Correlated barrier hopping of CuO nanoparticles

The ac conduction mechanism in copper oxide nanoparticles with 8 nm size, synthesized by a precipitation method was studied by analyzing ac conductivity in the frequency range of 50 Hz-1 MHz and in the temperature range of 373-573 K. X-ray diffraction and transmission electron microscopy(TEM) were employed for the structural and morphological characterization of CuO nanoparticles. The experimental and theoretical investigations suggested that the ac conduction mechanism in CuO nanoparticles can be successfully explained by a correlated barrier hopping model, which provided reasonable values for the maximum barrier height and characteristic relaxation time. It was also found that bipolaron hopping become prominent up to a particular temperature and beyond that single polaron hopping predominates. Physical parameters such as hopping distance and density of defect states were also calculated. Photoluminescence studies confirm the presence of a surface defect in CuO nanoparticles.     

Dynamics of femtosecond laser-produced plasma ions

We investigated the ion laser-produced plasma plume generated during ultrafast laser ablation of copper and silicon targets in high vacuum. The ablation plasma was induced by ≈50 fs, 800 nm Ti:Sa laser pulses irradiating the target surface at an angle of 45°. An ion probe was used to investigate the time-of-flight profiles of the emitted ions in a laser fluence range from the ablation threshold up to ≈10 J/cm². The angular distribution of the ion flux and average velocity of the produced ions were studied by moving the ion probe on a circle around the ablation spot. The angular distribution of the ion flux is well described by an adiabatic and isentropic model of expansion of a plume produced by laser ablation of solid targets. The angular distribution of the ion flux narrows as the laser pulse fluence increases. Moreover, the ion average velocity reaches values of several tens of km/s, evidencing the presence of ions with kinetic energy of several hundred eV. Finally, the ion flux energy is confined in a narrow angular region around the target normal.     

A novel method for studying the buckling of nanotubes considering geometrical imperfections

Buckling of nanotubes has been studied using many methods such as molecular dynamics (MD), molecular mechanics, and continuum-based shell theories. In MD, motion of the individual atoms is tracked under applied temperature and pressure, ensuring a reliable estimate of the material response. The response thus simulated varies for individual nanotubes and is only as accurate as the force field used to model the atomic interactions. On the other hand, there exists a rich literature on the understanding of continuum mechanics-based shell theories. Based on the observations on the behavior of nanotubes, there have been a number of shell theory-based approaches to study the buckling of nanotubes. Although some of these methods yield a reasonable estimate of the buckling stress, investigation and comparison of buckled mode shapes obtained from continuum analysis and MD are sparse. Previous studies show that the direct application of shell theories to study nanotube buckling often leads to erroneous results. The present study reveals that a major source of this error can be attributed to the departure of the shape of the nanotube from a perfect cylindrical shell. Analogous to the shell buckling in the macro-scale, in this work, the nanotube is modeled as a thin-shell with initial imperfection. Then, a nonlinear buckling analysis is carried out using the Riks method. It is observed that this proposed approach yields significantly improved estimate of the buckling stress and mode shapes. It is also shown that the present method can account for the variation of buckling stress as a function of the temperature considered. Hence, this can prove to be a robust method for a continuum analysis of nanosystems taking in the effect of variation of temperature as well.     

Screening for oxidative damage by engineered nanomaterials: a comparative evaluation of FRAS and DCFH

Several acellular assays are routinely used to measure oxidative stress elicited by engineered nanomaterials (ENMs), yet little comparative evaluations of such methods exist. This study compares for the first time the performance of the dichlorofluorescein (DCFH) assay which measures reactive oxygen species (ROS) generation, to that of the ferric-reducing ability of serum (FRAS) assay, which measures biological oxidant damage in serum. A diverse set of 28 commercially important and extensively characterized ENMs were tested on both the assays. Intracellular oxidative stress was also assessed on a representative subset of seven ENMs in THP-1 (phorbol 12-myristate 13-acetate matured human monocytes) cells. Associations between assay responses and ENM physicochemical properties were assessed via correlation and regression analysis. DCFH correlated strongly with FRAS after dose normalization for mass (R ² = 0.78) and surface area (R ² = 0.68). Only 10/28 ENMs were positive in DCFH versus 21/28 in FRAS. Both assays were strongly associated with specific surface area and transition metal content. Qualitatively, a similar response ranking was observed for acellular FRAS and intracellular reduced:oxidized glutathione ratio (GSH:GSSG) in cells. Quantitatively, weak correlation was found between intracellular GSSG and FRAS or DCFH (R ² < 0.25) even after calculating effective dose to cells. The FRAS assay was more sensitive than DCFH, especially for ENMs with low to moderate oxidative damage potential, and may serve as a more biologically relevant substitute for acellular ROS measurements of ENMs. Further in vitro and in vivo validations of FRAS against other toxicological endpoints with larger datasets are recommended.     

