High Power 200 GHz Pulsed/Continuous Wave (CW) Microwave Source for Dynamic Nuclear Polarization (DNP) Spectroscopy

Lead Research Organisation: University of Warwick
Department Name: Physics

Abstract

Our vision is to create a spectrometer for Nuclear Magnetic Resonance (NMR) that can detect signals that are hundreds of times weaker than can be achieved with even the very best conventional spectrometers. NMR methods are firmly established as a primary analytical tool in chemistry, are increasingly influential for characterisation in materials science and have revolutionised medical imaging. Despite the great success of NMR there remains a huge demand to push the boundaries by increasing the sensitivity and speed of the technique. This will enable NMR to be used in the study of a broad range of problems, including catalysis, batteries and fuel cells where today its impact is limited through lack of sensitivity. Furthermore, it is widely appreciated that structural information is key for understanding biological processes (e.g. protein folding, signal transduction etc.) and many problems will only be soluble if the sensitivity of NMR is dramatically increased.

Dynamic Nuclear Polarisation (DNP) offers the exciting possibility to greatly increase the sensitivity of NMR by exploiting the inherently much larger polarisation of electron spins as compared to nuclear spins (e.g. ~ 2500 times for 13C). The DNP infrastructure at Warwick was funded by a £3.74M Basic Technology project (EP/D045967/1). All components of the DNP systems developed functioned at or above their design targets, except for the gyrotron microwave source which did not meet the necessary power/stability requirements for routine operation/exploitation. Nevertheless, large enhancements (60x) were achieved. The proposed new "turn-key" microwave source will provide significantly enhanced performance, is much more stable, agile, versatile and has significantly lower running costs than the gyrotron microwave source used to date. It will enable the continued rapid development and exploitation the DNP capabilities at Warwick. Development work will be done in collaboration with researchers at the Universites of Nottingham, St Andrews and Southampton while the enhanced DNP capabilities will be exploited by the wider vibrant UK MR community who will have access to a tool which enables research on systems previously out of reach. The research impact will be significant since the sensitivity enhancements in many applications are likely to be in excess of a few 100 times. The new capability will of course stimulate as yet unforeseen activities through the proposed pilot studies.

The project objectives are:

(a) Provision of a shared UK resource for CW DNP-enhanced solid-state NMR at a fraction of the cost of the current less able commercial system and with performance better than the current state of the art.

(b) The development of pulsed DNP techniques with higher sensitivity than the current CW methodologies. This is possible because the new source can provide microwave pulses as well as continuous output and would be a unique capability.

(c) DNP studies utilizing polarization sources with short electron relaxation times. This is possible because of the high power and versatility of the new microwave source and should greatly enhance the range of applicability of the enhancement technique.

Planned Impact

The strategic equipment requested (200 GHz pulsed/CW source for Dynamic Nuclear Polarisation (DNP) enhanced Nuclear Magnetic Resonance (NMR)) is first and foremost a tool for enabling spectacular signal enhancements in solid-state NMR spectroscopy. Enhancements of >100x will be achievable making impossible experiments possible and dramatically broadening the application areas of NMR. The last two years has seen a burst of publications from overseas laboratories illustrating that the utilization of continuous wave DNP-enhanced NMR has become more widespread and is already acknowledged as a valuable tool to increase the sensitivity of multidimensional solid-state NMR essential for biomolecular and surface studies. The implications for a wide range of surface science and materials problems from fuel cells and batteries to catalytic converters are enormous.

UK companies manufacturing, developing and selling MR equipment and software will benefit through targeted collaborative R&D on DNP leading to innovative and accelerated technology development. Thomas Keating (winner of 2012 Queen's Award for Enterprise) is just such a company who are already supplying hardware for DNP spectrometers. UK based companies are world-leaders in superconducting magnet manufacture, and excel in the development and exploitation of MR. Such businesses will only be sustained through continued innovation.

The strategic equipment enables the development of DNP methodologies and techniques, since it has the capability to do what other systems cannot. This should impact across the whole application field of MR providing larger signal enhancements even in situations where DNP has not previously been effective.Users of MR in analytical and R&D applications will benefit from the greater sensitivity enabled through DNP enhancement techniques, increasing the reach and exploitation of MR in the pharmaceutical, materials, foodstuffs and biomedical fields.

In the medium-to-long-term, society stands to benefit heavily from these scientific advances as fuel cells, batteries and catalytic converters help the transition to a low-carbon economy, while pharmaceutical breakthroughs improve the health and quality of life of our ageing population.

The users of the strategic equipment will benefit from the research and training on a state-of-the-art DNP-enhanced solid-state NMR spectrometer. For young researchers who use the equipment it will not only benefit their immediate research but the exposure to cutting-edge technologies and methodologies will ensure they are attractive to employers in both academic and industrial environments.

The strategic equipment will give the UK a research advantage that will promote international collaboration and development since visitors will want to make use of the capability. New collaborations will be established, research income leveraged into the UK and through the expertise drawn inwards the UK research base strengthened.

