Self-assembly of oligosilanes: Synthesis and structure of 3,5-dehydroxyphenyl substituted oligosilanes

Disilanes and hexasilanes with terminal hydrogen-bond substituents, i.e., 3,5-dihydroxyphenyl groups, were synthesized. The structures were analyzed by X-ray diffraction and it was shown that the resulting molecular orientations were controlled by the hydrogen-bond network.     

Synthesis of(7e,9e,11e,13e)-18,18,18-trifluororetinal (all-trans 5-trifluoromethylretinal)

All-trans-18,18,18-trifluororetinal (2) was synthesized through trifluorocyclocitral (3) as a key intermediate.     

Development of a novel solid-phase extraction element for thermal desorption gas chromatography analysis

A novel solid-phase extraction element is developed for sorptive enrichment of dilute analytes from liquid samples with high extraction efficiencies due to its larger amounts of polydimethylsiloxane (PDMS) absorbent than the conventional syringe type of solid-phase microextraction (SPME). The extraction element is made of titanium (Ti) open tubular tube (30 mm x 1.2 mm i.d. x 1.6 mm o.d.) coated with a chemically bonded layer of PDMS (500 microm in thickness). The extraction element combined with thermal desorption-gas chromatography-mass spectrometry using a pyrolysis-gas chromatography-mass spectrometry system was used to extract and analyze a typical herbicide, bethrodine in water samples over a concentration range from 2.5 to 2.5 x 10(4) ng/l. Thus obtained calibration curve showed good linearity for the tested whole concentration range with regression coefficient of 0.992. Detection limit of 0.5 ng/l level was achieved and the reproducibility of the measurements for bethrodine at 10 ng/l level was found to be fairly good with relative standard deviation below 7.5%.     

Transition metal reactions of silanes II. The reaction of cycloalkenes with various hydrosilanes and carbon monoxide catalyzed by Co2(CO)8

The reaction of cycloalkenes(cyclopentene, cyclohexene, cycloheptene, cyclooctene, 1-methylcyclohexene, and norbornene) with Et₂MeSiH and carbon monoxide in the presence of Co₂(CO)₈ gave the corresponding diethylmethylsiloxymethylenecycloalkenes. In such reactions of cyclohexene, the following hydrosilanes gave the corresponding siloxymethylenecyclohexanes: Me₃SiH, EtMe₂SiH, Et₂MeSiH, Et₃SiH, PhMe₂SiH, Ph₂MeSiH. Effects of the reaction conditions(the pressure of carbon monoxide, the temperature, and the molar ratio of cyclohexene to Et₂MeSiH) were examined. The yield of diethylmethylsiloxymethylenecyclohexane increased remarkably with increasing molar ratio of cyclohexene to Et₂MeSiH. At higher temperature, the yield of the isomerization product, 1-(diethylmethylsiloxymethyl)-cyclohex-1-ene, increased.     

Radiation-induced postpolymerization of trioxane in the solid state. II. Kinetic study of radiation-induced postpolymerization of trioxane in dry and high-vacuum system

A kinetic study of the radiation-induced postpolymerization of trioxane in the solid state has been made. Trioxane was purified by sublimation through Ag₂O and Na–K alloy in vacuo and was both irradiated and polymerized in a super-dry system under high vacuum. In the present study it was found that the initial rate of polymerization is larger than that reported previously. It is reasonably suggested that the postpolymerization of trioxane consists of two stages, i.e., a very large rate at the first stage and a relatively small one at the second stage. By using the kinetic scheme proposed previously kinetic parameters at the second stage were determined. It was found that trioxane can be postpolymerized even at a temperature below 30°C with good reproducibility and that the overall activation energy of the polymerization was less than 15 kcal/mole. No chain-transfer reaction seems to occur except at low temperatures. These results have been discussed in comparison with data reported previously.     

Comparative study on pore structures of mesoporous ZSM-5 from resorcinol-formaldehyde aerogel and carbon aerogel templating

Resorcinol-formaldehyde aerogels and carbon aerogels of different mesoporosities have been used as templates for preparing bimodal zeolites of mesopores. Samples were thoroughly characterized with X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, N(2) adsorption at 77 K, as well as FT-IR spectroscopy and (29)Si nuclear magnetic resonance spectroscopy. The mesoporous ZSM-5 zeolites have additional mesopores of 9-25 nm in widths and 0.07-0.2 cm(3)/g in volumes, besides their perfect inherent micropores. Experimental results show the mesoporous systems of the finally obtained zeolites can be influenced by proper preparation of resorcinol-formaldehyde aerogels and carbon aerogels through solution chemistry. Consequently, zeolites of tunable mesoporosities can be prepared with this unique methodology.     

Performance of wide-pore silica- and polymer-based packing materials in polypeptide separation: effect of pore size and alkyl chain length

The effects of pore size and alkyl chain length of silica- and polymer-based packing materials in the elution of polypeptides with an acetonitrile gradient in the presence of trifluoroacetic acid were studied. Considerable differences were found in the performance of alkylsilylated phases prepared from various wide-pore silica particles assumed to have 30-50-nm pores. The pore size of such silica gels was found to be the critical factor in determining the efficiency for high-molecular-weight polypeptides. Silica C18 phases having small pore volumes below 20 nm pore diameter showed comparable performances to C4 and C8 phases for polypeptides with molecular weights of up to 80,000, and were more stable. Polymer-based packing materials with adequate pore size provided excellent column efficiencies and recoveries for polypeptides with higher chemical stabilities than silica-based materials.     

Reaction of tertiary cyclopropyl silyl ethers with diethylaminosulfur trifluoride. Part 2: The Friedel-Crafts allylation and cyclopropylation of electron-rich aromatic compounds

The reaction of tertiary cyclopropyl silyl ethers with diethylaminosulfur trifluoride in electron-rich aromatic compounds causes the Friedel-Crafts alkylation to produce allylated or cyclopropylated aromatic compounds.     

Novel peptides bearing pyrene and coumarin units with or without beta-cyclodextrin in their side chains exhibit intramolecular fluorescence resonance energy transfer

Novel peptides bearing the pyrene/coumarin FRET pair in their side chains have been designed and synthesized. Peptide 1 having endogenous beta-cyclodextrin (beta-CD) in the side chain exhibits FRET in aqueous solution, indicating that coumarin, being accommodated into the CD cavity, is separated from pyrene. Guest-induced quenching of the fluorophores in 1 indicates that coumarin, being excluded from the CD cavity, comes into close contact with pyrene. Peptide 2 shows FRET only after addition of external beta-CD that again reflects the idea that beta-CD surely caps the coumarin unit in its hydrophobic cavity, and, therefore, quenching of the fluorophores can be prevented in FRET peptide probes. With this strategy, various peptide-based FRET probes can be developed that would be useful for studying biological phenomena in living cells.     

Nucleation and size distribution of nucleus during induction period of polyethylene crystallization

The crystallization process from supercooled melt results in the formation of nanosize nuclei in the earlier stage (induction period) through subsequent attachment or detachment of repeating unit to nuclei. The size distribution of nucleus f(N(j),t) in the induction period of nucleation process from the melts has not been experimentally confirmed yet by direct observation. The reason is that the number density of nuclei nu is too small to be detected experimentally. In our previous work, we showed the direct evidence of nucleation experimentally by means of small angle x-ray scattering (SAXS) technique. Further we have succeeded to observe the nucleation and f(N(j),t) of polymer crystallization from the melts by SAXS using synchrotron radiation. We increased nu by adding a nucleating agent to a polymer (polyethylene). The time evolution of f(N(j),t) was observed for the first time.