First Precision Spectroscopy of Pionic Atoms at RI Beam Factory

We conducted an inclusive missing-mass spectroscopy of ¹²²Sn (d, ³He) reaction near the π¯ emission threshold at an incident energy of T _d = 250 MeV/nucleon. The experiment sets its goals to the research and development of the high precision spectroscopy of pionic atoms at the RI beam factory (RIBF) of RIKEN, which precedes a new project, pionic atom factory project (piAF), to observe pionic atoms systematically. Here, we report the preliminary results of the pilot experiment.     

Fusing C<Subscript>60</Subscript> units without Stone–Wales bond rotations

Abstract  Using ab-initio calculation, we have explored new chemical paths for the coalescence of C₆₀ units into higher fullerenes and novel structures. Besides the Stone–Wales paradigm used for rationalizing the fusion of fullerenes and nanotubes, we demonstrated that an alternative path exists for the fusion of two C₆₀ units. This path uses successive “π–π” additions and subsequent bond reorganizations to lead to a specific C₁₂₀ peanut-like structure. The energies of the chemical barriers, the intermediate structures, and the final product are markedly lower than their counterparts found in the chemical paths based on Stone–Wales bond rotations. The results rationalize the existence of a temperature range in which peanut-like structures are obtained during thermal treatment of peapod structures. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Theoretical studies to understand surface chemistry on carbon anodes for lithium-ion batteries: how does vinylene carbonate play its role as an electrolyte additive?

To elucidate the role of vinylene carbonate (VC) as a solvent additive in organic polar solutions for lithium-ion batteries, reductive decompositions for vinylene carbonate (VC) and ethylene carbonate (EC) molecules have been comprehensively investigated both in the gas phase and in solution by means of density functional theory calculations. The salt and solvent effects are incorporated with the clusters (EC)nLi+(VC) (n = 0-3), and further corrections that account for bulk solvent effects are added using the polarized continuum model (PCM). The electron affinities of (EC)nLi+(VC) (n = 0-3) monotonically decrease when the number of EC molecules increases; a sharp decrease of about 20.0 kcal/mol is found from n = 0 to 1 and a more gentle variation for n > 1. For (EC)nLi+(VC) (n = 1-3), the reduction of VC brings about more stable ion-pair intermediates than those due to reduction of the EC molecule by 3.1, 6.1, and 5.3 kcal/mol, respectively. This finding qualitatively agrees with the experimental fact that the reduction potential of VC in the presence of Li salt is more negative than that of EC. The calculated reduction potentials corresponding to radical anion formation are close to the experimental potentials determined with cyclic voltammetry on a gold electrode surface (-2.67, -3.19 eV on the physical scale for VC and EC respectively vs experimental values -2.96 and -2.94 eV). Regarding the decomposition mechanisms, the VC and EC moieties undergo homolytic ring opening from their respective reduction intermediates, and the energy barrier of VC is about one time higher than that of EC (e.g., 20.1 vs 8.8 kcal/mol for (EC)2Li+(VC)); both are weakly affected by the explicit solvent molecules and by a bulk solvent represented by a continuum model. Alternatively, starting from the VC-reduction intermediate, the ring opening of the EC moiety via an intramolecular electron-transfer transition state has also been located; its barrier lies between those of EC and VC (e.g., 17.2 kcal/mol for (EC)2Li+(VC)). On the basis of these results, we suggest the following explanation about the role that VC may play as additive in EC-based lithium-ion battery electrolytes; VC is initially reduced to a more stable intermediate than that from EC reduction. One possibility then is that the reduced VC decomposes to form a radical anion via a barrier of about 20 kcal/mol, which undergoes a series of reactions to give rise to more active film-forming products than those resulting from EC reduction, such as lithium divinylene dicarbonate, Li-C carbides, lithium vinylene dicarbonate, R-O-Li compound, and even oligomers with repeated vinylene and carbonate-vinylene units. Another possibility starting from the VC-reduction intermediate is that the ring opening occurs on the unreduced EC moiety instead of being on the reduced VC, via an intramolecular electron transfer transition state, the energy barrier of which is lower than that of the former, in which VC just helps the intermediate formation and is not consumed. The factors that determine the additive functioning mechanism are briefly discussed, and consequently a general rule for the selection of electrolyte additive is proposed.     

Total synthesis of (+/-)-trachyspic acid and determination of the relative configuration

[reaction: see text] The first total synthesis of (+/-)-trachyspic acid, a tumor cell heparanase inhibitor, was accomplished based on Cr(II)/Ni(II)-mediated reaction of the aldehyde containing the citric acid moiety and the long-chain triflate, and the relative configuration of this natural product was determined.     

