Structural studies of nano silica employing on-line ultrasonic studies

Monodispersed, nano silica particles have been prepared by sol-gel hydrolysis and condensation of the metal alkoxide using pH buffer. The prepared particles are characterised by XRD, FTIR, BET, SEM, TEM measurements. The measurements reveal that the size and shape of silica particles depend on concentration of water. In addition, the ultrasonic longitudinal velocity and attenuation of the nano silica particles have been measured at a frequency of 5?MHz over a wide range of temperatures from 300?K to 1150?K in nano silica. The different structural transitions, such as monoclinic, orthorhombic, orthorhombic with a non-integral super lattice, stable orthorhombic and hexagonal, which exist in silica are explained based on on-line high-temperature ultrasonic velocity and attenuation measurements.     

An absolute method for determination of misalignment of an immersion ultrasonic transducer

An absolute methodology has been developed for quantification of misalignment of an ultrasonic transducer using a corner-cube retroreflector. The amplitude based and the time of flight (TOF) based C-scans of the reflector are obtained for various misalignments of the transducer. At zero degree orientation of the transducer, the vertical positions of the maximum amplitude and the minimum TOF in the C-scan coincide. At any other orientation of the transducer with the horizontal plane, there is a vertical shift in the position of the maximum amplitude with respect to the minimum TOF. The position of the minimum (TOF) remains the same irrespective of the orientation of the transducer and hence is used as a reference for any misalignment of the transducer. With the measurement of the vertical shift and the horizontal distance between the transducer and the vertex of the reflector, the misalignment of the transducer is quantified. Based on the methodology developed in the present study, retroreflectors are placed in the Indian 500 MWe Prototype Fast Breeder Reactor for assessment of the orientation of the ultrasonic transducer prior to the under-sodium ultrasonic scanning for detection of any protrusion of the subassemblies.     

Acoustic and Thermodynamic Properties of Binary Liquid Mixtures of Benzaldehyde in Hexane and Cyclohexane

Densities and ultrasonic speeds of binary mixtures of benzaldehyde with n-hexane and cyclohexane at 30 °C were measured over the entire composition range. From these experimental data, the adiabatic compressibility (K _S ), intermolecular free length (L _f), acoustic impedance (Z), relative association (R _a) and relaxation strength (r) were calculated. Also, the excess adiabatic compressibility (K _S ^E), intermolecular free length (L _f^E), acoustic impedance (Z ^E), and ultrasonic velocity (U ^E) were calculated. The observed variation of these parameters helps in understanding the nature of interactions in these mixtures. Further, theoretical values of the ultrasonic speed were evaluated using theories and empirical relations. The relative merits of these theories and relations were discussed.     

Magnesium ion conducting polyvinyl alcohol–polyvinyl pyrrolidone-based blend polymer electrolyte

Structural, thermal, electrical and electrochemical behaviour of polymer blend electrolytes comprising polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) as host polymers and Mg(ClO₄)₂ as dopant salt have been investigated. The changes in the structural properties on the incorporation of dopant in the blends were investigated by XRD and FTIR analyses. Thermal properties of pure PVA–PVP blend and their complexes were examined by DSC to measure how the thermal transitions of the prepared films were affected by different concentration of Mg(ClO₄)₂. The ionic conductivity and dielectric behaviour were explored using A.C. impedance spectroscopy. The trend of ionic conductivity increases almost proportionally to the content of magnesium salt and can be related to an increase of amorphous phase at high level of dopant salt. The electrochemical stability of the optimum conducting blend polymer electrolyte is found to be ～3.5 V. The Mg²⁺ transference number for the sample with optimized conductivity was found to be 0.31.     

Vibrational spectral studies on charge transfer and ionic hydrogen‐bonding interactions of nonlinear optical material L‐arginine nitrate hemihydrate

The near infrared Fourier‐transform (NIR FT)‐Raman and Fourier‐transform infrared (FT‐IR) spectroscopies supported by HF/6‐31G(d) computations have been employed to derive equilibrium geometry, vibrational wavenumbers and the first hyperpolarizability of the nonlinear optical (NLO) material, L ‐arginine nitrate (LAN) hemihydrate. The reasonable NLO efficiency, predicted for the first time in this novel compound, has been confirmed by Kurtz–Perry powder second harmonic generation (SHG) experiments. The changes in the atomic charge distribution among different groups due to the presence of strong electronegative atoms and the shrinking of N O bonds of nitrate anion and C N bonds of guanidyl group have been analyzed. The splitting of the carboxylate stretching modes, blue shifting of methine vibrations and the electronic effects such as backdonation and induction on the methylene hydrogen atoms have also been examined in detail. The intense low wavenumber H‐bond Raman vibrations due to electron–phonon coupling and nonbonded interactions in making the LAN molecule NLO active have been discussed based on the vibrational spectral features. The natural bond orbital (NBO) analysis and HF computations confirm the occurrence of strong intra‐ and intermolecular N H·O and O H·O ionic hydrogen bonding between charged species providing the noncentrosymmetric structure in the LAN crystal. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational spectra and scaled quantum chemical studies of the structure of Martius yellow sodium salt monohydrate

