•A mechanism of adsorption of hematin onto a pre-treated GCE is proposed.•Adsorption relies on the formation of an axial bond between hematin and the electrode.•The modified electrode presents a ...biomimetic behavior for peroxidases.•Lithium ions act as non competitive inhibitors toward the biomimetic sensor.•H2O2 could be detected and quantified at a nanomolar range.
An electrochemical pre-treatment of a glassy carbon electrode in sodium bicarbonate solution was performed to adsorb hematin (aHtin-GCE), an iron (III) porphyrin present in heme-containing proteins, in order to prepare a new biomimetic sensor for peroxidases. The aHtin-GCe presented peroxidase catalytic activity and a biomimetic behavior related to enzymes responsible for the reduction of H2O2. The previous glassy carbon surface functionalization in bicarbonate solution also proved to be an essential parameter to be controlled as it provides carboxylic acids terminations, which stabilizes the hematin molecule on the electrode surface. The aHtin-GCE kinetics fitted with the Michaelis–Menten model assume the formation of an enzyme-substrate complex in which H2O2 bonds to the electrochemically reduced iron(II) center with further reduction of the peroxide to peroxyl radical. The observation that lithium ions act as competitive inhibitors toward H2O2 also provided the insight toward the application of the aHtin-GCE as a model dispositive to evaluate peroxidase inhibitors. The aHtin-GCE peak current presented a linear correlation with the concentration of H2O2 from the 400nM to 800nM range with an experimental LoD of 0.11μM.
The electrochemical oxidation of dipyrone (MTM) in aqueous medium was characterized using antipyrine (AA), 4-aminoantipyrine (4AA), 4-methyl-aminoantipyrine (MAA) and 4-dimethyl-aminoantipyrine ...(DMAA) as model molecules for the elucidation of all MTM voltammetric signals.
The MTM and the other pyrazolones show up to four oxidation electrochemical processes. The voltammograms obtained in AA solutions presented an irreversible electrochemical oxidation process involving one electron at Eap3, which is common to all pyrazolone derivatives, while the amino pyrazolones present electrochemical oxidation processes at Eap0 or Eap1. The stabilization of the oxidation products depends on different effects: the proton release added to the thermodynamic stability, in the case of the imine formation at Eap0 (4AA and MAA) and the hyperconjugation (σ-stabilization) in the case of iminium formation (DMAA and MTM) at Eap1. The process observed at Epa0 corresponds to the pH-dependent oxidation of the primary and secondary enamines, while the process observed at Eap1 occurs in the tertiary enamines, is pH independent. The oxidation peak potential follows the order: MAA < 4AA < DMAA < MTM and it was demonstrated that DMAA in an aqueous medium can simulate the MTM in an aprotic medium; therefore, the analytical MTM determination can be performed using the DMAA aqueous analytical curve. DMAA and MTM analytical curves, presented a linear range from 10 μmol L−1 to 100 μmol L−1 with a LOD of 1.94 and 2.97 μM for DMAA and MTM, respectively, LOQ of 6.48 and 9.91 μM (n = 10) and, sensitivity of 0.96 μA/μM for DMAA and 0.92 μA/μM; with a recoveries of 95–105% for MTM.
•The MTM and the pyrazolones shows up to four oxidation electrochemical processes.•An electrochemical mechanism to the antipyrine group oxidation was proposed.•DMAA in aqueous medium can simulate the MTM in aprotic medium to quantify MTM.•The strength of the reducing agents follows the order MAA > 4AA > DMAA > MTM > AA.
