Presence Of Hydroquinone Research Articles

Integrated Amperometric Affinity Biosensors Using Co2+–Tetradentate Nitrilotriacetic Acid Modified Disposable Carbon Electrodes: Application to the Determination of β-Lactam Antibiotics

A novel strategy for the construction of disposable amperometric affinity biosensors is described in this work. The approach uses a recombinant bacterial penicillin binding protein (PBP) tagged by an N-terminal hexahistidine tail which was immobilized onto Co(2+)-tetradentate nitrilotriacetic acid (NTA)-modified screen-printed carbon electrodes (SPCEs). The biosensor was employed for the specific detection and quantification of β-lactam antibiotics residues in milk, which was accomplished by means of a direct competitive assay using a tracer with horseradish peroxidase (HRP) for the enzymatic labeling. The amperometric response measured at -0.20 V versus the Ag pseudoreference electrode of the SPCE upon the addition of H2O2 in the presence of hydroquinone (HQ) as redox mediator was used as the transduction signal. The developed affinity sensor allowed limits of detection to be obtained in the low part-per-billion level for the antibiotics tested in untreated milk samples. Moreover, the biosensor exhibited a good selectivity against other antibiotics residues frequently detected in milk and dairy products. The analysis time was of approximately 30 min.

Optical fiber spectroelectrochemical device for detection of catechol at press-transferred single-walled carbon nanotubes electrodes

A new long-optical-pathway spectroelectrochemical cell for absorptometric measurements in the UV-Vis region was developed. This cell consists of two optical fibers brought face to face and fixed on the working electrode support. As a proof of concept, the spectroelectrochemical cell was applied to the determination of catechol using a press-transferred single-walled carbon nanotube film as the working electrode. Voltabsorptometry was demonstrated to be very helpful in understanding the mechanism of catechol oxidation. The experiments showed that the main oxidation product is o-benzoquinone, but other soluble side products are also observed. Multivariate calibration explains the selection of 390 nm as the best wavelength for the univariate absorptometric determination of catechol, avoiding the interference of oxidation side products. Catechol was quantified using both the electrochemical and the spectroscopic signal, demonstrating that this hybrid technique is an autovalidated analytical method. Dual detection of catechol was also carried out using amperometric spectroelectrochemistry. Finally, spectroelectrochemistry was used to quantify catechol in the presence of hydroquinone.

An amperometric affinity penicillin-binding protein magnetosensor for the detection of β-lactam antibiotics in milk

The preparation, characterization and performance evaluation of an amperometric affinity disposable magnetosensor, based on the use of a recombinant penicillin-binding protein (PBP) and screen-printed carbon electrodes (SPCEs), for the specific detection and quantification of β-lactam antibiotic residues in milk are reported. The PBP was immobilized onto His-Tag-Isolation-modified magnetic beads (His-Tag-Isolation-MBs), and a direct competitive assay using a tracer with horseradish peroxidase (HRP) for the enzymatic labeling was performed. The amperometric response obtained at -0.20 V vs. the Ag pseudo-reference electrode of the SPCE after the addition of H2O2 in the presence of hydroquinone (HQ) was used as the transduction signal. The developed methodology showed very low detection limits (in the low ppb level) for the 6 antibiotics tested in untreated milk samples, and a good selectivity against other antibiotic residues frequently detected in milk and dairy products. Due to the bioreceptor employed, this methodology was able to detect only the active form of β-lactam antibiotics with high affinities for both penicillins and cephalosporins. Moreover, the analysis took only 30 min.

Thermal diffusivity measurement for urchin-like gold nanofluids with different solvents, sizes and concentrations/shapes

The thermal properties of nanofluids are an especially interesting research topic because of the variety of potential applications, which range from bio-utilities to next-generation heat-transfer fluids. In this study, photopyroelectric calorimetry for measuring the thermal diffusivity of urchin-like colloidal gold nanofluids as a function of particle size, concentration and shape in water, ethanol and ethylene glycol is reported. Urchin-like gold nanoparticles were synthesised in the presence of hydroquinone through seed-mediated growth with homogeneous shape and size ranging from 55 to 115 nm. The optical response, size and morphology of these nanoparticles were characterised using UV-visible spectroscopy and transmission electron microscopy. The thermal diffusivity of these nanofluids decreased as the size of the nanoparticles increased, and the enhancement depended on the thermal diffusivity of the solvent. The opposite effect (increase in thermal diffusivity) was observed when the nanoparticle concentration was increased. These effects were more evident for urchin-like gold nanofluids than for the corresponding spherical gold nanofluids.