The FT‐IR and Raman spectra of Martius Yellow sodium salt Monohydrate (MYM) [2, 4‐dinitro‐1‐naphthol sodium salt] in solid‐phase have been measured. The geometry, intramolecular hydrogen bonding and harmonic vibrational wavenumbers of MYM have been investigated with the help of B3LYP density functional theory (DFT) methods. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The existence of intramolecular C H···O improper, blue‐shifted hydrogen bonding was investigated by means of the NBO analysis. The infrared and Raman spectra were predicted theoretically from the calculated intensities. The observed and the calculated spectra were found to be in good agreement. Copyright © 2009 John Wiley & Sons, Ltd.     

FT‐Raman,IR and UV‐visible spectral investigations and ab initio computations of a nonlinear food dye amaranth

Amaranth (E123, Food Red 9, FD & C Red 2) is a sulfonated azo dye used as a color additive in foodstuffs, pharmaceuticals and cosmetics. FT‐IR and FT‐Raman spectra of amaranth were recorded and analyzed. Density functional theory (DFT) calculations were performed to derive the equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The results of the optimized molecular structure gave clear evidence for the intramolecular charge transfer (ICT) and intramolecular hydrogen bonding in the molecule. Azo stretching wavenumbers are lowered owing to conjugation and π‐electron delocalization. Time‐dependent density functional theory (TD‐DFT) calculations of the electronic spectra were performed on the optimized structure and compared with the experimental UV‐visible spectrum. Vibrational spectra, natural bonding orbitals (NBO) analysis and optimized geometry indicate C H·N hydrogen bonding in the molecule. The first hyperpolarizability of the molecule was calculated. The optical nonlinearity of the dye is due to the donation of the electron density from the hydroxyl group of the conjugated system via naphthalene ( 2 ) ring into π*‐orbital of the azo moiety. Copyright © 2008 John Wiley & Sons, Ltd.     

NIR‐FT Raman,FT‐IR and surface‐enhanced Raman scattering spectra,with theoretical simulations on chloramphenicol

Chloramphenicol (CLM), originally derived from the bacterium Streptomyces venezuelae, is an inhibitor of bacterial ribosomal peptidyl transferase activity. The near infrared Fourier transform (NIR‐FT) Raman, surface‐enhanced Raman spectroscopy (SERS) and Fourier transform infrared (FT‐IR) spectral analyses of CLM, a potential antibacterial drug for the treatment of typhoid fever, were carried out along with density functional computations. The vibrational spectral analysis reveals that the CH₂ asymmetric and symmetric stretching modes are shifted to higher wavenumbers than the computed values, owing to the electronic effects resulting from induction of methylene group with the adjacent electronegative atom. The lowering of CO stretching wavenumber is due to the presence of the strong electronegative atom, nitrogen, attached to the carbonyl carbon, causing large degree of molecular π‐electron delocalization and redistribution of electrons, which weakens the CO bond. The absence of a C H stretching vibration and the observed C H out‐of‐plane bending modes suggest that the CLM molecule may be adsorbed in a flat orientation with respect to the silver surface. Copyright © 2008 John Wiley & Sons, Ltd.     

Microwave-Mediated Modification of Selected Limonoids with DMAB Reagent and Antibacterial Studies

N,N-Dimethylaniline.borane (DMAB) is a stable, multifaceted electrophilic boron agent that displays hydroboration of C = C as well as selective reduction of functional groups under reflux, microwave, and ultrasound conditions. Natural products contain a plethora of functional groups that govern the specific bioactivity. It will be interesting to correlate the change in a functional group with the concern for change in bioactivity. Current research emphasizes the influence of microwave irradiation on moderately reactive DMAB reagent towards the functional group modification of selected limonoid-phytochemicals of Meliaceae family viz. cedrelone, azadirone, nimbin, and azadiradione. DMAB conveniently reduces the ketone, epoxide group into alcohol, and does a hydroboration reaction on the C = C bond. It does not show interest to reduce the ester group irrespective of 30 min of MW irradiation. Except for these reducing properties, the reagent DMAB unveils chemo-selective nature in respect of different functional groups and utilizes in an asymmetric synthesis. The coalescence of amine.borane with microwave irradiation brings forth a commodious and prompt method for the selective reduction of functional groups. The bioactive efficacy of modified phytochemicals is further taken for the antimicrobial studies.