1,720,992 research outputs found
Arylferrocenylmethanols: a new family of ferrocenes to be used as mediators in biosensors
No full textArylferrocenylphenylmethanols, ArFcPhCOH, were prepared from the corresponding aryl ferrocenyl ketones, ArCOFc, prepared by Friedel-Crafts acylation. pKa values of ArCOFc were determined in sulfuric acid. The electrochemical properties of ArFcPhCOH were investigated. Copyright © 2003 John Wiley & Sons, Ltd
Favorskii Rearrangement of alfa-Chloroketones Induced by Electrogenerated Superoxide Ion
No full textA deeper insight into the oxidative mechanism of caffeine and related xanthines: may caffeine be considered as an antioxidant?
No full textCaffeine (CAF) is present in many consumer products as coffee, tea, chocolate, soft and energy drinks, resulting the most widely consumed psychoactive substance in human dietary. Many of its physiological effects are well known. Recently, antioxidant properties have been suggested for CAF that seems showing protective effects against oxidative stress (OS).Inert to hydrogen (H)/electron (E) scavengers as ABTS·+ and DPPH, CAF has been proposed as an excellent HO· scavenger.
The oxidative path of CAF in aqueous medium has been widely studied since 70s4, but until today the mechanism through which CAF and related xanthines might exert their antioxidant activity is not fully understood.
The electrochemical oxidation of CAF, theobromine (TBr) and theophylline (TPh) was studied in aprotic medium by ciclyc voltammetry and controlled potential electrolysis carried out in UV cell modified for spectroelectrochemistry, to investigate on the radical intermediates involved in the primary oxidative process and their possible fate. The chemical oxidation of the same xanthines was carried out with PbO2, superoxide radical anion and galvinoxyl free radical and reactions were monitored via UV spectrophotometry, to investigate on the reactivity towards reactive oxygen species (ROS).
Antioxidant activity based on electron transfer (ET) and/or H-atom transfer (HT) mechanisms was evaluated
Reactivity of electrogenerated superoxide ion. Part 3. Oxidative cleavage and reduction of some cyclohexanones
No full textThe structure modifications induced by electrogenerated
superoxide ion in 4-substituted cyclohexanones are related to
the reactivity of O2
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as base, and electron-donor.
The formation of dicarboxylic acids (50-70% yield, after 8 F
per mole of substrate had flowed) implies the participation of
unreduced O2.
Redox cycles involving O2/O2
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, O2/O2H. and ketone/alcohol
systems may be considered as an hypothesis
Recent advances in electrochemical chitosan-based chemosensors and biosensors: applications in food safety
Full text linkChitosan is a biopolymer derived from chitin. It is a non-toxic, biocompatible, bioactive, and biodegradable polymer. Due to its properties, chitosan has found applications in several and different fields such as agriculture, food industry, medicine, paper fabrication, textile industry, and water treatment. In addition to these properties, chitosan has a good film-forming ability which allows it to be widely used for the development of sensors and biosensors. This review is focused on the use of chitosan for the formulation of electrochemical chemosensors. It also aims to provide an overview of the advantages of using chitosan as an immobilization platform for biomolecules by highlighting its applications in electrochemical biosensors. Finally, applications of chitosan-based electrochemical chemosensors and biosensors in food safety are illustrated
Functionalization of single-wall carbon nanotubes: a new promising nanomaterial for neurotransmitters detection.
No full textKinetic evaluation of the standard rate constant from cyclic voltammetric data at SWCNT-modified tungsten microelectrodes
Full text linkThe electrochemical properties and the kinetic evaluation at Single-Walled Carbon Nanotubes (SWCNTs) -modified tungsten (W) microelectrodes have been studied and compared with those of Glassy Carbon (GC) bare electrodes. Field Emission Scanning Electron Microscopy (FEG-SEM) and Raman spectroscopy have been used to characterize the modified-electrode morphology and microstructure, respectively. Cyclic voltammetry (CV) has been used to study the electrochemical performances, with seven different redox systems serving as probes (Fe(CN) 63-/4-; Ru(NH3) 63+/2+, Ir(Cl)62-/3-, catechol, dopamine, ferrocene monocarboxylic acid and caffeic acid). The analytical response for different systems is, highly reproducible for each type of tungsten microelectrode modified with SWCNT coating by Chemical Vapor Deposition method (CVD). For all seven redox systems, the forward reaction peak current varies linearly with the square root of scan rate (v)1/2, indicative of electrode reaction kinetics controlled by mass transport (semi-infinite linear diffusion) of the reactant. Apparent heterogeneous electron-transfer rate constants, Koapp for all seven redox systems have been determined from ∆Ep-v experimental data, according to the method described by Nicholson. Koapp values of 1.02-1.17 cm/s have been observed for Ru(NH3) 63+/2+, Ir(Cl)62-/3-, and Fe(CN) 63-/4- without any extensive electrode pretreatment (e.g., polishing). Lower Koapp values of 10-6-10-2 crn/s have been found for catechol, dopamine, ferrocene monocarboxylic acid, and caffeic acid. The voltammetric responses for Ru(NH3) 63+/2+, Ir(Cl)62-/3-, and Fe(CN) 63-/4- have also been examined at SWCNT modified W electrodes in different solutions pH (1.1 -10.0), and the corresponding ∆Ep, ipox, ipred and Koapp values for the most part, have been unaffected by the solution pH. This is probably related to the absence of oxygen-functionalities at SWCNT-modified W microelectrodes, which is in contrast to the typical behaviour of the oxygenated, Sp2 carbon electrodes, such as glassy carbon or graphite
Determination of caffeine @ gold nanoparticles modified gold (Au) electrode: a preliminary study
No full textCaffeine is a natural alkaloid exerting many physiological effects,
such as stimulation of the central nervous system, diuresis and
gastric acid secretion. It is widely distributed in plant products and
beverages and its quantification is mainly of pharmaceutical and
alimentary concern. In this paper, we describe an electrochemical
study based on the modification of a gold electrode (Au) surface by
deposition of functionalized gold nanoparticles by Cyclic Voltammetry
(CV). The oxidation system is characterized by an anodic peak in the
positive-going step and by the absence of any cathodic peak on the
reverse scan, indicating that the oxidation is irreversible. At the
modified electrode, the voltammetric peak height increases vs. that
@ the bare one, depending on the nanoparticles functionalization.
