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In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of a molecule. Chemical shifts are also used to describe signals in other forms of spectroscopy such as photoemission spectroscopy.
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. This spectroscopy is based on the measurement of absorption of electromagnetic radiations in the radio frequency region from roughly 4 to 900 MHz. Absorption of radio waves in the presence of magnetic field is accompanied by a special type of nuclear transition, and for this reason, such type of spectroscopy is known as Nuclear Magnetic Resonance Spectroscopy. The sample is placed in a magnetic field and the NMR signal is produced by excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is detected with sensitive radio receivers. The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups. As the fields are unique or highly characteristic to individual compounds, in modern organic chemistry practice, NMR spectroscopy is the definitive method to identify monomolecular organic compounds.
Nuclear magnetic resonance spectroscopy of proteins is a field of structural biology in which NMR spectroscopy is used to obtain information about the structure and dynamics of proteins, and also nucleic acids, and their complexes. The field was pioneered by Richard R. Ernst and Kurt Wüthrich at the ETH, and by Ad Bax, Marius Clore, Angela Gronenborn at the NIH, and Gerhard Wagner at Harvard University, among others. Structure determination by NMR spectroscopy usually consists of several phases, each using a separate set of highly specialized techniques. The sample is prepared, measurements are made, interpretive approaches are applied, and a structure is calculated and validated.
The residual dipolar coupling between two spins in a molecule occurs if the molecules in solution exhibit a partial alignment leading to an incomplete averaging of spatially anisotropic dipolar couplings.
Physical organic chemistry, a term coined by Louis Hammett in 1940, refers to a discipline of organic chemistry that focuses on the relationship between chemical structures and reactivity, in particular, applying experimental tools of physical chemistry to the study of organic molecules. Specific focal points of study include the rates of organic reactions, the relative chemical stabilities of the starting materials, reactive intermediates, transition states, and products of chemical reactions, and non-covalent aspects of solvation and molecular interactions that influence chemical reactivity. Such studies provide theoretical and practical frameworks to understand how changes in structure in solution or solid-state contexts impact reaction mechanism and rate for each organic reaction of interest.
Magnetic Resonance in Chemistry is a monthly peer-reviewed scientific journal covering the application of NMR, ESR, and NQR spectrometry in all branches of chemistry. The journal was established in 1969 and is published by John Wiley & Sons. The editors-in-chief are Roberto R. Gil and Gary E. Martin.
Herbert Sander Gutowsky was an American chemist who was a professor of chemistry at the University of Illinois Urbana-Champaign. Gutowsky was the first to apply nuclear magnetic resonance (NMR) methods to the field of chemistry. He used nuclear magnetic resonance spectroscopy to determine the structure of molecules. His pioneering work developed experimental control of NMR as a scientific instrument, connected experimental observations with theoretical models, and made NMR one of the most effective analytical tools for analysis of molecular structure and dynamics in liquids, solids, and gases, used in chemical and medical research, His work was relevant to the solving of problems in chemistry, biochemistry, and materials science, and has influenced many of the subfields of more recent NMR spectroscopy.
In vivo magnetic resonance spectroscopy (MRS) is a specialized technique associated with magnetic resonance imaging (MRI).
Carbohydrate NMR spectroscopy is the application of nuclear magnetic resonance (NMR) spectroscopy to structural and conformational analysis of carbohydrates. This method allows the scientists to elucidate structure of monosaccharides, oligosaccharides, polysaccharides, glycoconjugates and other carbohydrate derivatives from synthetic and natural sources. Among structural properties that could be determined by NMR are primary structure, saccharide conformation, stoichiometry of substituents, and ratio of individual saccharides in a mixture. Modern high field NMR instruments used for carbohydrate samples, typically 500 MHz or higher, are able to run a suite of 1D, 2D, and 3D experiments to determine a structure of carbohydrate compounds.
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is widely used to determine the structure of organic molecules in solution and study molecular physics and crystals as well as non-crystalline materials. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI).
Instrumental analysis is a field of analytical chemistry that investigates analytes using scientific instruments.
Antony John Williams is a British chemist and expert in the fields of both nuclear magnetic resonance (NMR) spectroscopy and cheminformatics at the United States Environmental Protection Agency. He is the founder of the ChemSpider website that was purchased by the Royal Society of Chemistry in May 2009. He is a science blogger and an author.
