Ferroin Concentration Research Articles

Studies on the Interaction of Ion Exchange Resins with Initial Catalyst Concentrations of a Chemical Oscillator using Spectrophotometric and Electrochemical Methods

Ion exchange resins are well known because of their vast applications in the processes like water softening, catalysis, waste water treatment, hydrometallurgy and chromatography. In the present investigation based on the interaction of different ion exchangers with ferroin to be used as catalyst in a nonlinear chemical reaction, quantitative estimation of Fe2+ was done by loading it on three different ion exchange resins, viz. Dowex Marathon C Na, Amberlite IRC86 and Dowex m4195 at different loading time intervals. The supernatant containing the residual ferroin was separated from ion exchange resins and added directly to the substrate molecule of the chemical oscillator as catalyst and the series of reaction systems were monitored by potentiometry and spectrophotometry and the results obtained were confirmed by advanced cyclic voltammetry as a supportive technique. Thus, the effect of catalyst after its interaction with ion exchange resins at optimal level was monitored. At the same time, it was found that the concentration of ferroin to be involved in the Belousov−Zhabotinsky reaction as a catalyst in the present interactive systems can be estimated up to 10–5 M and even lower, depending on the experimental conditions.

Long-Lasting Complex Reaction Behavior in a Closed Ferroin-Bromate-Hydroxybenzenesulfonate System.

The bromate-phenolsulfonate reaction was found to exhibit spontaneous oscillations in a batch reactor, where the addition of small amounts of ferroin would result in nonoscillatory behavior. As the ferroin concentration was increased, the system produced very rich nonlinear behavior, including three isolated oscillatory regimes that were separated by as long as 48 h nonoscillatory period. The long-lasting nonlinear behavior may be attributed to the slow desulfonation of phenolsulfonate in an acidic solution, forming phenol-like intermediates. However, unlike the bromate-phenol oscillator, oxygen was found to greatly influence the reaction, and various complex oscillations could be observed by tuning the oxygen concentration. Mechanistic studies performed through employing 1H NMR spectroscopy and mass spectrometry to measure intermediate species at different stages of the reaction were able to identify 1,4-benzoquinone, 2-bromo-1,4-benzoquinone, 2,6-dibromo-1,4-benzoquinone, and 2,4,6-tribromophenol as major components during the reaction.

Adsorption studies of ferroin in aqueous solution onto graphite oxide

The adsorption of ferroin by graphite oxide was studied by changing different parameters, i.e., pH, duration, concentration of ferroin, adsorbent dose, and temperature. The removal of ferroin in aqueous solution by graphite oxide increases with increase in contact time, adsorbent dose, pH, and temperature. The reaction rate of adsorption of ferroin onto graphite is a multilayer phenomenon and was found to follow pseudo second order kinetics. At 60 °C with pH 4, we observe an adsorption rate of graphite oxide with a capacity of 0.00692 mg per 10 mg of ferroin due to the presence of surface oxygen functional groups that dictate the adsorption capacity. Optimal conditions for adsorption of ferroin onto graphite oxide were determined and reported.

Complex spatiotemporal behavior in the photosensitive ferroin-bromate-4-nitrophenol reaction.

Investigation illustrates that the bromate-4-nitrophenol reaction in a stirred batch reactor undergoes spontaneous oscillations under very broad initial reactant concentrations. The addition of ferroin has subtle influences on the nonlinear behavior, in which the frequency and total number of oscillations were greatly reduced at a low or high ferroin concentration, as opposed to the significant increase at a moderate ferroin concentration. Temporal oscillations with a modulating frequency were also observed in the ferroin-bromate-4-nitrophenol system. In a capillary tube the ferroin-bromate-4-nitrophenol reaction generated propagating wave trains with various complex behaviors such as period-doubled intermittent propagation failure. Illumination was found to have a profound effect on the temporal oscillations in the bromate-4-nitrophenol reaction and on those long lasting wave activities. Spectroscopic studies were able to identify 1,4-benzoquinone, 2-bromo-1,4-benzoquinone, and 2-bromo-4-nitrophenol as major components during the reaction.

