1991 Nobel Prize in Chemistry
Reason for Award
for his contributions to the development of the methodology of high-resolution nuclear magnetic resonance (NMR) spectroscopy
Laureates
Switzerland
Explanation
Everything around us, including our bodies, is made of tiny atoms. NMR is like a microscope that uses a strong magnet and radio waves to peek at how those atoms are arranged. Richard Ernst made NMR pictures clearer and much faster, just like adding more frames to a movie makes it smoother. Thanks to his ideas, scientists can build medicines more precisely and even check what is inside juice without opening the bottle. The same tricks are used today in hospital MRI scanners that look inside our bodies.
Related Keywords
nuclear magnetic resonance spectroscopy
An analytical technique that measures the resonance of nuclear spins in a strong magnetic field to infer molecular structure and dynamics. Nuclei placed in the field acquire an energy gap and absorb electromagnetic radiation at characteristic frequencies. Because the frequencies shift slightly with chemical environment, peak positions encode atom type and bonding. The method is non-destructive, applicable to liquids, solids, and biological samples, and offers high quantitative accuracy. Medical MRI scanners are an imaging application built on the same NMR principles.
high-resolution NMR
An NMR measurement optimized for uniform magnetic field and narrow linewidths, allowing tiny chemical-shift differences to be resolved. Samples are usually dissolved to enhance motional averaging while shim coils and magnetic shielding reduce field inhomogeneities to below 1 ppb. Sharply separated peaks reveal fine couplings and subtle interactions, indispensable for molecular identification, quantification, stereochemical analysis, and reaction monitoring. In solids, similar resolution is achieved by combining with MAS (magic angle spinning).
Fourier transform
A mathematical operation that converts a time-domain signal into its frequency-domain representation. In NMR, the FID captured after a pulse is sampled and a fast Fourier transform (FFT) simultaneously yields the spectrum. Compared with step-wise frequency sweeping, speed and sensitivity improve dramatically. Digital processing permits window-functions and zero-filling to tailor resolution and S/N at will. The same algorithm underlies MRI k-space reconstruction and FT-ICR mass spectrometry.
pulse NMR
An NMR approach that excites nuclear spins with short radio-frequency pulses instead of continuous waves, then analyzes the ensuing time-decay signal. By tailoring pulse flip angles, phases, and delays one can perform selective inversion, echo formation, cross-polarization and many other experiments. Besides improving sensitivity and speed, pulse methods facilitate quantitative measurement of relaxation and diffusion. Sophisticated pulse sequences are employed in spectroscopy and imaging (MRI) alike. Ernst’s work laid the foundation for this field.
chemical shift
A slight change in nuclear resonance frequency caused by variations in the surrounding electron cloud; it constitutes the x-axis of an NMR spectrum. Reported in ppm, the shift reveals the chemical and stereochemical environment of each atom. For example, proximity to aromatic rings or electronegative atoms decreases shielding, shifting the line down-field. Ppm notation enables comparison across different magnet strengths. In solid-state NMR, chemical shift anisotropy (CSA) provides additional structural insight.
coupling constant
The spacing of line splittings arising from spin–spin interactions with neighboring or more distant nuclei, measured in hertz. It provides clues to bond order and geometry. In Ernst’s multi-dimensional NMR, J-coupling correlation peaks appear along both axes, enabling deduction of bonding networks even in complex molecules. Couplings become wider in solids due to anisotropy, but sensitivity can be recovered using cross-polarization. Chemists rely on coupling constants for structural determination in synthesis and natural-products research.
multidimensional NMR
An NMR technique that introduces two or more time axes and displays correlations on a plane or in higher-dimensional space. Experiments such as COSY, HSQC, and NOESY reveal bonding and spatial proximity at a glance. Dimensionality resolves peak overlap, enabling analysis of large biomolecules. Although acquisition time grows exponentially, non-uniform sampling and compressed sensing mitigate the burden. Ernst’s theoretical work founded this field.
structure determination
The process of determining the atomic arrangement and three-dimensional conformation of molecules or materials; NMR complements X-ray crystallography and cryo-EM. NMR exploits chemical shifts, J-couplings, NOE distances, and residual dipolar couplings to generate constraints for computational modeling. A unique advantage is access to dynamic structures in solution. It is invaluable for elucidating drug-binding modes and protein-folding mechanisms. Enhanced sensitivity in high-resolution NMR has pushed the molecular-weight limit upward.
protein NMR
A technique for determining backbone and side-chain assignments and 3-D structure of isotopically labeled proteins via multi-dimensional NMR. Sequential assignments are achieved with 3D experiments centered on HSQC, while NOESY provides spatial distances. Conformational fluctuations and interactions can be monitored in real time, supporting drug-screening applications. For proteins above ~30 kDa, TROSY and perdeuteration reduce relaxation losses, extending the feasible size range. Ernst’s multi-dimensional FT concept is the direct foundation of protein NMR.
nuclear Overhauser effect
A phenomenon in which cross-relaxation between different nuclear spins modulates signal intensity, providing distance information for atoms within roughly 5 Å. Cross-peak intensities in a NOESY spectrum allow quantitative distance restraints for structural modeling. It is crucial for studying protein dynamics in solution and ligand–receptor interactions. In solid-state NMR it can trace proton dynamics as well. High-resolution, multi-dimensional NMR techniques have made detection and interpretation of the NOE straightforward.