A simple electrochemical method for the determination of hydroxyl free radicals without separation process

Generally speaking, measurement of hydroxylated radical products of salicylic acid requires a fussy separation process. In this study, we describe a simple method to electrochemically detect hydroxyl radicals (*OH) using 4-hydroxybenzoic acid (4-HBA) as the *OH trap. The *OH is generated by the Fenton reaction from iron (II) sulfate and hydrogen peroxide in a phosphate buffer solution. Experimental results show that our method can detect the OH with high sensitivity without any separation process. The differential pulse voltammetric responses show a linear dependence on the concentration of *OH in a range of 2.0x10(-6) and 1.0x10(-3)M with a determination limit down to 5.0x10(-7)M. As a demonstration, the kinetics of the Fenton reaction was mapped by measuring the reaction product of hydroxyl radical trapped by 4-HBA. The result is in good agreement with that reported previously. All the results show that the present approach could provide a simple, inexpensive and promising method for biomedicine and iatrology.     

A ratiometric fluorescent probe for imaging hydroxyl radicals in living cells

A novel fluorescent probe, the detection mechanism of which is based on the 'on-off' switching of a FRET triggered by the *OH-induced cleavage of a DNA strand, has been developed for the ratiometric imaging of *OH.     

A new simple and rapid electrochemical method for the determination of hydroxyl radical generated by Fenton reaction and its application

A simple and rapid electrochemical method to detect the hydroxyl radical is described. This method employed the reaction between.OH and dimethyl sulfoxide (DMSO) to generate quantitatively formaldehyde, which then reacted with hydrazine hydrochloride at pH 6.2. The product showed a second-order derivative cathodic wave with the peak potential of -1.08 V( vsSCE) by single sweep oscillopolarography. The electrochemical behavior of the product was investigated by single sweep oscillopolarography and cyclic voltammetry. The experimental conditions for the measurement were optimized and the scavenging activity of some flavonoids on hydroxyl radicals was studied.     

Probing hydroxyl radicals and their imaging in living cells by use of FAM-DNA-Au nanoparticles

The incorporation of gold nanoparticles (Au NPs) as quencher modules in fluorescent probes for DNA damage caused by intracellular hydroxyl radicals (HO*) is reported. Au NPs of 15 nm diameter were decorated with DNA oligomers terminating in thiol functions in their 3' positions and possessing 5' fluorophore modifications. The Au NPs, which have high extinction coefficients, functioned as excellent fluorescent quenchers in the fluorophore-Au NP composites. FRET is switched off as a factor of HO*-induced strand breakage in the single-stranded DNAs, restoring the fluorescence of the quenched fluorophores, which can be followed by spectrofluorimetry. In vitro assays with HO*-generating Fenton reagent demonstrated increases in fluorescence intensity with a linear range from 8.0 nM to 1.0 microM and a detection limit as low as 2.4 nM. Confocal microscopic imaging of macrophages and HepG2 revealed that the probe is cell-permeable and intracellular HO*-responsive. The unique combination of good selectivity and high sensitivity establishes the potential value of the probe for facilitating investigations of HO*-mediated cellular homeostasis and injury.     

A rapid and sensitive electrochemical sensor for hydroxyl free radicals based on self-assembled monolayers of carboxyl functionalized graphene

Journal of Solid State Electrochemistry - In this work, carboxyl-functionalized graphene (CFG) was immobilized on glassy carbon electrode (GCE) by self-assembled monolayers (SAMs) based on covalent...     

High-performance liquid chromatographic determination of methanesulphinic acid as a method for the determination of hydroxyl radicals

For the determination of hydroxyl radicals, dimethyl sulphoxide was used as a molecular probe and the methanesulphinic acid produced was determined by high-performance liquid chromatography of its Fast Yellow GC salt derivative. The results for hydroxyl radicals formed using the Fenton and hypoxanthine-xanthine oxidase systems agreed well with the theoretical values. Interferences from phenols, aromatic amines and amino acids, which give coloured substances by reaction with the diazonium salt, could be avoided. The recovery of methanesulphinic acid added to liver homogenates and incubated for 1 h at 37°C was 70.2 ± 2.1%. The detection limit for methanesulphinic acid in a sample solution was ca. 8 ng/ml.     

