The Nobel Prize in Chemistry 1991
Richard R. Ernst
Scientific progress can be said to be determined not only by the ingenuity of basic findings but also by the key developments that expand their use. A prime example is Richard Ernst's advances that have successfully brought a technique known as nuclear magnetic resonance, or NMR, to the scientific and medical mainstream.
In the late 1940s, Felix Bloch and Edward Purcell discovered NMR, a method that manipulates the weak magnetic spin of subatomic particles with magnetic fields and radio waves in a way that unmasks the identity of the atoms in which they reside. When Ernst entered the field in the late 1950s, NMR was an interesting tool, though its low sensitivity and the need for large samples made it far from being the method of choice to solve complicated chemical structures.
Ernst's revolutionary answer to the problem was to retune the traditional method for obtaining NMR signals. Instead of subjecting atomic nuclei in a sample to a slow sweep of radio frequencies, Ernst bombarded them with a short and intense radio pulse, recorded the response, and used a mathematical formula to tease apart the same NMR patterns that would have been obtained from the traditional method. Researchers could now use hundreds of pulses in the time taken to obtain a single slow sweep, and combining the signals from these pulses increased the sensitivity of NMR dramatically. This brought NMR into a new age, in which it finally became possible to detect weak, inaudible notes produced by small amounts of material, or from elements with magnetic nuclei that are rare in nature.
Ernst's other major development was to devise a way of striking nuclei with a sequence of two or more pulses at varying time intervals. The time between pulses allowed interactions between adjacent nuclei in the molecule to evolve before being hit with another pulse. This so-called added dimension in radiofrequency made it possible to discover, among other things, which atoms were close in space to each other in a molecule. Together, both of Ernst's advances have been instrumental in establishing NMR as an essential technique in structure determination and in medical imaging.