Syntheses and Structures of Ruthenium(II) N,S‐Heterocyclic Carbene Diphosphine Complexes and their Catalytic Activity towards Transfer Hydrogenation

Phosphine exchange of [Ru^IIBr(MeCOO)(PPh₃)₂(3‐RBzTh)] (3‐RBzTh=3‐benzylbenzothiazol‐2‐ylidene) with a series of diphosphines (bis(diphenylphosphino)methane (dppm), 1,2‐bis(diphenylphosphino)ethylene (dppv), 1,1′‐bis(diphenylphosphino)ferrocene (dppf), 1,4‐bis(diphenylphosphino)butane (dppb), and 1,3‐(diphenylphosphino)propane (dppp)) gave mononuclear and neutral octahedral complexes [RuBr(MeCOO)(η²‐P₂)(3‐RBzTh)] (P₂=dppm ( 2 ), dppv ( 3 ), dppf ( 4 ), dppb ( 5 ), or dppp ( 6 )), the coordination spheres of which contained four different ligands, namely, a chelating diphosphine, carboxylate, N,S‐heterocyclic carbene (NSHC), and a bromide. Two geometric isomers of 6 ( 6a and 6 b ) have been isolated. The structures of these products, which have been elucidated by single‐crystal X‐ray crystallography, show two structural types, I and II, depending on the relative dispositions of the ligands. Type I structures contain a carbenic carbon atom trans to the oxygen atom, whereas two phosphorus atoms are trans to bromine and oxygen atoms. The type II system comprises a carbene carbon atom trans to one of the phosphorus atoms, whereas the other phosphorus is trans to the oxygen atom, with the bromine trans to the remaining oxygen atom. Complexes 2 , 3 , 4 , and 6a belong to type I, whereas 5 and 6 b are of type II. The kinetic product 6 b eventually converts into 6a upon standing. These complexes are active towards catalytic reduction of para‐methyl acetophenone by 2‐propanol at 82 °C under 1 % catalyst load giving the corresponding alcohols. The dppm complex 2 shows the good yields (91–97 %) towards selected ketones.     

Dynamics of biphotonic intensity holographic gratings based on dye-doped liquid crystal films

The dynamics of biphotonic intensity holographic gratings (BIHGs) based on dye-doped liquid crystal (DDLC) films, including optical and thermal effects, are studied. Experimental results indicate that the formation of a BIHG involves bulk reorientation and surface adsorption. The former yields a transient biphotonic grating; the latter results in a persistent biphotonic grating. Additionally, the dynamic behaviours of the biphotonic diffraction signals are different from those of a conventional one-photonic diffraction signal, and depend on the intensity(polarization) of the green(red) pump-beam. The effect of ambient temperature on the diffraction efficiency of a BIHG is also studied: a higher ambient temperature prevents more dye molecules from being adsorbed on the substrate.     

PhotochemCAD‡: A Computer-Aided Design and Research Tool in Photochemistry

A database of absorption and fluorescence spectra, including molar absorption coefficients and fluorescence quantum yields, has been compiled for 125 photochemically relevant compounds. An accompanying program enables calculation of oscillator strengths, natural radiative lifetimes, transition dipole moments, Forster energy-transfer rates, multicomponent analysis, simulations of fluorescence spectra upon energy transfer among linear arrays of pigments, calculations of blackbody radiator curves at different temperatures and Lorentzian and Gaussian peak distributions. The program runs under Windows 95 and is equipped with extensive literature references and help features.     

A novel algorithm for chromatogram matching in qualitative analysis

The matching of the pattern of peaks produced during gas chromatography is of importance to many applications. At present, this task is generally performed manually, but this generates the usual problems associated with human inspection, such as a lack of objectivity and reproducibility, proneness to errors, and practical restriction of the volume of data which can reasonably be processed. This paper explores the use of a novel algorithm for automation of this task. The performance of the method on well controlled simulated data sets and real chromatograms is used to show not only how problems of manual inspection can be circumvented, but also how the existence of such a powerful method should open up the possibility of many new analyses for quality control, discrimination of varieties of sample, and the identification of specific components within a sample.     

Fabrication of a metal nanoparticles and polymer nanofibers composite material by an in situ chemical synthetic route

This work demonstrated a facile route for the synthesis of poly(3,5-dimethyl aniline) nanofibers by polymerization of 3,5-dimethyl aniline using Pd-acetate as the oxidant. The reduction of Pd ion is accompanied by oxidative polymerization of 3,5-dimethyl aniline, leading to a metal-polymer composite material. Palladium nanoparticles (approximately 2 nm) are uniformly distributed throughout the polymer that makes the composite material a unique morphology. The resultant composite material was characterized by means of different techniques. IR and Raman spectra provide the information on the chemical structure of the polymer. TEM images show the morphology of the polymer and size of the metal particles.     

1JNH values show that N1...N3 hydrogen bonds are stronger in dsRNA A:U than dsDNA A:T base pairs

Here, we show that 1JNH values are on average 0.4 Hz less negative for double-stranded RNA A:U than for DNA A:T base pairs, which, according to existing theory, suggests that RNA N1...N3 hydrogen bond distances are about 0.02 A shorter than those of DNA. Also, there is a statistically relevant trend between 1JNH and 2hDelta13C2 values, which supports the original hypothesis that 2hDelta13C2 values are also sensitive to hydrogen bond distances. Finally, a context dependence is observed for these values, which suggests that hydrogen-bonding and base-stacking interactions are coupled.     

Intercellular communication: the Drosophila innexin multiprotein family of gap junction proteins

Gap junctions belong to the most conserved cellular structures in multicellular organisms, from Hydra to man. They contain tightly packed clusters of hydrophilic membrane channels connecting the cytoplasms of adjacent cells, thus allowing direct communication of cells and tissues through the diffusion of ions, metabolites, and cyclic nucleotides. Recent evidence suggests that gap junctions are constructed by three different families of four transmembrane proteins: the Connexins and the Innexins found in vertebrates and in invertebrates, respectively, and the Innexin-like Pannexins, which were recently discovered in humans. This article focuses on the Drosophila Innexin multiprotein family, which is comprised of eight members. We highlight common structural features and discuss recent findings that suggest close similarities in cellular distribution, function, and regulation of Drosophila Innexins and vertebrate gap junction proteins.