Raviraj M. Kulkarni

Electro-sensing base for mefenamic acid on a 5% barium-doped zinc oxide nanoparticle modified electrode and its analytical application

In the present work, surface enhanced electro-oxidation of mefenamic acid (MFA) at a glassy carbon electrode modified with 5% barium doped ZnO nanoparticles was studied. Cyclic voltammograms with a maximum peak current at pH 5 in the pH range of 3.0–11.0 were recorded at a scan rate of 50 mV s−1, with a distinct oxidation peak in the range of 0.2–1.0 V (versus Ag/AgCl). Two protons and electrons accompanied the electrode reaction. Based on the experimental results, a possible electro-oxidation mechanism for MFA was proposed. Quantitative analysis of MFA was carried out using a differential-pulse voltammetric method (DPV). Linearity was observed in the range of 500 nM to 10.0 × 103 nM. LOD and LOQ were calculated to be 6.02 nM and 20 nM, respectively. In addition, the developed method was used in the in vitro analysis of MFA in pharmaceutical formulations and spiked human urine samples.

Transformation of levofloxacin during water chlorination process: kinetics and pathways

The kinetics and mechanism of removal of the fluoroquinolone antibacterial levofloxacin (LFC) by free available chlorine (FAC) during water chlorination processes have been investigated for the first time between pH values 4.2 and 8.5. The pH-dependent second-order rate constants were found to decrease with increase in pH (e.g. apparent second order rate constant; k″app = 20 dm3 mol −1 s −1 at pH 4.2 and k″app = 1dm3 mol −1 s −1 at pH 8.5 and at 25°C). The products of the reaction were determined by liquid chromatography and high resolution mass spectrometry. There are two plausible pathways for the LFC chlorination. The major channel is electrophilic halodecarboxylation of the quinolone moiety in which HOCl reacts at tertiary N(4) amine to form a reactive chlorammonium intermediate (R3N(4)Cl+) that can catalytically halogenate LFC, and the minor channel is chlorination at the piperazinyl moiety in which HOCl reacts at tertiary N(4) amine to form a reactive chlorammonium intermediate (R3N(4)Cl+) followed by intermediate degradation both at the piperazinyl and quinolone moieties with successive chlorination. The effect of temperature on the rate of the reaction was studied at four different temperatures and rate constants were found to increase with increase in temperature and the thermodynamic activation parameters Ea, DLH≠, DLS≠ and ΔG≠ were evaluated and discussed.

Kinetics, thermodynamic, and adsorption studies on removal of chromium(VI) using Tulsion A-27(MP) resin

ABSTRACT The kinetics, thermodynamic, and adsorption studies on removal of chromium(VI) from aqueous and in presence of industrial solvents 2-methoxyethanol and 2-ethoxyethanol with macroporous resin Tulsion A-27 was studied at varying concentration of Cr(VI), adsorbent dosage, pH, contact time, and temperature. Batch shaking sorption experiments were carried out to evaluate the performance of Tulsion A-27(MP) anion exchange resin in the removal of Cr(VI) from aqueous and mixed aqueous solvents, 2-methoxyethanol and 2-ethoxyethanol. The concentrations of Cr(VI) in aqueous and mixed aqueous solvents were determined by UV-Visible spectrophotometer. As the adsorption process is pH dependent, it showed maximum removal efficiency of Cr(VI) in the pH range of 5–6 for an initial chromium concentration of 0.0011 M. Effect of temperature on the equilibrium constant was studied and the thermodynamic parameters were evaluated. Kinetic experiments revealed the dominance of adsorption. The sorption models, Langmuir an...

Oxidative transformation of antiretroviral drug zidovudine during water treatment with permanganate: reaction kinetics and pathways

AbstractThe presence of the pharmaceutical substances in the water has been reported by many studies and has attracted attention across the world. The mechanistic insight into oxidation of antiretroviral drug zidovudine (ZDV) by potassium permanganate was investigated between the pH values 3.0 and 9.0. The pH-dependent second-order rate constants were determined and rate constants decreased with an increase in pH. The products of the reaction were identified by high-resolution mass spectrometry. A probable mechanism is proposed which involves the formation of an intermediate complex between permanganate and ZDV, which further undergoes degradation in subsequent fast steps to form various oxidized products. The different parameters like effect of initially added products, solvent polarity, ionic strength, temperature, and pH on the rate of the oxidative degradation of ZDV by permanganate were systematically studied. The various activation parameters were determined from the effect of variation in temperatu...

Mechanistic and spectroscopic investigations of Ru3+-catalyzed oxidative degradation of azidothymidine by heptavalent manganese at environmentally relevant pH

AbstractThe rapid increase in the population across the world has increased the consumption of pharmaceutical substances. These pharmaceutical substances have penetrated into the water through various ways. Mechanistic and spectroscopic investigations of Ru3+-catalyzed oxidative degradation of azidothymidine (AZT) by heptavalent manganese was studied for the first time. The values of pH-dependent apparent second-order rate constant show that Ru3+ accelerates the rate of the oxidative degradation of AZT by heptavalent manganese eight times faster than uncatalyzed reaction. Ru3+ catalytic oxidative degradation of AZT by heptavalent manganese was greatly depending on the pH. The removal of the AZT by heptavalent manganese in the presence of Ru3+ shows unit order with respect to heptavalent manganese, Ru3+, and AZT. The influences of dielectric constant, ionic strength, pH, addition of monomer, variation in catalyst concentration, etc. on the rate of the reaction were studied thoroughly and discussed in detai...

Study of the Effect of Nano-silica Particles on Resin-Bonded Moulding Sand Properties and Quality of Casting

The cast quality in chemical bonded sand mould system is influenced primarily by sand mould properties such as, compression strength, permeability, gas evolution, and collapsibility. Amount of resin and hardener, curing time and number of strokes influence the sand mould properties. The experiments are conducted with the above mentioned input output, as per Taguchi’s L9 orthogonal array. Pareto analysis of variance is conducted to determine the percent contribution of inputs on output, individually. The optimal factor level is determined for each output separately. The conflicting requirements in foundry sand mould properties can be solved by multiple objective optimization. Principal component analysis is applied to determine the relative importance of individual output. Grey relational analysis is used to convert multiple objective functions to a single objective function for optimization task. Pareto analysis is utilized to determine the optimal input factor combination and their relative percent contribution towards moulding sand properties. The nano-silica particles are used as additive to enhance the moulding sand properties. The results have shown that, the nano-silica particles pose a remarkable improvement in sand mould properties and casting quality.

Deamination and decarboxylation of L-thyroxine by Chloroamine-T (CAT) in acidic medium: A mechanistic and kineitc study

In this manuscript, we report a spectrophotometric study (at 25°C) of oxidation of L-thyroxine by Chloramine T and their mechanistic pathway. The reactions are first-order with respect to both LTX and CAT. Protonated Chloramine-T, TsNHCl, have been suggested as the reactive species of CAT. The Stochiometry of the reaction is 1 : 1. The main products, 2-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl] acetaldehyde was separated, and identified by column chromatography, TLC and FT-IR. The reaction fails to initiate polymerization in the presence of acrylonitrile under the experimental conditions employed. Investigations of the reaction at different temperatures allowed the determination of the activation parameters and a tentative reaction mechanism in good consistency with the kinetic results is discussed.