483 resultados para Eigenfunctions Hydrogen Atom Schrodinger Elliptical Spherical Polar
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A new solid state synthetic route has been developed toward metal and bimetallic alloy nanoparticles from metal salts employing amine-boranes, as the reducing agent. During the reduction, amine-borane plays a dual role: acts as a reducing agent and reduces the metal salts to their elemental form and simultaneously generates a stabilizing agent in situ which controls the growth of the particles and stabilizes them in the nanosize regime. Employing different amine-boranes with differing reducing ability (ammonia borane (AB), dimethylamine borane (DMAB), and triethylamine borane (TMAB)) was found to have a profound effect on the particle size and the size distribution. Usage of AB as the reducing agent provided the smallest possible size with best size distribution. Employment of TMAB also afforded similar results; however, when DMAB was used as the reducing agent it resulted in larger sized nanoparticles that are polydisperse too. In the AB mediated reduction, BNHx polymer generated in situ acts as a capping agent whereas, the complexing amine of the other amine-boranes (DMAB and TMAB) play the same role. Employing the solid state route described herein, monometallic Au, Ag, Cu, Pd, and Ir and bimetallic CuAg and CuAu alloy nanoparticles of <10 nm were successfully prepared. Nucleation and growth processes that control the size and the size distribution of the resulting nanoparticles have been elucidated in these systems.
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In the present work the structural and spectral characteristics of acetazolamide have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. Based on these results, we have discussed the correlation between the vibrational modes and the structure of the dimers of acetazolamide. The calculated vibrational spectra of three dimers of acetazolamide have been compared with observed spectra, and the assignment of observed bands was carried out using potential energy distribution. The observed spectra agree well with the values computed from the OFT. A comparison of observed and calculated vibrational spectra clearly shows the effect of hydrogen bonding. The frequency shifts observed for the different dimers are in accord with the hydrogen bonding in acetazolamide. Natural bond orbital (NBO) analyses reflect the charge transfer interaction in the individual hydrogen bond units and the stability of different dimers of acetazolamide. (C) 2012 Elsevier B.V. All rights reserved.
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Transmission loss (TL) of an elliptical cylindrical chamber muffler having a single side/end inlet and multiple side/end outlet is analyzed by means of the 3-D semi-analytical formulation based upon the modal expansion (in terms of the angular and radial Mathieu functions) and the Green's function. The acoustic pressure response obtained in terms of Green's function is integrated over surface area of the side/end ports (modeled as rigid pistons) and upon subsequent division by the port area, yields the acoustic pressure response or impedance Z] matrix parameters due to the uniform piston-driven model. The 3-D semi-analytical results are found to be in excellent agreement with the results obtained by means of 3-D FEA (SYSNOISE) simulations, thereby validating the semi-analytical procedure suggested in this work. Parametric studies such as the effect of chamber length (L), angular and axial locations of the ports, interchanging the locations of inlet and outlet ports as well as the addition of an outlet port for double outlet mufflers on the TL performance are reported, thereby leading to the formulation of design guidelines for obtaining muffler configurations exhibiting a broad-band TL spectrum. One such configuration is an axially long chamber having side-inlet and side-outlet ports such that one of the side ports is located at half the axial length on themajor/minor axis and the other side port is located at three-quarters (or one-quarter) of the axial length on the minor/major axis. (C) 2012 Institute of Noise Control Engineering.
