Search

Triflic acid functionalized carbon@silica composite (CStar@SiO2TfOH) was synthesized by the partial carbonization of starch in the presence of silica followed by the immobilization of triflic acid and its catalytic activity was explored for the three component synthesis of hexahydroacridine‐1,8‐diones and indeno[1,2‐b]indole‐9,10‐diones. CStar@SiO2‐TfOH was characterized using different techniques, such as Fourier‐Transform Infrared Spectroscopy (FTIR), Thermogravimetricanalysis (TGA), X‐ray Powder Diffraction (XRD), Energy Dispersive X‐ray (EDX), Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HR‐TEM) and was found to be recyclable upto five runs without any noticeable change. Further, the intermediate formed during the preparation of hexahydroacridine‐1,8‐dione has been isolated and its structure was confirmed by single crystal X‐ray crystallography which confirms the proposed mechanism. Also, to confirm the structure of 4b,9b‐dihydroxy‐5‐(4‐chlorophenyl)‐7,7‐dimethyl‐4b,5,7,8‐tetrahydroindeno[1,2‐b]indole‐9,10(6H,9bH)‐dione we have performed the DFT study and found that the 1H and 13C chemical shift values and IR wavenumbers predicted by B3LYP method were very close to the experimentally determined values. [ABSTRACT FROM AUTHOR]

A detailed study on the effects of core halogenation of tetraazaperopyrene (TAPP) derivatives is presented. Its impact on the solid structure, as well as the photophysical and electrochemical properties, has been probed by the means of X-ray crystallography, UV/Vis and fluorescence spectroscopy, high-resolution electron energy loss spectroscopy (HREELS), cyclic voltammetry (CV), and DFT modeling. The aim was to assess the potential of this approach as a construction principle for organic electron-conducting materials of the type studied in this work. Although halogenation leads to a stabilization of the LUMOs compared to the unsubstituted parent compound, the nature of the halide barely affects the LUMO energy while strongly influencing the HOMO energies. In terms of band-gap engineering, it was demonstrated that the HOMO-LUMO gap is decreased by substitution of the TAPP core with halides, the effect being found to be most pronounced for the iodinated derivative. The performance of the recently reported core-fluorinated and core-iodinated TAPP derivatives in organic thin-film transistors (TFTs) was investigated on both a glass substrate, as well as on a flexible plastic substrate (PEN). Field-effect mobilities of up to 0.17 cm2 Vs−1 and on/off current ratio of >106 were established. [ABSTRACT FROM AUTHOR]

Recent progress in high-resolution structural study of rhodopsin has been enabled by a novel selective extraction procedure with rod photoreceptor cells. In this study, we applied the method for rapid and efficient preparation of a purified analogue pigment using bovine rod outer segment membranes with 9- cis-retinal. After complete bleaching of the membranes and subsequent regeneration with the exogenous retinal, 9- cis-rhodopsin is selectively extracted from the membranes using combination of zinc and heptylthioglucoside. The solubilized sample, even with a small amount of contaminating retinal oximes, is shown to be pure enough for three-dimensional crystallization. The X-ray diffraction from 9- cis-rhodopsin crystals was examined and the electron density map at 2.9 Å resolution in the chromophore region can be fitted well with the model of 9- cis-retinal Schiff base. [ABSTRACT FROM AUTHOR]

A binary complex of the ammonia channel Amt1 from Methanococcus jannaschii and its cognate PII signalling protein GlnK1 has been produced and characterized. Complex formation is prevented specifically by the effector molecules Mg-ATP and 2-ketoglutarate. Single-particle electron microscopy of the complex shows that GlnK1 binds on the cytoplasmic side of Amt1. Three high-resolution X-ray structures of GlnK1 indicate that the functionally important T-loop has an extended, flexible conformation in the absence of Mg-ATP, but assumes a compact, tightly folded conformation upon Mg-ATP binding, which in turn creates a 2-ketoglutarate-binding site. We propose a regulatory mechanism by which nitrogen uptake is controlled by the binding of both effector molecules to GlnK1. At normal effector levels, a 2-ketoglutarate molecule binding at the apex of the compact T-loop would prevent complex formation, ensuring uninhibited ammonia uptake. At low levels of Mg-ATP, the extended loops would seal the ammonia channels in the complex. Binding of both effector molecules to PII signalling proteins may thus represent an effective feedback mechanism for regulating ammonium uptake through the membrane. [ABSTRACT FROM AUTHOR]

A series of undoped and doped barium titanate powders were prepared and examined by: X-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, particle size, ζ-potential, specific surface area, differential scanning calorimetry (DSC), impedance spectroscopy, and secondary-ion mass spectrometry. The doped samples were prepared by two different methods: (1) coating powders with chlorides and (2) mixing chlorides in a hydrothermal reactor. Different distribution profiles of the dopant atoms were observed for the two incorporation methods. Two TC peaks were detected by DSC for samples doped by coating. Analysis of electrical measurements revealed time constant distributions that were more spread in samples that had a core–shell structure. [ABSTRACT FROM AUTHOR]

The article describes three-dimensional (3D) reconstruction of the v-AlCrFe phase by electron crystallography. High-resolution transmission-electron microscopy (HREM) images and selected-area electron diffraction patterns from 13 different zone axes were combined to give a 3D potential map. Electron crystallography is a powerful method for solving structures of crystals with submicrometre sizes, which are too small for X-ray crystallography. 3D reconstruction from HREM images offers a new possibility for ab initio structure determination of inorganic compounds existing only with very small crystal sizes.