Neutral molecular radicals have received increasing attention as building blocks for functional molecular materials owing to their intrinsic conductive and magnetic properties. However, for these systems to be technologically viable, the molecular framework must be capable of stabilizing the unpaired electron, but also enable a degree of control and modulation of the desired properties. To achieve these goals, the design of the radical template requires consideration of the intrinsic effects on the electronic structure and those from a supramolecular perspective. In that regard, thiazyl radicals are promising candidates, as their physical attributes can be tuned systematically for the application at hand. In the pursuit of tunable thiazyl frameworks, two thiatriazinyl radicals have been synthesized and functionalized with heteroaromatic substituents. The contrasting nature between the attached thienyl and pyridyl substituents was evident upon establishing the preparative routes towards the neutral radical, and further demonstrated when the radicals were characterized spectroscopically. Structural analysis has emphasized the ability for the heteroaromatic moieties to direct the assembly of molecules into different supramolecular arrangements, in addition to self-associating into tightly bound structures. While dimerization voids the spin properties of these radicals, the redox-versatile thiatriazinyls were designed to explore the physical properties originating from metal coordination. Using the more robust anionic precursor, a dinuclear dysprosium complex was isolated and structurally analyzed, where oxidation of the ligand occurred in the process. A mechanism towards the self-assembly of the complex has been proposed by NMR studies using the isostructural yttrium analogue, which has provided insights on the metal-ligand reactivity. Furthermore, single-molecule magnet behaviour was observed for the dysprosium complex following magnetic investigations. In contrast to thiatriazinyls, the resonance-stabilized pyridine-bridged bisthiadiazinyls can remain undimerized in the solid state. Three derivatives have been developed with thienyl attachments and vary by the atomic substitution at the basal carbon position (i.e., R = H, F, Cl). Solution measurements illustrated spin delocalization extending across the π-framework, while halogenation provided a handle to fine-tune the energies of frontier molecular orbitals. Moreover, the ability of the thienyl rings to engage in various interactions was manifested in the polymorphic behaviour for each derivative. The solid-state structures were analyzed from single-crystal X-ray diffraction and highlighted the range of supramolecular architectures afforded by these systems. Lastly, two crystallographic phases of a bisdithiazolyl derivative were isolated selectively, such that the low-temperature phase possess an unprecedented high-symmetry trigonal space group. The mix-matched sizes of the beltline substituents afforded a honeycomb arrangement of stacked radicals. Magnetic measurements depicted a transition to an antiferromagnetically ordered state below 8 K, from which a high-temperature series expansion function was developed to model the magnetic data. Analysis of the results suggest the presence of two equivalent spin-spiral sublattices spanning across the crystal lattice three-dimensionally.

The Ph.D. thesis was focused on EPR study of redox reactions of selected types of phenols, secondary amines and diperoxy coumpounds. Within the study some redox agents were employed in nonpolar, in some special cases also in polar solvents. EPR spectra of generated radical products were interpreted using spectral simulation. Study of radical reactions under participation of phenols was preferentially concentrated on the behavior of para methyl substituted phenols, where the instability of this substituent in relation to the applied redox agents was evaluated. The tendency towards the abstraction of hydrogen from methyl group, representing the paralell mechanism to the hydrogen abstaction from phenolic OH group was proved. The generated benzyl radicals were undirectly detected in the form of adducts with aromatic nitroso compounds. These adducts undergo the consecutive transformations, leading to the formation of new types of phenoxy radicals. The study of the decomposition of NH bonds was performed with substituted N,N´-paraphenylenediamines, 1-anilino-1-phenylpentane-3-ones and amino substituted 1,3-dimethyluracils. By the oxidation with 3-chloroperbenzoic acid the corresponding nitroxyl radicals were prepared. In the case of 1-anilino-1-phenylpentane-3-ones the aminyl radicals were prepared by the oxidation with PbO2, which existence was evidenced by spin trapping method with nitrosobenzene. In the framework of the investigation of the decomposition of -O-O- bonds the oxygen centred radicals, generated from peroxidic compounds of Luperox type using selected redox agents were detected by spin trapping method. The analysis of EPR spectra documented that primary alkoxyl radicals undergo the consecutive fragmentation, which leads in the presence of oxygen to the formation of secondary alkoxyl radicals. The generation of oxygen centred radicals during the decomposition was indirectly proved in the presence of model phenolic compounds, where due to the abstraction of hydrogen from phenolic OH group the phenoxyl radicals are formed.