Thermal diffusivity measurement of spherical gold nanofluids of different sizes/concentrations

In recent times, nanofluids have been studied by their thermal properties due to their variety of applications that range from photothermal therapy and radiofrequency hyperthermia (which have proven their potential use as coadjutants in these medical treatments for cancer diseases) to next-generation thermo-fluids. In this work, photoacoustic spectroscopy for a specific study of thermal diffusivity, as a function of particle size and concentration, on colloidal water-based gold nanofluids is reported. Gold nanoparticles were synthetized in the presence of hydroquinone through a seed-mediated growth with homogenous sizes and shapes in a range of 16 to 125 nm. The optical response, size and morphology of these nanoparticles were characterized using ultraviolet–visible spectroscopy and transmission electron microscopy, respectively. Thermal characterizations show a decrease in the thermal diffusivity ratio as the nanoparticle size is increased and an enhancement in thermal diffusivity ratio as nanoparticle concentration is added into the nanofluids. Compared with other techniques in the literature such as thermal lens and hot wire method, this photoacoustic technique shows an advantage in terms of precision, and with a small amount of sample required (500 μl), this technique might be suitable for the thermal diffusivity measurement of nanofluids. It is also a promising alternative to classical techniques.

Disposable amperometric magneto-immunosensor for direct detection of tetracyclines antibiotics residues in milk

The preparation and performance of a disposable amperometric magneto-immunosensor, involving the use of a selective capture antibody immobilized on the surface of protein G-functionalized magnetic beads (ProtG-MBs) and screen-printed carbon electrodes (SPCEs), for the specific detection and quantification of tetracyclines (TCs) residues in milk is reported. A direct competitive immunoassay using a tracer with horseradish peroxidase (HRP) for the enzymatic labeling was performed. The amperometric response measured at −0.2V vs. the silver pseudo-reference electrode of the SPCE upon the addition of H2O2 in the presence of hydroquinone (HQ) as redox mediator was used as transduction signal. The developed methodology showed very low limits of detection (in the low ppb level) for 4 tetracycline antibiotics tested in untreated milk samples, and a good selectivity against other antibiotic residues frequently detected in milk and dairy products. The usefulness of the magneto-immunosensor was demonstrated by analyzing UHT whole milk samples spiked with 44ngmL−1 tetracycline (TC) as well as a reference milk containing a certified oxytetracycline (OTC) content. These features, together with the short analysis time (30min), the simplicity, and easy automation and miniaturization of the required instrumentation make the developed methodology a promising alternative in the development of devices for on-site analysis.

The influence of hydroquinone on tyrosinase kinetics

In vitro studies, using combined spectrophotometry and oximetry together with hplc/ms examination of the products of tyrosinase action demonstrate that hydroquinone is not a primary substrate for the enzyme but is vicariously oxidised by a redox exchange mechanism in the presence of either catechol, l-3,4-dihydroxyphenylalanine or 4-ethylphenol. Secondary addition products formed in the presence of hydroquinone are shown to stimulate, rather than inhibit, the kinetics of substrate oxidation.

Application of tubular tetrapod magnesium oxide in a biosensor for hydrogen peroxide

Tubular tetrapod magnesium oxide (tt-MgO) can be synthesized by thermal evaporation of Mg metal powder with a pre-grown tetrapod ZnO template. The morphology and structure of the tt-MgO were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A composite prepared from tt-MgO, nafion and horseradish peroxidase was employed to modify a gold electrode to result in an electrochemical biosensor for hydrogen peroxide that displays excellent sensitivity and rapid response in the presence of hydroquinone as a mediator. Its sensitivity is 335.4 μA mM-1 cm-2, its response is linear in the range from 1.0 to 450 μM, and the detection limit is 0.3 μM. These results demonstrate that tt-MgO provides a promising material for the designs of biosensors.

