P. Manisankar

Electroanalysis of some common pesticides using conducting polymer/multiwalled carbon nanotubes modified glassy carbon electrode.

The cyclic voltammetric behaviour of three common pesticides such as isoproturon (ISO), voltage (VOL) and dicofol (DCF) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNTs/GCE), polyaniline (PANI) and polypyrrole (PPY) deposited MWCNT/GCE. The modified electrode film was characterized by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The electroactive behaviour of the pesticides was realized from the cyclic voltammetric studies. The differential pulse voltammetric principle was used to analyze the above-mentioned pesticides using MWCNT/GCE, PANI/MWCNT/GCE and PPY/MWCNT/GCE. Effects of accumulation potential, accumulation time, Initial scan potential, amplitude and pulse width were examined for the optimization of stripping conditions. The PANI/MWCNT/GCE performed well among the three electrode systems and the determination range obtained was 0.01-100 mgL(-1) for ISO, VOL and DCF respectively. The limit of detection (LOD) was 0.1 microgL(-1) for ISO, 0.01 microgL(-1) for VOL and 0.05 microgL(-1) for DCF on PANI/MWCNT/GCE modified system. It is significant to note that the PANI/MWCNT/GCE modified system results in the lowest LOD in comparison with the earlier reports. Suitability of this method for the trace determination of pesticide in spiked samples was also realized.

A facile, water mediated, microwave-assisted synthesis of 4,6-diaryl-2,3,3a,4-tetrahydro-1H-pyrido[3,2,1-jk]carbazoles by a domino Fischer indole reaction–intramolecular cyclization sequence

An environmentally benign, facile and efficient synthesis of a series of 4,6-diaryl-2,3,3a,4-tetrahydro-1H-pyrido[3,2,1-jk]carbazoles was achieved in water with good yield by the reaction of diastereomerically pure 2-(3-oxo-1,3-diarylpropyl)-1-cyclohexanones with phenylhydrazine hydrochloride under microwave irradiation. The transformation presumably proceeds via a domino Fischer indole reaction–intramolecular cyclisation sequence.

Synthesis of 3-heteroarylthioquinoline derivatives and their in vitro antituberculosis and cytotoxicity studies.

A series of 3-heteroarylthioquinoline derivatives has been synthesized by the Friedlander annulation of 2-[(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]-1-aryl-1-ethanone/2-(1,3-benzothiazol-2-ylsulfanyl)-1-aryl-1-ethanone/1-aryl-2-[(2-phenyl-2H-1,2,3,4-tetraazol-5-yl)sulfanyl]-1-ethanone with 2-aminobenzophenone in good yields using YbCl(3) as the catalyst. These compounds have been screened for their in vitro activity against Mycobacterium tuberculosis H37Rv (MTB) and among the 21 compounds screened, 2-[2-(4-bromophenyl)-4-phenyl-3-quinolyl]sulfanyl-5-methyl-1,3,4-thiadiazole (5d) and 2-[2-(4-chlorophenyl)-4-phenyl-3-quinolyl]sulfanyl-5-methyl-1,3,4-thiadiazole (5c) were found to be the most active compounds with MIC of 3.2 and 3.5 μM respectively against MTB. The cytotoxic effects against mouse fibroblasts (NIH 3T3) in vitro were evaluated for 5c and 5d, which displayed no toxic effects (IC(50) > 1000 μM) against the mouse fibroblast cell line NIH 3T3.

A highly sensitive electrochemical biosensor for catechol using conducting polymer reduced graphene oxide-metal oxide enzyme modified electrode.

The fabrication, characterization and analytical performances were investigated for a catechol biosensor, based on the PEDOT-rGO-Fe2O3-PPO composite modified glassy carbon (GC) electrode. The graphene oxide (GO) doped conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) was prepared through electrochemical polymerization by potential cycling. Reduction of PEDOT-GO was carried out by amperometric method. Fe2O3 nanoparticles were synthesized in ethanol by hydrothermal method. The mixture of Fe2O3, PPO and glutaraldehyde was casted on the PEDOT-rGO electrode. The surface morphology of the modified electrodes was studied by FE-SEM and AFM. Cyclic voltammetric studies of catechol on the enzyme modified electrode revealed higher reduction peak current. Determination of catechol was carried out successfully by Differential Pulse Voltammetry (DPV) technique. The fabricated biosensor investigated shows a maximum current response at pH 6.5. The catechol biosensor exhibited wide sensing linear range from 4×10(-8) to 6.20×10(-5)M, lower detection limit of 7×10(-9)M, current maxima (Imax) of 92.55µA and Michaelis-Menten (Km) constant of 30.48µM. The activation energy (Ea) of enzyme electrode is 35.93KJmol(-1) at 50°C. There is no interference from d-glucose and l-glutamic acid, ascorbic acid and o-nitrophenol. The PEDOT-rGO-Fe2O3-PPO biosensor was stable for at least 75 days when stored in a buffer at about 4°C.

Synthesis and in vitro antimicrobial evaluation of novel fluoroquinolone derivatives.

A series of 1-ethyl-6,8-difluoro-4-oxo-7(4-aryl piperazin-1-yl) 1,4-dihydro-quinoline-3-carboxylic acid derivatives (6a-f) and 1-ethyl-6,8-difluoro-4-oxo-7(4-piperidin-1-yl) 1,4-dihydro-quinoline-3-carboxylic acid derivatives (7a-e) were synthesized and evaluated for antibacterial and antifungal activities. The antimicrobial activities of the compounds were assessed by the microbroth dilution technique. The compounds were also evaluated for antifungal activity against Candida albicans (ATCC 90028) and Cryptococcous neoformans (ATCC 14116) pathogens. The preliminary in vitro evaluation studies revealed that some of the compounds have promising antimicrobial activities.

