No abstract

New solid solution nanocrystals with fluorite-type cubic structure in the ceria (CeO 2 )-yttrium niobate (1/4Y 3 NbO 7 ) system were directly formed at 120°C-240°C from the precursor solution mixtures of (NH 4 )Ce(NO 3 ) 6 , YCl 3 Á6H 2 O, and NbCl 5 under mild hydrothermal conditions in the presence of aqueous ammonia. The hydrothermal formation of cubic solid solution nanocrystals in the wide composition range of CeO 2 (mol%) = 10-100 in the CeO 2 -1/4Y 3 NbO 7 system was effectively achieved via the assistance of the presence of CeO 2 component more than 10 mol% as a promoter with the same fluorite-type structure. The optical band gap of the solid solutions gradually decreased with increased CeO 2 component. The high phase stability of the solid solutions in the CeO 2 -1/4Y 3 NbO 7 system was confirmed, i.e., the single cubic phase of the solid solutions was maintained after heat treatment at 600°C-1500°C for 1 h in air. The presence of Y 3 NbO 7 as an inhibitor and the substitutional incorporation of Y 3 NbO 7 into the lattice, CeO 2 effectively controlled the crystallite growth of CeO 2 , and nano-sized cubic solid solutions with high specific surface areas were maintained after heat treatment up to 800°C-1000°C for 1 h air.

C19-diterpene alkaloids are a class of alkaloids with pharmacologically important activities having an intricately fused hexacyclic ABCDEF-ring system. Here we report expeditious assembly of the ACE-ring substructure 4a by applying a three-component coupling strategy. A radical-polar crossover reaction between an AE-ring radical precursor, a C-ring radical acceptor and an aldehyde was realized by the actions of EtB and O, resulting in the installation of three new stereocenters and extension of the carbon chain corresponding to the B-ring. As the ACE-ring 4a possesses the correct C4,11-quaternary and C10-tertiary carbons, 4a would serve as an advanced intermediate for constructing the entire C19-diterpene alkaloid structures.