The magnets must also have exceptionally high stability for indefinite time periods (months to years), implying that they are typically constructed from persistent superconducting materials. Field strengths in NMR magnets are limited by the properties of these materials, making high-field NMR one of the important scientific drivers for the continuing development of advanced superconducting materials and magnet technology. Higher magnetic fields lead to better NMR data for two main reasons. The first

is spectral resolution: selleck kinase inhibitor The NMR frequency of the nucleus of a particular atom in a molecule or material is proportional to the strength of the external field, but is also affected by the atom’s local chemical and structural environment. As the external field increases, differences between NMR frequencies of different atoms become proportionally larger and easier to measure. One of the most important advances in modern NMR methodology, beginning in the mid-1970s, is the development of “multidimensional” NMR

spectroscopy, in which NMR frequencies detected in multiple time periods within a single RF pulse sequence are correlated with one another. In an N-dimensional NMR spectrum, CDK assay the effect of increasing magnetic field on spectral resolution occurs in each dimension, so that the number of distinct NMR frequencies

that can be measured (which determines the size and complexity of molecules and materials that can be studied by NMR) can increase as roughly the Nth power of the field strength (BN). In practice, in a 3D NMR spectrum of a biological macromolecule such as a protein in aqueous solution in a field of approximately 20 T, NMR signals from more than 10,000 1H, 13C, and 15N nuclei can be resolved from one another and measured accurately. The second main reason Tolmetin why higher fields lead to better NMR data is sensitivity: In available magnets, NMR frequencies typically lie in the 100–1000 MHz range, corresponding to photon energies of 4 × 10−7 to 4 × 10−6 eV (5–50 mK). These low energies imply that the degree of nuclear alignment induced by the magnetic field (i.e., the fractional difference between nuclear spin momenta parallel and antiparallel to the field direction, called the nuclear spin polarization) is typically only 10−6–10−5 at ambient temperature and is proportional to the field strength. NMR signal amplitudes are proportional to the nuclear spin polarization. Because NMR signals are detected inductively, the signal amplitudes are also proportional to NMR frequencies themselves. Thus, signal-to-noise ratios in NMR spectra can be proportional to B2.