Endothelium-derived vasodilators, i.e., nitric oxide (NO), prostacyclin (PGI2) and prostaglandin E2 (PGE2), play important roles in maintaining cardiovascular homeostasis. C-reactive protein (CRP), a biomarker of inflammation and cardiovascular disease, has been shown to inhibit NO-mediated vasodilation. The goal of this study was to determine whether CRP also affects endothelial arachidonic acid (AA)-prostanoid pathways for vasomotor regulation. Porcine coronary arterioles were isolated and pressurized for vasomotor study, as well as for molecular and biochemical analysis. AA elicited endothelium-dependent vasodilation and PGI2 release. PGI2 synthase (PGI2-S) inhibitor trans-2-phenyl cyclopropylamine blocked vasodilation to AA but not to serotonin (endothelium-dependent NO-mediated vasodilator). Intraluminal administration of a pathophysiological level of CRP (7 μg/mL, 60 min) attenuated vasodilations to serotonin and AA but not to nitroprusside, exogenous PGI2, or hydrogen peroxide (endothelium-dependent PGE2 activator). CRP also reduced basal NO production, caused tyrosine nitration of endothelial PGI2-S, and inhibited AA-stimulated PGI2 release from arterioles. Peroxynitrite scavenger urate failed to restore serotonin dilation, but preserved AA-stimulated PGI2 release/dilation and prevented PGI2-S nitration. NO synthase inhibitor L-NAME and superoxide scavenger TEMPOL also protected AA-induced vasodilation. Collectively, our results suggest that CRP stimulates superoxide production and the subsequent formation of peroxynitrite from basal released NO compromises PGI2 synthesis, and thus endothelium-dependent PGI2-mediated dilation, by inhibiting PGI2-S activity through tyrosine nitration. By impairing PGI2-S function, and thus PGI2 release, CRP could promote endothelial dysfunction and participate in the development of coronary artery disease.

Les spirooxindoles se retrouvent fréquemment dans les produits naturels et les composés biologiquement actifs. Certains principes actifs pharmaceutiques contenant un motif spirooxindole ont également été décrits, stimulant un grand intérêt pour la construction et la modification de ce squelette. Cependant, peu de travaux ont été réalisés pour remplacer le carbonyle en position 2 par un autre groupe fonctionnel d’intérêt. Basées sur l’expertise reconnue de notre équipe en désaromatisation d’indoles par umpolung et l’importance des fonctions CF₃ et PO(OR)₂ nous avons entrepris la synthèse de 3,3-spiroindolines substitueés en position 2 par un trifluoromethyl ou un phosphonate. Nous avons ainsi généré des radicaux trifluoromethyl ou phosphonyl par oxydation respective de trifluoromethyl sulfinate de sodium et de phosphites. Les espèces radicalaires obtenues peuvent ensuite s’additionner sur la position 2 des indoles et effectuer la désaromatisation d’indoles. / Spirooxindoles are frequently found in natural products and biologically active compounds. Certain pharmaceutical active ingredients containing a spirooxindole motif have also been described, stimulating great interest in the construction and modification of this structures. However, not a lot of work has been done to replace the carbonyl in position 2 with another functional group of interest. Based on the recognized expertise of our team in deflation of indoles by umpolung and the importance of CF₃ and PO(OR)₂ functions, we have undertaken the synthesis of 3,3-spiroindolines substituted in position 2 by a trifluoromethyl or a phosphonate . We have thus generated trifluoromethyl or phosphonyl radicals by respective oxidation of sodium trifluoromethyl sulfinate and phosphites. The radical species obtained can then be added to the position 2 of the indoles and perform the dearomatization of indoles.