Publications

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Description Our vision is to create a spectrometer for Nuclear Magnetic Resonance (NMR) that can detect signals that are hundreds of times weaker than can be achieved with even the very best conventional spectrometers. NMR methods are firmly established as a primary analytical tool in chemistry, are increasingly influential for characterisation in materials science and have revolutionised medical imaging. Despite the great success of NMR there remains a huge demand to push the boundaries through increasing the sensitivity and speed of technique. This will enable NMR to be used in the study a broad range of problems, including catalysis, batteries and fuel cells where today its impact is limited through lack of sensitivity. Furthermore, it is widely appreciated that structural information is key for understanding biological processes (e.g. protein folding, signal transduction etc.) and many problems will only be soluble if the sensitivity of NMR is dramatically increased.
Dynamic Nuclear Polarisation (DNP) offers the exciting possibility to greatly increase the sensitivity of NMR by exploiting the inherently much larger polarisation of electron spins as compared to nuclear spins (e.g. ~ 2,500 times for 13C). The electron polarisation is transferred to the nuclear polarisation to enhance the NMR sensitivity. In this project we have focused on DNP NMR of solid state samples. By spinning the sample (usually at a frequency of 10 to 100 kHz) at the magic angle ( 54.74°) with respect to the direction of the magnetic field, the normally broad lines in solid state NMR spectra become narrower, increasing the resolution for better identification and analysis of the spectrum. The original DNP infrastructure at Warwick was funded by a £3.74M Basic Technology project (EP/D045967/1). In this project we replaced a complex gyrotron microwave source, which did not meet the necessary power/stability requirements for routine operation/exploitation, with a "turn-key" microwave source to provide significantly enhanced performance. The new source is much more stable, agile, and versatile and has significantly lower running costs than the gyrotron microwave source used to date.
In our proof of principle studies significant DNP enhancements (up to 120 times) have been achieved in a wide range of samples with different radicals. Our work demonstrates that an existing conventional solid-state NMR system can be adapted to run DNP experiments via the use of a solid state microwave source and an Extended Interaction Klystron microwave amplifier. Future exploitation the DNP capabilities at Warwick will be exploited by the wider vibrant UK MR community who will have access to a tool which enables research on systems previously out of reach.
Exploitation Route Our work demonstrates that an existing conventional solid-state NMR system can be adapted to run DNP experiments via the use of a solid state microwave source and an Extended Interaction Klystron microwave amplifier. Sensitivity enhancements of > 100 times are possible to enable research on systems previously out of reach.
Sectors Aerospace, Defence and Marine,Agriculture, Food and Drink,Chemicals,Energy,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

URL http://www2.warwick.ac.uk/fac/sci/physics/research/condensedmatt/magneticresonancecluster/dnp/facilities/
 
Description Contract Research Measurements for Johnson Matthey Technology Centre: Dynamic Nuclear Polarization enhanced Magic Angle Spinning Nuclear Magnetic Resonance was used to study functionalised silica particles (used in catalysis) and Metal Oxide Frameworks used in the removal of toxic gases. DNP provided over a factor 600 time saving for acquiring natural abundance 15N spectra of functionalised silica, enabling an otherwise prohibitive characterisation method to become routine. See Dynamic Nuclear Polarization enhanced NMR at 187 GHz/284 MHz using an Extended Interaction Klystron amplifier, Thomas F. Kemp, Hugh R.W. Dannatt, Nathan S. Barrow, Anthony Watts, Steven P. Brown, Mark E. Newton, Ray Dupree, 2016, Journal of Magnetic Resonance 265 77-82, DOI: 10.1016/j.jmr.2016.01.021. We have subsequently published on a new all optical method of electorn and nuclear spin polarisation in diamond (All-optical hyperpolarization of electron and nuclear spins in diamond, B. L. Green, B. G. Breeze, G. J. Rees, J. V. Hanna, J.-P. Chou, V. Ivády, A. Gali, and M. E. Newton, Phys. Rev. B 96, 054101 - Published 1 August 2017) and the mechanism is being investigated.
First Year Of Impact 2015
Sector Chemicals,Environment,Pharmaceuticals and Medical Biotechnology
Impact Types Economic

 
Description Johnson Matthey Technology Centre - DNP 
Organisation Johnson Matthey
Department Johnson Matthey Technology Centre
Country United Kingdom 
Sector Private 
PI Contribution Magic Angle Spinning (MAS) NMR is widely used for obtaining structural and dynamic information about solids, however its use is often limited by sensitivity both because of the small nuclear magnetic moment and the fact that many experiments involve isotopes of low natural abundance. Dynamic Nuclear Polarisation (DNP) involves the transfer of the much larger thermal polarisation of electron spins to nearby nuclei by microwave irradiation at the appropriate frequency to induce electron-nuclear transitions and in principle could increase the sensitivity by the ratio of the electron and nuclear gyromagnetic moments ˜660 for 1H. The effective enhancement achieved was e = 25 as the amount of sample and linewidths are unchanged. As DNP offers over a factor 600 time saving for acquiring natural abundance 15N spectra of functionalised silica, DNP enables an otherwise prohibitive characterisation method to become routine.
Collaborator Contribution Provision of Samples (3-aminopropyl Functionalised silica (Davisil G636, 60 Å pore size))
Impact Publication: Dynamic Nuclear Polarization enhanced NMR at 187 GHz/284 MHz using an Extended Interaction Klystron amplifier http://dx.doi.org/10.1016/j.jmr.2016.01.021
Start Year 2015