Department of Chemistry
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Item Steric interactions between mobile ligands facilitate complete wrapping in passive endocytosis(APS, 2018-09) Jana, Pritam KumarReceptor-mediated endocytosis is an ubiquitous process through which cells internalize biological or synthetic nanoscale objects, including viruses, unicellular parasites, and nanomedical vectors for drug or gene delivery. In passive endocytosis the cell plasma membrane wraps around the “invader” particle driven by ligand-receptor complexation. By means of theory and numerical simulations, here we demonstrate how particles decorated by freely diffusing and nonmutually interacting (ideal) ligands are significantly more difficult to wrap than those where ligands are either immobile or interact sterically with each other. Our model rationalizes the relationship between uptake mechanism and structural details of the invader, such as ligand size, mobility, and ligand-receptor affinity, providing a comprehensive picture of pathogen endocytosis and helping the rational design of efficient drug delivery vectors.Item Irreversible transition of amorphous and polycrystalline colloidal solids under cyclic deformation(APS, 2018-12) Jana, Pritam KumarCyclic loading on granular packings and amorphous media leads to a transition from reversible elastic behavior to an irreversible plasticity. In the present study, we investigate the effect of oscillatory shear on polycrystalline and amorphous colloidal solids by performing molecular dynamics simulations. Our results show that close to the transition, both systems exhibit enhanced particle mobility, hysteresis, and rheological loss of rigidity. However, the rheological response shows a sharper transition in the case of the polycrystalline sample as compared to the amorphous solid. In the polycrystalline system, we see the disappearance of disclinations, which leads to the formation of a monocrystalline system, whereas the amorphous system hardly shows any ordering. After the threshold strain amplitude, as we increase the strain amplitude both systems get fluid. In addition to that, particle displacements are more homogeneous in the case of polycrystalline systems as compared to the amorphous solid, mainly when the strain amplitude is larger than the threshold value. We do not see any effect of oscillation frequency on the reversible-irreversible transition.Item Study on metal nanoparticles synthesis and orientation of gemini surfactant molecules used as stabilizer(Elsiever, 2015-05-01) Pande, Surojit; Saha, Subit Kumar; Gangopadhyay, SubhashisIn the present study, we report the synthesis of gold (Au), silver (Ag), and gold–silver alloy (Au–Ag) nanoparticles (NPs) by seed-mediated method using gemini surfactant, containing diethyl ether spacer group as a stabilizer. As-synthesized NPs are found very much stable and have been characterized using UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and zeta potential techniques. The orientation of gemini surfactant molecules surrounding the metal NPs has been investigated exploiting twisted intramolecular charge transfer (TICT) fluorescence properties of a probe 4-(N,N-dimethylamino) cinnamaldehyde (DMACA). The quenching efficiencies of different NPs have been performed in the fluorescence of DMACA and are found to be different. This effect can be related to the location of DMACA as well as the electro-negativity of the metals as the extent of orientation of the surfactant molecules around NPs controls the location of DMACA in a bilayer. To support the location of DMACA, fluorescence quenching studies with cetylpyridinium chloride (CPC) as an external quencher have also been carried out.Item Highly sensitive fluorescent imidazolium-based sensors for nanomolar detection of explosive picric acid in aqueous medium(Elsiever, 2016-06-28) Sakhuja, Rajeev; Pant, Debi D.Two novel fluorescent coumaryl linked imidazolium salts have been synthesized, characterized and found to be highly selective for nanomolar detection of commonly used explosive picric acid, over other aromatic explosives in aqueous medium. The compounds are highly photostable and are practically applicable for sensing picric acid in real environmental samples, in presence of interfering aromatic/non-aromatic explosives and metal ions. In solution, the high sensitivity of the sensors toward picric acid can be predominantly attributed to the ground-state charge-transfer complex formation based on UV–vis studies, time resolved fluorescence results and DFT calculations.Item Detection of Hg2+ ions in aqueous medium using an indole-based fluorescent probe: Experimental and theoretical investigations(Elsiever, 2017-12) Sakhuja, Rajeev; Pant, Debi D.Mercury pollution is a widespread danger to human health and environment. Due to limitations associated with the existing Hg2+ chemosensors, development of new, efficient and selective chemosensors capable of sensing mercury ions in aqueous medium remains a demanding area of research. In this regard, an indole-based fluorescent probe has been synthesized and characterized by detailed spectroscopic analysis. The probe showed a high selectivity and sensitivity towards Hg2+ by giving significant fluorescence quenching over other tested cations in H2O/DMF (7:3, v/v) medium. The