BIOLOGICAL IMPLICATIONS OF THE REACTIONS OF THIOCYANATE (SCN

Hypochlorous acid (HOCl) is one of the major neutrophil-derived oxidants used to kill invading pathogens. However, excess or misplaced production of HOCl can damage host tissue as it reacts indiscriminately with biological molecules such as amino acids. Chloramines are a major product of the reaction between HOCl and amino acids. As they decompose, protein-bound chloramines can permanently damage proteins by altering their structures and function. Thiocyanate (SCN-) reacts efficiently with HOCl and thus is able to limit its propensity to inflict host tissue damage. The concentration of SCN- in human physiologic fluids varies depending on the source of fluid and the individuals dietary and smoking habits. For example, normal human blood plasma has micromolar levels of SCN- while the oral cavity has millimolar concentrations.The first chapter of this dissertation covers the objectives of the research and the introduction of the important themes. The second chapter summarizes the experimental methods and the analytical techniques used to conduct the research. The third chapter of this dissertation is focused on the reaction of SCN- with chloramines. We found that SCN- reacts efficiently with chloramines in small molecules, in proteins, and in Escherichia coli cells to give OSCN- and the parent amine. We also observed that chloramines react faster with OSCN- than SCN-. This suggests that the reductions of chloramines by SCN- and OSCN- have potential biological significance as they may repair some of the damage infected by HOCl on proteins.Under slightly acidic pH conditions, chloramines disproportionate to dichloramines. In the fourth chapter, the reactivity of dichloramines towards thiols was examined. We found that at equimolar concentrations, the dichloramines react much faster with thiols than monochloramines. Chlorotaurine reacts with thiols with a (pH-dependent) pseudo-second order rate constant of 102 M-1s-1 while the rate constant for dichlorotaurine is 106 M-1s-1 at pH 7.4. These results suggest that the more stable dichloramines (e.g. those on lysine residues and on taurine) may be playing a role, at least in part, in the killing of phagocytosed bacteria.The fifth chapter of this dissertation evaluates the biological significance of the reaction of SCN- with chloramines. To achieve this goal, we investigated the extent to which SCN- restored the activity of glutathione reductase (GR) and also how it affected the population of viable A549 lung cancer cells after treatment with HOCl. Under certain conditions, we found that approximately half of GR activity that was inactivated by a large molar excess of HOCl was recovered after incubation with SCN-. We speculate that the cysteine active site of the protein was protected from irreversible over-oxidation by its hydrophobicity. The observed reversibility upon reaction with thiocyanate is attributed to a chlorinated key histidine. The viability studies of A549 cells incubated with HOCl for 20 min and then with SCN- show a significant increase in the proportion of live cells and a decrease in the proportion of necrotic cells. We surmise based on these results that early SCN- intervention (20 min) after the exposure of A549 cells to low concentrations of HOCl can repair and reverse some of the damage. Overall, the results of the investigation described in this dissertation indicate that SCN- may play a more active role in quenching chloramines in vivo than has been previously appreciated

Ruthenium complexes with lumazine derivatives: structural, electrochemical, computational and radical scavenging studies

In this research study, the formation and characterization of new ruthenium(II) and (III) complexes encompassing multidentate ligands derived from 6-acetyl-1,3, 7-trimethyllumazine (almz) are reported. The 1:1 molar coordination reactions of trans-[RuCl2(PPh3)3] with N-1-[1,3, 7-trimethyllumazine]benzohydride (bzlmz) and 6-(N-methyloxime)- 1,3,7-trimethyllumazine (ohlmz) formed a diamagnetic ruthenium(II) complex, cis-[RuCl2(bzlmz)(PPh3)] (1), and paramagnetic complex, cis-[RuIIICl2(olmz)(PPh3)] (2) [Holmz = 6-(N-hydroxy-N0-methylamino)-1,3,7-trimethyllumazine], respectively. These ruthenium complexes were characterized via physico-chemical and spectroscopic methods. Structural elucidations of the metal complexes were confirmed using single crystal X-ray analysis. The redox properties of the metal complexes were investigated via cyclic voltammetry. Electron spin resonance spectroscopy confirmed the presence of a paramagnetic metal centre in 2. The radical scavenging activities of the metal complexes were explored towards the DPPH and NO radicals. Quantum calculations at the density functional theory level provided insight into the interpretation of the IR and UV–Vis experimental spectra of 1

