Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6424. Adviser: Ralph G. Nuzzo. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6426. Advisers: Paul J.A. Kenis; Andrzej Wieckowski. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2006. / "Title from dissertation home page (viewed June 28, 2007)." Source: Dissertation Abstracts International, Volume: 67-06, Section: B, page: 3105. Adviser: Gary M. Hieftje.

<p> Cytochrome P450s (P450s) are a superfamily of enzymes that catalyze oxidation of unactivated hydrocarbons. However, the means by which P450s control (1) regioselectivity of their activity and (2) specificity in their molecular recognition remain largely elusive. Toward investigation of the role of dynamics in the regioselectivity of the archetypal cytochrome P450cam (P450cam), two-dimensional infrared spectroscopy has been applied with heme-bound carbon monoxide (CO) as an infrared probe of the active site. The data support a model for P450cam regioselectivity in which binding of different substrates to P450cam variably stabilizes the active site into two distinct states, each associated with different dynamics linked to different levels of regioselectivity. To investigate the role of conformational heterogeneity in P450cam substrate specificity, infrared spectoscopy was combined with the site-specific incorporation of nitrile probes at distinct P450cam microenvironments. This approach enabled differentiation of changes experienced at each of those environments when <i> d</i>-camphor and/or CO binds to the active site. Finally, the impact of conformational heterogeneity on the affinity of substrate molecular recognition by wild-type and mutant P450cam was evaluated using both CO and nitrile probes. This study suggests that the nature of the conformations populated in the unbound states influences the affinity for different substrates. Collectively, these studies provide new insight into the roles of conformational heterogeneity and dynamics in P450cam activity. Furthermore, these studies help to lay the foundation for efforts toward understanding the roles of conformational heterogeneity and dynamics in the function of human P450s, for which unraveling the mechanisms involved in Phase I metabolism is a topic of great pharmacological concern. </p><p>

Doctor of Philosophy / Department of Chemistry / Peter M.A. Sherwood / Thin films can be created on the surface of a metal, protecting it from oxidation and corrosion. Phosphate films have historically been a common choice for these corrosion resistant films. In this dissertation, the oxidation of vanadium metal by water and atmosphere is studied. Also, a series of phosphate films on the surface of vanadium metal were created and are studied as potential corrosion resistant films. Lastly, an independent study identifying the oxidation state of copper in a biological sample is carried out. To characterize these thin films, X-ray Photoelectron Spectroscopy (XPS) is employed. The reaction of vanadium metal with the atmosphere and distilled, de-ionized, water is studied. The core level and valence band results are explored and compared to calculated valence band spectra for some vanadium oxides. The etching of vanadium metal and reaction of the etched metal with a phosphoric acid solution are studied. Synthesized vanadium phosphate compounds serve as model compounds for the analysis of a phosphate coating created on the surface of vanadium metal by the reaction of vanadium metal with phosphoric acid by a newly developed bench top method. The core level and valence band regions for the compounds and coating are discussed along with cluster and band structure calculations for interpretation. The variation in the coating on vanadium metal by biasing the metal at different potentials during reaction is also studied. Coatings are also created on vanadium metal using different forms of phosphorus oxy-acid. An analysis of the various coatings is performed by XPS and accompanied by predictive calculations. In an additional study, the oxidation state of copper in a biological compound is identified. The analysis makes use of satellite features commonly seen in XPS to make the determination. A discussion of the origin of these features and the energy of the shifts is given, along with the results for the other core level XPS regions for the compound.

