Structural and electronic properties of polyyne and cumulene chains with phenylene as central aromatic group: a density functional theory study

Structural Chemistry - The present work studies effects of the introduction of phenylene group as the central aromatic group on the structural and electronic properties of polyyne (Pol-[HCN]2Ph)...     

Oxycodone N‐oxide

The title compound, (5R,9R,13S,14S,17R)‐14‐hydroxy‐3‐methoxy‐17‐methyl‐4,5‐epoxymorphinan‐6‐one N‐oxide, C₁₈H₂₁NO₅, has been prepared in a diastereomerically pure form by the reaction of oxycodone with 3‐chloroperbenzoic acid and subsequent crystallization of the product from chloroform. The crystal packing shows that the molecule exhibits intramolecular O—H...O [D...A = 2.482 (2) Å] hydrogen bonding. In addition, there are weak intermolecular C—H...O interactions which, along with van der Waals forces, stabilize the structure. The new chiral center at the 17‐position is demonstrated to be R.     

Electrical resistance measurements under pressure on NbTe2 single crystal

Transition metal dichalcogenides, because of their layered structure, are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transitions under pressure. Here we report the details of the preparation and characterization of single crystals of NbTe₂ and the results of electrical resistance measurements under pressure carried out on it to investigate this possibility. Single crystals were grown by the chemical vapor transport technique, using iodine as a transporting agent. The composition of the grown crystals was confirmed on the basis of Energy Dispersive Analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray Diffraction (XRD) studies. Electrical resistance was measured employing a Bridgman anvil set up to 10?GPa and diamond anvil cell (DAC) assembly up to 25?GPa. A technique slightly modified from that described in the literature for carrying out electrical resistivity measurements in the diamond anvil cell (DAC) under pressure has been standardized.     

Supramolecular Control of Singlet Oxygen Generation

Singlet oxygen (¹O₂) is the excited state electronic isomer and a reactive form of molecular oxygen, which is most efficiently produced through the photosensitized excitation of ambient triplet oxygen. Photochemical singlet oxygen generation (SOG) has received tremendous attention historically, both for its practical application as well as for the fundamental aspects of its reactivity. Applications of singlet oxygen in medicine, wastewater treatment, microbial disinfection, and synthetic chemistry are the direct results of active past research into this reaction. Such advancements were achieved through design factors focused predominantly on the photosensitizer (PS), whose photoactivity is relegated to self-regulated structure and energetics in ground and excited states. However, the relatively new supramolecular approach of dictating molecular structure through non-bonding interactions has allowed photochemists to render otherwise inactive or less effective PSs as efficient ¹O₂ generators. This concise and first of its kind review aims to compile progress in SOG research achieved through supramolecular photochemistry in an effort to serve as a reference for future research in this direction. The aim of this review is to highlight the value in the supramolecular photochemistry approach to tapping the unexploited technological potential within this historic reaction.     

Hydrolysis and Extraction Properties of Aroylhydrazones Derived from Nicotinic Acid Hydrazide

The kinetics of hydrolysis of N′-salicylidene-3-pyridinecarbohydrazide (1) and N′-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide (2) were investigated in the dioxane/water (1/1, volume ratio) solvent system in acidic and basic media, and the corresponding reaction mechanisms were proposed. The kinetic results suggest that in the acidic solutions the rate-determining step of the hydrolysis reaction is the attack of a water molecule on the protonated azomethine group, whereas in the basic medium it is the attack of water on the completely deprotonated hydrazone. By analyzing the temperature dependence of the reaction rates, the thermodynamic activation parameters, i.e. activation enthalpy and entropy, were also evaluated and discussed. The complexation reactions of vanadium(V) with aroylhydrazones 1 and 2 as well as the extraction of V(V) from aqueous to an organic phase were studied spectrophotometrically. The optimum conditions for complex formation and extraction of vanadium(V) into chloroform solutions of compounds 1 or 2 have been evaluated. Based on the results obtained by Job’s method and the equilibrium shift method, the stoichiometries of the complexes were determined to be 1:1. The effect of foreign ions on V(V) extraction by compound 2 has been determined as well.     