Coordination of di- and triimine ligands at ruthenium(II) and ruthenium(III) centers: structural, electrochemical and radical scavenging studies

Herein, we explore the coordination of di- and triimine chelators at ruthenium(II) and ruthenium(III) centers. The reactions of 2,6-bis-((4- tetrahydropyranimino)methyl)pyridine (thppy), N1,N2-bis((3-chromone) methylene)benzene-1,2-diamine (chb), and tris-((1H-pyrrol-2-ylmethylene) ethane)amine (H3pym) with trans-[RuIICl2(PPh3)3] afforded the diamagnetic ruthenium(II) complex cis-[RuCl2(thppy)(PPh3)] (1) and the paramagnetic complexes [mer-Ru2(μ-chb)Cl6(PPh3)2] (2), and [Ru(pym)] (3), respectively. The complexes were characterized by IR, NMR, and UV–vis spectroscopy and molar conductivity measurements. The structures were confirmed by single crystal X-ray diffraction studies. The redox properties of the metal complexes were probed via cyclic- and squarewave voltammetry. Finally, the radical scavenging capabilities of the metal complexes towards the NO and 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH) radicals were investigate

Ruthenium complexes with Schiff base ligands containing benz(othiazole/imidazole) moieties: Structural, electron spin resonance and electrochemistry studies

Novel ruthenium(II/III) complexes of Schiff bases containing benzimidazole (bz) or benzothiazole (bs) moieties were isolated: the diamagnetic ruthenium complex, cis-[RuIICl2(bzpy)(PPh3)2] (1) was formed from the 1:1 M reaction between N-((pyridine-2-yl)methylene)-1H-benzimidazole (bzpy) and metal precursor, trans-[RuCl2(PPh3)3]. The same metal precursor, when reacted with the benzimidazole-derived Schiff bases [N-(2-hydroxybenzylidene)-benzothiazole (Hbsp) and N-(2-hydroxybenzylidene)-benzimidazole (Hbzp)], afforded the paramagnetic ruthenium(III) complexes [RuCl(bsp)2(PPh3)] (2) and trans-[RuCl(bzp)(PPh3)2] (3), respectively. These metal complexes were characterized via IR, mass and UV–Vis spectroscopy, elemental analysis, single crystal XRD analysis as well as conductivity measurements. Their redox properties were probed by voltammetry and accompanying UV–Vis spectroelectrochemistry experiments. Structural features of complex 1 were further investigated by multinuclear (1H and 31P) NMR spectroscopy

Synthetic, characterization and cytotoxic studies of ruthenium complexes with Schiff bases encompassing biologically relevant moieties:

This research study describes the formation and characterization of novel paramagnetic ruthenium complexes, cis-Cl, trans-P-[RuIIICl2(carboim)(PPh3)2] with bidentate chelating carbohydrazide Schiff bases (carboim = bpc for 1, ttc for 2 and tpc for 3). These metal complexes were synthesized by the equimolar coordination reactions of trans-[RuCl2(PPh3)2] with N-[1,3-benzothiazole-2-ylmethylidene]pyridine-2-carbohydrazide (Hbpc), N-((uracil-5-yl)methylene)thiophene-2-carbohydrazide (Httc) and N-[(uracil-5-yl)methylidene]pyridine-2-carbohydrazide (Htpc), respectively. Physicochemical techniques including nuclear magnetic resonance-, electron-spin resonance- and infrared spectroscopy, UV–Vis spectrophotometry, voltammetry as well as molar conductivity measurements provided definitive determinations of the respective ruthenium compounds’ structures

Anticancer evaluation of ruthenium (III) complexes with N-donor ligands tethered to coumarin or uracil moieties:

In this study, the synthesis and characterization of new paramagnetic ruthenium(III) complexes: cis-[RuCl2(urdpa)] (1) {Hurdpa = 6-((bis(pyridin-2-ylmethyl)amino)methyl)uracil} and fac-[RuCl3(chrdpa)] (2) {chrdpa = 4-((bis(pyridin-2-ylmethyl)amino)methyl)-7-methoxycoumarin} are reported. These metal complexes have been comprehensively characterized by an array of physicochemical techniques and the X-ray solid-state structures of 1 and Hurdpa have been attained