The electrochemical behaviour of the cytosine nucleoside analogue and anti-cancer drug gemcitabine (GEM) was investigated at glassy carbon electrode, using cyclic, differential pulse and square wave ...voltammetry, in different pH supporting electrolytes, and no electrochemical redox process was observed. The evaluation of the interaction between GEM and DNA in incubated solutions and using the DNA-electrochemical biosensor was studied. The DNA structural modifications and damage were electrochemically detected following the changes in the oxidation peaks of guanosine and adenosine residues and the occurrence of the free guanine residues electrochemical signal. The DNA–GEM interaction mechanism occurred in two sequential steps. The initial process was independent of the DNA sequence and led to the condensation/aggregation of the DNA strands, producing rigid structures, which favoured a second step, in which the guanine hydrogen atoms, participating in the C–G base pair, interacted with the GEM ribose moiety fluorine atoms.
•Gemcitabine has no redox activity.•Gemcitabine-DNA interaction evaluated with a DNA-electrochemical biosensor.•Variation and occurrence of new DNA oxidation peaks.•Gemcitabine caused condensation of dsDNA.•Gemcitabine caused release of guanine residues and formation of abasic sites.
Sulfasalazine (SSZ) is a pharmaceutical compound used for the treatment of rheumatoid arthritis. The electrochemical oxidation of SSZ at a glassy carbon electrode was studied by cyclic, differential ...pulse and square wave voltammetry in a wide pH range. For electrolytes with pH<11.0, the oxidation is an irreversible, diffusion‐control, pH‐dependent process that involves the transfer of one electron and one proton from the hydroxyl group of the salicylic moiety. For pH>11.0 the oxidation is pH‐independent, and a pKa≈11 was determined. The formation of a quinone‐like oxidation product that undergoes two electrons and two protons reversible redox reaction was observed. Also, UV‐vis spectra of SSZ were recorded as a function of supporting electrolytes pH. An electrochemical oxidation mechanism was proposed.
We estimated dry season survival of imperiled salmonids in an intermittent coastal stream in California across 4 years (2009–2012). Our study encompassed two dry and two wet winters, allowing us to ...explore patterns of survival across and within dry seasons with different antecedent precipitation. Apparent survival of age-0+ steelhead trout (Oncorhynchus mykiss) was higher following wet winters compared with dry winters. Moreover, antecedent precipitation was positively correlated with cumulative survival of age-0+ steelhead. Within years, apparent survival of steelhead varied among weeks with a tendency to decrease in the late summer, indicating that fish exhibited some resistance to seasonal drought. Additionally, we found a slight but significant survival advantage for age-0+ coho salmon (Oncorhynchus kisutch) compared with equal-aged steelhead. Our results emphasize the influence of antecedent precipitation in driving the survival of imperiled salmonids and highlight that these fishes are somewhat resistant to seasonal drought, at least to a point.
Carbon paste modified electrodes (CPME) were prepared from composites containing lignin or oxidized lignin adsorbed onto graphite, but no voltammetric signal was observed in K4Fe(CN)6 solutions, ...probably due to the low conductivity of these composites. Gold nanoparticles were produced on both composites using the reducing properties of the lignin, which was able to reduce Au3+, from HAuCl4 at pH 4.7, although only Au/graphite/lignin(oxi) composite has shown better characteristics to the electrochemical purposes. There were differences in FTIR spectra between lignin and lignin(oxi) and TEM images were used to explain the results. The better composite to prepare CPME was that containing 0.2% of gold and 2.5% of oxidized lignin, with the percentages expressed in relation to the graphite mass, and admitting that the Au3+ reduction, from the HAuCl4 solution, was quantitative. The proportion of 2:1 (w/w) of Au/lignin(oxi)/graphite composite to the mineral oil (nujol) was used to prepare the CPME with catalytic properties toward the oxidation of dopamine and ascorbic acid and reduction of nitrite and iodate in the positive potential range.
