Anion sensing 'venus flytrap' hosts: a modular approach

A series of podands based on three hydrogen bonding 'arms' have been prepared and their affinities for simple inorganic anions measured.     

A biosynthetic proposal for ring formation in the antitumor agent halichomycin. Asymmetric synthesis of the AB-carbon backbone of halichomycin

[reaction: see text] A biosynthetic proposal for ring formation in the antitumor agent halichomycin is presented in which macrocyclization of the putative prehalichomycin intermediate 1 is the first step. Compound 2 then undergoes dehydration to the alpha-keto N-acylimine 3 followed by tandem nucleophilic addition of the C(16)-hydroxyl to form the hemimacrolactam. A stereospecific Michael ring closure and enol protonation complete C-ring assembly. So far, synthetic efforts toward 1 have resulted in 8.     

Bis(carbene)pyridine complexes of Cr(III): exceptionally active catalysts for the oligomerization of ethylene

Pincer-heterocyclic carbene complexes of Cr(III), of the form [2,6-(1-alkylimidazol-2-ylidene)pyridine]CrCl3, have been prepared and evaluated as catalysts for the oligomerization of ethylene to alpha-olefins. In combination with methylaluminoxane cocatalyst, exceptionally high activities are obtained, ranging up to ca. 40 000 g mmol-1 bar-1 h-1.     

Enhanced Anion Binding from Unusual Coordination Modes of Bis(thiourea) Ligands in Platinum Group Metal Complexes

Treatment of a range of bis(thiourea) ligands with inert organometallic transition‐metal ions gives a number of novel complexes that exhibit unusual ligand binding modes and significantly enhanced anion binding ability. The ruthenium(II) complex [Ru(η⁶‐p‐cymene)(κS,S′,N‐ L³ ?H)]⁺ ( 2 b ) possesses juxtaposed four‐ and seven‐membered chelate rings and binds anions as both 1:1 and 2:1 host guest complexes. The pyridyl bis(thiourea) complex [Ru(η⁶‐p‐cymeme)(κS,S′,N_py‐ L⁴ )]²⁺ ( 4 ) binds anions in both 1:1 and 1:2 species, whereas the free ligand is ineffective because of intramolecular NH???N hydrogen bonding. Novel palladium(II) complexes with nine‐ and ten‐membered chelate rings are also reported.     

An improved error bound for a finite element approximation of a model for phase separation of a multi-component alloy

Using the approach of Rulla (1996 SIAM J. Numer. Anal. 33, 68-87)for analysing the time discretization error and assuming moreregularity on the initial data, we improve on the error boundderived by Barrett and Blowey (1996 IMA J. Numer. Anal. 16,257-287) for a fully practical piecewise linear finite elementapproximation with a backward Euler time discretization of amodel for phase separation of a multi-component alloy.     

A simple chemical model for clathrate hydrate inhibition by polyvinylcaprolactam

A dimeric model compound gives structural insight into the mode of interaction of low dosage hydrate inhibitors with water.     

Spectrophotometric determination of the rare earths yttrium and cerium by bromopyrogallol red

A method is described for the spectrophotometric determination of microgram quantities of rare carths, yttrium and cerous cerium ions, using the colour of the complexes formed with bromopyrogallol red. The procedure has been applied to pure solutions containing 10–50 μg of the element.