The many limits of mixed means

The sequences introduced by Carlson (1971) are variants of the Gauss arithmetic geometric sequences (which have been elegantly discussed by D. A. Cox (1984, 1985)). Given (complex)a ₀,b ₀ we define

High-performance liquid chromatography and thin-layer chromatography assays for Devil's Club (Oplopanax horridus)

Devil's root, Oplopanax horridus, is a widely used folk medicine in Alaska and British Columbia. The inner bark of the root and stem has been used to treat colds, cough, fever, and diabetes. The present study involves the development of high-pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC) methods to detect the presence of trans-nerolidol and sterols in the root bark. The HPLC and TLC analytical methods presented are suitable for the characterization and identification of Oplopanax horridus.     

Self-assembly of a hydrophobic groove

Heptakis(2,6-di-O-methyl)-β-cyclodextrin interacts with 5,15-diphenylporphine to produce a 2:1 complex in dimethyl sulfoxide. This complex possesses a hydrophobic groove that circumscribes the metal binding site of the porphyrin moiety.     

Solvent dependence of the 2-naphthyl(carbomethoxy)carbene singlet-triplet energy gap

The solvent dependence of the 2-naphthyl(carbomethoxy)carbene (2) singlet-triplet energy gap has been examined by time-resolved infrared (TRIR) and computational methods. The ground state of 2 changes from the triplet state in hexane to the singlet state in acetonitrile. Preferential stabilization of the singlet carbene is the result of its increased dipole moment in polar solvents. Variable-temperature TRIR experiments provide measurements of the enthalpic and entropic differences between (1)2 and (3)2 and suggest that solvent and geometry effects on the entropy of singlet and triplet carbenes can offset differences arising from spin multiplicity. B3LYP calculations using the polarizable continuum solvation model (PCM) reproduce the general trends in enthalpic differences seen experimentally.     

Analysis of aromatic compounds in gasoline with flow-switching comprehensive two-dimensional gas chromatography

A comprehensive two-dimensional gas chromatography (GC x GC) instrument has been created by coupling a flow-switching modulator and a standard gas chromatograph. The instrument was used to characterize the aromatic composition of gasoline. The high-resolution separation produced by flow-switching GC x GC allowed gasoline aromatics to be fully resolved from saturated components. The aromatic compounds were further separated into groups having the same carbon number. A standard gasoline sample was analyzed to evaluate the quantitative accuracy and precision of this technique. The data show that flow-switching GC x GC produces results that are comparable to gas chromatography-mass spectrometry (GC-MS) and thermal modulation GC x GC. The simple, low-cost, and robust nature of flow-switching GC x GC makes it an ideal technique for the routine analysis of aromatic compounds in gasoline.     

The oxymercuration—demercuration of alkenylsilanes in aqueous tetrahydrofuran

The oxymercuration—demercuration (OM—DM) of representative trimethylsilylalkenes in aqueous tetrahydrofuran was investigated. Vinyltrimethylsilane gives only the anti-Markovnikov alcohol, 2-trimethylsilylethanol in 90% yield. Allyltrimethylsilane gives mainly allylmercuric acetate which reacts further to give a 1,3-dimercurated-2-propanol. This species reacts slowly with allyltrimethylsilane to give allylmercuric acetate. 3-Buten-1-yltrimethylsilane gives only the Markovnikov product, 1-trimethylsilyl-3-butanol in 99% yield. cis-1-Propenyl-trimethylsilane gives 1-trimethylsilyl-2-propanol in 44% yield along with cleavage products. The formation of one of these products, 2-propanol, was found by PMR to arise from the OM—DM of cis-1-propenylmercuric acetate which gives the 1,1-dimercurated-2-propanol. While the oxymercuration of cis-1-propenyl-mercuric acetate is regiospecific giving exclusive placement of the mercury α to the silicon, it is completely nonstereospecific giving equal amounts of diastereomeric adducts. The OM—DM of 2-propenyl trimethylsilane (XIX) leads only to desilylation and oxidation products. Possible reasons for the diverse behavior of these silylated alkenes are discussed.