Biomedical subjects
Publications and source records attributed to Tarasankar Pal.
Coinage metal chalcogenides in their nanoregime have been synthesized in aqueous medium at room temperature by mixing the nanoparticles of silver or copper with selenium nanoparticles which are authenticated by UV-vis, XRD and TEM analyses.
A new solid-phase catalyst has been designed and reported here for the catalytic reduction of o-nitrobenzoic acid to anthranilic acid. Electrostatic field force helps immobilization, in turn deposition of silver nanoparticles onto solid resin surfaces and reduction of o-nitrobenzoic acid through effective catalysis. While characterization of catalyst particles has been performed by different physical methods (XRD, XPS, SEM, TEM, and EDX) in a worthwhile fashion, selective reduction of o-nitrobenzoic acid has also been achieved conveniently (approximately 95%). Different thermodynamic parameters for the reduction reaction have been presented from varied experimental conditions. Novelty of this work lies with the catalytic efficiency of nanometer size silver particles immobilized solid-phase matrix for one step synthesis of anthranilic acid over bulk silver.
Silver nanoparticle aggregates were synthesized in large scale using resorcinol under alkaline condition to obtain an assembly of silver clusters. Stable dispersion of the cluster in aqueous medium has been examined out of resorcinol-capped silver nanoparticle assemblies. The UV-vis spectroscopy during the particle evolution has been studied in detail. From the high-resolution TEM (HRTEM) image and XRD pattern it was confirmed that the particles are made of pure silver only. The capping action of resorcinol has been authenticated from the FTIR spectra. UV-vis spectroscopy and TEM images reveal that the temperature, effect of vibrational energy, heat shock, and time-dependent particle evolution have unique bearing on the stability and surface properties of the clusters. The concentrations of silver nitrate, resorcinol, and NaOH have important influence on the particle evolution and its size. TEM images incite us to examine the aggregates to capitulate surface-enhanced Raman scattering (SERS) to the single molecular level using crystal violet (CV) and cresyl fast violet (CFV) as molecular probes. The SERS intensity of CV increases with increasing the size of the silver aggregate.
This article reports the reduction of methylene blue (MB) by thiocyanate ions (SCN(-)) in aqueous and micellar solutions. Thiocyanate ions are found to be an effective reducing agent for the decolorization of methylene blue under ambient condition. Effects of salting-in and salting-out agents have been investigated for real-time application in the reduction process. The salting-in agent urea has been found to uniquely enhance the rate of the reduction of MB by thiocyanate ion in the presence of micelles. Again, the catalytic activity of nanoparticles in the reduction of MB has also been studied. Detailed kinetic and thermodynamic aspects have been considered to realize the interaction between methylene blue and thiocyanate. Kinetic studies revealed that the reaction is reversible and follows first-order reaction kinetics.
Bimetallic nanoshells on functionalized polystyrene beads have been fabricated through a layer-by-layer deposition technique exploiting electrostatic interaction. The synthesis has been achieved through the immobilization and successive reduction of the corresponding precursor ions. It has been shown that the thickness of the shell can be controlled by a number of cyclic depositions of respective metals onto the surface of the polystyrene beads.
In this paper a convenient route for synthesizing Au(core)-Pd(shell) bimetallic nanoparticles in toluene has been reported as a result of co-reduction of gold(III) and palladium(II) precursors in toluene. N,N-Dimethyldodecylamine was used as a capping agent for the core-shell particles, which not only imparts stability to the organosol but also controls morphology of the evolved particles. The particles were characterized using UV-visible, transmission electron microscopy, and X-ray diffraction measurements. All results substantiate the formation of core-shell structure of the synthesized particles.
Gold nanoparticles have been prepared by UV photoactivation in the presence of a biopolymer, sodium alginate. The particles are characterized by UV-vis spectra and TEM studies. Both particle size and the UV-visible absorption peak are dependent on the sodium alginate concentration. The effects of various other parameters such as change of light source, cell material of the reaction chamber, heating effect, irradiation time, and HAuCl4 concentration are studied. The particles are spherical and in situ stabilized by the biopolymer. The method is very simple and reproducible.
Gold nanoparticles of variable sizes have been synthesized in toluene employing two-phase (water-toluene) extraction of AuCl4- followed by its reduction with sodium borohydride in the presence of a series of cationic surfactants of a homologous series having the general formula C(n)TAC. The solubility features of the gold particles in the organic solvent have been accounted qualitatively by calculating the van der Waals interaction potential between the particles. The effect of thermal energy and medium dielectric constant on the stability of metal particles has been studied by measuring the surface plasmon resonance. The stabilization of surfactant-mediated gold particles as hydrosol or organosol has been elucidated by considering the double-layer interaction as a function of the dielectric constant of the solvent medium. The influence of the counterion of the phase transfer reagent and stabilizing ligand on the photochemical stability of the gold colloids has been investigated. The fluorescence probe 1-methylaminopyrene (MAP) was considered for the surface functionalization of the gold particles, and it has been found that there is an enhancement of molecular fluorescence from the gold-probe assembly.
Fe3O4 nanoparticles with size approximately 13 nm have been prepared successfully in aqueous micellar medium at approximately 80 degrees C. To make Fe3O4 nanoparticles resistant to surface poisoning a new route is developed for coating Fe3O4 nanoparticles with noble metals such as gold or silver as shell. The shell thickness of the core-shell particles becomes tunable through the adjustment of the ratio of the constituents. Thus, the route yields well-defined core-shell structures of size from 18 to 30 nm with varying proportion of Fe3O4 to the noble metal precursor salts. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FTIR, differential scanning calorimetry (DSC), Raman and temperature-dependent magnetic studies.
