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For the first time, a Ti3C2Tx–MXene and poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS) composite-modified electrode has been developed for electrochemical detection of the bilirubin (BR) by molecularly imprinted ortho-phenylenediamine (o–PD). BR is a biomarker for liver-related diseases. High levels of BR imply liver dysfunction; hence, its exact and rapid measurement is indispensable to its immediate diagnosis and treatment. The synergistic effects of MXene and PEDOT: PSS not only enhanced the electrochemical conductivity and provided a large electroactive surface area for better MIP polymerization but also improved the sensitivity, stability, and electro-catalytic activity of the developed electrode. This is the first study to combine MXene/PEDOT: PSS and molecularly imprinted orthophenylenediamine for BR sensing, which individually have demonstrated potential, but whose combined effects have never been explored in the context of BR detection. The successful synthesis and deposition of composite is confirmed by field emission scanning electron microscopy (FESEM) along with energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The electrochemical properties and surface morphology of the prepared electrode at every modification step were characterized by electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS), and FESEM respectively. The MXene/PEDOT: PSS composite as an electrode modifier exhibited sensing of BR in the clinical relevant range of BR in human serum 0.1–20 mg/dL with a detection limit of 0.002 mg/dL. Additionally, the prepared electrode has excellent reproducibility, stability, selectivity, and repeatability and also showed acceptable results for the sensing of BR in human serum sample. [ABSTRACT FROM AUTHOR]

The formation of a nanocomposite coating based on reduced graphene oxide (RGO) and poly(o-phenylenediamine) (PPD) in the chemical reaction of graphene oxide (GO) and o-phenylenediamine (OPD) has been studied by cyclic voltammetry (CVA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It has been shown that the action of cyclic polarization provides a more uniform structure of the nanocomposite films (decrease in the corrugation effect). In addition, it has been found that the polarization of GO films containing the OPD monomer distributed inside to the PPD synthesis potentials leads to the formation of uniformly distributed globular structures, which most probably correspond to a polymer electrochemically synthesized in the space between the GO nanosheets. [ABSTRACT FROM AUTHOR]

We report on an electrode for the amperometric determination of lorazepam. A glassy carbon electrode was coated with a molecular imprint made by electropolymerization of ortho-phenylenediamine and filled with multiwalled carbon nanotubes and gold nanoparticles, which enhances the transmission of electrons. The sensor was studied with respect to its response to hexacyanoferrate (III) as a probe and by electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The linear response range to Lorazepam is from 0.5 nM to 1.0 nM and from 1.0 nM to 10.0 nM, with a detection limit of 0.2 nM (at an S/N of 3). The electrode was successfully applied to determine Lorazepam in spiked human serum. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The carcinogenicity of ortho-phenylenediamine ( o-PD) was examined by administrating o-phenylenediamine dihydrochloride ( o-PD2HCl) in dinking water to groups of 50 F344/DuCrj rats and 50 Crj:BDF mice of both sexes for 2 years. The drinking water concentration of o-PD2HCl was 0, 500, 1,000 or 2,000 ppm (wt/wt) for male rats; 0, 250, 500 or 1,000 ppm for female rats; 0, 500, 1,000 or 2,000 ppm for male mice; and 0, 1,000, 2,000 or 4,000 ppm for female mice. Two-year administration of o-PD2HCl produced a dose-dependent increase in the incidences of hepatocellular adenomas and carcinomas in rats of both sexes and in female mice, and hepatocellular adenomas in male mice. In mice, the incidences of hepatocellular adenomas were increased at the lowest dose used in both males and females. Metastasis from hepatocellular carcinomas of rats occurred predominantly in the lung. Incidences of transitional cell papillomas and carcinomas in the urinary bladder were noted in male rats administered 2,000 ppm, together with an increased incidence of papillary and/or nodular hyperplasia of transitional epithelium. In mice, the incidence of papillary adenomas in the gall bladder, which is rare in mice, was increased in both males and females administered 2,000 ppm. Thus, o-PD is carcinogenic in two species, i.e., rats and mice of both sexes. [ABSTRACT FROM AUTHOR]

Kinetics of ortho-phenylenediamine (PDA) oxidation has been investigated in the “pseudoperoxidase” system, Methemalbumin-H2O2, in the presence of 2-amino-4- tert-butylphenol (ATBP), 2-amino-4,6-di tert-butylphenol (ADTBP) and its four N-acyl derivates, as well as flavonoids (quercetin, morin, silibin, hesperidin and naringin). Under standard experimental conditions (20°C, phosphate buffered saline, pH 7.4, containing 5.25% ethanol and DMF) ATBP, ADTBP and two its N-acyl-derivatives and also all five flavonoids inhibited PDA oxidation with different efficiency, which was characterized in terms of the inhibition constants, Ki, M, or the percent of inhibition degree at the maximal concentrations of these inhibitors. Quercetin (Ki = 7.7 × 10−5 M) and ATBP (Ki = 1.26 × 10−4 M) were the most effective antioxidants. Using these characteristics and other required criteria, the pairs PDA-quercetin and PDA-ATBP were proposed for a practical application in the test-systems for evaluation of total antioxidant activity of biological objects. [ABSTRACT FROM AUTHOR]

