The specific absorption and re-emission of electromagnetic radiation at characteristic wavelengths by atomic nuclei in a magnetic field. It is abbreviated NMR. The wavelength of the radiation absorbed depends on the type of nucleus, the intensity of the magnetic field, and the local chemical environment in which the nucleus resides. It is the latter effect (called the chemical shift), by which atoms of specific elements in different chemical compounds show a different resonance frequency, which gives rise to the greatest utility of this phenomenon in analyzing the chemical structure of substances. Similar effects of the chemical environment permit the discrimination of different types of living tissue by virtue of their different chemical composition, thus permitting utilization of the phenomenon in medical diagnostic instruments, especially for magnetic resonance imaging.
A spectroscopic technique used to determine the 3-D structure of small- to medium-sized proteins. NMR is based on resonant absorption of electromagnetic radiation by the magnetic dipole moments of atomic nuclei in an applied magnetic field.
(NMR) - the absorption or emission of electromagnetic energy by nuclei in a static magnetic field, after excitation by a suitable RF magnetic field. The peak resonance frequency is proportional to the magnetic field, and is given by the Larmor equation. Only nuclei with a non-zero spin exhibit NMR.
a technique for elucidating molecular structures by utilising the principle that nuclei of some isotopes behave like spinning magnets which when exposed to a particular magnetic field and electromagnetic wave length (radiowaves) can absorb energy.
(NMR) A technique for determining the three-dimensional structure of large molecules.
(NMR) A method which uses value of the absorption energy for the change in spin of a nucleus to characterize the local structure around the atom containing that nucleus. In the solid state, NMR is used to investigate the magnetic properties of a material.
A procedure used to determine the property of electrons in motion around an atomic nucleus that can be perturbed with the addition of a magnetic field, and used to determine the structure of a molecule. In protein studies, NMR is used to determine structure. See also Structural Biology.
NMR spectroscopy makes it possible to discriminate nuclei, typically protons, in different chemical environments. The electron distribution gives rise to a chemical shift of the resonance frequency. The chemical shift of a nucleus is expressed in parts per million (ppm) by its frequency, n, relative to a standard, ref, and defined as = 106 (n - ref)/o, where o is the operating frequency of the spectrometer. It is an indication of the chemical state of the group containing the nucleus. More information is derived from the spin-spin couplings between nuclei, which give rise to multiplet patterns. Greater detail may be derived from two- or three- dimensional techniques. These use pulses of radiation at different nuclear frequencies, after which the response of the spin system is recorded as a free- induction decay (FID). Multidimensional techniques, such as COSY and NOESY, make it possible to deduce the structure of a relatively complex molecule such as a small protein (molecular weight up to 25,000).
resonance of protons to radiation in a magnetic field
A diagnostic test that uses the properties of different substances in a magnetic field to produce images of the brain, spinal cord, and other parts of the body.
NMR spectroscopy is useful for chemical analysis and determining the structure of molecules because the resonance frequency of a particular element are influenced by the atom's chemical surroundings. It can determine the chemical structure of organic compounds.
See Magnetic Resonance Imaging.
Nuclear magnetic resonance (NMR) is a type of radio-frequency spectroscopy based on the magnetic field generated by the spinning of electrically charged atomic nuclei. This nuclear magnetic field is caused to interact with a very large (1 T - 5 T) magnetic field of the instrument magnet. NMR techniques have been applied to studies of electron densities and chemical bonding and has become a fundamental research tool for structure determinations in organic chemistry.
nmr) spectroscopy: a form of spectroscopy which depends on the absorption and emission of energy arising from changes in the spin states of the nucleus of an atom. [For aggregates of atoms, as in molecules, minor variations in these energy changes are caused by the local chemical environment. The energy changes used are in the radiofrequency range of the electromagnetic spectrum and depend upon the magnitude of an applied magnetic field.
A spectroscopic technique used by scientists to elucidate chemical structure and molecular dynamics. [ Chapter 1
An imaging technique which relies on the way some atoms have a nucleus that spins. When a sample is put in a magnetic field, some of its nuclei align themselves with that field. Radio waves tuned to the frequency at which those nuclei spin (or resonate) are used to knock them out of alignment. When the radio is turned off, the nuclei fall back into line, releasing pulses of radio waves that the imaging machine uses to build up a picture.
Nuclear magnetic resonance (NMR) is a physical phenomenon based upon the magnetic properties of an atom's nucleus. All nuclei that contain odd numbers of nucleons and some that contain even numbers of nucleons have an intrinsic magnetic moment. The most commonly used nuclei are hydrogen-1 and carbon-13, although certain isotopes of many other elements nuclei can also be observed.