Doctor of Philosophy / Department of Chemistry / Christopher T. Culbertson / My doctoral dissertation consists of three fundamental studies: 1) synthesis of biocompatible materials that can be used as microfluidic substrates, 2) characterizing these materials with respect to properties important to microfluidic fabrication, biochemical separations and concentration enrichment, and 3) employing these novel devices for real world applications in bioanalytical chemistry. The surface properties of a substrate will dramatically affect the resolution and efficiency that can be obtained for a specific CE separation. Thus, the ability to modify the surface is very useful in tailoring a microfluidic chip to a specific separation mode. The substrates we have synthesized for microfluidic devices include metal oxide modified poly(dimethylsiloxane) (PDMS), poly(ethyleneoxide)-PDMS (PEO-PDMS) coblock polymers, and surfactant coated PDMS. The metal oxide modified PDMS materials we synthesized include silica-PDMS, titania-PDMS, vanadia-PDMS and zirconia-PDMS. The surfaces of these materials were characterized using contact angle, X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electroosmotic mobility (EOM) measurements. All of the metal oxide modified PDMS surfaces were significantly more hydrophilic than native PDMS, suggesting potential application in separations of biopolymers. In addition to being more hydrophilic the EOF and zeta potential of the channels were stable and quite durable with aging. Well characterized silane chemistry was used to derivitize the surface of the PDMS metal oxide surfaces allowing a number of different functionalities to be placed on the surface. This method has the potential for wide applicability in many different fields, but specifically for the fabrication of microstructures that need specific surface chemistries. We have also made a number of advancements using sol-gel chemistry and laminar flow within microfluidic channels to fabricate nanoporous membranes. Sol-gel patterned membranes are a simple and facile method of incorporating nanoscale diameter channels within a microfluidic manifold. These membranes have been used to perform preconcentration of amino acids, proteins and small particles for further analysis and separation using CE. We are also using these membranes for further study in desilanization and protein recrystallization studies.

Global energy demand is predicted to increase at an alarming rate over the next century; in order to meet this demand while also limiting the effects of runaway climate change, society will need to shift toward renewable sources of energy. Many of the fundamental chemical transformations that store renewable energy as fuel require the addition or removal of protons. Optimization of catalysts that carry out these transformations can be achieved with proton management at the molecular level. Deliberate construction of molecular catalysts with an intramolecular proton relay is one strategy for controlling the movement of protons during catalysis. These so-called “hangman” catalysts have been shown to increase the rate of catalysis in the cases of hydrogen evolution, oxygen reduction, hydrogen peroxide dismutation, and olefin epoxidation. A new class of hangman porphyrins is now available on the gram scale and can easily be further modified, allowing for unprecedented control the strength and character of pendant proton relays. Using iron complexes of these new hangman porphyrins, the level of control over proton management is demonstrated with the variation in the rates of hydrogen evolution electrocatalysis depending on the nature of the proton relay in the second coordination sphere. Understanding the fundamental electron transfer reactions of reactive oxygen species (ROS) is important in the chemistry of renewable energy storage, but also in a biological context. Hydrogen bond donors are known to affect the electron transfer reactivity of ROS, with the strength of the hydrogen bond determining the nature of oxygen-oxygen bond activation. The catalytic performance of iron corroles towards peroxide dismutation is markedly enhanced by the presence of a pendant hydrogen bond donor which is also capable of transferring protons to bound substrates. Contrary to hangman corroles, the six hydrogen bond donors in hexacarboxamide cryptand do not readily transfer protons, allowing it to facilitate the chemically reversible two-electron reduction of dioxygen to “naked” peroxide dianion. Using electrochemical techniques and computational modeling, it is possible to use cryptand-encapsulated peroxide as a model for the electron transfer reactions within lithium-oxygen batteries. / Chemistry and Chemical Biology

In order to meet the ever-increasing demand for energy, a worldwide transition away from fossil fuels to renewable solar–fuels is required. However, the intermittency of local insolation mandates a cost-effective and efficient storage scheme. Using solar-derived electricity to drive the thermodynamically uphill water splitting reaction to generate dihydrogen and dioxygen is one promising method of storing solar energy in fuels. This “artificial photosynthesis” scheme requires the execution of two half-reactions, one involving the oxidation of water to O2—the oxygen evolution reaction (OER)—and the other entailing the reduction of hydrogen ions to H2—the hydrogen evolution reaction (HER). Accomplishing these electrocatalytic reactions stresses the development of catalysts that are capable of mediating reactions that are in net multi-electron, multi-proton transformations. Transition metal oxides are known to be promising candidates for mediating the OER and their electrocatalytic properties have been studied extensively and optimized for operation at pH extremes. In contrast, intermediate pH OER has been relatively underexplored and the influence of proton-coupled electron transfer (PCET) reactions on OER kinetics of these materials at close-to-neutral pH has for long remained unclear. The OER studies described here have focused on elucidating the underlying mechanistic basis for the catalytic behavior of a class of structurally disordered first-row transition metal oxides, with an emphasis on intermediate-pH catalysis and proton–electron coupling. At a fundamental level, understanding how protons and electrons may be managed and coupled to engender improved activity remains of great importance to the design of new electrocatalysts. To this end, the synthesis and study of homogeneous HER catalysts bearing functional groups in the second coordination sphere that can modulate proton–electron coupling is particularly interesting. The HER studies presented here discuss this important issue within the context of metalloporphyrin catalysts possessing proton relays. / Chemistry and Chemical Biology

