Theoretical study on interaction of hydrogen with single-walled boron nitride nanotubes. II. Collision, storage, and adsorption

Collision and adsorption of hydrogen with high incident kinetic energies on a single-walled boron nitride (BN) nanotube have been investigated. Molecular-dynamics (MD) simulations indicate that at incident energies below 14 eV hydrogen bounces off the BN nanotube wall. On the other hand, at incident energies between 14 and 22 eV each hydrogen molecule is dissociated at the exterior wall to form two hydrogen atoms, but only one of them goes through the wall. However, at the incident energies between 23 and 26 eV all of the hydrogen atoms dissociated at the exterior wall are found to be capable of going inside the nanotube and then to recombine to form hydrogen molecules inside the nanotube. Consequently, it is determined that hydrogen should have the incident energy >22 eV to go inside the nanotube. On the other hand, we find that the collisions using the incident energies >26 eV could result in damaging the nanotube structures. In addition our MD simulations find that hydrogen atoms dissociated at the wall cannot bind to either boron or nitrogen atoms in the interior wall of the nanotube.     

Synthesis of well-defined norbornenyl-terminated poly(alkyl methacrylate)s by group transfer polymerization and their grafting-through ring-opening metathesis polymerization

Highly efficient syntheses of poly(alkyl methacrylate)-based brush polymers were accomplished via a facile group transfer polymerization (GTP) and a consecutive grafting-through ring-opening metathesis polymerization. The GTP system, composed of the norbornenyl-methyl trimethylsilyl ketene acetal initiator and the N-(trimethylsilyl) bis(trifluoromethanesulfonyl)imide catalyst, rapidly and quantitatively generates norbornenyl-terminated poly(alkyl methacrylate) macromonomers with very narrow polydispersities (M_w/M_n < 1.10). The ring-opening metathesis polymerization of methacrylate macromonomers using Grubbs third generation catalyst successfully generated a group of methacrylate-based brush polymers, which assured the high quality of the macromonomers obtained from GTP.     

Catalytic asymmetric methallylation of ketones with an (H8-BINOLate)Ti-based catalyst

The first catalytic asymmetric methallylation of ketones is reported. The catalyst, which is generated from titanium tetraisopropoxide, H8-BINOL, 2-propanol, and tetramethallylstannane, reacts with ketones in acetonitrile to afford tertiary homoallylic alcohols in fair to excellent yields (55-99%) and fair to high enantioselectivities (46-90%). Ozonolysis of the resulting products provides access to chiral beta-hydroxy ketones, which are not readily prepared from direct asymmetric aldol reaction of acetone with ketones.     

Migration of human neural stem cells toward an intracranial glioma

Many in vivo and in vitro studies have demonstrated the targeted migration of neural stem cells (NSC) to infiltrating brain tumors, including malignant glioma, highlighting a potential therapeutic approach. However, there is not enough information to apply this approach to clinical therapy. The most important things in stem cell therapy for brain tumors involve selecting the appropriate neural progenitor type and optimizing the efficiency of the cell engraftment. By histological analysis using two different live-dyes, human NSCs were shown to migrate away from the transplanted site in the direction of the expanding C6 glioma and to intermix with the tumor bed, especially with the tumor core. This intermixing occurred within 7 days when NSCs were implanted into glioma model. The time course of migratory HB1.F5 with the greatest mobility of three NSC lines was as follows. As early as 3 days after transplantation, several NSCs were found leaving the implant site, primarily approaching microsatellites and frontier cells located near the site of NSC implantation. Through 7 days post-transplantation, massive numbers of NSCs continued to be attracted to and interspersed with C6 glioma, and were finally distributed extensively throughout the whole tumor bed, including the core and penumbra of the tumor mass. However, NSCs appeared to penetrate into the tumor mass very well, whereas normal fibroblast cells could not migrate. These findings strengthen the potential for human NSCs as attractive vehicles to improve therapeutic gene delivery to cancer or glioma if they are optimized to selectively kill neoplastic cells.     

Synthesis of 7-deoxycholic amides or cholanes containing distinctive ion-recognizing groups at C3 and C12 and evaluation for ion-selective ionophores

Tweezer-type ionophores containing C3-bipyridyl and C12-dithiocarbamoyl groups, or C3-bithiophenyl with C12-dithiocarbamoyl groups on a 7-deoxycholic amide or cholane derivatives were designed and synthesized. Potentiometric evaluation of the PVC membranes containing those deoxycholic amides/cholanes linked with unsymmetrically substituted tweezer-type bipyridyl or bithiophenyl with dithiocarbamoyl moieties proved their good affinity and selectivity for silver(I) ion. Especially, ionophores with bithiophenyl moiety on the 3α-position and diphenylaminothioxomethylthioacetyloxy group on 12α-position of cholan-24-amide or cholane reveal the most excellent result with a theoretical slope value of 59 mV/decade.     

A flow visualization study on self-ignition of high pressure hydrogen gas released into a tube

Hydrogen is known as one of the green energy sources for fuel cells and hydrogen-fueled cars in the next generation. The storage of high-pressure hydrogen gas conditions is preferred to its storage in cryogenic liquid state. However, cases of unidentified self-ignitions were reported, notably when the high-pressure hydrogen gas suddenly leaked out. Only a few of numerical simulations have shown visually the processes of the self-ignition inside a tube. This paper presents a flow visualization study to investigate the self-ignition mechanism in a test tube i.e. how the ignition process is initiated and the flame propagates. In addition to visualization, measurement of a number of pressure and light sensors installed in the tube supported the analysis of the self-ignition and flame propagation. The test result showed that self-ignition takes place at the boundary layer behind the front center of mixing zone at first, and the flame propagates to the front of mixing zone and tail of the mixing zone along the boundary layer. It showed that self-ignition is accompanied with complex mixing induced by shock interaction with the mixing front. It is also suggested that the self-ignition boundary has a certain critical threshold of static pressure at the boundary layer, based on various burst pressures of hydrogen.     

Grid-based Thomas-Fermi-Amaldi equation with the molecular cusp condition

First, the Thomas-Fermi-Amaldi (TFA) equation was formulated with a newly derived condition to remove the singularities at the nuclei, which coincided with the molecular cusp condition. Next, the collocation method was applied to the TFA equation using the grid-based density functional theory. In this paper, the electron densities and the radial probabilities for specific atoms (He, Be, Ne, Mg, Ar, Ca) were found to agree with those from the Thomas-Fermi-Dirac (TFD) method. Total energies for specific atoms (He, Ne, Ar, Kr, Xe, Rn) and molecules (H2,CH4) were also found to be close to those from the Hartree-Fock method using the Pople basis set 6-311G relative to the TFD method. In addition, the computational expense to determine the electron density and its corresponding energy for a large scale structure, such as a carbon nanotube, is shown to be much more efficient compared to the conventional Hartree-Fock method using the 6-31G Pople basis set.