In 2010, comet 103P/Hartley 2 was observed pre- and post-perihelion using the George and Cynthia Mitchell Integral Field Spectrometer on the 2.7-m telescope at McDonald Observatory in Texas. Data for gaseous radicals C2, C3, CH, CN, and NH2 were collected over six nights from 15 July to 10 November. The spectral data were used to create coma maps for each of the observed species, and the maps were processed using radial and azimuthal mean division techniques to create enhanced images of the coma, revealing subtle morphological features. 340 enhanced coma images were created for each observation and species. Visual inspection reveals that the coma is heterogeneous between the five detected radicals, and statistical analyses verify this result. To compliment the ongoing investigation of Hartley 2 as studied by the EPOXI flyby mission, findings from other researchers (Belton et al., 2012; Syal et al., 2012; and Thomas et al., 2012) are used to characterize the nucleus spin state and identify dust jet locations on the nucleus. With rotational period measurements from EPOXI, dust jet vectors on the nucleus surface are rotated to relevant observation times in November to compare the computed jet directions with the radical densities in the coma. Dust jet sites on the smaller nucleus lobe show a stronger correlation with high radical concentrations than the dust sites on the larger nucleus lobe. Production rates for potential parentage of radical species are calculated using the radial outflow Haser model (Haser, 1957), which are compared to mixing ratios relative to water from separate campaigns to constrain parentage. NH3 is likely the sole producer of NH2, whereas CN may be produced from a combination of HCN, C2N2, and CH3CN. Traditional parentage of C2, C3, and CH do not yield acceptable fits or suitable mixing ratios with the Haser model, and it is possible that extended coma ices having relatively short scale lengths greatly contribute to production of these radicals. These results provide further evidence that the Hartley 2 nucleus is heterogeneous in composition, and the rotational analysis indicates that specific jet sites are correlated with certain radical species.

