Preparation and colloidal stability of monodisperse magnetic polymer particles

A previously proposed method was examined for producing monodisperse, submicrometer-sized magnetic polymer particles. The method applies soap-free emulsion polymerization during which Fe3O4 magnetic nanoparticles are heterocoagulated onto precipitated polymer nuclei. To chemically fix the magnetic particles to the polymer nuclei, vinyl groups were introduced on the Fe3O4 particles in a preliminary surface modification reaction with methacryloxypropyltrimethoxysilane, and methacryloxypropyldimethoxysilane (MPDMS) was added to reaction systems of the soap-free emulsion polymerization. The colloidal dispersion stability of magnetic polymer particles was improved by the addition of an ionic monomer, sodium p-styrenesulfonate (NaSS), during the polymerization. The polymerizations were carried out with styrene monomer and potassium persulfate initiator in ranges of NaSS concentrations (0-2.4 x 10(-3) M), NaSS addition times (60-80 min), and monomer concentrations (0.3-0.6 M) at fixed concentrations of 1.6 x 10(-2) M initiator and 1.3 x 10(-2) M MPDMS for pH 4.5 adjusted with a buffer system of [CH3COOH]/[NaOH]. The addition of NaSS during the polymerization could maintain the dispersion stability of magnetic polymer particles during the polymerization. Selection of the reaction conditions enabled the preparation of colloidally stable, submicrometer-sized magnetic polymer particles that had coefficients of variation of distribution smaller than the standard criterion for monodispersity, 10%.     

Colorimetric determination of traces of tin with dithiol

Procedures are given for the determination of traces of tin with dithiol (4-methyl-1,2-dimer-captobenzene) by visual color comparison and absorptiometric measurement, with special reference to silicate rocks, meteorites, and sulfides. The sensitivity is 1 p.p.m. Sn with 0.5 g of sample. Tin is separated by distillation of the bromide. Provision is made for the presence of selenium.     

Molecular dynamics study of thermal phenomena in an ultrathin liquid film sheared between solid surfaces: the influence of the crystal plane on energy and momentum transfer at solid-liquid interfaces

A molecular dynamics study has been performed on a liquid film sheared between moving solid walls. Thermal phenomena that occur in the Couette-like flow were examined, including energy conversion from macroscopic flow energy to thermal energy, i.e., viscous heating in the macroscopic sense, and heat conduction from the liquid film to the solid wall via liquid-solid interfaces. Four types of crystal planes of fcc lattice were assumed for the surface of the solid wall. The jumps in velocity and temperature at the interface resulting from deteriorated transfer characteristics of thermal energy and momentum at the interface were observed. It was found that the transfer characteristics of thermal energy and momentum at the interfaces are greatly influenced by the types of crystal plane of the solid wall surface which contacts the liquid film. The mechanism by which such a molecular scale structure influences the energy transfer at the interface was examined by analyzing the molecular motion and its contribution to energy transfer at the solid-liquid interface.     

Hydrogen isotope behavior and its interaction with post irradiated energetic helium in SiC

The D₂ ⁺ was irradiated into SiC up to the saturation and thereafter He⁺ irradiation was performed to elucidate interaction mechanism between hydrogen isotope retained in SiC and irradiated energetic He⁺ by means of X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). It was found that D was trapped by both of Si and C by D₂ ⁺ irradiation and only D bound to Si interacted with irradiated He⁺ in the initial He⁺ irradiation stage. Some damaged structures were introduced into SiC by both of D₂ ⁺ and He⁺ irradiation. By heating after the irradiation experiments, most of SiC structure was recovered at the temperature above 1000 K. However, some free C was migrated toward the surface and aggregated on the surface of SiC. This fact indicates that the C impurity would contaminate the plasma and/or the tritium breeding materials, which is thought to be contacted with the SiC inserts.     

Right-handed helical structure of expanded oligo(L-leucine) containing [Ru(terpyridine)2]2+ moieties

Expanded oligo(l-leucine)s, containing an alternate arrangement of a bis(terpyridine)ruthenium(II) moiety and a l-leucine residue, were synthesized and characterized by 1H NMR, UV, CD, and electrochemical properties. The intensity of CD spectra per ruthenium unit increased with the elongation of the peptide chain. 1H NMR analysis of a tetramer indicated the right-handed helical structure in acetonitrile.     

Rotational isomerism involving an acetylenic carbon IV: synthesis and structure of bis(1,1';3',1"-terphenyl-2'-yl)ethynes: molecular design of sterically congested alkynes toward restricted rotation about acetylenic axis

The title diphenylethyne derivative with 4-methylphenyl (tolyl) groups at all the ortho positions was synthesized by the Stille or Sonogashira coupling from the corresponding iodide. The X-ray structure revealed that the two terminal phenyl groups at the sp carbons are twisted by 63 degrees out of the coplanar conformation to avoid steric interactions between the tolyl groups. The relative stabilities of possible conformers were analyzed by the PM3 calculations. The axially chiral derivative with two methoxymethyl groups showed no evidence of restricted rotation about the acetylenic axis by VT NMR measurements, its barrier being less than 35 kJ mol(-1). The spectroscopic features and reactivities of this sterically congested alkyne are also described.     

