Maja C. Milenković

Oxygen centered radicals in iodine chemical oscillators.

The existence of free radicals in iodine-based oscillatory systems has been debated for some time. Recently, we have reported the presence of reactive oxygen species (ROS) in the iodide-peroxide system in acidic medium, which is common to all iodine--based oscillatory systems ( J. Phys. Chem. A 2011 , 115 , 2247--2249 ). In this work, the goal was to identify the ROS produced in this system using an EPR spin trap which can distinguish between hydroxyl (HO(•)) and hydroperoxyl (HOO(•)) radicals. The formation of the hydroperoxyl radical was observed and a possible explanation for the low EPR signal of hydroxyl radical was proposed.

Radicals in the Bray–Liebhafsky Oscillatory Reaction

This study investigates the formation of free radicals in the Bray-Liebhafsky (BL) oscillatory reaction. The results indicate that radicals are produced during both monotonous and oscillatory dynamics observed as the change of the electron paramagnetic signal (EPR) of the spin-probe TEMPONE. EPR spin-trapping with DEPMPO suggested that the most abundant radical produced in the BL reaction is an iodine-centered radical. The EPR spectrum of the DEPMPO/iodine-centered radical adducts has not been previously reported. This study may aid in establishing a more realistic reaction mechanism of the BL reaction and related chemical oscillators.

Role of free radicals in modeling the iodide-peroxide reaction mechanism.

The mechanism of monotonous decomposition of hydrogen peroxide by iodide in acidic medium is investigated at room temperature. For this purpose, O(2) pressure, I(-), I(2), and I(3)(-) concentrations are simultaneously monitored, establishing a useful framework for better understanding of the reaction mechanism and testing various models. The possibility of nonradical and radical approaches to describe experimental data is examined. Results suggest that the best description of experimentally recorded components is obtained by introducing free radicals into the model of the reaction.

The kinetics of iodide oxidation by hydrogen peroxide in acid solution

The kinetics of the complex reaction between I− and H2O2 in acid media was investigated. The particular attention was focused on the determination of the rate constant of the reaction between HIO and H2O2 involved in the investigated complex process. The examination of the whole kinetics was performed by simultaneously monitoring the evolution of O2 pressure, I3− and I− concentrations. We modeled the behavior of experimentally followed components based on Liebhafsky’s research. Our preliminary results suggest a significantly higher rate constant (3.5 × 107 M−1 s−1) of the reaction between HIO and H2O2 as those proposed in the literature.

A Potential Source of Free Radicals in Iodine-Based Chemical Oscillators

The iodide-peroxide system in an acidic medium was investigated as a potential source of free radicals in iodine-based chemical oscillators. The radicals were detected by EPR spin-trapping using spin-trap 5-(tert-butoxycarbonyl)-5-methyl-1-pyrroline N-oxide (BMPO), which forms stable spin-adducts with oxygen-centered radicals. The iodide-peroxide system is introduced as an easily available laboratory source of free radicals.

Influence of Chemically Inert Cations on the Hydrogen-bond Network in the Bray-Liebhafsky Oscillatory Reaction

The influence of the chemically inert alkali metal cations on the Bray-Liebhafsky oscillatory reaction dynamics was investigated by the addition of the same amount of various sulfates to the reaction mixture. Beside the expected changes related to the altered acidity of the sulfuric acid solution, subtle changes dependent on cation dimensions were noticed. Larger cations have more impact on the Bray-Liebhafsky reaction dynamics. Analysing the mean ionic activity of salts, it is suggested that the effects may be related to the altered extent of water hydrogen bonding and specific role of bulk water in the reaction mechanism.