Profiles

Photograph of Andrew J. Pell

Andrew Pell

Assistant Professor

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Works at Department of Materials and Environmental Chemistry
Telephone 08-16 23 76
Email andrew.pell@mmk.su.se
Visiting address Svante Arrhenius väg 16 C
Room C520
Postal address Institutionen för material- och miljökemi 106 91 Stockholm

About me

I graduated in 2005 with an MSci from the University of Cambridge in Natural Sciences, specializing in chemistry.  I stayed at Cambridge to complete a PhD in solution NMR under the supervision of James Keeler in 2009, where I worked on the development of new methods in what is now known as pure-shift NMR. Afterwards I moved to the Centre de RMN à Très Hauts Champs at the Ecole Normale Supérieure de Lyon to perform postdoctoral work in paramagnetic solid-state NMR on materials and metalloproteins with Guido Pintacuda and Lyndon Emsley.  I returned to Cambridge in 2014 for a second postdoctoral position with Clare P. Grey on paramagnetic solid-state NMR of lithium-ion battery materials.

Since April 2016 I have held the position of assistant professor at the Department of Material and Environmental Chemistry at Stockholm University.

Research

Solid-state NMR spectroscopy of materials

My research interests concern the development and application of solid-state nuclear magnetic resonance (NMR) spectroscopy to materials.

Solid-state NMR is an efficient tool for the characterization of micro-crystalline, poorly crystalline, or materials with structural or compositional disorder including organometallic complexes, inorganic frameworks, battery materials, and biological systems. In combination with other techniques, NMR can provide unique insights into the analysis of the reaction mechanism of catalysts, the description of surface chemistry processes, and in the characterization of molecular binding.

Paramagnetic NMR

Paramagnetic metal ions are present at the active sites of many catalytic and electrochemical processes that are at the core of modern chemistry, and are the key constituents of many new versatile materials. As such they have a tremendous impact on industry, energy, and the environment. The key to being able to understand and explain the function and macroscopic bulk properties of these materials is to obtain a picture of their local three-dimensional structure.

The aim of our research in this area is to provide a robust tool for characterizing systems containing paramagnetic metal ions down to the molecular or atomic level, and therefore to provide a link between the structure and the bulk properties of such paramagnetic systems. To achieve this aim we develop new solid-state NMR techniques in combination with novel theoretical and computational methods.

However paramagnetic systems have resisted NMR characterization since paramagnetic centres with large magnetic moments result in signals with extremely large shifts, large shift anisotropies, and very short relaxation times.  On the one hand these effects provide a direct probe of the electronic structure in these compounds. On the other hand these same effects present a problem for spectroscopy, and mask the information that can usually be extracted from a diamagnetic molecule.

This field has experienced a real revolution in recent years, due to a combination of improved radiofrequency (RF) probe technology and better RF irradiation schemes.  These developments have opened the door to measuring and exploiting paramagnetic effects as a source of structural and electronic information.

However despite this recent progress, many issues remain to be addressed before paramagnetic NMR can become a routine tool for the studying systems of increasing complexity that are increasingly playing a part in chemistry and biology. We aim to address the barriers that currently oppose the acquisition and interpretation of the NMR spectra, and to extend the fields of application, attacking relevant chemical and biological problems, with novel techniques to determine structure.

ID Seymour, DS Middlemiss, DM Halat, NM Trease, AJ Pell, CP Grey, Characterising oxygen local environments in paramagnetic battery materials via 17O NMR and DFT calculations, J Am Chem Soc138, 9405—9408 (2016)

AJ Pell, G Pintacuda, Broadband solid-state MAS NMR of paramagnetic systems, Prog Nucl Magn Reson Spectrosc, 84—85, 33—72 (2015)

J Xu, DH Lee, RJ Clément, X Yu, M Leskes, AJ Pell, G Pintacuda, X-Q Yang, CP Grey, YS Meng, Identifying the critical role of Li substitution in P2-Nax[LiyNizMn1-y-z]O2 (0 < x, y, z < 1) intercalation cathode materials for high-energy Na-ion batteries, Chem Mater, 26, 1260—1269 (2014) — top 1% most cited in field

NC George, AJ Pell, G Dantelle, K Page, A Llobet, M Balasubramanian, G Pintacuda, BF Chmelka, R Seshadri, Local environments of dilute activator ions in the solid-state lighting phosphor Y3Al5O12, Chem Mater, 25, 3979—3995 (2013)

RJ Clément, AJ Pell, DS Middlemiss, FC Strobridge, JK Miller, MS Whittingham, L Emsley, CP Grey, G Pintacuda, Spin-transfer pathways in paramagnetic lithium transition metal phosphates from combined broadband isotropic solid-state MAS NMR spectroscopy and DFT calculations, J Am Chem Soc, 134, 17178—17185 (2012) — spotlight article

AJ Pell, G Pintacuda, L Emsley, Single crystal nuclear magnetic resonance in spinning powders, J Chem Phys, 135, 144201 (2011) — cover article

New methods in broadband, high-resolution 14N NMR

Nitrogen is one of the most important elements found in chemistry, materials science, and biology.  It is found in many diverse systems including pharmaceutical molecules, polymers, supramolecular assemblies, and biological macromolecules where it often plays a crucial role in providing structural stability, and information coding, via hydrogen bonding.  However whilst solid-state NMR should be the method of choice to probe both the atomic-level structure and dynamic processes, it has yet to emerge as a widely-used tool for probing this broad variety of nitrogen environments.  This is because although the most abundant isotope 14N has a high natural abundance of 99.6%, the combination of the integer spin of I=1, typical quadrupolar interaction strengths of a few MHz, and a low gyromagnetic ratio result in very broad NMR signals of very low sensitivity.  Whilst these effects in principle provide a direct probe of the local nitrogen structure and dynamics in these systems, they also present a substantial problem for spectroscopy, resulting in very poor sensitivity and resolution, which make it difficult to extract useful information.

Here we aim to design, optimize, and implement new experimental NMR schemes to observe 14N atomic environments.  Recently we have proposed a new pulse scheme for broadband 14N double-quantum NMR using a combination of fast MAS >50 kHz and low RF field strengths that are capable of excitation with high sensitivity, using ideas that we have previously developed for paramagnetic systems. This initial breakthrough has yielded some very promising results there is still considerable scope for optimization.  This development of the arsenal of techniques for 14N solid-state NMR is the key to making progress in the structural characterization of the wide variety of systems described above.

AJ Pell, KJ Sanders, S Wegner, G Pintacuda, CP Grey, Low-power broadband solid-state MAS NMR of 14N, J Chem Phys, 146, 194202 (2017)

Group members

Postdoctoral researchers

Dr Aleksander Jaworski

Dr Jinqin Yang (co-supervisor with Prof. Niklas Hedin and Prof. Alexander Lyubartsev)

PhD research students

Wassilios Papawassiliou

Rihards Aleksis

José Pedro Albuquerque de Carvalho

Former group members

Elodie Guillard (intern 2018)

Positions

We are always looking for masters students, PhD students, and postdocs. Interested candidates should send a cover letter and CV by email. Masters and PhD candidates should have a background in chemistry, physics, or materials science.  Postdoctoral candidates should have a strong background in experimental or theoretical NMR spectroscopy.

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Last updated: January 20, 2020

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