Dynamic nuclear polarization (DNP) results from transferring spin polarization from electrons to atomic nuclei,thereby aligning the nuclear spins to the extent that electron spins are aligned. Note that the alignment of electron spins at a given magnetic field and temperature is described by the Boltzmann distribution under the thermal equilibrium. It is also possible that those electrons are aligned to a higher degree of order by other preparations of electron spin order such as:chemical reactions,optical pumping and spin injection. DNP is considered one of several techniques for hyperpolarization. DNP can also be induced using unpaired electrons produced by radiation damage in solids.
In chemistry,a nitrene or imene is the nitrogen analogue of a carbene. The nitrogen atom is uncharged and monovalent,so it has only 6 electrons in its valence level—two covalent bonded and four non-bonded electrons. It is therefore considered an electrophile due to the unsatisfied octet. A nitrene is a reactive intermediate and is involved in many chemical reactions. The simplest nitrene,HN,is called imidogen,and that term is sometimes used as a synonym for the nitrene class.
A 1,2-rearrangement or 1,2-migration or 1,2-shift or Whitmore 1,2-shift is an organic reaction where a substituent moves from one atom to another atom in a chemical compound. In a 1,2 shift the movement involves two adjacent atoms but moves over larger distances are possible. In the example below the substituent R moves from carbon atom C2 to C3.
Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a method for studying materials that have unpaired electrons. The basic concepts of EPR are analogous to those of nuclear magnetic resonance (NMR),but the spins excited are those of the electrons instead of the atomic nuclei. EPR spectroscopy is particularly useful for studying metal complexes and organic radicals. EPR was first observed in Kazan State University by Soviet physicist Yevgeny Zavoisky in 1944,and was developed independently at the same time by Brebis Bleaney at the University of Oxford.
The triphenylmethyl radical (often shorted to trityl radical) is an organic compound with the formula (C6H5)3C. It is a persistent radical. It was the first radical ever to be described in organic chemistry. Because of its accessibility,the trityl radical has been heavily exploited.
Chih-Kung Jen was a Chinese physicist who emigrated to the U.S. and participated in some of the 20th century's major scientific,political and social developments in both the United States and China.
The ethynyl radical (systematically named λ3-ethyne and hydridodicarbon(C—C)) is an organic compound with the chemical formula C≡CH (also written [CCH] or C
2H). It is a simple molecule that does not occur naturally on Earth but is abundant in the interstellar medium. It was first observed by electron spin resonance isolated in a solid argon matrix at liquid helium temperatures in 1963 by Cochran and coworkers at the Johns Hopkins Applied Physics Laboratory. It was first observed in the gas phase by Tucker and coworkers in November 1973 toward the Orion Nebula,using the NRAO 11-meter radio telescope. It has since been detected in a large variety of interstellar environments,including dense molecular clouds,bok globules,star forming regions,the shells around carbon-rich evolved stars,and even in other galaxies.
Harden M. McConnell was an American physical chemist. His many awards included the National Medal of Science and the Wolf Prize,and he was elected to the National Academy of Science."
David Hardy Whiffen FRS was an English physicist and pioneer of infrared and Electron Spin Resonance known for the "Whiffen Effect".
Alan Carrington CBE,FRS was a British chemist and one of the leading spectroscopists in Britain in the late twentieth century.
Jack H. Freed is an American chemist known for his pioneering work in electron paramagnetic resonance spectroscopy. He is the Frank and Robert Laughlin Professor of Physical Chemistry,emeritus,at Cornell University in Ithaca,New York.
J. Hugh Nichols served as the County Executive of Howard County,Maryland.
Alexander L’vovich Kovarski is a Russian physical chemist,professor,member of Russian Academy of Natural Sciences,and member of American Chemical Society. His main research area is physical chemistry of polymers and composites,magnetic resonance of free radicals and nano-sized systems.
Merriweather Park at Symphony Woods is a large central park in downtown Columbia,Maryland. The park includes the Chrysalis,a 2016 amphitheater with lawn seating. The Chrysalis has hosted musical performances,ballet,plays,Maker Faire,and numerous community events.
Electron spin resonance dating,or ESR dating,is a technique used to date materials which radiocarbon dating cannot,including minerals,biological materials,archaeological materials and food. Electron spin resonance dating was first introduced to the science community in 1975,when Japanese nuclear physicist Motoji Ikeya dated a speleothem in Akiyoshi Cave,Japan. ESR dating measures the amount of unpaired electrons in crystalline structures that were previously exposed to natural radiation. The age of a substance can be determined by measuring the dosage of radiation since the time of its formation.
George Daniels Watkins is an American solid-state physicist.
A trivalent group 14 radical (also known as a trivalent tetrel radical) is a molecule that contains a group 14 element (E = C,Si,Ge,Sn,Pb) with three bonds and a free radical,having the general formula of R3E•. Such compounds can be categorized into three different types,depending on the structure (or equivalently the orbital in which the unpaired electron resides) and the energetic barrier to inversion. A molecule that remains rigidly in a pyramidal structure has an electron in a sp3 orbital is denoted as Type A. A structure that is pyramidal,but flexible,is denoted as Type B. And a planar structure with an electron that typically would reside in a pure p orbital is denoted as Type C. The structure of such molecules has been determined by probing the nature of the orbital that the unpaired electron resides in using spectroscopy,as well as directly with X-ray methods. Trivalent tetrel radicals tend to be synthesized from their tetravalent counterparts (i.e. R3EY where Y is a species that will dissociate).
Electron resonance imaging (ERI) is a preclinical imaging method,together with positron emission tomography (PET),computed tomography scan,magnetic resonance imaging (MRI),and other techniques. ERI is dedicated to imaging small laboratory animals and its unique feature is the ability to detect free radicals. This technique could also be used for other purposes such as material science,quality of food,etc.
Stable and persistent phosphorus radicals are phosphorus-centred radicals that are isolable and can exist for at least short periods of time. Radicals consisting of main group elements are often very reactive and undergo uncontrollable reactions,notably dimerization and polymerization. The common strategies for stabilising these phosphorus radicals usually include the delocalisation of the unpaired electron over a pi system or nearby electronegative atoms,and kinetic stabilisation with bulky ligands. Stable and persistent phosphorus radicals can be classified into three categories:neutral,cationic,and anionic radicals. Each of these classes involve various sub-classes,with neutral phosphorus radicals being the most extensively studied. Phosphorus exists as one isotope 31P (I = 1/2) with large hyperfine couplings relative to other spin active nuclei,making phosphorus radicals particularly attractive for spin-labelling experiments.
