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51.
52.
An efficient fluorescent probe (E)-N1-((E)-2-((pyren-7-yl)methyleneamino)ethyl)-N2-((pyren-7-yl)methylene)ethane-1,2-diamine (L) has been synthesized by a facile one-step condensation reaction. L can selectively detect Cd(2+) in presence of other common metal ions in 0.1 M HEPES buffered DMSO-water (4?:?1, v/v) medium. The detection limit of Cd(2+) is 1.8 × 10(-8) M. Cd(2+) can effectively convert the excimer emission of L into its monomer emission which in turn exhibits a time-dependent red-shift. 相似文献
53.
Animesh K. Ojha Patrice Donfack Arnulf Materny 《Journal of Raman spectroscopy : JRS》2012,43(9):1183-1190
Complex concentration‐dependence of surface‐enhanced Raman scattering (SERS) and UV–Vis absorption of Ag‐nanoparticles (AgNPs) mixed with Gly has been observed. Surprisingly, with decreasing Gly concentration, a new band in UV–Vis absorption of AgNPs/Gly mixtures is found to red‐shift with increasing intensity, until a turning point at a critical concentration. Further diluting Gly, the new band blue‐shifts with decreasing intensity. Similarly, the SERS intensities of Gly bands at 615 and 905 cm–1 consistently increase with decreasing Gly concentrations, reaching maxima at the critical concentration. This agrees consistently with the variation in position and intensity of the new developing plasmon absorption band. Interestingly, transmission electron microscopy (TEM) revealed Gly‐induced modifications of AgNPs, including a reassembling and increasing aspect ratio with deceasing Gly concentration. The concentration‐dependent behavior of UV–Vis absorption, SERS, and TEM of AgNPs/Gly mixtures could be due to the complex nature of Gly‐AgNPs interaction depending on the molecular density, as supported by TEM images. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
54.
Debamitra Chakravorty Saravanan Parameswaran Vikash Kumar Dubey Sanjukta Patra 《Applied biochemistry and biotechnology》2012,167(3):439-461
Organic solvent-stable lipases have pronounced impact on industrial economy as they are involved in synthesis by esterification, interesterification, and transesterification. However, very few of such natural lipases have been isolated till date. A study of the recent past provided few pillars to rely on for this work. The three-dimensional structure, inclusive of the surface and active site, of 29 organic solvent-stable lipases was analyzed by subfamily classification and protein solvent molecular docking based on fast Fourier transform correlation approach. The observations revealed that organic solvent stability of lipases is their intrinsic property and unique with respect to each lipase. In this paper, factors like surface distribution of charged, hydrophobic, and neutral residues, interaction of solvents with catalytically immutable residues, and residues interacting with essential water molecules required for lipase activity, synergistically and by mutualism contribute to render a stable lipase organic solvent. The propensity of surface charge in relation to stability in organic solvents by establishing repulsive forces to exclude solvent molecules from interacting with the surface and prohibiting the same from gaining entry to the protein core, thus stabilizing the active conformation, is a new finding. It was also interesting to note that lipases having equivalent surface-exposed positive and negative residues were stable in a wide range of organic solvents, irrespective of their LogP values. 相似文献
55.
A new family of tetranuclear nickel cube complexes [Ni(4)L(4)(solv)(4)] (1, solv = MeOH; 2, solv = H(2)O; H(2)L = pyrazole-based tridentate {ONO} ligand) has been studied in detail, in particular by X-ray diffraction and superconducting quantum interference device (SQUID) magnetometry. Different solvates 1·H(2)O, 2·4C(3)H(6)O, 2·CH(2)Cl(2), and 2·H(2)O were obtained in crystalline form. Only small structural variations were found for the Ni-O-Ni angles of the [Ni(4)O(4)] cores of those compounds, but these slight variations have dramatic consequences for the magnetic properties. [Ni(4)L(4)(MeOH)(4)]·H(2)O (1·H(2)O) and [Ni(4)L(4)(H(2)O)(4)]·H(2)O (2·H(2)O) can be reversibly interconverted in the solid state by exposure to the respective solvent, MeOH or H(2)O, and this goes along with a switching of the spin ground state from magnetic (S(T) = 4) to diamagnetic (S(T) = 0). Likewise the (irreversible) loss of lattice solvent in [Ni(4)L(4)(H(2)O)(4)]·4C(3)H(6)O (2·4C(3)H(6)O) to give 2·2C(3)H(6)O changes the ground state from S(T) = 4 to S(T) = 0. In view of these dramatic solvatomagnetic effects for the present [Ni(4)L(4)(solv)(4)] complexes, which occur upon extrusion of lattice solvent or facile exchange of coordinated solvent molecules while keeping the robust [Ni(4)O(4)] core intact, a note of care is issued: whenever magnetic data are obtained for powdered material or for crystals that easily loose lattice solvent molecules, the magnetic properties may not necessarily reflect the situation observed in the corresponding single crystal diffraction study. Finally, a thorough analysis of the present series of complexes as well as other {Ni(4)(μ(3)-OR)(4)} cubes reported in the literature confirms that a correlation between the (Ni-O-Ni)(av) bond angle and J in [Ni(4)O(4)] cubane complexes does indeed exist. 相似文献
56.
