Electron paramagnetic resonance spectroscopy stable free radicals

One of the earliest reports of LO inhibition concerned the effects of ortho-dihydroxybenzene (catechol) derivatives on soybean 15-LO [58]. Lipophilic catechols, notably nordihydroguaiaretic acid (NDGA) (19), were more potent (10 /zM) than pyrocatechol itself. The inactivation was, under some conditions, irreversible, and was accompanied by oxidation of the phenolic compound. The orfAo-dihydroxyphenyl moiety was required for the best potency, and potency also correlated with overall lipophilicity of the inhibitor [61]. NDGA and other phenolic compounds have been shown by electron paramagnetic resonance spectroscopy to reduce the active-site iron from Fe(III) to Fe(II) [62] one-electron oxidation of the phenols occurs to yield detectable free radicals [63]. Electron-poor, less easily oxidized catechols form stable complexes with the active-site iron atom [64]. 

The existence of free hydroxyl radicals in photo-initiated AOPs can be proven by applying a well-established method, the so-called spin trapping technique. The diamagnetic spin trap 5,5 -dimethyl-1-pyrroline N-oxide (DMPO) forms a stable paramagnetic spin-adduct with OH radicals. Its formation can be detected by electron paramagnetic resonance (EPR) spectroscopy. The underlying chemistry of... 

Simatos et al. (1981) measured the mobility of a spin-label probe, TEMPO, a stable free radical commonly used for electron paramagnetic resonance (EPR) spectroscopy. She found that the probe showed no mobility below a critical that correlated to Wq. A critical a also existed at which the probe demonstrated a partitioning into a dissolved and a solid-like state. This critical a could represent the moisture content correlating to Tg, though this concept had not been introduced in foods at that time. The partitioning of a... 

Electron spin resonance spectroscopy (ESR), also known as electron paramagnetic resonance (EPR), is based on the property that an unpaired electron placed in a magnetic field shows a typical resonance energy absorption spectrum sensitive to its environment. Recently, this technique, which was primarily developed for biological studies of membrane properties, has been adapted for the study of adsorbed polymer/surfactant layers. The mobility of the ESR probe (stable free radical incorporated into the polymer or surfactant molecule) depends of orientation of the surfactant or polymer and the viscosity of the local environment around the probe. 

Another useful method for investigations of water/C02 emulsions and microemulsions is electron paramagnetic resonance (EPR) spectroscopy, because no transparent samples are necessary [9,13]. Furthermore, data from EPR experiments can provide information about the polarity of the local environment of the EPR-active compound. The diagnostic unpaired electron(s) can be introduced either through stable free radicals or by using transition metal ions such as Mn. The active moieties may be incorporated directly in the surfactant [17,18] or added as a soluble probe molecule such as TEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidin-Toxyl) [9]. 

Electron paramagnetic resonance (EPR), also called electron spin resonance (ESR) spectroscopy, is used to determine the electron spin for atoms with unpaired electrons. Most atoms have electrons that are paired together, because this makes them more stable. But radicals do not have spin pairs, and they can be tested using this method. Free radicals are often short-lived species, but they are also very important in the outcome of a chemical reaction. So when you can track their progress, you can better understand the mechanisms of chemical reactions. 

---