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Complexation Model (complexation + model)
Selected AbstractsChemical reactivity of microbe and mineral surfaces in hydrous ferric oxide depositing hydrothermal springsGEOBIOLOGY, Issue 3 2007S. V. LALONDE ABSTRACT The hot springs in Yellowstone National Park, USA, provide concentrated microbial biomass and associated mineral crusts from which surface functional group (FG) concentrations and pKa distributions can be determined. To evaluate the importance of substratum surface reactivity for solute adsorption in a natural setting, samples of iron-rich sediment were collected from three different springs; two of the springs were acid-sulfate-chloride (ASC) in composition, while the third was neutral-chloride (NC). At one of the ASC springs, mats of Sē -rich Hydrogenobaculum -like streamers and green Cyanidia algae were also collected for comparison to the sediment. All samples were then titrated over a pH range of 3,11, and comparisons were made between the overall FG availability and the concentration of solutes bound to the samples under natural conditions. Sediments from ASC springs were composed of hydrous ferric oxides (HFO) that displayed surface FGs typical of synthetic HFO, while sediments from the NC spring were characterized by a lower functional group density, reflected by decreased excess charge over the titration range (i.e., lower surface reactivity). The latter also showed a lower apparent point of zero charge (PZC), likely due the presence of silica (up to 78 wt. %) in association with HFO. Variations in the overall HFO surface charge are manifest in the quantities and types of solutes complexed; the NC sediments bound more cations, while the ASC sediments retained significantly more arsenic, presumably in the form of arsenate (H2AsO4,). When the microbial biomass samples were analyzed, FG concentrations summed over the titratable range were found to be an order of magnitude lower for the Sē-rich mats, relative to the algal and HFO samples that displayed similar FG concentrations on a dry weight basis. A diffuse-layer surface complexation model was employed to further illustrate the importance of surface chemical parameters on adsorption reactions in complex natural systems. [source] Fluorescence Regeneration as a Signaling Principle for Choline and Carnitine Binding: A Refined Supramolecular Sensor System Based on a Fluorescent Azoalkane,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2006H. Bakirci Abstract The fluorescent azoalkane, 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), forms inclusion complexes with p -sulfonatocalix[4]arene (CX4). The binding constants are on the order of 103,M,1 in water. The addition of CX4 to DBO solutions results in an efficient fluorescence quenching (up to 90,%). This supramolecular system can be used as a truly water-soluble sensor system to signal the binding of organic ammonium ions over a large pH range. Addition of choline and carnitine derivatives and tetraalkylammonium ions results in regeneration of this fluorescence, from which the binding constants (KC,=,103,105,M,1) are calculated by means of a competitive complexation model. Electrostatic effects are observed, namely, a more-than-one order of magnitude weaker binding of the carnitines in neutral solution. [source] Ethylene Polymerization Kinetics with a Heterogeneous Metallocene Catalyst , Comparison of Gas and Slurry PhasesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Michiel F. Bergstra Abstract Summary: Ethylene homopolymerizations were executed with a supported Ind2ZrCl2/MAO catalyst using the so-called Reactive Bed Preparation method. This RBP method combined a slurry polymerization with a gas phase polymerization with the same polymerizing particles, i.e., a reactive bed. Polymerization kinetics were measured with high accuracy and reproducibility. Slurry and gas phase polymerization rates showed the same dependency on monomer bulk concentration. A complexation model has been proposed to describe the non-first order polymerization rate-monomer concentration dependence observed. This model also explains the non-Arrhenius temperature dependence and the observed pressure dependence of the activation energy of the commonly used polymerization rate model: Rp,=,kp,ˇ,C*,ˇ,M. [source] Metallocene-Catalyzed Gas-Phase Ethylene Copolymerization: Kinetics and Polymer PropertiesMACROMOLECULAR REACTION ENGINEERING, Issue 8 2009Michiel F. Bergstra Abstract The influence of 1-hexene is examined on the kinetics of ethylene copolymerization with a metallocene catalyst in gas phase. A model is derived, which is able to describe a large reaction rate increase due to a small amount of incorporated comonomer. This complexation model describes the measured reaction rates for ethylene and 1-hexene, and the co-monomer incorporation. Polymer properties were analyzed, such as comonomer weight fraction. The density, melting point, and molecular weight of the produced polymer decreased with increase in 1-hexene gas concentration. The in situ 1-hexene sorption is estimated and follows Henry's law, but seems much higher than reported in the literature. [source] | ||||||||||