High Resolution Solid State Nitrogen-14 NMR

Through the development of novel experimental and computational methods, we aim to make solid state NMR spectroscopy of the major naturally occurring isotope of nitrogen much easier and more informative. 14N NMR used to be very hard due to the electric quadrupole moment of 14N nuclei, which generates very broad spectral lines. We found a promising way around this problem -- it potentially opens a new route to the characterization of a huge range of biomolecules, natural materials and drugs, including fibrillar proteins, which are key targets for the understanding of amyloid diseases. Within this project we will develop high-resolution 14N NMR methods and use them to gain insight into structural and dynamic information for systems where 15N enrichment is difficult or impossible, e.g. environmental samples, natural materials and tissue biopsies.

NMR is a powerful technique for the analysis of structure and dynamics of molecules and solid state NMR is uniquely positioned to study a range of materials, from non-crystalline biological solids, such as fibrils or membrane proteins, to amorphous glasses. Despite its high natural abundance (99.6%), 14N isotope has received relatively little attention because it is a spin-1 nucleus with a large quadrupolar interaction that makes excitation and detection of the NMR spectrum difficult. Accordingly, most solid-state NMR studies to date have utilized materials artificially (and very expensively) enriched with the 15N isotope, for which high-resolution NMR spectra can be measured.

Despite the difficulty associated with observing 14N, its large quadrupolar interaction is an excellent reporter of the local environment that is far more sensitive than other NMR interactions, with the potential to provide unique insights into structure and dynamics of nitrogen-containing materials. In the last five years, an increasing amount of attention has been given to 14N and its solid state NMR spectroscopy. Recent developments include indirect detection of the fundamental 14N NMR transition, as well as the detection of the partially forbidden higher order transition, known as the overtone transition, which has much sharper lines. Although the sensitivity and spectral resolution of these methods is improving, they are currently not sufficiently robust and sensitive to make them widely applicable.

Our group is involved in these efforts. We have obtained a range of exciting preliminary results to support our research targets, demonstrating that major improvements are obtainable for signal intensity, site resolution, accurate and efficient data simulation, and that 14N does not necessarily constrain us to small molecules -- even data on small proteins can be obtained.

To realise the potential of 14N NMR, these preliminary result must be followed by focused research in two keys areas:

Firstly, there is a need to develop methods for the efficient excitation of both the fundamental and overtone transitions. To achieve this goal we will use state-of-the-art computational and mathematical tools to boost the excitation efficiency. A key component to this will be the use of optimal control theory that has the ability to optimize experimental methods to deliver performance figures close to the theoretical limit, often more than an order of magnitude higher than those obtained through more conventional means.

Secondly, we believe that the sensitivity and resolution obtained in the 14N NMR spectra can be significantly enhanced. Preliminary overtone data indicate that significant narrowing of resonances, and gains in efficiency can be achieved through the development of new pulse sequences and the optimisation of acquisition conditions.

Alignment with EPSRC and RCUK Strategy

The latest experimental and computational methods will be used in this project to deliver new methods for the characterisation of systems at the molecular level. The three key development areas in the project Objectives are aligned with the following strategic areas:

1) Simulation software development creates theoretical research infrastructure, whose impact is comparable to that of quantum chemistry packages such as CASTEP, Gaussian and ADF. Its wider significance is in combining theoretical research and high performance computing to enhance quantum mechanical simulation capability for spin processes in physical, chemical, biological and medical imaging contexts. Developments in this area are aligned with EPSRC themes in Physical Sciences (fundamental magnetic resonance and spin dynamics research), Mathematical Sciences (algebraic developments underpinning new spin dynamics simulation algorithms, numerical analysis), ICT (new algorithms and software), and Engineering (optimal control theory).

2) New experimental methods will contribute to a growth of the understanding of how to efficiently manipulate spin systems at the edge of what can be achieved analytically. This will be of interest to all magnetic resonance users, beyond the remit of 14N NMR research. This aligns well with the EPSRC's Physical Sciences (fundamental magnetic resonance and spin dynamics research) theme.

3) New technologies for the study of "difficult" pharmaceutical and biomolecular systems (those not amenable to X-ray crystallography and conventional NMR) will allow their structures to be investigated with hitherto unprecedented level of detail. This target is aligned with the Chemical Structure section within the Physical Sciences area, with Chemical Biology and Biological Sciences and Computational and Theoretical Chemistry. It is also aligned with structural biology initiatives of BBSRC, MRC and the Wellcome Trust. These developments may, in the longer term, open up opportunities for the detection of novel biomarkers important for the prediction and early diagnosis of disease.

Personnel Training

The PhD student will be trained in a multi-disciplinary environment and will acquire many complementary research skills. This will help alleviate the shortage of highly trained researchers who can work at the interface between the physical sciences and biology. The applicants a members of a number of graduate training schemes (this is discussed in Pathways to Impact).

Economic Impact

Our research will influence a number of industries within the UK, in particular:

1) Pharmaceutical industry -- the methods developed here will facilitate to multiple stages of the drug discovery pipeline, from the understanding of basic biomolecular structure and function, to the development of new drugs, through to the characterization of drug polymorphs and formulations, which is a key step in the protection of intellectual property.

2) UK is the European leader in NMR and a base for some of the major magnet and spectrometer manufacturers. The methods developed within this project will enhance the usefulness of quadrupole NMR and potentially lead to its more widespread adoption, indirectly supporting the UK manufacturing industry.

Societal Impact

Our research will contribute to the influence that scientific research has on society, with the potential to improve our understanding of biomolecular structures. Examples include understanding the structure, function and behaviour of biopolymers, the development of novel materials, studying the molecular properties of amyloid deposits to aid the development of treatments for amyloid diseases (i.e. Alzheimer's, Parkinson's). In the longer term, these methods may provide us with new analytical methods for the identification of novel biomarkers linked to a broad range of diseases.