Surface site density and utilization of platinum group metal (PGM)-free Fe–NC and FeNi–NC electrocatalysts for the oxygen reduction reaction

Pyrolyzed iron-based platinum group metal (PGM)-free nitrogen-doped single site carbon catalysts (Fe–NC) are possible alternatives to platinum-based carbon catalysts for the oxygen reduction reaction (ORR). Bimetallic PGM-free M₁M₂–NC catalysts and their active sites, however, have been poorly studied to date. The present study explores the active accessible sites of mono- and bimetallic Fe–NC and FeNi–NC catalysts. Combining CO cryo chemisorption, X-ray absorption and ⁵⁷Fe Mössbauer spectroscopy, we evaluate the number and chemical state of metal sites at the surface of the catalysts along with an estimate of their dispersion and utilization. Fe L_3,2-edge X-ray adsorption spectra, Mössbauer spectra and CO desorption all suggested an essentially identical nature of Fe sites in both monometallic Fe–NC and bimetallic FeNi–NC; however, Ni blocks the formation of active sites during the pyrolysis and thus causes a sharp reduction in the accessible metal site density, while with only a minor direct participation as a catalytic site in the final catalyst. We also use the site density utilization factor, ϕ_{SDsurface/bulk}, as a measure of the metal site dispersion in PGM-free ORR catalysts. ϕ_{SDsurface/bulk} enables a quantitative evaluation and comparison of distinct catalyst synthesis routes in terms of their ratio of accessible metal sites. It gives guidance for further optimization of the accessible site density of M–NC catalysts.

The gravimetric surface density and ORR catalytic turnover frequency of Fe–NC and Fe/Ni–NC catalysts were investigated. Both catalysts feature chemically identical Fe sites, but the presence of Ni lowered the gravimetric surface density of Fe sites.     

Synthesis of spiro[4.5]decane and bicyclo[4.3.0]nonane ring systems by self-cyclization of (Z)- and (E)-2-(trimethylsilylmethyl)pentadienal derivative

The two title carbon frameworks were synthesized utilizing a new type of iron-induced cyclization reaction of 2-(trimethylsilylmethyl)pentadienal. 2-Methylspiro[4.5]dec-2-en-1-one was obtained from (Z)- and (E)-4-cyclohexylidene-2-(trimethylsilylmethyl)but-2-enal. It was found that the (Z)-substrate isomerized to (E)-intermediate followed by cyclization to afford the initial product, 2-methylenespiro[4.5]dec-3-en-1-ol, which was isomerized to the above product. The cyclization of 4-(4-alkyl)cyclohexylidene-2-(trimethylsilylmethyl)but-2-enal proceeded stereoselectively. While, (E)-3-(cyclohex-1-en-1-yl)-2-(trimethylsilylmethyl)prop-2-en-1-al cyclized immediately affording 8-methylenebicyclo[4.3.0]non-9-en-7-ol. The corresponding (Z)-isomer gave several cyclization products as a complex mixture.     

Regioselective nucleophilic addition of triphenylphosphine to the nitrosylruthenium alkynyl complexes having a hydrotris(pyrazol-1-yl)borate: formation of phosphonio-alkenyl, alkynyl, and allenyl species

A nitrosylruthenium alkynyl complex of TpRuCl(C[triple bond]CPh)(NO)(1a) was reacted with PPh3 in the presence of HBF4.Et2O at room temperature to give a beta-phosphonio-alkenyl complex (E)-[TpRuCl{CH=C(PPh3)Ph}(NO)]BF4(2.BF4). On the other hand, for gamma-hydroxyalkynyl complexes TpRuCl{C[triple bond]CC(R)2OH}(NO)(R = Me (1b), Ph (1c), H (1d)), similar treatments with PPh3 were found to give gamma-phosphonio-alkynyl [TpRuCl{C[triple bond]CC(Me)2PPh3}(NO)]BF4(3.BF4),alpha-phosphonio-allenyl [TpRuCl{C(PPh3)=C=CPh2}(NO)]BF4(4.BF4), and a novel product of gamma-hydroxy-beta-phosphonio-alkenyl (E)-[TpRuCl{CH=C(PPh3)CH2OH}(NO)]BF4(5.BF4), respectively. Dominant factors for the selectivity in affording 3-5 were associated with the steric congestion and electronic properties at the gamma-carbons, along with those around the metal fragment. From the bis(alkynyl) complex TpRu(C[triple bond]CPh)2(NO)6, a bis(beta-phosphonio-alkenyl)(E,E)-[TpRu{CH=C(PPh3)Ph}2(NO)](BF4)2{7.(BF4)2} was produced at room temperature. However, similar reactions at 0 degrees C gave an alkynyl beta-phosphonio-alkenyl complex (E)-[TpRu(C[triple bondCPh){CH=C(PPh3)Ph}(NO)]BF4(8.BF4) as a sole product, of which additional hydration in the presence of HBF4.Et2O afforded a [small beta]-phosphonio-alkenyl ketonyl (E)-[TpRu{CH2C(O)Ph}{CH=C(PPh3)Ph}(NO)]BF(.9BF4). Five complexes, 2-5 and 7 were crystallographically characterized.     

Ru3(CO)12-catalyzed C-H/CO/olefin coupling of N-pyridylindolines. Direct carbonylation at a C-H bond delta to the pyridine nitrogen

The reaction of N-pyridylindolines with CO and ethylene in the presence of Ru3(CO)12 results in direct carbonylation at a C-H bond delta to the pyridine sp2 nitrogen, which represents a new type of C-H/CO/olefin coupling. The presence of a pyridine ring as a directing group on the substrates is essential for the reaction to proceed. The choice of N,N-dimethylacetamide (DMA) as the solvent is crucial for the reaction to proceed efficiently.