Synthesis of Gossypium hirsutum‐derived silver nanoparticles and their antibacterial efficacy against plant pathogens

Malvaceae and Brassicaceae family crops are economically important; however, their production has been markedly decreased in recent years due to various plant pests. Hence, the search for novel classes of efficient biological approaches continues due to unavailability of precise pesticides. The present study was designed to synthesize, characterize and evaluate the efficacy of silver nanoparticles (AgNPs) obtained using stem extract of Gossypium hirsutum (cotton plant) against plant pathogens Xanthomonas axonopodis pv. malvacearum and Xanthomonas campestris pv. campestris. Biosynthesized AgNPs were characterized using UV–visible spectrophotometry, Dynamic Light Scattering, Scanning Electron Microscopy combined with energy‐dispersive X‐ray analysis and Fourier transform infrared spectroscopy. The synthesized AgNPs were spherical in shape with size ranging from 20 to 100 nm. The characterized AgNPs were investigated for their efficacy against bacterial plant pathogens using the paper disc method. In vitro studies with two concentrations of AgNPs (50 and 100 μg mL^?1) showed zone of inhibition 11.0 ± 1.0 and 12.3 ± 0.5 mm for X. axonopodis pv. malvacearum and 9.7 ± 0.6 and 15.33 ± 1.0 mm for X. campestris pv. campestris. Furthermore, the AgNPs exhibited strong antioxidant activity, and a phytotoxicity study on Vigna unguiculata (cowpea plant) showed no toxicity. Overall, the findings suggest that G. hirsutum stem extract could be efficiently used in the synthesis of AgNPs and showed antimicrobial activity against plant pathogens. Hence, the synthesized nanoparticles could be used to combat plant pathogens in the agriculture sector.     

Total synthesis of (±) aspidostomide B,C, regioisomeric N-methyl aspidostomide D and their derivatives

A full account of the total synthesis of aspidostomide B, C, their analogues and our synthetic efforts towards the synthesis of aspidostomide D, which led to the synthesis of regioisomeric N-methyl aspidostomide D, its analogues via epoxide opening strategy is presented. The synthesis of regioisomeric N-methyl aspidostomide D involves an efficient, five-step sequence, with 36.3% overall yield, starting from 3,4,5-tribromo-1H-pyrrole-2-carboxylic acid. The key features of this protocol are intramolecular cyclization, dehydration, oxidation, and a Lewis acid-mediated regioselective epoxide ring opening by C-3 position of 2,5-dibromo-1H-indole to furnish the title compounds.     

Intermolecular energy transfer in mixed laser dyes: photophysical properties of triplet states

Triplet-singlet energy transfer in laser dyes have been studied in EPA at 77K using N₂ laser as an excitation source. Phosphorescence of the donor (D) and the delayed fluorescence of the acceptor (A) and their lifetimes have been measured for coumarin 102 (D)-rhodamine B(A) and 9(10H)-acridone (D)-rhodamine 6G(A) dye systems as a function of acceptor concentration. These data yield energy transfer rate constants of ∼10³ dm³ mol⁻¹ s⁻¹ for the donor acceptor combinations, consistent with the Forster mechanism. The phosphorescence quantum efficiency and other spectral parameters are also reported.     

Thermo‐Viscoelastic Response of Polycarbonate Reinforced with Short Glass Fibers

Observations are reported for oscillatory torsion tests at several temperatures ranging from room temperature to 100 °C on a polymer composite consisting of a polycarbonate matrix reinforced with short glass fibers. Constitutive equations are derived for the linear viscoelastic behavior of the polymer composite, which is treated as an equivalent heterogeneous network of chains bridged by junctions (entanglements and glass fibers). The network is thought of as an ensemble of meso‐regions with arbitrary shapes and sizes. With reference to the concept of cooperative relaxation, the time‐dependent response of an ensemble is associated with the rearrangement of meso‐domains. The rearrangement events occur at random times as meso‐regions are agitated by thermal fluctuations. Stress–strain relations for isothermal deformation of an ensemble of meso‐domains are derived by using the laws of thermodynamics. The governing equations are determined by five adjustable parameters that are found by fitting the experimental data. The effects of temperature and filler content on the material parameters are studied in detail.

The shear modulus G GPa versus the content of short glass fibers ν wt.‐%. Symbols: treatment of observations in oscillatory torsion tests at T = 25 (unfilled circles) and T = 100 °C (filled circles). Solid lines: approximation of the experimental data by Equation (27). Curve 1: G₀ = 1.05, G₁ = 3.83 × 10⁻². Curve 2: G₀ = 0.91, G₁ = 3.65 × 10⁻².     

