Crystallization process analysis for Se<Subscript>0.95</Subscript>In<Subscript>0.05</Subscript> and Se<Subscript>0.90</Subscript>In<Subscript>0.10</Subscript> chalcogenide glasses using the contemporary isoconversional models

Carrying out crystallization studies for both Se_0.95In_0.05 and Se_0.90In_0.10 chalcogenide glasses under non-isothermal conditions at different heating rates, it was realized that a rate controlling process occurs where random nucleation of one- to two-dimensional growth is accompanied with the introduction of up to 10 at% In into glassy Se matrix. The crystallization kinetics together with its dimensionality has been studied using the four currently used isoconversional models (Kissinger–Akahira–Sunose, Ozawa–Flynn–Wall, Tang, and Starink). The activation energy of crystallization (E _c) has been determined using these indicated four models where a satisfactory concurrence is achieved. The value of E _c shows a decrease while increasing both the In-content as well as the extent of crystallization.     

Study of glass transition kinetics of selenium matrix alloyed with up to 10% indium

Glassy selenium matrix alloyed with up to 10% indium, namely Se_0.95In_0.05 and Se_0.9In_0.1, was prepared by the melt quenching technique. Differential thermal analysis (DTA) has been used to study the glass transition kinetics of the two binary Se–In alloys in comparison with that of pure Se. DTA scans were recorded at different constant heating rates (β = 1:20 °/min). The glass transition temperature (T _g) is found to be shifting to a higher value with increasing of both β and In-content. Such a configurationally response is related to the observed increase of the stability parameters accompanied with the introduction of In into the Se matrix. The activation energy of glass transition (E _g) has been determined using two different non-isothermal models (Moynihan and Kissinger) where a good coincidence is obtained. The compositional dependence (0:10% In) of all considered parameters is discussed in terms of the introduced structural matrix.     

Mechanistic study of the deamination reaction of guanine: a computational study

The mechanism for the deamination of guanine with H(2)O, OH(-), H(2)O/OH(-) and for GuaH(+) with H(2)O has been investigated using ab initio calculations. Optimized geometries of the reactants, transition states, intermediates, and products were determined at RHF/6-31G(d), MP2/6-31G(d), B3LYP/6-31G(d), and B3LYP/6-31+G(d) levels of theory. Energies were also determined at G3MP2, G3MP2B3, G4MP2, and CBS-QB3 levels of theory. Intrinsic reaction coordinate (IRC) calculations were performed to characterize the transition states on the potential energy surface. Thermodynamic properties (ΔE, ΔH, and ΔG), activation energies, enthalpies, and Gibbs free energies of activation were also calculated for each reaction investigated. All pathways yield an initial tetrahedral intermediate and an intermediate in the last step that dissociates to products via a 1,3-proton shift. At the G3MP2 level of theory, deamination with OH(-) was found to have an activation energy barrier of 155 kJ mol(-1) compared to 187 kJ mol(-1) for the reaction with H(2)O and 243 kJ mol(-1) for GuaH(+) with H(2)O. The lowest overall activation energy, 144 kJ mol(-1) at the G3MP2 level, was obtained for the deamination of guanine with H(2)O/OH(-). Due to a lack of experimental results for guanine deamination, a comparison is made with those of cytosine, whose deamination reaction parallels that of guanine.     

2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester: crystal structure, DFT calculations and biological activity evaluation

In the present study, structural properties of 2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester have been studied extensively by spectral methods and X-ray crystallography. Quantum mechanical calculations of energies, geometries, vibrational wavenumbers, NMR and electronic transitions were carried out by DFT using B3LYP functional combined with 6-31G(d) basis set. Natural bond orbitals (NBO) analysis and frontier molecular orbitals were performed at the same level of theory. DFT calculations showed good agreement between the theoretical and experimental values of optimized and X-ray structure as well as between the vibrational and NMR spectroscopy. The title compound was screened for its antibacterial activity referring to Tetracycline as standard antibacterial agent.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures VII. Ternary mixtures of enantiotropes

Transition temperatures of the ternary mixtures, prepared from compounds of the two series, 4-hexadecyloxyphenyl 4-substituted benzoates (Ia,b) and 4-substituted phenyl 4-hexadecyloxy benzoates (IIa,b) have been determined by differential scanning calorimetry and identified with polarized light microscopy. The cyano and nitro derivatives, in both series, were used because their molecules form enantiotropic phases. A new method was elaborated for the elucidation of the eutectic composition of any ternary system from the knowledge of the eutectic composition of the three individual binary mixtures.     

