This page details the the history of NMR and its uses in science and medicine. Below are several links to jump directly to the indicated topic.
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The Development of NMR
In the early 20th century, physicists made great strides in the field of quantum theory. Niels Bohr, a Danish physicist, published several papers leading to the explanations of phenomena that could not be explained by classical mechanics. Emission and absorption spectra could be easily explained using the ideas proposed by quantum theory. Soon after quantum theory first emerged, George Uhlenbeck and Samuel Goudsmit introduced the intrinsic property of electrons that Pauli would later dub spin (which he did shortly after the science of quantum mechanics was officially formulated by Schödinger and Heisenberg).
In 1933, two German physicists - the Otto Stern and Walther Gerlach - they used a molecular beam apparatus to detect nuclear magnetic moments, also known as nuclear spin by observing the deflection of a beam of hydrogen atoms (work for which Stern would earn a Nobel prize in 1943). Although the details of the theory are quite complex, the deflection had be the result of nuclear magnetic moment only (electron spin would not be a contributor to this deflection). A few years later, Dutchman C.J. Gorter attempted to study the paramagnetism of atomic nuclei in the presence of a magnetic field using the resonance properties of protons discovered by Stern and Gerlach. He was unsuccessful, but his published works brought, for the first time, to the attention of the scientific community the possibilities of taking advantage of nuclear resonance methods.
A year after Gorter's work was published, an Austrian scientist named Isidor Rabi conducted an experiment involving the projection of a beam of LiCl molecules through a strong magnetic field. He realized that when a second, oscillating magnetic field was applied at a right angle to the first, resonance occured in specific nuclei when the second field approached the Larmor frequency of the nucleus in question. The absorption of this energy was visualized as a drop in the intensity of the LiCl beam as the strength of the oscillating magnetic field was increased. This groundbreaking observation led to two major outcomes - a Nobel prize for Rabi in 1944 for what was, essentially, the discovery/invention of nuclear magnetic resonance, and also to solid evidence that could be used to predict the nuclear resonances of other compounds.
It did not take long for Rabi's work to make an impact - in 1945, Harvard researchers Edward Mills Purcell and Robert Pound assembled a device (which was, essentially, the first NMR machine) which used radio frequency waves to detect hydrogen-nuclei absorbance in a one-kilogram sample of paraffin wax.
Albert Overhauser, in 1955, predicted that small changes in electron spin population within a sample would result in a large change in the polarization of nuclear spin. This would lead to very important tools for the determination of the structures of large and complex molecules, and ultimately to the advanced NMR devices in use today.
Where Does NMR Fit Into the Discipline of Spectroscopy?
Spectroscopy is the study of the interaction of electromagnetic radiation with matter. Nuclear magnetic resonance spectroscopy involves the use of the resonance properties of some atomic nuclei to study physical, chemical, and biological properties of matter. Radio frequency waves are used to cause excitation of protons between their low and high energy states to achieve this phenomenon.
NMR is commonly used as a means of studying chemical structure using relatively straightforward, one-dimensional techniques. Some other techniques are:
In terms of the range of light involved in NMR spectroscopy, radio frequency waves (10-1 to 101 meters for wavelength) are used to stimulate the nuclei of atoms into their excited states. Waves of very specific energies are required to stimulate various nuclei.
NMR by itself does not always provide enough information for the identification of an unknown compound - it must sometimes be combined with data from IR absorbance spectra, and sometimes with that from a mass spectrometer. For magnetic resonance imaging (MRI) applications in the medical imaging field, the signal from NMR is interpreted across a two- or three-dimensional range to form an image of body tissues. Special pulse techniques of NMR are used to achieve these images. The resolution of MRI at its very best is believed to be in the neighborhood of about 10 microns (1.0 x 10-5 meters). Current technology offers a resolution of about 50 microns, which, as you can see in the MRI gallery, is more than sufficient to offer extremely detailed scans of body tissues. This application in its pure form does not require data from other spectroscopy techniques for identification of specific molecules; however, a relatively new technique known as in vivo magnetic resonance spectroscopy is used to not only generate images of body tissues, but to also identify specific tissues and compound types using solely NMR data, avoiding risky or dangerous invasive procedures. More information on this technique can be found here.
The Significance of NMR to Science and Society
Nuclear magnetic resonance has a wide range of practical and scientific applications. Click here for a discussion of some of the many applications of NMR technology.
What Will the Future of NMR Offer?
Perhaps the most promising near-future application of NMR is the in vivo technique discussed above. While it is currently being used for some diagnoses, the technique is truly in its infancy. Currently, only proton NMR is used in in vivo applications. It is entirely possible (and entirely likely) that NMR for other nuclei (particularly 13C, 14N and 15N, 17O, and 31P due to those elements' importance in human chemistry) will prove to offer valuable insight into body systems, and as a result will see development in the near future.