Relaxation structure analysis of Li inserted γ-Fe2O3

γ-Fe₂O₃ has a spinel structure with cation vacancy and is expected to perform as a favorable electrode material for secondary lithium-ion battery. When lithium is inserted electrochemically into γ-Fe₂O₃, prolonged potential change is observed after the insertion. In this study, we inserted various amount of Li into γ-Fe₂O₃ (x = 0.66, 1.1, 1.5 in terms of Li_XFe₂O₃), then made the circuit open, measured X-ray diffraction (XRD) patterns at various elapsed time, and analyzed the crystal structure change of γ-Fe₂O₃ with time by the Rietveld method. The X-ray Rietveld analysis revealed that the iron occupancy of 8a site decreased and that of 16c site increased with lithium insertion process and after lithium insertion, the iron occupancy of 8a site increased and that of 16c site decreased gradually with relaxation time. It is indicated that lithium prefer 8a site to occupy kinetically, on the other hand, prefer 16c site thermodynamically.     

Selective growth of ZnO nanodots prepared by metalorganic chemical vapor deposition on focused-ion beam-nanopatterned substrates

Selective formation of ZnO nanodots grown by metalorganic chemical vapor deposition (MOCVD) was achieved on focused-ion beam (FIB)-nanopatterned SiO₂ and Si substrates. The selective formation characteristics, dimension, and density of ZnO nanodots on FIB-nanopatterned substrates strongly depended on the FIB-patterning and MOCVD-growth conditions. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned SiO₂ substrates is attributed to a surfactant effect of the implanted Ga which leads to the formation of the preferred nucleation sites for the growth of ZnO nanodots, while that of ZnO nanodots on nanopatterned Si substrates is mainly considered in terms of the generation of surface atomic steps and kinks, which are created by Ga⁺ ion sputtering, on the patterned Si areas.     

Study on interaction between Tb(III) and poly(N-isopropylacrylamide)

A new kind of the thermo-sensitive and fluorescent complex of poly(N-isopropylacrylamide) (PNIPAM) and Tb(III) was synthesized by free radical polymerization, in which PNIPAM was used as a polymer ligand. The complex was characterized by using X-ray photoelectron spectroscopy (XPS), ultraviolet-visual (UV), Fourier transform infrared (FT-IR) and fluorescence spectroscopy. The results from the experiments indicated that there is a strong interaction between PNIPAM and Tb(III), leading to a decrease in the electron density of nitrogen and oxygen atoms and an increase in the electron density of Tb(III) in the PNIPAM containing Tb(III) by contrast with PNIPAM and Tb(III), respectively, meanwhile, exhibiting that the Tb(III) is mainly bonded to oxygen atoms in the polymer chain of PNIPAM and formed the complex of PNIPAM-Tb(III). After forming the PNIPAM-Tb(III) complex, the emission fluorescence intensity of Tb(III) in the PNIPAM-Tb(III) complex is significantly enhanced because the effective intramolecular energy transfer from PNIPAM to Tb(III). Especially, the emission intensity of the fluorescence peak at 547 nm can be increased as high as 145 times comparing with that of the pure Tb(III). The intramolecular energy transfer efficiency for fluorescence peak at 547 nm can reach as high as 68%. The fluorescence intensity is related the weight ratio of Tb(III) and PNIPAM in the PNIPAM-Tb(III) complex. When the weight ratio is 1.4%, the maximum fluorescence enhancement can be obtained. Nevertheless, the lower critical solution temperature of PNIPAM containing a low content of Tb(III) has not obviously changed after the formation of the complex of PNIPAM-Tb(III) by the interaction between PNIPAM and Tb(III). This novel thermosensitive and fluorescence characterization of the PNIPAM-Tb(III) complex may be useful in the fluorescence systems and the biomedical field.     

Electron Temperatures and Electron Densities in Microwave Helium Discharges with Pressures Higher than 0.1 MPa

We adopted laser Thomson scattering for measuring the electron density and the electron temperature of microwave plasmas produced in helium at the pressures higher than the atmospheric pressure. The electron density decreased while we observed the increase in the electron temperature with the pressure. These are reasonable results by considering the decrease in the reduced electric field, the dominant loss of electrons via three‐body recombination with helium as the third body, and the production of electrons with medium energy via heavy particle collisions at the high gas pressure. The temporal variation of the electron temperature had the rise and the fall time constants of approximately 10 ns. The rapid heating and cooling of the electron temperature are due to the fast energy transfer from electrons to helium because of the high collision frequency in the high‐pressure discharge. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study on the pressure induced charge transfer phase transition in (C5H11)4N(FeFe(C2O2S2)3) by means of μSR spectroscopy