In this report, selenious acid (H2SeO3) has been exploited to study the decolorization of a cationic dye, dimethylmethylene blue (DMMB) with UV-light. Micelles have effectively been employed as organized media to promote the rate of decolorization of the dye molecules. Micellar catalysis has been explained as a consequence of electrostatic, hydrophobic and charge transfer interactions. It has also been shown that strong charge transfer and electrostatic interaction lead to an appreciable enhancement of the reaction rate in micelle, whereas, weak hydrophobic interaction is of marginal importance. Existence of monomer-dimer equilibrium for the dye molecules under certain selective environments has been identified spectrophotometrically. Then the shift of dimer-monomer equilibrium of the dye has been successfully studied in aqueous and micellar environments exploiting photodecolorization process for the dye in solution. 'Salting-in' and 'salting-out' agents were introduced into the reaction mixture to examine the viability of the dye decolorization process for dye contaminated water samples.
A solution phase approach to synthesize a new metal-semiconductor nanocomposite, AuSe nanoalloy has been reported. The synthesis has been achieved through UV-photoactivation of preformed Au and Se nanoparticles in micelle. Non-ionic surfactant Triton X-100 was exploited as a micellar medium for effective fusion of gold and selenium particles under UV. Both physical and chemical studies have been performed to characterize the composition and morphology of the particles. UV-visible, TEM, SEM, XPS and AFM analyses were done for characterization purpose. The optical properties of nanocomposites have been substantiated through their interaction with a fluorescent probe, eosin in aqueous solution. The spectroscopic investigation of dye-metal-semiconductor assembly has been examined critically. It has been found that the dye experiences J and H types of aggregation on the surfaces of gold and selenium nanoparticles respectively. Again, the composition dependent change of the emission profile of the probe on different nanocomposite surfaces has been rationalized in accordance with the molecular dimerization of the dye.
The immobilization of gold nanoparticles in anion exchange resin and their quantitative retrieval by means of a cationic surfactant, cetylpyridinium chloride, is studied. The resin-bound gold nanoparticles (R-Au) have been used successfully as a solid-phase catalyst for the reduction of 4-nitrophenol by sodium borohydride. At the end of the reaction, the solid matrix remains activated and separated from the product. The recycling of catalyst particles after the quantitative reduction of 4-nitrophenol and the recovery of gold nanoparticles with unaffected particle morphology from the resin-bound gold nanoparticle entity have been reported.
Ligands with a beta-diketone skeleton have been employed for the first time as reductant to produce ligand stabilized gold nanoparticles of different shapes from aqueous HAuCl(4) solution. Evolution of stable gold nanoparticles follows first order (k approximately equal to 10(-2) min(-1)) kinetics with respect to Au(0) concentration. Growth of particles of different shapes (spherical or triangular or hexagonal) goes hand in hand under the influence of different beta-diketones, which have excellent capping and reducing properties. Chlorine insertion was observed to take place in the beta-diketone skeleton.
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A new fluorescent probe, methylamino derivative of pyrene, has been considered to characterize the concentration dependent emission behavior of an aqueous solution of anionic surfactants, viz., SDS, DSS, and SDBS. It was found that the emission of the probe is uniquely sensitive to the changes in surfactant (anionic) concentration due to the functional group effect of the probe over the parent moiety, pyrene. Here, 1-methylaminopyrene (MAP) showed significant quenching of emission well below the critical micellar concentration (cmc) of the surfactant. Excimer emission of the probe due to the formation of premicellar aggregates of the surfactant solutions at a concentration close to but below the cmc and again an enhanced emission of the probe above the cmc were observed as a consequence of definite MAP-surfactant interactions. These observations assisted the possible quantification ofsurfactant concentrations and their chain length dependent premicellar aggregate formations. Significant monomer emission in relation to probe distribution in micelle was analytically authenticated. Dynamic light scattering (DLS) studies revealed the incorporation of the probe molecules in the micellar core. The fluorophore emission showed nonlinear behavior when the surfactant concentration was far above the cmc. Abrupt changes in the emission characteristics in relation to the micellar concentration led to the determination of the cmc of the surfactants.
We report an impregnation technique for immobilization of silver(I) gelatin complex on silica gel. Subsequent UV exposure of the dry impregnated silica gel deposited silver nanoparticles on the solid matrix. Conventional techniques (UV-visible spectroscopy, TEM, EDAX, and thermal analysis) have been used to identify and characterize silver particles on silica surfaces. The photoproduced silver particles have shown unique SERS activity that authenticates the presence of silver nanoclusters in the silica matrix. Hence, the surface of the silica matrix remains SERS-active for months. This surface activity of the silica matrix inspired us to successfully study the catalytic reduction of nitro-compounds in aqueous, organic, and three different micellar media. Different thermodynamic parameters for the reduction processes have also been evaluated. Catalytic activity of the particles in micelles is explained in the light of hydrophobic and electrostatic interactions between the substrate and the micelles.
A solution phase UV-irradiation technique has been exploited to produce an AuSe nanoalloy through fusion of preformed Au (photoproduced) and Se (chemically prepared) in a micellar (TX-100) medium.
Evolution of exclusively spherical tiny gold nanoparticle aggregates is reported by UV photoactivation of aqueous HAuCl4 solution in cetyltrimethylammonium chloride micelles. In the photoactivation process, citrate is introduced for the first time to obtain aggregates of interacting particles with a tight size distribution. It is seen that the spectrum is substantially altered from the usual Au plasma resonance while the particles are present in the aggregate. Due to the interparticle interaction, the solution renders a blue color. Blue-pink color transformation of the gold sol has been observed in relation to the change in the interparticle distances without any change in the aspect ratio of the particles.