DFT study on H2O activation by stepped and planar Rh surfaces

In this research the effect of steps (lower coordinated surface atoms) and the presence of pre-adsorbed oxygen on the activation energy of water are studied with DFT. Without oxygen water activation is found to be structure insensitive. When oxygen is adsorbed on the surface and acts as the acceptor for the hydrogen at the step edge, the barrier will decrease significantly.     

Coordination properties of ionic liquid-mediated chromium(II) and copper(II) chlorides and their complexes with glucose

The structural and coordination properties of complexes formed upon the interaction of copper(II) and chromium(II) chlorides with dialkylimidazolium chloride (RMIm(+)Cl(-)) ionic liquids and glucose are studied by a combination of density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS). In the absence of the carbohydrate substrate, isolated mononuclear four-coordinated MeCl(4)(2-) species (Me = Cu, Cr) dominate in the ionic liquid solution. The organic part of the ionic liquid does not directly interact with the metal centers. The interactions between the RMIm(+) cations and the anionic metal chloride complexes are limited to hydrogen bonding with the basic Cl(-) ligands and the overall electrostatic stabilization of the anionic metal complexes. Exchange of Cl(-) ligands by a hydroxyl group of glucose is only favorable for CrCl(4)(2-). For Cu(2+) complexes, the formation of hydrogen bonded complexes between CuCl(4)(2-) and glucose is preferred. No preference for the coordination of metal chloride species to specific hydroxyl group of the carbohydrate is found. The formation of binuclear metal chloride complexes is also considered. The reactivity and selectivity patterns of the Lewis acid catalyzed reactions of glucose are discussed in the framework of the obtained results.     

Synthesis of 1,3-diamino-7,8,9,10-tetrahydropyrido[3,2-f]-quinazolines. Inhibitors of Candida albicans dihydrofolate reductase as potential antifungal agents

A series of novel 1,3-diamino-7,8,9,10-tetrahydropyrido[3,2-f]quinazolines were synthesized starting from 6-amino-5-cyanoquinoline (4). These compounds inhibited Candida albicans dihydrofolate reductase with K_i values of ≤0.60 aM. One analogue exhibited moderate in vivo efficacy in a C. albicans-infected mouse model.     

Synthesis of poly(benzyl glutamate‐b‐styrene) rod‐coil block copolymers by dual initiation in one pot

We have developed a metal free synthetic pathway to homopolypeptide rod‐coil block copolymers. The concept was proven for the synthesis of poly(benzyl‐L ‐glutamate‐b‐styrene). A dual initiator containing a primary amine and a nitroxide group was used in a macroinitiation approach with high initiation efficiency. Good control over the molecular weight in the ring opening polymerization of benzyl‐L ‐glutamate N‐carboxyanhydride was obtained in DMF at 0 °C yielding poly(benzyl‐L ‐glutamates) with low polydispersities around 1.1. The almost quantitative incorporation of the dual initiator was confirmed by MALDI‐ToF analysis. Macroinitiation of styrene by nitroxide‐mediated controlled radical polymerization yielded the block copolymer with high structural control. The diblock structure was confirmed by molecular weight increase upon macroinitiation by size exclusion chromatography and retention time comparison with homopolymers using gradient polymer elution chromatography. Both polymerizations were also successfully conducted in one pot without intermediate isolation owing to the high compatibility of both polymerization techniques. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3068–3077, 2008     

Cumulated double bond systems as ligands : I. Dialkylsulfurdiimine compounds of platinum

The preparations and properties of a new series of compounds of the formula trans-[PtCl₂(dialkylsulfurdiimine)L] are reported. In the case of the dimethyl-, diethyl-, diisopropyl- and dineopentyl-sulfurdiimine platinum compounds two isomers are present in solution, but only one isomer was observed for the di-t-butylsulfurdiimine derivative. ¹H and ¹³C NMR data show that the two isomers interconvert intramolecularly by two different routes. In one of the isomeric forms, unusually large low-field chemical shifts indicate the existence of non-bonded metal—alkyl interactions.     

ChemInform Abstract: An ab initio Study of Possible Pathways in the Thermal Decomposition of NaAlH4

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

An ab initio study of possible pathways in the thermal decomposition of NaAlH4

Density functional theory (DFT) has been used to study the structural stability of possible intermediate alanate structures, Na₅Al₃H₁₄ and Na₂AlH₅, in the thermal decomposition of NaAlH₄. Na₅Al₃H₁₄ crystallizes in the space group P4/mnc with lattice constants , and c/a=1.52. It is shown that both Na₅Al₃H₁₄ and Na₂AlH₅ have the right thermodynamics and can fit in as an intermediate state during the thermal decomposition process of NaAlH₄. The heat of formation of Na₅Al₃H₁₄ is −60 kJ/mol H₂, which is intermediate between that of NaAlH₄ (−51 kJ/mol H₂) and Na₃AlH₆ (−69.7 kJ/mol H₂). An alternative decomposition pathway based on Na₂AlH₅ has also been discussed. Frequency analysis showed that the least energetic Na₂AlH₅ structure has imaginary frequencies, implying that it is unstable. The presence of soft phonon modes also shows that Na₅Al₃H₁₄ is mechanically metastable. These results are consistent with the notion that they are the intermediate states that lead to the formation of AlH₃. This facilitates the mass transport of aluminum atoms in the decomposition pathway of NaAlH₄.     

Continuous-flow single-molecule CE with high detection efficiency

This paper describes the use of two-beam line-confocal detection geometry for measuring the total mobility of individual molecules undergoing continuous-flow CE separation. High-sensitivity single-molecule confocal detection is usually performed with a diffraction limited focal spot (approximately 500 nm in diameter), which necessitates the use of nanometer-sized channels to ensure all molecules flow through the detection volume. To allow for the use of larger channels that are a few micrometers in width, we employed cylindrical optics to define a rectangular illumination area that is diffraction-limited (approximately 500 nm) in width, but a few micrometers in length to match the width of the microchannel. We present detailed studies that compare the performance of this line-confocal detection geometry with the more widely used point-confocal geometry. Overall, we found line-confocal detection to provide the highest combination of signal-to-background ratio and spatial detection efficiency when used with micrometer-sized channels. For example, in a 2 microm wide channel we achieved a 94% overall detection efficiency for single Alexa488 dye molecules when a 2 microm x 0.5 microm illumination area was used, but only 34% detection efficiency with a 0.5 microm-diameter detection spot. To carry out continuous-flow CE, we used two-beam fluorescent cross-correlation spectroscopy where the transit time of each molecule is determined by cross-correlating the fluorescence registered by two spatially offset line-confocal detectors. We successfully separated single molecules of FITC, FITC-tagged glutamate, and FITC-tagged glycine.