Chemistry Commons^™

Design, Synthesis And Study Of Redox And Optoelectronic Properties Of Aromatic Oxidants And Polycyclic Aromatic Hydrocarbons, Mohammad Mosharraf Hossain

Dissertations (1934 -)

Organic materials play a significant role for the next generation photovoltaic devices that convert solar energy into usable forms of energy. In this regard, polycyclic aromatic hydrocarbons (PAHs) are fundamental tools in the developing area of molecular electronics and photovoltaics as they show excellent optical/electronic properties and are well-suited for applications in such developing areas as flexible display devices, field effect transistors and solar cell panels. Design and synthesis of novel materials for photovoltaics applications would require the proper understanding the mechanism of charge transport and identification of the structural features necessary in a particular molecular wire or PAH. To …

The Photodynamic And Structural Analyses Of Advanced Materials For Solar Fuel Conversion, Brian Pattengale

Dissertations (1934 -)

Mitigating the current and future climate and pollution issues that have been brought on by the combustion of fossil fuels is of utmost importance and will rely on, in part, the availability of renewable fuel sources. Of the possible sources of energy, solar is abundant, but must be harnessed efficiently and stored as a solar fuel to overcome the current storage issues that limit photovoltaic cells. One such fuel, H2(g), represents a carbon-neutral source of energy if it can be efficiently liberated from water via the water splitting reaction. Thus, much attention is focused on designing materials to perform the …

Photoremovable Protecting Groups Based On Electrocyclization With Leaving Group Expulsion Via A Proposed Zwitterion, Gilbert Ndzeidze

Dissertations (1934 -)

The triplet excited state of thioxanthone produced by photolysis undergoes reversible triplet energy transfer with a trimethylene - linked benzothiophene-2-carboxanilide ring system. The ensuing electrocyclic ring closure of the anilide moiety produces a putative zwitterionic intermediate that is capable of expelling leaving groups (LG-) from the C-3 position of the benzothiophene ring. Stern-Volmer quenching studies with cyclohexadiene as quencher furnish the rate constants for the triplet excitation transfer in the forward and reverse directions, which can be expressed as an equilibrium constant K = 0.058. Overall, the rate of triplet excited state reaction becomes K x kr = 5.7 x …

Functional And Structural Studies Of Cytochromes P450 By Resonance Raman Spectroscopy, Yilin Liu

Dissertations (1934 -)

Cytochrome P450 is a broad class of heme monooxygenase enzymes which catalyze various oxidative transformations. There are two main kinds of mammalian P450s: steroidogenic and drug metabolizing P450s. The first project involves a steroidogenic P450, CYP17A1, occupying a central role in the biosynthesis of steroid hormones. It catalyzes hydroxylation reaction on pregnenolone and progesterone, generating 17OH-pregnenolone and 17OH-progesterone, presumably utilizing a “Compound I” species. However, these hydroxylated products can be further processed in a second oxidative cycle to cleave the C17–C20 bond to form dehydroepiandrosterone or androstenedione, respectively, a crucial step in androgen production. Interestingly, it is well known that …

Ruthenium-Catalyzed Dehydrogenative And Dehydrative C-H Coupling Reactions Of Arenes With Alcohols And Carbonyl Compounds, Hanbin Lee

Dissertations (1934 -)

Despite their outstanding achievements, the requirement of preformed functional groups and wasteful byproduct formation are inherent disadvantages associated with the transition metal catalyzed cross-coupling methods. Inspired by the needs for green and sustainable chemistry, transition metal catalyzed dehydrogenative and dehydrative coupling methods have been recognized as environmentally sustainable and atom economical synthetic routes for the new C-C bond formation. The catalytic activation of C-H and C-O bonds allows the formation of coupling products from ubiquitous hydrocarbon substrates by releasing hydrogen or water byproduct. However, these novel protocols require relatively harsh conditions due to their low reactivity of C-H and C-O …

Synthesis And Study Of The Electrochemical And Optoelectronic Properties Of Π-Conjugated Poly-P-Phenylene-Based Molecular Wires, Anitha Boddeda

Dissertations (1934 -)

Organic photovoltaics will play an important role in supplementing the energy needs of the twenty first century in a most cost-effective way to convert the solar energy into usable forms of energy. One of the bottlenecks in promoting widespread use of photovoltaic devices for solar energy storage is the inefficiency of the devices, which in part arises due to the inefficient charge separation and long-range charge transport. Design and synthesis of efficient charge-transfer materials would require one to first identify and establish the structural features necessary in a given molecular wire, which may promote effective charge transfer to long distances. …

Computational Modeling Of S-Thiolation Reaction: Toward Discovering The Enzymatic Mechanisms Of Endogenous Hno Formation, Elena Ivanova

Dissertations (1934 -)

S-nitrosothiols (RSNOs) have long been proposed as potential sources of the elusive endogenous nitroxyl (HNO) via S-thiolation reaction with thiols. It is however not clear how S-thiolation can compete with the trans-S-nitrosation pathway commonly observed in vitro. Based on the insights into the highly unusual, antagonistic chemical nature of RSNO molecules, we hypothesize that, while difficult in vitro, S-thiolation could easily lend itself to enzymatic catalysis. To explore this possibility, we adopted a bottom-up computational approach that aims to identify possible catalytic mechanisms able to steer the RSNO + thiol reaction toward HNO production. Inspired by recent discovery of small …

Investigation Of The Use Of A Plasticizer-Polymer Sensor Coating With Improved Long-Term Stability In The Liquid Phase, Laura Jeanne Alderson

Master's Theses (2009 -)

