Reactions of Oxiranes and Carbonyl Compounds Catalyzed by Ammonium Decatungstocerate(IV)

Various types of oxiranes react with acetone in the presence of catalytic amounts of ammonium decatungstocerate(IV) icosahydrate, (NH₄)₈[CeW₁₀O³⁶] ? 20H₂O, to give the corresponding 1,3-dioxolanes in excellent yields.     

Synthesis and Characterization of Nano Silica Supported Tungstophosphoric Acid: An Efficient, Reusable Heterogeneous Catalyst for the Synthesis of Azlactones

A rapid and scale up protocol for the synthesis of azlactones by the Erlenmeyer method under solvent-free conditions was developed. Tungstophosphoric acid supported on nano-silica, TPA@nano-SiO₂ was used as a heterogeneous catalyst for the synthesis of a wide range of azlactone derivatives. The catalyst was characterized by physicochemical measurements. The procedure was simple and permitted the quantitative isolation of products and catalyst under thermal conditions. The recycled catalyst was reused more than 5-times without loss of catalytic activity.     

Ammonium decatungstocerate (IV): an efficient catalyst for ring opening of epoxides with aromatic amines

A mild, convenient and efficient ring opening of oxiranes with aromatic amines was catalyzed by ammonium decatungstocerate (IV) in acetonitrile. The reaction afforded the corresponding products in 92–100% yields. The catalyst was reused for several times with consistent activity.     

K5CoW12O40⋅3H2O: A Novel Cobalt Polyoxometalate Catalyst for Conversion of Epoxides to Acetonides

A mild and efficient preparation of 1,3-dioxolanes from epoxides and acetone has been carried out in high to excellent yields under catalysis of potassium dodecatungstocobaltate trihydrate (K₅CoW₁₂O₄₀3H₂O) (0.01 molar equiv.).     

Palladium Nanoparticles Immobilized on Nano‐Silica Triazine Dendritic Polymer (Pdnp‐nSTDP): An Efficient and Reusable Catalyst for Suzuki–Miyaura Cross‐Coupling and Heck Reactions

A new catalyst based on palladium nanoparticles immobilized on nano‐silica triazine dendritic polymer (Pd_np‐nSTDP) was synthesized and characterized by FT‐IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X‐ray, transmission electron microscopy and elemental analysis. The size of the palladium nanoparticles was determined to be 3.1±0.5 nm. This catalytic system showed high activity in the Suzuki–Miyaura cross‐coupling of aryl iodides, bromides and chlorides with arylboronic acids and also in the Heck reaction of these aryl halides with styrenes. These reactions were best performed in a dimethylformamide (DMF)/water mixture (1:3) in the presence of only 0.006 mol% and 0.01 mol% of the catalyst, respectively, under conventional conditions and microwave irradiation to afford the desired coupling products in high yields. The Pd_np‐nSTDP was also used as an efficient catalyst for the preparation of a series of star‐ and banana‐shaped compounds with a benzene, pyridine, pyrimidine or 1,3,5‐triazine unit as the central core. Moreover, the catalyst could be recovered easily and reused several times without any considerable loss of its catalytic activity.     

Optimal design of EMAT transmitters

A three-part finite element model is developed that characterizes the ultrasonic pulse produced by an electromagnetic acoustic transducer (EMAT). The model represents several significant improvements over previously published works, as follows: (a) spatial inhomogeneities in the magnetic flux density are calculated and then incorporated in the determination of body forces, (b) an improved model of the electromagnetic induction phenomenon is formulated, allowing a more accurate evaluation of the ultrasonic pulse launched by an EMAT transmitter and (c) results from the model are compared directly with experimental measurements, yielding discrepancies of the order of 15% in the amplitude of the ultrasonic pulse. The new model is used to optimize the design of the EMAT system. In particular, a parametric study was conducted on the effects of varying an EMAT's magnet-to-coil width ratio. For the EMAT configuration considered, significant improvements can be achieved in the ultrasonic beam amplitude and profile by increasing the ratio to about 1.2; further increases in magnet dimensions yield only marginal improvements in the ultrasonic beam, at the cost of excessive EMAT size.     

Effect of diazoxide, an ATP-dependent potassium-channel opener, on isolated aortae of normal and diabetic rats

1. The effect of diazoxide on the potassium-induced contraction and its inhibitory effect on noradrenaline-induced contraction were studied in the isolated aortic rings of normal and streptozocin-treated diabetic rats. 2. Diazoxide relaxed potassium-induced contraction in normal and diabetic rat aortae. There was no statistically significant difference in the relaxing effect of diazoxide in these two groups of rats. Glibenclamide inhibited the relaxing effect of diazoxide in normal and diabetic rat aortae to the same extent. Pretreatment of tissues with diazoxide prevented the noradrenaline-induced contraction. This inhibitory effect significantly differed between normal and diabetic rats. 3. It is concluded that, in the rat aorta, the state of potassium channels and the potency of diazoxide to open these channels are not affected by experimental diabetes. The observed differences between the responses of normal and diabetic aortae to the inhibitory effect of diazoxide on noradrenaline-induced contraction can be attributed to a mechanism(s) other than potassium-channel opening by diazoxide, which might be modified in diabetes, or to different consequences after potassium-channel opening in diabetic tissues compared with normal tissues.