Determination of rare-earth elements in a limestone geological standard reference material by ICP-MS following solvent extraction.

Rare-earth elements in a limestone geological standard (JLs-1) were determined by inductively coupled plasma mass spectroscopy (ICP-MS) using phosphoric acid 2-ethylhexyl ester solvent extraction, which had been established for seawater analysis. First, the limestone sample was divided into two fractions: acetic acid soluble (carbonate fraction) and insoluble (residue). A modification of the method was undertaken to achieve quantitative recovery. With this method most of the REEs in the carbonate fraction were quantitatively recovered, except for the heaviest three REEs (Tm, Tb and Lu). The reason for the poor recoveries of the three elements was investigated, but still remained unclear. The mass-spectroscopic interference of BaO with Eu made an accurate determination of both lighter REEs and Eu at the same time impossible. The precision of this method was better than 20%. The data adopted after analytical consideration were consistent with those previously reported.     

Enhanced absorption and fluorescence efficiency of silylethynyl-functionalized oligothiophenes and thieno[3,2-b]thiopahene

Silylethynyl-substituted oligothiophenes and thieno[3,2-b]thiophene were synthesized by the Sonogashira coupling reaction. The absorption and fluorescence maxima of these compounds shifted to longer wavelength, and they exhibited higher absorption coefficients and quantum yields than the corresponding unsubstituted molecules and tert-butylethynyl derivatives. From the DFT calculation, the energy band gap between HOMO and LUMO decreases by the introduction of a silicon atom. Thus, silyl groups can play important role in enhancing the quantum efficiency and decreasing the band-gap of chromophores. Hence, Silylethynyl group can serve as a highly efficient auxiliary for use in optical devices.     

Assemblies of functional small-sized molecules having 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl responsive to heat and pH in water and their water proton relaxivities

1,3,5-Triureabenzene derivatives carrying alkyl (C(n)) and poly(ethylene glycol) (Eg(m)) chains C(n)Eg(3) (1, 2, and 3, n = 6, 7, and 8, respectively) and C(n)N(X)Eg(m) (4 and 5, X = M (methyl), n = 6 and 8, respectively, m = 3; 6 and 7, X = T (2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO), n = 6, m = 3 and 6, respectively) were prepared. All compounds in aqueous solutions exhibited the lower critical solution temperature (LCST) phenomena unique for small-sized molecules and formed self-assemblies above the transition temperature, T(t), of the LCST. Only compound 3 formed a hydrogel with a minimum gelation concentration of 0.5 mM (0.05 wt %). In 1.0 mM aqueous solution, the T(t) values were determined to be in the range of 12-40 °C. In addition, the T(t) values for 4-7 containing tertiary amine also responded to the solution pH with high sensitivity. The LCST behaviors for all compounds were reversible in the cycles of warming and cooling. The water proton relaxivities, r(1), for 6 and 7 carrying TEMPO were altered below and above T(t) and were largely reduced by the formation of self-assemblies above T(t). Compound 6 showed r(1) values at 25 °C of 0.92 and 0.23 mM(-1) s(-1) at pH 7.0 and 6.0, respectively. In transmission electron microscopy (TEM) images, globular particles with polydispersity were observed, and their average hydrodynamic diameters (D(H)) were determined to be in the range of 2400-730 nm by dynamic light scattering. In the TEM and scanning electron microscopy images of a xerogel sample of 3, bundles of fibers with a diameter of ca. 10 nm and a network structure, respectively, were observed.     

PdPt Nanocubes: A High‐Performance Catalyst for Hydrolytic Dehydrogenation of Ammonia Borane

An effective way to improve the catalytic activity of metal‐based nanostructured materials is to control the size, shape, or composition. Here, the bimetallic PdPt nanoparticles (NPs) show significant dependency on the shape for catalytic hydrolysis of ammonia borane. The catalytic activity of PdPt cubic nanoparticles (cNPs) is found to be the best compared with the activities of spherical nanoparticles (sNPs) of Pd, Pt, and PdPt and cNPs of Pd under the same reaction conditions. The turnover frequency (50.02 min^?1) of PdPt cNPs for ammonia borane hydrolysis is among the values of the most active catalysts. This high catalytic performance of PdPt cNPs encourages the approach of shape and composition control for various catalytic applications.     

Photosalient Effect of Diarylethene Crystals of Thiazoyl and Thienyl Derivatives

The photoresponse of diarylethene crystals is found to depend on the intensity of UV light, that is, photoinduced bending is switched to photosalient phenomena by increasing the light intensity. The change in the size of the crystal unit cell upon UV irradiation is larger for asymmetric diarylethenes with thiazole and thiophene rings than that for the corresponding symmetric diarylethenes. As a result, the crystals of an asymmetric diarylethene show much more drastic photosalient effects than those of the corresponding symmetric diarylethene crystals upon UV irradiation. It is also found that the crystals of diarylethene, which have not previously been reported to exhibit a photosalient effect, show photosalient phenomena upon irradiation with strong UV light. Furthermore, the dependence of photosalient phenomena on the size and shape of the crystals is reported.     

