NMR improvements earn chemistry Nobel.

A Swiss physical chemist who helped advance nuclear magnetic resonance (NMR) technology has won the 1991 Nobel Prize in Chemistry. Richard R. Ernst, 58, of the Federal Institute of Technology in Zurich, improved upon NMR techniques initially developed in 1945. His contributions paved the way for magnetic resonance imaging (MRI), a biomedical technique for depicting tissues deep within the body.

The Royal Swedish Academy of Sciences in Stockholm, which announced the $1 million award last week, calls NMR spectroscopy "perhaps the most important instrumental measuring technique within chemistry."

Basically, nuclear magnetic resonance works because atoms placed in a very strong magnetic field align with the field and behave as though they were spinning tops. The atomic tops wobble at certain frequencies, depending on what other atoms are nearby.

For imaging, scientists or physicians then bombard these atoms with high-frequency radio waves. When the radio waves encounter atoms wobbling at the same frequency as the waves, they cause the atoms to resonate. After the radio waves are turned off, the atoms give off a pulse of energy. A detector picks up the timing and type of pulses, which reveal the kinds of atoms emitting them. Thus, scientists can discern the chemical makeup of a sample.

Ernst spurred this technology by increasing its sensitivity and by making it easier to interpret the pulses. In 1966, he and a U.S. colleague, Weston A. Anderson, changed the type of radio wave from slow sweeps to short, intense pulses. Then Ernst discovered that he could obtain even more information about a sample by using sequences of short pulses of radio waves and varying the timing of the pauses in between. He later applied a mathematical technique called Fourier transformation to NMR spectroscopy and further increased NMR's sensitivity.

These and other advances have made it possible to determine the three-dimensional structure of large, complex molecules that contain hundreds of atoms, to examine interactions between molecules, to study molecular motion and rates of chemical reactions, and to image soft tissues not clearly revealed by X-rays.

Ernst learned of his Nobel last week from a pilot during a transatlantic flight.