Synthesis of amphiphilic polysiloxanes and their properties for formation of nano-aggregates

In this study, we prepared amphiphilic polysiloxanes by introduction of hydrophobic and hydrophilic parts into a water-soluble poly(3-aminopropyl)siloxane. Fatty acid (lauroyl, myristoyl, palmitoyl, and stearoyl) chlorides and gluconolactone were employed as the reactants for the hydrophobic and hydrophilic parts, respectively. The reaction of the poly(3-aminopropyl)siloxane with fatty acid chlorides was performed in water/DMF, followed by the reaction with gluconolactone in DMSO, giving the corresponding amphiphilic polysiloxanes. The results of the NMR spectra, SEM observations, and DLS measurements indicated the formation of nano-aggregates from the amphiphilic polysiloxanes in water. These analytical data also suggested that the structures and functionalities of the hydrophobic parts affected the formation properties of the nano-aggregates.     

Visualizing Progressive Atomic Change in the Metal Surface Structure Made by Ultrafast Electronic Interactions in an Ambient Environment

Understanding the atomic and molecular phenomena occurring in working catalysts and nanodevices requires the elucidation of atomic migration originating from electronic excitations. The progressive atomic dynamics on metal surface under controlled electronic stimulus in real time, space, and gas environments are visualized for the first time. By in situ environmental transmission electron microscopy, the gas molecules introduced into the biased metal nanogap could be activated by electron tunneling and caused the unpredicted atomic dynamics. The typically inactive gold was oxidized locally on the positive tip and field‐evaporated to the negative tip, resulting in the atomic reconstruction on the negative tip surface. This finding of a tunneling‐electron‐attached‐gas process will bring new insights into the design of nanostructures such as nanoparticle catalysts and quantum nanodots and will stimulate syntheses of novel nanomaterials not seen in the ambient environment.     

Stabilization effects of carboxylate on pyrotechnic compositions including Mg powder in water

Magnesium powder is a common fuel in the field of pyrotechnics. The metal corrodes easily under wet conditions. This can lead to problems such as spontaneous ignition and deterioration of combustion performance when the powder is used in humid areas. For pyrotechnic compositions containing magnesium, harmful stabilizers are often used. In this study, we researched a less harmful replacement for the stabilizer and selected linseed oil, which is used as cooking oil. Experiments were conducted to examine linseed oil’s stabilization effects against magnesium corrosion when it is in contact with an oxidizer under humid conditions by coating magnesium powder and soaking it in aqueous oxidizer solutions. The oxidation of linseed oil led to its polymerization, because of which the stabilizing effect of linseed oil was lost. Stearic acid, which is a saturated fatty acid, was also examined for its stabilizing effects. Melted stearic acid was mixed with magnesium, and coating of stearic acid on magnesium particles was confirmed. The effect of stearic acid coating is more prominent than that of simple mixing of stearic acid with Mg. The stabilization effect of linseed oil and stearic acid coating shows that unharmful organic stabilizers can also be used in pyrotechnic compositions containing Mg.

     

First enantioselective synthesis of (-)- and (+)-virgatusin, tetra-substituted tetrahydrofuran lignan

The first highly enantioselective syntheses of tetra-substituted tetrahydrofuran lignan, (-)- and (+)-virgatusin, were achieved. Hemiacetal was stereoselectively obtained from Evans's syn-aldol product as a single isomer. This hemiacetal was converted to (-)-virgatusin via hydrogenolysis. (+)-Virgatusin was also synthesized through the same process. The enantiomeric excess of the both enantiomers was determined as more than 99% ee.     

Oxygen-sensing mechanism of HemAT from Bacillus subtilis: a resonance Raman spectroscopic study

Resonance Raman (RR) evidence for structural linkage between the distal side of heme pocket and the signaling domain of an oxygen sensing hemoprotein, HemAT-Bs, is reported. The band-fitting analyses of the RR spectra in the Fe-O2 stretching (nuFe-O2) region revealed the presence of three conformers with nuFe-O2 at 554, 566, and 572 cm-1, which reflect different H-bond strengths on the bound O2 molecule. While recent X-ray analysis for CN--bound HemAT-Bs suggested the importance of Thr95 and Tyr70, the species with the strongest H-bond (554 cm-1) was deleted in the T95A mutant and also by removal of the linker and signal domains; however, the Y70F mutant maintained the same three conformers. A scheme for specific O2 sensing and signaling mechanism is discussed.     

Synthesis of Light-emitting Silicon Nanoparticles by Intense Pulsed ion-beam Esvaporation

Synthesis of photoluminescent Si nanoparticles has been successfully prepared using an intense pulsed ion-beam evaporation (IBE) technique in vacuum. Si nanoparticles are produced by the IBE method without any post-annealings. Photoluminescence (PL) mainly in blue range with a peak of 455 nm and a shoulder near 510 nm is observed in as-deposited Si nanoparticles at room temperature. The blue light emission is relatively stable with no noticeable change, as the samples have already stored in air more than 4 months. The observed PL does not fit the quantum confinement model, since a majority of particle size is around ~20 nm, estimated by SEM and XRD measurements. Moreover, hydrofluoric acid (HF) corrosion tests on the Si nanoparticles also indicate a correlation between the presence of the surface oxide layers and the PL. Oxide-related luminescence is likely the source of this blue light emission.     

Seed polymerization of tetraethyl orthosilicate in the presence of anionic and cationic polystyrene colloidal spheres

Kinetic analyses are made for the seed polymerization of tetraethyl orthosilicate (TEOS) in the presence of anionic and cationic polystyrene colloidal sphere seeds by turbidity and dynamic light-scattering measurements. Transmission-electron microscopy pictures of the spheres formed are also used. The seed polymerization of TEOS is difficult to take place on the surface of anionic polystyrene spheres (44–212 nm in diameter). On the other hand, the reaction proceeds easily on the cationic polystyrene spheres. Hairy and soft surfaces of polystyrene spheres will disturb the seed polymerization. Furthermore, the electrostatic attraction between the anionic hydrolytic products of TEOS molecules and cationic polystyrene spheres plays an important role for the seed polymerization.