K. Chandrasekara Pillai

Nafion–RuO2–Ru(bpy)32+ composite electrodes for efficient electrocatalytic water oxidation

Abstract Electrocatalytic water oxidation to evolve O2 was studied on a Nafion–RuO2–Ru(bpy)32+ composite electrode. The O2 evolution current efficiency was largely improved for the multi-component electrode over the Nafion–RuO2 and Nafion–Ru(bpy)32+ individuals. The redox mediation through the Ru(bpy)32+ was found to dominate over the RuO2 catalytic effect in the water oxidation mechanism. The specific surface area of the RuO2, which was prepared at different temperatures (300–700°C), used in fabricating the composite electrode also played an important role in the overall water oxidation mechanism. Both the reaction and electrode parameters were optimized to get effective electrocatalytic current values in this study.

Studies of electrochemical behaviour of RuO2-PVC film electrodes: dependence on oxide preparation temperature

Abstract Ruthenium dioxide electrodes, prepared on a Pt substrate using coatings of PVC-RuO2 mixed in THF (designated as RuO2-PVC film electrode) have been studied for their redox behaviour in 1 M NaOH using variable scan cyclic voltammetry. The various redox transitions in the oxidation state of the central metal ion are characterized using electrochemical parameters such as peak potential, peak current, and surface charge. The effect of oxide preparation temperature, in the range 300–700 °C, on the redox characteristics has also been studied and correlated with the electrochemically active surface area (as measured using small amplitude cyclic voltammetry) and the true surface area (by the BET method).

Development and validation of indirect RP-HPLC method for enantiomeric purity determination of d-cycloserine drug substance

A new chiral purity method was developed for D-cycloserine (D-cys) by reverse phase HPLC and validated. Chiral derivatizing reagents, viz., o-phthalaldehyde and N-acetyl-L-cysteine were utilized in this method. The resultant diastereomers were resolved using Zorbax SB Phenyl HPLC column under isocratic elution. A mobile phase of 95:05 (v/v), 20mM Na(2)HPO(4) (pH 7), and acetonitrile, respectively, was used with the flow rate of 1.0 mL/min and UV detection at 335 nm. The method development with different chiral stationary phases and chiral derivatization reagents were also investigated. The stability of diastereomer derivative and influence of organic modifier and pH of the mobile phase were studied and optimized. The stability-indicating capability of the method was established by performing stress studies under acidic, basic, oxidation, light, humidity and thermal conditions. The detection and quantitation limit of L-cycloserine (L-cys) were 0.015 and 0.05% (w/w), respectively. A linear range from 0.05 to 0.30% (w/w) was obtained with the coefficient of determination (r(2)) 0.998. The recovery obtained for L-cys was between 92.9 and 100.2%. This method was applied successfully in pharmaceutical analysis to determine the content of L-cys in D-cys bulk drug.

Identification, isolation, characterization and response factor determination of process-related impurity in meprobamate drug substance

This paper describes identification and characterization of a process-related impurity of meprobamate drug substance observed in HPLC-UV method. Forced degradation studies were carried out under acidic, basic, oxidation, light and thermal conditions to assess the nature of the impurity. The pure impurity was obtained by preparative LC isolation and analyzed by NMR and mass. Structural elucidation by spectral data and formation of this impurity were discussed in detail. The structure of the process-related impurity was established as carbamic acid-2-carbamoyloxymethyl-2-methyl-pent-3-enyl ester (olefin). Also, the relative response factor, linearity, detection limit (DL), quantitation limit (QL) and recovery were determined for meprobamate and the impurity. Good linearity was obtained for the impurity over the concentration range of 0.03-0.20% (w/w) with the coefficient of determination (r(2)) of 0.999. The DL and QL of olefin impurity were 0.0003 and 0.001% (w/w), respectively. The isolated impurity was co-injected with meprobamate sample to confirm the retention time in HPLC.

Using RuO2 anode for chlorine dioxide production in an un-divided electrochemical cell.

Chlorine dioxide is a well known powerful disinfectant. Although there are several chemical and electrochemical methods developed for on-line chlorine dioxide generation, the details are mostly confined as patents. We studied in this work the electrochemical generation of dissolved chlorine dioxide from an un-buffered solution of sodium chlorite and sodium chloride mixture in an un-divided electrochemical cell set-up with RuO(2)-coated-Ti anode and Pt-coated-Ti cathode under constant current mode. Various process parameters including feed flow rate (10 to 150 ml/min), feed solution pH (2.3 to 9.4), concentration of sodium chloride (0 to 170 mM), concentration of sodium chlorite (0 to 7.7 mM), and the applied current (100 to 1,200 mA) were optimized. Experiments were conducted by performing single pass experiments, with no circulation. The current efficiency and the power consumption were calculated for the optimized conditions, and compared with IrO(2) electrode of our previous investigation.

