Thermal neutron effect on YBa2Cu3O7

High-Tc superconductor YBa₂Cu₃O₇ was irradiated by thermal neutrons. Significant effects on the critical temperature were found. The changes were also investigated by X-ray diffraction technique.⁶⁵Cu (n, )⁶⁶Cu was the only reason for the degradation in superconducting properties. The existence of an isotope effect is argued.     

High resolution 13C-NMR spectroscopy of sodium carboxy methyl cellulose

Results of NMR studies on intact sodium carboxy methyl cellulose (SCMC) are presented. Similar studies in the literature are all on partially depolymerized SCMC. The degree of substitution and the relative distribution of substituents at OH-2, OH-3, and OH-6 of anhydro D -glucose residue in intact SCMC were determined by high resolution ¹³C-NMR spectroscopy (125 MHz). It is observed that the degree of substitution at OH-6 is almost equal to that at OH-3. In two SCMC samples, which are widely different in molecular weight and degree of substitution (ds), the relative reactivity order of the hydroxyl groups was found to be OH-2 > OH-6 ? OH-3. The NMR assignments were based on calculated shifts of carbons of anhydroglucose moiety in an oligosaccharide due to substitution.     

Theoretical studies on nonlinear optical properties of formaldehyde oligomers by ab initio and density functional theory methods

The first and second hyperpolarizability beta and gamma are obtained for formaldehyde oligomers (H2CO)n (n = 1-7) using computational methods. We have used the finite field (FF) approach and hyperpolarizability density analysis (HDA) to predict the microscopic first and second nonlinear hyperpolarizability of the formaldehyde oligomers. The spatial contributions of electrons to the hyperpolarizability by using plots of HDA are presented. It has been found from the numerical stability checking of the hyperpolarizability calculations that the calculated values by FF method are more stable than those by HDA approach. The values of beta are zero when n is even as the molecule possesses centrosymmetry, and when n is odd, the differences among beta values are not clear. The gamma values are increased with increase in n.     

Chemoselective hydrogenation of substituted nitroaromatics using novel water-soluble iron complex catalysts

Chemoselective hydrogenation of substituted nitroaromatic compounds by water-soluble iron complex catalysts with molecular hydrogen has been reported for the first time. This biphasic catalyst presents an opportunity for a solvent-free hydrogenation. This catalyst system provides a low-cost, efficient alternative to the selective but environmentally unacceptable stoichiometric reductions as well as the supported noble metal catalysts used for hydrogenation. An efficient recycling strategy has resulted in a cumulative turnover number above 6000.     

Removal of VOCs from air by membrane-based absorption and stripping

Atmospheric emission of volatile organic compounds (VOCs) such as toluene, xylene, acetone etc. from industrial facilities causes serious environmental problems and financial losses. Existing technologies for VOC emission abatement have many strengths as well as considerable limitations. A regenerative absorption-based process for removal of VOCs from N₂ in an inert, nonvolatile, organic liquid flowing in compact hollow fiber devices has been studied here. These devices eliminate flooding, loading and entrainment encountered in conventional absorption units. Detailed experimental results and theoretical analyses for absorption studies were communicated elsewhere. The overall performance of the combined absorption-stripping process is described here; it appears to be controlled by stripping due to the low temperature and the lower membrane surface area in the stripper. The difference between only absorption and combined absorption-stripping results was more pronounced for VOC-absorbent systems having higher Henry's law constant and diffusivity. A theoretical model has been developed from first principles to simulate the behavior of the membrane stripper; this has been combined with the model for the membrane absorber to determine the overall process performance. Simulated results obtained from the mathematical models agree well with the experimental results for combined absorption-stripping. Simulation results suggest that higher stripping temperature and larger stripper area enhance the performance considerably.     

Computer Simulation of Eley‐Rideal Reactions Over Rough Surface

The effect of surface roughness on an Eley‐Rideal reaction mechanism is studied. The rough surfaces are generated over a 2‐dimensional square lattice using the random deposition model. In an Eley‐Rideal reaction mechanism, a reacting particle approaches from the bulk and reacts with an active site upon collision with it. Three different rough surfaces are considered for the study. Multifractal scaling analysis is performed where the complex distribution of reaction probabilities is analyzed. Two cases of reactions are considered. 1) The reacting particle reacts at its first contact to the surface and 2) the reacting particle diffuses till it finds the lowest‐height position and reacts. The results obtained from the above two cases are compared. Significant differences between τ(q) and f(α) multifractal spectra for these two cases are found. The larger deviation from linearity in the τ(q) curves for the latter than the former gives wider f(α) spectra, indicating greater heterogeneity in the reaction probability distribution. Dynamic scaling theory is also applied on the Eley‐Rideal reaction mechanism over the surface with different surface roughnesses to obtain the two scaling parameters α_d and β_d. The values of α_d and β_d are found to be negative.     

Anchored Pd complex in MCM-41 and MCM-48: novel heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols

We report here, for the first time, synthesis of anchored Pd complexes in mesoporous supports such as MCM-41 and MCM-48 as true heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols to give excellent conversion ( approximately 100%) and regioselectivity ( approximately 99%) for 2-arylpropionic acids. The catalysts were characterized by powder-XRD, 31P CP-MAS NMR, FT-IR, TEM, XPS and ICP-AES. Recycle studies with these anchored Pd mesoporous catalysts were performed to confirm true heterogeneity.     

Simultaneous Determination of Enalapril and Losartan in Pharmaceutical Preparations by UV Spectrophotometry and LC

The simultaneous determination of enalapril (Ena) and losartan (Los) in solid dosage forms were done by two methods. The first method involves spectrophotometric determination using the simultaneous equation method at 222 and 250 nm for Ena and Los, respectively. The second method involved an RP-LC method of analysis using methanol:water:acetonitrile (45:35:20% v/v) as the mobile phase. Both methods were satisfactorily validated as per ICH guidelines.