Disposable and integrated amperometric immunosensor for direct determination of sulfonamide antibiotics in milk

The preparation and performance of a disposable amperometric immunosensor, based on the use of a selective capture antibody and screen-printed carbon electrodes (SPCEs), for the specific detection and quantification of sulfonamide residues in milk is reported. The antibody was covalently immobilized onto a 4-aminobenzoic acid (4-ABA) film grafted on the disposable electrode, and a direct competitive immunoassay using a tracer with horseradish peroxidase (HRP) for the enzymatic labeling was performed. The amperometric response measured at −0.2V vs the silver pseudo-reference electrode of the SPCE upon the addition of H2O2 in the presence of hydroquinone (HQ) as mediator was used as transduction signal. The developed methodology showed very low limits of detection (in the low ppb level) for 6 sulfonamide antibiotics tested in untreated milk samples, and a good selectivity against other families of antibiotics residues frequently detected in milk and dairy products. These features, together with the short analysis time (30min), the simplicity, and easy automation and miniaturization of the required instrumentation make the developed methodology a promising alternative in the development of devices for on-site analysis.

Amperometric sulfide detection using Coprinus cinereus peroxidase immobilized on screen printed electrode in an enzyme inhibition based biosensor

In the present work, an amperometric inhibition biosensor for the determination of sulfide has been fabricated by immobilizing Coprinus cinereus peroxidase (CIP) on the surface of screen printed electrode (SPE). Chitosan/acrylamide was applied for immobilization of peroxidase on the working electrode. The amperometric measurement was performed at an applied potential of −150mV versus Ag/AgCl with a scan rate of 100mV in the presence of hydroquinone as electron mediator and 0.1M phosphate buffer solution of pH 6.5. The variables influencing the performance of sensor including the amount of substrate, mediator concentration and electrolyte pH were optimized. The determination of sulfide can be achieved in a linear range of 1.09–16.3μM with a detection limit of 0.3μM. Developed sensor showed quicker response to sulfide compared to the previous developed sulfide biosensors. Common anions and cations in environmental water did not interfere with sulfide detection by the developed biosensor. Cyanide interference on the enzyme inhibition caused 43.25% error in the calibration assay which is less than the amounts reported by previous studies. Because of high sensitivity and the low-cost of SPE, this inhibition biosensor can be successfully used for analysis of environmental water samples.

Natural polyphenols as safe alternatives to hydroquinone for the organocatalyzed reduction of dioxygen dissolved in water by diethylhydroxylamine (DEHA)

Reduction of dioxygen dissolved in water by diethylhydroxylamine (DEHA) in the presence of hydroquinones or quinones as organocatalysts is investigated with regard to reaction rate and catalyst turnover. Eleven p-benzoquinone derivatives bearing various electron-donating, electron-withdrawing and bulky substituents are studied. The catalytic activity of four benzenediols (hydroquinone, resorcinol, catechol and 4-tert-butylcatechol) and of four benzenetriols (hydroxyquinol, phloroglucinol, pyrogallol and 5-tert-butylpyrogallol) is compared. Mechanistic and kinetic studies indicate that the rate-determining step is the regeneration of hydroquinones through the reduction of the corresponding benzoquinones by DEHA. Then, eight natural polyphenols are tested as alternative catalysts to the potential carcinogen hydroquinone. Four of them (purpurin, myricetin, gallic acid and propyl gallate) exhibit some catalytic activity and gallic acid is shown to be even more efficient than hydroquinone itself. A further improvement of the catalytic system is achieved by adding catalase to disproportionate the generated hydrogen peroxide, which is detrimental for the catalyst. Thus, the oxygen scavenging system DEHA–gallic acid–catalase is found to be not only greener but also more efficient than the current system DEHA–hydroquinone since it gives water instead of hydrogen peroxide as the final reduction product of dioxygen.

Hydroquinone Synthesis of Silver Nanoparticles from Silver Bromide Suspensions

The results of research into the preparation of silver nanoparticles using photoreduction in the presence of hydroquinone as the reductant were discussed. Substrates for the synthesis of silver nanoparticles were ultrafine crystalline gelatine-stabilised aqueous suspensions of silver bromide. The influence of the reductant to substrate molar ratio and the medium’s pH to the ecient production of silver nanoparticles were studied. The properties of resultant silver particles were examined using UV-Vis spectroscopy. Transmission electron microscopy was used for the photomicrography of silver nanoparticles suspensions.

