Polymerization of substituted olefins initiated by organometallic compounds of titanium (IV)

Polymerization tests were carried out in homogeneous systems on various substituted olefins CH₂=CRZ (R = H or CH₃; Z = CN, COOR, C₆H₅ or OCOR) with compounds of titanium (IV) Ti X_4?x Y_x (X and/or Y = Cl, OR, NR₂, C₅H₅, OCH₂ CF₃, CH₃, C₆H₅ …) or with the bimetallic complex CH₃Ti(OR)₃, Al(CH₃)₃. The activity of the initiator varies with the co-ordination environment of the titanium and to a considerable extent with the functional groups linked to the olefin.     

Molecular Level Characterization of the Structure and Interactions in Peptide‐Functionalized Metal–Organic Frameworks

We use density functional theory, newly parameterized molecular dynamics simulations, and last generation ¹⁵N dynamic nuclear polarization surface enhanced solid‐state NMR spectroscopy (DNP SENS) to understand graft–host interactions and effects imposed by the metal–organic framework (MOF) host on peptide conformations in a peptide‐functionalized MOF. Focusing on two grafts typified by MIL‐68‐proline ( ‐Pro ) and MIL‐68‐glycine‐proline ( ‐Gly‐Pro ), we identified the most likely peptide conformations adopted in the functionalized hybrid frameworks. We found that hydrogen bond interactions between the graft and the surface hydroxyl groups of the MOF are essential in determining the peptides conformation(s). DNP SENS methodology shows unprecedented signal enhancements when applied to these peptide‐functionalized MOFs. The calculated chemical shifts of selected MIL‐68‐NH‐ Pro and MIL‐68‐NH‐ Gly‐Pro conformations are in a good agreement with the experimentally obtained ¹⁵N NMR signals. The study shows that the conformations of peptides when grafted in a MOF host are unlikely to be freely distributed, and conformational selection is directed by strong host–guest interactions.     

Synthesis and microstructural TEM investigation of CaCu3Ru4O12 ceramic and thin film

CaCu₃Ru₄O₁₂ (CCRO) is a conductive oxide having the same structure as CaCu₃Ti₄O₁₂ (CCTO) and close lattice parameters. The later compound is strongly considered for high density parallel plates capacitors application due to its so-called colossal dielectric constant. The need for an electrode inducing CCTO epitaxial growth with a clean and sharp interface is therefore necessary, and CCRO is a good potential candidate. In this paper, the synthesis of monophasic CCRO ceramic is reported, as well as pulsed laser deposition of CCRO thin film onto (001) NdCaAlO₄ substrate. Structural and physical properties of bulk CCRO were studied by transmission electron microscopy and electron spin resonance. CCRO films and ceramic exhibited a metallic behavior down to low temperature. CCRO films were (001) oriented and promoted a CCTO film growth with the same orientation.     

Modeling of Induction Plasma Process for Fullerene Synthesis: Effect of Plasma Gas Composition and Operating Pressure

A mathematical model has been developed on the continuous synthesis of fullerenes by direct evaporation of carbon-containing materials using induction thermal plasma technology. The main purpose of this study is to numerically investigate the effect of plasma gas composition and operating pressure on the fullerene formation. The simulation results confirmed that Ar–He mixture plasma is more efficient than argon plasma in terms of the particle evaporation, generation of fullerene precursors, fullerene growth and their annealing, and that low pressure operation would decrease the overall yield rate of fullerenes by enhancing the radial diffusion of carbon vapors towards the reactor walls. Thus an operating condition of relatively high helium content in the plasma gas and elevated gas pressure seems much more desirable for achieving a high yield rate of fullerenes. This conclusion is in line with the experimental evidences reported previously.     

Lax equations in 10-dimensional supersymmetric classical Yang-Mills theories

Savelies and the author recently showed that there exists an on-shell light-cone gauge where the nonlinear part of the field equations reduces to a (super) version of the Yang equations that can be solved using methods inspired by those previously developed for the self-dual Yang-Mills equations in four dimensions. Here the analogy between these latter theories and the present ones is extended by writing a set of super linear partial differential equations that have consistency conditions derivable from the supersymmetric Yang Mills equations in 10 dimensions and are analogues of the Belavin-Zakharov Lax pair. In the simplest example of the two-pole ansatz, the same solution-generating techniques work as in the derivation of the multi-instanton solutions in the late 1970s. The present Lax representation, however, is only a consequence of Gn-tead of being equivalent to) the field equations, in contrast to the Belavin-Zakharov Lax pair. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 123, No. 2, pp. 189–197, May, 2000.     

Infrared reflectivity spectroscopy of electron-phonon interactions

The crucial role of electron-phonon interactions and their signatures in optical conductivity deduced from the analysis of infrared-visible reflection spectra is reviewed. The usefulness of a general phenomenological model able to describe the couplings of phonons, polarons, plasmon, superconducting condensate, is discussed. Among other examples of applications, the problem of the signature of Cooper pair condensation in the superconducting phase of high-T _c cuprates is discussed in the framework of London and Mattis-Bardeen models.     

Stereoselective Total Synthesis of Sesquiterpenoids: (+)-Sativene and (+)-Cyclosativene

Abstract

The well-known tricyclic sesquiterpenoid (?)-sativene, isolated in 1965 from Helminthosporium sativum and shown to possess structure and absolute configuration as indicated by structure 1 ³, has been implicated^3,4 as an intermediate in the biogenesis of the fungal toxin (?)-helminthosporal (2)⁵. Two total syntheses of the racemic modification of sativene have been reported^6,7. A closely related sesquiterpenoid, (+)-cyclosativene, was isolated from Abies magnifica A. Murr. and was shown to possess structure 3 ^8,9. The absolute configuration of this material, although not established unambiguously, has been proposed¹⁰ as indicated by formula 3. The total synthesis of cyclosativene has not as yet been achieved directly, although it has been obtained indirectly via acid-promoted rearrangement of sativene^8,9,11,12. We report herein a total synthesis of (+)-sativene (4) and (+)-cyclosativene (3) via a stereoselective route which unambiguously establishes the absolute configuration of both natural products.     

N‐Trifluoromethyl Hydrazines,Indoles and Their Derivatives

Reported herein is the first efficient strategy to synthesize a broad range of unsymmetrical N‐CF₃ hydrazines, which served as platform to unlock numerous currently inaccessible derivatives, such as tri‐ and tetra‐substituted N‐CF₃ hydrazines, hydrazones, sulfonyl hydrazines, and valuable N‐CF₃ indoles. These compounds proved to be remarkably robust, being compatible with acids, bases, and a wide range of synthetic manipulations. The feasibility of RN(CF₃)‐NH₂ to function as a directing group in C?H functionalization is also showcased.