MBE growth of multiple quantum wells with room-temperature exciton peaks at 1.3 μm

multiple quantum wells have been grown lattice matched on InP substrates by taking into account the time dependence of the fluxes as the shutters open and close. RHEED oscillations are observed and used to calibrate layer thicknesses and growth quality. The half width of the lowest exciton peak is 12 meV.     

Microcomputer-aided high-speed potentiometric titration system by linear titration plots

Summary An apparatus for high-speed potentiometric titration was assembled and its advantage was demonstrated. Titrant additions were made stepwise in large volumes. The optimum increment volumes were automatically chosen by microcomputer, depending upon the sample concentration. Time intervals between the successive additions were controlled so as to add a new increment immediately after the electrode was equilibrated. On-line calculation of the equivalence volume was conducted based upon linear titration plots, using only four titration points before the equivalence point. The apparatus was capable of determining the concentration of strong and weak monoprotic acids in less than 22s with relative standard deviations of 0.1–0.2%.

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Potentiometrisches Titrationssystem hoher Geschwindigkeit, das auf linearen Titrationskurven beruht und mit einem Mikrocomputer arbeitet

Zusammenfassung Der Aufbau des Geräts wird beschrieben und seine Vorzüge werden diskutiert. Die Zugabe des Titrationsmittels erfolgt stufenweise in großen Anteilen. Die optimalen Volumina werden automatisch je nach Konzentration von einem Mikrocomputer bestimmt. Die Zeitintervalle zwischen den Zugaben werden so gesteuert, daß jeweils nach Gleichgewichtseinstellung der Elektrode eine neue Zugabe erfolgt. Aufgrund linearer Eichkurven erfolgt die online Berechnung des Äquivalenzvolumens, wobei nur vier Titrationspunkte vor dem Äquivalenzpunkt verwendet werden. Mit Hilfe des Gerätes können starke und schwache monoprotische Säuren in weniger als 22 s mit einer relativen Standardabweichung von 0,1–0,2% bestimmt werden.

     

Polymere Brenzcatechin-Derivate. 2. Mitt. Über die alternierende Copolymerisation von 4-Propenyl-brenzcatechin-Derivaten mit Maleinsäureanhydrid durch Tributylboran

Ohne Zusammenfassung     

Theoretical study on the photochromic cycloreversion reactions of dithienylethenes; on the role of the conical intersections

The mechanism of the photochromic cycloreversion reactions is theoretically examined in a model system of dithienylethenes by means of the CASSCF and CASPT2 methods. The structures of its conical intersections (CIs), which are the branching points of the internal conversions, were obtained. The analyses of the minimum energy paths from the Franck-Condon states and the CI points suggest that the cycloreversion reaction occurs during the intramolecular vibrational energy redistribution (IVR) toward the quasi-equilibrium on the 2A state. The current study of the model system will provide a basic insight for the photochromic molecular design.     

Nickel enolates in the Ni(CO)4 -induced carbonylation of gem-dibromocyclopropanes with silylamine or silylsulfide

Silyl compounds (N,N-dialkyltrimethylsilylamine, 1-(trimethylsilyl)-imidazole and phenylthiotrimethylsilane) were successfully used in the Ni(CO)₄ -induced carbonylation reactions of gem-dibromocyclopropanes. The nickel carbenoid and enolate complexes are considered to be involved as key intermediates. Protonation afforded the cyclopropanecarboxylic acid derivatives. The presence of an electrophile achieved another stereoselective carbon-carbon bond formation via the nickel enolate intermediate.     

Complete mitochondrial DNA sequence of a tadpole shrimp (Triops cancriformis) and analysis of museum samples

The complete mitochondrial DNA (mtNDA) of the tadpole shrimp Triops cancriformis was sequenced. The sequence consisted of 15,101 bp with an A+T content of 69%. Its gene arrangement was identical with those sequences of the water flea (Daphnia pulex) and giant tiger prawn (Penaeus monodon), whereas it differed from that of the brine shrimp (Artemia franciscana) in the arrangement of its genes for tRNAs. Phylogenetic analysis revealed T. cancriformis to be more closely related to the water flea than to the brine shrimp and giant tiger prawn. We also compared the 16S rRNA sequences of five formalin-fixed tadpole shrimps that had been collected in five different locations and stored in a museum. The sequence divergence was in the range of 0-1.51%, suggesting that those samples were closely related to each other.