Lack of Linear Free Energy Relationships in the p-Toluenesulfonic Acid Mediated Chromium(VI) Oxidation of Organic Sulfides

 The oxidation of methylphenyl sulfide by imidazolium dichromate in acetonitrile mediated by p-toluenesulfonic acid is first order in IDC and TsOH and zero order in MeSPh in the concentration range studied. The IDC oxidation of 14 para-, meta-, and ortho-substituted phenylmethylsulfides at 20–45°C conforms to the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental temperature range.     

New polymorphs of alumina

Abstract

We present the results of high-pressure, high-temperature studies on xerogel gamma alumina which is made up of nanocrystalline alumina and an amorphous phase. Not many studies of this type have been reported on xerogel materials. At about 5 GPa and 1400°C, the xerogel alumina transforms into a polymorphic mixture containing α Al₂O₃, B Al₂O₃ and C Al₂O₃ where the last two phases have B Ln₂O₃ and C Ln₂O₃ type structures respectively. Here Ln stands for the rare earths. The xerogel alumina containing 1 wt.% Cr₂O₃ under these conditions transforms into a polymorphic mixture containing Al₂O₃, k' Al₂O₃ and H Al₂O₃ where H Al₂O₃ has the H Ln₂O₃ type structure. For the first time, the observation of rare earth sesquioxide structures of alumina is reported. At about 5 GPa at 27°C, the xerogel aluminal transforms to an amorphous phase. The results are discussed using the free energy diagram for xerogels proposed by R. Roy (J. Amer. Cer. Soc., 52, 344, 1969; 67, 468, 1984).     

Which density functional is close to CCSD accuracy to describe geometry and interaction energy of small noncovalent dimers? A benchmark study using Gaussian09

A benchmark study on all possible density functional theory (DFT) methods in Gaussian09 is done to locate functionals that agree well with CCSD/aug‐cc‐pVTZ geometry and Ave‐CCSD(T)/(Q‐T) interaction energy (E_int) for small non‐covalently interacting molecular dimers in “dispersion‐dominated” (class 1), “dipole‐induced dipole” (class 2), and “dipole‐dipole” (class 3) classes. A DFT method is recommended acceptable if the geometry showed close agreement to CCSD result (RMSD < 0.045) and E_int was within 80–120% accuracy. Among 382 tested functionals, 1–46% gave good geometry, 13–44% gave good E_int, while 1–33% satisfied geometry and energy criteria. Further screening to locate the best performing functionals for all the three classes was made by counting the acceptable values of energy and geometry given by each functionals. The meta‐generalized gradient approximation (GGA) functional M06L was the best performer with total 14 hits; seven acceptable energies and seven acceptable geometries. This was the only functional “recommended” for at least two dimers in each class. The functionals M05, B2PLYPD, B971, mPW2PLYPD, PBEB95, and CAM‐B3LYP gave 11 hits while PBEhB95, PW91B95, Wb97x, BRxVP86, BRxP86, HSE2PBE, HSEh1PBE, PBE1PBE, PBEh1PBE, and PW91TPSS gave 10 hits. Among these, M05, B971, mPW2PLYPD, Wb97x, and PW91TPSS were among the “recommended” list of at least one dimer from each class. Long‐range correction (LC) of Hirao and coworkers to exchange‐correlation functionals showed massive improvement in geometry and E_int. The best performing LC‐functionals were LC‐G96KCIS and LC‐PKZBPKZB. Our results predict that M06L is the most trustworthy DFT method in Gaussian09 to study small non‐covalently interacting systems. © 2013 Wiley Periodicals, Inc.     

Synthesis and Characterization of Rare Earth Orthovanadate (RVO4; R = La, Ce, Nd, Sm, Eu & Gd) Nanorods/Nanocrystals/Nanospindles by a Facile Sonochemical Method and Their Catalytic Properties

We report herein on an efficient sonochemical method for the synthesis of rare earth orthovanadate nanorods/nanoparticles/nanospindles, (general formula RVO₄; R = La, Ce, Nd, Sm, Eu and Gd). TGA, XRD, FTIR, Raman, UV–Vis, and TEM studies are employed for their characterization and for understanding their morphologies. In order to vary the textural properties of the rare earth vanadates, two surfactants, polyethylene glycol (PEG) and amphiphilic triblock copolymer Pluronic P123, are chosen in the preparation. While the sonochemical synthesis in the presence of PEG results in the formation of nearly spherical nanoparticles of LaVO₄, CeVO₄, SmVO₄ and EuVO₄, the same technique yields nanorods and nanospindles of NdVO₄ and GdVO₄, respectively. When P123 is used as the surfactant, the morphologies of RVO₄ are strikingly different, and in most cases nanorods and nanospindles are formed. The photocatalytic activities of the rare earth orthovanadate have been evaluated by studying the degradation of methylene blue, and CeVO₄ seems to be the best catalyst in the heterogeneous photolysis. The electrocatalytic activity of the vanadates has been examined by studying the hydrogen evolution reaction using a linear sweep voltammogram technique in 1 M of a H₂SO₄ solution. GdVO₄ seems to be the best electrocatalyst. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural, optical and thermal investigations on Dy doped NaF–Li2O–B2O3 glasses

Structural, optical and thermal properties of Dy³⁺ doped lithium fluoroborate glasses have been studied for various concentrations of Dy³⁺ from 0.5 to 5 wt%. The XRD studies confirm the amorphous nature of the glasses while the FTIR spectra reveal the presence of BO₃ and BO₄ local structural units. The UV–VIS–NIR absorption studies were carried out to calculate the bonding parameters ( and δ), to identify the ionic/covalent nature of the glasses. The JO parameters, experimental and theoretical oscillator strengths were also determined and reported. The luminescence spectra have been studied to determine the radiative transition probability (A), stimulated emission cross section () and the experimental and calculated branching ratios (β_R) for the excited levels that include ⁴F_9/2→⁶H_11/2, ⁶H_13/2, and ⁶H_15/2 transitions. The variation of optical properties with varying concentrations of dysprosium oxide content in the glasses are reported and discussed. The thermal behavior of Dy³⁺ doped lithium fluoroborate glasses have been reported by recording DSC thermograms.     

Spontaneous Symmetry Breaking in the Formation of Supramolecular Polymers: Implications for the Origin of Biological Homochirality

Aqueous solutions of the achiral, monomeric, nucleobase mimics (2,4,6‐triaminopyrimidine, TAP, and a cyanuric acid derivative, CyCo6) spontaneously assemble into macroscopic homochiral domains of supramolecular polymers. These assemblies exhibit a high degree of chiral amplification. Addition of a small quantity of one handedness of a chiral derivative of CyCo6 generates exclusively homochiral structures. This system exhibits the highest reported degree of chiral amplification for dynamic helical polymers or supramolecular helices. Significantly, homochiral polymers comprised of hexameric rosettes with structural features that resemble nucleic acids are formed from mixtures of cyanuric acid (Cy) and ribonucleotides (l‐, d ‐pTARC) that arise spontaneously from the reaction of TAP with the sugars. These findings support the hypothesis that nucleic acid homochirality was a result of symmetry breaking at the supramolecular polymer level.     

Preparation and Characterization of Mn Doped ZnO Nanorods

Physics of the Solid State - Mn doped ZnO nanorods were prepared by chemical precipitation method. The micro-structural and structural properties of the nanorods were calculated from the X-ray...