Date of Award
Doctor of Philosophy (PhD)
Biomedical and Chemical Engineering and Sciences
D. Andrew Knight
Kelli Z. Hunsucker
Christopher D. Chouinard
Porphyrins are differentiated π-conjugated compounds with unique photochemical and redox properties. The tetrapyrrole macrocycle core of porphyrins is extremely favorable for the complexation of metal ions, resulting in hybrid metal-organic molecules with good catalytic properties. Porphyrin-based systems are known for their oxidative properties and are frequently utilized as bio-mimicking catalysts and environmental remediation agents. My current research aims at both of these aspects. One of the most efficient methods to create photocatalytic systems with outstanding features and applicability is the use of porphyrins on supported solid materials. A series of novel mesoporous silicate-embedded metalloporphyrins were prepared via conjugation of novel organo-silicate sorbent synthesized using 50:50 1,4- bis(trimethoxysilylethyl)benzene and 1,2-bis(trimethoxysilyl)ethane (ED-13) and porphyrin (meso-tetra(4-carboxyphenyl)porphyrin (C4TPP) or 5-mono(4- carboxyphenyl)porphyrin (C1TPP)) using simple amide coupling chemistry. The metalation was achieved by refluxing the given materials and water-soluble metal ion salt in H2O for 12 hours. Characterization by BET shows retention of mesoporous characteristics for the given materials after metalation. Additional studies were done using solid-state fluorescence showing fluorescence quenching in the region of 600-800 nm upon excitation at 415 nm, confirming the coordination of metal ions to the porphyrin center. These materials are shown to act as decontaminating agents in the presence of light (Xe lamp). To understand the influence of coordinated metal ions and the effect of reaction solvents, studies were done wherein the rate of photolysis of DPBF was monitored using fluorescence spectroscopy at 450 nm and UV-VIS spectroscopy at 410 nm. The spectroscopic studies show degradation of DPBF in presence of light confirming ROS generation. Further investigations were carried out to analyze the products after the photolysis of DPBF using LC-MS, showing the generation of singlet oxygen (1O2). Future studies involving mechanistic pathways for the deactivation of singlet oxygen (1O2) will be conducted. Porphyrin-based catalytic oxidation is one of the most representative biomimetic catalysis. A novel aqueous-based Rh(III) system was modeled on a previously reported rhodium(III) tetra(p-sulfonatophenyl)porphyrin complex Na3[(TSPP)Rh(H2O)2] and shown to degrade simple tertiary amines catalytically via N-dealkylation pathway in the presence of acid under aerobic conditions, at 80 °C. Rh(III) complex (1) was synthesized using meso-tri(4-sulfonatophenyl)mono(4- carboxyphenyl) porphyrin from a direct reaction of free porphyrin and metal chloride salt refluxed in MeOH/DMF. 1 was characterized using UV-Vis and proton NMR spectroscopy, and high-resolution mass spectrometry. 1 was shown to remove synthetic opioid - fentanyl from the solution at 37 °C in the absence of acid. The breakdown products were determined using liquid chromatography ion mobilitymass spectrometry (LC-IM-MS) and suggest a tandem N-dealkylation oxidative pathway with an unusual ring opening of the piperidine ring. Additionally, 1 was successfully conjugated onto the surface of 20 nm diameter gold nanoparticles (AuNPs) ( 1@Au) (~280 copies per AuNP) via EDC-NHS coupling using the carboxy group on 1. No breakdown of fentanyl was seen for studies done using 1@Au showing deactivation of the catalyst after conjugation onto AuNPs. We suggest the integration of 1 on other nanoparticle platforms to study the influence of the carboxy group present in the given porphyrin for the inactivation of fentanyl.
Pal, Hemant, "1. Influence of Metal Ions and Solvents on the Photo-generation of Reactive Oxygen Species in Mesoporous Silicate Embedded Porphyrins 2.Water-Soluble Rhodium(III) Porphyrin Complex for the Biological Inactivation of Fentanyl" (2023). Theses and Dissertations. 1265.
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