Growth, spectral, and thermal characterization of 2-hydroxy-3-methoxybenzaldehyde semicarbazone

2-Hydroxy-3-methoxybenzaldehyde semicarbazone (HMBS) has been synthesized from 2-hydroxy-3-methoxybenzaldehyde and semicarbazide hydrochloride using sodium acetate as catalyst. Good quality single crystals of HMBS were successfully grown by slow evaporation method at room temperature using a mixture of DMF and ethanol as solvent. Fourier transform infrared and Fourier transform Raman spectral studies have been performed to identify the functional groups. Single-crystal XRD study was conducted to obtain the crystal structure and lattice parameters. The grown crystal was subjected to ¹H- and ¹³C-NMR spectral studies in order to confirm its structure and purity. The compound crystallizes into a monoclinic P21/c space group. Intermolecular hydrogen-bonding interactions facilitate unit cell packing in the crystal lattice. The UV–Vis spectrum confirmed the transparency of the compound between the wavelengths 420 and 1,100 nm, which is a characteristic property of a nonlinear optical (NLO) material. The thermal decomposition of the compound under static air atmosphere was investigated by simultaneous TG–DTG at a heating rate of 10 °C min^?1. The NLO property of HMBS was confirmed from the second-harmonic generation by Kurtz–Perry powder test.     

Fabrication of oligo‐glycerol based hydrolase responsive amphiphilic nanocarriers

Herein, we report on the synthesis of a new class of novel non‐ionic amphiphiles using triglycerol as a core, which is further functionalized with hydrophilic units poly(ethylene glycol) monomethyl ether (M_n: 350 and 550) and a pair of hydrophobic alkyl chains (C₁₈ or C₁₅) via chemo‐enzymatic approach. Fluorescence measurements and dynamic light scattering studies showed that all of the synthesized amphiphilic systems spontaneously self‐ assemble in aqueous solution, which is further confirmed by the transmission electron microscopy. Encapsulation of hydrophobic moieties like Nile red and nimodipine was studied using ultraviolet‐visible (UV‐vis) and fluorescence spectrometer techniques. A cytotoxicity study of the amphiphiles using A549, HeLa, and MCF7 cell, which showed that all of the synthesized nanocarriers are well tolerated at the concentrations studied. The release profile of encapsulated Nile red in synthesized amphiphilic system was studied in the presence of the immobilized enzyme (Novozym 435).     

Electrochemical doping in electrolyte-gated polymer transistors

By comparing the changes in pi-pi* absorption with the transconductance in PEO-LiClO4 electrolyte-gated FETs, we have demonstrated that the high channel currents obtained at low gate voltages result from reversible electrochemical doping of the semiconducting polymer film. At low temperatures, the conductivity of the electrochemically doped poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT-C14, is nonlinear with a crossover from dsigma(T)/dT > 0 to dsigma(T)/dT approximately 0 as a function of the source-drain voltage. High current densities, up to 10(6) A/cm2 at 4.2 K, can be sustained in the electrochemically doped PBTTT-C14 films.     

Unique bonding pattern and resulting bond stretch isomerism in

The bond‐stretch isomers are characterized by a principal change in the bond‐length with the rest of the molecule being unaltered. The electronic structure regulates the bond stretch isomerism phenomenon in which has been investigated with density functional theory, ab initio CASSCF, highly efficient n‐electron valence state perturbation theory and multireference configuration interaction calculations. Two isomers are distinguished on different potential energy surfaces and the corresponding avoided crossing is also studied in details. The bonding pattern in two isomers are analysed through adaptive natural density partitioning analysis and quantum theory of atoms in molecules analysis. The bonds in both the isomers primarily involve the 2p orbitals, which overlap face‐to‐face in long‐bond isomer. Whereas, in‐plane π‐bonding occurs at the short‐bond isomer leading to unusual bent bond. © 2015 Wiley Periodicals, Inc.     

Selectivity in Garratt-Braverman cyclization: an experimental and computational study

Bispropargyl sulfones equipped with aromatic rings of dissimilar nature were synthesized. Under basic conditions, these sulfones isomerized to the bisallenic sulfones, creating a competitive scenario between two alternate Garratt-Braverman (GB) cyclization pathways. The observed product distribution ruled out the involvement of any ionic intermediate and supported the diradical mechanism with greater involvement of the electron-rich aromatic ring via the more nucleophilic radical. DFT-based calculations supported the diradical mechanism along with the observed selectivity.