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Hopf bifurcations of a Lengyel-Epstein model involving two discrete time delays are investigated. First, stability analysis of the model is given, and then the conditions on parameters at which the system has a Hopf bifurcation are determined. Second, bifurcation analysis is given by taking one of delay parameters as a bifurcation parameter while fixing the other in its stability interval to show the existence of Hopf bifurcations. The normal form theory and the center manifold reduction for functional differential equations have been utilized to determine some properties of the Hopf bifurcation including the direction and stability of bifurcating periodic solution. Finally, numerical simulations are performed to support theoretical results. Analytical results together with numerics present that time delay has a crucial role on the dynamical behavior of Chlorine Dioxide-Iodine-Malonic Acid (CIMA) reaction governed by a system of nonlinear differential equations. Delay causes oscillations in the reaction system. These results are compatible with those observed experimentally. [ABSTRACT FROM AUTHOR]

The oscillatory Briggs‐Rauscher (BR) reaction was applied on solid insoluble materials i. e. bentonite clays. Under the same BR experimental conditions, the addition of identical masses of bentonite of different origin resulted in different effects on oscillatory time duration (τ): no influence, quenching, or prolongation. It was found that the following bentonite properties: montmorillonite/beidellite ratio; cation exchange capacity; principal exchange cation; extent of iron leaching in acidic environment of BR reaction; and specific surface area of clay were not exclusively responsible for observed behavior. On the other hand, the influence of added mass, for all investigated clays, resulted in the same behavior pattern. The increase of the mass of added clay increased τ up to the certain maximal value (τmax, mmax) characteristic for each clay. Further increase of mass resulted in quenching. Therefore, (τmax, mmax) pair can be regarded as the "fingerprint" characteristic of bentonite useful for identification of its origin. Furthermore, the addition of naturally occurring and non‐toxic clay in an oscillatory reaction can offer a versatile approach to tune the oscillation dynamics of nonlinear chemical systems. [ABSTRACT FROM AUTHOR]

A generalized Lengyel–Epstein oscillating reaction model is proposed and analyzed. The existence of limit cycles is proved using Hopf and Bautin bifurcation theory. We analyze the dynamics of the well known chlorine dioxide–iodine–malonic acid reaction, using a differential equations system. The numerical results are shown and these agree with the experimental data reported in the literature. We found that the oscillatory behavior depends on the stoichiometric coefficients and the reactant concentrations. This work gives valuable information for applications like design, optimization, dynamics and control of the industrial chemical reactors. [ABSTRACT FROM AUTHOR]

The present work proposes the development of an analytical procedure for paracetamol determination in pharmaceutical formulations using a system of continuous flow analysis associated with potentiometric detection allowing the study of the Belousov–Zhabotinskii (BZ) oscillating reaction. This method is based on paracetamol determination using the disturbance in the oscillation pattern of the BZ reaction promoted by this substance. The analytical curve showed the detection and quantification limits of 4 × 10–6 and 1.2 × 10–5 M, respectively. The relative standard deviation (n = 6) of the standard solution with paracetamol concentration of 6 mM was 2.3%. The analysis of real samples by the proposed and official methods (spectrophotometry/UV) showed similar results. [ABSTRACT FROM AUTHOR]

Many kinds of stimuli-responsive polymer and gels have been developed and applied to biomimetic actuators or artificial muscles. Electroactive polymers that change shape when stimulated electrically seem to be particularly promising. In all cases, however, the mechanical motion is driven by external stimuli, for example, reversing the direction of electric field. On the other hand, many living organisms can generate an autonomous motion without external driving stimuli like self-beating of heart muscles. Here we show a novel biomimetic gel actuator that can walk spontaneously with a wormlike motion without switching of external stimuli. The self-oscillating motion is produced by dissipating chemical energy of oscillating reaction. Although the gel is completely composed of synthetic polymer, it shows autonomous motion as if it were alive.

The hydrogenase-catalyzed oxidation of H 2 includes an autocatalytic step in the reaction cycle. The reaction also exhibits different pH dependence in the H 2 oxidation and in the proton reduction directions. This is not only due to the pH titration of the amino acid side chains as protons are also either the substrates or the products of the reaction. Utilizing the autocatalytic nature of the hydrogenase reaction and the multiple roles of protons therein, together with appropriate limitation of the substrate (gaseous H 2 ) supply, oscillations can be induced in the system. The reaction oscillates both in space and in time, and can last for days with decreasing frequency until reaching chemical equilibrium. Of all biological oscillating systems described so far, this one is the simplest in that it has the fewest biological components. [ABSTRACT FROM AUTHOR]

