Triazolinediones as highly enabling synthetic tools

Triazolinediones (TADs) are unique reagents in organic synthesis that have also found wide applications in different research disciplines, in spite of their somewhat "exotic" reputation. In this review, we offer two case studies that demonstrate the possibilities of these versatile and reliable synthetic tools, namely, in the field of polymer science as well as in more recently emerging applications in the field of click chemistry. As the general use of triazolinediones has always been hampered by the limited commercial and synthetic availability of such reagents, we also offer a review of the available TAD reagents, together with a detailed discussion of their synthesis and reactivity. This review thus aims to serve as a practical guide for researchers that are interested in exploiting and further developing the exceptional click -like reactivity of triazolinediones in various applications

S-nitrosothiols: novel decomposition pathways including reactions with sulfur and nitrogen nucleophiles

Spectrophotometric (including stopped-flow) techniques were used to examine the kinetics of NO-group transfer reactions (transnitrosation) between S-nitrosothiols (RSNO) and a wide range of sulfur/nitrogen nucleophiles in aqueous solution. A metal-ion chelator was added in all experiments to prevent RSNO decay and NO liberation catalysed by copper ions. In most cases reaction was envisaged as rate- determining attack of the nucleophile at the nitrogen atom of the -SNO moiety, and hence S-nitrosothiols essentially acted as electrophilic nitrosating agents. Sulfite, thiosulfate, thiourea, thiocyanate and thiomethoxide, were sufficiently nucleophilic to induce nitrosothiol decomposition at physiological pH. Reaction with sulfide (pH > 7.4) afforded the orange-yellow anion, SSNO, and embodies a potential quantitative test for RSNOs. S-Nitrosopenicillamine was reactive enough to allow a thorough investigation into its reaction at basic pH with primary, secondary (creating carcinogenic N-nitrosamines), and tertiary amines, as well as ambident (e.g. thiomorpholine) and alpha nucleophiles (e.g. azide ion). Parallels could be made with analogous studies using other nitroso compounds such as MNTS. The generality of the reaction of a S-nitrosothiol with a large excess of the corresponding or a different thiol was also assessed. Ammonia and not nitric oxide was confirmed as the primary nitrogenous product of this highly complicated process. Mechanistic details of the copper(I) catalysed decomposition of some novel S- nitroso derivatives (e.g. a synthesised S-nitroso-1 -thiosugar) are reported. The two- stage degradation pathway involved an initial Cu(^+) promoted component that halted at incomplete conversion, and was accompanied by a large thermal reaction. An explanation of this unique pattern has been offered in terms of the generation of a disulfide-Cu(^2+) complex, in which copper is/is not accessible to reduction

Responsive lanthanide complexes for metal ion sensing

The speciation and distribution of zinc (II) within cells is not well established and the range of zinc (II) probes available are of limited use. The quest was to develop responsive lanthanide complexes to bind selectively and respond (by change in hydration state) to biologically relevant concentrations of zinc at physiological pH for possible application in MRI and luminescence. A pyridyl sulfonamide ligand with an a-CH(_2)NHSO(_2)CF(_3) substituent was found to have the desired properties for strong zinc (II) coordination. The presence of a methyl group at 6', inhibited the formation of related square planar copper (II) complexes. Pyridyl amide appended europium and gadolinium (III) complexes, based on cyclen were developed with C(_2) and (C_3) spacers separating the macrocyclic ring and the amide. The mono-aqua C(_2) complex exhibited fast water exchange, due to the steric hindrance of the seven-membered chelate between the amide carbonyl and the lanthanide centre. The increase in steric hindrance caused by the eight-ring chelate in the C(_3) analogue rendered it q = 0. A trifluoromethanesulfonamide moiety at the 6' position of the pyridine group resulted in a mono-aqua complex for the C(_2) and C(_3) appended systems. This system showed no change in hydration state on addition of Zn(^2+). The addition of a-N- carboxyalkyl groups to give a GdaD03A system resulted in the formation of q = 2 complexes which showed no zinc (II) responsive properties. However, the C(_2)- linked species exhibited a high binding affinity to HSA which resulted m a dramatic increase in the relaxivity. Eu and Gd complexes of an octadentate N(_5)O(_3) pyridyl sulfonamide containing ligand were developed as pH and pZn responsive probes. The pyridyl nitrogen bound irreversibly to the lanthanide centre, resisting protonation even in the presence of zinc and copper ions, for which the pyridyl sulfonamide group has an establiblished high affinity

