Very Low Field 2.35 T Solid State NMR Console and Fast MAS NMR Probe for the Study of Paramagnetic Materials Systems

Lead Research Organisation: University of Warwick
Department Name: Physics

Abstract

The aim of this proposal is to expand the capability base that solid state NMR community has at its disposal so that more materials and chemistry systems can be effectively studied with this technique. Solid state NMR usually confines itself to the study of diamagnetic materials and compounds; i.e. systems that do not possess unpaired electrons in their electronic structure. Many modern materials and chemical systems being developed possess transition metals and/or rare earth species as part of the elemental composition; these introduce unpaired electrons into these systems and thus promote paramagnetic characteristics which are incompatible with the conventional NMR methodology. Our traditional mindset of how we approach the typical NMR measurement needs to be adjusted as our typical drive to higher external magnetic field strengths is counterproductive in this case. The electron polarisation that gives rise to paramagnetic anisotropies and shifts scales linearly with magnetic field, and these effects greatly detract from conventional NMR data thus masking the information that is normally sought. Severe cases of paramagnetism can preclude the NMR measurement of some systems completely.

The most direct way to address this solid state NMR challenge is to attempt measurements in a much reduced (rather than increased) magnetic field, and to spin the sample at very high MAS frequencies. This low field/fast MAS methodology maximises the chance for NMR data to be elucidated from these systems, however these types of NMR spectrometers are very rare commodities worldwide. While many thousand NMR instruments exist throughout the world at fields of 7.05 T (300 MHz for 1H) and above, only a handful of operational low field spectrometers exist to undertake these type of measurements; furthermore, the UK is not well catered for in this field of spectroscopy apart from very limited proof-of-concept pilot studies that have demonstrated this idea. This new capability will be as easy to operate as conventional solid state NMR instrumentation and no specific additional training is required to enable its usage for data acquisition. The impact of this methodology is expected to influence the fields of catalysis and energy materials (battery materials, solid oxide and H conduction fuel cells, hydrogen storage materials, supported metal nanoparticles systems, zeolites, nuclear waste glasses etc.), general organometallc and inorganic chemistry, and the emerging field of medical engineering (rare earth doped biomaterials for oncology and blood vessel growth stimulation applications). It is also expected that this methodology will bridge across to established techniques such as EPR, and emerging technologies such as DNP, both of which employ different strategies for the manipulation of the paramagnetic interaction. These relationships are expected to stimulate a more vibrant magnetic resonance community that will be capable of collaboratively tackling the challenging research issues that confront the UK. Academic collaborators at Cambridge, Birmingham, Imperial, Queen Mary, Kent, UCL and Lancaster, and industrial partners such as Johnson Matthey and Unilever are all acutely aware of these new solid state NMR possibilities and flexibility that this methodology offers, and they eagerly await the improvements to the measurement technology that a low field/fast MAS combination can offer.

The specific objectives that shape this proposal are:

(a) to deliver a shared low-field/fast MAS solid state NMR resource to the UK magnetic resonance community that will augment the current UK suite of solid state NMR instrumentation in existence,

(b) to put in place a state-of-the-art solid state NMR console and appropriate fast MAS probe technology capable of delivering the most modern experiments,

(c) to align this methodology with established characterisation technologies such as EPR and emerging experimental initiatives such as DNP.

Planned Impact

The equipment requested under this EPSRC Strategic Equipment call is a low field solid state NMR spectrometer (2.35 T, 100 MHz for 1H) coupled with very fast MAS probe technology (vr > 60 kHz) is the first true low field spectrometer purposely configured to undertake measurements on paramagnetic samples within the UK. It will provide the best prospect to study materials and chemical systems that have previously proven intractable to solid state NMR measurement, and it will position the UK as one of the very few countries to possess this capacity in its research and characterisation infrastructure. All of this equipment (console and probe) will be very state-of-the-art in design and capability, and demands no further training or knowledge than that currently required for standard solid state NMR spectrometer operation; furthermore, it will be accessible to investigators who wish to directly undertake their own measurements in able to facilitate the most immediate impact in their research.
The ease of implementation of this strategic equipment will particularly benefit young researchers who will gain experience and expertise within their research projects and characterisation methodology that was previously unavailable. Such benefits will enhance their personal research profiles and make them more attractive prospects to both academic and industrial employers.

This strategic equipment will provide the UK with a research advantage and new collaborations on all levels are expected to emanate. In particular, new international collaborations will be actively encouraged with CEA (Saclay, France), PNNL (Richland, WA, USA), ANSTO (Lucas Heights, Australia), and increased collaboration between UK research groups will be key in maintaining and strengthening this research advantage and being able to leverage research funds through more enterprising and exciting science.

There are very distinct and instantaneous benefits to some high-profile energy materials and medical engineering research programs within key topics of Greenhouse gas emissions, renewable energy resources, aging population issues and drug delivery/targeting technology. Being able to access data from this technique will positively influence these programs and convey and short term benefits with relevant scientific advances. This, in turn, will thus deliver medium to long term societal gains that will be experienced internationally.

UK manufacturing companies specialising in magnets and magnetic resonance technology will also be very keen participants in this project. The worldwide difficulties with liquid He supply have stimulated the development of cryogen-free magnets, and UK companies such as Cryogenics are keen to develop, test and ultimately supply a new cryogen-free magnet system with appropriate field homogeneity to couple with this new low field/fast MAS capability. This relationship will help position a UK technology manufacturer as a market leader with these products. We intend to support this with a KTP fellowship (currently under joint Warwick/Cryogenics preparation) to provide the training of a young researcher in solid state NMR and magnet technologies.

Publications

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Porras-Vazquez JM (2013) Investigation into the effect of Si doping on the performance of Sr(1-y)Ca(y)MnO(3-d) SOFC cathode materials. in Dalton transactions (Cambridge, England : 2003)

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McCloy J (2019) Crystallization study of rare earth and molybdenum containing nuclear waste glass ceramics in Journal of the American Ceramic Society

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Djordjevic I (2020) CaproGlu: Multifunctional tissue adhesive platform. in Biomaterials

 
Description We have demonstrated and developed low field/fast MAS NMR spectroscopy as an effective characterisation technique for the study of paramagnetic systems commonly found in battery and energy materials applications. The findings obtained through these types of measurements can be integrated with other techniques such as EPR and DNP which focus on the intrinsic paramagnetism of the system being studied.
Exploitation Route The instrumentation that was funded in this Strategic Equipment Grant was set-up to be a shared facility with the UK magnetic resonance community. Within this arrangement, the advancements achieved with this approach and this instrumentation can be extended to external users in a collaborative arrangement across any field of materials research.
Sectors Chemicals,Energy,Environment,Healthcare,Pharmaceuticals and Medical Biotechnology