2014 Spring Seminar Series

Thursday, April 17, 2014

Environmental Applications and Potential Implications of Polymer Nanocomposites
Howard Fairbrother
Johns Hopkins University, Department of Chemistry


T.B.A.
Thursday, April 17, 2014
CEB 218 (810 South Clinton Street)
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Tuesday April 8th, 2014

Single Molecule Investigations of Heterogeneous Catalysts: Probing solvent effects, active site heterogeneity and adsorbate dynamics
Robert M. Rioux
The Pennsylvania State University, Department of Chemical Engineering


T.B.A.
Tuesday April 8th, 2014
CEB 218 (810 South Clinton Street)
Metal nanoparticles are key components in the advancement of future energy technologies since they are catalytically active for several organic-inorganic syntheses, electron-transfer, and energy conversion reactions. They directly promote chemical conversion and/or facilitate chemical transport to active interfaces. A detailed understanding of the relation between structure and properties of nanoparticles will lead to tailored catalytic properties. Although these structure-function relationships are pursued by many researchers; they are typically limited to ensemble-level approaches where the intrinsic catalytic behavior of individuals is masked due to the asynchronicity of their behaviors during catalytic turnover. We employ a single molecule approach utilizing a two-state (pro-fluorescent to fluorescent) reduction reaction to examine the catalytic behavior of individual Au nanoparticles with single turnover resolution.Through kinetic modeling and isotopic labeling, we demonstrate competitive binding between solvent and substrate accounts for differences in observed catalytic rates at the ensemble level. Temperature-dependent measurements of the catalytic activity of single nanoparticles reveals heterogeneous in reactivity and kinetic parameters which are due to static dispersion even though the dispersion varies temporally; these variations are ascribed to the intrinsic reactivity of populations of indistinguishable active sites. Approaches to selectively titrate distinct active site populations on the surface of individual Au nanoparticles have enabled us to distinguish between their intrinsic kinetic behavior and utilizing ideal models of nanoparticle structures confirm their identity and concentration. The ability to probe reaction dynamics during single molecule catalysis studies utilizing an experimental and theoretical approach to understand delayed rise times in fluorescent response will be discussed.

Thursday April 3rd, 2014

Interfacial Rheology of Biological Interfaces
Gerald Fuller
Stanford University, Department of Chemical Engineering


11:00A.M.
Thursday April 3rd, 2014
CEB 218 (810 South Clinton Street)
Biological systems are normally high-interface systems and these surfaces are laden with biological molecules and cells that render them rheologically complex. The resulting nonlinearities with response to surface stresses and strain are often essential to their proper function and these are explored using recently developed methods that reveal interfacial moduli and microstructure. Two applications are discussed: 1. The tear film of the eye is a composite structure of an aqueous solution of protein and biomacromolecules. This thin layer is further covered by a film comprised of meibomian lipids excreted during each blink. The purpose of the meibum has been largely unexplained although one prevailing suggestion is that it suppresses evaporation. Recent measurements in our laboratory demonstrate that this layer is strongly viscoelastic and this property has dramatic effects on the dynamics of the moving contact line and stability against dewetting. 2. Vascular endothelial cells line the interior walls of our blood vessels and are sensitive to surface shear stresses. These stresses are known to affect the shape and orientation of endothelial cells. It is evident that the spatial homogeneity of flow can affect vascular health and it is well-documented that lesions form in regions of high curvature, bifurcations, and asperities in blood vessels. Experiments are described where stagnation point flows are used to create regions of well controlled flow stagnation and spatial variation of wall shear stresses. Live-cell imaging is used to monitor the fate of cells attached to surfaces experiencing flow impingement and it is revealed that endothelial cells migrate and oriented in such flows to create remarkable patterns of orientation and cell densification.

Friday March 14th, 2014

Mechanisms that Control CaCO3 Biomineralization During Reactive Transport and the Implications for Pore Space Alteration, Fluid Flow, and Mixing
Charles J. Werth
Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign


2:00-3:00 P.M.
Friday March 14th, 2014
CEB 218 (810 South Clinton Street)
Calcium carbonate (CaCO3 ) is among the most abundant and reactive minerals comprising the < 5km deep subsurface of the Earth’s crust. Precipitation and dissolution reactions have been linked to bioremediation, carbon sequestration, and enhanced oil recovery sites, and are implicated in pore space alteration and process efficacy. In this study, microbial CaCO3 biomineralization in a model reservoir is evaluated using a silicon-etched microfluidic reactor that has a uniform pore network. Acetate and nitrate are mixed in the pore network, which promotes growth of a Pseudomonas stutzeri st. DCP-Ps1 inoculum. After sufficient biomass growth occurs, elevated Ca2+ is introduced to evaluate if carbonate precipitation occurs and can be attributed to the increase in pH, microbial nucleation sites, factors linked to biological activity (e.g., enzyme production), or some combination of these. The results have direct implications for permeable reservoirs targeted for bioremediation, carbon sequestration, and/or enhanced oil recovery.

Thursday Feb 20th, 2014

Silicate Prodrug-Loaded Nanoparticles
Chris Macosko
University of Minnesota, Department of Chemical Engineering and Materials Science


11:00 A.M.
Thursday Feb 20th, 2014
CEB 218 (810 South Clinton Street)
Nanoparticles of highly insoluble drugs can be created by flash nanoprecipitation, FNP. Turbulent mixing combined with a polymer stabilizer produces particles in the 100 nm size range, ideal for passive targeting of tumors and advantageous to increase solubility. We have used FNP to create nanoparticles containing a series of labile silicate prodrugs having customized hydrophobic character and hydrolysis rates. These are stabilized with poly(ethyleneglycol)-b-poly(lactic-co-glycolic acid) with well controlled molecular weights and narrow polydispersities. The particles are highly loaded and release studies indicate that hydrolysis occurs inside the particles with the drug released at rates controlled by the stereo-electronic character of the silicate. A MDMB231 (breast cancer) cell culture assay with paclitaxel-silicate loaded particles demonstrated in vitro efficacy. In vivo studies on mouse models with MDMB231tumors will also be reported.

 
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