Degradation of Trace Organic Chemicals and Antibiotic Resistant Bacteria/Genes during Conventional and Advanced Oxidation Processes

This PhD thesis investigated the elimination of trace organic chemicals (e.g., antibiotics) and their related biological risks (i.e., antibiotic resistant bacteria and genes) in urban wastewater effluent. The efficiency of an emerging water treatment technology, UV-based advanced oxidation process, was explored in comparison to conventional disinfection (e.g., chlorination, chloramination). Detailed studies focused on the degradation kinetics and mechanisms of contaminants and genes, as well as the effect of various water matrix components on treatment efficiency

The utilization of flavonoids as inhibitors of urease and as antimalarial agents and the discovery of bacterial methionine aminopeptidase inhibitors

This dissertation explores the inhibition of prominent enzymatic pathways important for both medicinal and agricultural applications. The research involved three distinct projects: First, an enzymatic urease inhibitory assay was optimized for plate-based screening of tree bark extracts to compare with ex vivo results from simulated-barn floor manure slurry assays performed by Dr. Wayne Zeller (USDA, Madison, WI). It wafs discovered that the measured ammonia abatement activities of each extract exhibited a correlation in both the enzymatic and ex vivo assays. Second, aminoalkylated quercetin analogs were synthesized and screened for antimalarial activity. The most potent species were found to exhibit sub-micromolar inhibitory values against multidrug-resistant strains of Plasmodium falciparum, the malarial parasite. Finally, a library of potential inhibitors of methionine aminopeptidase, an enzyme necessary for bacterial proliferation, were synthesized or purchased and screened for enzymatic inhibitory activity. A number of sub-micromolar inhibitors were discovered, and the most potent compounds were screened in a host-cell viability assay by Dr. Jonathon Audia (USA, Mobile, AL)

Gasotransmitter Detection Methodologies for Real-time Analysis and Studying Molecular Transport

Gasotransmitters are a family of gaseous signaling molecules comprised of nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S). As these molecules play key roles in numerous biological processes, they have been widely investigated for their potential as multifunctional therapeutic agents. Unfortunately, their small size, volatility, and low physiological concentrations make them particularly difficult to quantify and characterize in situ. Herein, the development of several analytical methodologies is described for real-time, selective detection of H2S and characterization of therapeutic NO doses in cystic fibrosis (CF)-relevant media. Two platforms for the direct, electrochemical detection of H2S were devised to contend with the passivating effects of elemental sulfur, H2S’s oxidative byproduct. First, triple pulse amperometry (TPA) was employed to mitigate sulfur adsorption. Inhibiting adsorption was achieved by cycling between three electrochemical actions: oxidizing adsorbed sulfur to sulfate, repelling sulfate off of the electrode surface, and quantifying H2¬S via low potential oxidation. As an alternative technique, constant potential amperometry (CPA) exploited unavoidable sulfur adsorption to precondition the electrode surface with a stable and reproducible sulfur layer. Both methodologies facilitated long-term, stable performance with sufficient sensitivity, rapid response times, wide linear dynamic ranges, and biologically-relevant detection limits. Additional selectivity toward H2S was imparted upon both TPA and CPA sensors by electrodepositing permselective films on the electrode surface. While CPA sensors saw significant improvements against numerous biological interferents, TPA damaged the films which led to inconsistent results. The ortho-phenylenediamine-modified (o-PD) CPA sensor was deemed the optimal design for further work in biological media. A planar carbon electrode system, combining the o-PD-modified CPA methodology and a fluorinated xerogel, was developed to utilize the sensor for cellular measurements. The bilaminar design was found to be highly selective for H2S, while also exhibiting low detection limits (<100 nM). To demonstrate the in situ application of the planar sensor, H2S released from stimulated human endothelial cells was quantified in real-time. Stimulated cells released sustained H2S levels for hours before returning to baseline. Cellular viability assays demonstrated that minimal cytotoxicity occurred during these measurements. Finally, the utility of exogeneous NO as a CF therapeutic was explored as a function of its mode of delivery and volatility in proteinaceous media. Bactericidal assays were performed by dosing CF-relevant bacteria with either gaseous NO (gNO) or NO-releasing chitosan oligosaccharides. Under all tested conditions, the NO-releasing chitosan required lower levels of NO in solution to elicit antibacterial action. Additionally, NO diffusion was tracked through increasingly complex barriers (buffered saline, artificial sputum media, and lung tissue). Diffusion though the tissue was an order of magnitude slower than the other two solutions, although artificial sputum media saw a significant decrease in diffusion coefficients compared to saline.Doctor of Philosoph