Rupali Gupta

Co(II)-porphyrin-decorated carbon nanotubes as catalysts for oxygen reduction reactions: an approach for fuel cell improvement

The development of high-performance and cost-effective catalysts for the oxygen reduction reaction (ORR) is essential for the advancement of fuel cells. In this work, three different functionalized cobalt porphyrins, meso-tetraphenylporphyrinatocobalt(II) (CoTPP), meso-tetrakis(4′-hydroxyphenyl)porphyrinatocobalt(II) (CoTHPP) and meso-tetrakis(4′-carboxy-phenyl)porphyrinatocobalt(II) (CoTCPP), are prepared. These porphyrins are immobilized non-covalently on multiwalled carbon nanotubes (MWCNTs) and used for the ORR in 0.1 M HClO4, 0.1 M phosphate buffer solution (pH 7.0) and 0.1 M KOH media. The composite materials are characterized by using spectroscopic and electrochemical techniques and their oxygen reduction efficiencies are compared in different media. Kinetic interpretations and hydrodynamic voltammetry (in three media) studies demonstrated that the MWCNT–CoTPP, MWCNT–CoTHPP and MWCNT–CoTCPP composite materials exhibit significant efficiency with decreased overpotential, considerable methanol tolerance and long term operational stability (up to 3000 cycles) for the ORR similar to commercially available platinum carbon (Pt–C) catalysts. These results reveal that the new MWCNT–cobalt porphyrin composite materials can be a potential alternative to the expensive Pt–C catalysts or other commercial cathode materials in fuel cells.

Synthesis and characterization of gold nanoparticles incorporated bentonite clay for electrocatalytic sensing of arsenic(III)

AbstractIn the present manuscript, a simple and easy route to synthesize bentonite (bt) clay-supported gold nanoparticles (Au NPs) is reported (represented as Au-bt). Application of this new environmentally benign material in electrocatalytic determination of arsenite (As(III)) was studied. The successful synthesis and incorporation of Au NPs into the bt clay is supported by spectroscopic, microscopic and electrochemical methods. The synthesized Au-bt material was used to modify glassy carbon electrode (GC) by the evaporation of Au-bt aqueous suspension dropped on the surface of the GC (GC/Au-bt). Cyclic voltammetry and chronoamperometry studies of As(III) solutions were performed with this GC/Au-bt electrode which act as efficient platform for the electro-oxidation of As(III) to As(V) at a very low overpotential. Kinetic parameters were evaluated for the oxidation of As(III) at the GC/Au-bt platforms. A wide linear calibration range for the determination of As(III) from 1 to 1700 μM was obtained with high reproducibility and stability. A limit of detection, 0.1 μM was achieved with high sensitivity. Additionally, it showed a good selectivity for the determination of As(III) in the presence of copper(II) and other interfering ions suggesting a promising new route for trace level determination of As(III) in neutral conditions. Graphical AbstractBentonite clay supported, gold nanoparticle-based, biocompatible material was synthesized (represented as Au-bt) and it shows remarkable elecrocatalytic activity for As(III) oxidation. Based on the electrocatalytic activity of synthesized Au-bt material, As(III) determination is demonstrated in neutral electrolyte solution.

Methylene blue incorporated mesoporous silica microsphere based sensing scaffold for the selective voltammetric determination of riboflavin

This study reports the simple, selective and sensitive voltammetric detection of riboflavin (RF) using methylene blue (MB) incorporated sulfonic acid functionalized mesoporous silica microspheres (MSM), represented as MB-SO3H-MSM. MB-SO3H-MSM is synthesized and characterized by spectroscopic and microscopic methods. This material is coated on a glassy carbon (GC) electrode (symbolized as GC/MB-SO3H-MSM) to utilize it in electroanalytical applications. The electrochemical behavior of MB-SO3H-MSM is established using the GC/MB-SO3H-MSM electrode by cyclic voltammetry (CV) and electrochemical impedance spectroscopy techniques. The electrochemical behavior of RF at the GC/MB-SO3H-MSM electrode is also studied by CV. Compared to bare GC and SO3H-MSM coated GC, the GC/MB-SO3H-MSM electrode shows favorable electron transfer kinetics as well as an enhanced and stable electrochemical response of RF. Furthermore CV and differential pulse voltammetry (DPV) are used for the quantitative determination of RF at the GC/MB-SO3H-MSM electrode. The DPV response shows two linear calibration ranges of 10.0 nM to 15.0 μM and 15.0 to 50.0 μM. The detection limit based on the first linear calibration range is calculated as 5.0 nM with a sensitivity of 393.0 μA mM−1 cm−2. The fabricated sensing scaffold shows an excellent selectivity for RF over other soluble vitamins and interfering ions. The stability, reproducibility and determination of RF in pharmaceutical products are also demonstrated effectively.

