Amino acid radicals and radical cations formed through oxidation are characterized by Time-resolved Electron Paramagnetic Resonance (TREPR) spectroscopy. These oxidation processes occur through single-electron transfer events to excited triplet state anthraquinone photo-sensitizers, and by hydrogen atom transfer to hydroxyl radicals created in situ. The identity of the radicals formed by electron transfer is strongly dependent on the pH of the solution. In particular, a previously hypothesized cyclic methionine radical cation structure is directly observed on the sub-microsecond timescale. The uncharged carbon radicals formed by hydroxyl attack in oxygenated environments are found to form peroxyl adducts with molecular oxygen. The structures of these radicals are deduced by computer simulation of magnetic parameters. The radical intermediates created upon oxidation of diglycine by anthraquinone photosensitizers are used as probes for microscopic water pools formed in reverse micelles. A new "micro-reactor" model is used to simulate the chemically induced dynamic electron polarization of the TREPR radical signals. Radical diffusion coefficients are generated from these simulations from which the viscosities of the water pools can be calculated. Also, radicals formed from direct oxidation of the reverse micelle surfactant are observed and characterized by TREPR, the products are analyzed by chemically induced dynamic nuclear polarization.