W Tungsten

A series of 1-alkyl-3-methylimidazolium fluorohydrogenate salts (CxMIm(FH)2F, x=8, 10, 12, 14, 16, and 18) have been characterized by thermal analysis, polarized optical microscopy, IR spectroscopy, X-ray diffraction, and anisotropic ionic conductivity measurements. Liquid crystalline mesophases with a smectic A interdigitated bilayer structure are observed from C10 to C18, showing a fan-like or focal conic texture. The temperature range of the mesophase increases with the increase in the alkyl chain length (from 10.1 °C for C10MIm(FH)2F to 123.1 °C for C18MIm(FH)2F). The distance between the two layers in the smectic structure gradually increases with increasing alkyl chain length and decreases with increasing temperature. Conductivity parallel to the smectic layers is around 10 mS cm−1 regardless of the alkyl chain length, whereas that perpendicular to the smectic layers decreases with increasing alkyl chain length because of the thicker insulating sheet with the longer alkyl chain.Ion-conductive layer: The (FH)2F− salts combined with 1-alkyl-3-methylimidazolium cations with long alkyl chains show smectic A2 liquid crystalline mesophases. Highly anisotropic conductivity was observed in the smectic layer structure (see graphic).

A series of cationic and neutral RuII complexes of the general formula [Ru(L)(X) (tBuCN)4]+X− and [Ru(L)(X)2(tBuCN)3)], that is, [Ru(CF3SO3){NCC(CH3)3}4(IMesH2)]+[CF3SO3]− (1), [Ru(CF3SO3){NCC(CH3)3}4(IMes)]+[CF3SO3]− (2), [RuCl{NCC(CH3)3}4(IMes)]+Cl− (3), [RuCl{NCC(CH3)3}4(IMesH2)+Cl−]/[RuCl2{NCC(CH3)3}3(IMesH2)] (4), and [Ru(NCO)2{NCC(CH3)3}3(IMesH2)] (5) (IMes=1,3-dimesitylimidazol-2-ylidene, IMesH2=1,3-dimesityl-imidazolin-2-ylidene) have been synthesized and used as UV-triggered precatalysts for the ring-opening metathesis polymerization (ROMP) of different norborn-2-ene- and cis-cyclooctene-based monomers. The absorption maxima of complexes 1–5 were in the range of 245–255 nm and thus perfectly fit the emission band of the 254 nm UV source that was used for activation. Only the cationic RuII-complexes based on ligands capable of forming μ2-complexes such as 1 and 2 were found to be truly photolatent in ROMP. In contrast, complexes 3–5 could be activated by UV light; however, they also showed a low but significant ROMP activity in the absence of UV light. As evidenced by 1H and 13C NMR spectroscopy, the structure of the polymers obtained with either 1 or 2 are similar to those found in the corresponding polymers prepared by the action of [Ru(CF3SO3)2(IMesH2)(CH-2-(2-PrO)-C6H4)], which strongly suggest the formation of Ru-based Grubbs-type initiators in the course of the UV-based activation process. Precatalysts that have the IMesH2 ligand showed significantly enhanced reactivity as compared with those based on the IMes ligand, which is in accordance with reports on the superior reactivity of IMesH2-based Grubbs-type catalysts compared with IMes-based systems.ROMPing around: A series of cationic and neutral RuII complexes based on N-heterocyclic carbenes have been synthesized and investigated for use as latent initiators for the photoinitiated ROMP by using different norborn-2-ene- and cis-cyclooctene-based monomers.

No longer hidden! An extension of the capabilities of the X-ray diffraction experiment is introduced. Locations of electron pairs within a molecule can be measured and made visible (see figure). This is demonstrated on a series of epoxides, for which ring strain, crystal, and substituent effects can be quantified. Comparison with experimental and theoretical electron-density analyses shows the advantages of the new method.

An effective chemoenzymatic strategy is reported that has allowed the construction, for the first time, of a focused microarray of synthetic N-glycans. Based on modular approaches, a variety of N-glycan core structures have been chemically synthesized and covalently immobilized on a glass surface. The printed structures were then enzymatically diversified by the action of three different glycosyltransferases in nanodroplets placed on top of individual spots of the microarray by a printing robot. Conversion was followed by lectin binding specific for the terminal sugars. This enzymatic extension of surface-bound ligands in nanodroplets reduces the amount of precious glycosyltransferases needed by seven orders of magnitude relative to reactions carried out in the solution phase. Moreover, only those ligands that have been shown to be substrates to a specific glycosyltransferase can be individually chosen for elongation on the array. The methodology described here, combining focused modular synthesis and nanoscale on-chip enzymatic elongation, could open the way for the much needed rapid construction of large synthetic glycan arrays.Go nano! Arrays of immobilised carbohydrates can be enzymatically processed with the help of glycosyl transferases in nanodroplets placed on top of individual spots. This methodology opens the way for the stereospecific on-chip construction of glycan arrays with very high ligand densities by using immobilised synthetic glycan scaffolds and minute amounts of recombinant glycosyltransferases (see figure).

