Dependence of electron paramagnetic resonance spectral lineshapes on molecular tumbling: Nitroxide radical in water:glycerol mixtures

2016 ◽  
Vol 45A (5) ◽  
pp. e21423 ◽  
Author(s):  
Ashley Clark ◽  
Jessica Sedhom ◽  
Hanan Elajaili ◽  
Gareth R. Eaton ◽  
Sandra S. Eaton
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Nitroxide Radical ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic

scholarly journals Dihydroxy-Substituted Coumarins as Fluorescent Probes for Nanomolar-Level Detection of the 4-Amino-TEMPO Spin Label

2019 ◽  
Vol 20 (15) ◽  
pp. 3802 ◽  
Author(s):  
Krzysztof Żamojć ◽  
Magdalena Zdrowowicz ◽  
Aleksandra Hać ◽  
Maciej Witwicki ◽  
Paweł Błażej Rudnicki-Velasquez ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Electron Paramagnetic Resonance ◽  
Cancer Cells ◽  
Fluorescence Intensity ◽  
Spin Label ◽  
Nitroxide Radical ◽  
Prostate Cancer Cells ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic ◽  
Substituted Coumarins

This paper reports on dihydroxycoumarins as fluorescent probes suitable for the detection and determination of the nitroxide radical, namely 4-amino-TEMPO. Since 4-amino-TEMPO is used as a spin label for the detection of various radicals and damage caused by these species, its determination under physiological conditions might help us to understand the mechanism of the oxidative stress. Among different coumarins studied, only dihydroxy-substituted derivatives show high sensitivity, specificity, and selectivity for the nitroxide radical. In this assay, dihydroxy-substituted coumarins under the action of 4-amino-TEMPO show a very fast and significant increase in fluorescence intensity and lifetime. Among them 6,7-dihydroxycoumarin (esculetin) exhibits the strongest fluorescence enhancement (up to 40 times), with an estimated limit of detection equal to 16.7 nM—a significantly lower value when compared with UV-Vis or electron paramagnetic resonance (EPR) spectroscopy. The method is characterized by an easy procedure of sample preparation and very short time of analysis. The mechanism of the interaction between 6,7-dihydroxycoumarin and 4-amino-TEMPO has been examined with the use of a series of complementary techniques, such as steady-state and time-resolved fluorescence spectroscopy, UV-Vis spectroscopy, electron paramagnetic resonance spectroscopy, potentiometric titration, and high-performance liquid chromatography. It has been proven that the only route of the reaction in the system studied is a proton transfer from the molecule of esculetin to the amino group of the nitroxide. Biological studies performed on prostate cancer cells, breast cancer cells, and normal skin fibroblasts revealed significant anticancer properties of 6,7-dihydroxycoumarin, which caused a considerable decrease in the viability and number of cancer cells, and affected their morphology, contrary to normal fibroblasts. Furthermore, the experiment performed on prostate cancer cells showed that fluorescence emission of esculetin is closely related to intracellular pH—the higher pH, the higher observed fluorescence intensity (in accordance with a chemical experiment). On the other hand, the studies performed in different pH levels revealed that when pH of the solution increases, the observed fluorescence intensity enhancement under the action of 4-amino-TEMPO decreases (better sensing properties of esculetin towards the nitroxide in lower pH).

ANTIOXIDANT ACTIVITY OF SOME TYPES OF WHITE WINES AND JUICES INVESTIGATED BY EPR SPECTROSCOPY

2008 ◽  
Vol 22 (27) ◽  
pp. 2689-2698 ◽  
Author(s):  
DINA PETRISOR ◽  
GRIGORE DAMIAN ◽  
SIMION SIMON ◽  
ANAMARIA HOSU ◽  
VASILE MICLAUS
Keyword(s):  
Antioxidant Activity ◽  
Electron Paramagnetic Resonance ◽  
Epr Spectroscopy ◽  
Nitroxide Radical ◽  
Paramagnetic Species ◽  
Paramagnetic Resonance ◽  
White Wines ◽  
Antioxidant Characteristics ◽  
Electron Paramagnetic ◽  
Stable Free Radicals

Two types of white wines with different places of provenience, and a few types of commercial and natural juices were chosen for preliminary studies of their antioxidant characteristics by using Electron Paramagnetic Resonance (EPR) spectroscopy. Antioxidant capacity of these samples was assessed using stable free radicals such as nitroxide radical Tempol (2,2,6,6-tetramethyl-4-hydroxypiperidine-oxyl), as a paramagnetic agent. The inhibition by antioxidants of the absorbance of the paramagnetic species was found to decrease in time with different rates, and was correlated to the antioxidant activity of the studied samples. The obtained results permit us to make a brief evaluation of the main antioxidative characteristics of the studied wines and juices samples.

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