A General Catalyst Based on Cobalt Core–Shell Nanoparticles for the Hydrogenation of N-Heteroarenes Including Pyridines

Herein, we report the synthesis of specific silica-supported Co/Co₃O₄ core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased.     

Stored energy release behaviour of disordered carbon

The use of graphite as a moderator in a low temperature thermal nuclear reactor is restricted due to accumulation of energy caused by displacement of atoms by neutrons and high energetic particles. Thermal transients may lead to a release of stored energy that may raise the temperature of the fuel clad above the design limit. Disordered carbon is thought to be an alternative choice for this purpose. Two types of disordered carbon composites, namely, CB (made up of 15 wt. % carbon black dispersed in carbonized phenolic resin) and PAN (made up of 20 vol. % chopped polyacrylonitrile carbon fibre dispersed in carbonized phenolic resin matrix) have been irradiated with 145 MeV Ne⁶⁺ ions at three fluence levels of 1.0×10¹³, 5.0×10¹³ and 1.5×10¹⁴ Ne⁶⁺/cm², respectively. The XRD patterns revealed that both the samples remained disordered even after irradiation. The maximum release of stored energy for CB was 212 J/g and that of PAN was 906 J/g. For CB, the release of stored energy was a first order reaction with activation energy of 2.79 eV and a frequency factor of 3.72×10²⁸ per second. 13% of the defects got annealed by heating up to 700 °C. PAN showed a third-order release rate with activation energy of 1.69 eV and a frequency factor of 1.77×10¹⁴ per second. 56% of the total defects got annealed by heating it up to 700 °C. CB seems to be the better choice than PAN as it showed less energy release with a slower rate. PACS 61.80.Jh; 61.80.-x; 61.43Er; 61.43.-j; 68.43.Vx     

Self-assembly of nanoparticles on the surface of ionic crystals: Structural properties

With a suitable combination of ligand-stabilised nanoparticle suspension and ionic salt solutions, it is possible to produce microcrystals that are coated with nanoparticles. The self-assembly process of coating microcrystals by gold nanoparticles (NP) is mediated by the crystal lattice. This is the so-called CLAMS process - a generic process for self-organisation of nanoparticles on the surface of crystals [M. Murugeshan, D. Cunningham, J.-L. Martnez-Albertos, R. Vrcelj, B.D. Moore, Chem. Commun. (2005) 2677]. We are exploring here the structural properties of these self-assembled structures by using different imaging techniques.     

Spectral and voltammetric studies on titanium substituted Keggin-type heteropolyanions

Bonding and redox properties of mono- and dititanium substituted 12-heteropolytungsto-phosphates and their complexes with bivalent Mn, Co, Ni and Cu are studied by UV-Vis, ESR and cyclicvoltammetric techniques. The heteropoly blue analogue [Ti^IIITi^IVW₁₀PO₄₀]⁸⁻ is unstable and its presence in solution is proved by optical and ESR spectroscopy. ESR results reveal that the odd electron is trapped on the titanium atom at 77 K. The optical electronegativity of Ti(III) in this heteropoly blue is estimated to be 2.4 from the intervalence charge transfer (IVCT) bands. X-ray powder diffraction results show that the complexes K₅M^II[Ti₂W₁₀PO₄₀].xH₂O(M^II = Cu or Mn) are isomorphous with K₇[Ti₂W₁₀PO₄₀].6H₂O. Electronic spectroscopy indicates very high symmetry around the bivalent metal ion M in the K₅M^II[Ti₂W₁₀PO₄₀].xH₂O complexes. This high symmetry is confirmed in K₅Cu[Ti₂W₁₀PO₄₀] by the observation of dynamic Jahn-Teller (JT) distortion at 300 K and static JT distortion at 77 K.     