Biofilm formation by Streptococcus pyogenes: Modulation of exopolysaccharide by fluoroquinolone derivatives

Biofilm formation by Streptococcus pyogenes has been demonstrated as a potentially important mechanism contributing to antibiotic treatment failure. S. pyogenes is the frequent cause of purulent infections in humans and also, it could play a significant role in recurrent and chronic infections. S. pyogenes biofilm communities tend to exhibit significant tolerance to antimicrobial challenge during infections. The fluoroquinolone derivatives have been previously reported from our laboratory as effective agents against human bacterial pathogens. Therefore, in the present study, we observed the effect of these fluoroquinolones on biofilm formation. Quantitative analysis using 2,3-bis (2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide (XTT) at the biofilm inhibitory concentrations (BIC), the compounds 6a, 6c, 7b and 7c reduced 61-71% biofilm and sub-BIC (0.5 and 0.25 BIC) significantly reduced biofilm formation by up to 30-38% and 16-18%, respectively. The Fourier Transform Infrared (FTIR) spectrum of the control and treated S. pyogenes revealed the shift in the chemical entity corresponding to the exopolysaccharide (EPS). The GC/MS analysis showed that the EPS of S. pyogenes has the most abundant neutral sugars l-glucose and d-mannose which is not detected in the fluoroquinolone treated EPS.

Investigation on the Usage of Clay Modified Electrode for the Electrochemical Determination of Some Pollutants

Abstract Redox behavior of three pollutants, namely endosulfan (EN), o-chlorophenol (OCP) and direct orange 8 (DO8) were investigated electrochemically using sodium montmorillonite clay modified glassy carbon electrode. Influence of pH, scan rate and concentration were studied on the voltammetric response. Suitable medium for the electrochemical studies of EN was pH 1.0 and for other two pollutants pH 13.0. EN exhibited one well-defined reduction peak accounting for irreversible 2e− transfer and leading to the removal of one chlorine atom. OCP underwent one electron oxidation to the formation of phenoxy radical resulting in an oxidation peak. DO8 showed two peaks for reductions and two peaks for oxidation as a result of the reduction of azo group and oxidation of phenoxide group. These electrochemical reactions of the three pollutants reveals the suitability of clay modified electrode for the electroanalysis. A differential pulse stripping voltammetric procedure for the determination of these pollutants was developed. The limits of determination for EN, OCP and DO8 are 5–300, 10–800 and 50–800 ppb, respectively.

Enhanced Sensing of Carbendazim, a Fungicide on Functionalized Multiwalled Carbon Nanotube Modified Glassy Carbon Electrode and Its Determination in Real Samples

An electrochemical sensor was developed by modifying a glassy carbon electrode (GCE) with functionalized multiwalled carbon nanotubes (FMWCNTs). The fabricated electrode was used to examine the redox behavior of carbendazim (CAR) in different pH solutions (pH 1.0–13.0). Surface morphology of the modified film was studied by scanning electron microscopy (SEM). An electroanalytical procedure for the determination of CAR was developed by adsorptive differential pulse stripping voltammetry (DPSV) over the range 0.01–5 × 104 µ g L−1. The developed procedure was also validated in real samples such as soil and water samples, and the applicability of the reported method is highly encouraging.

Electroanalysis of Endosulfan and o -Chlorophenol in Polypyrrole Coated Glassy Carbon Electrode

Electroanalysis of endosulfan, an important organochlorine pesticide and o -chlorophenol, a toxic pollutant was carried out with polypyrrole coated glassy carbon electrode. Pyrrole was electropolymerised on glassy carbon electrode potentiostatically at 0.9 V. Cyclic voltammogram, square wave voltammogram, differential pulse stripping voltammogram and square wave stripping voltammogram under their optimum experimental conditions were obtained for the determination of both compounds. On polypyrrole coated electrode, higher peak current response was observed with differential pulse and squarewave stripping techniques. Comparatively better analytical signal was noticed with square waveform than the differential pulse form. Optimum stripping voltammetric conditions were arrived and the calibration plot was made. The determination limit is 2.457 2 10 m 3 and 23.346 mM for endosulfan and 7.779 2 10m 3 and 26.916 mM for o-chlorophenol.

Electrochemical detection of mercury using biosynthesized hydroxyapatite nanoparticles modified glassy carbon electrodes without preconcentration

An electrochemical method for the determination of trace levels of mercury(II) ions using hydroxyapatite (HA) nanoparticles modified glassy carbon electrode (GCE) by square wave voltammetry is described for the first time. HA nanoparticles biosynthesized using Aloe vera plant (Av) extract exhibited improved electrocatalytic activity towards Hg2+ ions when compared to pristine HA. The Av-HA modified GCE showed an excellent selectivity and improved sensitivity towards the detection of Hg2+ without requiring preconcentration of mercury during voltammetric detection. Operational parameters such as pH, supporting electrolyte and scanning potential range were optimized. Under the optimum experimental conditions, the anodic peak current is proportional to the concentrations of mercury over a wide range of 2.0 × 10−7 to 2.1 × 10−4 M with the lowest detectable concentration of 141 nM. The Av-HA modified GCE showed good selectivity towards mercury in the presence of potential interferents such as copper, lead, cadmium, silver and zinc. The fabricated sensor displayed good reproducibility and is suitable for the determination of mercury in tap water and industry waste water.