Nuclear magnetic resonance crystallography is a method which utilizes primarily NMR spectroscopy to determine the structure of solid materials on the atomic scale. Thus, solid-state NMR spectroscopy would be used primarily, possibly supplemented by quantum chemistry calculations, powder diffraction etc. If suitable crystals can be grown, any crystallographic method would generally be preferred to determine the crystal structure comprising in case of organic compounds the molecular structures and molecular packing. The main interest in NMR crystallography is in microcrystalline materials which are amenable to this method but not to X-ray, neutron and electron diffraction. This is largely because interactions of comparably short range are measured in NMR crystallography.
Gary Martin is an American chemist and expert in the fields of both NMR spectroscopy and medicinal chemistry. He is a distinguished fellow at the Merck Research Laboratories. He is also a photographer specializing in the capture of images of lighthouses, especially under conditions of extreme weather.
Nucleic acid NMR is the use of nuclear magnetic resonance spectroscopy to obtain information about the structure and dynamics of nucleic acid molecules, such as DNA or RNA. It is useful for molecules of up to 100 nucleotides, and as of 2003, nearly half of all known RNA structures had been determined by NMR spectroscopy.
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Gareth Alun Morris FRS is a Professor of Physical Chemistry, in the School of Chemistry at the University of Manchester.
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A chemical graph generator is a software package to generate computer representations of chemical structures adhering to certain boundary conditions. The development of such software packages is a research topic of cheminformatics. Chemical graph generators are used in areas such as virtual library generation in drug design, in molecular design with specified properties, called inverse QSAR/QSPR, as well as in organic synthesis design, retrosynthesis or in systems for computer-assisted structure elucidation (CASE). CASE systems again have regained interest for the structure elucidation of unknowns in computational metabolomics, a current area of computational biology.
References
- ↑ Jaspars, Marcel (1 January 1999). "Computer assisted structure elucidation of natural products using two-dimensional NMR spectroscopy". Natural Product Reports. 16 (2): 241–248. doi:10.1039/A804433C.
- ↑ Elyashberg, Mikhail; Argyropoulos, Dimitris (July 2021). "Computer Assisted Structure Elucidation (CASE): Current and future perspectives". Magnetic Resonance in Chemistry. 59 (7): 669–690. doi:10.1002/mrc.5115. S2CID 226987735.
- ↑ Nuzillard, Jean-Marc; Massiot, Georges (1991). "Logic for structure determination". Tetrahedron. 47 (22): 3655–3664. doi:10.1016/S0040-4020(01)80878-4.
- ↑ Nuzillard, Jean-Marc; Plainchont, Bertrand (June 2018). "Tutorial for the structure elucidation of small molecules by means of the LSD software" (PDF). Magnetic Resonance in Chemistry. 56 (6): 458–468. doi:10.1002/mrc.4612. PMID 28543725. S2CID 31073776.
- ↑ Steinbeck, Christoph (Nov–Dec 2001). "SENECA: A platform-independent, distributed, and parallel system for computer-assisted structure elucidation in organic chemistry". Journal of Chemical Information and Computer Sciences. 41 (6): 1500–1507. doi:10.1021/ci000407n. PMID 11749575.
- ↑ Lindel, Thomas; Junker, Jochen; Köck, Matthias (1999). "2D-NMR-Guided Constitutional Analysis of Organic Compounds Employing the Computer Program COCON". European Journal of Organic Chemistry. 1999 (3): 573–577. doi:10.1002/(SICI)1099-0690(199903)1999:3<573::AID-EJOC573>3.0.CO;2-N.
- ↑ Köck, Matthias; Lindel, Thomas; Junker, Jochen (Aug 2021). "Incorporation of 4J-HMBC and NOE Data into Computer-Assisted Structure Elucidation with WEBCOCON". Molecules. 26 (16): 4846. doi: 10.3390/molecules26164846 . PMC 8398166 . PMID 34443433.
- ↑ Kessler, Pavel; Godejohann, Markus (June 2018). "Identification of tentative marker in Corvina and Primitivo wines with CMC-se". Magnetic Resonance in Chemistry. 56 (6): 480–492. doi:10.1002/mrc.4712. PMID 29330878. S2CID 1725448.
- ↑ Elyashberg, Mikhail; Williams, Antony (Nov 2021). "ACD/Structure Elucidator: 20 Years in the History of Development". Molecules. 26 (21): 6623. doi: 10.3390/molecules26216623 . PMC 8588187 . PMID 34771032.
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