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An important issue regarding the mechanism of heterogeneous epoxidation of ethylene on silver (Ag) is related to the formation of CÀO bonds. [1][2][3] There are two possible ways for the CÀO bonds to form: It is conceivable that the dominant pathway would proceed through either a concerted addition of surface oxygen to the C = C bond of ethylene or by sequential formation of the two CÀO bonds by a creation of an asymmetric surface intermediate (Scheme 1).It has been shown previously in temperature-programmed desorption (TPD) experiments that a surface intermediate formed on Ag(111) upon adsorption of ethylene oxide (EO) at about 250 K under ultrahigh vacuum (UHV) conditions reacts at about 310 K to reform EO plus small amounts of other products, including ethylene.[4] High-resolution electron energy loss spectroscopy (HREELS) was used to identify this surface intermediate as the asymmetric structure shown in Scheme 1, namely a surface oxametallacycle.[4] This work Scheme 1. Possible intermediates in ethylene epoxidation on Ag: a) in the concerted addition of ethylene to oxygen and b) in the sequential formation of CÀO bonds (surface oxametallacycle).

The long-sought cubic gauche phase of polymeric nitrogen (cg-PN) with nitrogen-nitrogen single bonds has been synthesized together with a related phase by a radio-frequency plasma reaction under near-ambient conditions. Here, we report the synthesis of polymeric nitrogen using a mixture of nitrogen and argon flowing over bulk β-sodium azide or β-sodium azide dispersed on 100 nm long multiwall carbon nanotubes. The cg-PN phase is identified by Raman and attenuated total reflection-Fourier transform infrared spectroscopy, and powder X-ray diffraction. The synthesis of the cubic gauche allotrope of high energy density polymeric nitrogen under near-ambient conditions should therefore enable its optimized production and applications as a “green” energetic material and a potential catalyst for different chemical reactions.

The dissolution rate and the oral bioavailability of nitrendipine were significantly affected by the crystal size, and the oral bioavailability could be improved significantly by preparing it as nanocrystals. FaSSIF can be used to predict differences in oral absorption of crystals with different particle sizes.