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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.
Solid-state NMR (ssNMR) spectroscopy is a technique for characterizing atomic level structure in solid materials e.g. powders, single crystals and amorphous samples and tissues using nuclear magnetic resonance (NMR) spectroscopy. The anisotropic part of many spin interactions are present in solid-state NMR, unlike in solution-state NMR where rapid tumbling motion averages out many of the spin interactions. As a result, solid-state NMR spectra are characterised by larger linewidths than in solution state NMR, which can be utilized to give quantitative information on the molecular structure, conformation and dynamics of the material. Solid-state NMR is often combined with magic angle spinning to remove anisotropic interactions and improve the resolution as well as the sensitivity of the technique.
Carbon-13 (C13) nuclear magnetic resonance is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR and allows the identification of carbon atoms in an organic molecule just as proton NMR identifies hydrogen atoms. 13C NMR detects only the 13
C
isotope. The main carbon isotope, 12
C
is not detected. Although much less sensitive than 1H NMR spectroscopy, 13C NMR spectroscopy is widely used for characterizing organic and organometallic compounds.
Proton nuclear magnetic resonance is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the structure of its molecules. In samples where natural hydrogen (H) is used, practically all the hydrogen consists of the isotope 1H.
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.
Vanadium oxytrichloride is the inorganic compound with the formula VOCl3. This yellow distillable liquid hydrolyzes readily in air. It is an oxidizing agent. It is used as a reagent in organic synthesis. Samples often appear red or orange owing to an impurity of vanadium tetrachloride.
Nuclear magnetic resonance quantum computing (NMRQC) is one of the several proposed approaches for constructing a quantum computer, that uses the spin states of nuclei within molecules as qubits. The quantum states are probed through the nuclear magnetic resonances, allowing the system to be implemented as a variation of nuclear magnetic resonance spectroscopy. NMR differs from other implementations of quantum computers in that it uses an ensemble of systems, in this case molecules, rather than a single pure state.
In nuclear chemistry and nuclear physics, J-couplings are mediated through chemical bonds connecting two spins. It is an indirect interaction between two nuclear spins that arises from hyperfine interactions between the nuclei and local electrons. In NMR spectroscopy, J-coupling contains information about relative bond distances and angles. Most importantly, J-coupling provides information on the connectivity of chemical bonds. It is responsible for the often complex splitting of resonance lines in the NMR spectra of fairly simple molecules.
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.
Phosphorus-31 NMR spectroscopy is an analytical chemistry technique that uses nuclear magnetic resonance (NMR) to study chemical compounds that contain phosphorus. Phosphorus is commonly found in organic compounds and coordination complexes, making it useful to measure 31P NMR spectra routinely. Solution 31P-NMR is one of the more routine NMR techniques because 31P has an isotopic abundance of 100% and a relatively high gyromagnetic ratio. The 31P nucleus also has a spin of 1⁄2, making spectra relatively easy to interpret. The only other highly sensitive NMR-active nuclei spin 1⁄2 that are monoisotopic are 1H and 19F.
Fluorine-19 nuclear magnetic resonance spectroscopy is an analytical technique used to detect and identify fluorine-containing compounds. 19F is an important nucleus for NMR spectroscopy because of its receptivity and large chemical shift dispersion, which is greater than that for proton nuclear magnetic resonance spectroscopy.
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).
Cobalt-59 nuclear magnetic resonance is a form of nuclear magnetic resonance spectroscopy that uses cobalt-59, a cobalt isotope. 59Co is a nucleus of spin 7/2 and 100% abundancy. The nucleus has a magnetic quadrupole moment. Among all NMR active nuclei, 59Co has the largest chemical shift range and the chemical shift can be correlated with the spectrochemical series. Resonances are observed over a range of 20000 ppm, the width of the signals being up to 20 kHz. A widely used standard is potassium hexacyanocobaltate (0.1M K3Co(CN)6 in D2O), which, due to its high symmetry, has a rather small line width. Systems of low symmetry can yield broadened signals to an extent that renders the signals unobservable in fluid phase NMR, in these cases signals can still be observable in solid state NMR.
The chemical shift index or CSI is a widely employed technique in protein nuclear magnetic resonance spectroscopy that can be used to display and identify the location as well as the type of protein secondary structure found in proteins using only backbone chemical shift data The technique was invented by David S. Wishart in 1992 for analyzing 1Hα chemical shifts and then later extended by him in 1994 to incorporate 13C backbone shifts. The original CSI method makes use of the fact that 1Hα chemical shifts of amino acid residues in helices tends to be shifted upfield relative to their random coil values and downfield in beta strands. Similar kinds of upfield and downfield trends are also detectable in backbone 13C chemical shifts.
Gareth Alun Morris FRS is a Professor of Physical Chemistry, in the School of Chemistry at the University of Manchester.
Vanadyl perchlorate or vanadyl triperchlorate is a golden yellow coloured liquid or crystalline compound of vanadium, oxygen and perchlorate group. The substance consists of molecules covalently bound and is quite volatile; it ignites organic solvents on contact and explodes at temperatures above 80 °C.
Nitrogen-15 nuclear magnetic resonance spectroscopy is a version of nuclear magnetic resonance spectroscopy that examines samples containing the 15N nucleus. 15N NMR differs in several ways from the more common 13C and 1H NMR. To circumvent the difficulties associated with measurement of the quadrupolar, spin-1 14N nuclide, 15N NMR is employed in samples for detection since it has a ground-state spin of ½. Since14N is 99.64% abundant, incorporation of 15N into samples often requires novel synthetic techniques.
Platinum-195 nuclear magnetic resonance spectroscopy is a spectroscopic technique which is used for the detection and characterisation of platinum compounds. The sensitivity of the technique and therefore its diagnostic utility have increased significantly starting from the 1970s, with 195Pt NMR nowadays considered the method of choice for structural elucidation of Pt species in solution.
References
- ↑ Rehder, D.; Polenova, T.; Bühl, M. (2007). Vanadium-51 NMR. Annual Reports on NMR Spectroscopy. Vol. 62. pp. 49–114. doi:10.1016/S0066-4103(07)62002-X. ISBN 9780123739193.
- ↑ Howarth, Oliver W. (1990). "Vanadium-51 NMR". Progress in Nuclear Magnetic Resonance Spectroscopy. 22 (5): 453–485. doi:10.1016/0079-6565(90)80007-5.
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