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In this communication, we report the synthesis and characterisation of a new luminescent liquid crystalline material, 4,6-bis (4-butoxyphenyl)-2-methoxynicotinonitrile (3). We have confirmed its structure by Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy, elemental analysis and X-ray single crystal diffraction studies. The newly synthesised compound crystallises in a monoclinic system with the space group C2/c and its cell parameters are found to be a?=?25.181(4) angstrom, b?=?15.651(4)angstrom, c?=?12.703(19) angstrom, V?=?4880.4 (16) angstrom, Z?=?8. The results indicate that the presence of weak CH center dot center dot center dot O and CH center dot center dot center dot N hydrogen bonding as short-range intermolecular interactions are responsible for the formation of its crystal assembly. The measured torsion angle shows the existence of a distorted structure for the molecule wherein 4-butoxyphenylene ring substituent at the fourth position of the central pyridine ring forms a torsion angle chiC(4), C(3), C(10), C(19)] of 40.55 degrees. Its liquid crystalline behaviour was investigated with the aid of polarised optical microscopy and differential scanning calorimetry. The study reveals that the compound displays a broad nematic phase in the range of 78112 degrees C. Further, solution phase optical studies indicate that it is a blue light emitter in different non-polar and polar organic solvents at a concentration of 10-5M.
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The Hooghly River estuary provides a unique experimental site to understand the effect of monsoonal river discharge on freshwater and seawater mixing. Water samples collected bi-weekly for a duration of 17 months were analyzed for salinity, delta O-18,delta C-13(DIC), as well as delta D to investigate the differential mixing of freshwater and seawater. The differences in salinity and delta O-18 of samples collected during low and high tides on the same day are strongly correlated suggesting a well mixed water column at our sampling site. Low salinity and depleted delta O-18 during monsoon is consistent with increased river discharge as well as high rainfall. We identified different slopes in a delta O-18 versus salinity plot for the estuary water samples collected during monsoon and non-monsoon seasons. This is driven by composition of the freshwater source which is dominated by rainwater during monsoon and rivers during non-monsoon months. Selected delta D analyses of samples indicate that groundwater contributes significantly to the Hooghly Estuary during low rainfall times of the year. delta C-13(DIC) measured in the water recorded low values towards the end of monsoon indicating low productivity (i.e. increased organic respiration) while progressively increasing delta C-13(DIC) values from October till January as well as during some of the pre-monsoon months can be explained by increasing productivity. Very low delta C-13(DIC) (similar to-20%0) suggests involvement of carbon derived from anaerobic oxidation of organics and/or methane with potential contribution from increased anthropogenic water supply. An estimate of seawater incursion into the Hooghly Estuary at different times of the year is obtained by using salinity data in a two-component mixing model. Presence of seawater was found maximum (31-37%) during February till July and lowest (less than or equal to 6%) from September till November. We notice a temporal offset between Ganges River discharge farther upstream at Farakka and salinity variation at the Hooghly Estuary. We believe that this time lag is a result of the physical distance between Farakka and Kakdweep (our sampling location) and put constraints on the travel time of river water during early monsoon. (c) 2012 Published by Elsevier B.V.
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Unambiguous evidence for the engagement of CF3 group in N-H center dot center dot center dot F-C hydrogen bond in a low polarity solvent, the first observation of its kind, is reported. The presence of such weak molecular interactions in the solution state is convincingly established by one and two-dimensional H-1, F-19, and natural abundant N-15 NMR spectroscopic studies. The strong and direct evidence is derived by the observation of through-space couplings, such as, (1h)J(FH), (1h)J(FN), and (2h)J(FF), where the spin polarization is transmitted through hydrogen bond. In an interesting example of a molecule containing two CF3 groups getting simultaneously involved in hydrogen bond, where hydrogen bond mediated couplings are not reflected in the NMR spectrum, F-19-F-19 NOESY experiment yielded confirmatory evidence. Significant deviations in the strengths of (1)J(NH), variable temperature, and the solvent induced perturbations yielded additional support. The NMR results are corroborated by both DFT calculations and MD simulations, where the quantitative information on different ways of involvement of fluorine in two and three centered hydrogen bonds, their percentage of occurrences, and geometries have been obtained. The hydrogen bond interaction energies have also been calculated.