Development and validation of rapid ion-chromatographic method with conductivity detection for trace level determination of allylamine in sevelamer drug substances.

A sensitive and rapid ion chromatography (IC) method was developed for the low level determination of allylamine (AAM) in sevelamer (SVM) drug substances, i.e., sevelamer hydrochloride (SVH) and sevelamer carbonate (SVC). This method utilized a Dionex Ion Pack CS14 IC column, a mobile phase of 10mM methane sulfonic acid with conductivity detection. The total chromatographic run time was as short as 8 min. The various factors involved in the sample preparation such as, extraction solvent, extraction time and stirrer speed were evaluated. This method was validated as per United States Pharmacopoeia (USP) and International Conference on Harmonization (ICH) guidelines in terms of detection limit, quantitation limit, linearity, precision, accuracy, specificity and robustness. Linearity of the method was very good over the concentration range of 9-750 μg/mL with the coefficient of determination (r(2)) 0.999. The detection and quantitation limit of AAM were 2.7 and 9.0 μg/mL, respectively. The recovery data obtained for AAM were between 97% and 109%. Also, the specificity of the method was proved through IC coupled with mass spectrometer (IC-MS). The developed method was found to be robust and applied successfully to determine the content of AAM in Sevelamer bulk drugs.

Surfactant structural effects on mediated electrocatalytic dechlorination: Links between the micellar enhancement of dechlorination reactions and micellar properties

Electrocatalytic dechlorination mediated by micelle-solubilized electrocatalysts has attracted considerable current interest for pollutant degradation. Aggregation in micellar assemblies and their interactions with the additives in solution are affected by the surfactant structure. By choosing appropriate surfactant molecules, the system properties may be altered to achieve enhanced dechlorination efficiency. Cetyltrimethylammonium bromide-based surfactants with different hydrocarbon lengths and headgroup structures were studied for their structural effects on [Co(I)(bipyridine)3]+-mediated dechlorination reactions. A widely used pollutants allyl chloride derivatives were studied as the substrates. The performance of the surfactants towards various dechlorination reactions was evaluated by cyclic voltammetry (CV) based on the catalytic efficiency. Key micellar parameters were determined by CV and rotating disc electrode using [Co(II)(bipyridine)3]2+ as the micelle-solubilized redox probe. The surfactants affected the dechlorination reaction to different extents, correlating well with their structure. The catalytic efficiency was explained by the interactions of the Co(II)/Co(I) with the surfactant hydrophobic tail and headgroup. This is the first report quantitatively linking the performance of the surfactants in dechlorination reactions with their molecular structure, showing that is possible to use variant surfactant structures to tune the micellar properties for their application towards the enhanced dechlorination of organic pollutants. Substrate structure-susceptibility to reduction relationships were also discussed.

Studies on Effective Generation of Mediators Simultaneously at Both Half-Cells for VOC Degradation by Mediated Electroreduction and Mediated Electrooxidation

Of the several electrochemical methods for pollutant degradation, the mediated electrooxidation (MEO) process is widely used. However, the MEO process utilizes only one (anodic) compartment toward pollutant degradation. To effectively utilize the full electrochemical cell, an improved electrolytic cell producing both oxidant and reductant mediators at their respective half-cells, which can be employed for treating two pollutants simultaneously, was investigated. The cathodic half-cell was studied first toward maximum [CoI(CN)5]4– (Co+) generation (21%) from a [CoII(CN)6]3– precursor by optimizing several experimental factors such as the electrolyte, cathode material, and orientation of the Nafion324 membrane. The anodic half-cell was optimized similarly for higher Co3(SO4)2 (Co3+) yields (41%) from a CoIISO4 precursor. The practical utility of the newly developed full cell setup, combining the optimized cathodic half-cell and optimized anodic half-cell, was demonstrated by electroscrubbing experiments with simultaneous dichloromethane removal by Co+ via the mediated electroreduction process and phenol removal by Co3+ via the MEO process, showing not only utilization of the full electrochemical cell, but also degradation of two different pollutants by the same applied current that was used in the conventional cell to remove only one pollutant.