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Chemistry & Chemical Biology Department Theses and Dissertations
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Browsing Chemistry & Chemical Biology Department Theses and Dissertations by Author "Basu, Partha"
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Item Investigating the Photophysical Properties of Potential Organic Lead Sensors(2023) Quinones, Carlos; Basu, Partha; Deng, Yongming; Pu , JingzhiLeadGlow (LG) was reported in 2009 for its ability to both sensitively and selectively detect Pb2+ in aqueous solutions. Utilizing the synthetic approach of LG, it is possible to generate a class of novel fluorophores. A derivative of first-generation LG was synthesized and reported here for the first time, intuitively named LG2. Both compounds contain interesting photophysical properties that have not been extensively researched prior to this work. Because of this, photophysical properties of both LG and LG2 are unveiled here for the first time. These properties were investigated by determinations of quantum yield (QY), average fluorescence lifetime, and DFT calculations. LG was found to have a higher QY (0.057) than LG2 (0.011); however, LG2 displays an average fluorescence lifetime (3.186 ns) 5x greater than that of LG. Both LG and LG2 are synthesized via Hg2+-facilitated desulfurization of their respective thiocarbonyls, resulting in a turn-on fluorescence feature. The thiocarbonyl-containing fluorophores (SLG and SLG2) display quenched fluorescence compared to their oxo-derivatives (LG and LG2), this work attempts to investigate the mechanism(s) responsible. A whole class of LeadGlow compounds can be synthesized and could be potentially used as fluorescence-based sensors.Item Molecular cloning, heterologous expression, and steady-state kinetics of camplyobacter jejuni periplasmic nitrate reductase(2020-08) Mintmier, Breeanna; Basu, Partha; Georgiadis, Millie; Deiss, Frédérique; Minto, RobertMononuclear molybdenum enzymes catalyze a variety of reactions that are essential in the cycling of nitrogen, carbon, arsenic, and sulfur. For decades, the structure and function of these crucial enzymes have been investigated to develop a fundamental knowledge for this vast family of enzymes and the chemistries they catalyze. The dimethyl sulfoxide reductase (DMSOR) family is the most diverse family of molybdoenzymes and, the members of this family catalyze a myriad of reactions that are important in microbial life processes. Periplasmic nitrate reductase (Nap) is an important member of the DMSO reductase family that catalyzes the reduction of nitrate (NO3-) to nitrite (NO2-), and yet the physiological role of Nap is not completely clear. Enzymes in this family can transform multiple substrates; however, quantitative information about the substrate preference is sparse and more importantly, the reasons for the substrate selectivity are not clear. Substrate specificity is proposed to be tuned by the ligands coordinating the molybdenum atom in the active site. As such, periplasmic nitrate reductase is utilized as a vehicle to understand the substrate preference and delineate the mechanistic underpinning of these differences. To this end, NapA from Campylobacter jejuni has been heterologously overexpressed, and a series of variants, where the molybdenum-coordinating cysteine has been replaced with another amino acid, has been produced. The kinetic and biochemical properties of these variants will be discussed and compared with those of the native enzyme, providing quantitative information to understand the function.Item Understanding the Role of Ligand Oxidation State: Design, Synthesis, and Reactivity of Electronically Asymmetric Molybdenum Dithiolene Complexes(2019-08) Dille, Sara A.; Basu, Partha; Minto, Robert; Lei, Li; Pu, JingzhiMononuclear molybdopterin enzymes are a large class of enzymes that are present in all phyla of life. All pterin containing enzymes posses a molybdopterin cofactor made up of a molybdenum metal center coordinated directly by a dithiolene ligand, which is appended to a pyranopterin cofactor. The majority of these enzymes catalyze oxygen atom transfer reactions that are concomitant with a transfer of two-electrons. We are hypothesizing that by altering the oxidation states of the dithiolene, the reactivity of the cofactor can be tuned for different substrates. This investigation focuses on the synthesis and characterization of oxo-MoIV(dithiolene) complexes that possess a fully reduced dithiolene ligand (dithiolene) and a fully oxidized dithiolene ligand (dithione). These complexes are designed to represent the asymmetry of the dithiolene ligand that is observed in the crystal structures of the DMSO reductase family. Asymmetric oxo-MoIV(dithiolene) complexes exhibit a unique structural property, a large fold angle along the S•••S vector of the dithione ligand. These complexes also show a positive solvatochromic effect in a range of polar to nonpolar solvents. The rich electrochemical properties of these redox active complexes and other characterization details such as IR, and NMR studies will be presented. Effects on the reactivity of these complexes using biologically relevant substrates will be discussed. The oxygen atom transfer reactivity has been probed by mass spectrometry and NMR spectroscopy. The presented complexes aide in highlighting the effect redox state of the dithiolene ligand has in modulating reactivity