Structure of Alkali Lignins Fractionated from Ricinus communis and Bagasse. 3. IR Spectra

Abstract

The lignin fractions isolated by one- and multistage soda and sulfate cookings showed almost identical IR spectra, indicating the similarity of the lignin skeletal structure throughout the plant. However, the absorbances reveal some differences. Similarity of the spectra includes: 1) chelation and bonding of the hydroxyl groups. 2) Stretching vibration of C-H bonds in methyl, methoxyl, and methylene groups. 3) Stretching vibration of C≡N. 4) Carbonyl unconjugated β-ketone, conjugated acids, or esters at 1725 cm^?1. There is no change in the intensity of absorption at this band from that at 1515 cm^?1 with the cooking stage. 5) Aromatic skeletal vibration at 1610 and 1515 cm^?1, affected by ring substituents at 1425 cm^?1. 6) The band at 1465 cm^?1 showed a higher intensity for soda and soluble kraft lignins than for insoluble kraft ones. 7) The band at 1370 cm^?1, assigned to phenolic OH bending, is affected by the methoxyl group. 8) The absence of condensed guaiacyl and the presence of syringyl and uncondensed guaiacyl. Assignments for hardwood lignin are shown for soda and soluble kraft lignins of bagasse, while those for softwood lignin are shown for soda, soluble, and insoluble kraft lignins of Ricinus communis and for insoluble kraft lignin of bagasse. A relation exists between the carbohydrate's lignin and the band at 920 cm^?1. Lignins from Ricinus communis are of higher guaiacyl to syringyl ratios than those from bagasse. The presence of C—S vibration and the absence of thiol groups for kraft lignins are indicated.     

Study of thermal stabilization for polystyrene/carbon nanocomposites via TG/DSC techniques

The degradability and durability for polymer–nanocomposites under various environmental conditions are from the essential fields of research. This study was carried out to examine the thermal stability of polystyrene loaded by carbon (C) nanoparticles up to 20 wt% content. The thermal degradation of PS/C nanocomposites were studied by thermogravimetry analysis and differential scanning calorimetry (DSC) under non-isothermal condition and inert gas atmosphere at constant heating rate 10 °C min^?1. The variation of degradation characteristic temperatures as a function of C content has been a non-monotonic behavior. The obtained results suggested that the C nanoparticles act as a promoter slowing down the degradation and providing a protective barrier to the nanocomposite, except 5 wt% C content. The latter exception was confirmed by DSC curve through the emergence of a small endothermic peak before the fundamental endothermic, melting, one.     

Theoretical study on the unimolecular decomposition of thiophenol

The potential energy surface for the unimolecular decomposition of thiophenol (C(6)H(5)SH) is mapped out at two theoretical levels; BB1K/GTlarge and QCISD(T)/6-311+G(2d,p)//MP2/6-31G(d,p). Calculated reaction rate constants at the high pressure limit indicate that the major initial channel is the formation of C(6)H(6)S at all temperatures. Above 1000 K, the contribution from direct fission of the S-H bond becomes important. Other decomposition channels, including expulsion of H(2) and H(2)S are of negligible importance. The formation of C(6)H(6)S is predicted to be strong-pressure dependent above 900 K. Further decomposition of C(6)H(6)S produces CS and C(5)H(6). Overall, despite the significant difference in bond dissociation, i.e., 8-9 kcal/mol between the S-H bond in thiophenol and the O-H bond in phenol, H migration at the ortho position in the two molecules represents the most accessible initial channel.     

Crude peroxidase from onion solid waste as a tool for organic synthesis. Part II: oxidative dimerization-cyclization of methyl p-coumarate, methyl caffeate and methyl ferulate

The ability of a crude onion peroxidase preparation to act as a biocatalyst for the oxidative dimerization-cyclization of methyl p-coumarate, methyl caffeate and methyl ferulate is presented. The products of the reaction have been fully characterized and were found to possess potent antioxidant activity in a ferric reducing antioxidant power (FRAP) assay.