Retarded Solid‐State Rotations of an Oval‐Shaped Guest in a Deformed Cylinder with CH–π Arrays

Upon encapsulating an oval‐shaped hydrocarbon guest, a cylindrical host deforms its shape to maximize intermolecular contacts. Structure–assembly relationship studies with a series of hydrocarbon guests disclosed the importance of molecular shapes and CH–π contacts. Multiple contacts and weak CH–π hydrogen bonds resulted in an optimal assembly; however, the shape deformation resulted in severe retardation of rotational motions in the crystal. Thus, unlike a circular guest, the oval‐shaped guest did not change its orientation in the host. Unexpectedly, the planar guest did not affect the packing structure to form a double helix in intertwined host arrays.     

Synthesis of Functionalized Ketones from Acid Chlorides and Organolithiums by Extremely Fast Micromixing

Synthesis of ketones containing various functional groups from acid chlorides bearing electrophilic functional groups and functionalized organolithiums was achieved using a flow microreactor system. Extremely fast mixing is important for high chemoselectivity.     

Palladium(0)‐Mediated Rapid Methylation and Fluoromethylation on Carbon Frameworks by Reacting Methyl and Fluoromethyl Iodide with Aryl and Alkenyl Boronic Acid Esters: Useful for the Synthesis of [11C]CH3?C‐ and [18F]FCH2?C‐Containing PET Tracers (PET=Positron Emission Tomography)

A new synthetic methodology for the rapid methylation and fluoromethylation on aryl and alkenyl frameworks by using methyl and fluoromethyl iodide with an organoboronic acid ester has been developed under the simple and mild conditions of [Pd₂(dba)₃]/P(o‐CH₃C₆H₄)₃/K₂CO₃ (dba= dibenzylideneacetone) in DMF at 60 °C for 5 min (see scheme). This boron protocol provides a firm chemical basis for the synthesis of ¹¹C‐ and ¹⁸F‐incorporated PET tracers.

     

Viscoelastic behavior of PMMA/grafted PBA nanoparticle systems in the molten state

The viscoelastic properties of poly(methyl methacrylate) (PMMA)/grafted poly(butyl acrylate) (PBA) nanoparticle systems were investigated. The rubber particles consist of PBA core (60 nm in diameter) and grafted PMMA shell. The grafting degree, defined as the weight ratio of grafted PMMA to PBA particles, ranges from 0.8 to 1.5. Two series of samples, A series with 7.5 wt.% of PBA content and B series with 12 wt.% of PBA content, were used. The systems exhibited fast and slow relaxation process, the former reflecting the relaxation of the matrix PMMA chains and the latter being attributed to grafted PBA particles. For A series samples, time-temperature superposition (TTS) was held well over the frequency (ω) and temperature (T) ranges measured. However, for B series samples, TTS was not satisfied at low ω due to the particle-particle interaction of grafted PBA particles, although the samples obeyed TTS at high ω associated with the relaxation with entanglement of matrix PMMA. At high T and low ω region, the B series samples showed a sol-gel transition at elevating T and the critical gel behavior characterized with a power-law relationship, G′ = G″/tan(nπ/2) ∝ ωⁿ, was observed. This behavior suggested formation of a self-similar, fractal structure of grafted PBA particles. The critical gel temperature (T _gel) and the critical exponent (n) were determined for the B series samples. TEM observations revealed that as-prepared A and B samples had well-dispersed particles but the B samples after viscoelastic measurements had fragmented networks of the PBA particles, confirming that the sol-gel transition occurred for the PMMA/grafted PBA systems at elevating T.     

Proton-neutron correlations in nuclei with N = 30

Structure of the nuclei with N = 30 and Z = 20–28 is investigated by the nuclear shell model within the proton-neutron configurations (1f_{$\text{7}\text{2}$})^z?20_p × (2p_{$\text{3}\text{2}$}, 2p_{$\text{case1}\text{2}$}, 1f_{$\text{case5}\text{2}$})²_n. Effective proton-neutron interactions determined by a least-squares fit to the observed spectra of N = 29 nuclei are adopted. Agreement of the calculated spectra with experimental spectra is satisfactory. Strong correlations between protons and neutrons break down the pairing scheme and lower the first J = 2 levels in doubly even nuclei, which is shown from the resultant wave functions. A relation between the shell model and collective rotational model is discussed concerning the calculated rotation-like spectrum of ⁵⁶Fe. Electromagnetic properties and spectroscopic factors of single-nucleon transfer reactions are calculated. They are in good agreement with experiments.