This paper reports a new method for determination of VB (pyridoxine hydrochloride) by its perturbation effects on a novel Belousov-Zhabotinskii (BZ) oscillating system. This novel BZ system, in which malic acid serves as the substrate, contains an enzyme-like complex, macrocyclic complex {[CuL](ClO)}, as catalyst. The ligand L in the complex is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. Results show that the addition of pyridoxine hydrochloride can perturb the oscillation amplitude and period, and the change of the oscillation amplitude is linearly proportional to the concentration of pyridoxine hydrochloride in the range of 5×10−2.5×10 M. The obtained RSD with seven samples is 3.073%. An assay of pharmaceutical tablets of vitamin B was evaluated. Some foreign ions were studied with respect to their possible influence on the determination of pyridoxine hydrochloride. The factors which influence this reaction include the concentration of reactant, the temperature of the reaction, property of catalyst, etc. Furthermore, the possible reaction mechanism has been proposed using the Field-Körös-Noyes (FKN) model. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A new chlorine dioxide-iodine-sodium thiosulfate chemical oscillatory reaction was studied by the UV-Vis spectrophotometric method. The initial concentrations of sodium thiosulfate, chlorine dioxide, iodine, sulfuric acid, and pH have great influences on the oscillations observed at wavelength 238 nm. The oscillations occur as long as the reactants are mixed. The amplitude and the number of oscillations are associated with the initial concentrations of reactants. The equations for the triiodide ion reaction rate changes with reaction time and the initial concentrations in the oscillation stage are an attenuation sine function. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction. [ABSTRACT FROM AUTHOR]

Abstract: As a novel biomimetic gels deffering from conventonal stimuli-responsive polymer gels, we have developed a “self-oscillating” gel that swells and deswells periodically under constant condition without on–off switching of external stimuli. The gel is composed of poly(N-isopropylacrylamide) to which the catalyst of the oscillating chemical reaction, called Belousov–Zhabotinsky reaction, is covalently immobilized. The chemical oscillation is converted to the mechanical oscillation of the gel through the change in hydrophilicity of polymer chains with the redox changes of the immobilized catalyst. By utilizing the self-oscillating gel, several kinds of functional material systems such as biomimetic actuators, etc. are expected. Here we review a potential application to functional surface to realize autonomous mass-transport by utilizing the peristaltic motion of the gel. With the propagation of the chemical wave, the loaded cargo is autonomously transported on the surface. In order to fabricate the self-driven gel conveyer for a wider use including biomedical applications, the interactions between the self-oscillating gel and the loaded gel cargo were investigated and their influence on the transport phenomena were evaluated. [Copyright &y& Elsevier]

Abstract: Hexaarylbisimidazole (HABI) is a well established photoinitiator in the graphics industry which undergoes in the absence of other reaction partners a fully reversible homolytic bond cleavage into two lophyl radicals L ingly we now found oscillations of the radical concentration at low temperature in a solution of o-Cl-HABI in toluene, which is an indication of a more complex photochemistry of the HABI/lophyl system. Furthermore this reaction is a very simple example of an oscillating chemical system working under non-flow conditions which involves only one initial reactant. A possible reaction mechanism based on kinetic simulations is proposed. [Copyright &y& Elsevier]

a novel biomimetic polymer gel, we have been studying polymer gel with an autonomous self-oscillating function since it was firstly reported in 1996. For developing the polymer gels, we utilized an oscillating chemical reaction, called the Belousov-Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer gel is composed of a poly( N-isopropylacrylamide) network in which the metal catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous swelling-deswelling changes (in the case of gel) or cyclic soluble-insoluble changes (in the case of uncross-linked polymer) without any on-off switching of external stimuli. Several kinds of functional material systems utilizing the self-oscillating polymer and gel such as biomimetic actuators, mass transport surface, etc. are expected. Here, these recent progress on the self-oscillating polymer and gels and the design of functional material systems are summarized. [ABSTRACT FROM AUTHOR]

Many kinds of stimuli-responsive polymer and gels have been developed and applied to biomimetic actuators or artificial muscles. Electroactive polymers that change shape when stimulated electrically seem to be particularly promising. In all cases, however, the mechanical motion is driven by external stimuli, for example, reversing the direction of electric field. On the other hand, many living organisms can generate an autonomous motion without external driving stimuli like self-beating of heart muscles. Here we show a novel biomimetic gel actuator that can walk spontaneously with a wormlike motion without switching of external stimuli. The self-oscillating motion is produced by dissipating chemical energy of oscillating reaction. Although the gel is completely composed of synthetic polymer, it shows autonomous motion as if it were alive. [ABSTRACT FROM AUTHOR]

Many kinds of stimuli-responsive polymer and gels have been developed and applied to biomimetic actuators and artificial muscles. In particular, electroactive polymers that change shape when stimulated electrically are promising. In all cases, however, the mechanical motion is driven by external stimuli, for example, reversing the direction of electric field. On the other hand, many living organisms can generate an autonomous motion without external driving stimuli, for example the self-beating heart muscle. Here we show novel bending- stretching, self-walking and peristaltic motion of polymer gel actuators without switching of external stimuli. The self-oscillating motion is produced by dissipating chemical energy of an oscillating reaction, i.e., the Belouzov-Zhabotinsky (BZ) reaction occuring inside the gel. Although the gel is a synthetic polymer, it shows autonomous motion as if it is alive. [ABSTRACT FROM AUTHOR]