Metal nanoparticle-decorated titanium dioxide (M@TiO₂) materials are an increasingly popular class of heterogeneous catalyst, useful in both photochemical and thermal systems. Heterogenous catalysts offer the advantage of reusability and ease of catalyst separation, when compared to similar homogeneous systems. M@TiO₂ catalysts also have the benefit of water/air environment stability, strong photoactivity for oxidation and reduction reactions, as well as easy and low cost synthesis of the catalyst. Other heterogeneous catalysts can offer better activity for certain reactions; however, M@TiO₂ materials are extremely versatile in a variety of different reactions and applications, and often are cheaper than other alternatives. In this dissertation, M@TiO₂ catalysts will be evaluated in hydrogen generation, solvent radical chemistry, and organic synthesis utilizing calcium carbide. Firstly, M@TiO₂ were evaluated for photocatalytic hydrogen generation from pure water splitting, and with the presence of sacrificial electron donors (SEDs) such as methanol. Efficient pure water splitting is of great interest for fuel production as it offers a perfect cycle with hydrogen gas burning to reform water as the only product. However, quite often SEDs are utilized to boost hydrogen gas generation due to poor conversion from pure water. It is often assumed that a photocatalyst effective with a SED will also be effective with water splitting. This assumption was tested, by comparing a variety of different M@TiO₂ photocatalysts for both water splitting, and SED-based hydrogen generation. Interestingly, it was found that the trends of hydrogen generation between photocatalysts are not the same in pure water splitting, as when SEDs are present. For example, Pd@TiO₂ shows great activity with a 1% methanol solution; however, no considerable H₂ generation for pure water splitting. This shows that the mechanisms of hydrogen generation with water splitting, and when SEDs are present, are very different and not directly comparable. It was also found that M@TiO₂ materials offer decent hydrogen generation rates, especially when considering the overall cost of the material. M@TiO₂ materials were then tested for their ability to photocatalytically form usable free-radicals from ethers. This was evaluated with scavenging of generated radicals by TEMPO, as well as monitoring the resulting H₂ production during the reduction portion of the system. Overall, it was found that M@TiO₂ photocatalysts are exceptional at forming radicals from ethers. All the ethers tested are able to undergo proton-coupled electron transfer (PCET) with the hole of TiO₂, as seen by the H₂ generation observed. The main considerations are instead for the ether-radical, and if the radical will fragment or primarily undergo other reactions. This led to only some of the ethers being able to form TEMPO-ether adducts. The photogenerated hole of TiO₂ is also strong enough to form benzylic radicals from toluene, highlighting the further versatility of the catalyst. To further explore TiO₂-generated radicals, heterogeneous laser flash photolysis techniques were then developed. Laser flash photolysis of TiO₂ suspensions is an uncommon, and underdeveloped technique in the research field. It was considered if low concentration suspensions of TiO₂ could allow for lowered impact from the absorbance and scattering from the TiO₂ particles. This allowed for monitoring the transient absorbance of a benzylic radical from the reaction between 1,1-diphenylethylene and 1,3-dioxolane solvent radicals formed by the photogenerated hole of TiO₂. The strength of this transient signal also showed dependence on the solvent, with 1,4-dioxane showing lower signal as expected from it's reactivity. This technique, with further development, should prove useful in expanding the kinetic evaluation of radicals generated by TiO₂ suspensions. Finally, Pd@TiO₂ was evaluated as a thermal catalyst for a Sonogashira-like reaction between calcium carbide and bromobenzene in DMSO under low water conditions. This palladium catalyst was effective in catalyzing the reaction; however, the more interesting aspect was in the chemistry of the calcium carbide itself. Calcium carbide is typically used for the in-situ formation of acetylene gas through the addition of water. However, it was found that in DMSO with low amounts of water, the formation of a soluble ethynyl calcium hydroxide intermediate could be selected for. This allowed for a more controlled and effective coupling with bromobenzene in solution. Further expansion on the use of this intermediate may be invaluable in expanding calcium carbide chemistry beyond the formation of acetylene gas.

<p> There is only one unambiguous report in the literature of anchimeric assistance by the π-bond in a free radical reaction. It was the purpose of this work to investigate the possibility of such acceleration in the thermal homolysis of 7-norbornene peresters. Two such t-butyl peresters, the isomeric syn- and anti-7-norbornene percarboxylates as well as t-butyl 7-norbornane percarboxylate, were prepared and their decomposition was studied by kinetic methods and product analysis.</p> <p> The homolysis of 7-norbornene peresters is shown to occur with rate-determining perester O-O bond rupture, the transition state of which may be a hybrid of radical and polar structures. A low order of anchimeric acceleration may also assist the decomposition of the syn compound.</p> <p> The pKa values for syn- and anti- 7-norbornene- and 7-norbornane- carboxylic acid are reported.</p> / Thesis / Doctor of Philosophy (PhD)

The decomposition of nitrosyl disulfonate ion was studied in strongly alkaline solution of 10-2 to 5 m sodium hydroxide. The decomposition was found to be first-order in both hydroxide and nitrosyl disulfonate ions. A multi-step mechanism involving sulfite ion, sulfite ion radical and nitrosyl monosulfonate ion radical as intermediates was proposed, with the initiating step being the SN2 replacement of a sulfite ion by a hydroxide ion. The rate constant for the initiating step ranged from 1.2 x 10-7 to 2.25 x 10-5 M-1s-1 for the solution concentration range of the study. The products of the decomposition were identified as hydroxylamine disulfonate ion, hydroxylamine trisulfonate ion, and nitrite ion. The proposed mechanism was applied to the previously studied decomposition in mildly alkaline to slightly acidic, and nonaqueous solutions and found to explain all the reported observations if the side reactions involving the hydrolysis and reversion of hydroxylamine disulfonate ion were included.

No description available.

No description available.