Spatial arrangement of metal nanoparticles supported by porous polymer substrates studied by transmission electron microtomography

Fine metal particles (nanoparticles) stabilized on porous (polymeric) substrates can be considered as a model system of a high-performance catalyst. In the present study, the substrate was made using the periodic microphase-separated structure of a block copolymer as the template, and the Pd nanoparticles were formed inside the porous material by reduction of the Pd2+ ions with 1-propanol as the reductant. The three-dimensional morphology of such a polymer-Pd hybrid material was studied by transmission electron microtomography. The characteristic structural parameters of the hybrid, e.g., the penetration of the Pd nanoparticles into the polymer substrate, number density of the Pd nanoparticles, and size distribution of the Pd nanoparticles, were measured for the first time.     

Combustion mechanism of ultralean rotating counterflow twin premixed flame

In our previous numerical studies [Nishioka Makihito, Zhenyu Shen, and Akane Uemichi. “Ultra-lean combustion through the backflow of burned gas in rotating counterflow twin premixed flames.” Combustion and Flame 158.11 (2011): 2188–2198. Uemichi Akane, and Makihito Nishioka. “Numerical study on ultra-lean rotating counterflow twin premixed flame of hydrogen–air.” Proceedings of the Combustion Institute 34.1 (2013): 1135–1142]. we found that methane– and hydrogen–air rotating counterflow twin flames (RCTF) can achieve ultralean combustion when backward flow of burned gas occurs due to the centrifugal force created by rotation. In this study, we investigated the mechanisms of ultralean combustion in these flames by the detailed numerical analyses of the convective and diffusive transport of the main species. We found that, under ultralean conditions, the diffusive transport of fuel exceeds its backward convective transport in the flame zone, which is located on the burned-gas side of the stagnation point. In contrast, the relative magnitudes of diffusive and convective transport for oxygen are reversed compared to those for the fuel. The resulting flows for fuel and oxygen lead to what we call a ‘net flux imbalance’. This net flux imbalance increases the flame temperature and concentrations of active radicals. For hydrogen–air RCTF, a very large diffusivity of hydrogen enhances the net flux imbalance, significantly increasing the flame temperature. This behaviour is intrinsic to a very lean premixed flame in which the reaction zone is located in the backflow of its own burned gas.     

Local structural analysis of In-doped Bi2Se3 topological insulator using X-ray fluorescence holography

We performed X-ray fluorescence holography measurements on an In-doped Bi₂Se₃ topological insulator and obtained an in-plane atomic image in the vicinity of In. We found that atomic images at the positions of the first nearest neighbors (NNs) are very weak whereas those at the positions of the second and the third NNs are relatively strong. On the basis of the fact that In is half of the atomic number of Bi, we attributed the origin of this feature to the clustering of the In atoms in the Bi plane. We calculated the intensity of the atomic images and confirmed that the formation of In cluster results in a decrease by 30% in the first NN atomic image intensity. However, the decrease in the magnitude is not enough to explain the experimental results, suggesting another contribution such as the lattice distortions. The effect of the lattice distortion on the atomic image intensity is discussed on the basis of the simulation including the positional fluctuation of In atoms.     

Molecular Design for Reversing the Photoswitching Mode of Turning ON and OFF DNA Hybridization

A new photoswitch for DNA hybridization involving para‐substituted azobenzenes (such as isopropyl‐ or tert‐butyl‐substituted derivatives) with L ‐threoninol as a linker was synthesized. Irradiation of the modified DNA with visible light led to dissociation of the duplex owing to the destabilization effect of the bulky substituent on the trans‐azobenzene. In contrast, trans‐to‐cis isomerization (UV light irradiation) facilitated duplex formation. The direction of this photoswitching mode was entirely reversed relative to the previous system with an unmodified azobenzene on D ‐threoninol whose trans form turned on the hybridization, and cis form turned it off. Such reversed and reversible photoswitching of DNA hybridization was directly demonstrated by using fluorophore‐ and quencher‐attached oligonucleotides. Furthermore, it was revealed that the cis‐to‐trans thermal isomerization was greatly suppressed in the presence of the complementary strand owing to the formation of the more‐stable duplex in the cis form.     

Average electron tunneling route of the electron transfer in protein media

We present a new theoretical method to determine and visualize the average tunneling route of the electron transfer (ET) in protein media. In this, we properly took into account the fluctuation of the tunneling currents and the quantum-interference effect. The route was correlated with the electronic factor in the case of ET by the elastic tunneling mechanism. We expanded by the interatomic tunneling currents 's. Incorporating the quantum-interference effect into the mean-square interatomic tunneling currents, denoted as , we could express as a sum of variant Planck's over 2pi(2). Drawing the distribution of on the protein structure, we obtain the map which visually represents which parts of bonds and spaces most significantly contribute to . We applied this method to the ET from the bacteriopheophytin anion to the primary quinone in the bacterial photosynthetic reaction center of Rhodobacter sphaeroides. We obtained 's by a combined method of molecular dynamics simulations and quantum chemical calculations. In calculating , we found that much destructive interference works among the interatomic tunneling currents even after taking the average. We drew the map by a pipe model where atoms a and b are connected by a pipe with width proportional to the magnitude of . We found that two groups of 's, which are mutually coupled with high correlation in each group, have broad pipes and form the average tunneling routes, called Trp route and Met route. Each of the two average tunneling routes is composed of a few major pathways in the Pathways model which are fused at considerable part to each other. We also analyzed the average tunneling route for the ET by the inelastic tunneling mechanism.     

Atomic electron-pair distances and subshell radii in position and momentum space

For the 53 neutral atoms from He to Xe in their ground states, the average distances < u> _{n l , n ′ l ′} in position space and < v> _{n l , n ′ l ′} in momentum space between an electron in a subshell nl and another electron in a subshell n ^′ l ^′ are studied, where n and l are the principal and azimuthal quantum numbers of an atomic subshell, respectively. Analysis of 1700 subshell pairs shows that the electron-pair distances < u> _{n l , n ′ l ′} in position space have an empirical but very accurate linear correlation with a one-electron quantity U _{n l , n ′ l ′}≡L _r +S _r ²/(3L _r ), where L _r and S _r are the larger and smaller of subshell radii < r> _{n l} and < r> _{n ′ l ′}, respectively. The correlation coefficients are never smaller than 0.999 for the 66 different combinations of two subshells appearing in the 53 atoms. The same is also true in momentum space, and the electron-pair momentum distances < > _{n l , n ′ l ′} have an accurate linear correlation with a one-electron momentum quantity V _{n l , n ′ l ′}≡L _p +S _p ²/(3L _p ), where L _p and S _p are the larger and smaller of average subshell momenta < p> _{n l} and < p> _{n ′ l ′}, respectively. Trends in the proportionality constants between < u> _{n l , n ′ l ′} and U _{n l , n ′ l ′} and between < > _{n l , n ′ l ′} and V _{n l , n ′ l ′} are discussed based on a hydrogenic model for the subshell radial functions. Received: 8 April 1998 / Accepted: 6 July 1998 / Published online: 18 September 1998