Crystal Structure of Regularly Th‐Symmetric [U(NO3)6]2− Salts with Hydrogen Bond Polymers of Diamide Building Blocks

Hexanitratouranate(IV), [U(NO₃)₆]^2?, has been crystallized with anhydrous H⁺‐involving hydrogen bond polymers connected by selected diamide building blocks. Thanks to the significant moderation of electrostatic interactions between the anions and cations, the molecular structure of [U(NO₃)₆]^2? in these compounds is regularly T_h‐symmetric. The f–f transitions stemming from 5f² configuration of U⁴⁺ are strictly forbidden by the Laporte selection rule in such a centrosymmetric system, so that the obtained compounds are nearly colourless in contrast to other U^IV species usually coloured in green.     

用反应48Ca+254Es合成119号元素的可能性研究

利用最近发展起来的两步模型分析重离子核反应48Ca+254Es 的熔合过程。在这个模型中,熔合过程被分为前后独立的两个过程,即粘连过程和形成过程。本研究组计算了对应的粘连概率和形成概率,并结合适用于蒸发过程的统计蒸发模型,计算了该反应合成119 号超重元素的剩余截面,即当Elab = 250:2 MeV时,得到最大剩余截面为0.7 pb。Two-step model is adopted to analyze the fusion process of heavy-ion reaction 48Ca+254 Es. Based on this model, the fusion process is divided into two consecutive steps, i.e., the sticking step and the formation step, and corresponding sticking probability and formation probability are calculated. Combining the statistical evaporation model for the evaporation stage, the maximum evaporation residue cross section for reaction 48Ca+254 Es is 0.7 pb at 4n, Elab =250.2 MeV.     

Energy transfer induced enhancement of localized exciton emission in ZnO nanoparticle–anthracene hybrid films

Optically transparent and high‐quality hybrid ZnO nanoparticle and anthracene embedded polyphenylsiloxane (PPS) glass films were spin‐coated on quartz substrates. A strong Förster resonant energy transfer (FRET) process was indicated by the observation of quenching of the ZnO emission and an enhancement of the anthracene emission at room temperature. The efficiency of this energy transfer between ZnO and the S₁ vibronic states of the anthracene molecules can be optimized to exceed 90%.

     

Real-Space Distribution of Local WO(4) Ordering in Negative Thermal Expansive ZrW(2)O(8)

Solids usually expand when they are heated. This is quite common behavior of solids; however, there are some exceptions. Zirconium tungstate (ZrW(2)O(8)) is a prototype material among them, because it has the highest degree of negative thermal expansion (NTE) over broad temperature range. Intensive investigation of NTE mechanisms has suggested the importance of metal-oxygen polyhedra. However, most of the studies have been done with volume-averaged techniques, and microscopic information has been lacking. Here, our electron microscopy observations have unraveled the real-space distribution of local WO(4) tetrahedra ordering for the first time. We have found that (i) the WO(4) ordering is partly inverted; (ii) WO(4) is disordered on the nanoscale; and (iii) doping with scandium enhances the WO(4) disordering. These findings led to construction of a microstructure model for ZrW(2)O(8), providing a new structural perspective for better understanding of local structure and its role in phase transitions.     

Synthesis of optically active medium-sized α-aminolactams via ring-closing metathesis

The synthesis of optically active medium-sized α-aminolactams via ring-closing metathesis is described. The amidation of optically active N-Boc-allylglycine derivatives with N-protected alkenylamine, and ring-closing metathesis resulted in the formation of medium-sized α-aminolactams with good yield.     

Visible light-emitting and temperature-sensitive copolymer gel/ZnO nanocomposites loaded with surface-modified ZnO nanoparticles having polyethylene glycol chains

New visible light-emitting and temperature-sensitive poly(VCL-co-SA)/ZnO gel nanocompsites (GNs) 4 loaded with surface-modified ZnO nanoparticles NPs 3 with polyethylene glycol (PEG) chains were successfully prepared by the cross-linking of N-vinylcaprolactam (VCL), sodium acrylate (SA) and tetraethylene glycol dimethacrylate (TEGDM) in the presence of NPs 3. The NPs 3 having nanostructured size were prepared from ZnO NPs 2 with 2-bromo-2-methylpropionyl linkages on the surface, and sodium alcoholate of polyethylene glycol monomethyl ether (PEGME). The NPs 3 and the GNs 4 were characterized by FTIR, UV–vis absorption and photoluminescent (PL) spectroscopies, X-ray analysis measurements, TEM and SEM observations and dynamic light scattering (DLS) measurements. The measurements indicated that the GNs 4 with wurtzite crystal structures based on the ZnO NPs show absorptions and yellow light-emitting properties arising from the NPs 3, except for the GNs 4 containing a high weight % of NPs 3. The size of the GNs 4 drastically decreased with increasing temperature in the range of 20–35 °C, probably because of the induction of steric hindrance and enhancement of hydrophilic PEG chain concentrations inside the GN networks 4.     