Conformational control of TTFV π-frameworks through naphthyl substituents

With 1- or 2-naphthyl substituted at the vinyl positions, the conformation of the tetrathiafulvalene vinylogue π-framework can be greatly modified from completely planar to highly twisted, and the structural changes lead to markedly different electronic and electrochemical behaviours.     

Isothermal crystallization studies of poly(butylene terephthalate) composites

Different crystallization kinetic models (Avrami and Tobin) have been applied to study the crystallization kinetics of virgin poly(butylene terephthalate) (PBT) and filled PBT systems under isothermal experimental conditions. The experimental data have been analyzed with a nonlinear, multivariable regression program. The kinetic parameters for the isothermal crystallization have been determined. The analysis results indicate that both models satisfactorily represent the isothermal crystallization kinetics. PBT crystallizes most slowly. The presence of nanoclays or nanofibers, added as fillers, enhances the crystallization rate of PBT composites. An analysis of the kinetic data with the Avrami and Tobin models has shown little change in the crystallization exponent compared with that of virgin PBT. The crystallization rate constant decreases with a rise in the temperature for the two models. This trend has been observed for similar polyester systems reported in the literature. The dispersion of the clay layers in the PBT nanocomposites has been characterized with wide‐angle X‐ray diffraction and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1344–1353, 2007     

Numerical solution of the heat equation by infinite-order ordinary differential equations

A numerical algorithm is given for solving a class of infinite-order differential equations previously discussed by the authors. These equations yield solutions to certain time-dependent boundary-value problems for the heat equation. An extrapolation process is given for increasing the speed of convergence of the sequence generated by the method. © 1992 John Wiley & Sons, Inc.     

Suppression of electron-transfer characteristics of ferrocene by OTS monolayer on a silicon/electrolyte interface

The passivating behavior of self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) on an n-type Si(100) electrode with and without a redox species like ferrocene in a polar non-aqueous medium has been investigated using techniques like contact angle measurements, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to understand the role of the monolayer. The electron-transfer behavior of ferrocene is found to be drastically affected by the presence of monolayer and the reasons for these are analyzed as a function of the change in resistance, dielectric thickness and coverage of the monolayer. Electrochemical impedance analysis in the presence of ferrocene gives the monolayer coverage as 0.998 and the apparent rate constant calculated from this gives 4.85 x 10(-12) cm s(-1) in comparison with 4.4 x 10(-8) cm s(-1) for a similar electrode without any monolayer. A positive shift of 200 mV in the flat-band potential after monolayer formation also suggests the covalent coupling of the silane monolayer offering a protective barrier.     

Micropencils and microhexagonal cones of ZnO

Shape selective synthesis of ZnO micropencils and microhexagonal cones has been demonstrated using a controlled method of modified vapor deposition. A plausible growth mechanism based on the results of scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, and differential thermal analysis is proposed. Our results suggest that growth of micropencil takes place as per the vapor-liquid-solid progression while the microhexagonal cones grow in two steps following a vapor-solid/vapor-liquid-solid mechanism. Moreover, the geometry, the location of substrate and temperature are found to have key roles in governing the morphology. XPS studies clearly demonstrate the presence of Si species as SiO and SiO2, which act as catalysts enabling nucleating sites for ZnO microstructural growth.     

Synthesis, characterization of chemically deposited indium selenide thin films at room temperature

Polycrystalline In₂Se₃ semiconducting thin films were prepared by using relatively simple chemical bath deposition method at room temperature by the reaction between indium chloride, tartaric acid, hydrazine hydrate and sodium selenosulphate in an aqueous alkaline medium. Various preparative conditions of thin film deposition are outlined. The as grown films were found to be transparent, uniform, well adherent and red in color. The films were characterized using X-ray diffraction (XRD), scanning electron microscopy, atomic absorption spectroscopy and energy dispersive atomic X-ray diffraction (EDAX). The XRD analysis of the film showed the presence of polycrystalline nature with hexagonal crystal structure. SEM study revels that the grains are homogenous, without cracks or pinholes and well covers the glass substrate. The optical absorption and electrical conductivity was measured. The direct optical band gap value for the films was found to be of the order of 2.35 eV at room temperature and have specific electrical conductivity of the order of 10⁻² (Ω cm)⁻¹ showing n-type conduction mechanism. The utility of the adapted technique is discussed from the view-point of applications considering the optoelectric and structural data.