Benzene is one of the volatile organic compounds present in crude oil and gasoline. Leakage from underground storage tanks or hazardous waste sites can introduce benzene contamination into nearby groundwater. Benzene is a known carcinogen and its exposure is limited by the Environmental Protection Agency to 5 parts per billion (ppb) in drinking water. Early, accurate detection of the presence of benzene contamination in groundwater supplies is extremely important. Shear horizontal surface acoustic wave (SH-SAW) devices with a chemically sensitive coating can be used for the detection of volatile organic compounds in liquid, such as BTEX (benzene, toluene, ethylbenzene and …

Photochemical Electrocyclic Ring Closure And Elimination Reactions Of N-(Oxothioxanthenyl)Naphthothiophene Carboxamides, Himali Devika Jayasekara

Dissertations (1934 -)

Photochemical cleavage reactions have found a widespread used in biological applications that require the photorelease of biologically active molecules such as proteins, peptides, neurotransmitters, and nucleotide phosphates. This research focuses on the design of photoremovable protecting groups which can be utilized to release these biomolecules by photolysis. These biomolecules are attached to the photoremovable protecting group at the sites of functional groups that are present within these substrates. Such functional groups are carboxylates, phosphates, thiolates, or phenolates, which upon exposure to light, are released as anions of varying basicities. The photochemical reaction involved is an electrocyclic ring closure between aromatic …

Toward Electronic Materials Based On Metal Pincer-Type Complexes, Jeewantha Sampath Hewage

Master's Theses (2009 -)

There is currently a lot of interest in developing electrically conducting or semiconducting metal-organic frameworks (MOF's), highly porous materials constructed by organic ligands bridging metal centers. Typically MOF's are non-conducting and, moreover, they are susceptible to hydrolytic degradation. If hydrolytically stable and electrically conducting MOFs could be realized, then revolutionary new technologies could be envisioned. Currently, organic dicarboxylates are used as bridging organic ligands and one simple strategy to obtain the desired materials is to explore other ligand systems. Pincer ligands are organic compounds that are uninegative and bind metals in a tridentate, meridional fashion with two five-member chelate rings. …

Photochemical Elimination Reactions That Proceed Via Triplet Excited State Electrocyclic Ring Closures, Himali Devika Jayasekara

Master's Theses (2009 -)

Cage compounds have become an important tool for the study of biological processes. The research focuses on new cage compounds that can unmask functional groups present in biologically important molecules such as proteins, peptides, and oligonucleosides. The project focuses on certain functional groups that are often difficult to release photochemically. These are the thiolate groups present in cysteine residues of proteins and peptides. Thiolate groups are fairly basic leaving groups, unlike the more labile groups such as the carboxylates that are present in proteins and peptides, or the phosphate groups present in nucleosides. The research takes advantage of the ability …

Expulsion Of Leaving Groups From Zwitterionic Intermediates Generated Via Photochemical Electrocyclic Ring Closure Reactions And An Investigation On Tpe Oligomers, Tasnuva Shahrin

Dissertations (1934 -)

Photochemical cleavage reactions have been found widespread use in biological applications that require intracellular photochemical release of biologically active substrates such as peptides, proteins, neurotransmitters, or nucleotide phosphates. The research is to devise photoremovable protecting groups (cage compounds) that can be used to deprotect those biological substrates by irradiation. A number of photocleavage reactions have been developed in recent years which release chlorides, hydroxides, carboxylates, thiolates, and phenolates leaving groups for use in such applications. Nevertheless, photochemical elimination reactions that expel such leaving group anions remain quite uncommon. The cleavage of cage compounds via photolysis requires heterolysis of a bond …

Design, Synthesis And Study Of Polycyclic Aromatic Hydrocarbons And Their Cation Radicals, Tushar Navale

Dissertations (1934 -)

The unifying theme of most of optoelectronic devices revolves around the charge carrier mobility of the organic materials used in the conductive layers, which is a measure of how easily the electron/hole moves in a particular pi conjugated organic material. When pi conjugated materials are incorporated in these devices, molecules are generally layered in random orientation. Consequently, the efficiency of charge transport in the conducting layers of these devices is governed not only by the intramolecular electron/hole transport through the backbone of the molecule but also by the intermolecular electron/hole transport between the molecules and hence packing of these molecules …

Design And Synthesis Of Polycyclic Aromatic Hydrocarbons For Emission And Through-Space Charge Delocalization Studies, Vijay Vyas

Dissertations (1934 -)

Over the past decades, a variety of pi-conjugated organic materials have been explored as potential charge transport materials in conducting layers of photovoltaic devices. The performance of these devices critically depend on the efficiency with which the charge carriers (electrons and/or holes) move within the pi-conjugated materials present in their hole and electron conducting layers before their collection at the electrode. Hence, a large amount of research effort is devoted not only to the preparation of new pi-conjugated organic molecules for charge transport applications but also in understanding the nature of charge transport along the molecule (intra-chain) as well as …

Design, Synthesis And Study Of The Bridged And Cofacially-Arrayed Poly-P-Phenylene Molecular Wires, Matthew J. Modjewski

Master's Theses (2009 -)

Two novel series of bridged and cofacially-arrayed poly-p-phenylenes have been designed synthesized and studied. The bridged poly-p-phenylenes have been synthesized from a readily available diacetylenic precursor utilizing three high yielding steps, and their structures were determined by 1H/13C NMR spectroscopy as well as X-ray crystallography. The racemization barrier between the two atropoisomers was found to be ~12 Kcal mol-1; the versatility of the synthesis employed was extended to synthesis a triply bridged tetra-p-phenylene and a quadruply bridged penta-p-phenylene.

The cofacially-arrayed poly-p-phenylenes have shown that the X-ray crystal structures of the neutral compounds are largely dominated by C-H--π-interactions interactions while the …