Abstract: Ag/Al2O3 is an active catalyst for selective catalytic reduction (SCR) of NO x using long paraffins as reducing agents. In view of the important role of surface nitrates in this catalytic chemistry, their formation on the Ag/Al2O3 catalyst, i.e. on the alumina support and on the silver species, was quantified in this study under typical reaction conditions of 500–1000 ppm NO x , 6% O2 and 12% H2O. The NO x adsorption capacity and the stoichiometry of nitrate formation and elimination reactions were determined as function of the temperature and the composition of the NO x using volumetric determinations in a flow system. The silver chemistry was investigated using in situ DR UV–vis spectroscopy. In the presence of water, nitrate formation out of NO2 proceeds according to two different mechanisms depending on the state of silver as Ag(0) or Ag(I) on the catalyst. Minute concentrations of hydrogen (3500 ppm) are responsible for Ag(I) reduction. The study reveals the origin of the promotion of the low temperature SCR-NO x activity of Ag/Al2O3 by hydrogen. Hydroxylation–dehydroxylation of the alumina surface of Ag/Al2O3 catalyst was found to be an oscillating reaction, whereas the alumina support itself did not display this phenomenon. [Copyright &y& Elsevier]

To study the effect of strong iron-ligands on steel corrosion, mild steel electrodes were immersed in solutions containing 20 mM phosphate buffer (pH=7.2) and between 0.01 mM and 1 M of either the iron(II)-chelators 2,2′-bipyridine or FerroZine, or the iron(III)-chelators citrate or acetylacetonate. Resulting surface reactions were investigated by quantifying the electrochemical potential (E), the electrochemical polarization resistance (Rp), the corrosion current (Icorr) and the release of iron into solution. The surface was further analyzed by scanning electron microscopy (SEM/SEM-EDAX) and atomic force microscopy. Concentrations of 0.1 mM of any of the chelators led to slight, temporary changes in E, Icorr and Rp. Concentrations of 10 mM resulted in characteristic changes of E, which were the same for all chelators and in the precipitation of FePO4 in the case of citrate and acetylacetonate, or vivianite [Fe3(PO4)2 · 8H2O] in the case of bipyridine and FerroZine. Concentrations of 1 mM of both iron(III)-chelators led to a temporary drop of E similar to that found with 0.1 mM chelator. With iron(II)-chelators, E dropped to about −500 mV before oscillating for several days. The amplitudes of the oscillations were up to 200 mV with periods of 30 and 20–25 min for bipyridine and FerroZine, respectively. [Copyright &y& Elsevier]

Potentiodynamic and impedance spectroscopy measurements were performed on ARMCO iron, steels (C30, C40, C50), cast iron and graphite electrodes in a bath of industrial composition: CrO3 250 g dm−3, H2SO4 2.5 g dm−3. Attention focused on the electrochemical reactions occurring before the start of the chromium deposition. The electrochemical evidence is markedly affected by the chemical nature of the cathode. This is rationalized by proposing a reaction mechanism involving the formation, depending on the chemical nature of the substrate, of a passive adsorbed film consisting of mixed chromium and iron oxides. Moreover, the proposed overall scheme accounts for the presence of periodic current oscillations observed both in potentiodynamic and potentiostatic curves. In close agreement, impedance spectra show negative loops when measured at the corresponding potentials. [ABSTRACT FROM AUTHOR]

We report an “intelligent” gel that undergoes autonomous swelling-deswelling oscillations without reliance on alterations in external conditions; this aspect reminds us of the heartbeat. The mechanical oscillation in our gel system was produced via an oscillating chemical reaction similar to a metabolic reaction, called the Belousov-Zhabotinsky (BZ) reaction. We have succeeded in synthesizing an ionic gel consisting of the cross-linked N-isopropylacrylamide (NIPAAm) chain to which ruthenium tris(2,2′-bipyridine) [Ru(bpy)3] was covalently bonded. This Ru(bpy)3 complex acts as a catalyst for the BZ reaction; thus, the BZ reaction occurring within the gel matrix generates periodic redox changes of the catalyst moiety: Ru(bpy)3 2+⇆Ru(bpy)3 3+. This chemical oscillation is converted into the mechanical oscillation of the polymer network. As a result, the gel exhibits a periodic swelling-deswelling change. When the gel size is smaller than the chemical wavelength, the redox change occurs homogeneously in the gel. In this case, the volume change is isotropic and the gel beats as a whole, like a heart muscle cell. In the case of a large rectangular gel, the total length of the gel periodically changes with the propagation of chemical waves. The dynamic behavior that locally shrunken (or swollen) parts propagate is similar to the peristaltic motion observed in worms. This is the first study to achieve spontaneous volume oscillation of gels without external stimuli. Self-oscillation may be useful in a number of important applications to biomaterials, such as pulse generators or chemical pacemakers, self-walking actuators or micropumps with peristaltic motion, and devices for signal transmission. [ABSTRACT FROM AUTHOR]

Chemiluminescence accompanying the oxidation of 3-aminophthalhydrazide (luminol) with sodium ferrate (vi) in an alkaline solution is studied. The powerful initial light flash flaring up at the moment of mixing the reactants is followed by a continuous low-intensity luminescence in the heterogeneous system formed. The addition of Cu2+ ions during this period results in a new chemiluminescence flash with an oscillating character. [ABSTRACT FROM AUTHOR]