Electronic structures of size-selected single-layered platinum clusters on silicon(111)-7x7 surface at a single cluster level by tunneling spectroscopy

Tunneling spectra of size-selected single-layered platinum clusters (size range of 5-40) deposited on a silicon(111)-7x7 surface were measured individually at a temperature of 77 K by means of a scanning tunneling microscope (STM), and the local electronic densities of states of individual clusters were derived from their tunneling spectra measured by placing an STM tip on the clusters. In a bias-voltage (V(s)) range from -3 to 3 V, each tunneling spectrum exhibits several peaks assignable to electronic states associated with 5d states of a constituent platinum atom and an energy gap of 0.1-0.6 eV in the vicinity of V(s)=0. Even when platinum cluster ions having the same size were deposited on the silicon(111)-7x7 surface, the tunneling spectra and the energy gaps of the deposited clusters are not all the same but can be classified in shape into several different groups; this finding is consistent with the observation of the geometrical structures of platinum clusters on the silicon(111)-7x7 surface. The mean energy gap of approximately 0.4 eV drops to approximately 0.25 eV at the size of 20 and then decreases gradually as the size increases, consistent with our previous finding that the cluster diameter remains unchanged, but the number density of Pt atoms increases below the size of 20 while the diameter increases, but the density does not change above it. It is concluded that the mean energy gap tends to decrease gradually with the mean cluster diameter. The dependence of the mean energy gap on the mean Pt-Pt distance shows that the mean energy gap decreases sharply when the mean Pt-Pt distance exceeds that of a platinum metal (0.28 nm).     

Awareness, Belief, and Communication Reaching Consensus

This article studies graph-theoretical conditions under which communication will lead to consensus among players about their decisions in circumstances where there are more than two players and they interact in pair without public announcement. It is shown that consensus on their decisions can be guaranteed if the communication graph contains no cycle. Where none of the requirements for player's knowledge is imposed as in the standard model of knowledge with partitional information structure.     

Fe fine particles encapsulated by titanium oxides with high magnetization for biomedical application

Iron (Fe) fine particles encapsulated by titanium oxide (TiO₂) were synthesized through a solid-phase reaction. The structure of Fe cores and TiO₂ shells consisted of α-Fe and rutile TiO₂, respectively. The average particle size was 0.8 μm, in which a Fe particle with a diameter of ∼750 nm was encapsulated by a TiO₂ shell with a thickness of ∼100 nm. The Fe particles had a high saturation magnetization of 127 Am²/kg and low coercivity of 1.6 kA/m. They also exhibited excellent corrosion resistance, similar to Fe₃O₄ in a soaking test.     

Improved synthesis of the polyhydroxylated central part of phoslactomycin B

A new approach to the C(7)-C(13) intermediate for the synthesis of phoslactomycin B was investigated. Asymmetric dihydroxylation of the β,γ-unsaturated ester proceeded cleanly to afford the β-hydroxyl-γ-lactone with 97.6% ee, which upon protection as the PMB ether followed by hydride reduction furnished a diol. After selective protection of the prim-OH, oxidation of the sec-OH and chelation-controlled addition of CH₂CHMgBr afforded the C(7)-C(11) segment. Later on, the C(11) stereocentre was constructed by the asymmetric transfer hydrogenation using the Noyori catalyst.     

Design and synthesis of a library of BODIPY-based environmental polarity sensors utilizing photoinduced electron-transfer-controlled fluorescence ON/OFF switching

We systematically examined the mechanism of the solvent polarity dependence of the fluorescence ON/OFF threshold of the BODIPY (boron dipyrromethene) fluorophore and the role of photoinduced electron transfer (PeT). In a series of BODIPY derivatives with variously substituted benzene moieties at the 8-position, the oxidation potential of the benzene moiety became more positive and the reduction potential of the BODIPY fluorophore became more negative as the solvent polarity was decreased; consequently, the free energy change of PeT from the benzene moiety becomes larger in a more nonpolar environment. Utilizing this finding, we designed and synthesized a library of probes in which the threshold of fluorescence ON/OFF switching corresponds to different levels of solvent polarity. These environment-sensitive probes were used to examine bovine serum albumin (BSA) and living cells. The polarity at the surface of albumin was concluded to be similar to that of acetone, while the polarity of the internal membranes of HeLa cells was similar to that of dichloromethane.     

Clarification of band structure at metal-diamond contact using device simulation

The mechanism of low-threshold electron emission from heavily nitrogen-doped diamond was clarified using computer simulation. Possibility of internal field emission at metal-diamond contact was evaluated expecting that the electron injection can explain the low-threshold electron emission. As a result, it was proved that electron injection could be achieved even for a deep donor of 1.7 eV, when donor concentration exceeded 1e20 cm⁻³. The result was in good agreement with previous experiments.     

pH-Responsive PEGylated nanogels as targetable and low invasive endosomolytic agents to induce the enhanced transfection efficiency of nonviral gene vectors

A pH-responsive PEGylated nanogel was successfully prepared by means of emulsion copolymerization of 2-(N,N-diethylamino)ethyl methacrylate (AMA) with heterobifunctional poly(ethylene glycol) (PEG) bearing a 4-vinylbenzyl group at the α-end and a lactose moiety at the ω-end in the presence of potassium persulfate and ethyleneglycol dimethacrylate as a cross-linker. Polyplex micelle composed of PEG-block-poly(l-lysine) copolymer and plasmid DNA (PEG-b-PLL/pDNA) exhibited a far more efficient transfection ability in the presence of lac-nanogel-8k-1.0% (PEG, M _n = 8000; cross-linking density, 1.0%) than the PEG-b-PLL/pDNA polyplex micelle alone (in the absence of lac-nanogel-8k-1.0%), suggesting that an appreciable fraction of lac-nanogel-8k-1.0% along with the PEG-b-PLL/pDNA polyplex micelle is taken up into the HuH-7 cells through the asialoglycoprotein receptor-mediated endocytosis process mediated by the cluster of a large number of lactose moieties on the surface of lac-nanogel-8k-1.0%, followed by the effective disruption of the endosome by the buffer effect of the unprotonated PAMA core in lac-nanogel-8k-1.0%. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Low-energy impact of X-(H2O)n (X = Cl,I) onto solid surface

We investigated dissociation of X-(H2O)n (X = Cl, I, n = 13-31) by the impact onto a (La0.7Ce0.3)B6(100) surface at a collision energy Ecol of 1-5 eV per water molecule in a tandem time-of-flight mass spectrometer equipped with a translation-energy analyzer. The mechanism of the dissociation was elucidated on the basis of the measurements of the mass spectrum and the translational energies of the product anions, X-(H2O)m (m = 0-4), scattered from the surface. It was concluded that (1) the parent cluster anion impacted on the surface undergoes dissociation on the surface under quasiequilibrium with its characteristic time varying with Ecol and n, and (2) the total collision energy introduced is partitioned preferentially to the translational motions of the products on the surface and to the rotational, the vibrational, and the lattice vibrational motions (surface) in this order. The quasiequilibrium model is applicable, even at the collision energy as low as 1 eV, because the translational modes are found to be statistically distributed while the other modes are not much populated by dynamical and energetics limitation.     

Molecular assembly composed of a dendrimer template and block polypeptides through stereocomplex formation

A 2nd generation polyamideamine (PAMAM) dendrimer bearing right-handed helices to its eight terminals was shown to accommodate eight left-handed helices via stereocomplex formation to generate molecular assemblies of disk structure with 13-14 nm diameter and 6 nm thickness.