Electron spin resonance studies of solvation using nitroxide radicals as probes.

Over recent years electron spin resonance has been used to investigate solvation phenomena. This technique is useful for measuring processes occurring on a rapid timescale and is therefore suited for examining solutions. Several paramagnetic probes have been employed in such studies. Increasingly, nitroxide radicals have proved to be useful spin probes. The probe concentrations used in e.s.r. investigations of solvation are usually low and do not therefore appreciably effect the solvent composition. The initial chapters of this thesis are concerned with contemporary theories of solvation and those principles of e.s.r. which are relevant to solvation studies. A broad description of the structure and properties of water and aqueous solutions is given in chapter one. A review of how spectroscopic techniques have been used, by the Leicester group over recent years, to probe solvation effects is also included in this chapter. Chapter trove deals with factors perturbing the g and tensors of nitroxide radicals and the various mechanisms of line broadening encountered. The use of ditherier buty1 nitroxide as a spin probe in studying binary aqueous solutions is introduced in chapter three. Both the nitrogen hyperfine coupling constant and linewidths of this radical reveal changes in the solvent medium. In the succeeding chapter this study is extended to examine changes in solvation in electrolyte containing solutions. The e.s.r. results recorded in this study of aqueous and methanolic salt solutions are compared with near infra-red studies of similar systems. The fifth chapter describes a study of Heisenberg Spin Exchange for tertiary butyl nitroxide in several solvents. Water is shown to exert an anomalous effect on the observed exchange rate; this is interpreted in terms of water structure effects. The sixth chapter examines the information which can be obtained from studies of tertiary butyl nitroxide in frozen solutions. Solid state spectra in frozen matrices are used to estimate the spin distribution in the radical t-butyl-N-benzoyl nitroxide. The final chapter deals with the role of t-butyl-N-benzoyl nitroxide as a spin probe. The data is interpreted in the same manner as the tertiary butyl nitroxide results and reveals that t-butyl-N-benzoyl nitroxide is less suitable as a probe of the aqueous environment. Several useful computer programs, which were used to analyze some of the data collected throughout this study, are documented in the Appendix.