Bhavana Deore

Enantioselective uptake of amino acid with overoxidized polypyrrole colloid templated with L-lactate

An overoxidized polypyrrole colloid, which can recognise enantiomers of amino acids has been prepared by a newly developed molecular imprinting technique. A polypyrrole colloid, which had been polymerised from a mixture of pyrrole (monomer), polyvinylpyrrolidone (steric stabiliser), peroxodisulfate (oxidant) and L-lactate (dopant), was overoxidized to create a dopant-complementary cavity. The enantioselectivity of the overoxidized colloid was evaluated by comparing the uptake of L-alanine and L-cysteine with that of the respective D-enantiomers. The L/D uptake ratios for these amino acids were about 2, while phenylalanine showed suppressed uptake for both the enantiomers. The absence of phenylalanine uptake can be explained in terms of the molecular size, which is too large to be accommodated by the cavity created by L-lactate. In contrast, a colloid templated with L-phenyllactate took up L-phenylalanine with a higher enantioselectivity of about 7. A colloid templated with L-lactate was applied to surface chirality analysis through enantioselective adsorption on cysteine-modified gold surfaces. Quartz microbalance experiments and scanning electron microscope observation of the gold surface revealed that the colloidal particle has higher affinity to a surface modified with L-cysteine than to one modified with D-cysteine.

Characterisation of polypyrrole nano-films for membrane-based sensors

Thin polypyrrole nano-films were formed chemically by interfacial polymerisation. An interesting feature of this chemical synthesis is that compact ultra thin polypyrrole films of 50 nm thickness doped with sulphate are obtained by a simple technique, although, films grown in the presence of different dopants were thicker (100 nm). Oxidative polymerisation allowed reproducible synthesis of very thin films in a very short time. Assessment of the surface of the films by atomic force microscopy indicated a strong influence on experimental conditions such as pH, nature and size of the dopant ions.

Fabrication Process and Characterization of a Novel Structural Isomer Sensor Molecularly Imprinted Overoxidized Polypyrrole Film

The preparation process of a molecularly imprinted overoxidized-polypyrrole film has been studied with the quartz crystal microbalance. The film has been derived from 1-naphthalenesulfonate (1-NS)-doped polypyrrole through overoxidation. The extraction of I-NS (dedoping) has created a shape-complementary cavity at the surface. The resulting overoxidized-polypyrrole film imprinted with 1-NS exhibited an excellent selectivity to the structural isomer, 1-NS. Aqueous 0.010 M 1-NS showed a frequency decrease of 110 Hz, while 2-NS shows only a negligible change. Thus, the shape-complementary cavity can recognize the difference in the spatial configuration of the SO - 3 substituent between the 1 and 2 positions.

Enantioselective uptake of amino acids using an electromodulated column packed with carbon fibres modified with overoxidised polypyrrole

A column packed with carbon fibres modified with overoxidized polypyrrole was utilised for the enantioselective uptake of glutamic acid. The polypyrrole prepared with L-glutamate as a dopant was electrochemically overoxidised to create a complementary cavity for the dopant. The target amino acid enantiomers were taken up and released by applying potential to the carbon fibre stationary phase. The uptake performance of an overoxidised polypyrrole modified carbon fibre electrode was investigated by optimising various important overoxidation parameters such as an overoxidation medium and applied potential. Under optimised conditions of overoxidation and with a column wash between the consecutive measurements, the reproducible uptake of L-glutamic acid was almost six times higher than that of D-glutamic acid. Further, in a comparison, the recognition ability of overoxidized polypyrrole with a pseudo-template cavity was examined.

An Overoxidized Polypyrrole/Dodecylsulfonate Micelle Composite Film for Amperometric Serotonin Sensing

An amperometric serotonin (5-hydroxytryptamine) sensor, based on an overoxidized polypyrrole (oPPy) modified electrode, is described. An oPPy composite film has been electrochemically synthesized through overoxidation of polypyrrole doped with a dodecylsulfonate micelle, Although the oPPy composite film was electroinactive, differential pulse voltammetry revealed that a glassy carbon (GC) electrode coated with the composite film had about four-fold higher sensitivity toward the neurotransmitter serotonin than a bare GC electrode with a linear response range of 1 to 100 μM (a correlation coefficient of 0.996). The oPPy modified electrode showed excellent reproducibility and stability for determination of serotonin at trace level concentrations (detection limit: I μM).

Pulsed amperometric detection of underivatized amino acids using polypyrrole modified copper electrode in acidic solution.

The successful pulsed amperometric detection of underivatized amino acids have been carried out in an acidic media on a polypyrrole (PPy) modified Cu electrode. The formation of PPy film doped with glutamate (glu) on a Cu electrode surface changes the mechanism of Cu dissolution. After application of multistep potential waveform, the PPy film was glu free due to the electro-reduction and overoxidation. High anodic potential polarization treatment yielded partially overoxidized PPy film as long as the Cu surface dissolution and amino acid permeation through the film was well controlled. This overoxidized PPy film acted as a charge and size exclusion barrier in order to improve the selectivity and stability of a Cu electrode. Various process parameters such as film modification time, detection and cleaning potential and pH of solution have been optimized to maximize the beneficial electrocatalytic properties of the electrode surface. At an optimized condition, detection limits for positively charged histidine and arginine are 19 and 22 pg respectively, whereas the neutral amino acids detected in amounts of 0.9-2.3 ng. Furthermore, the PPy coated Cu electrode response was long lived, stable and reproducible.