Enantioselective addition Of diketene to aldehydes promoted by chiral schiff base—titanium alkoxide complex. Application to asymmetric synthesis of potential inhibitors of HMG coenzyme reductase

Highly enantioselective addition of diketene to aldehydes was achieved by using novel Schiff base—titanium alkoxide complexes. Up to 92% ee of 5-hydroxy-3-oxoesters was obtained. This procedure provides an efficient method for the asymmetric synthesis of potential inhibitors of HMG coenzyme reductase.     

Preparation and mesostructure control of highly ordered zirconia particles having crystalline walls

Mesostructured zirconia particles having monoclinic-type crystalline walls were prepared using a low-temperature crystallization technique. Crystalline zirconia particles with highly-ordered mesostructures were obtained through the sol–gel process of zirconium sulfate tetrahydrate at 333 K in the presence of molecular self-assemblies of cetyltrimethylammonium bromide (CTAB) or mixtures of CTAB and anionic molecules such as sodium dodecyl sulfate and sodium p-toluenesulfonate. Variations in the molar ratios of CTAB and the chemical species of anionic molecules led to the variations in the periods of highly-ordered zirconia having crystalline walls. Calcination of the mesostructured zirconia particles prepared using templates consisting solely of CTAB yielded crystalline mesoporous zirconia particles.     

Focus on Extracellular Vesicles: Development of Extracellular Vesicle-Based Therapeutic Systems

Many types of cells release phospholipid membrane vesicles thought to play key roles in cell-cell communication, antigen presentation, and the spread of infectious agents. Extracellular vesicles (EVs) carry various proteins, messenger RNAs (mRNAs), and microRNAs (miRNAs), like a “message in a bottle” to cells in remote locations. The encapsulated molecules are protected from multiple types of degradative enzymes in body fluids, making EVs ideal for delivering drugs. This review presents an overview of the potential roles of EVs as natural drugs and novel drug-delivery systems.     

Relationship Between Structure and Coordination Strength of N and N,O-Hybrid Donor Ligands with Trivalent Lanthanides

ABSTRACT

To effectively separate lanthanides (Ln(III)) from actinides (An(III)), symmetrical 2,2′-bipyridyl (Bpy), 1,10-phenanthroline (Phen), and unsymmetrical N-methyl-N-tolyl-1,10-phenanthroline-2-carboxamide (MeTol-PTA) were investigated. According to the crystal structures and EXAFS experiments, the decreasing ionic radius from light to heavy Ln led to decreases in the Ln–N (Bpy) and Ln–N (Phen) distances, while log β simply increased due to the electrostatic interaction and the order of Ln–O (MeTol-PTA) < Ln–N (Bpy, Phen) < Ln–N (MeTol-PTA) was obtained. This indicated that the bulky phenanthroline moiety of MeTol-PTA may not allow N (MeTol-PTA) to come close to Ln. Consequently, the log β of MeTol-PTA exhibited a local maximum (around Nd).     

Determination of Precise Unit-Cell Parameters of the α-Tricalcium Phosphate Ca3(PO4)2 Through High-Resolution Synchrotron Powder Diffraction

Unit-cell parameters of the α-tricalcium phosphate [TCP; Ca₃(PO₄)₂] were investigated using high-resolution synchrotron powder diffraction and the Rietveld method. The diffraction experiment was conducted at 29°C at the BL-15XU experimental station of SPring-8, Japan. Precise unit-cell parameters of the α-TCP were obtained; a =12.87271 (9), b =27.28034(8), c =15.21275(12) Å, α=γ=90°, and β=126.2078(4)°. The calculated density of α-TCP (2.8677 g/cm³) is smaller than that of β-TCP, indicating the "looser" structure of α-TCP.     

Fracture Resistance Behavior of High‐Thermal‐Conductivity Silicon Nitride Ceramics

Silicon nitride ceramics were prepared from a high‐purity silicon powder doped with 2 mol% Y₂O₃ and 5 mol% MgO as sintering additives via a route of sintering of reaction‐bonded silicon nitride (SRBSN). The materials sintered at 1900°C for 3, 6, 12, and 24 h had thermal conductivities of 109, 125, 146, and 154 W/m/K, and four‐point bending strengths of 786, 676, 608, and 505 MPa, respectively. The fracture toughness values, determined by the single‐edge‐precracked‐beam (SEPB) method, were 8.4, 8.6, 9.7, and 10.7 MPa m^1/2 for the materials sintered for 3, 6, 12, and 24 h, respectively, which were similar to the results measured by the chevron‐notched‐beam (CNB) test method. The materials sintered for longer times (12 and 24 h) showed stronger R‐curve behaviors over longer range of crack extension, in comparison with the materials sintered for shorter times (3 and 6 h).     

Effect of oxygen potential on the sintering behavior of MgO-based heterogeneous fuels containing (Pu, Am)O2−x

The effect of oxygen potential on the sintering behavior of MgO-based heterogeneous fuels containing (Pu, Am)O_2−x was experimentally investigated. Sintering tests in various atmospheres, i.e. air, moisturized 4%H₂-Ar, and 4%H₂-Ar atmosphere, were carried out. The sintering behavior was found to be significantly affected by the oxygen potential in the sintering atmosphere. The sintered density decreased with decreasing oxygen potential. The (Pu, Am)O_2−x phase sintered in a reductive atmosphere had hypostoichiometry. The aggregates of the (Pu, Am)O_2−x phase sintered in the reductive atmosphere grew, in comparison with those in the oxidizing one. The sintering mechanism was discussed in terms of the difference in sintering behavior of (Pu, Am)O_2−x and MgO.     

Transient current mapping obtained from silicon photodiodes using focused ion microbeams with several hundreds of MeV

Single Event Effects (SEEs) triggered by energetic heavy ions traversing a sensitive parts of electric devices have been studied using high-energy heavy ion microbeams connected with Transient Ion Beam Induced Current (TIBIC) measuring system at the Japan Atomic Energy Agency (JAEA) Takasaki Ion Accelerators for Advanced Radiation Applications (TIARA) facility. In the TIBIC system, SEE for semiconductor device, that is fast charge collection, has been observed in timescales of the order of picoseconds. In this paper, we show successful demonstration of the performance of the system, in which clear images of TIBIC map have been observed for Si pin photodiodes irradiated by 260 MeV ²⁰Ne⁷⁺ and also by 520 MeV ⁴⁰Ar¹⁴⁺ microbeams.     

Chemical reaction kinetics dataset of Cs-I-B-Mo-O-H system for evaluation of fission product chemistry under LWR severe accident conditions

In order to improve LWR source term under severe accident conditions, the first version of a fission product chemistry database named ‘ECUME’ was developed. The ECUME is intended to include several datasets of major chemical reactions and their effective kinetic constants for representative severe accident sequences. It is expected that the ECUME can serve as a fundamental basis from which fission product chemical models can be elaborated for use in the severe accident analysis codes. The implemented chemical reactions in the first version were those for representative gas species in Cs-I-B-Mo-O-H system from 300 to 3000 K. The chemical reaction kinetic constants were evaluated from either literature data or calculated values using ab-initio calculations. The sample chemical reaction calculation using the presently constructed dataset showed meaningful kinetics effects at 1000 K. Comparison of the chemical equilibrium compositions by using the dataset with those by chemical equilibrium calculations has shown rather good consistency for the representative Cs-I-B-Mo-O-H species. From these results, it was concluded that the present dataset should be useful to evaluate fission product chemistry in Cs-I-B-Mo-O-H system under LWR severe accident conditions, where kinetics effects should be considered.