A viscosity self-oscillation of polymer solution induced by the Belousov-Zhabotinsky reaction under acid-free condition

We succeeded in measuring a viscosity self-oscillation induced by the Belousov-Zhabotinsky (BZ) reaction for a polymer solution on the constant temperature condition under acid-free condition. The polymer chain is consisted of N-isopropylacrylamide, ruthenium complex as a catalyst of the BZ reaction, and an acrylamide-2-methylpropanesulfonic acid (AMPS) as a pH and the solubility control site. The viscosity self-oscillation for the AMPS-containing polymer solution was attributed to the difference between viscosities for the polymer solution in the reduced and oxidized states. The effects of the polymer concentration and the temperature of the polymer solution on the viscosity self-oscillation were investigated. As a result, the viscosity self-oscillating behavior significantly depended on the polymer concentration and the temperature of the polymer solution. The period of the viscosity self-oscillation decreased with increasing temperature in accordance with the Arrenius equation.     

Self-oscillation of polymer chains with rhythmical soluble-insoluble changes

Self-oscillation of polymer chains in an aqueous solution has been achieved. The ruthenium catalyst for the Belousov-Zhabotinsky reaction was polymerized by using N-isopropylacrylamide and dissolved into the solution containing the BZ substrates. Periodical soluble-insoluble changes of the polymer chain were spontaneously induced by the BZ reaction. The conformational oscillations of the polymer were measured as the optical transmittance changes of the solution. This is the first report that rhythmical and reversible soluble-insoluble changes of polymer chains are realized under constant and homogeneous conditions. The transducing system from chemical energy of the BZ reaction to optical information has been constructed.     

Self-oscillating soluble-insoluble changes of a polymer chain including an oxidizing agent induced by the Belousov-Zhabotinsky reaction

A new type of self-oscillating polymer was prepared by utilizing the Belousov-Zhabotinsky reaction. In this study, capture sites with a positive charge for an oxidizing agent as a counterion were incorporated into the copolymer of N-isopropylacrylamide and the ruthenium complex as a catalyst. Soluble-insoluble self-oscillation of the polymer was first achieved without adding an oxidizing agent. The effect of temperature on the self-oscillating behavior was investigated. It was clarified that the polymer had two advantageous characteristics because of the higher LCST; one is to enable self-oscillation around body temperature, and the other is to cause the oscillation for a longer time without intermolecular aggregation among the polymer chains in the reduced state. This achievement of self-oscillation of polymer chains including an oxidizing agent may lead to their practical use under oxidant-free conditions.     

Numerical evidence of complex nonlinear phenomena of the Belousov-Zhabotinsky oscillatory reaction under batch conditions

By numerical calculations based on our previously proposed model with Br₂O intermediate species we were able to simulate complex evolution of the Belousov-Zhabotinsky (BZ) reaction under batch conditions. In the defined region of initial malonic acid concentration [MA]₀ (1.00 × 10^?3 mol dm³ ≤ [MA]₀ ≤ 1.50 mol dm^?3) different sequences of regular and complex periodic and aperiodic oscillations were obtained. It is noticed that the bromine evaporation significantly affects the dynamics of the reaction.     

Microwave assisted synthesis of nitro phenols from the reaction of phenols with urea nitrate under acid-free conditions

Urea nitrate was found to be an inexpensive, acid-free, and safe nitrating agent that provides mononitration of phenols and substituted phenols in excellent yields with exclusive ortho-selectivity under microwave irradiation. Microwave assisted reactions reduced the reaction times substantially and enhanced the product yields from good to excellent within shorter reaction times.     

Highly efficient Wacker oxidation catalyzed by heterogeneous Pd montmorillonite under acid-free conditions

Palladium-montmorillonite was proven to be highly efficient for the Wacker oxidation of terminal olefins to the corresponding methyl ketones. The catalyst was reusable while maintaining high activity and selectivity.     

Malonic acid concentration as a control parameter in the kinetic analysis of the Belousov-Zhabotinsky reaction under batch conditions

