Identification of Individual Reaction Steps in Complex Radical Reactions Involving Gold Nanoparticles.

A triple-jump model is invoked to help identify individual reaction steps in complex chemical reactions involving radical reactants in the presence of gold nanoparticles. The model consists of three sequential reaction phases: production of radicals, stabilization of radicals, and conversion from radical intermediates to final products. Isolated reaction phases were studied with electron paramagnetic resonance spectroscopy. As examples of the model, we investigated the spin trapping reaction with BMPO and the hydroxylation of 3-CCA, and the results supported the model. For X-ray irradiation of gold nanoparticle aqueous solutions, hydroxyl radicals were found to be scavenged by nanoparticles in the first phase. The stabilization phase was largely unaffected by gold nanoparticles, whereas conversion of radical intermediates was catalyzed. Such a step-wise model is thus proven useful for determining the exact catalytic step in the presence of nanoparticle catalysts in complex reactions such as DNA strand breaks, polymerization and hydroxylation that are important to many fields including X-ray nanochemistry.