Medium and structural effects on the ionization constants of some pyrazole carboxylic acid derivatives

Abstract  Stoichiometric ionization constants of some pyrazole carboxylic acids [4-benzoyl-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-benzoyl-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1,5-diphenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1-(3-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid, 4-(ethoxycarbonyl)-1-(4-nitrophenyl)-5-phenyl-1H-pyrazole-3-carboxylic acid] were determined in ethanol–water mixtures of 50, 60, 70% ethanol (v/v) by a potentiometric titration method. Titrations were performed in an ionic strength of 0.10 M NaCl at 25.0 ± 0.1 °C using an Orion 960 automatic titrator under a nitrogen atmosphere. Using the potentiometric titration data, ionization constants were calculated in three different ways. The effects of structure and solvent on the acidity of pyrazole carboxylic acids are also discussed. Graphical abstract        

Optical absorption spectrum of Cu2O-CaO-P2O5 glasses

Homogeneous CaO-P₂O₅ and Cu₂O-CaO-P₂O₅ glasses were prepared using a melt-quenched method under controlled conditions. The binary glasses were found to be colourless and transparent while the ternary glasses changed from light green to dark green as the Cu₂O content increased. From the absorption edge studies, the values of the optical band gap, E_opt and Urbach energy, ΔE were evaluated. The position of the absorption edge and hence the optical band gap were found to depend on the glass composition. Analysis of the optical band gap shows that for the binary glasses, the value increases as the content of CaO decreases, while for the ternary glasses, the value of the optical band gap increases as the content of the Cu₂O decreases. The density of the glasses was also measured and was found to increase with the increase in CaO and Cu₂O contents.     

Characterization of thermal, optical and carrier transport properties of porous silicon using the photoacoustic technique

In this work, the porous silicon layer was prepared by the electrochemical anodization etching process on n-type and p-type silicon wafers. The formation of the porous layer has been identified by photoluminescence and SEM measurements. The optical absorption, energy gap, carrier transport and thermal properties of n-type and p-type porous silicon layers were investigated by analyzing the experimental data from photoacoustic measurements. The values of thermal diffusivity, energy gap and carrier transport properties have been found to be porosity-dependent. The energy band gap of n-type and p-type porous silicon layers was higher than the energy band gap obtained for silicon substrate (1.11 eV). In the range of porosity (50-76%) of the studies, our results found that the optical band-gap energy of p-type porous silicon (1.80-2.00 eV) was higher than that of the n-type porous silicon layer (1.70-1.86 eV). The thermal diffusivity value of the n-type porous layer was found to be higher than that of the p-type and both were observed to increase linearly with increasing layer porosity.     

Supramolecular Architecture in the 1:1 Co-Crystallization of 6,7-Dimethoxy-2-methyl-4-phenylisoquinolinium Cation with Perchlorate Anion

Abstract  X-ray crystallographic analysis of the title organic ion–pair complex, C₁₈H₁₈NO₂ ⁺ · ClO₄ ⁻, reveals that 6,7-dimethoxy-2-methyl-4-phenylisoquinolinium cation is co-crystallized with perchlorate counter-anions in 1:1 ratio. The complex crystallizes in space group P 2 ₁ /n, with a = 8.0226(7) ?, b = 12.2552(7) ?, c = 17.9734(16) ?, β = 93.908(7) °, Z = 4, D _x  = 1.431 g/cm³. Aromaticity of isoquinolinium fragment is considerably deformed by the existence of C–H···O type weak H-bonds, leading to chains of topology C ₃ ³(12)[R ₁²(4)] running along b-axis of the unit cell and pseudo-cyclic centrosymmetric R ₄⁴(24)[2R ₁²(4)] synthons. The weak H-bonds serve to stabilize both the extended structure and molecular geometry of the title complex, in particular the disordered perchlorate anion whose components adopt a distorted tetrahedron. Index Abstract  Molecular and the extended structure of 6,7-dimethoxy-2-methyl-4-phenylisoquinolinium perchlorate, C₁₈H₁₈NO₂ ⁺ · ClO₄ ⁻, were determined by single crystal X-ray diffraction study.     

Low and high temperature bromination of exocyclic dienes: high temperature bromination. Part 16

The electrophilic addition of bromine to an exocyclic diene, 5,6-dimethylenebicyclo[2.2.1]hept-2-ene, in CCl₄ at 0°C led to the formation of non-rearranged (73%) and rearranged products (27%). However, high temperature bromination of the exocyclic diene at 77°C suppressed the formation of the rearranged products. Similarly, bromination of 9,10-dimethylenetricyclo[6.2.1.0^2,7]undeca-2,4,6-triene at −10°C gave only the exo-1,2-addition product. Bromination at +5°C resulted in the formation of a mixture consisting of exo-1,2- and 1,4-addition products in a ratio of (1:4). High temperature bromination at 77°C resulted in the formation of the endo-1,2-addition product. Furthermore, it has been shown that the 1,4-addition product converts smoothly to the 1,2-addition product. The formation mechanism of the products is discussed and supported by calculations.     

