Felipe Fantinato Hudari

The oxidation of p-phenylenediamine, an ingredient used for permanent hair dyeing purposes, leads to the formation of hydroxyl radicals: Oxidative stress and DNA damage in human immortalized keratinocytes.

The hair-dyeing ingredient, p-phenylenediamine (PPD), was previously reported to be mutagenic, possibly by inducing oxidative stress. However, the exact mechanism of PPD in inducing oxidative stress upon skin exposure during hair-dyeing in human keratinocytes remains unknown. The aim of our studies was therefore to investigate the toxicity of PPD and its by-products in human immortalized keratinocytes (HaCaT) after auto-oxidation and after reaction with hydrogen peroxide (H2O2). We found that the PPD half maximal effective cytotoxic concentration (EC50) to HaCaT is 39.37 and 35.63 μg/mL after 24 and 48 h, respectively, without addition of H2O2 to induce oxidation. When PPD (10 or 100 μg/mL) is combined with 10.5 μg/mL of H2O2, intracellular ROS production by HaCaT after 1 h was significantly increased and enhanced levels of DNA damage were observed after 4 h of exposure. After 24 h incubations, 20 μg/mL of PPD increased the level of DNA oxidation in HaCaT. Also, we found that the in vitro reaction between PPD and H2O2, even below the maximum allowance by cosmetic industries, released hydroxyl radicals which can damage DNA. Taken together, we conclude that PPD alone and when combined with H2O2 increases the formation of reactive oxygen species in human keratinocytes, leading to oxidative stress and subsequent DNA damage. These alterations suggest that the mechanism by which PPD exposure, alone or combined with H2O2, damages keratinocytes by the formation of the high reactive HO∙ radicals.

Adsorptive stripping voltammetry for simultaneous determination of hydrochlorothiazide and triamterene in hemodialysis samples using a multi-walled carbon nanotube-modified glassy carbon electrode

Hemodialysis is the most commonly used method for the treatment of chronic kidney disease. In this procedure, some patients use diuretics to control weight gain and blood pressure. In this work, a voltammetric sensor based on a glassy carbon electrode modified with carbon nanotubes (GCE/MWCNT) is described for the simultaneous determination of the diuretics hydrochlorothiazide (HCT) and triamterene (TRT). The oxidation of the diuretics on the GCE/MWCNT surface was observed at 1.01 and 1.17V for HCT and TRT, respectively, allowing simultaneous determination, which was not possible with the unmodified glassy carbon electrode. The GCE/MWCNT electrode provided 6-fold and 10-fold gains in anode peak intensity for HCT and TRT, respectively, compared to the unmodified electrode. After optimization of the conditions (pH, accumulation time, and accumulation potential), analytical curves were constructed for the analytes in the range from 1.0 × 10-7 to 2.0 × 10-5molL-1. The detection limits for HCT and TRT were 2.8 × 10-8 and 2.9 × 10-8molL-1, respectively. A high performance liquid chromatography method with diode array detection was also developed for the determination of HCT and TRT in hemodialysis samples, for comparison with the electroanalytical method.

Advances and Trends in Voltammetric Analysis of Dyes

Since 1856 when W. H. Perkin synthesized the first synthetic dye (Mauveine), a wide variety of colors and shades are produced and used in several commercial products. The occurrence in water and wastewater has gained controversy regarding their toxicity and mutagenicity and it has been regulation by several regulatory agencies. Thus, analytical methods able to determine these colorings in several matrices with high sensitive and robust enough are relevant. Among several analytical methods, the use of electroanalytical methods, especially the voltammetric techniques, are of great interest due to the high selectivity, sensitivity, use of low quantity of sample, little or without sample treatment, and low waste generation, which contributes to reduced environmental impact. Over the past decades, the technical based on current-potential curves by using of static electrodes have gained considerable progress, as minimizing the effect of capacitive current and the possibility of pre-concentration of the analyte at the electrode surface, which has reflected in lower detection levels. The present work gives an overview about the analytical methods available in literature focusing on electroanalysis of dyes by using voltammetric techniques. The advances of the electroanalytical techniques and the use of different modifiers to increase sensitivity and selectivity are reviewed.

Enhanced Detection of Ponceau 4R Food Dye by Glassy Carbon Electrode Modified with Reduced Graphene Oxide

This paper reports the development of a glassy carbon electrode modified with a reduced graphene oxide (r-GO/GCE) for the determination of the food dye named Ponceau 4R (PNC). The modified sensor presented excellent signal gain in relation to the GCE and GCE modified with graphene oxide besides exhibiting well defined oxidation peaks for PNC at potential of 0.61 V. Through the application of square wave voltammetry using the medium of 0.1 mol L Britton-Robinson (BR) buffer (pH 5.0), analytical curves were constructed under optimized conditions, where linear regions were found within the range of 0.200 to 20.0 μmol L. The limits of detection and quantification were 2.84 × 10 and 9.46 × 10 mol L, respectively. The sensor was successfully applied towards the determination of PNC in instant juice sample. A comparison made between the result obtained through the application of this sensor and via the high-performance liquid chromatography (HPLC) technique showed no significant difference between the two methods.

Reagentless Detection of Low-Molecular-Weight Triamterene Using Self-Doped TiO2 Nanotubes

TiO2 nanotube electrodes were self-doped by electrochemical cathodic polarization, potentially converting Ti4+ into Ti3+, and thereby increasing both the normalized conductance and capacitance of the electrodes. One-hundred (from 19.2 ± 0.1 μF cm-2 to 1.9 ± 0.1 mF cm-2 for SD-TNT) and two-fold (from ∼6.2 to ∼14.4 mS cm-2) concomitant increases in capacitance and conductance, respectively, were achieved in self-doped TiO2 nanotubes; this was compared with the results for their undoped counterparts. The increases in the capacitance and conductance indicate that the Ti3+ states enhance the density of the electronic states; this is attributed to an existing relationship between the conductance and capacitance for nanoscale structures built on macroscopic electrodes. The ratio between the conductance and capacitance was used to detect and quantify, in a reagentless manner, the triamterene (TRT) diuretic by designing an appropriate doping level of TiO2 nanotubes. The sensitivity was improved when using immittance spectroscopy (Patil et al. Anal. Chem. 2015, 87, 944-950; Bedatty Fernandes et al. Anal. Chem. 2015, 87, 12137-12144) (2.4 × 106 % decade-1) compared to cyclic voltammetry (5.8 × 105 % decade-1). Furthermore, a higher linear range from 0.5 to 100 μmol L-1 (5.0 to 100 μmol L-1 for cyclic voltammetry measurements) and a lower limit-of-detection of approximately 0.2 μmol L-1 were achieved by using immittance function methodology (better than the 4.1 μmol L-1 obtained by using cyclic voltammetry).