Improved photostability of hydrophobic natural dye incorporated in organo-modified hydrotalcite

β-carotene and annatto extract are typical carotenoids used as safe colorants for foods. However, the instability against irradiation limits their wide use. The improvement of stability was investigated by the intercalation of dye into the interlayer space of the anion-exchangeable clay, hydrotalcite. A hydrophobic environment was constructed in the interlayer space of the hydrotalcite by its modification with anionic surfactants (dodecyl sulfate and dodecylbenzene sulfonate). The lipophilic β-carotene and annatto dye were successfully incorporated into the organo-modified hydrotalcite, and the incorporated dyes exhibited improved photostability under visible irradiation from a 100 W halogen lamp (190 klux) in the air. The effect of the stabilization on the anionic annatto dye was higher by the incorporation in the modified hydrotalcite than that in the modified cation exchangeable clay, suggesting that the polarity of the clay sheet had some influence on the stabilization of the incorporated dye. The stabilization effect of β-carotene was not so significant as that of the annatto dye, because sufficient intercalation of non-polar β-carotene might require stronger hydrophobic environment. The π–π interaction between the β-carotene and the benzene ring of dodecylbenzene sulfonate was found to contribute to the stability enhancement.     

New surface-modified zinc oxide nanoparticles with aminotriethylene oxide chains linked by 1,2,3-triazole ring: Preparation, and visible light-emitting and noncytotoxic properties

Novel surface-modified, visible light-emitting and noncytotoxic ZnO nanoparticles (NPs) (ZPAZ) having aminotriethylene oxide chains linked by 1,4- and/or 1,5-disubstituted 1,2,3-triazole rings were prepared from ZnO NPs (ZPA) with ethynyl groups on the surfaces and an azide derivative of triethylene oxide chain linking terminal amino group (ATA) via 1,3-dipolar azide/alkyne click reaction by heating without Cu(I) catalyst. FTIR spectroscopy, elemental analysis, XRD analysis and TEM observation suggested that the resulting ZPA and ZPAZ NPs have the particle sizes below 10 nm in diameters, triethylene oxide chains linking the terminal amino groups and wurtzite crystal structure. UV-vis absorption spectrum of the ZPAZ NPs in methanol showed maximum absorption band at 346.5 nm, supporting the TEM observation. PL spectra depicted that the ZPA and ZPAZ NPs display broad light green and lightly greenish yellow visible light emitting bands in methanol. Zeta potentials measured in distilled water suggested that the ZPAZ NPs have a low tendency to aggregate and possess better stability than the ZPA NPs. Cytotoxicity assay revealed that the ZPAZ NPs, having water-dispersion properties, are noncytotoxic at low concentrations and almost all RAW264.7 cells are alive after 24 h of treatment.     

Mechanism of atomic-scale passivation and flattening of semiconductor surfaces by wet-chemical preparations

Atomic arrangements of Si(001), Si(110) and 4H-SiC(0001) surfaces after wet-chemical preparations are investigated with scanning tunneling microscopy. Their passivated structures as well as the surface formation mechanisms in aqueous solutions are discussed. On both Si(001) and Si(110) surfaces, simple 1 × 1 phases terminated by H atoms are clearly resolved after dilute HF dipping. Subsequent etching with water produces the surfaces with 'near-atomic' smoothness. The mechanisms of atomic-scale preferential etching in water are described in detail together with first-principles calculations. Furthermore, 4H-SiC(0001), which is a hard material and where it is difficult to control the surface structure by solutions, is flattened on the atomic scale with Pt as a catalyst in HF solution. After a mechanism is proposed based on electroless oxidation, the flattened surface mainly composed of a 1 × 1 phase is analyzed. The obtained results will be helpful from various scientific and technological viewpoints.     

Asymmetric cycloaddition reactions of diazoesters with 2-alkenoic acid derivatives catalyzed by binaphthyldiimine-Ni(II) complexes

The catalytic activity of chiral binaphthyldiimine (BINIM)-Ni(II) complexes for asymmetric enantioselective diazoalkane cycloadditions of ethyl diazoacetate with 3-acryloyl-2-oxazolidinone and 2-(2-alkenoyl)-3-pyrazolidinone derivatives was evaluated. The cycloadditions of 3-acryloyl-2-oxazolidinone and its 5,5-dimethyl derivative, in the presence of the BINIM-Ni(II) complex (10 mol %; prepared from (R)-BINIM-4Ph-2QN (ligand C) and Ni(ClO(4))(2)·6H(2)O) afforded 2-pyrazolines having a methine carbon substituted with an oxazolidinonyl group in moderate ratios (70:30 to 72:28), along with high enantioselectivities (90-92% ee) via 1,3-proton migration. On the basis of the investigations on the counteranions of the Ni(II) complex, the N-substituent of pyrazolidinone, and reaction temperatures, the optimal enantioselectivity (97% ee) and ratio (85:15) of 2-pyrazoline were obtained for the reaction of 2-acryloyl-1-benzyl-5,5-dimethyl-3-pyrazolidinone in the presence of (R)-BINIM-4Ph-2QN-Ni(II) ((R)-C/Ni(II)) complex prepared using Ni(BF(4))(2)·6H(2)O. In the cases of 1-benzyl-2-crotonoyl-5,5-dimethyl-3-pyrazolidinone, 1-benzyl-2-(2-butenoyl)-5,5-dimethyl-3-pyrazolidinone, and 1-benzyl-5,5-dimethyl-2-(3-ethoxycarbonyl)propenoyl-3-pyrazolidinone, the use of the (R)-BINIM-2QN-Ni(II) ((R)-A/Ni(II)) complex gave good to high enantioselectivities (85-93% ee) with the sole formation of the 2-pyrazoline having a methine carbon substituted with a pyrazolidinonyl group. Relatively good enantioselectivity (77% ee) was observed for the reaction between 2-acryloyl-5,5-dimethyl-1-naphthylmethyl-3-pyrazolidinone and an α-substituted diazo ester, ethyl 2-diazo-3-phenylpropanoate, which has yet to be employed as a diazo substrate in asymmetric cycloaddition reactions catalyzed by a chiral Lewis acid.