Synthetic study of manzamine B: synthesis of the tricyclic central core by an asymmetric Diels-Alder and RCM strategy

Tricyclic core of manzamine B was successfully synthesized through asymmetric Diels-Alder reaction and RCM strategy. Cr-salen-F complex was found to be the most effective catalyst in DA reaction of aminodienes with heterocyclic dienophiles to give up to 97% ee. In the construction of 11-membered ring by RCM, first-Grubbs cat. gave better stereoselectivity.     

13C-selective two-stage IRMPD of mixtures of CHClF2 and HI

The ¹³C-selective infrared multiple-photon decomposition (IRMPD) of mixtures of CHClF₂ and HI was examined in collimated and focused beam geometries using a CO₂TEA laser. The carbon-containing products were CH₂F₂ and CHF₂I. The former product showed remarkably high ¹³C atom concentrations beyond 95% under selected experimental conditions, while the latter contained 25% or less. The observed results can be explained satisfactorily in terms of the consecutive two-stage IRMPD process occurring in a single irradiation procedure, where the first-stage IRMPD of natural CHClF₂ produces ¹³C-enriched CHF₂I via the insertion of the initial decomposition fragment CF₂ into HI, and the second stage is the subsequent ¹³C-selective IRMPD of the CHF₂I to form a CHF₂ radical and an I atom. The CHF₂ radical reacts with HI to form CH₂F₂. Decomposition probabilities of ¹²CHClF₂ and ¹³CHClF₂ were measured as a function of laser fluence to optimize enrichment conditions. Furthermore, partial decomposition probabilities or relative production yields were measured as functions of laser line, pressure of HI, and pressure of CHClF₂. Both stages showed high ¹³C selectivities in the irradiation with the laser radiation around 1040 cm^–1 and at fluences below 4 J cm^–2. This mixture is one of the most promising chemical systems for the production of highly enriched ¹³C.     

Modeling and analysis of nonholonomic dynamic systems with a class of rheonomous affine constraints

This paper is devoted to modeling and theoretical analysis of dynamic control systems subject to a class of rheonomous affine constraints, which are called $A$ -rheonomous affine constraints. We first define $A$ -rheonomous affine constraints and explain their geometric representation. Next, a necessary and sufficient condition for complete nonholonomicity of $A$ -rheonomous affine constraints is shown. Then, we derive nonholonomic dynamic systems with $A$ -rheonomous affine constraints (NDSARAC), which are included in the class of nonlinear control systems. We also analyze linear approximated systems and accessibility for the NDSARAC. Finally, the results are applied to some physical examples in order to check the application potentiality.     

Ab initio study of the polymerisation of cyclopentasilane

The molecular structures and vibration modes of cyclopentasilane (Si₅H₁₀) have been examined by employing ab initio and density-functional methods. Three different structures of Si₅H₁₀ with different symmetries are analysed, and the results show that the envelope (C _s ) and the twist (C₂) forms have similar energies and that the planar form (D_5h ) is about 50 meV less stable than the C _s and C₂ forms. The excited-state potential energy surface of Si₅H₁₀ is performed using the CIS electronic energy calculation. The ring-open reaction of Si₅H₁₀ is investigated in detail by using the first-principles molecular-dynamics simulation for screening the reaction pathways. The formation of Si–H–Si is found to play an important role in the ring-open reaction.     

Effects of spin ordering on phonon and plasmon spectra,and dielectric properties in magnetic semiconductors

Effects of spin ordering on the phonons, plasmons, and dielectric properties have been investigated for many magnetic crystals, such as Cr-spinels, EuX (X = O, S, Se, Te), and fluorite-type compounds. Of these phenomena, the static dielectric constant and Raman scattering have been extensively discussed. However, the dielectric parameters obtained from infrared spectra have not been discussed in spite of observed various phenomena arising from the direct coupling of spin system with phonons or electrons. Furthermore, these microscopic phenomena can be combined with the macroscopic dielectric values with respect to the spin ordering effect. It will ascertain the mechanism of the spin ordering effect on the values. From this point of view, we review the spin-dependent phenomena on the frequencies of TO and LO phonon modes, phonon damping, optical and static dielectric constants, effective charge, and also on plasmon parameters in the spinel type magnetic semiconductors.     

In situ observation of containerless solidification from undercooled Lu2O3 and Y2O3 melts

Containerless solidification processes in undercooled Lu₂O₃ and Y₂O₃ melts were investigated using an aerodynamic levitation furnace and a high-speed video. Double recalescence, indicative of two successive phase transitions, was observed for both oxides. The melting point following the first recalescence (T _M1) was higher than that of the second (T _M2) for Y₂O₃, which suggests that Y₂O₃ has a phase transition from a melt to a high temperature phase at T _M1, and then to a room temperature phase at T _M2. Two solid phases of Lu₂O₃ were also identified at T _M1 and T _M2. However, in contrast to Y₂O₃, T _M1 was lower than T _M2 for Lu₂O₃. This implies that the first crystallized phase from a melt is a metastable phase. The life duration of this metastable Lu₂O₃ was in the order of tens of milliseconds.     

Morphology-mechanical property relationship of a polystyrene-polybutadiene-polystyrene block copolymer and its blends with homopolymers

The morphology-mechanical property relation was investigated on a polystyrene-polybutadiene-polystyrene (SBS) block copolymer and its blends with polystyrenes (PS) and polybutadienes (PB) cast from a THF/MEK mixture (T/M) and a cyclohexane/benzene mixture (C/B). As-cast films with alternating lamellar morphology such as SBS (T/M) always show high moduli and “plastic-torubber” transitions, while those with PS-dispersed-in-PB-matrix morphology always exhibit low moduli and crosslinked rubberlike behavior. All these systems undergo strain-induced softening, accompanying breakdown of glassy PS domains, and show rubberlike behavior, regardless of the sample prehistory. However, upon annealing under adequate conditions, all these softened systems eventually revert to their original morphology and behavior.     

Electrochemical detection for dynamic analyses of a redox component in droplets using a local redox cycling-based electrochemical (LRC-EC) chip device

This report describes the electrochemical detection of a redox component in droplets using a local redox cycling-based electrochemical (LRC-EC) chip device consisting of 256 sensors. The time-course analyses showed that the redox compound in the droplet was dynamically changed during droplet evaporation or mass transfer through a water/oil interface.     

Iron-catalysed cross-coupling of halohydrins with aryl aluminium reagents: a protecting-group-free strategy attaining remarkable rate enhancement and diastereoinduction

Non-protected halohydrins are cross-coupled with aryl aluminium reagents to produce aryl alkanols in the presence of the iron-bisphosphine catalysts. Remarkable reaction rate enhancement and diastereoinduction are realized by the in situ generated aluminium alkoxides, offering a new method for the reactivity and selectivity control of the iron-catalysed cross-coupling reaction.