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Domain swapping is an interesting feature of some oligomeric proteins in which each protomer of the oligomer provides an identical surface for exclusive interaction with a segment or domain belonging to another protomer. Here we report results of mutagenesis experiments on the structure of C-terminal helix swapped dimer of a stationary phase survival protein from Salmonella typhimurium (StSurE). Wild type StSurE is a dimer in which a large helical segment at the C-terminus and a tetramerization loop comprising two beta strands are swapped between the protomers. Key residues in StSurE that might promote C-terminal helix swapping were identified by sequence and structural comparisons. Three mutants in which the helix swapping is likely to be avoided were constructed and expressed in E. coli. Three-dimensional X-ray crystal structures of the mutants H234A and D230A/H234A could be determined at 2.1 angstrom and 2.35 angstrom resolutions, respectively. Contrary to expectations, helix swapping was mostly retained in both the mutants. The loss of the crucial D230 OD2- H234 NE2 hydrogen bond (2.89 angstrom in the wild type structure) in the hinge region was compensated by new inter and intra-chain interactions. However, the two fold molecular symmetry was lost and there were large conformational changes throughout the polypeptide. In spite of these changes, the dimeric structure and an approximate tetrameric organization were retained, probably due to the interactions involving the tetramerization loop. Mutants were mostly functionally inactive, highlighting the importance of precise inter-subunit interactions for the symmetry and function of StSurE.
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Nanostructured Pd-modified Ni/CeO2 catalyst was synthesized in a single step by solution combustion method and characterized by XRD, TEM, XPS, TPR and BET surface analyzer techniques. The catalytic performance of this compound was investigated by performing the water gas shift (WGS) and catalytic hydrogen combustion (CHC) reaction. The present compound is highly active and selective (100%) toward H-2 production for the WGS reaction. A lack of CO methanation activity is an important finding of present study and this is attributed to the ionic substitution of Pd and Ni species in CeO2. The creation of oxide vacancies due to ionic substitution of aliovalent ions induces dissociation of H2O that is responsible for the improved catalytic activity for WGS reaction. The combined H-2-TPR and XPS results show a synergism exists among Pd, Ni and ceria support. The redox reaction mechanism was used to correlate experimental data for the WGS reaction and a mechanism involving the interaction of adsorbed H-2 and O-2 through the hydroxyl species was proposed for CHC reaction. The parity plot shows a good correspondence between the experimental and predicted reaction rates. (c) 2012 Elsevier B.V. All rights reserved.
Resumo:
The acoustical behaviour of an elliptical chamber muffler having a side inlet and side outlet port is analyzed in this paper, wherein a uniform velocity piston source is assumed to model the 3-D acoustic field in the elliptical chamber cavity. Towards this end, we consider the modal expansion of the acoustic pressure field in the elliptical cavity in terms of the angular and radial Mathieu func-tions, subjected to the rigid wall condition. Then, the Green's function due to the point source lo-cated on the side (curved) surface of the elliptical chamber is obtained. On integrating this function over the elliptical piston area on the curved surface of the elliptical chamber and subsequent divi-sion by the area of the elliptic piston, one obtains the acoustic pressure field due to the piston driven source which is equivalent to considering plane wave propagation in the side ports. Thus, one can obtain the acoustic pressure response functions, i.e., the impedance matrix (Z) parameters due to the sources (ports) located on the side surface, from which one may also obtain a progressive wave rep-resentation in terms of the scattering matrix (S). Finally, the acoustic performance of the muffler is evaluated in terms of the Transmission loss (TL) which is computed in terms of the scattering pa-rameters. The effect of the axial length of the muffler and the angular location of the ports on the TL characteristics is studied in detail. The acoustically long chambers show dominant axial plane wave propagation while the TL spectrum of short chambers indicates the dominance of the trans-versal modes. The 3-D analytical results are compared with the 3-D FEM simulations carried on a commercial software and are shown to be in an excellent agreement, thereby validating the analyti-cal procedure suggested in this work.