Selective fluorination of adamantanes by an electrochemical method

Selective fluorination of adamantanes was achieved by the electrochemical fluorination method, using Et 3N-5HF as electrolyte and a fluorine source. Mono-, di-, tri-, and tetrafluoroadamantanes were selectively prepared from adamantanes by controlling the oxidation potential, and the fluorine atoms were introduced selectively at the tertiary carbons. Adamantanes that have functional groups such as ester, cyano, and acetoxymethyl were also fluorinated selectively.     

Highly sensitive electrochemical detection of living cells based on diamond microelectrode arrays

The new boron-doped nanocrystalline diamond microelectrode arrays (BNCD-MEAs) with 16 channels were designed to detect biological signals from some activated cancer cells. Upon recordings of the released H₂O₂ from cancer cells stimulated by ascorbic acid (AA), it can readily detect the reactive oxygen species (ROS) released from target cells, which will be helpful for the cancer cell recognition and also beneficial for further studying the cause of relevant disease.     

A new simple and sensitive fluorometric method for the determination of hydroxyl radical and its application

A simple and sensitive fluorometric method to detect the hydroxyl radical is described. This method employs the reaction between OH and dimethyl sulfoxide (DMSO) to generate quantitatively formaldehyde, which then reacts with ammonia and 1,3-cyclohexanedione (CHD) at pH 4.5. The product produces the characteristic fluorescence with its excitation and emission wavelength at 400.4 and 452.3 nm, respectively. The quantitative analysis of hydroxyl radical can be done through the determination of the fluorescence intensity. By the developed method, the scavenging abilities of some amino acids and flavonoids on hydroxyl radical are studied.     

Effects of some factors during electrochemical degradation of phenol by hydroxyl radicals

Hydroxylation of aromatic compounds has been used extensively as a measure of hydroxyl radicals (OH) formation. In this paper, salicylic acid (2-HBA) was used to trap OH in the process of electrolysis with a couple of Ti-base lead dioxide electrodes in different conditions. Aqueous solution of 2-HBA, a couple of Ti-base lead dioxide electrodes and an AC power were used in the course of OH formation, and then the solution containing 2-HBA and 2,5-dihydroxybenzoic acid (2,5-DHBA) was analyzed by High Performance Liquid Chromatography (HPLC) with fluorescence detector. This method can help us to better understand the reaction mechanism of OH from the viewpoint of quantity.In the same conditions of electrolysis, Total Organic Carbon (TOC) of phenol solutions were detected to identify the effects of some factors during this electrochemical process, because the strong oxidation ability of OH can mineralize the organic pollutants totally and finally achieve the goal of water treatment. The results show that high pH value of electrolyte and high frequency of the AC power are favorable for the generation of OH, however, CO₃²⁻ is opposite to them.     

Removal of proteinaceous soils using hydroxyl radicals generated by the electrolysis of hydrogen peroxide

We have developed here for the first time a novel method to generate hydroxyl radicals, *OH, by applying slightly negative electric potentials (-0.2--0.8 V vs Ag/AgCl) to the surface of a metal (or metal oxide) that is in contact with hydrogen peroxide solution containing a supporting electrolyte. Namely, *OH radicals were generated at the surface by the electrolysis of hydrogen peroxide according to the equation, H2O2+e- --> *OH+OH-. This method was used to clean a stainless steel fouled with a model protein, beta-lactoglobulin. The *OHs generated at the surface were effective in removing beta-lactoglobulin that had been irreversibly adsorbed, by several minutes of treatment at room temperature (22+/-2 degrees C). The removal rates measured for various concentrations of H2O2 and supporting electrolyte and different potentials were determined exclusively by the electric current.     

Selective spectrofluorimetric method for paracetamol determination through coumarinic compound formation

A spectrofluorimetrical selective method was designed for determination of paracetamol in tablets. This important technique can be characterized by its sensitivity, simplicity, celerity and cheaper cost than current official methods. The employed methodology involves coumarinic compound formation obtained by reaction between paracetamol and ethylacetoacetate (EAA) in the presence of sulphuric acid as catalyst. The reaction product is highly fluorescent at 478 nm, being excited at 446 nm.The linear concentration range of the application was 0.1-0.4 μg/ml of paracetamol and the detection limit was 57 ng/ml.The influence of different variables was studied and optimized through chemometric techniques. Applying the above-mentioned method good results were obtained with regard to pharmaceutical formulations containing paracetamol. Therefore, it is relevant to suggest this profitable technique for medicament control analysis.     

