Diamagnetic muon yields of metal acetylacetonates

Diamagnetic muon yields /P_D/ in various metal acetylacetonates were measured at room temperature by the muon spin rotation technique. We have found a clear difference in P_D between complexes of typical elements and those of transition elements. We suggest that partially filled inner orbitals play some important role in determining the diamagnetic yield in these complexes.     

Size-Selective Harvesting of Extracellular Vesicles for Strategic Analyses Towards Tumor Diagnoses

Extracellular vesicles (EV), typified by exosomes or microvesicles, are expected to be effective diagnostic markers for cancers. The sizes of the vesicles range from 20 to 1000 nm, but the size-dependent variations of the contents of EVs are still poorly understood. We succeeded in the size-selective harvesting of the vesicles by utilizing the molecular weight-dependent characteristics of a variety of polyethylene glycols (PEG) as precipitating reagents and analyzed the antigens displayed on the surfaces of the vesicles and the miRNAs included in the vesicles from each size group. As a result, the relatively larger (<100 nm) particles precipitated by PEG5k clearly exhibited the greatest amount of epithelial cell adhesion molecule (EpCAM), from both breast cancer (MCF-7) and colon cancer (HCT116) cells, and a larger quantity of microRNA (miRNA) specific to breast cancer cells (miRNA155 for MCF-7) seemed to be contained in the PEG-precipitated particles. The results demonstrated that the quantities of both the tumor-specific miRNA and protein were similarly distributed among the several classes of the size-sorted EVs and that the size-selective harvesting of EVs may be informative for strategic analyses towards the diagnoses of cancers.     

Spin dynamics in crystalline and amorphous DyAg

Crystalline (cr-) Dyag [CsC] structure] orders antiferro-magnetically with T_N≅60K; amorphous (am-) DyAg ferro-magnetically with T_C≈-18K. We measured the longitudinal field (LF) μ⁺SR relaxation functions G_ZZ(t) for 5K<T<300K using surface muons. In the paramagnetic state. cr-DyAg gives an exponential G_ZZ (t) in the relaxation rate rising first slowly then more rapidlynear T_N; no decoupling is observed in LF up to 0.4T. In the ordered state we see a Lorentzian Kubo-Toyabe G_ZZ(t), becoming nearly static at the lowest temperatures. Its static width is very narrow (Δ≈-7 MHz), and full dceoupling is achieved here in 0.1 T. On approaching T_N, the fluctuation rate and the static width increase mootonically bt the field distribution remains Loratzian. A LF of 0.4T is then insufficient to quench the fast exponential relaxation. In paramagnetic am-DyAg, the μ⁺ depolarization is always much faster then in cr-DyAg. At lower temperatures it is better described by a root-exponential than an exponential G_ZZ(t). Below T_C an exponentially relaxing signal with 1/3 amplitude is seen. The decoupling effect of LF up to 0.4T was negligible at all temperatures.     

Muon spin relaxation in diluted triangular‐lattice antiferromagnet

Zero and longitudinal field μSR measurements on diluted triangular‐lattice antiferromagnet LuFeMgO₄ have revealed gradual and highly anisotropic slowing‐down of spin fluctuation. Relaxation rate \lambda in the condition with initial muon spins perpendicular to the hexagonal c‐plane shows divergent behavior while that in the parallel configuration remains finite. At certain temperature range the fluctuation of spins is suppressed by a small external magnetic field. Monte Carlo calculation suggests that the correlation time for z(c)‐component of spins diverges first on cooling. This revised version was published online in July 2006 with corrections to the Cover Date.     

The low temperature hyperfine structure of quartz under uniaxial pressure

The uniaxial pressure dependence of the muonium hyperfine tensor was measured at 80 K. Uniaxial pressures (0 and 0.2 GPa) were applied along the a‐axis of quartz, and the hyperfine tensor was measured by applying various transverse fields between 0 and 7 G. The structure appears to be the result of the three chemically equivalent sites in quartz. When pressure is applied perpendicular to the crystallographic c‐axis of quartz, the symmetry of these sites is broken such that two chemically inequivalent sites are observed. The resulting hyperfine structure is discussed and qualitative explanations are proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Salt‐Free Reduction of Nonprecious Transition‐Metal Compounds: Generation of Amorphous Ni Nanoparticles for Catalytic C–C Bond Formation

A salt‐free procedure for the generation of a wide variety of metal(0) particles, including Fe, Co, Ni, and Cu, was achieved using 2,3,5,6‐tetramethyl‐1,4‐bis(trimethylsilyl)‐1,4‐diaza‐2,5‐cyclohexadiene ( 1 ), which reduced the corresponding metal precursors under mild conditions. Notably, Ni particles formed in situ from the treatment of Ni(acac)₂ (acac=acetylacetonate) with 1 in toluene exhibited significant catalytic activity for reductive C? C bond‐forming reactions of aryl halides in the presence of excess amounts of 1 . By examination of high‐magnification transmission electron microscopy images and electron diffraction patterns, we concluded that amorphous Ni nanoparticles (Ni aNPs) were essential for the high catalytic activity.     

Influence of RNA Strand Rigidity on Polyion Complex Formation with Block Catiomers

Polyion complexes (b‐PICs) are prepared by mixing single‐ or double‐stranded oligo RNA (aniomer) with poly(ethylene glycol)‐b‐poly(l ‐lysine) (PEG‐PLL) (block catiomer) to clarify the effect of aniomer chain rigidity on association behaviors at varying concentrations. Here, a 21‐mer single‐stranded RNA (ssRNA) (persistence length: 1.0 nm) and a 21‐mer double‐stranded RNA (small interfering RNA, siRNA) (persistence length: 62 nm) are compared. Both oligo RNAs form a minimal charge‐neutralized ionomer pair with a single PEG‐PLL chain, termed unit b‐PIC (uPIC), at low concentrations (<≈0.01 mg mL⁻¹). Above the critical association concentration (≈0.01 mg mL⁻¹), ssRNA b‐PICs form secondary associates, PIC micelles, with sizes up to 30–70 nm, while no such multimolecular assembly is observed for siRNA b‐PICs. The entropy gain associated with the formation of a segregated PIC phase in the multimolecular PIC micelles may not be large enough for rigid siRNA strands to compensate with appreciably high steric repulsion derived from PEG chains. Chain rigidity appears to be a critical parameter in polyion complex association.