Intracardiac repair in tetralogy of Fallot. Hemodynamic studies following corrective surgery.

Experience with the first 100 cases with tetralogy of Fallot subjected to intracardiac repair are presented. In this series there was an early hospital mortality of 12 per cent and 6 late deaths occurred. Eighty out of 82 survivors were available for follow-up and 33 of these underwent postoperative catheterization studies. The functional status of the survivors revealed excellent results in 89 per cent, good in 8 per cent, fair in 1 per cent and poor in 2 per cent. This is the largest series reported from India.

Non-enzymatic electrochemical sensing platform based on metal complex immobilized carbon nanotubes for glucose determination

This work demonstrates the preparation of an electrochemical sensing platform (ESP) based on nickel salophen (abbreviated as NiII–S, where salophen is N,N′-bis(salicylidene)-1,2-phenylenediamine) immobilized multiwall carbon nanotubes (MWCNT) for electrochemical sensing of glucose in an alkaline medium. NiII–S is immobilized onto MWCNT by stirring MWCNT and NiII–S in DMF (MWCNT–NiII–S). The MWCNT–NiII–S is characterized by physicochemical and electrochemical techniques. Then, a glassy carbon (GC) electrode was modifies with the MWCNT–NiII–S composite (GC/MWCNT–NiII–S) and it exhibits efficient electrocatalytic activity towards glucose oxidation when compared to GC modified with NiII–S. Cyclic voltammetry and chronoamperometry techniques are performed to understand the reaction kinetics and to determine the kinetic parameters such as electron transfer coefficient, rate constant of electrode reaction and catalytic rate constant. At the GC/MWCNT–NiII–S ESP a linear calibration range for the glucose determination is observed from 500 nM to 20 mM with a limit of detection of 80 nM (S/N = 3) and sensitivity of 70 μA mM−1. Further, the present ESP is successfully utilized for the detection of glucose in a human blood serum sample with a good recovery (96.4–104.1%).

Non-enzymatic Determination of Uric Acid by Ion Exchange Voltammetry at a Permselective Electrochemical Sensing Platform

Abstract Here we demonstrate a new strategy for electrochemical determination of uric acid (UA) using a cationic polymer as an electrochemical sensing platform (ESP). The cationic polymer is based on branched polyethylenimine (BPEI) cross-linked with ethylene glycol diglycidyl ether (EGDE). Ion exchange property of this cross linked cationic polymer (BPEI-EGDE) with negatively charged electroactive species is studied by cyclic voltammetry. Furthermore, this cationic cross-linked BPEI-EGDE polymer is coated on a glassy carbon electrode (GC) to construct the ESP for the quantitative analysis of biologically important molecule, UA at pH 7.0. It shows efficient oxidation of UA with respect to bare GC due to favorable electrostatic interaction of anionic UA with the positively charged BPEI-EGDE film. Finally it is demonstrated that the BPEI- EGDE films can be used as efficient ESP for non-enzymatic UA determination in the concentration range of 5 to 1500 µM with a sensitivity of 153 µA μM-1cm-2.

Synthesis of some Mannich bases of isatin-3-(4′-phenyl-3′-thiosemicarbazone) and their antibacterial activity

Some Mannich bases of isatin-3-(4′-phenyl-3′-thiosemicarbazone) have been prepared by employing formaldehyde and different secondary amines. These Mannich bases have been characterized on the basis of different physico-chemical evidences. These behave as Lewis-bases and have been estimated accordingly in non-aqueous media. Like some alkaloids they also form the reineckate complexes which serve for their estimation. Antibacterial activity of the synthesized Mannich bases has been studied by employingEscherichia coli andStaphylococcus aureus as bacterial strains.