Use of fast‐growing domesticated and/or genetically modified strains of fish is becoming increasingly common in aquaculture, increasing the likelihood of deliberate or accidental introductions into ...the wild. To date, their ecological impacts on ecosystems remain to be quantified. Here, using a controlled phenotype manipulation by implanting growth hormone in juvenile Atlantic salmon (Salmo salar), we found that growth‐enhanced fish display changes in several phenotypic traits known to be important for ecosystem functioning, such as habitat use, morphology and excretion rate. Furthermore, these phenotypic changes were associated with significant impacts on the invertebrate community and key stream ecosystem functions such as primary production and leaf‐litter decomposition. These findings provide novel evidence that introductions of growth‐enhanced fish into the wild can affect the functioning of natural ecosystems and represent a form of intraspecific invasion. Consequently, environmental impact assessments of growth‐enhanced organisms need to explicitly consider ecosystem‐level effects.
•Cresyl violet electropolymerized in neutralized ternary deep eutectic solvent (DES).•Ternary DES comprised of choline chloride, ethylene glycol and acetic acid.•Formation of anthraquinone groups ...during electropolymerization on carbon nanotubes.•Electrochemical, microscopic and impedance evaluation of polymerization conditions.•Sensor applied to determination of hydroquinone in dermatological cream.
The phenazine dye cresyl violet (CVio) has been evaluated as precursor for the preparation of a new electrochemical sensor based on poly(cresyl violet) deposited on multiwalled carbon nanotube (CNT) modified glassy carbon electrodes (GCE) in neutralized acid-doped ternary deep eutectic solvents (DES). DES with choline chloride as hydrogen bond acceptor and with different hydrogen bond donors (HBD), namely acetic acid, ethylene glycol and oxalic acid were evaluated for CVio electropolymerization by potential cycling. The best polymer films were obtained in ternary DES with the two HBD acetic acid plus ethylene glycol doped with H2SO4 and followed by NaOH neutralization. Electrochemical characterization (voltammetric and electrochemical impedance) showed the formation of anthraquinone groups during electropolymerization, which is initiated on the CNT by the formation of a cation radical. Anthraquinones in the polymer film led to an increased response at the modified electrode for the determination of hydroquinone (H2Q) with low LOD (0.25 µmol L−1) in a broad linear range (1–80 µmol L−1), with good reproducibility, repeatability, and stability. The sensor was successfully applied to the quantification of H2Q in dermatological creams with no matrix effect towards hydroquinone response.
Display omitted
In this paper, the electrochemical determination of the N-nitrosodiphenylamine was proposed comparing the voltammetric response of two non-modified carbon electrodes: a glassy carbon (GCE) and a ...solid graphite-polyurethane composite (GPUE). The surfaces of the electrodes were characterized by atomic force microscopy. The electroactive areas of GCE and GPUE were 0.040 and 0.068 cm2, respectively, calculated from chronocoulometry measurements using K4Fe(CN)6 as probe and the integrated form of Cottrell Equation. Cyclic voltammograms obtained for N-nitrosodiphenylamine using both electrodes indicated anodic and cathodic peaks (vs. Ag/AgCl (3.0 mol L−1 KCl), in agreement with the literature. At GCE, the electrochemical reduction of the molecule is a diffusion-controlled process, whereas at GPUE some degree of adsorption was also observed. Square wave and differential pulse voltammetry were explored in order to optimize the best analytical performance for the quantification of the molecule. Under optimal conditions, linear range (sensitivity and limit of detection) for GCE and GPUE of 8.02 to 46.6 μmol L−1 (1.09 μA L μmol−1 cm−2 and 4.54 μmol L−1) and of 2.51 to 17.5 μmol L−1 (5.50 μA L μmol−1 cm−2 and 0.270 μmol L−1) were obtained, respectively. Considering higher sensitivity and lower detection limits values, the GPUE was selected for the quantification of N-nitrosodiphenylamine in synthetic urine samples. The developed method presented a competitive detection limit compared to other sensors reported in the literature, considering the use of a non-modified electrode, with low cost of fabrication, easiness of surface renovation, and sustainability.
•GCE and GPUE were characterized by chronocoulometry, AFM, and EIS.•Voltammetric performances of the electrodes were compared in NDPhA determination.•Higher sensitivity and lower limit of detection were found in SWV using GPUE.•NDPhA was determinate for the first time in urine samples.
PDF