The peroxidase-catalyzed oxidation of 3,3",5,5"-tetramethylbenzidine (TMB), ortho-phenylenediamine (PDA), and 5-aminosalicylic acid (5-ASA) is significantly accelerated in the presence of 2-aminothiazole (AT) and melamine (MA), and an increase in their concentrations is associated with a parallel increase in the kcat and Km values for TMB and PDA. The activation of the peroxidase-catalyzed oxidation of TMB and PDA is quantitatively characterized by a coefficient (degree) α (M–1) which significantly depends on pH in the range 6.2-6.4, 6.4-7.4, and 6.0-7.4 for the TMB–AT, TMB–MA, and PDA–MA pairs, respectively. An increase in the coefficient α with increase in pH confirms nucleophilicity of activation of the peroxidase-catalyzed oxidation of the aromatic amines in the presence of AT and MA. Under optimal conditions the coefficients α for the TMB–AT, PDA–AT, TMB–MA, and PDA–MA pairs vary in the limits of (1.90-3.53)·103 M–1. [ABSTRACT FROM AUTHOR]

The mutagenic potential of ortho-phenylenediamine - known by studies on Salmonella typhimurium - was studied in mice, Chinese hamsters and Guinea pigs with the use of the micronucleus test. In bone marrow of all three species, chromosomal damage was detected following intraperitoneal injections of the test chemical, this damage was seen also after peroral administration to mice. Four derivatives of ortho-phenylenediamine containing one or two methyl-, nitro- or chlorosubstituents in 4- or 5-position of the aromatic ring were studied in mice. Of these the 4-methyl-derivative induced micronuclei, the 4-nitro-, 4,5-dimethyl-, and 4,5-dichloroderivatives were inactive. The results indicate that the chemical nature and the number of substituents influence the chromosome damaging potential. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence method is described for the determination of the anticancer drug 6-mercaptopurine (6-MP). The method is based on the use of fluorescent MoS2 quantum dots (MQDs) and of the enzyme horseradish peroxidase (HRP). In the absence of 6-MP, HRP catalyzes the oxidation of o-phenylenediamine (OPD) by H2O2 to form 2,3-diaminophenazine (DAP). This leads to quenching of the violet fluorescence of MQDs (measured at excitation/emission wavelengths of 360/415 nm), while the strong yellow fluorescence of DAP (peaking at 560 nm) becomes increasingly strong. In the presence of 6-MP, however, it will be preferentially oxidized by the HRP/H2O2 system to form a disulfide dimer. Hence, less H2O2 is available for the oxidation of OPD and less DAP will be formed. This results in the recovery of the violet fluorescence and a decrease of the yellow fluorescence. The ratio of the two signals can be used to quantify either H2O2 or 6-MP. Linear responses are observed for H2O2 in 0.5-140 μM concentration range, and for 6-MP in the 0.5-70 μM concentration range, with detection limits of 0.1 μM and 0.29 μM, respectively. The method was applied to the determination of 6-MP in spiked human urine and gave satisfactory results.Schematic of an enzymatic fluorometric method for determination of 6-mercaptopurine (6-MP). It is based on the presence of 6-MP that can inhibit the HRP-catalyzed oxidation of o-phenylenediamine (OPD) to form 2,3-diaminophenazine (DAP). Hence, the fluorescence resonance energy transfer (FRET) between DAP and MoS2 quantum dots (MQDs) is suppressed. [ABSTRACT FROM AUTHOR]

The authors describe a dual-mode (colorimetric-fluorometric) nanoprobe for H2O2 that was fabricated by covering molybdenum disulfide nanosheets (MoS2 NS) with ortho-phenylenediamine (OPD). The probe (OPD-MoS2 NS) was applied to the optical determination of H2O2, to the quantitation of cell numbers, and to the detection of intracellular concentrations of H2O2. Oxidation by H2O2 leads to a colored and fluorescent product (oxidized OPD) with absorption/excitation/fluorescence peaks at 450/450/557 nm. The nanoprobe can detect H2O2 in down to 500 nM concentrations, and HeLa cells at levels of 100 cells mL−1. The detection limit for intracellular H2O2 is in the 5.5 to 12.6 μM concentration range when the method is applied to cells at levels of 102-106 cells mL−1. Due to its good biocompatibility and easy cell uptake, the nanoprobe also permits sensitive fluorometric imaging of intracellular H2O2. It can also comparatively discriminate the change of intracellular oxidation state in living cancerous and normal cells.A dual-mode (colorimetric-fluorometric) detection nanoplatform based on OPD-modified MoS2 nanosheets is used to quantitatively detect H2O2, cell numbers and intracellular H2O2. The MoS2 nanoprobes also permit sensitive fluorescence imaging of intracellular H2O2, and can discriminate intracellular oxide states in living cancerous and normal cells. [ABSTRACT FROM AUTHOR]