Design and optimization of porous ceramic supports for asymmetric ceria-based oxygen transport membranes

The microstructure, mechanical properties and gas permeability of porous supports of Ce0.9Gd0.1O1.95−δ (CGO) were investigated as a function of sintering temperature and volume fraction of pore former for use in planar asymmetric oxygen transport membranes (OTMs). With increasing the pore former content from 11 vol% to 16 vol%, the gas permeabilities increased by a factor of 5 when support tapes were sintered to comparable densities. The improved permeabilities were due to a more favourable microstructure with larger interconnected pores at a porosity of 45% and a fracture strength of 47±2 MPa (m=7). The achieved gas permeability of 2.25×10−15 m2 for a 0.4 mm thick support will not limit the gas transport for oxygen production but in partial oxidation of methane to syngas at higher oxygen fluxes. For integration of the CGO support layer into a flat, asymmetric CGO membrane, the sintering activity of the CGO membrane was reduced by Fe2O3 addition (replacing Co3O4 as sintering additive)

New fluorescence methods for protein folding and conformational studies

Fluorescence spectroscopy has been extensively used in the study of protein folding, dynamics and function. Fluorescence resonance energy transfer (FRET), in particular, has proven to be very useful in this regard. However, FRET studies commonly employ exogenous fluorescent dyes, which may cause undesirable consequences, such as those due to nonspecific labeling or the bulky size of the probes. Amino acid fluorophores, therefore, provide an attractive alternative for FRET applications as they are smaller and easy to incorporate into the protein of interest. In the first part of this thesis, we explore the applicability of an amino acid FRET pair, p-cyanophenylalanine (Phe CN) and tryptophan (Trp), to the study of protein folding using two model protein systems. We demonstrate that quantitative information regarding the folding/unfolding process can be extracted from a single FRET titration experiment using a theoretical method we developed. Subsequently, we show that this FRET pair can be used in conjunction with a stopped-flow technique to directly dissect the binding and folding kinetics of intrinsically disordered proteins. Building on this work, we show that other non-natural amino acids, such as 7-azatryptophan (7AW) and 5-hydroxytryptophan (5HW), can also be used as FRET acceptors to PheCN, each with specific advantages over Trp. Finally, we demonstrate that PheCN, Trp and 7AW constitute a multi-FRET system that can be used to simultaneously monitor relative movements between different regions of a protein, thus allowing additional structural information to be extracted from a single FRET experiment. In the second part of this thesis, we expand the utility of fluorescence correlation spectroscopy (FCS) to the study of membrane proteins. We illustrate, using the Influenza A M2 proton channel as a model, how fluorescence fluctuations that arise from a single extrinsic fluorophore (from both a photoinduced electron transfer process and motions of the fluorophore) can be used to probe the dynamics and/or conformational distributions of proteins embedded in a membrane environment

New fluorescence methods for protein folding and conformational studies

Fluorescence spectroscopy has been extensively used in the study of protein folding, dynamics and function. Fluorescence resonance energy transfer (FRET), in particular, has proven to be very useful in this regard. However, FRET studies commonly employ exogenous fluorescent dyes, which may cause undesirable consequences, such as those due to nonspecific labeling or the bulky size of the probes. Amino acid fluorophores, therefore, provide an attractive alternative for FRET applications as they are smaller and easy to incorporate into the protein of interest. In the first part of this thesis, we explore the applicability of an amino acid FRET pair, p-cyanophenylalanine (Phe CN) and tryptophan (Trp), to the study of protein folding using two model protein systems. We demonstrate that quantitative information regarding the folding/unfolding process can be extracted from a single FRET titration experiment using a theoretical method we developed. Subsequently, we show that this FRET pair can be used in conjunction with a stopped-flow technique to directly dissect the binding and folding kinetics of intrinsically disordered proteins. Building on this work, we show that other non-natural amino acids, such as 7-azatryptophan (7AW) and 5-hydroxytryptophan (5HW), can also be used as FRET acceptors to PheCN, each with specific advantages over Trp. Finally, we demonstrate that PheCN, Trp and 7AW constitute a multi-FRET system that can be used to simultaneously monitor relative movements between different regions of a protein, thus allowing additional structural information to be extracted from a single FRET experiment. In the second part of this thesis, we expand the utility of fluorescence correlation spectroscopy (FCS) to the study of membrane proteins. We illustrate, using the Influenza A M2 proton channel as a model, how fluorescence fluctuations that arise from a single extrinsic fluorophore (from both a photoinduced electron transfer process and motions of the fluorophore) can be used to probe the dynamics and/or conformational distributions of proteins embedded in a membrane environment

Does Spatial Structure Persist Despite Resource and Population Changes? Effects of Experimental Manipulations on Coyotes

We tested the influence of a change in food resource distribution on space use and diet of coyotes (Canis latrans). We focused on 2 facets of space use: maintenance of home ranges by residents, and establishment of home ranges by immigrants after a coyote removal program. The study was conducted on 2 populations of coyotes in southern Texas. In both populations, a clumped, high-quality food source was added to randomly selected feeding stations to measure the influence of food distribution and abundance on home-range patterns, trespassing rates, and consumption of native prey. In established home ranges, coyotes visited and foraged at stations regularly and were found closer to stations during the treatment period. Although there was no overall treatment effect on home-range size (F = 1.66, d.f. = 5, P = 0.15), home ranges without supplemental food remained stable in size, whereas home ranges that had received supplemental food increased during the posttreatment period (t = 2.09, d.f. = 1, P = 0.04). Core areas showed a similar trend; there was no overall treatment effect (F = 1.51, d.f. = 2, P = 0.24); however, core areas of home ranges that received supplemental food were smaller than those of controls during the treatment period (t = 2.71, d.f. = 1, P \u3c 0.01). There were no statistical differences in occurrence of any species, such as small mammals or white-tailed deer (Odocoileus virginianus), in scats of treatment versus control coyotes. Coyotes within the study site after removals were located closer to feeding stations during treatment than posttreatment (F = 8.83, d.f. = 1, P \u3c 0.02,n = 897) periods, yet home-range size with supplemental food was larger than home-range size during the posttreatment period. Our findings suggest that a resource other than food influences coyote spatial patterns

Nanostructured materials for photoelectrochemical hydrogen production using sunlight

Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface.The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3.Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented.ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures.The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings