The aqueous reference for ESR oximetry

A paramagnetic molecular voltmeter

“…In particular, the relaxation rates become extremely large for tempone with added Fe(CN) 6 3-above 10 mM, suggesting coordination forces that are strong enough between these two smallest agents to form a complex. This may be similar to the evidence for a hydrophobic interaction between oxygen and small nitroxides found by Diakova and Bryant (86). Nevertheless, in all cases there is an extensive linear range over which relaxivities can be measured (Table 2).…”

Electron spin resonance

“…The results imply that nitroxide based ESR oximetry may suffer a reference concentration shift of about a factor of two if the aqueous nitroxide spectrum is used as the reference. 11 A study has been made of the molecular dynamics of the spin probe TEMPO (2,2,5,5-teramethylpyrroline-N-oxyl) dissolved in some ionic liquids. In some examples, the effect of restricted rotational motion can be rationalised according to simple hydrodynamic theories (e.g.…”

“…Two distinct adsorbed fractions are detected in each sample, characterised by activation energies in the range 2-6 kJ/mol and 12-16 kJ/mol, respectively. 204 In order to provide a check of the compatibility of the activation parameters determined using methods of muon spectroscopy with the more common approach of using stable spin-probes (nitroxides) and measuring the temperature dependence of their ESR spectra, nitroxide radicals (11), (12) were formed by adding the light hydrogen isotope, muonium to the spin traps DMPO (5,5-dimethyl-1-pyrroline-N-oxide) and PBN (N-tert-butyl-a-phenylnitrone) adsorbed as 30 wt% ethanol solutions in silica-gel.…”

Complexation of molecular oxygen with nitroxide radicals adsorbed on the surface of silica and MCM-41

“…This effect is used for the determination of oxygen concentrations in liquid and biological objects. [8][9][10][11][12][13][14] The observed strong broadening effect is caused by high oxygen concentration and accessibility of adsorbed radicals for oxygen molecules.The change of ESR spectrum after oxygen inflow at 77 K is presented in Figure 2, which shows the spectra normalized to 2 25 G 1 Figure 1 ESR spectra of TEMPO adsorbed on silica surface (1) under vacuum and (2) in the presence of 106 Torr O 2 at 293 K. † The stable radicals 2,2,6,6-tetramethylpiperidine oxyl (TEMPO) and 2,2,6,6-tetramethyl-4-oxopiperidine oxyl (TEMPON) were used without additional purification. Experiments were carried out in quartz ESR ampoules with an inner diameter of ~3 mm equipped with a vacuum valve.…”

“…This effect is used for the determination of oxygen concentrations in liquid and biological objects. [8][9][10][11][12][13][14] The observed strong broadening effect is caused by high oxygen concentration and accessibility of adsorbed radicals for oxygen molecules.…”