Somik Banerjee

Biocompatible novel starch/polyaniline composites: Characterization, anti-cytotoxicity and antioxidant activity

Starch/polyaniline composites have been synthesized using oxidative polymerization of polyaniline in an aqueous dispersion of starch isolated from Colocasia esculenta corm. Scanning electron micrographs reveals the growth of polyaniline over the surface of the starch granules. DPPH scavenging and haemolysis prevention assay have been performed to estimate the antioxidant activity and cytotoxicity of the composites. Formation of new properties of the composites as compared to starch and poloyaniline was evident from the X-ray diffraction analysis (XRD). Characterization done using UV-Vis, FTIR and DSC analysis provide evidence of composite formation. Composite possesses antioxidant nature which increases with the concentration of polyaniline. The haemolysis prevention activity of these novel composite materials is found to increase as compared to the pure polyaniline with minor compromise in the antioxidant activity. The materials show tremendous potential for biomedical applications.

Antioxidant activity and haemolysis prevention efficiency of polyaniline nanofibers.

Polyaniline (PAni) nanofibers have been synthesized by interfacial polymerization using hydrochloric acid (HCl) and camphor sulfonic acid (CSA) as dopants. The powder x-ray diffraction pattern of bulk polyaniline reveals ES I structure and has been indexed in a pseudo-orthorhombic lattice. The broadening of (110) reflection in the nanofiber samples has been analysed in terms of domain length and strain using a convolution method employing a Voigt function. The increase in d spacing for the (110) reflection in HCl-doped PAni nanofibers have been assigned to the change in structural conformation due to the increase in the tilt angle of the polymer chain, which is also evident from microRaman spectra. UV-vis spectra of the PAni nanofibers exhibit a remarkable blueshift in the absorption bands attributed to pi-pi* and pi-polaron band transitions indicating a reduction in particle size, which is also observed in TEM micrographs. The antioxidant activity of the polyaniline nanofiber samples has been investigated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay by employing UV-visible spectroscopy. It has also been observed that polyaniline nanofibers are able to protect the haemolysis of red blood cells (RBCs) from cytotoxic agents, namely H(2)O(2). The observed enhancement in the antioxidant and haemolysis prevention activity of the PAni nanofibers as compared to bulk has been attributed to the reduction in particle size and changes in structural conformation, as evident from TEM, XRD and microRaman spectroscopy.

Dielectric spectroscopy for probing the relaxation and charge transport in polypyrrole nanofibers

Conductivity relaxation and charge transport mechanisms in polypyrrole (PPy) nanofibers synthesized using a micellar polymerization technique with varying surfactant concentration has been investigated by dielectric relaxation spectroscopy. TEM micrographs depict that the increasing surfactant concentration leads to the reduction of the nanofiber diameter. X-ray diffraction studies show that domain length in the PPy nanofibers decreases with decreasing fiber diameter whereas the strain caused due to dislocations and point defects increases. The permittivity spectra reveal that the relaxation mechanism in PPy nanofibers are dominated by hopping of trapped charges. Two relaxation peaks in the impedance spectra are attributed to the two-phase structure in the PPy nanofibers; the lower frequency peak is ascribed to the phase of oxidized repeat units and the higher frequency peak to the reduced repeat units of PPy nanofibers. The occurrence of relaxation peaks at different frequencies in the impedance and modu...

Swift heavy ion irradiation induced enhancement in the antioxidant activity and biocompatibility of polyaniline nanofibers

