Nitroxide group

There are only a few fimctional groups that contain an unpaired electron and yet are stable in a wide variety of structural environments. The best example is the nitroxide group, and numerous specific nitroxide radicals have been prepared and characterized. The unpaired electron is delocalized between nitrogen and oxygen in a structure with an N—O bond order of 1.5. 

Many nitroxides are very stable under normal conditions, and heterolytic reactions can be carried out on other fimctional groups in the molecule without destroying the nitroxide group. Nitroxides are very useful in biochemical studies by virtue of being easily detected paramagnetic probes. ... 

One obvious way in which to attach a nitroxide group to B12 is to simple alkylate Cob(I)aiamin with a suitable nitroxide derivative. This would result in having the nitroxide covalently bound to the corrinoid at the upper axial coordination position of the cobalt. Such a procedure is outlined in Fig. 19. In this reaction 4-bromoacetamido 2,2,6,6-tetra-methylpiperidine-N-oxyl is used to alkylate Cob(I)alamin. This results in a Co(III)-nitroxalkylcobalamin. The corresponding cobinamide can then be produced by hydrolyzing the ribose-phosphate linkage (119). 

It is quite common to observe that the lines in a nitroxide spectrum show variations in width. One feature which contributes to this is the anisotropy of the nitroxide grouping, as a consequence of which the high field component of the nitrogen triplet may be perceptibly broadened. This effect is particularly noticeable when free tumbling of the nitroxide molecule is restricted either by the viscosity of the solvent or when the radical is incorporated into a very large (e.g. polymer) molecule. This selective line broadening is, of course, one of the principal sources of information in spin-labelling experiments (Berliner, 1976). 

Using the grafting-from method with NMP requires the synthesis and (co)polymerization of monomers that contain the nitroxide group [Hawker et al., 2001]. A halogen-containing monomer such as vinyl chloroacetate or p-chloromethylstyrene is reacted with an HO-containing alkoxyamine to yield a vinyl alkoxyamine, which is used as a NMP initiator to... 

In the present section we show how the immunochemistry of model membranes can depend on the lateral mobilities of membrane components. Most of our studies of the immunochemistry of model membranes have taken advantage of the discovery by Humphries and McConnell21 that it is possible to prepare specific antibodies against the paramagnetic nitroxide group... 

Spin traps come in basically two types nitroso compounds and nitrone compounds. Reactive free radicals react with the carbon of the nitrone functional group to form a radical adduct that always has a nitroxide group, which is an unusually stable type of free radical. Nitrones are the most useful spin traps for the in vivo detection of free radical metabolites because of the stability of the resulting radical adduct. However, identification of the parent radicals can be difficult because adducts derived from different radicals often have very similar EPR spectra. A comprehensive review of this area through 1992 has recently been published [48]. 

The localization of a nitroxide in a membrane [30] depends upon the relative polarity of the nitroxide moiety and other polar groups that may be present in the molecules. If the nitroxide group is the only polar group, then the molecule will orient itself in the membrane so that the nitroxide is located in the aqueous phase. The cholestane spin label is one such example. If groups more polar than the nitroxide are present, then the nitroxide will be found within the bilayer. For example, doxyl-labeled fatty acids are oriented such that the carboxyl group is in the aqueous layer and the nitroxide is down within the membrane. 

The molecules used in this study were 4/,4 -dimethylspiro [5-andro-stan-l/ -ol-3-2 -( l, 3 -oxazolidine-3-oxyl)] and 4, 4 -dimethylspiro[choles-tane-3-2 -(l, 3 -oxazolidine-3 -oxyl)]. To simplify identification we refer to them as 612 and 611 respectively, their source (8) catalog numbers. Figure 1 shows the structure of these compounds along with their identifying numbers. Note that the major parts of the two molecules—namely the steroid skeleton and nitroxide group—are the same. The difference in these molecules occurs at the 17 position at one end of the ellipsoid. ... 

It may be seen from the clear aromatic vibronic progression that the fluorescence spectrum is that of phenanthrene, the chromophore present in TMDBIO. This fluorescence, before trapping of the alkyl radicals, was suppressed by the spin-orbit coupling of the nitroxide group located on the iso-indoline framework as seen from its structure (Introduction). The dependence of the fluorescence on the nitroxide concentration may be seen in Figure 6. 

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