of molecular biosciences related projects that utilise electron paramagnetic resonance (EPR) spectroscopy and will have a major impact in the biomedical sciences and structural biology at the Universities of St Andrews and Dundee and beyond.EPR is an ideal method for obtaining specific information at the nanoscale, as it is exquisitely sensitive to the magnetic spins of radicals and other paramagnetic centres. These are of interest as many are hotspots of biochemical activity. Recently, the number of applications utilising EPR has greatly increased. This increase was catalysed by new technology which allows researchers to selectively introduce spins into biomolecules and use them as molecular beacons. The magnetic moments of the spins interact with the magnetic moments of other paramagnets or magnetic nuclei and thus magnetically illuminate their surroundings. It has become increasingly popular to use measurements of the long-range distances between the spins to map the nanoworlds of protein conformations and interactions quite as if navigating by the relative positions and brightness of lighthouses.Recently, developments have started to transform this science. While spins are commonly manipulated by on/off electromagnetic irradiation, the advent of arbitrary waveform generators has opened up a whole new universe allowing access to new realms of information in experiments. This technology is often proposed to be the future of EPR and the analogous advancements have wholly transformed the field of nuclear magnetic resonance. Now that the more demanding technical requirements of EPR are fulfilled it seems a logical imperative to upgrade to this technology as the upgrade even just means a moderate additional cost compared to the initial investment.A second development concerns the need to cool the spins to extremely low temperatures using liquid helium. Helium is an expensive, finite resource that has proven to be highly susceptible to disruption in the supply chain and poses a considerable safety hazard. Traditionally, liquid helium would be connected to the spectrometer before performing EPR experiments. Recently, cryogen-free cryostats have been developed using closed-cycle cooling that operates like an ultra-low temperature refrigerator. In these cryostats, used helium is cooled by electrically driven compression and expansion cycles to re-liquefy and thus be recycled. This greatly improves reliability and sustainability. Significantly, this also reduces risks to the researchers whilst performing experiments. Additionally, the increased stability means that the facility can operate around the clock and for a longer period of time, allowing more experiments to be performed and more scientific questions to be answered in a given time, thereby substantially improving the efficiency of the facility.The Universities of St Andrews and Dundee have developed an extensive programme of biological applications using this methodology and now seek to implement cryogen-free arbitrary waveform EPR to enhance existing facilities for projects investigating biomedical challenges and opportunities in the bio-based economy of the future.