Paper (and other cellulose-based materials such as cotton thread and fabrics) are underexploited as materials for the construction of “high-tech” and “lab-on-a-chip” devices. One major drawback of paper is its tendency to absorb water from the environment and, with wetting, to change its mechanical properties; other challenges relate to control over the attachment of molecules (e.g. antibodies, DNA) and cells on its surface, and to the addition of electronic function. The goal of this thesis is to develop paper as a substrate for a range of applications— microfluidics, substrates for electronic systems and MEMS, low-cost diagnostics, cell biology, and optics. The approach involves chemically modifying the surface of the paper to provide new functions without altering any of its defining properties: mechanical flexibility, foldability, light weight, gas permeability, and low cost. The first part of my thesis describes the modification of paper by silanization with organosilanes such as alkyl- and fluoroalkyl trichlorosilanes in the gas phase. Here, silanization is used to lower the surface free energy of the paper and to minimize the tendency of paper to absorb liquids and vapors, and especially water. Chapter 1 and Appendix 3 demonstrate that the combination of long fluoroalkyl chains of grafted siloxanes with the micro-scale roughness and porosity of paper yielded a material that is omniphobic (both hydrophobic and oleophobic), while preserving the properties of mechanical flexibility and low resistance to transport of gas of the untreated paper. Appendix 3 shows that features of omniphobic paper can be used to construct microtiter plates and liquid-filled gas sensors using standard paper folding techniques, while Appendix 4 shows that new type of microfluidic device fabricated by carving microchannels into the surface of omniphobic paper. The resulting devices have open, unobstructed channels (with dimensions as small as 45 μm) and thus exhibit fluid dynamics similar to conventional PDMS-based microfluidics, but are much lighter and have the potential to be much less expensive than PDMS-based devices. The second part of my thesis is focused on engineering the surface of paper to enable efficient immobilization of capture and target molecules for bioanalysis. In one approach, described in Appendix 5, we exploit the ease with which the surface chemistry of paper (i.e. the surface of the cellulose fibers making up the paper) can be modified, in order to enhance the immobilization of antibodies and antigens on the surface of the paper via hydrophobic interactions, while preventing the wicking of the fluids into the paper substrate. As an application in low-cost diagnostics, we describe a low-cost electrochemical device for ELISA intended for use in resource-limited settings. In a second approach, described in Chapter 2, we developed of an efficient procedure for assembling microarrays of ssDNA and proteins on paper, at the lowest practical cost. This method starts with the synthesis of DNA oligonucleotides covalently linked to paper, and proceeds to generate ssDNA arrays that, through hybridization with complementary strands of DNA, are capable of simultaneously capturing DNA, DNA-conjugated protein antigens, and DNA-conjugated antibodies. The third part of my thesis describes the simple, inexpensive fabrication of electrodes for paper-based electrochemical systems. A first method describes, in Appendix 6, the development of inkjet printing as a method for high resolution printing of conductive patterns on omniphobic “RF” paper, both to extend its promise as a substrate for paper electronics, and to enable us to integrate it into our program in low-cost, paper based diagnostics. A second method, described in Chapter 3, circumvents the need for printing, and instead focuses on the fabrication and reconfiguration of simple, versatile, and inexpensive electroanalytical devices in which conventional stainless-steel pins—in unmodified form or after coating with a carbon paste—are used as electrodes. / Chemistry and Chemical Biology

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