Paramagnetic probes

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. ... 

Studies on the formation and reactivity of P-centered radicals continue to be a versatile source of mechanistic information and reactions of interest in synthetic chemistry. Various new persistent or stable P-centered radicals have been described and could find applications as paramagnetic probes. The possibility of influencing the properties of organic free radicals bearing an appropriately located phosphorus group should find interesting applications. 

PGSE-NMR provides direct information on the translational mobility of a liquid medium capable of swelling a given CFP. The self-diffusion coefficient of the swelling agent is found to be related to the nanoporosity of the matrix as determined from ISEC and to the rotational correlation time of a suitable paramagnetic probe (ESR) [22]. 

In a fourth experiment, a paramagnetic probe can be used to determine the proximity from the ATP-binding site of non-competitive inhibitors. An MnATP probe is generated by the addition of Mn ions to ATP [51]. The... 

In the absence of an endogenous centre, the specificity of relaxation data can be improved by introducing in known positions paramagnetic probes. The unpaired electron spin enhances the relaxation rate of the surrounding nuclei in a distance-dependent fashion. In this way, it is possible to evaluate specific interaction sites between a marked polymer and the small molecules. 

This approach was followed by Yushmanov for the localization of papaverine in ionic micelles.42 Another interesting application was reported by Chien43 who measured 19F NMR relaxation times of trifluor-omethyl labelled atrazine induced by paramagnetic probes gadolinium ethylenediamine tetraacetic acid and 2,2,6,6-tertramethyl-piperidine-N-oxyl. The results showed that atrazine solubilized by humic micelles occupied a hydrophobic domain accessible only to neutral hydrophobic molecules. 

Hyperfine interaction has also been used to study adsorption sites on several catalysts. One paramagnetic probe is the same superoxide ion formed from oxygen-16, which has no nuclear magnetic moment. Examination of the spectrum shown in Fig. 5 shows that the adsorbed molecule ion reacts rather strongly with one aluminum atom in a decationated zeolite (S3). The spectrum can be resolved into three sets of six hyperfine lines. Each set of lines represents the hyperfine interaction with WA1 (I = f) along one of the three principal axes. The fairly uniform splitting in the three directions indicates that the impaired electron is mixing with an... 

MCBRIDE Paramagnetic Probes of Layer Silicate Surfaces... 

The Na+- and Ca2+-saturated montmorilIonite, saponite and beidel-lite were obtained from Dr. J. L. McAtee, Chemistry Department, Baylor University. These minerals had been purified and prepared by methods described by Callaway and McAtee (15). Included in this paper for purposes of comparison are relevant data from previous studies in which hectorite and vermiculite had been doped with paramagnetic probes ( 7, 10). The chemical formulae of the low-Fe smectites and mermiculite are reported in Table I. 

The paramagnetic probes detected heterogeneity of swelling behavior in smectites that was not obvious from X-ray diffraction data, presumably caused by variation of charge density on different clay layers within the same smectite sample. 

Two different kinetic approaches have been used to obtain mechanistic information [15,16]. Kinetic studies carried out by EPR spectroscopy using fusinite as a paramagnetic probe of the oxygen concentration allowed the oxidizability of poly(hydrosilane)s to be obtained [15]. Oxidizability values of 1.8 x 10 and... 

This task can be achieved by increasing the molecular size of the paramagnetic complex. In fact, by considering the paramagnetic probe as an isotropically tumbling sphere, it is expected that and molecular size (commonly assumed to increase linearly with the molecular weight) are... 

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