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No description available.

Cell membranes are integral for many biological processes. In addition to containing and protecting cellular contents and maintaining the chemical integrity of the cell, these interfaces host a variety of ligand-receptor interactions. These ligand-receptor interactions are important for cell signaling and transport and the ability to monitor them is key to understanding these processes. In addition, therapeutics and drug discovery is also aided by membrane-specific study, as the majority of drugs target receptors associated with the cell surface. The cell membrane can be effectively mimicked by the use of supported lipid bilayers, which provide a robust platform exhibiting the lateral fluidity and composition associated with cell membranes. The ability to study both ligand-receptor interactions as well as small molecule-membrane interactions on these model membranes is aided by the fact that these assays can be multiplexed and are amenable to use with low sample volumes with high throughput. Our laboratory has recently developed a strategy for fluorescent microscopy studies of ligand-receptor interactions on supported lipid bilayers without the use of fluorescently-labeled analytes. This technique involves the incorporation of pH-sensitive fluorophores into the composition of the supported lipid bilayer as embedded reporter dyes. It was determined that this assay can operate as either a “turn-on” or a “turn-off” sensor depending on the analyte to be detected. It was additionally found that modulating the ionic strength of the operating buffer allows for tuning the operating pH and sensitivity of the assay. This label-free technique can be utilized to monitor small peptide interactions with bilayers containing specific phospholipids. Basic amino acid sequences which are associated with transporting contents across membranes or anti-microbial activity can be monitored binding to negatively charged bilayers without the use of labels. Not only is this a sensitive technique for detecting small peptides, but thermodynamic data can be extracted as well. In a final set of experiments, the interaction of proteins with phosphatidylserine (PS) in supported lipid bilayers is observed by utilizing PS-Cu2+-induced quenching of fluorophores. Disruption of this metal-phospholipid, specifically by Ca2+-dependent protein kinases, results in a turn-on fluorescent assay, which can be used to monitor the binding of the protein to PS and the effects of other metal interference.

Zugl.: Berlin, Techn. Univ., 2006

Single-site catalysts revolutionized the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently used commercially to produce commodity and differentiated-commodity resins. The key to their rapid success and industrial implementation resides in the fact that they can be used without major modifications in the polymerization reactors that previously used heterogeneous Ziegler-Natta and Phillips catalysts. Since most of these industrial processes use slurry or gas-phase reactors, soluble single-site catalysts must be supported on adequate carriers that ensure not only high activity, but also the formation of polymer particles with the proper morphology and bulk densities. Metallocene catalysts have been supported on a variety of carriers, but supporting late transition metal catalysts has not been investigated in detail, despite their very interesting properties such as tolerance to polar comonomers and impurities, activity in the absence of MAO, and the formation of short chain branches by the chain walking mechanism. The research work of this PhD thesis intends to fill this gap, by developing supported late transition metal catalysts with high catalyst activities towards ethylene polymerization and good polymer particle morphology. The effects of catalyst structure and polymerization conditions on silica-supported nickel diimine catalysts are discussed in Chapter 3. Compared with the equivalent homogeneous catalysts, the covalently-attached supported catalysts had high activities, produced spherical polyethylene particles with good morphologies, and polyethylene with higher melting temperatures, higher molecular weight averages, and broader molecular weight distributions. Borates used as internal activators during the synthesis of these supported catalysts successfully activated the nickel diimine complexes. In Chapter 4, MgCl2/alcohol adducts are recrystallized with alkylaluminum compounds and used as catalysts supports for nickel diimine complexes functionalized with amine groups. Polymerization results were compared with those of the equivalent SiO2-supported nickel diimine catalysts. MgCl2-based supported nickel diimine catalysts had high catalyst activity without the use of activators, and it was possible to control polymer molecular weight averages by changing the support composition. Although linear low density polyethylene made with metallocenes offers superior mechanical properties such as excellent toughness, impact strength and clarity, it suffers from poor processability. To overcome some of these disadvantages, Chapter 5 introduces methods to produce bimodal polyethylene resins using supported hybrid early and late transition metal catalyst systems. The presence of short chain branches in the higher molecular weight component is attributable to the incorporation of alpha-olefin molecules by the metallocene sites, while the nickel diimine catalyst sites produce chains with a distribution of short chain branch sizes through the chain walking mechanism. Finally, in Chapter 6 supporting a nickel diimine catalyst onto organo-modified montmorillonite (MMT) to prepare polyethylene/clay nanocomposites through in-situ polymerization is described. The thermal properties and crystallinity of the nanocomposites could be controlled by varying the fraction of MMT in the nanocomposite, and the dispersion of the MMT layers in the polymer matrix were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