Animesh K. Ojha Sunil K. Srivastava B. P. Asthana Ranjan K. Singh 《Journal of Raman spectroscopy : JRS》2007,38(2):159-165
The isotropic and anisotropic parts of the Raman spectra of NH2 bending and ν(CO) stretching modes of HCONH2 in a hydrogen‐bonding solvent, methanol, at different concentrations have been analyzed carefully in order to study the noncoincidence effect (NCE). In neat HCONH2, the experimentally measured values of noncoincidence Δνnc are ∼11 and ∼18 cm−1 for the NH2 bending and ν(CO) stretching modes, which reduce to 0.45 and 1.14 cm−1, respectively at the concentration of HCONH2 in mole fraction, χm = 0.1. The experimental results have been explained on the basis of two models, namely, the microscopic prediction of Logan and the macroscopic model of Mirone and Fini. The relative success of the two models in explaining the experimental data for both the modes have been discussed. It has been observed that in case of the ν(CO) stretching vibrational mode the Logan model can reproduce the experimental data rather precisely, whereas in the case of the NH2 bending mode, Mirone and Fini model yields more accurate results. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
57.
Animesh K. Ojha Sunil K. Srivastava S. Schlücker W. Kiefer B. P. Asthana Ranjan K. Singh 《Journal of Raman spectroscopy : JRS》2007,38(12):1656-1664
A concentration‐dependent Raman study of the ν(C Br) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH3OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm−1in the case of 2Br‐p and at ∼618 cm−1 in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(C Br) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
58.
D Chakravorty 《Journal of Non》1974,15(2):191-198
Electrically conducting layers have been induced in some alkali-containing silicate glasses by subjecting them to a Na+?Ag+ ion-exchange reaction followed by a reduction treatment in hydrogen. The surface resistances of the ion-exchanged and reduced glasses range from 0.15ohm/square to 4.1 ohm/square depending on the glass composition. Most of the layers give TCR values around 2000 ppm/K. The microstructural studies of the ion-exchanged and reduced layers confirm that such high surface conductances arise due to the formation of continuous chains of metallic silver and bismuth droplets in a glass matrix. 相似文献
59.
Herein, we report the controlled and direct fabrication of Cu2O/CuO thin film on the conductive nickel foam using electrodeposition route for the electrochemical reduction of carbon dioxide (CO2) to methanol. The electrocatalytic reduction was performed in CO2 saturated aqueous solution consisting of KHCO3, pyridine and HCl at room temperature. CO2 reduction was carried out at a constant potential of −1.3 V for 120 min to study the electrochemical performance of the prepared electrocatalysts. Cu2O/CuO shows better electrocatalytic activity with highest current density of 46 mA/cm2. The prepared catalyst can be an efficient and selective electrode for the production of methanol. 相似文献
60.
Arghya Chakravorty Emilio Gallicchio Emil Alexov 《Journal of computational chemistry》2019,40(12):1290-1304
A novel grid-based method is presented, which in conjunction with a smooth Gaussian-based model of atoms, is used to compute molecular volume (MV) and surface area (MSA). The MV and MSA are essential for computing nonpolar component of free energies. The objective of our grid-based approach is to identify solute atom pairs that share overlapping volumes in space. Once completed, this information is used to construct a rooted tree using depth-first method to yield the final volume and SA by using the formulations of the Gaussian model described by Grant and Pickup (J. Phys Chem, 1995, 99 , 3503). The method is designed to function uninterruptedly with the grid-based finite-difference method implemented in Delphi, a popular and open-source package used for solving the Poisson–Boltzmann equation (PBE). We demonstrate the time efficacy of the method while also validating its performance in terms of the effect of grid-resolution, positioning of the solute within the grid-map and accuracy in identification of overlapping atom pairs. We also explore and discuss different aspects of the Gaussian model with key emphasis on its physical meaningfulness. This development and its future release with the Delphi package are intended to provide a physically meaningful, fast, robust and comprehensive tool for MM/PBSA based free energy calculations. © 2019 Wiley Periodicals, Inc. 相似文献