Nuclear magnetic resonance activity

Both °B and "B nuclei are NMR (nuclear magnetic resonance) active. Because of the high content, high resonant frequency, and lower nuclear quadrupole moment, the NMR spectroscopy of the "B nucleus is generally observed [66]. Trivalent or quadrivalent boron can be comfortably differentiated by means of a chemical shift of "B trivalent>0 ppm>quadrivalent (d value). Thus, the electron density on the boron atom can also estimated with the chanical shift. In this way, "B NMR spectroscopy is a potent tool for structural analyses of boron-containing materials. 

As with other diffraction techniques (X-ray and electron), neutron diffraction is a nondestructive technique that can be used to determine the positions of atoms in crystalline materials. Other uses are phase identification and quantitation, residual stress measurements, and average particle-size estimations for crystalline materials. Since neutrons possess a magnetic moment, neutron diffraction is sensitive to the ordering of magnetically active atoms. It differs from many site-specific analyses, such as nuclear magnetic resonance, vibrational, and X-ray absorption spectroscopies, in that neutron diffraction provides detailed structural information averaged over thousands of A. It will be seen that the major differences between neutron diffraction and other diffiaction techniques, namely the extraordinarily... 

Urry, D. W. Nuclear magnetic resonance and the conformation of membrane-active peptides. In Enzymes of Biological Membranes, Vol. 1, (ed. Martonosi, A ), p. 31, Plenum Publishing Corp., New York 1976... 

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

Nagayama et al. [36] studied a-sulfonation using nuclear magnetic resonance (NMR). They reported the presence of two intermediates. The first intermediate is the adduct of S03 to the carbonyl oxygen formed at low temperatures. In contrast to the mechanism of Stein et al., they did not propose a rearrangement of this intermediate but a second addition of S03 to the activated a-hydrogen to give the second intermediate. The reaction of the intermediate with sodium hydroxide can lead to the disodium salt if the neutralization is immediate or to the sodium a-sulfo fatty acid ester if the neutralization is delayed. 

Flohr S, Kurz M, Kostenis E, Brkovich A, Fournier A, Klabunde T. Identification of nonpeptidic urotensin II receptor antagonists by virtual screening based on a pharmacophore model derived from structure-activity relationships and nuclear magnetic resonance studies on urotensin II. J Med Ghent 2002 45 1799-805. 

Exchange reactions can be sometimes investigated by the techniques of polari-metry, nuclear magnetic resonance and electron spin resonance. The optical activity method requires polarimetric measurements on the rate of racemization in mixtures of d-X (or /-X) and /-Y (or d-Y). 

The development and reports of methods for colorless chlorophyll derivative (RCCs, FCCs, and NCCs) analysis are relatively recent and the structures of the compounds are being elucidated by deduction from their chromatographic behaviors, spectral characteristics (UV-Vis absorbance spectra), mass spectrometry, and nuclear magnetic resonance analysis. The main obstacle is that these compounds do not accumulate in appreciable quantities in situ and, moreover, there are no standards for them. The determination of the enzymatic activities of red chlorophyll catabolite reductase (RCCR) and pheophorbide a monoxygenase (PAO) also helps to monitor the appearance of colorless derivatives since they are the key enzymes responsible for the loss of green color. ... 

Electrochemical nuclear magnetic resonance (NMR) is a relatively new technique that has recently been reviewed (Babu et al., 2003). NMR has low sensitivity, and a typical high-held NMR instrument needs 10 to 10 NMR active atoms (e.g., spins), to collect good data in a reasonable time period. Since 1 cm of a single-crystal metal contains about 10 atoms, at least 1 m of surface area is needed to meet the NMR sensitivity requirement. This can be met by working with carbon-supported platinum... 

The release of iron from intracellular ferritin stores is thought to involve the reduction of Fe to Fe " (Funk et al., 1985) and one would expect this reduction to be fecilitated by the low oxygen tension, increased levels of reducing species and the low pH shown by nuclear magnetic resonance (NM to be as low as 6.9 after only 6 h of cold storage (Fuller et al., 1988). Exogenous redox-active quinones such as adriamycin have been shown to catalyse lipid peroxidation in the presence of ferritin under hypoxic conditions (Vile and Winterbourne, 1988), and lipid peroxidation is stimulated in micro-somes in the presence of purified ferritin and flavin... 

As active substances are separated and purified they are characterized by a combination of spectroscopic analyses and chemical correlations. Particularly useful spectroscopic analysis techniques are nuclear magnetic resonance (proton and carbon), mass spectrometry and Infra-red and ultraviolet spectrophotometry. 

In general, several spectroscopic techniques have been applied to the study of NO, removal. X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) are currently used to determine the surface composition of the catalysts, with the aim to identify the cationic active sites, as well as their coordinative environment. 

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