Addition of aryl radicals generated from electrochemical reduction of aryl halides on carbon-carbon double bonds.

Aryl radicals generated by electrochemical reduction of aryl halides in aprotic medium react with styrene and its derivatives to give arylated addition compounds.     

Simple and sensitive determination of hydroxyl radical in atmosphere based on an electrochemically activated glassy carbon electrode

The hydroxyl radical (?OH) plays important roles in environment and health problems. However, the short life time and low concentrations of ?OH limited its detection. In this work, a simple method has been successfully performed for the sensitive detection of hydroxyl radical based on an activated glassy carbon electrode (AGCE).4-hydroxybenzoic acid (4-HBA) was used as a trapping agent for ?OH radicals, leading to the production of electroactive 3,4-dihydroxybenzoic acid (3,4-DHBA). Different procedures including polarisation and cyclic voltammetry in acid or base solutions have been used to activate the glassy carbon electrodes. The electrochemical behaviours of 3,4-DHBA on these activated electrodes were studied and compared. Experimental results showed that the glassy carbon electrode polarised in H₂SO₄ (AGCE-P/H₂SO₄) has the greatest sensitivity and reproducibility to 3,4-DHBA. 3,4-DHBA performed a linear relationship from 1.0 × 10^?7 to 1.0 × 10^?4 M on the AGCE-P/H₂SO₄. The detection limit was down to 6.2 × 10^?8 M. This method has been successfully applied for the detection of hydroxyl radical levels in atmosphere without separation and purification process.     

Selective determination of arbutin in cosmetic products through online derivatization followed by disposable electrochemical sensor

An online derivatization followed by a disposable electrochemical sensor was used for the determination of arbutin (AR) in cosmetic products. The AR was chemically oxidized by MnO2 and subsequently reduced at inexpensive screen-printed carbon electrodes using a low detection potential which improved the selectivity of the method. The effects of various parameters, such as solution pH, detection potential, and flow rate of the mobile phase, were studied in detail. Under optimal conditions [pH 1.6 (0.1 M H3PO4), detection potential 0.0 V (versus Ag/AgCl), flow rate 0.6 mL/min], the linear range for AR was 0.1-1500 ppm (r2 = 0.999) with LOD of 30.06 ppb (S/N = 3). The practical application of the proposed method was demonstrated by the determination of arbutin concentration in commercial cosmetic products.     

A graphene-based electrochemical sensor for sensitive determination of caffeine

An electrochemical sensor based on the electrocatalytic activity of graphene (Gr) for sensitive detection of caffeine is presented. The electrochemical behaviors of caffeine on Nafion-Gr modified glassy carbon electrode (Nafion-Gr/GCE) were investigated by cyclic voltammetry and differential pulse voltammetry. The results showed that the Nafion-Gr/GCE exhibited excellent electrocatalytic activity to caffeine. Caffeine can be effectively accumulated at Nafion-Gr/GCE and produce a sensitive anodic peak. Such electrocatalytic behavior of Gr is attributed to its unique physical and chemical properties, e.g., subtle electronic characteristics and strong adsorptive capability. This electrochemical sensor shows an excellent performance for detecting caffeine with a detection limit of 1.2×10(-7) M (S/N=3), a reproducibility of 5.2% relative standard deviation, and a satisfied recovery from 98.6% to 102.0%. The sensor shows great promise for simple and sensitive determination of caffeine.     

Electron spin resonance studies and theoretical quantum calculations of free radicals generated from anthracenetrione by electrochemical and microsomal reduction

The ESR spectra of radicals obtained by electrolytic reduction of 4,4-dimethylanthracene-1,9,10 (4H)-trione (1) and the regioisomeric quinones 8-acetyloxymethyl-4,4,5-trimethyl- (2), and 5-acetyloxy-methyl-4,4,8-trimethyl-(4H)-1,9,10-anthracenetrione (3) were measured in DMSO and analyzed by quantum chemical calculations. The electrochemistry of these compounds was characterized using cyclic voltammetry, in DMSO and DMF solvents and compared with nifurtimox. The quinones were also reduced by microsomal NADPH-cytochrome P-450 reductase and the corresponding radicals species were also detected by ESR spectroscopy. AMI, INDO, and ADF calculations were performed to obtain the optimized geometries, theoretical hyperfine constants, and spin distributions, respectively. Density functional theory was used to rationalize the reduction potential of these compounds.