We have investigated the magnetic properties of iron mixed-valence complexes, (n-C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (dto = C₂O₂S₂, n = 3, 5), in which not only a ferromagnetic transition but also a novel charge transfer phase transition (CTPT) take place [1]. This CTPT can be observed under ambient pressure for n = 3, while it appears abruptly above 0.5 GPa for n = 5 [2]. Recently, we have measured the muon spin relaxation (μSR) for the CTPT of n = 3, which revealed the dynamical process of electron-transfer between Fe^II and Fe^III and its frequency was estimated at about 0.1 MHz [3]. To investigate the pressure induced CTPT for n = 5, we carried out the μSR measurement for n = 5 at 150 K between 0.30 and 0.64 GPa with the ⁴He gas-operated pressure system. The asymmetry of the muon spin relaxation for n = 5 with Cu-Be pressure cell was almost constant up to 0.55 GPa, while it rapidly decreased with increasing pressure above 0.60 GPa. This result shows that the applied pressure causes the spin fluctuation due to the CTPT, which induces the decrease of the asymmetry of muon spin relaxation. This experiment can correctly decide the phase transition pressure from the absence to the appearance of the CTPT for n = 5.     

Preparation of highly dispersible and tumor-accumulative, iron oxide nanoparticles Multi-point anchoring of PEG-b-poly(4-vinylbenzylphosphonate) improves performance significantly

This paper describes the preparation of iron oxide nanoparticles, surface of which was coated with extremely high immobilization stability and relatively higher density of poly(ethylene glycol) (PEG), which are referred to as PEG protected iron oxide nanoparticles (PEG-PIONs). The PEG-PIONs were obtained through alkali coprecipitation of iron salts in the presence of the PEG-poly(4-vinylbenzylphosphonate) block copolymer (PEG-b-PVBP). In this system, PEG-b-PVBP served as a surface coating that was bound to the iron oxide surface via multipoint anchoring of the phosphonate groups in the PVBP segment of PEG-b-PVBP. The binding of PEG-b-PVBP onto the iron oxide nanoparticle surface and the subsequent formation of a PEG brush layer were proved by FT-IR, zeta potential, and thermogravimetric measurements. The surface PEG-chain density of the PEG-PIONs varied depending on the [PEG-b-PVBP]/[iron salts] feed-weight ratio in the coprecipitation reaction. PEG-PIONs prepared at an optimal feed-weight ratio in this study showed a high surface PEG-chain surface density (≈0.8 chainsnm(-2)) and small hydrodynamic diameter (<50 nm). Furthermore, these PEG-PIONs could be dispersed in phosphate-buffered saline (PBS) that contains 10% serum without any change in their hydrodynamic diameters over a period of one week, indicating that PEG-PIONs would provide high dispersion stability under in vivo physiological conditions as well as excellent anti-biofouling properties. In fact we have confirmed the prolong blood circulation time and facilitate tumor accumulation (more than 15% IDg(-1) tumor) of PEG-PIONs without the aid of any target ligand in mouse tumor models. The majority of the PEG-PIONs accumulated in the tumor by 96 h after administration, whereas those in normal tissues were smoothly eliminated by 96 h, proving the enhancement of tumor selectivity in the PEG-PION localization. The results obtained here strongly suggest that originally synthesized PEG-b-PVBP, having multipoint anchoring character by the phosphonate groups, is rational design for improvement in nanoparticle as in vivo application. Two major points, viz., extremely stable anchoring character and dense PEG chains tethered on the nanoparticle surface, worked simultaneously to become PEG-PIONs as an ideal biomedical devices intact for prolonged periods in harsh biological environments.     

Copper-catalyzed γ-selective and stereospecific allylic alkylation of ketene silyl acetals

Copper-catalyzed allylic alkylation of ketene silyl acetals proceeded with excellent γ-E-selectivity. Efficient α-to-γ chirality transfer with anti-selectivity occurred in the reaction of enantioenriched secondary allylic phosphates, affording enantioenriched β-branched γ,δ-unsaturated esters. Excellent functional group compatibility was observed.     

Fluorous solvent for cell culture

Incubation of mouse melanoma B16 cells in fluorous solvents with low boiling point such as perfluoromethylcyclohexane, 1,1,1,3,3,3-hexafluoro-2-propanol, ethylpentafluoropropionate resulted in cell death. However, cells lived up to 2 days in fluorous alcohols such as 2,2,3,3,4,4,5,5-octafluoro-1-pentanol and 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol with relatively higher fluorine content. Remarkably, cells survived deprived of nutrition up to 4 days when incubated in 2,2,3,3,4,4,5,5,6,6,6-undecafluoro-1-hexanol or in 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptanol that have the most number of fluorine atoms (11 and 12, respectively) among the perfluoroalkyl alcohols used, and with boiling points of 128 °C and 169 °C, respectively.