published_or_final_version / Chemistry / Master / Master of Philosophy

Polymer-supported reagents and catalysts, which allow for simple product separation and easy recycling, have been widely studied in the context of organic synthesis. The past decade has witnessed a number of new variations of polymeric materials, and among the most frequently immobilized functionalities are amines that possess versatile synthetic utilities. Polymers with new structures and improved properties for use in synthesis have been continuously developed since the support may impact the chemical reactions in which they are used in various ways. A new heterogeneous polystyrene-based amine, rasta resin-DMAP, has been synthesized and used in addition reactions of carbon dioxide to epoxides to afford cyclic carbonate products. This new material was found to be a more efficient catalyst than divinylbenzene cross-linked polystyrene supported DMAP, and was readily recycled without significant loss of catalytic activity. Compared to polymers bearing a single functionality, polymers possessing multiple different functional groups attached to a single polymer backbone would have greater potential utility, especially in reactions requiring multiple catalysts or reagents. As an example of this concept, a bifunctional polystyrene bearing both DMAP and piperazine groups has been prepared and applied as an organocatalyst for decarboxylative Doebner-Knoevenagel reactions of arylaldehydes and mono-ethyl malonate to produce (E)-,-unsaturated esters in high yields. Additionally, both non-cross-linked and cross-linked bifunctional polystyrenes featuring amine and thiourea groups have been developed, and their catalytic performance were evaluated in reactions of nitroalkenes with either nitroalkanes or sulfur ylides. Both polymers proved to be efficient catalysts in these reactions and the insoluble polymer demonstrated high recyclability. Control experiments using monofunctional polymers indicated that both catalytic groups of these bifunctional polymers are essential and they could work cooperatively to achieve efficient catalysis. Finally, a second generation bifunctional phosphine-amine polymer, rasta resin-PPh3-NBniPr2, was prepared and examined in tandem Wittig-reductive aldol reactions. In these reaction cascades, the phosphine oxide groups generated from the Wittig reaction served as the catalyst for the reductive aldol reaction, and moderate yields of structurally diverse -hydroxy ketones could be obtained from one-pot processes involving 5 sequential reactions. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Increased levels of carbon dioxide in the atmosphere are now widely attributed as a leading cause for global climate change. As such, research efforts into the capture and sequestration of CO2 from large point sources (flue gas capture) as well as the ambient atmosphere (air capture) are gaining increased popularity and importance. Supported amine materials have emerged as a promising class of materials for these applications. However, more fundamental research is needed before these materials can be used in a practically relevant process. The following areas are considered critical research needs for these materials: (i) process design, (ii) material stability, (iii) kinetics of adsorption and desorption, (iv) improved sorbent adsorption efficiency and (v) understanding the effects of water on sorbent adsorption behavior. The aim of the studies presented in this thesis is to further the scientific community’s understanding of supported amine adsorbents with respect to stability, adsorption efficiency and adsorption behavior with water.

Single-site catalysts revolutionized the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently used commercially to produce commodity and differentiated-commodity resins. The key to their rapid success and industrial implementation resides in the fact that they can be used without major modifications in the polymerization reactors that previously used heterogeneous Ziegler-Natta and Phillips catalysts. Since most of these industrial processes use slurry or gas-phase reactors, soluble single-site catalysts must be supported on adequate carriers that ensure not only high activity, but also the formation of polymer particles with the proper morphology and bulk densities. Metallocene catalysts have been supported on a variety of carriers, but supporting late transition metal catalysts has not been investigated in detail, despite their very interesting properties such as tolerance to polar comonomers and impurities, activity in the absence of MAO, and the formation of short chain branches by the chain walking mechanism. The research work of this PhD thesis intends to fill this gap, by developing supported late transition metal catalysts with high catalyst activities towards ethylene polymerization and good polymer particle morphology. The effects of catalyst structure and polymerization conditions on silica-supported nickel diimine catalysts are discussed in Chapter 3. Compared with the equivalent homogeneous catalysts, the covalently-attached supported catalysts had high activities, produced spherical polyethylene particles with good morphologies, and polyethylene with higher melting temperatures, higher molecular weight averages, and broader molecular weight distributions. Borates used as internal activators during the synthesis of these supported catalysts successfully activated the nickel diimine complexes. In Chapter 4, MgCl2/alcohol adducts are recrystallized with alkylaluminum compounds and used as catalysts supports for nickel diimine complexes functionalized with amine groups. Polymerization results were compared with those of the equivalent SiO2-supported nickel diimine catalysts. MgCl2-based supported nickel diimine catalysts had high catalyst activity without the use of activators, and it was possible to control polymer molecular weight averages by changing the support composition. Although linear low density polyethylene made with metallocenes offers superior mechanical properties such as excellent toughness, impact strength and clarity, it suffers from poor processability. To overcome some of these disadvantages, Chapter 5 introduces methods to produce bimodal polyethylene resins using supported hybrid early and late transition metal catalyst systems. The presence of short chain branches in the higher molecular weight component is attributable to the incorporation of alpha-olefin molecules by the metallocene sites, while the nickel diimine catalyst sites produce chains with a distribution of short chain branch sizes through the chain walking mechanism. Finally, in Chapter 6 supporting a nickel diimine catalyst onto organo-modified montmorillonite (MMT) to prepare polyethylene/clay nanocomposites through in-situ polymerization is described. The thermal properties and crystallinity of the nanocomposites could be controlled by varying the fraction of MMT in the nanocomposite, and the dispersion of the MMT layers in the polymer matrix were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Universiẗat, Diss., 1993--Marburg.