Phosphonate‐Modified UiO‐66 Brønsted Acid Catalyst and Its Use in Dehydra‐Decyclization of 2‐Methyltetrahydrofuran to Pentadienes

Phosphorus‐modified all‐silica zeolites exhibit activity and selectivity in certain Brønsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well‐defined sites, we report the incorporation of Brønsted acidity to metal–organic frameworks with the UiO‐66 topology, achieved by attaching phosphonic acid to the 1,4‐benzenedicarboxylate ligand and using it to form UiO‐66‐PO₃H₂ by post‐synthesis modification. Characterization reveals that UiO‐66‐PO₃H₂ retains stability similar to UiO‐66, and exhibits weak Brønsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra‐decyclization of 2‐methyltetrahydrofuran (2‐MTHF). For the later reaction, the reported catalyst exhibits site‐time yields and selectivity approaching that of phosphoric acid on all‐silica zeolites. Using solid‐state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.     

Periodic Mesoporous Silicas and Organosilicas: An Overview Towards Catalysis

Micelle-templated mesoporous and organic–inorganic hybrid mesoporous materials are important in many fields of material research, especially for hosting catalysts in confined space. Among this class, the recent discovery of periodic mesoporous organosilicas (PMOs) represent an exciting new group of organic–inorganic nanocomposites targeted for a broad range of applications ranging from catalysis to microelectronics. Compared to the earlier generation of organic–inorganic hybrid mesoporous samples, obtained by the cocondensation reaction or by the grafting reaction, PMOs represent the right combination of organic and inorganic groups in the frame wall positions. This article reviews the current state of art in organic–inorganic hybrid mesoporous material research with special emphasis over periodic mesoporous organosilica materials having various redox centers (Ti, V, Cr) suitable for oxidation reactions as well as acidic sites (Al, –SO₃H) for the organic transformation of bulky molecules.     

Comparative Pharmacokinetics Profile of Vasa Swaras with Vasicine and Vasicinone

An RP-LC method was developed and validated for comparing the pharmacokinetics profile of Vasa Swaras (leaf juice of Adhatoda vasica Nees., Fam. Acanthaceae) with that of the pure vasicine and vasicinone (chief marker compounds of A. vasica) upon oral administration of Vasa Swaras in rats, and also in different animal groups. Significant difference with p < 0.05 was found in the oral bioavailability of vasicine and vasicinone when administered as Vasa Swaras and as single vasicine and/or vasicinone. Vasicine and vasicinone were found to be more bioavailable from Vasa Swaras than pure vasicine and/or vasicinone.     

Constraints on dark matter annihilation from M87

As the largest mass concentrations in the local Universe, nearby clusters of galaxies and their central galaxies are prime targets in searching for indirect signatures of dark matter annihilation (DMA). We seek to constrain the dark matter annihilation emission component from multi-frequency observations of the central galaxy of the Virgo cluster. The annihilation emission component is modeled by the prompt and inverse-Compton gamma rays from the hadronization of annihilation products from generic weakly interacting dark matter particles. This component is fitted to the excess of the observed data above the spectral energy distribution (SED) of the jet in M87, described with a best-fit synchrotron-self-Compton (SSC) spectrum. While this result is not sufficiently significant to claim a detection, we emphasize that a dark matter “double hump signature” can be used to unambiguously discriminate the dark matter emission component from the variable jet-related emission of M87 in future, more extended observation campaigns.     

Quantitative Analysis of Flavonoids in Annona squamosa Leaf Extracts and Its Pellet Formulation by Validated High-Performance Thin-Layer Chromatographic Technique

JPC – Journal of Planar Chromatography – Modern TLC - Annona squamosa, commonly known as custard apple, possesses various medicinal properties such as antimicrobial, insecticidal,...     

Retention and selectivity of stationary phases for hydrophilic interaction chromatography

More and more polar stationary phases have become available for the separation of small polar compounds in the past decade as hydrophilic interaction chromatography (HILIC) continues to find applications in new fields (e.g., metabolomics and proteomics). Bare silica phases remain popular, especially in the bio-analytical area. A wide range of functional groups (e.g., amino, amide, diol, sulfobetaine, and triazole) have been employed as polar stationary phases for HILIC separation. This review provides a survey of the popular stationary phases commercially available and discusses the retention and selectivity characteristics of the polar stationary phases in HILIC. The purpose of the review is not to provide a comprehensive overview of literature reports, but rather focuses on findings that demonstrate retention and selectivity of the polar stationary phases in HILIC.     

Simulation of high capacity 40 Gb/s long haul DWDM system using different modulation formats and dispersion compensation schemes in the presence of Kerr's effect

In this paper, simulative analysis of 40 Gb/s long haul (500-2000 km) DWDM system with ultra high capacity upto 1.28 Tb/s has been carried out for carrier-suppressed return-to-zero (CSRZ), duobinary return-to-zero (DRZ) and modified duobinary return-to-zero (MDRZ) modulation formats. The DWDM system has been analyzed for the pre, post and symmetrical dispersion compensation schemes for 16 Channels with 25 GHz channel spacing in order to find the optimum modulation format for a high bit rate optical transmission system. The effect of variation in input power and transmission distances is observed in terms of Q value and eye opening for various formats. It is found that symmetrical compensation is superior to pre and post dispersion compensation schemes. It has also been observed that the performance of DWDM system is severely limited by the four-wave mixing (FWM) effect and is determined that MDRZ format seems to be the best choice for the transmission distance beyond 1550 km despite slightly more complex transmitter and receiver configuration. Further, symmetrical compensation scheme has been investigated for 32×40 Gb/s MDRZ format for faithful transmission over 1450 km.     

Preparation of cholesterol oxidase nanoparticles and their application in amperometric determination of cholesterol

Highly dispersed platinum nanoparticles were deposited on gram quantities of non-functionalized multiwalled carbon nanotubes (MWCNTs) by atomic layer deposition (ALD) in a fluidized bed reactor at 300 °C. (Methylcyclopentadienyl) trimethylplatinum and oxygen were used as precursors. The results of TEM analysis showed that ~1.3 nm Pt nanoparticles were highly dispersed on non-functionalized MWCNTs. The porous structures of MWCNTs did not change with the deposition of Pt nanoparticles. For comparison, the commercial 3 wt% Pt/C catalyst was also characterized. The ALD-prepared Pt/MWCNT was used for the hydrogenation of xylose to xylitol. The ALD-prepared Pt/MWCNT showed the best catalytic performance with 100 % conversion of xylose and 99.3 % selectivity to xylitol, compared to commercially available Pt/C, Ru/C, and Raney Ni catalysts. The stability of ALD produced Pt/MWCNT catalyst was higher than that of the commercial Pt/C, due to the presence of surface defects on the MWCNTs and the strong metal–support interaction for the ALD-prepared Pt/MWCNT catalyst.     

Templated crystal nucleation: mixed crystals of very different copper(II) N,N',N'-trimethyltriazacyclononane complexes

Templation of a daughter phase by a parent crystal results from an equilibrating mixture of two very different copper(ii) N,N',N'-trimethyltriazacyclononane complexes.     

Structural,electronic, optical,elastic and thermal properties of ZnXAs<Subscript>2</Subscript> (X = Si and Ge) chalcopyrite semiconductors

We report first principles calculations of solid state properties of ZnSiAs₂ and ZnGeAs₂ chalcopyrite semiconductors. The structural properties are calculated using a Full Potential Linearized Augmented Plane Wave method (FP-LAPW) of the Density Functional Theory (DFT). A Generalized Gradient Approximation (GGA) scheme proposed by Wu and Cohen (WC) has been chosen to calculate electronic and optical properties. Optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 30 eV. The elastic constants at equilibrium in tetragonal structure are also determined. Temperature effect on the volume, thermal expansion, heat capacity, Debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures and pressures and the silent results were interpreted. Finally using semi-empirical relation, we determined the hardness of the materials which attributed to different covalent bonding strengths.