The influence of the initial malonic acid concentration [MA]0 (8.00 x 10(-3) < or = [MA]0 < or = 4.30 x 10(-2) mol dm(-3)) in the presence of bromate (6.20 x 10(-2) mol dm(-3)), bromide (1.50 x 10(-5) mol dm(-3)), sulfuric acid (1.00 mol dm(-3)) and cerium sulfate (2.50 x 10(-3) mol dm(-3)) on the dynamics and the kinetics of the Belousov-Zhabotinsky (BZ) reactions was examined under batch conditions at 30.0 degrees C. The kinetics of the BZ reaction was analyzed by the earlier proposed method convenient for the examinations of the oscillatory reactions. In the defined region of parameters where oscillograms with only large-amplitude relaxation oscillations appeared, the pseudo-first order of the overall malonic acid decomposition with a corresponding rate constant of 2.14 x 10(-2) min(-1) was established. The numerical results on the dynamics and kinetics of the BZ reaction, carried out by the known skeleton model including the Br2O species, were in good agreement with the experimental ones. The already found saddle node infinite period (SNIPER) bifurcation point in transition from a stable quasi-steady state to periodic orbits and vice versa is confirmed by both experimental and numerical investigations of the system under consideration. Namely, the large-amplitude relaxation oscillations with increasing periods between oscillations in approaching the bifurcation points at the beginning and the end of the oscillatory domain, together with excitability of the stable quasi-steady states in their vicinity are obtained.     

Investigation of the Belousov-Zhabotinsky reaction by thermal lensing

The supramolecular interaction of rubidate (chemically 2,3-naphthalenedicarboxylic acid, 1,4-dihydroxy-diethyl ester) and beta-cyclodextrin (beta-CD) has been studied by spectrofluorimetry. The influence of temperature on the supramolecular system has also been investigated and the thermodynamic parameters were calculated. The results show that beta-CD reacts with rubidate to form a 1:1 host-guest complex with an apparent association constant of 566+/-23 l mol(-1). It was also demonstrated that the thermodynamics of beta-CD-rubidate complex displayed a compensatory enthalpy-entropy relationship. Based on the significant enhancement of the fluorescence intensity of rubidate produced through complex formation, a spectrofluorimetric method for the determination of rubidate in bulk aqueous solution in the presence of beta-CD was developed. The linear relationship between the fluorescence intensity and rubidate concentration was obtained in the range from 2.7x10(-2) to 3.0 mug ml(-1), with a correlation coefficient of 0.9988. The detection limit was 8.2 ng ml(-1) and the relative standard deviation was 1.6%. There was no interference from the excipients normally used in tablet formulations. The application of the present method to the determination of rubidate in tablets gave satisfactory results and was compared with the reference method.     

The role of radicals in the Belousov-Zhabotinsky reaction

A new theory of the Belousov-Zhabotinsky (BZ) reaction, the Radicalator model, is presented. This model is based on a negative feedback loop involving a fast reaction between malonyl and bromine dioxide radicals. Experimental evidence for the validity of the model is given for BZ systems in 3 M and 1 M sulfuric acid solution.     

A mild and efficient reaction for conversion of carboxylic acids into acid bromides with ethyl tribromoacetate/triphenylphosphine under acid-free conditions

Acid bromides were prepared efficiently from carboxylic acids with readily available ethyl tribromoacetate and triphenylphosphine at room temperature under neutral conditions. The present process is applicable to the preparation of various acid bromides from aromatic and aliphatic carboxylic acids. Aromatic carboxylic acids were found to be more reactive than aliphatic carboxylic acids under reaction conditions.     

Hydrodeoxygenation of phenols as lignin models under acid-free conditions with carbon-supported platinum catalysts

Carbon-supported Pt catalysts are highly active and reusable for the aqueous-phase hydrodeoxygenation of phenols as lignin models without adding any acids. It is suggested that Pt/carbon facilitates the hydrogenation of phenols and the hydrogenolysis of the resulting cyclohexanols.     

Artificial-intelligence-based interpretation of feature sensitivities of the Belousov-Zhabotinsky reaction

A new approach is presented for analyzing kinetic models of relaxation-type oscillatory systems on the basis of numerical data. Feature sensitivities of the length of the two kinetic states of the Belousov-Zhabotinsky (BZ) reaction with respect to the rate constants of the model are explained by means of a logic-based inference system. The main kinetic roles of the individual reaction steps on the relaxing components are revealed, and a consistent interpretation of the kinetic states is given by this process. Both the high and the low set of rate constants were studied. According to our analysis, the bromous acid-hypobromous acid reaction is an important Br^? producing step of the model, and in the case of the low set, the bromate-bromous acid reaction is not the rate-determining step of the bromous acid autocatalysis.     

Energy storage in polymer chains under stress

The local conformation and storage of energy in individual polymer chains during a deformation of a bulk polymer sample are examined by the computer simulation of a relatively simple model. It is shown that as the interaction between the chain atoms and surrounding medium increases, rotational angle motion is suppressed during the deformation, and large amounts of energy are stored in backbone bond angle and bond length distortions. The relationship of this phenomena to T_g and the implications for chain relaxation are discussed.     

