New basic mesoporous silica catalyst obtained by ammonia grafting

NH3-treated mesoporous silica (FSM-16) contains SiNH2 sites which exhibit basic catalytic activity for Knoevenagel condensation; SiNH2 and SiOH pair sites formed at lower NH3-treatment temperatures exhibit higher turnover frequencies (TFs) in comparison with SiNH2 single sites.     

Iron(III) chloride-catalyzed convenient one-pot synthesis of homoallyl benzyl ethers starting from aldehydes

[reaction: see text] Iron(III) chloride-catalyzed effective allylation reactions of acetals with allyltrimethylsilane proceeded smoothly in high to excellent yields. In addition, this method could be applied to the one-pot synthesis of homoallyl benzyl ethers by a combination of dibenzyl acetalization of aldehydes and consecutive allylation of dibenzyl acetals.     

Enzymatic formation of unnatural novel polyketides from alternate starter and nonphysiological extension substrate by chalcone synthase

[reaction: see text] In the chalcone synthase (CHS) enzyme reaction, both the starter molecule and the extension unit of the polyketide chain elongation reaction were simultaneously replaced with nonphysiological substrates. When incubated with benzoyl-CoA and methylmalonyl-CoA as substrates, recombinant CHS from Scutellaria baicalensis afforded an unnatural novel triketide, 4-hydroxy-3,5-dimethyl-6-phenyl-pyran-2-one, along with a tetraketide, 4-hydroxy-3,5-dimethyl-6-(1-methyl-2-oxo-2-phenyl-ethyl)-pyran-2-one. On the other hand, the enzyme also accepted hexanoyl-CoA and methylmalonyl-CoA as substrates to produce an unnatural novel triketide, 4-hydroxy-3,5-dimethyl-6-pentyl-pyran-2-one.     

Solution-phase automated synthesis of tripeptide derivatives

An improved general method for automated synthesis of tripeptides was developed, in which methanesulfonic acid (MSA) was used in place of trifluoroacetic acid (TFA), thus making it possible to avoid, 1) corrosion of the apparatus by strong acid vapor, 2) formation of emulsions, and 3) use of the restricted solvent, dichloromethane. As an application of the automated synthesis apparatus, 216 fragment tripeptide derivatives were synthesized systematically using the MSA method, in excellent yield and with increased efficiency.     

Molecular hydrogen-originated protonic acid site as active site on solid acid catalyst

The protonic acid sites are formed from hydrogen molecules on Pt/SO₄ ^2--ZrO2 , and the resulting protonic acid sites act as active sites for acid-catalyzed reactions. Promotion of molecular hydrogen on the activities is observed not only for the Pt/SO₄ ^2--ZrO2, but also for the other catalysts such as a physical mixture of Pt/SiO2 and H-ZSM5, and Co.Mo/SiO2-/Al2O3 . A molecular hydrogen-originated protonic acid site is proposed as a widely applicable concept for an active site on solid acid catalysts.     

A liquid-phase peptide synthesis in cyclohexane-based biphasic thermomorphic systems

Combinations of typical organic solvents composed of cyclohexane and qualified aprotic polar organic solvents were found to realize an effective, biphasic thermomorphic system in arbitrary ratios of upper and lower phases that enable a practical application of a liquid-phase peptide synthesis.     

Thermometric titration of the dodecyl sulphate ion with metal-phenanthroline complexes

Docecyl sulphate forms precipitates with certain metal-1,10-phenanthroline complexes. This is the basis of a simple and direct thermometric titration of dodecyl sulphate with Cd(phen)(2+)(3).     

Synthesis, solid-state and solution structures of tris[(2-methoxymethyl)phenyl]germanes with a substituent on germanium

A series of tris[(2-methoxymethyl)phenyl]germanes with a substituent on germanium was prepared and their solid-state and solution structures were investigated by means of X-ray crystallography and NMR spectroscopy to elucidate the effect of the substituent on the hypercoordination of the germanium atom in triarylgermanes. It was shown that when the substituent is a halogen, the triarylgermanes tend to be pentacoordinated trigonal bipyramidal while the triarylgermane is tetrahedral with no coordination when the substituent is a phenyl group. The methyl derivative is a monocapped tetrahedron.     

Elementary processes of DNA surface hybridization resolved by single-molecule kinetics: implication for macroscopic device performance

Direct monitoring of single-molecule reactions has recently become a promising means of mechanistic investigation. However, the resolution of reaction pathways from single-molecule experiments remains elusive, primarily because of interference from extraneous processes such as bulk diffusion. Herein, we report a single-molecule kinetic investigation of DNA hybridization on a metal surface, as an example of a bimolecular association reaction. The tip of the scanning tunneling microscope (STM) was functionalized with single-stranded DNA (ssDNA), and hybridization with its complementary strand on an Au(111) surface was detected by the increase in the electrical conductance associated with the electron transport through the resulting DNA duplex. Kinetic analyses of the conductance changes successfully resolved the elementary processes, which involve not only the ssDNA strands and their duplex but also partially hybridized intermediate strands, and we found an increase in the hybridization efficiency with increasing the concentration of DNA in contrast to the knowledge obtained previously by conventional ensemble measurements. The rate constants derived from our single-molecule studies provide a rational explanation of these findings, such as the suppression of DNA melting on surfaces with higher DNA coverage. The present methodology, which relies on intermolecular conductance measurements, can be extended to a range of single-molecule reactions and to the exploration of novel chemical syntheses.

Hybridization of a single DNA molecule on a surface was investigated by electrical conductance measurements. The hybridization efficiency increases with increasing the DNA concentration, in contrast to preceding studies with ensemble studies.     

Effects of added nonionic surfactant and inorganic salt on the rheology of sugar surfactant and CTAB aqueous solutions

The effect of adding tri(oxyethylene) dodecyl ether (C₁₂EO₃) on the phase and rheological behavior of sucrose hexadecanoate and CTAB aqueous solutions in the presence of added salt (NaBr) was investigated. Viscoelastic solutions are formed in CTAB and C₁₆SE systems upon addition of lipophilic nonionic surfactant C₁₂EO₃. The zero-shear viscosity shows a maximum at a certain mixing fraction of C₁₂EO₃, except in the case of the aqueous CTAB/C₁₂EO₃ system in the absence of salt. The rheological properties are strongly affected by the addition of salt to the CTAB systems but they remain unaltered in the case of C₁₆SE systems. In ionic systems, the mixing fraction of C₁₂EO₃ for the maximum viscosity depends on salt concentration.