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.

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.

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.

A rapid and facile synthesis of nanofibrillar polyaniline using microwave radiation.

We present the first fast and facile microwave assisted synthesis of polyaniline (PANI) nanofibers ("MWA synthesis"). Under conventional synthesis (CS), the polymer was produced with 79.7% yield after 5 h at ambient temperature. However, under microwave irradiation, the nanofibers were produced with yield of 76.2% after only 5 min, i.e., with 78.8% after 20 min at ambient temperature. The FTIR and Raman spectra show the PANI structure in all samples either synthesized conventionally or in the microwave. SEM and TEM confirm the nanofibrillar morphology.

Energy dynamics in theBray-Liebhafsky oscillatory reaction.

Energy dynamics of the well-stirred, isothermally conducted Bray-Liebhafsky reaction is followed by monitoring the population of the first two vibration states of hydrogen peroxide. Excitations are detected by Raman spectroscopy showing periodical changes of the energy flow through the system, matching the periodicity of chemical oscillations. Well before chemical oscillation, rearrangement of energy provokes excessive excitation of the first vibration state of hydrogen peroxide followed by the phase-shifted excitation of the second state. The observed populations of excited states highly exceed equilibrium values, suggesting that the nonequilibrium distribution of energy related to the peculiar hydrogen bond network dynamics may be an important part of the reaction mechanism.

Excessive excitation of hydrogen peroxide during oscillatory chemical evolution.

The peculiar reaction dynamics of the Bray-Liebhafsky chemical oscillator is connected with the nonequilibrium periodic excitations of hydrogen peroxide embedded in a hydrogen-bonded water network. This was indicated by Raman spectroscopy that showed periodic, isothermal, and excessive excitation of the symmetric vibration of hydrogen peroxide. Since such an excessive excitation should be the result of a specific nonequilibrium energy distribution with the active participation of water, understanding this process can be of considerable importance in other systems in which water is the main constituent.