Noise-induced order in the chaos of the Belousov-Zhabotinsky reaction

Noise can stabilize a metastable state in such a way that the system remains in this state for a longer time than in the absence of noise. When this phenomenon is observed in chaos, it is called "noise-induced order." We have experimentally detected noise-induced order in the Belousov-Zhabotinsky reaction. That is, when noise is added to the chaos with the flow rate near the period-three oscillation, a decrease of the maximum Lyapunov exponent and a convergence of the Fourier spectrum are observed. Moreover, the analysis on the one-dimensional return map reveals that noise-induced order is caused by the convergence of the chaotic trajectory into the laminar region.     

Effect of electromagnetic radiation on the Belousov-Zhabotinsky oscillating reaction

The effect of electromagnetic radiation with a frequency close to the maximum of absorption of atmospheric oxygen on the Briggs-Rauscher self-oscillating reaction is described. It is shown that the radiation intensifies oxygen production and lengthens the duration of the self-oscillating regime by more than 20%.     

Photoexcited chemical wave in the ruthenium-catalyzed Belousov-Zhabotinsky reaction

The excitation of the photosensitive Belousov-Zhabotinsky (BZ) reaction induced by light stimulation was systematically investigated. A stepwise increase in the light intensity induced the excitation, whereas a stepwise decrease did not induce the excitation. The threshold values for the excitation were found to be a function of the initial and final light intensities, time variation in light intensity, and the concentration of NaBrO(3). The experimental results were qualitatively reproduced by a theoretical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that although the steady light irradiation is known to inhibit oscillation and chemical waves in the BZ system under almost all conditions, the stepwise increase in the light irradiation leads to the rapid production of an activator, resulting in the photoexcitation.     

Controlled excitations of the Belousov-Zhabotinsky reaction: Experimental procedures

The purpose of this research was to explore the unstirred, ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction as an experimental model for the response of excitable media to small perturbations (slightly larger than the threshold for excitations). Following Showalter et al. (Showalter, K.; Noyes, R. M.; Turner, H. J.Am. Chem. Soc. 1979, 101, 7463-69), we used a positively biased silver electrode to release silver ions into a BZ reaction mixture, removing bromide ions and causing an excitation if sufficient bromide was removed. We found (1) a scaling region in which the delay before activation increased linearly as the size of the perturbation decreased, qualitatively consistent with but not fully explained by the Oregonator of Field et al. (Field, R. J.; K?r?s, E.; Noyes, R. M. J. Am. Chem. Soc. 1972, 94, 8649-64); (2) evidence for a 10 s oligomerization time scale; and (3) that activations were always delayed until after the end of a pulse of current, with the delay essentially constant for sufficiently long pulses, an effect not seen in simple ODE models but consistent with the anomalously large current apparently required for activation (Showalter, K.; Noyes, R. M. J. Am. Chem. Soc. 1976, 98, 3730-31) and explainable by bromide transport. Overall, the BZ system appeared to be well-suited as an experimental prototype, despite its complexity.     

An elegant method to study an isolated spiral wave in a thin layer of a batch Belousov-Zhabotinsky reaction under oxygen-free conditions

A method to prepare a uniform thin layer of a batch Belousov-Zhabotinsky (BZ) reaction under oxygen-free conditions for the study of an isolated spiral wave is presented. After a first layer of gel soaked with the BZ solution has been delivered into the reactor, a single spiral wave was initiated, and finally the remaining reactor volume was filled with gel and BZ medium. The completely filled reactor is sealed gas-tightly, yielding oxygen-free, and thus more controlled, reaction conditions. A systematic study of the behaviour of an isolated spiral wave in a ferroin-catalyzed BZ reaction under batch conditions has been performed. Recipes for BZ media that support a slowly rotating meandering spiral were developed. In cases of extremely low excitability (i.e., relative large stimuli are required to induce a propagating wave), the number of petals in the trajectory of a spiral tip decreased due to aging of the reaction system. Since oxygen-free conditions are necessary for the study of the dynamics in three-dimensional excitable media, and the wave velocities of a spiral are sufficiently low, the developed chemical recipes are suitable for studies of the behaviour of scroll waves in three-dimensional systems by optical tomography.     

Realistic parameters for simple models of the Belousov-Zhabotinsky reaction

We use experimental results to estimate the values of parameters of simple models describing the time evolution of the Belousov-Zhabotinsky reaction proceeding in droplets surrounded by hydrocarbons. The equations with fitted parameters correctly describe the period of oscillations for a large class of experimental conditions at which the reaction is performed.