Hydroquinone-assisted assembly of coordination polymers from lanthanides and cucurbit[5]uril

Coordination polymers have been assembled from a series of eight different lanthanide ions (Ln3+) and cucurbit[5]uril (Q[5]) in the presence of hydroquinone (Hyq) as an organic structure inducer. X-ray diffraction analysis has revealed three distinct configurations of the coordination polymers formed with increasing atomic number of the lanthanide. The coordination of light lanthanide cations to Q[5] leads to the formation of linear one-dimensional coordination polymers; the coordination of intermediate lanthanide cations such as Eu(III) or Gd(III) leads to the formation of Q[5] pairs in which the two Q[5] molecules are connected by the Eu(III) or Gd(III) ions; and the coordination of heavy lanthanide cations to Q[5] leads to the formation of homochiral one-dimensional helical coordination polymers.

PREPARATION AND RECONGNITION PROPERTIES OF MOLECULARLY IMPRINTED POLYETHERSULFONE NANOFIBER MEMBRANES TOWARDS BISPHENOL A

Electrospinning technique was employed to prepare molecularly imprinted polyethersulfone(PES) nanofiber membranes for the recognition and binding of bisphenol A(BPA).The PES was used as functional polymer to provide functional groups that interact with the template during the electrospinning process.The template was removed to afford binding sites in the nanofiber membranes that are capable of selectively rebinding the target molecule.Effects of the electrospinning conditions such as template amounts in PES solution,electrospinning voltage and solvent on the imprinting efficiency of nanofiber membranes were investigated.The recognition experiments with the molecularly imprinted nanofibers(MINFs) showed that 10 wt% BPA MINFs had higher binding ability to the BPA than the nonimprinted nanofibers(NINFs).Competitive binding experiment showed that 10 wt% BPA MINFs had high selectivity to BPA in the presence of hydroquinone(HQ),resorcinol(RSO) or phenol,but NINFs had low selectivity to BPA in the presence of bis-(4-hydroxyphenyl) methane(BPF) or 4-tert-butylphenol(TBP).Scatchard analysis and two-site binding model indicated that MINFs had two types of binding sites,namely specific and non-specific binding sites,and had high equilibrium binding constants of the specific binding sites and apparent maximum numbers of binding sites for BPA.The binding kinetics of MINFs was also studied.

A Sandwich-type Amperometric Immunosensor Based on One-dimensional Assembly of Magnetic DNA Nanoprobes

Abstract A new type of one-dimensional magnetic nanoprobe was fabricated based on a DNA chain fixed with numerous Fe 3 O 4 (core)/ZrO 2 (shell) nanomagnetic beads (ZMPs) modified with horseradish peroxidase (HRP)-labeled anti-α-fetoprotein secondary antibody (AFPAb 2 ). An electrochemical immunosensor for AFP was developed using the nanoprobe DNA/(ZMPs-HRP-AFPAb 2 ) n and AFP-antibody (AFPAb 1 )-immobilized glassy carbon electrode (GCE) modified with nanogold. A sandwich-type immunocomplex could be formed between the immobilized AFPAb 1 on the GCE, the AFP sample, and the probe DNA/(ZMPs-HRP-AFPAb 2 ) n ; moreover, the linked HRP on the probes could catalyze the electrochemical reaction of carbamide peroxide in the presence of hydroquinone. Under optimal conditions, the immunosensor response showed a linear relationship with the AFP concentration in the range 0.01–25 μg L −1 , with a detection limit of 4 ng L −1 . The immunosensor was used to determine the AFP level in serum samples, and the results were satisfactory. The proposed amperometric immunosensor was sensitive, provided a rapid detection, and was controllable by a magnetic field. This study provides a strategy for the one-dimensional assembly and development of highly sensitive immunosensors.

A strategy for selective detection based on interferent depleting and redox cycling using the plane-recessed microdisk array electrodes

The fabrication, characterization and application of the plane-recessed microdisk array electrodes for selective detection are demonstrated. The electrodes, fabricated by lithographic microfabrication technology, are composed of a planar film electrode and a 32 × 32 recessed microdisk array electrode. Different from commonly used redox cycling operating mode for array configurations such as interdigitated array electrodes, a novel strategy based on a combination of interferent depleting and redox cycling is proposed for the electrodes with an appropriate configuration. The planar film electrode (the plane electrode) is used to deplete the interferent in the diffusion layer. The recessed microdisk array electrode (the microdisk array), locating within the diffusion layer of the plane electrode, works for detecting the target analyte in the interferent-depleted diffusion layer. In addition, the microdisk array overcomes the disadvantage of low current signal for a single microelectrode. Moreover, the current signal of the target analyte that undergoes reversible electron transfer can be enhanced due to the redox cycling between the plane electrode and the microdisk array. Based on the above working principle, the plane-recessed microdisk array electrodes break up the restriction of selectively detecting a species that exhibits reversible reaction in a mixture with one that exhibits an irreversible reaction, which is a limitation of single redox cycling operating mode. The advantages of the plane-recessed microdisk array electrodes are verified by detecting dopamine in the presence of ascorbic acid and detecting pyrocatechol in the presence of hydroquinone, i.e., the electrodes can work regardless of the reversibility of interfering species.