The best performances were observed @ Au electrode modified with
colloidal gold nanoparticles (AuNPs) stabilized into a chitosan matrix.
In order to optimize the influence of different electrolytes on the
sensor response, different electrolytic solutions (nitric acid, sulfuric
acid, phosphoric acid and hydrochloric acid) were used. The
electrochemical behavior of caffeine was also studied in aprotic
medium with the aim to clear up the different mechanisms the
oxidative process occurs through in aqueous and in aprotic medium
Electrochemical characterization of glass/Al reactions at high temperature
No full textA high temperature Al(-)/glass/stainless steel-O2(+) system, was studied and characterized by SEM and EDS analysis. Indeed, a potential ranging from 1.75 to 1.5 V between steel and aluminum, at a temperature above 500 C, has been observed. By connecting this package to a resistance, a current flow was detected. Above the aluminum melting point, there is a reaction between SiO 2 glass and metal, with formation of Al2O3 and Si, moreover there is a change in the soda-lime glass composition, a nucleation of crystalline phases in the glass itself, and the formation of a porous layer of alumina, with the typical inhomogeneity of a system heated at this temperature. It seems that the current passing through the glass phase, by the electric field generated by the formation of a metal/air cell, can influence the composition of the glass phase at high temperature and can inhibit the nucleation and the growth of crystalline zones.A high temperature Al(−)/glass/stainless steel–O2(+) system, was studied and characterized by SEM and
EDS analysis. Indeed, a potential ranging from 1.75 to 1.5 V between steel and aluminum, at a temperature
above 500 °C, has been observed. By connecting this package to a resistance, a current flow was detected.
Above the aluminum melting point, there is a reaction between SiO2 glass and metal, with formation of
Al2O3 and Si, moreover there is a change in the soda-lime glass composition, a nucleation of crystalline phases
in the glass itself, and the formation of a porous layer of alumina, with the typical inhomogeneity of a system
heated at this temperature. It seems that the current passing through the glass phase, by the electric field
generated by the formation of a metal/air cell, can influence the composition of the glass phase at high temperature
and can inhibit the nucleation and the growth of crystalline zones
Chemical Reversibility and Stable Low-Potential NADH Detection with Nonconventional Conducting Polymer Nanotubule Modified Glassy Carbon Electrodes
No full textStudies of the oxidation of â-nicotinamide adenine dinucleotide
(NADH) at glassy carbon (GCEs) electrode
surfaces, modified with nonconventional conducting polymer
nanotubules, are reported. In contrast to the situation
with conventional carbon electrodes, chemical reversibility
of the NADH oxidation reaction was achieved by means
of poly(1,2-diaminobenzene) conducting nanotubule coatings.
A ¢Ep of 425 mV (vs Ag/AgCl; pH 7.0) was
observed. The NADH amperometric response of the
conducting nanotubule modified GCEs was shown to be
extremely stable, with 98% of the initial response remaining
after 48 h of stirring in the presence of 1 10-4 M
NADH solutions (compared to 14% at the poly(1,2-
diaminobenzene) modified GCEs). The nonconventional
conducting polymer nanotubule-coated electrodes, when
tested in amperometric mode for NADH electrochemical
oxidation at an applied potential of 450 mV, showed a
sensitivity of 99 nA/mM, an operational stability for 2
days, a storage stability of 2 weeks at 4 °C, a linearity from
5 10-5 to 1 10-3 M, and good NADH chemical
reversibility, all of which make them useful tools for
dehydrogenase enzyme probe assembly
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