Stability of hydrophobic lipase derivatives immobilized on organic polymer beads

Lipase fromCandida rugosa was immobilized by attaching various hydrophobic groups to the enzyme molecule and adsorbing these hydrophobic lipase derivatives on several organic polymer beads. The immobilized enzymes were more thermostable in organic solvents compared to the native and modified Upases. Thermostability was highest with ΧAD2 beads, followed by ΧAD7 and RCOOH. Initially modifying the enzyme with hydrophobic modifiers did not have any effect on the enzyme thermostability. The best conditions for storing these enzyme preparations were at very low temperature in the lyophilized form and in a solution containing the reaction substrate. Interestingly, PEG-lipase immobilized on ΧAD7 beads showed increased operational stability when used in a stirred-tank reactor. The operational stability was further increased by a mild glutaraldehyde treatment of the enzyme preparation.     

Synthesis of some pyrazole‐3‐carboxylic acid‐hydrazide and pyrazolopyridazine compounds

Furan‐2,3‐diones 1a‐c react with various hydrazines 2a‐c under different conditions to yield the pyrazole‐3‐carboxylic acid‐hydrazide 3a‐d . Cyclocondensation reactions of 1a or 7 with phenylhydrazine lead to derivatives of pyrazolo[3,4‐d]pyridazinones 6 and 8 , respectively. The structures of all products were confirmed by elemental analysis, IR, ¹H‐ and ¹³C‐NMR spectroscopic measurements.     

Thermal explosion of nitrophenates of transition metals

The thermal decomposition studies on nitrophenates of copper, nickel and cobalt have been undertaken,-t curves show dehydration of these compounds at lower temperatures whereas dehydration cum decomposition seem to occur at higher temperatures leading to oxidative combustion of aromatic part. NO₂ gas is evolved during decomposition which seems to be responsible for oxidative reactions leading to detonation. The explosion temperature and velocity of detonation have been found to be linearly related with the number of nitro groups. The mechanism of thermal explosion has also been discussed.Thanks are due to Prof. S. Giri for providing laboratory facilities; and Aeronautics R&D Board, Ministry of Defence for financial assistance. Authors are also grateful to Shri I. P. S. Kapoor for helpful discussions.     

Electron beam crosslinking of poly(ethylene-co-vinyl acetate)/clay nanocomposites

Effect of electron beam irradiation on the thermal and mechanical properties of poly(ethylene-co-vinyl acetate) (EVA)/clay nanocomposites prepared by melt blending method has been investigated. The hot set test results show that elongation at high temperature under static load decreased with the increase of irradiation dose. The tensile modulus increased continuously with increasing dose. While the tensile strength increased up to 100 kGy, it decreased with further increase in dose. The elongation at break decreased continuously with increasing dose. Thermogravimetric analysis showed that thermal stability of the EVA/clay nanocomposites improved with increasing dose. The improvement in the mechanical and thermal properties is attributed to the formation of radiation-induced crosslinking as evidenced by the gel content results.     

Spectrophotometric flow-injection analysis of mercury(II) in pharmaceuticals with p-nitrobenzoxosulfamate

A new, simple and rapid spectrophotometric FI method for the accurate and precise determination of Hg(II) in pharmaceutical preparations has been developed. The method is based on the measuring the decrease of absorbance intensity of p-nitrobenzoxosulfamate (NBS) due to the complexation with Hg(II). The absorption peak of the NBS, which is decreased linearly by addition of Hg(II), occurs at 430 nm in 2×10⁻⁴ mol l⁻¹ HNO₃ as a carrier solution. Optimization of chemical and FI variables has been made. A micro column consisting of several packing materials applied instead of reaction coil was also investigated. A background level of Fe(III) maintained in reagent carrier solution with NBS was found useful for sensitivity and selectivity. Under the optimized conditions, the sampling rate was over 100 h⁻¹, the calibration curve obtained were linear over the range 1-10 μg ml⁻¹, the detection limit was lower than 0.2 μg ml⁻¹ for a 20 μl injection volume, and the precision [S_r=1% at 2 μg ml⁻¹ Hg(II) (n=10)] was found quite satisfactory. Application of the method to the analysis of Hg(II) in pharmaceutical preparations resulted a good agreement between the expected and found values.