Ostwald Ripening in Metallic Nanoparticles: Stochastic Kinetics

This paper looks at the factors that control Ostwald ripening in a bimodal silver nanocolloid system containing tabular particles having one dimension equal to or less than 5 nm. The test system was based on a seeded process using the staged addition of sodium borohydride and hydroquinone (HQ) to silver nitrate. The result was a blend of 20 nm spheres and 30 nm/4–5 nm nanodiscs. The mixture of morphologies allows for a greater differentiation in free energy stability between particles and consequently an accelerated rate of ripening. The rate of the ripening process is shown to be heavily dependent on the relative amount of spherical receptor particles as well as on the presence of hydroquinone as a redox catalyst. A stochastic model is proposed for stepwise adatom kinetics.

Utility of Certain Nucleophilic Aromatic Substitution Reactions for the Assay of Ethamsylate in its Dosage forms and in Presence of its Degradation Product

The study represents the first report on the development of spectrophotometric methods for determination of ethamsylate (EST) in the presence of hydroquinone as an impurity and/or acidic degradation product. The proposed methods are based on the reaction of EST through it,s secondary amino group either with 1,2-naphthoquinone-4-sulphonate sodium (NQS) at pH 10.7 or 2,4-dinitrofluorobenzene (DNFB) at pH 9.3 to form orange and yellow colored reaction products peaking at 478 and 387 nm for methods (I) and (II), respectively. The different experimental parameters affecting the development and stability of the reaction products in methods (I) and (II) were carefully studied and optimized. The absorbance-concentration plots were rectilinear over the concentration ranges of 2-30 and 2-14 µg mL−1 for methods (I) and (II), respectively. The lower detection limits were 0.13 and 0.19 µg mL−1 and the lower quantitation limits were 0.44 and 0.63 µg mL−1 for methods (I) and (II), respectively. Both methods were successfully applied to commercial ampoules and tablets.

Impact of hydroquinone on thermal and electrical properties of plasticized [poly(vinyl alcohol)]0.7(LiBr)0.3(H2SO4) 2.9 mol L −1 solid acid membrane

A novel multi-component system containing poly(vinyl alcohol), lithium bromide, sulfuric acid, ethylene carbonate and hydroquinone was prepared using a solution-casting technique. The presence of hydroquinone as a reducing agent in the inorganic–organic membrane structure thus produced was thought to lead to enhanced thermal stability of the membrane. The activation energy for the thermal decomposition of the product samples increased with increasing hydroquinone doping. The ionic conductivities of the films were determined from AC impedance measurements in the temperature range 300–373 K. The maximum conductivity was found to be 1.75 × 10−3 S cm−1 for a film doped with 4 wt% hydroquinone. The results give some insight into the potential utility of the membrane as a proton-conducting solid polymer electrolyte. Copyright © 2011 Society of Chemical Industry

Controllable Synthesis of Stable Urchin-like Gold Nanoparticles Using Hydroquinone to Tune the Reactivity of Gold Chloride

We reported an aqueous synthesis of urchin-like gold nanoparticles (NPs) in the presence of hydroquinone through a seed-mediated growth approach. By altering the feed ratio of hydroquinone, seeds, and additional HAuCl4, the diameters of urchin-like NPs were tunable from 55 to 200 nm. Accordingly, the centers of surface plasmon resonance absorption shifted from 555 to 702 nm. Systematical analysis revealed that the generation of urchin-like particles as well as their size evolution strongly depended on the reactivity of gold ions, mainly controlled by the concentration of hydroquinone. At low hydroquinone concentration, only spherical particles were achieved. The increase of the hydroquinone concentration promoted a kinetics-favored deposition of gold atoms on the (111) lattice planes and thereby the growth of branches. Moreover, the as-prepared urchin-like particles possessed good structural stability, which could be kept in the growth solution for more than 10 days without morphology variation.