Electrochemical Behaviour and Rapid Determination of L‐Dopa at Electrochemically Pretreated Screen Printed Carbon Electrode

A simple and rapid voltammetric method based on a disposable electrochemically pretreated screen‐printed carbon electrode is proposed for the determination of L ‐dopa. Under optimum differential pulse voltammetry conditions a limit of detection of 3.6×10^?7 M for L ‐dopa was obtained. The method was successfully applied to the determination of L ‐dopa in a commercial pharmaceutical formulation.     

Ambazone salt with p-aminobenzoic acid

In this study, we obtained a novel salt of ambazone (AMB) with p-aminobenzoic acid (PABA) that exhibits improved solubility and antibacterial activity. The salt was produced by solvent-drop grinding and characterized by powder X-ray diffraction, thermal analysis and Fourier transform infrared spectroscopy. The salt nature of the new form was confirmed by infrared spectroscopy based on the characteristic vibrational band of the protonated amino group. Based on the X-ray powder diffraction data, the compound crystallizes in the triclinic P_-1 space group with the following unit cell parameters: a = 14.294 Å, b = 9.162 Å, c = 8.777 Å, α = 95.90°, β = 100.63°, γ = 91.73°. Thermal analysis reveals the thermal events and different decomposition steps of this solid form as compared to the starting compounds. Powder dissolution measurements showed solubility improvement compared with pure ambazone of 2 and 3.3 times in water and phosphate buffer, respectively. Antibacterial tests showed higher activity of the salt to Gram-negative Escherichia coli and Salmonella bacteria as compared to AMB and PABA. The study demonstrates that the pharmaceutical salt of ambazone with p-aminobenzoic acid (AMB–PABA) can be a possible alternative to ambazone in the treatment of infections with Gram-negative bacteria.     

Proximal-gradient algorithms for fractional programming

In this paper, we propose two proximal-gradient algorithms for fractional programming problems in real Hilbert spaces, where the numerator is a proper, convex and lower semicontinuous function and the denominator is a smooth function, either concave or convex. In the iterative schemes, we perform a proximal step with respect to the nonsmooth numerator and a gradient step with respect to the smooth denominator. The algorithm in case of a concave denominator has the particularity that it generates sequences which approach both the (global) optimal solutions set and the optimal objective value of the underlying fractional programming problem. In case of a convex denominator the numerical scheme approaches the set of critical points of the objective function, provided the latter satisfies the Kurdyka-?ojasiewicz property.     

On the convergence rate improvement of a primal-dual splitting algorithm for solving monotone inclusion problems

We present two modified versions of the primal-dual splitting algorithm relying on forward–backward splitting proposed in V\(\tilde{\mathrm{u}}\) (Adv Comput Math 38(3):667–681, 2013) for solving monotone inclusion problems. Under strong monotonicity assumptions for some of the operators involved we obtain for the sequences of iterates that approach the solution orders of convergence of \(\mathcal{{O}}(\frac{1}{n})\) and \(\mathcal{{O}}(\omega ^n)\), for \(\omega \in (0,1)\), respectively. The investigated primal-dual algorithms are fully decomposable, in the sense that the operators are processed individually at each iteration. We also discuss the modified algorithms in the context of convex optimization problems and present numerical experiments in image processing and pattern recognition in cluster analysis.     

Photocatalytically-assisted electrochemical degradation of <Emphasis Type="Italic">p</Emphasis>-aminophenol in aqueous solutions using zeolite-supported TiO<Subscript>2</Subscript> catalyst

This paper reports the results of an investigation into enhancement of the electrochemical oxidation of p-aminophenol (4-AP) in an aqueous solution with a boron-doped diamond (BDD) electrode, assisted by photocatalysis using a zeolite-supported TiO₂ (Z-TiO₂) catalyst. The BDD electrode was characterised in 0.1 M Na₂SO₄-supporting electrolyte and the presence of 4-AP by open-circuit potential behaviour (OCP) and cyclic voltammetry (CV). The electrode behaviour was investigated in the dark and following UV irradiation and in the absence/presence of the Z-TiO₂ catalyst. The electro-oxidation process was carried out using chronoamperometry (CA) and multiple-pulsed amperometry (MPA) at the selected potential under potentiostatic conditions. The electrochemical degradation process of 4-AP on the BDD electrode was improved by the application of a pulsed potential, which allowed both in-situ electrochemical cleaning of the electrode and indirect oxidation of 4-AP by oxygen evolution. The application of photocatalysis using Z-TiO₂ in the 4-AP electrochemical degradation exhibited an enhanced effect when the anodic potential was set at +1.25 V vs. Ag/AgCl in the water stability region, close to the oxygen evolution potential.     

Sensitive detection of endocrine disrupters using ionic liquid--single walled carbon nanotubes modified screen-printed based biosensors

Simple and low cost biosensor based on screen-printed electrode for sensitive detection of some alkylphenols was developed, by entrapment of HRP in a nanocomposite gel based on single-walled carbon nanotubes (SWCNTs) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) ionic liquid. Raman and FTIR spectroscopy, CV and EIS studies demonstrate the interaction between SWCNTs and ionic liquid. The nanocomposite gel, SWCNT-[BMIM][PF₆] provides to the modified sensor a considerable enhanced electrocatalytic activity toward hydrogen peroxide reduction. The HRP based biosensor exhibits high sensitivity and good stability, allowing a detection of the alkylphenols at an applied potential of −0.2 V vs. Ag/AgCl, in linear range from 5.5 to 97.7 μM for 4-t-octylphenol and respectively, between 5.5 and 140 μM for 4-n-nonylphenol, with a response time of about 5 s. The detection limit was 1.1 μM for 4-t-octylphenol, and respectively 0.4 μM for 4-n-nonylphenol (S/N = 3).     

Green light radiation effects on free radicals inhibition in cellular and chemical systems

Free radicals generation is inhibited through green light (GL) irradiation in cellular systems and in chemical reactions. Standard melanocyte cultures were UV-irradiated and the induced cellular reactive oxygen species (ROS) were quantified by the fluorescence technique. The same cell cultures, previously protected by a 24h GL exposure, displayed a significantly lower ROS production. A simple chemical reaction is subsequently chosen, in which the production of free radicals is well defined. Paraffin wax and mineral oil were GL irradiated during thermal degradation and the oxidation products checked by chemiluminescence [CL] and Fourier transform infrared spectra [FT-IR]. The same clear inhibition of the radical oxidation of alkanes is recorded. A quantum chemistry modeling of these results is performed and a mechanism involving a new type of Rydberg macromolecular systems with implications for biology and medicine is suggested.