SBA-15 supported HPW: Effective catalytic performance in the alkylation of phenol

SBA-15 was synthesized using non-ionic surfactant as the structure directing agent at 40 °C. It was then impregnated with different loadings (10, 30, 50 and 70%) of phosphotungstic acid. They were characterized by XRD, N₂ adsorption, FT-IR and DRIFT techniques. The physicochemical characterization revealed that SBA-15 could accommodate discrete phosphotungstic acid due to its large pore volume and high surface area. The catalytic activity of these materials was examined in the vapour phase tert-butylation of phenol using tert-butyl alcohol as the alkylating agent. The influence of reaction parameters such as reaction temperature, reactant feed ratio, WHSV and time on stream was studied, and the results were correlated with physicochemical characteristics of the catalysts. 4-tert-Butyl phenol was observed as the major product with high selectivity. Among the catalysts, 30% phosphotungstic acid supported SBA-15 showed high phenol conversion under optimum conditions, which is significantly higher than either phosphotungstic acid loaded mesoporous AlPO or AlMCM-41.     

Kinetics and mechanism of oxidation of substituted benzaldehydes by quinolinium fluorochromate

The kinetics of oxidation of a number of meta- and para-substituted benzaldehydes by quinolinium fluorochromate, QFC has been studied in aqueous acetic acid medium in the presence of acid. The products of oxidation are the corresponding benzoic acids. The reaction is first order each in substrate, QFC and HClO₄. Electron-withdrawing substituents increase the rate, while electron-releasing substituents decrease it and the rate data obey Hammett's relationship. The reaction constant for the oxidation has a value of 1.16±0.07 at 30°C. The activation enthalpies and entropies are calculated and the possible mechanism for oxidation is discussed.     

Preparation and biological evaluation of the new chlorin photosensitizer T3,4BCPC for detection and treatment of tumors

The new water-soluble photosensitizer 5,10,15,20-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl]chlorin (T3,4BCPC) has been prepared, characterized and labeled with 99mTc radionuclide. The radiotracer was evaluated for tissue distribution in Wistar rats. Accumulation of administrated activities in the liver, kidney, bladder and large intestine at 4 h post-injection indicated that the labeled ligand was largely eliminated through the renal and partly through the hepatobiliary system. In vivo biodistribution studies of the labeled compound were carried out in rodent and murine tumor models in comparison with other tumor-seeking radiopharmaceuticals such as 99mTc(V)-dimercaptosuccinic acid (DMSA), 201thallous chloride (TlCl) and 99mTc-citrate using a gamma camera computer system. In N-nitrosomethylurea (NMU)-induced rat mammary tumors, the labeled ligand showed a five-fold tumor to muscle (T/M) ratio compared to 99mTc(V)-DMSA (3-fold) and 201TlCl (3-fold). In the case of C(3)H/J virus-induced spontaneous mammary tumors, the differences were not marked. However, in the transplanted rat C(6)-glioma, the T/M ratio of the labeled compound was appreciably higher (four-fold) than that noted with 99mTc(V)-DMSA (two-fold), 201TlCl (three-fold) and 99mTc-citrate (more than three-fold). These findings suggest that the radiolabeled T3,4BCPC may have potential for the detection of cancer. In order to ascertain the efficacy of the compound for photodynamic therapy applications, a preclinical PDT study was carried out in fibrosarcoma-bearing mice after injecting 5.0 mg/kg body weight of the T3,4BCPC. A laser dose of 20 mW for 60 s resulted in 80% destruction of tumors. These data suggest that this molecule could be useful for PDT of cancer. The labeled agent could also be useful in monitoring the progression/regression of tumors before, during, and after chemotherapy, radiation therapy or PDT.     

Biosynthesis of TiO2 Nanoparticles Using Edible Mushroom (Pleurotus djamor) Extract: Mosquito Larvicidal,Histopathological, Antibacterial and Anticancer Effect

Journal of Cluster Science - The titanium dioxide nanoparticles (TiO2NPs) were synthesized by the aqueous extract from P. djamor. The UV–Vis spectrum of TiO2NPs showed maximum absorption at...