Étude par spectroscopie infrarouge de la structure du cation mg(h2o)62+ dans quelques sels de magnésium hydratés

The infrared spectra of eight hexahydrated magnesium salts have been investigated in the 4000-2000 cm^?1 range. The stretching H₂O, D₂O and HDO water bands are discussed. Two types of hydrogen bond depending on the acceptor properties of the anion can be distinguished: the water molecules are bonded to anions or to other water molecules.     

Chiroptical switching polyguanidine synthesized by helix-sense-selective polymerization using [(R)-3,3'-dibromo-2,2'-binaphthoxy](di-tert-butoxy)titanium(IV) catalyst

A series of chiral binaphthyl titanium alkoxide complexes were synthesized. Among them, chiral titanium complex [(R)-3,3'-dibromo-2,2'-binaphthoxy](di-tert-butoxy)titanium(IV) (R-3) exists as a crystallographic C2 dimer in the solid state but a monomer in solution at room temperature. Application of R-3 in the helix-sense-selective polymerization of achiral carbodiimide, N-(1-anthryl)-N'-octadecylcarbodiimide (1), yielded a well-defined regioregular, stereoregular poly[N-(1-anthryl)-N'-octadecylguanidine] (poly-1b) with a relatively narrow polymer dispersity index of 2.7. Full racemization of poly-1b at +80 degrees C in toluene requires more than 100 h. Interestingly, poly-1b was found to undergo fast reversible chiroptical switching at +38.5 degrees C in toluene. Furthermore, at room temperature, poly-1b shows a positively signed Cotton effect in toluene, but negative ones in THF and chloroform, respectively. The chiroptical switching takes place around the toluene content of 90% (vol) in the mixed toluene/THF solvents. This is the first example of chiroptical switching phenomenon occurring in a helical polymer possessing no chiral moieties in the polymer chains. We believe this reversible chiroptical switching phenomenon occurs by reorientation of anthracene rings relative to the chain director.     

Conformal properties of nonpeeling vacuum space-times

In a previous paper we investigated a class ofnonpeeling asymptotic vacuum solutions which were shown to admit finite expressions for the Winicour-Tamburino energy-momentum and angular momentum integrals. These solutions have the property that $$\psi _0 = O(r^{ - 3 - \in _0 } ), \in _0 \leqslant 2$$ and $$\psi _1 = O(r^{ - 3 - \in _1 } ), \in _1< \in _0 and \in _1< 1$$ withψ ₂,ψ ₃, andψ ₄ having the same asymptotic behavior as they do for peeling solutions. The above investigation was carried out in the physical space-time. In this paper we examine the conformal properties of these solutions, as well as the more general Couch-Torrence solutions, which include them as a subclass. For the Couch-Torrence solutions $$\begin{gathered} \psi _0 = O(r^{ - 2 - \in _0 } ) \hfill \\ \psi _1 = O(r^{ - 2 - \in _1 } ), \in _1< \in _0 {\text{ }}and \in _1 \leqslant 2 \hfill \\ \end{gathered} $$ and , $$\psi _2 = O(r^{ - 2 - \in _2 } ),{\text{ }} \in _2< \in _1 {\text{ }}and \in _2 \leqslant 1$$ withψ ₃ andψ ₄ behaving as they do for peeling solutions. It is our purpose to determine how much of the structure generally associated with peeling space-times is preserved by the nonpeeling solutions. We find that, in general, a three-dimensional null boundary (?⁺) can be defined and that the BMS group remains the asymptotic symmetry group. For the general Couch-Torrence solutions several physically and/or geometrically interesting quantities     

Photoelectron spectroscopy of metal β-diketonato complexes

The electronic structures of yttrium(III), gadolinium(III) and ytterbium(III) tris-2,2,6,6-tetramethyl-3,5-heptanedione (tmhd) complexes have been investigated by HeI and HeII photoelectron spectroscopy (UPS), UDFT and OVGF calculations. We discuss metal-ligand bonding in the series of metal β-diketonato complexes on the basis of empirical arguments. The photoionization cross-sections and orbital energies of metal atoms must both be taken into account in order to rationalize changes in relative band intensities of the HeI/HeII spectra.     

All-catalytic, efficient, and asymmetric synthesis of alpha,omega-diheterofunctional reduced polypropionates via "one-pot" Zr-catalyzed asymmetric carboalumination-Pd-catalyzed cross-coupling tandem process

A highly efficient method for the synthesis of stereochemically pure (>/=99% ee and >50/1 dr) alpha,omega-diheterofunctional reduced polypropionates has been developed. The essential features of the method are represented by the conversion of inexpensive styrene into 2-methyl-4-phenyl-1-pentanol (1) in 50% yield over two steps from styrene via Zr-catalyzed asymmetric carboalumination (ZACA) reaction in the presence of (NMI)2ZrCl2 and Pd-catalyzed vinylation of the in situ generated isoalkylalanes in the presence of Zn(OTf)2 and a catalytic amount of Pd(DPEphos)Cl2. This ZACA-Pd-catalyzed vinylation may be repeated as needed without purification. After the final ZACA reaction, oxidation with O2 provides alpha-hydroxy-omega-phenyl reduced polypropionates, which can be fully or partially purified by chromatography. After acetylation, Ru-catalyzed oxidative cleavage of the Ph ring, and reduction with BH3.THF, the second chromatographic purification provides stereoisomerically pure alpha,omega-diheterofunctional reduced polypropionates (e.g., 9 and 11) that can be further converted to key intermediates 6 and 7 for the synthesis of ionomycin (4) and borrelidin (5), respectively, by known reactions.     

Was k?nnen Quantencomputer?

Quantencomputer benutzen seltsame Effekte der Quantenwelt, n?mlich sogenannte „verschr?nkte Zust?nde“, mit deren Hilfe man die „Bellschen Ungleichungen“ verletzen kann. Dazu beschreiben wir zun?chst ein Gedankenexperiment, das die Andersartigkeit der Quantenwelt eindrucksvoll vorführt. Dann wird die logische Struktur von Quantencomputern entwickelt. Dazu ben?tigt man nur Begriffe aus dem Grundstudium (lineare Algebra, unit?re Matrizen), insbesondere nur endlich dimensionale Vektorr?ume. Als Beispiel für die überlegenheit von Quantencomputern diskutieren wir den Such-Algorithmus von Grover.     

Matching the nanoporous carbon electrodes and organic electrolytes in double layer capacitors

In order to see how the power density of supercapacitors could be increased, a theoretical model of the nanoporous carbon electrode as a tier structure with transport channels has been developed. Also an experimental method has been developed to measure the rate of electrolyte transport through the porous electrode material. This method can be used for quick analysis and selection of electrodes. The results of modeling have been verified by testing the experimental EDLC prototypes with optimum electrode thickness and electrode porosity, the porosity being well matched with the size of ions in organic electrolytes. This enables us to reach a power density as high as 6–7 kW/L with a reasonably large energy density and high efficiency for both EDLC unit cells and stacks. PACS 82.47.Uv