Ultrasound-promoted synthesis of novel 2-chloroquinolin-4-pyrimidine carboxylate derivatives as potential antibacterial agents

Ultrasound-promoted reaction of substituted 2,4-dichloroquinolines (1) with ethyl 4-(3-hydroxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (2) in the presence of K₂CO₃ as mild base at moderate temperatures leads to 2-chloroquinolin-4-pyrimidine carboxylate derivatives (3) with high regioselectivity. All the compounds synthesized were characterized by use of spectral data and screened for their antibacterial activity against two Gram-positive (Staphylococcus aureus, Bacillus cereus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. Activity was moderate.     

Bismaleimide/rice husk silica reinforced composites

Silica derived from the renewable resource rice husk is modified using stearic acid and N-[4-(chlorocarbonyl)phenyl]maleimide. These materials are used as fillers in the bismaleimide, 4,4′-bismaleimidodiphenylmethane (BMIM), and thermally cured. The thermogravimetric (TG) curves for polyBMIM/silica composites showed no pronounced changes compared to the TG curve for the pure polyBMIM. Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods are used to compute the activation energy (E _a) for degradation. Silica and surface-modified silica using stearic acid dispersed by ultrasonication increase the activation energy for degradation and show considerable influence on the thermal stability of cured BMIM. The long alkyl chain present in the stearic acid modified silica and the bulky spacer present in the chemically modified silica definitely alter the degradation process of cured BMIM. The SEM studies indicated uniform dispersion of the silica particles in the polyBMIM.     

Biophysical characterization of thermophilic laccase from the xerophytes: Cereus pterogonus and Opuntia vulgaris

Biophysical characterization of laccase enzyme isoforms from two different xerophytic plants Cereus pterogonus and Opuntia vulgaris was carried out using EPR, fluorescence and circular dichroism (CD) spectroscopy while their thermal denaturation profiles were investigated employing differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). EPR analysis revealed the presence of endogenous copper. The hyperfine splitting of EPR spectrum reduced with increase in the complexity of enzyme protein. Raise in temperature did not alter the protein fluorescence emission suggestive of high temperature stability of the enzyme, causing the tryptophan and tyrosine residues to remain buried within the protein structure. Far-UV CD spectrum revealed existence of 60 % random coils in enzyme structure even at elevated temperatures and in presence of metal ions and protein denaturants. DSC analysis provided a Tm in the range 95–121 °C for the native and 158–199 °C for the metal associated laccase isoforms. Loss in weight of the enzyme protein by 10–18 % was noted up to 100 °C when determined through TGA. The thermostable plant xerophytic laccase enzyme isoforms will be of potential use in textile, dyeing, pulping and biotechnology applications.     

Green synthesis and characterization of gold nanoparticles using extract of anti-tumor potent Crocus sativus

In the present study, we have explored anti-tumor potent Crocus sativus (saffron) as a reducing agent for one pot size controlled green synthesis of gold nanoparticles (AuNps) at ambient conditions. The nanoparticles were characterized using UV–vis, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and FTIR analysis. The prepared AuNPs showed surface Plasmon resonance centered at 549 nm with average particle size of 15±5 nm. Stable, spherical and triangular crystalline AuNPs with well-defined dimensions were synthesized using anti-tumor potent Crocus sativus (saffron). Crystalline nature of the nanoparticles is confirmed from the HR-TEM, SAED and SEM images, and XRD patterns. From the FTIR spectra it is found that the biomolecules are responsible for capping in gold nanoparticles.     

Interaction of (G4)2 and (X4)2 DNA quadruplexes with Cu+, Ag+ and Au+ metal cations: a quantum chemical calculation on structural,energetic and electronic properties

Structural Chemistry - The present study is focused to cast light on the structural, electronic and energetic properties of isolated (G4)2 and (X4)2 DNA quadruplexes with transition metal cations...