Recently, boryl radicals have been the subject of revived interest. These structures were generated by hydrogen-abstraction reactions from the corresponding boranes (i.e., from amine or phosphine boranes). However, the classical issue remains their high BH bond-dissociation energy (BDE), thereby preventing a very efficient hydrogen-abstraction process. In the present paper, new N-heteroaryl boranes that exhibiting low BH BDE are presented; excellent hydrogen-transfer properties have been found. Both the generation and the reactivity of the associated boryl radicals have been investigated through their direct observation in laser flash photolysis. The boryl radical interactions with double bonds, oxygen, oxidizing agent, and alkyl halides have been studied. Some selected applications of N-heteroaryl boryl radicals as new polymerization-initiating structures are proposed to evidence their high intrinsic reactivity.Radical thoughts: New N-heteroaryl boranes that exhibit low BH bond-dissociation energy (BDE) are presented; excellent hydrogen-transfer properties have been found. Both the generation and the reactivity of the associated boryl radicals have been investigated through the direct detection of the different boryl radicals by laser flash photolysis (see graph).

Versatile routes that lead to a variety of functionalized enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines are based on chemo-, regio-, and stereocontrolled metal-catalyzed oxycyclization reactions of β,γ- and γ,δ-allendiols, which were readily prepared from (R)-2,3-O-isopropylideneglyceraldehyde. The application of PdII, PtII, AuIII, or LaIII salts as the catalysts gives controlled access to differently sized oxacycles in enantiopure form. Usually, chemoselective cyclization reactions occurred exclusively by attack of the secondary hydroxy group (except for the oxybromination of phenyl β,γ-allenic diols 3 b and 3 d) to an allenic carbon atom. Regio- and stereocontrol issues are mainly influenced by the nature of the metal catalysts and substituents.Se han encontrado rutas versátiles que conducen a tetrahidrooxepinas, dihidropiranos y tetrahidrofuranos funcionalizados enantiopuros, basadas en reacciones de oxiciclación quimio-, regio- y estereocontroladas de β,γ- y γ,δ-alenildioles catalizadas por metales. Los dioles de partida se prepararon fácilmente a partir de (R)-2,3-O-isopropilidengliceraldehido. La utilización de sales de PdII, PtII, AuIIIó LaIIIcomo catalizadores da lugar a un método de preparación controlada de oxaciclos de diferente tamaño en forma enantiopura. Normalmente, las reacciones de ciclación quimioselectiva ocurren exclusivamente por ataque del grupo hidroxilo secundario (excepto en la oxibromación de los fenil β,γ-alenildioles 3 b y 3 d) a uno de los carbonos alénicos. Tanto el control regio- como el estereoquímico están influídos por la naturaleza del metal y los sustituyentes.Diversely functionalized enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines are prepared by using a chemo-, regio-, and stereoselective methodology. This approach involves controlled Pd-, Pt-, Au-, or La-catalyzed oxycyclization reactions of β,γ- and γ,δ-allenic diols (see scheme; FG=functional group, Z=protecting group).

The mode of action of precious metal anticancer metallodrugs is generally believed to involve DNA as a target. However, the poor specificity of such drugs often requires high doses and leads to undesirable side-effects. With the aim of improving the specificity of a ruthenium piano-stool complex towards DNA, we employed a presenter protein strategy based on the biotin–avidin technology. Guided by the X-ray structure of the assembly of streptavidin and a biotinylated piano-stool, we explored the formation of metallodrug-mediated ternary complexes with the presenter protein and DNA. The assemblies bound more strongly to telomere G-quadruplexes than to double-stranded DNA; chemo-genetic modifications (varying the complex or mutating the protein) modulated binding to these targets. We suggest that rational targeting of small molecules by presenter proteins could be exploited to bind metallodrugs to preferred macromolecular targets.Match of the DNA: Chemo-genetic modifications of a ruthenium metallodrug-presenter protein assembly (varying the complex or mutating the presenter protein) modulates the binding to different DNA targets (see figure).

