Nuclear Magnetic Resonance

Magnetic resonance has formed a part of the interests of the PCL from remarkably early times in its development due to the enthusiasm and sheer experimental skill of Rex Richards, one of the few in the field actually to wind his own magnet! Following a brief period in the U.S. where he learned the technique from H.S. Gutowsky, he became the first in Europe to apply NMR to chemical systems, choosing them with great skill to yield meaningful results with the primitive apparatus which could then be assembled. This meant working in the solid state, for high-resolution was then unattainable, and he embarked on a series of papers on crystal hydrates, which were significant in bringing this new subject to the attentions of chemists everywhere; his study of `infusible white precipitate' struck a particular chord. His work was characterised by an insatiable need to innovate, and he constantly introduced new techniques into his laboratory. High resolution studies appeared when the time was ripe, but more remarkably so did experiments on nuclei other than hydrogen, an interest which filled the laboratory with thallium compounds, for instance, which would have caused apoplexy to the safety officers of today. He did very early work on nuclear-electron double resonance (the Overhauser effect) and, most significantly of all, on superconducting magnets with Martin Wood, with the embryonic Oxford Instruments Company. This led directly to the pioneering work of George Radda on NMR in living systems, carried out on one of Rex's early magnets, and it produced a major breakthrough years later, when the world's first reliable genuinely high-field and high-resolution spectrometer was produced for the Oxford Enzyme Group in collaboration with Bruker Spectrospin and Keith McLauchlan. This breakthrough was in large part the basis of NMR becoming applicable to biochemical systems.

The range of scientific problems Rex approached in his relatively short research career in the PCL was extraordinary, he was always on the look-out for new applications of a technique for which he was the ambassador par excellence. The fitting culmination of his research, sadly outside the PCL, was as Chairman of the prestigious Oxford Enzyme Group, of which he was a founding member.

Many who worked with him developed significant reputations of their own in later years, notably J.A.S. Smith, L. Pratt, R. Freeman, T.P. Schaefer, J.B. Leane, T.M. Connor, R.P.H. Gasser, E.O. Bishop, J.W. White, O.W. Howarth, B. Sheard, R.A. Dwek, D.F.S. Natusch, I.D. Campbell and H.D.W. Hill. That he attracted men of this calibre is perhaps the best illustration of the way in which he dominated the field of chemical NMR in Britain.

When Keith McLauchlan arrived on the scene in 1965, with his own reputation in double-resonance, double-quantum and oriented-molecule NMR, it was apparent that the interests of the Department would best be served by his changing his research interests, which he did after some early work on biological NMR. Rex had a great talent for stimulating and for pointing people in a good direction, and it was he who suggested that Keith should move away from NMR to electron spin resonance. Soon, together with Peter Atkins, a high-resolution spectrometer for the study of transients was built, which allowed short-lived free radicals in solution to be identified positively for the first time. This led directly to the discovery of electron spin polarization (non-Boltzmann populations) in the radicals, and to the forging of a direct experimental link between the photochemistry and photophysics of systems. This was highly original work and the group has been largely responsible for establishing the technique world-wide. It has enabled the identification of a new, very short-lived intermediate in reactions in solution, the spin-correlated radical pair, to the realisation that MAgnetic fields might affect Reaction Yields (the MARY experiment) and, in turn, to an interest in the possible effects of environmental fields on human life. Much effort has also gone into the development of the Reaction-Yield Detected Magnetic Resonance (RYDMR) method, here applied uniquely to reactions in solution. This experiment yields the spectrum of the radical pair itself and a detailed understanding of the kinetic processes occuring within it. P.J. Hore, of whom more below, started his research in this group.

In the early 1960's K.A. McLauchlan shared an office with Ray Freeman at the National Physical Laboratory, and in 1974 Freeman returned to Oxford after a very distinguished period in the U.S. with Varian Associates, during which he attained a major international reputation, both for the worth of his science and the exceptional quality of his presentation of it. His work here, however, transcended all that had gone before, and produced spectacular advances in technique. Together with the similar, independent, work of Ernst in Zürich, this period opened up the real power of Fourier Transform and two-dimensional NMR techniques, to the extent that today they dominate experimental effort. The methods developed included 2D-J-spectroscopy, heteronuclear shift correlation, selective excitation, composite pulses, broadband decoupling techniques, multiple quantum spectroscopy, Gaussian pulses etc. etc. The list of his co-workers contains many of the most respected names of their generation, including, G. Bodenhausen, G.A. Morris, D.L. Turner, M.H. Levitt, A. Bax, T.H. Mareci, T.A. Frenkiel, J. Keeler, A.J. Shaka, D. Neuhaus and S. Wimperis (about to return to the PCL as a Royal Society University Lecturer). Ray Freeman left the Laboratory in 1987 to become the John Humphrey Plummer Professor of Magnetic Resonance at Cambridge.

A NMR spectrometer in Peter Hore's laboratory located in the Rex Richards building.

In his turn, Peter Hore returned to the PCL (originally as a Junior Research Fellow in Freeman's laboratory, before election to a Lectureship in 1983) following a post-doctoral period with R. Kaptein, which saw early work on flash-photolysis NMR, and nuclear spin polarization in biochemical reactions. This work he continues in Oxford, applying it to important problems in protein folding. This, together with some work on the analysis of electron spin polarization in photosynthetic systems, done in collaboration with A.J. Hoff in Leiden, extends his interest in spin-correlated effects developed during his doctoral period, into significant new areas. Another major contribution is the development of maximum entropy methods for analysing the free-induction decays obtained in pulsed NMR, independent of Fourier transform methods.

Magnetic resonance has been one of the most fertile areas of physical chemistry research since Rex Richards did his first experiments here. It is remarkable that after forty years of development, the rate at which new techniques and applications are being elaborated is still increasing, and there are few areas of condensed-phase chemistry that it does not influence. We are proud that this Laboratory has contributed significantly to the advances that have been made.

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