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The enzyme, D-xylose isomerase (D-xylose keto-isomerase; EC 5.3.1.5) is a soluble enzyme that catalyzes the conversion of the aldo-sugar D-xylose to the keto-sugar D-xylulose. A total of 27 subunits of D-xylose isomerase from Streptomyces rubiginosus were analyzed in order to identify the invariant water molecules and their water-mediated ionic interactions. A total of 70 water molecules were found to be invariant. The structural and/or functional roles of these water molecules have been discussed. These invariant water molecules and their ionic interactions may be involved in maintaining the structural stability of the enzyme D-xylose isomerase. Fifty-eight of the 70 invariant water molecules (83%) have at least one interaction with the main chain polar atom.
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We report a special, hitherto-unexplored property of (-)-epigallocatechin gallate (EGCG) as a chiral solvating agent for enantiodiscrimination of alpha-amino acids in the polar solvent DMSO. This phenomenon has been investigated by H-1 NMR spectroscopy. The mechanism of the interaction property of EGCG with alpha-amino acids has been understood as arising out of hydrogen-bonded noncovalent interactions, where the -OH groups of two phenyl rings of EGCG play dominant roles. The conversion of the enantiomeric mixture into diastereomers yielded well-resolved peaks for D and L amino acids permitting the precise measurement of enantiomeric composition. Often one encounters complex situations when the spectra are severely overlapped or partially resolved hampering the testing of enantiopurity and the precise measurement of enantiomeric excess (ee). Though higher concentration of EGCG yielded better discrimination, the use of lower concentration being economical, we have exploited an appropriate 2D NMR experiment in overcoming such problems. Thus, in the present study we have successfully demonstrated the utility of the bioflavonoid (-)-EGCG, a natural product as a chiral solvating agent for the discrimination of large number of alpha-amino acids in a polar solvent DMSO. Another significant advantage of this new chiral sensing agent is that it is a natural product and does not require tedious multistep synthesis unlike many other chiral auxiliaries.
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We show that the third order optical nonlinearity of 15-atom gold clusters is significantly enhanced when in contact with indium tin oxide (ITO) conducting film. Open and close aperture z-scan experiments together with non-degenerate pump-probe differential transmission experiments were done using 80 fs laser pulses centered at 395 nm and 790 nm on gold clusters encased inside cyclodextrin cavities. We show that two photon absorption coefficient is enhanced by an order of magnitude as compared to that when the clusters are on pristine glass plate. The enhancement for the nonlinear optical refraction coefficient is similar to 3 times. The photo-induced excited state absorption using pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also show an enhancement by an order of magnitude. These results attributed to the excited state energy transfer in the coupled gold cluster-ITO system are different from the enhancement seen so far in charge donor-acceptor complexes and nanoparticle-conjugate polymer composites.
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A number of spectral analysis of surface wave tests were performed on asphaltic and cement concrete pavements by dropping freely a 6.5kg spherical mass, having a radius of 5.82cm, from a height (h) of 0.51.5m. The maximum wavelength ((max)), up to which the shear wave velocity profile can be detected with the usage of surface wave measurements, increases continuously with an increase in h. As compared to the asphaltic pavement, the values of (max) and (min) become greater for the chosen cement concrete pavement, where (min) refers to the minimum wavelength. With h=0.5m, a good assessment of the top layers of both the present chosen asphaltic and the cement concrete pavements, including soil subgrade, can be made. For a given h, as compared to the selected asphaltic pavement, the first receiver in case of the chosen cement concrete pavement needs to be placed at a greater distance from the source. Inverse analysis has also been performed to characterise the shear wave velocity profile of different layers of the pavements.
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We report the mechanical properties of a framework structure, Cu2F(HF)(HF2)(pyz)(4)](SbF6)(2)](n) (pyz = pyrazine), in which Cu(pyz)(2)](2+) layers are pillared by HF2- anions containing the exceptionally strong F-H center dot center dot center dot F hydrogen bonds. Nanoindentation studies on single-crystals clearly demonstrate that such bonds are extremely robust and mechanically comparable with coordination bonds in this system.