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So what is nuclear magnetic resonance (NMR) spectroscopy anyway?

NMR is perhaps best-known as the technology behind the magnetic resonance imaging (MRI) machines found in today?s hospitals. Doctors use MRI to scan patients and non-invasively view inside the body; similarly, scientists use a specialized, high-resolution NMR to scan test tubes filled with solutions of proteins, DNA, or other biological molecules to see what they look like.

Knowing the structure of molecules helps scientists understand how the body works. Moreover, structures are crucial to designing new and better drugs. In fact, there is no question that NMR is one of the most fundamental techniques in chemistry and biology today.

Discovered independently by two physicists in 1946?Edward Mills Purcell at Harvard University and Felix Bloch at Stanford University, who shared the 1952 Nobel Prize in physics for their discovery?NMR refers to the ability of atomic nuclei (the ?N? of NMR) to absorb energy and reorient themselves in a magnetic field (the ?M?) when exposed to radiation of a particular resonant frequency (the ?R?) in the radio band.

Later, another Nobel, the 1991 Nobel Prize for Chemistry, went to Richard R. Ernst at ETH in Z?ich for developing some of the fundamental tools used in NMR spectroscopy. Kurt W?hrich has won the 2002 Nobel Prize in Chemistry for his contribution towards developing these tools and for extending NMR to biology?by determining the three-dimensional structure of biological macromolecules in solution.

Physically, NMR is possible because atomic nuclei in proteins and DNA behave like tiny magnets and tend to align themselves with a magnetic field?analogous to how a magnetic compass needle aligns itself with the North Pole.

In an NMR experiment, a sample in a glass tube is inserted into the center of a ?spectrometer.? NMR spectrometers have extremely large and powerful magnets, and inside, the nuclei will align with the magnetic field. But an electromagnetic pulse of just the right frequency sent through the sample can cause the nuclei to realign. Then when the pulse is switched off, the nuclei reorient themselves. This reorientation causes small but measurable induced voltages, and it is this signal that is being measured in the NMR experiment. The NMR spectrometer scans such signals over a range of radio frequencies, and produces raw data, which is known as a spectrum. An NMR spectrum is unique for a particular molecule, and is influenced by the shape of the molecule in which the atoms reside. Thus NMR spectrometers can be used to solve the structures of proteins, DNA, or other important biological molecules.