The lithium salts of the chalcogenocarbonyl dianions [(E)C(PPh2S)2]2− (E=S (4 b), Se (4 c)) were produced through the reactions between Li2[C(PPh2S)2] and elemental chalcogens in the presence of tetramethylethylenediamine (TMEDA). The solid-state structure of {[Li(TMEDA)]2[(Se)C(PPh2S)2]}—[{Li(TMEDA)}24 c]—was shown to be bicyclic with the Li+ cations bis-S,Se-chelated by the dianionic ligand. One-electron oxidation of the dianions 4 b and 4 c with iodine afforded the diamagnetic complexes {[Li(TMEDA)]2[(SPh2P)2CEEC(PPh2S)2]} ([Li(TMEDA)]27 b (E=S), [Li(TMEDA)]27 c (E=Se)), which are formally dimers of the radical anions [(E)C(PPh2S)2]−. (E=S (5 b), Se (5 c)) with elongated central EE bonds. Two-electron oxidation of the selenium-containing dianion 4 c with I2 yielded the LiI adduct of a neutral selone {[Li(TMEDA)][I(Se)C(PPh2S)2]}—[{LiI(TMEDA)}6 c]—whereas the analogous reaction with 4 b resulted in the formation of 7 b followed by protonation to give {[Li(TMEDA)][(SPh2P)2CSS(H)C(PPh2S)2]}—[Li(TMEDA)]8 b. Attempts to identify the transient radicals 5 b and 5 c by EPR spectroscopy in conjunction with DFT calculations of the electronic structures of these paramagnetic species and their dimers are also described. The crystal structures of [{Li(TMEDA)}24 c], [{LiI(TMEDA)}6 c]⋅C7H8, [Li(TMEDA)]27 b⋅(CH2Cl2)0.33, [Li(THF)2]27 b, [Li(TMEDA)]27 c, [Li(TMEDA)]8 b⋅(CH2Cl2)2 and [Li([12]crown-4)2]8 b were determined and salient structural features are discussed.Versatility in chalcogenides: Tetradentate dimeric dianions [(SPh2P)2CEEC(PPh2S)2]2− (E=S, Se) with long, central chalcogen–chalcogen bonds (see figure) are formed by one-electron oxidation of the tridentate monomers [(E)C(PPh2S)2]2−. Two-electron oxidation of [SeC(PPh2S)2]2− produces the neutral selone [(Se)C(PPh2S)2] as a LiI adduct.

The cytostatic compounds cis-[Pt(A9pyp)(dmso)Cl2] (1) and [Pt(A9pyp)(dmso)(cbdca)] (2) (A9pyp=(E)-[1-(9-anthryl)-3-(2-pyridyl)-2-propenone) as carrier ligand; cbdca=cyclobutane dicarboxylate) have been found to add water across the enone CC bond of the ligand A9pyp. The water addition occurs in the presence of carbonate buffer, and has been followed in detail using NMR and ESI-MS spectroscopy. The spectroscopic data clearly indicate that the platinum(II) ion, the carbonate species, and the proximity of the enone CC bond to the metal ion, are all required for this unusual hydration. A difference in kinetics is observed between chloride and cbdca, showing that the Pt–ligand dissociation plays an important role in the hydration kinetics.Test the water! The cytostatic compounds cis-[Pt(A9pyp)(dmso)Cl2] (1) and [Pt(A9pyp)(dmso)(cbdca)] (2) (A9pyp=(E)-[1-(9-anthryl)-3-(2-pyridyl)-2-propenone) as carrier ligand; cbdca=cyclobutane dicarboxylate) have been found to add water across the enone CC bond of the ligand A9pyp. The water addition occurs in the presence of carbonate buffer, and has been followed in detail using NMR and ESI-MS spectroscopy.

A chiral polymer incorporating an (R,R)-salen moiety was synthesized by the polymerization of (R,R)-1,2-diaminocyclohexane with 2,5-dibutoxy-1,4-di(salicyclaldehyde)-1,4-diethynyl-benzene by a nucleophilic addition–elimination reaction. The fluorescence responses of the (R,R)-salen-based polymer toward various metal ions were investigated by fluorescence spectra. Compared with other cations, such as Na+, K+, Mg2+, Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Ag+, Cd2+, Hg2+, and Pb2+, Zn2+ can lead to a pronounced fluorescence enhancement as high as 7.8-fold together with an obvious blue-shift change of the chiral polymer. More importantly, the fluorescent color of the polymer changed to bright blue instead of weak yellow after addition of Zn2+, which can be easily detected by the naked eye. The results indicate that this kind of chiral polymer, incorporating an (R,R)-salen moiety as a receptor in the main chain backbone, can exhibit high sensitivity and selectivity for Zn2+ recognition.Sensing sensibility: A chiral polymer incorporating an (R,R)-salen moiety was synthesized and exhibits an excellent fluorescence response toward Zn2+. The fluorescent color of the polymer changed to bright blue instead of weak yellow after addition of Zn2+, which could be easily detected by the naked eye (see picture).