However, the technique of magic-angle spinning (MAS), first demon

However, the technique of magic-angle spinning (MAS), first demonstrated

in the late 1950s and improved dramatically in recent years, in which solid samples are rotated very rapidly about an axis at the “magic angle” θM   = cos−1 (1/3) to the magnetic field direction using a pneumatic turbine system, approximates the effects of rotational diffusion, producing solid state NMR line widths that can approach the line widths in solution NMR spectra. Some of the most exciting applications anti-CTLA-4 antibody of solid state NMR are possible only at very high magnetic fields. In solid state NMR of organic and biological systems, strong dipole–dipole interactions among 1H nuclei limit the achievable 1H NMR line widths, even under rapid MAS. Therefore, it is only at the highest available fields

that 1H NMR spectra of complex organic and biological systems become useful. Inorganic systems of practical and chemical interest (e.g., catalysts, glasses, battery materials) prominently contain elements whose NMR spectra are difficult or impossible to measure at low fields, because the nuclei have spin quantum numbers greater than 1/2 (e.g., 7Li, 17O, 27Al). These nuclei possess electric quadrupole interactions, which are averaged out to lowest order by MAS but make a second-order contribution to the NMR line Copanlisib mouse widths that is inversely proportional to the magnetic field strength. For these reasons, NMR spectra of many technologically important materials are useful only if very high field equipment is used, and are increasingly informative as the field increases. In studies of biological systems, NMR is one of the two major types of Tolmetin measurements that can be used to reveal the full 3D molecular structures of macromolecules, especially proteins and nucleic acids, the other being X-ray diffraction measurements on single crystals. In addition to purely structural information, NMR measurements have the unique capability of providing detailed, site-specific information about molecular motions in macromolecules, including motions that are essential for biological function. While X-ray diffraction

measurements are largely restricted to highly structurally ordered molecules in crystalline environments, NMR methods are applicable to proteins and nucleic acids in fluid environments that more closely resemble the cytoplasmic and membrane environments of cells. Perturbations of NMR signals due to intermolecular interactions are used in the screening of molecular libraries for binding to pharmaceutically important macromolecular targets, providing an efficient approach to the identification of new lead compounds in drug development. NMR methods are also applicable to molecules that are intrinsically disordered, resistant to crystallization, and (in the case of solid state NMR) inherently non-crystalline and insoluble.

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