Polyaniline (PAni) nanofibers doped with HCl and CSA have been irradiated with 90 MeV O(7+) ions with fluence of 3 x 10(10), 3 x 10(11) and 1 x 10(12) ions cm(-2). TEM micrographs show a decrease in the fiber diameter with increasing irradiation fluence, which has been explained on the basis of the Coulomb explosion model. XRD analysis reveals a decrease in the crystalline domain length and an increase in the strain. The increase in d-spacing for the (100) reflection with increasing irradiation fluence is ascribed to the increase in the tilt angle of the polymer chain, which is also evident from micro-Raman spectra. UV-vis spectra of the PAni nanofibers exhibit blue-shift in the absorption bands attributed to pi-pi* band transitions indicating a reduction in particle size after SHI irradiation; as also observed in TEM micrographs. Micro-Raman spectra also reveal a transition from the benzenoid to quinoid structures in the PAni chain as the fluence is increased. Although the quinoid unit has no hydrogen for DPPH scavenging, the antioxidant activity of PAni nanofibers is found to increase with increasing fluence. This has been attributed to the availability of more reaction sites as a result of fragmentation of the PAni nanofibers which compensates for the benzenoid to quinoid transition after irradiation. The biocompatibility of the PAni nanofibers is also found to increase with increasing irradiation fluence, indicating the possibility of employing swift heavy ion irradiation as an effective technique in order to modify conducting polymer nanostructures for biomedical applications.

Size Dependent Antioxidant Activity of Polypyrrole Nanofibers

Polypyrrole (PPy) nanofibers have been synthesized employing surfactant assisted miceller polymerization by varying the surfactant concentration. The synthesized nanofibers have been characterized using TEM, XRD, FTIR and UV‐Visible spectroscopy. TEM reveals that the diameter of the PPy nanowires decreases with the increase in surfactant concentration. X‐ray spectra shows an amorphous peak centered around 2θ = 24.6° which is attributed to the π‐π interaction of the partial PPy chains similar to that of aromatic groups. The domain length of the samples determined using the single‐line approximation technique, decreases with decreasing diameter whereas the strain in the material increases, which have been attributed to the reduction of size with increase in the surfactant concentration as revealed by TEM. The vibrational bands observed from the FTIR spectra confirm the formation of surfactant free PPy nanowires. UV‐Visible spectra shows a blue‐shift in the π‐π* absorption peak. Antioxidant activity of the s...

Swift heavy ion irradiation-induced structural and conformational changes in polypyrrole nanofibers

In the present paper, we report a detailed analysis of the fluence-dependent conformational and structural changes induced in the polypyrrole nanofibers (PPy NFs) upon swift heavy ion (SHI) irradiation. PPy NFs, synthesized using a cationic surfactant cetyltrimethylammonium bromide-assisted micellar polymerization technique, have been irradiated with 90 MeV O7+ ions at normal beam incidence with fluence varying from 3×1010 to 1×1012 ions/cm2 using a 15UD Pelletron accelerator under ultra-high vacuum. X-ray diffraction studies reveal a decrease in the domain length and an increase in the strain upon SHI irradiation. A decrease in the integral intensity upon SHI irradiation indicates the amorphization of the material. Micro-Raman (μR) studies confirm amorphization of the PPy NFs and also show that the PPy NFs get de-doped upon SHI irradiation. μR spectroscopy also reveals a benzenoid to quinoid transition in the PPy chain upon SHI irradiation.

Ion Irradiation Effects in some Electro-Active and Engineering Polymers Studies by Conventional and Novel Techniques

The effect of various radiations to a polymer is more complex and intense, compared to that in other materials, in view of the more complex structure and low bonding energies (5 10 eV for covalent bonds of the main carbon chain). Since the energy delivered to the polymer in most irradiations (including even beta and gamma rays of 1 to 10 MeV) exceeds this energy by many orders of magnitude, there is a high risk of radiation damage to all kind of polymers. However, engineering polymers (PC, PMMA, PVC, etc. and newer ones) as well as electro-active and other functional polymers (conducting polymers, polymer electrolytes) are finding ever increasing applications, often as nanocomposites, e.g. chemical and biomedical applications, sensors, actuators, artificial muscles, EMI shielding, antistatic and anticorrosion coatings, solar cells, light emitters, batteries and supercapacitors. Critical applications in spacecrafts, particle accelerators, nuclear plants etc. often involve unavoidable radiation environments. Hence, we need to review radiation damage in polymers and encourage use of newer tools like positron annihilation spectroscopy, micro-Raman spectroscopy and differential scanning calorimetry (DSC). Present review focuses on irradiation effects due to low energy ions (LEIs) and swift heavy ions (SHIs) on electro-active and engineering polymers, since gamma-and electron-beam-irradiations have been more widely studied and reviewed. Radiation damage mechanisms are also of great theoretical interest. Contents