Two-particle friction in a mesoscopic solvent

The effects of hydrodynamic interactions on the friction tensors for two particles in solution are studied. The particles have linear dimensions on nanometer scales and are either simple spherical particles interacting with the solvent through repulsive Lennard-Jones forces or are composite cluster particles whose atomic components interact with the solvent through repulsive Lennard-Jones forces. The solvent dynamics is modeled at a mesoscopic level through multiparticle collisions that conserve mass, momentum, and energy. The dependence of the two-particle relative friction tensors on the interparticle separation indicates the importance of hydrodynamic interactions for these nanoparticles.     

A novel dicationic phenoxaphosphino-modified Xantphos-type ligand: a ligand for highly active and selective, biphasic, rhodium catalysed hydroformylation in ionic liquids

A highly active and regioselective catalyst obtained from a novel dicationic ligand (1) and Rh(CO)2(acac) for hydroformylation of 1-hexene and 1-octene in ionic liquids is reported. Optimisation studies of various reaction parameters led to an unprecedentedly active (TOFs > 6200 mol mol(-1) h(-1), T= 100 degrees C), selective (l/b ratios > 40) and stable hydroformylation procedure. No catalyst leaching (Rh-loss < 0.07% of initial rhodium intake, P-loss < 0.4% of the initial phosphorus intake) or losses in performance could be measured during 1-octene hydroformylation recycle experiments in 1-butyl-3-methylimidazolium hexafluorophosphate. At low catalyst loadings activities and regioselectivities competitive with one-phase catalysis in conventional solvents were observed. At high catalyst loadings the system is extremely stable and has a long shelf-life as a result of the formation of stable, if inactive rhodium dimers.     

Farnesic acid glycerides from the nudibranch Archidoris odhneri

The dorid nudibranch Archidoris odhneri produces (all E)-2,3-dihydroxypropylfarnesate and its two monoacetoxy derivatives.     

Synthesis of certain 6-alkylthio-2,2′-anhydro-5-azauridines

β-D-Arabinofurano[1′,2′:4,5]oxazolo-s-triazin-4-one-6-thione ( 7b ) and its t-butyldimethylsilyl protected counterpart 7a were synthesized by treating the appropriate 2-amino-β-D-arabinofurano[1′,2′:4,5]-2-oxazoline with ethoxycarbonyl isothiocyanate. These 2,2′-anhydro-s-triazine nucleosides were then subjected to alkylation under similar reaction conditions. Alkylation of 3′,5′-bis(O-t-butyldimethylsilyl)-β-D-arabinofurano[1′,2′:-4,5]oxazolo-s-triazin-4-one-6-thione ( 7a ) provided the targeted S-alkylated nucleosides, i.e., the C6-SCH₃ ( 9a ), C6-SCH₂-CH = CH₂ ( 10a ), and C6-S-CH₂-C = CH ( 11a ), in reasonable yields. Attempted deprotection of these nucleosides failed. In order to circumvent this problem, 7b was alkylated with the same reagents. In each case, instead of the expected S-alkylated anhydronucleosides, a mixture of the 5-N-alkylanhydro-s-triazine-4,6-dione and 5-N-alkylanhydro-s-triazin-4-one-6-thione derivatives were obtained. The 2,2′-anhydro linkage of 7a was also found to be more stable than the s-triazine ring to mild base. Basic conditions displaced the C6-sulfur substituent and eventually caused ring opening of the s-triazine aglycone.     

