A generalized computer program for determining the kinetic mechanism of solid-state reactions

A consideration of the various types of reactions controlling kinetic processes in general appears to suggest that it is possible to express all such reactions by a differential equation of the form $\text{dα}\text{d}\text{t}$ = A exp(?E/RT)(1?α)ⁿαⁿ[?1n(1?α1]^pwhere α = fraction of the substance reacted, t = time of reaction, A = pre-exponential factor, E = energy of activation, R = universal gas content, and m, n, p are constants The presence (or absence) of the indices m, n, p, cr any combination of these, in this equation when it is fitted to a set of thermogravimetric data relating to the fraction of the substance decomposed and the absolute temperature can reasonably be expected to throw light on the mechanism of the process.This paper presents the features of a numerical algorithm for studying kinetic data on the above lines and suggests a possible scheme for predicting the most probable kinetic mechanism by a consideration of the differences of the predicted from the experimental values. A computer program was developed on an IBM 360 computer for implementing this scheme and evaluating the kinetic parameters from experimental thermogravimetric data. The values obtained from the program for a pyrolysis reaction which typifies the system and the inferences drawn therefrom regarding the relevant reaction mechanism are included.     

Microstress,strain, band gap tuning and photocatalytic properties of thermally annealed and Cu-doped ZnO nanoparticles

ZnO nanoparticles and Cu-doped ZnO nanoparticles were prepared by co-precipitation method. Also, a part of the pure ZnO nanoparticles were annealed at 750 °C for 3, 6, and 9 h. X-ray diffraction studies were carried out and the lattice parameters, unit cell volume, interplanar spacing, and Young’s modulus were calculated for all the samples, and also the crystallite size was found using the Scherrer method. X-ray peak broadening analysis was used to estimate the crystallite sizes and the strain using the Williamson–Hall (W–H) method and the size–strain plot (SSP) method. Stress and the energy density were calculated using the W–H method assuming different models such as uniform deformation model, uniform strain deformation model, uniform deformation energy density model, and the SSP method. Optical absorption properties of the samples were understood from their UV–visible spectra. Photocatalytic activities of ZnO and 5 % Cu-doped ZnO were observed by the degradation of methylene blue dye in aqueous medium under the irradiation of 20-W compact fluorescent lamp for an hour.     

Unstrained and strained flamelets for LES of premixed combustion

The unstrained and strained flamelet closures for filtered reaction rate in large eddy simulation (LES) of premixed flames are studied. The required sub-grid scale (SGS) PDF in these closures is presumed using the Beta function. The relative performances of these closures are assessed by comparing numerical results from large eddy simulations of piloted Bunsen flames of stoichiometric methane–air mixture with experimental measurements. The strained flamelets closure is observed to underestimate the burn rate and thus the reactive scalars mass fractions are under-predicted with an over-prediction of fuel mass fraction compared with the unstrained flamelet closure. The physical reasons for this relative behaviour are discussed. The results of unstrained flamelet closure compare well with experimental data. The SGS variance of the progress variable required for the presumed PDF is obtained by solving its transport equation. An order of magnitude analysis of this equation suggests that the commonly used algebraic model obtained by balancing source and sink in this transport equation does not hold. This algebraic model is shown to underestimate the SGS variance substantially and the implications of this variance model for the filtered reaction rate closures are highlighted.     

Formulation of betacyclodextrin based nanosponges of itraconazole

Nanosponges are betacyclodextrins crosslinked with carbonate bonds. The polymer formed is nanoparticulate in nature. Itraconazole is a BCS Class II drug that has a dissolution rate limited poor bioavailability. Rationale of the work was to enhance the solubility of Itraconazole so that the bioavailability problems are solved. Solid dispersion technique has been used for drug incorporation. The effect of a ternary component copolyvidonum on solubility of itraconazole has been studied. Phase solubility studies has been carried out with a rationale of comparing the solubilization efficiency of nanosponges, copolyvidonum and combination. The dispersions were characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and photon correlation spectroscopy (PCS). It was found that the solubility of itraconazole was enhanced more than 50-folds with a ternary solid dispersion system. Using copolyvidonum in conjunction with nanosponges helps to increase the solubilization efficiency of nanosponges as evident from the phase solubility studies.     

Hybrid density functional theory with a specific reaction parameter: hydrogen abstraction reaction of trifluoromethane by the hydroxyl radical

Potential energy surfaces are developed and tested for the OH + CHF₃ → H₂O + CF₃ reaction. The objective is to obtain surfaces that give calculated rate constants comparable to the experimental ones. The potential energy surfaces are constructed using hybrid and hybrid meta density functional theory methods (mPW1PW91, B1B95, and mPW1B95) with specific reaction parameters in conjunction with the 6–31+ G(d,p) basis set. The rate constants are calculated over the temperature range 200–1,500 K using variational transition state theory with multidimensional tunneling contributions. The hybrid density functional theory methods with specific-reaction-parameter Hartree-Fock exchange contributions (32.8–34.8% for mPW1PW91, 34.2–36.0% for B1B95, and 37.8–39.7% for mPW1B95, respectively) provide accurate rate constants over an extended temperature range. The classical barrier height for the hydrogen abstraction reaction is determined to be 6.5–6.9 kcal/mol on these potential energy surfaces, and the best estimate value is 6.77 kcal/mol. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Fabrication of carbon nano-tubes decorated with ultra fine superparamagnetic nano-particles under continuous flow conditions

Ultra fine (2-3 nm) magnetite (Fe(3)O(4)) nano-particles are uniformly deposited on single-walled carbon nano-tubes (SWCNTs) pre-functionalised with carboxylic acid groups using microwave radiation. The deposition process involves chemical precipitation associated with continuous flow spinning disc processing (SDP), as a rapid, environmentally friendly approach which is readily scalable for large scale synthesis. The resulting decorated SWCNTs are superparamagnetic with specific saturated magnetization of 30 emu g(-1).     

Ring opening of the cyclobutane in a thymine dimer radical anion

The reactions of hydrated electrons (e(aq) (-)) with thymine dimer 2 and thymidine have been investigated by radiolytic methods coupled with product studies, and addressed computationally by means of BB1K-HMDFT calculations. Pulse radiolysis revealed that one-electron reduction of the thymine dimer 2 affords the radical anion of thymidine (5) with t(1/2)<35 ns. Indeed, the theoretical study suggests that radical anion 3, in which the spin density and charge distribution are located in both thymine rings, undergoes a fast partially ionic splitting of the cyclobutane with a half-life of a few ps. This model fits with the in vivo observation of thymine dimer repair in DNA by photolyase. gamma-Radiolysis of thymine dimer 2 demonstrates that the one-electron reduction and the subsequent cleavage of the cyclobutane ring does not proceed by means of a radical chain mechanism, that is, in this model reaction the T(-)* is unable to transfer an electron to the thymine dimer 2.     

Cleavage of proteins by a mixed-ligand copper(II) phenolate complex: hydrophobicity of the diimine co-ligand promotes cleavage

The mixed-ligand copper(II) complex [Cu(tdp)(tmp)](ClO4), where H(tdp) is 2-[(2-(2-hydroxyethylamino)ethylimino)methyl]phenol and tmp is 3,4,7,8-tetramethyl-1,10-phenanthroline, exhibits cleavage of the proteins bovine serum albumin and lysozyme, producing approximately 5 and 4 kDa protein fragments respectively within a few minutes at micromolar concentrations. The hydrophobic tmp ligand recognizes the hydrophobic site and enhances protein binding and cleavage even at physiological pH and temperature.