association constant (Ka) was 6.4 × 103 M− 1 between sensor and Hg2+. The detection limit of sensor to Hg2+ was found to be 0.143 μM (143 nM). The experimental results have been verified with Density Functional Theory.Item Sensing of contaminants in potable water using TiO2 functional film(AIP, 2016) Shukla, Paritosh; Manjuladevi, V.; Gupta, Raj KumarThe piezoelectric based quartz crystal microbalance is employed for sensing contaminants in potable water. A spin coated thin layer of TiO2 nanoparticles was formed at the sensing area of a 5 MHz AT-cut quartz wafer. The thin film of TiO2 nanoparticles forms a mesoporous functional layer for the trapping of water borne contaminants. The morphology of the thin film of TiO2 nanoparticles was studied using field emission scanning electron microscope (FESEM). The surface morphology of the TiO2 nanoparticles reveals the mesoporous structures indicating large number of defects and porous sites. Such film was employed for the detection of water borne contaminants by detecting the piezoelectric response from a quartz crystal microbalance. We found the film to be very sensitive to the contaminants. The minimum detection limit was found to be 330 ppb. The effect of surface recharging was also studied by altering the physical conditions so that the film can be used for repetitive usage.Item Functionalized pyranopyrazole molecules as corrosion inhibitors for mild copper metal in HCl solution: synthesis, theoretical studies, and physical investigations(IOP, 2018-02-07) Shukla, Paritosh; Manohar, Prashant Uday; Pande, Surojit; Dalvi, AnshumanFive substituted pyranopyrazole (PPZ) derivatives were chemically synthesized by conventional and microwave assisted synthesis (MWA) methodology. Their differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) analyses, and the corrosion inhibitor properties on mild copper metal in 1 M HCl solution were investigated by SEM (Scanning Electron Microscopy), EDS (Energy Dispersive Spectroscopy), and XRD (x-ray Diffraction) all of which showed good anti-corrosion behavior. Further, mechanical property investigations were also performed by measuring the tensile strength of the PPZ-adsorbed Cu-strips. Finally, the inhibition action was evaluated by quantum chemical parameters. All the experimental results pointed that the molecules acted as excellent anti-corrosion surface active agents for copper metal.Item Enhanced electrical transport in ionic liquid dispersed TMAI-PEO solid polymer electrolyte(AIP, 2015-02-17) Kumar, Anil; Dalvi, AnshumanA polymer composite is prepared by dispersing ionic liquid [Bmim][BF4] in Polyethylene oxide-tetra methyl ammonium iodide composite and subsequent microwave treatment. X-ray diffraction patterns confirm the composite nature. To explore possibility of proton conductivity in these films, electrical transport is studied by impedance spectroscopy and DC polarization. It is revealed that addition of ionic liquid in host TMAI-PEO solid polymer electrolyte enhances the conductivity by ∼ 2 orders of magnitude. Polarization measurements suggest that composites are essentially ion conducting in nature. The maximum ionic conductivity is found to be ∼2 × 10−5 for 10 wt % ionic liquid.Item Li2SO4⎯Li2O⎯P2O5 ionic glass dispersed with [Bmim] [PF6] ionic liquid: Electrical transport and thermal stability investigations(AIP, 2014-02-17) Kumar, Anil; Dalvi, AnshumanA fast ionic composite is prepared by dispersion of Ionic liquid [Bmim][PF6] in Li2SO4⎯Li2O⎯P2O5 glass matrix by mixing and through grinding. Amorphous/glassy nature of the samples is confirmed by X-Ray diffraction (XRD). Surprisingly, the electrical conductivity of the samples is found to be increasing by ∼ 2 orders of magnitude and exhibits typical Arrhenius behavior with low activation energy. DC polarization and impedance spectroscopy measurements suggest that samples are essentially ionic in nature. The conductivity isotherms were also obtained at different temperatures (T < 100 °C) and found to be appreciably stable at least for ∼ 10 days.Item Ionic liquid dispersed Li+ ion oxide glasses and glass-ceramics: Assessment of electrical transport and thermal stability(Elsiever, 2015-12-01) Kumar, Anil; Dalvi, AnshumanEffect of ionic liquid (BMIM BF4) dispersion on Li+ ion oxide glass and glass-ceramics has been investigated. Addition of ionic liquid in a very small amount (0.5–5 wt.%) enhances the ionic conductivity significantly. For a typical glass composition 60Li2SO4-40(0.5Li2O–0.5P2O5), with grain size of ~ 50 nm, dispersion of ~ 5 wt.% ionic liquid leads to a conductivity rise of ~ 2–4 orders of magnitude. Structure of ionic liquid dispersed glass and glass-ceramic composites has been investigated by X-ray diffraction and FE-SEM, and thermal properties by DSC. It has been revealed by a galvanic cell method, impedance spectroscopy and dc polarization technique that these composites are essentially ionic in nature. Based on these investigations, a model for electrical transport has been proposed according to which Li+ ions are the majority charge carriers in these composites. The model suggests that ionic liquid acts like a filler between the glass/glass-ceramic grains and Li+ ions mainly migrate through these channels. These composites appear promising for Li+ ion battery applications.