Part I reports the stud y of the decomposition of nitrosyl disulfonate ion in DMSO, acetonitrile, and dichloromethane. A multi-step mechanism involving sulfite ion, sulfite ion radical, and nitrosyl monosulfonate radical as intermediates is proposed. The products of the decomposition are nitrosonium ion, hydroxylamine disulfonate ion, and hydroxylamine trisulfonate ion. A competitive chain reaction was observed when the decomposition occurred in DMSO. The chain reaction was insignificant in carefully dried acetonitrile and dichloromethane. Part II reports the study of the reaction between 2,2-diphenyl-1-picryl hydrazyl (DPPH) and nitrosyl disulfonate ion. Product analysis and kinetic data obtained from stopped-flow procedures suggest that the reaction involves the attack of nitrosyl disulfonate ion on the para-phenyl position of DPPH followed by hydrogen migration to form a substituted hydrazine.

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The function of biomacromolecules is controlled by their structure and conformational flexibility. Investigating the structure of biologically important macromolecules can, therefore, yield information that could explain their complex biological function. In addition to X ray crystallography and nuclear magnetic resonance (NMR) methods, pulsed electron paramagnetic resonance (EPR) methods, in particular the pulsed electron electron double resonance (PELDOR) technique has, during the last decade, become a valuable tool for structural determination of macromolecules. Long range distance constraints obtained from pulsed EPR measurements, make it possible to carry out structural refinements on structures from NMR and X ray methods. In addition, EPR yields distance distributions that give information about structural flexibility. The use of EPR for structural studies of biomacromolecules requires in most cases site specific incorporation of paramagnetic centres known as spin labelling. To date, spin labelling nucleic acids has required complex spin labelling chemistry. The first application of a site directed and noncovalent spin labelling method for distance measurements on DNA is described. It is demonstrated that noncovalent spin labelling with a rigid spin label can afford detailed information on internal DNA dynamics using PELDOR. Furthermore, it is shown that noncovalent spin labelling can be used to study DNA protein complexes. PELDOR can also yield information about spin label orientation. Therefore, spin labels with limited flexibility can be used to measure the relative orientation of the spin labelled sites. Although information on orientation can be obtained from 9.7 GHz PELDOR measurements in selected applications, measurements at 97 GHz or higher, increases orientation selection. It is shown that PELDOR measurements on semi rigid and rigid nitroxide biradicals using a home built high power 97 GHz EPR spectrometer (Hiper) and model based simulations yield quantitative information on spin label orientations and dynamics. The most widely used spin labels for EPR studies on biomacromolecules are the aminoxyl (nitroxide) radicals. The major drawbacks of nitroxide spin labels include low sensitivity for distance measurements, fast spin spin relaxation in solution and limited stability in reducing environments. Carbon centered triarylmethyl (trityl) radicals have properties that could eliminate some of the limitations of nitroxide spin labels. To evaluate the use of trityl spin labels for nanometer distance measurements, models systems with trityl and nitroxide spin labels were measured using PELDOR and Double Quantum Coherence (DQC). This study shows that trityl spin labels yield reliable information on interlabel distances and dynamics, establishing the trityl radical as a viable spin label for structural studies on biomacromolecules.

Positively charged aromatic carbon-centered σ-type mono-and biradicals have been studied previously in the gas phase. However, very little is known about the properties of related polyradicals. In this dissertation, the reactions of series of quinolinium-and acridinium-based bi-, tri-, and tetraradicals were studied with cyclohexane and allyl iodide in the gas phase by using tandem mass spectrometry. I atom abstraction and allyl group abstraction were observed as dominant reactions for all the studied radicals upon reactions with allyl iodide. Sequential H atom abstractions were observed as the major reactions for the studied bi-and tetraradicals upon reactions with cyclohexane. Surprisingly, triradicals appeared to undergo addition followed by elimination of a H atom as one of the major reactions upon interactions with cyclohexane. Vertical electron affinity and spin-spin coupling between radical sites were found to control the radical reactivities.<div><br></div><div>The radical site(s) which react first with cyclohexane were experimentally determined. For the studied biradicals, the first reacting radical sites were found to be the ones that are predicted to be more reactive based on the reactivities of related monoradicals. For the studied triradicals, the first reacting radical sites are the ones that are least strongly coupled to the other radical sites. For tetraradicals, the first two sites reacting with cyclohexane are more weakly coupled than the other two radical sites.<br></div><div><br></div><div>The mechanisms for the reactions of the triradicals with cyclohexane were proposed based on tandem mass spectrometry experiments and supported by quantum chemical calculations. Briefly, the least strongly coupled radical site of a triradical reacts with cyclohexane first by abstracting a H atom. The more reactive radical site insome of the produced biradicals will then abstract a H atom from the cyclohexyl radical within the product collision complex to generate a monoradical and cyclohexene. Some of these monoradicals undergo addition to cyclohexene within this product complex,followed by elimination of a H atom. When allowed to react with allyl iodide, all of the monoradicals and most of the biradicals demonstrated predominant I atom abstraction. The quinolinium-based meta-and para-benzynes exhibited allyl group abstraction as the major reaction. The triradicals with a meta-benzyne moiety in the pyridinium ring demonstrated dominant allyl group abstraction, which is likely to occur at the pyridinium moiety. The reaction efficienciesof these triradicals toward allyl iodide are correlated with their calculated vertical electron affinities. The other triradicals showed I atom abstraction as the major reaction. These triradicals react with allyl iodide through different mechanisms compared to those mainly abstract an allyl group. Therefore, their reactivities are not directly related to their calculated vertical electron affinities.<br></div><div><br></div><div>In the tetraradicals, spin-spin coupling between all the radical sites affects their reactivities. The coupling of the radicals in a benzyne moiety is weakened by the couplings of radical sites between two benzyne moieties. This interaction results in higher reaction efficiencies for the tetraradicals than the related benzynes. Particularly, the 2,4,7,8-tetradehydroquinolinium cation was found to have much higher reactivity than the related meta-benzyne, the 2,4-didehydroquinolinium cation. This was rationalized based on the low distortion energy of the meta-benzyne moiety in the tetraradical.<br></div><div><br></div><div>Spin-spin coupling between the radical sites in bi-, tri-, and tetraradicals significantly affect their reactivity. To better understand the relation between the effects of spin-spin coupling and the spatial distance between two radical sites, a series of acridinium-based mono-and biradicals were studied in the gas phase. The acridinium-based monoradicals are less reactive than the related quinolinium-based monoradicals, which is possibly because of the steric hindrance of the additional benzene ring. Unlike quinolinium-based biradicals, which are less reactive than the related monoradicals, acridinium-based biradicals showed higher reactivities than the monoradicals with similar vertical electron affinities. In order to better illustrate the coupling strength in the studied biradicals, the natural logarithm of their total reaction efficiencies toward cyclohexane was plotted as a function of their calculated vertical electron affinities. The plots indicate that the coupling of quinolinium-based biradicals hinders the radical reactivity, while for acridinium-based biradicals, the coupling is negligibly weak and the biradicals react as two individual monoradicals.<br></div>

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published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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