Angular polycyclic thiophenes containing two thiophene rings. I

We describe the synthesis of thieno[2,3-c]dibenzothiophene ( 6 ), thieno[3,2-c]dibenzothiophene ( 10 ), thieno-[3,2-a]dibenzothiophene ( 14 ), thieno[2,3-a]dibenzothiophene ( 16 ), benzo[1,2-b:4,3-b]bisbenzo[b]thiophene ( 18 ), benzo[1,2--6:3,4-b]bisbenzo[b]thiophene ( 20 ), benzo[2,1--6:3,4-b]bisbenzo[b]thiophene ( 22 ), benzo[1,2-b:3,4-g]bisbenzo[b]thiophene ( 27 ), benzo[1,2-b:4,3-e]bisbenzo[b]thiophene ( 29 ), benzo[2,1--6:3,4-g]bisbenzo[b]thiophene ( 36 ), benzo[2,1--6:4,3-e]bisbenzo[b]thiophene ( 38 ), benzo[1,2--6:4,3-g]bisbenzo[b]thiophene ( 41 ), benzo[1,2-b:4,5-g]bisbenzo[b]thiophene ( 42 ), benzo[1,2-b:3,4-e]bisbenzo[b]thiophene ( 44 ) and benzo-[1,2-b:5,4-e]bisbenzo[b]thiophene ( 45 ).     

Probing charge-transfer processes in helium nanodroplets by optically selected mass spectrometry (OSMS): charge steering by long-range interactions

Electron impact ionization of a helium atom in a helium nanodroplet is followed by rapid charge migration, which can ultimately result in the localization of the charge on an atomic or molecular solute. This process is studied here for the cases of hydrogen cyanide, acetylene, and cyanoacetylene in helium, using a new experimental method we call optically selected mass spectrometry (OSMS). The method combines infrared laser spectroscopy with mass spectrometry to separate the contributions to the overall droplet beam mass spectrum from the various species present under a given set of conditions. This is done by vibrationally exciting a specific species that exists in a subset of the droplets (for example, the droplets containing a single HCN molecule). The resulting helium evaporation leads to a concomitant reduction in the ionization cross sections for these droplets. This method is used to study the charge migration in helium and reveals that the probability of charge transfer to a solvated molecule does not approach unity for small droplets and depends on the identity of the solvated molecule. The experimental results are explained quantitatively by considering the effect of the electrostatic potential (between the charge and the embedded molecule) on the trajectory of the migrating charge.     

The synthesis of substituted pyrazino[2,3-d]-1,2,4-triazolo[4,3-b]pyridazines

The synthesis of 1,2,4-triazolo[4,3-b]pyridazines and the unknown ring system, pyrazino[2,3-d]-1,2,4-triazolo[4,3-b]pyridazine, has been achieved. The preparation of the new tricyclic 1,2,4-triazole was accomplished first by ring closure of the triazole ring followed by formation of the pyrazine ring. Substitution of the pyrazino[2,3-d]-1,2,4-triazolo[4,3-b]pyridazine ring system was carried out in order to provide information of its reactivity and to provide a variety of interesting compounds for biological testing.     

Photocyclization of 2-(naphth-1-yl)-3-(thien-2-yl)propenoic acid and the total assignment of the 1H- and 13C-NMR spectra of the product

Photocyclization of the substituted 2-(naphth-1-yl)-3-(thien-2-yl)propenoic acid ( 3 ) in the presence of iodine and air in a benzene-cyclohexane mixture afforded a separable mixture of three compounds, phenanthro[2,1-b]thiophene-10-carboxylic acid ( 4 ), phenanthro[2,1-b]thiothene ( 5 ), and naphtho[1,8-cde]-thieno[3,2-g][2]benzopyran ( 6 )     

The synthesis of substituted [1]benzothieno[2,3-c]quinolines and their N-methyl quaternary salts

Four substituted [1]benzothieno[2,3-c]quinolines 14a-14d were prepared by photocyclization of the appropriate carboxamides 8a-8d to the corresponding [1]benzothieno[2,3-c]quinolin-6(5H)-ones 12a-12d followed by chlorination to 6-chloro[1]benzothieno[2,3-c]quinolines 13a-13d and dechlorination resulting in the title compounds. Treatment of 14a-14d with iodomethane furnished the corresponding N-methyl quaternary salts 5a-5d .