A tripodal sulfur ligand for the selective ruthenium-catalysed hydrogenation of dimethyl oxalate

The first example of a catalyst utilising a sulfur-based ligand [MeC(CH2SBu)3] for the selective hydrogenation of dimethyl oxalate to methyl glycolate is reported.     

Constraints on Contact Angles for Multiple Phases in Thermodynamic Equilibrium

For three or more fluid phases in thermodynamic equilibrium and in contact with a solid surface, the Young equation can be used to find relations between the contact angles for different pairs of fluids. For an n-fluid-phase system, n(n-1)/2 contact angles can be defined, but there are (n-1)(n-2)/2 constraints between them, leaving only n-1 independent values of the contact angle. These constraints are very powerful in limiting and determining possible types of wetting behavior. The consequences are discussed for three- and four-phase flow. They have important applications for the understanding of gas injection processes in petroleum reservoirs. Copyright 2001 Academic Press.     

Analytical chemistry and the cone penetrometer: In situ chemical characterization of the subsurface

The development of novel microanalytical techniques forin situ chemical characterization of the terrestrial subsurface environment has grown significantly over the last decade, particularly those instruments that are interfaced to the cone penetrometer. Cone penetrometer testing (CPT) has emerged as an effective means to introduce samplers and probes forin situ analysis of contaminants in soil and groundwater matrices. A variety ofin situ chemical samplers for CPT have been developed that can be driven into the subsurface to collect soil gas, groundwater, or soil samples at depth, thus providing a means of determining the vertical and horizontal extent of contamination. Cone penetrometer testing is also being explored as a means to deliverin situ subsurface sensor probes, including probes based on laser-induced fluorescence, Raman, and infrared spectroscopies for organics; on laser-induced breakdown and X-ray fluorescence spectroscopies for heavy metals; and on passive gamma-ray spectroscopy for radionuclides. The range of analytical technologies used in CPT for the determination of organic and inorganic species in the subsurface is described.     

Darstellung und Kristallstruktur von Na2Mn3O7

Synthesis and Crystal-Structure of Na₂Mn₃O₇ Single crystals of Na₂Mn₃O₇ have been grown hydrothermally applying high oxygen pressure (p = 2 kbar). The new compound cystallizes triclinic; space group P1 ; a = 6.636(6) Å, b = 6.854(6) Å, c = 7.548(6) Å, α = 105.76(6)°, β = 106.86(6)°, γ = 111.60(6)°; Z = 2. The crystal structure has been solved and refined to R = 7.9% and R_w = 6.2% (diffractometer data, 1044 independent reflexions). The crystal structure consists of Mn₃O₇^2? anions with manganese coordinated octahedrally by oxygen. These layered anions are hold together by Na⁺ ions (coordination numbers 5 and 6).     

Integration of continuous-flow sampling with microchip electrophoresis using poly(dimethylsiloxane)-based valves in a reversibly sealed device

Here we describe a reversibly sealed microchip device that incorporates poly(dimethylsiloxane) (PDMS)-based valves for the rapid injection of analytes from a continuously flowing stream into a channel network for analysis with microchip electrophoresis. The microchip was reversibly sealed to a PDMS-coated glass substrate and microbore tubing was used for the introduction of gas and fluids to the microchip device. Two pneumatic valves were incorporated into the design and actuated on the order of hundreds of milliseconds, allowing analyte from a continuously flowing sampling stream to be injected into an electrophoresis separation channel. The device was characterized in terms of the valve actuation time and pushback voltage. It was also found that the addition of sodium dodecyl sulfate (SDS) to the buffer system greatly increased the reproducibility of the injection scheme and enabled the analysis of amino acids derivatized with naphthalene-2,3-dicarboxaldehyde/cyanide. Results from continuous injections of a 0.39 nL fluorescein plug into the optimized system showed that the injection process was reproducible (RSD of 0.7%, n = 10). Studies also showed that the device was capable of monitoring off-chip changes in concentration with a device lag time of 90 s. Finally, the ability of the device to rapidly monitor on-chip concentration changes was demonstrated by continually sampling from an analyte plug that was derivatized upstream from the electrophoresis/continuous flow interface. A reversibly sealed device of this type will be useful for the continuous monitoring and analysis of processes that occur either off-chip (such as microdialysis sampling) or on-chip from other integrated functions.     

Enzyme activity control by responsive redoxpolymers

A new thermoresponsive poly-N-isopropylacrylamide (PNIPAM)-ferrocene polymer was synthesized and characterized. PNIPAMFoxy bears additional oxirane groups which were used for attachment by a self-assembly process on a cysteamine-modified gold electrode to create a thin hydrophilic film. The new redox polymer enabled electrical communication between the cofactor pyrrolinoquinoline quinone (PQQ) of soluble glucose dehydrogenase (sGDH) and the electrode for sensitive detection of this enzyme as a prospective protein label. The temperature influence on the redox polymer/enzyme complex was investigated. An inverse temperature response behavior of surface bound PNIPAMFoxy compared to the soluble polymer was found and is discussed in detail. The highest efficiency of mediated electron transfer for the immobilized PNIPAMFoxy with sGDH was observed at 24 degrees C, which was twice as high as that of its soluble counterpart. A steady-state electrooxidation current densitiy of 4.5 microA.cm-2 was observed in the presence of 10 nM sGDH and 5 mM glucose. A detection limit of 0.5 nM of soluble PQQ-sGDH was obtained.     

Fatty acid chemistry at the oil-water interface: self-propelled oil droplets

Fatty acids have been investigated as boundary structures to construct artificial cells due to their dynamic properties and phase transitions. Here we have explored the possibility that fatty acid systems also demonstrate movement. An oil phase was loaded with a fatty acid anhydride precursor and introduced to an aqueous fatty acid micelle solution. The oil droplets showed autonomous, sustained movement through the aqueous media. Internal convection created a positive feedback loop, and the movement of the oil droplet was sustained as convection drove fresh precursor to the surface to become hydrolyzed. As the system progressed, more surfactant was produced and some of the oil droplets transformed into supramolecular aggregates resembling multilamellar vesicles. The oil droplets also moved directionally within chemical gradients and exhibited a type of chemotaxis.