Cerimetric determination of simvastatin in pharmaceuticals based on redox and complex formation reactions

Two sensitive spectrophotometric methods are described for the determination of simvastatin (SMT) in bulk drug and in tablets. The methods are based on the oxidation of SMT by a measured excess of cerium (IV) in acid medium followed by determination of unreacted oxidant by two different reaction schemes. In one procedure (method A), the residual cerium (IV) is reacted with a fixed concentration of ferroin and the increase in absorbance is measured at 510 nm. The second approach (method B) involves the reduction of the unreacted cerium (IV) with a fixed quantity of iron (II), and the resulting iron (III) is complexed with thiocyanate and the absorbance measured at 470 nm. In both methods, the amount of cerium (IV) reacted corresponds to SMT concentration. The experimental conditions for both methods were optimized. In method A, the absorbance is found to increase linearly with SMT concentration (r = 0.9995) whereas in method B, the same decreased (r = -0.9943). The systems obey Beer’s law for 0.6-7.5 and 0.5-5.0 μg mL-1 for method A and method B, respectively.

Perturbations of the Briggs–Rauscher oscillating system by iron–phenanthroline complexes

Perturbations of the oscillatory regime of the Briggs–Rauscher (BR) reaction by the iron(II)–phenanthroline (ferroin) complex were observed in batch conditions. The path of the perturbation (immediate quenching of oscillations – inhibition time – resumption of oscillations) is similar to that provoked by antioxidant free-radical scavengers; however, perturbations occur in a ferroin concentration range much lower than that in which antioxidants act. To investigate this effect, reactions between the iron(II)–or iron(III)–phenanthroline (ferriin) and reagents or intermediates of the BR system were studied in detail. Results of these studies showed that the interaction of the ferroin/ferriin couple with iodine production is responsible for the observed perturbation. A mechanistic interpretation involving HOO radical is proposed.

Complex Behavior in Coupled Bromate Oscillators

In this study, coupled bromate-oscillators constructed by adding 1,4-cyclohexanedione (1,4-CHD) to the ferroin-catalyzed Belousov-Zhabotinsky reaction are investigated in a batch reactor under anaerobic conditions. Various complex behaviors such as sequential oscillations and bursting phenomena are observed. At low concentrations of ferroin or malonic acid (MA), the development of sequential oscillations is found to depend on the ratio of [1,4-CHD]/[ferroin] and [1,4-CHD]/[MA] rather than their absolute concentrations. As the concentration of MA or ferroin was increased gradually, however, the minimum 1,4-CHD concentration required to induce complex oscillations reaches a plateau. Perturbations by light illustrate that the first oscillatory window is governed by the ferroin-MA-BZ mechanism, whereas the 1,4-CHD-bromate oscillator plays a prominent role during the non-oscillatory evolution and the second oscillatory window. Our conclusion is further supported by numerical simulations in which sequential oscillations observed in experiments are qualitatively reproduced by a modified FKN mechanism.

The influence of visible light on the formation of revival waves in the 1,4-cyclohexanedione–bromate–ferroin reaction

Revival waves, which emerge spontaneously long after the oscillatory bromate–1,4-cyclohexanedione–ferroin reactions become quiescent, are found susceptible to the illumination of visible light. Depending on the intensity and the duration of the light perturbation, an illumination can drive the system either to a reduced reaction state with a high concentration of ferroin, or to an oxidized state with a high concentration of ferriin. When hydroquinone, a main product from 1,4-cyclohexanedione oxidation, is used to gradually replace 1,4-cyclohexanedione as the reductants, the induction period of the formation of revival waves is shortened significantly; however, there is no clear difference in their photosensitivity. These new experimental results suggest that the observed photosensitivity is determined by the photochemistry of the products of hydroquinone.

Mechanistic studies on the bromate–1,4-cyclohexanedione–ferroin oscillatory system

A chemical mechanism including 22 reactions and 15 species is suggested for describing the dynamical behavior of the ferroin controlled BrO3−–1,4-cyclohexanedione (CHD) batch oscillator. The model represents an extended version of the mechanism developed to explain the oscillations in the ferroin-free BrO3−–CHD system. The kinetics and rate constants for some additional reactions such as ones between ferriin and CHD, BrCHD (2-bromo-1,4-cyclohexanedione) and H2Q (1,4-hydroquinone) and between ferroin and bromate were determined and incorporated in the mechanism of the BrO3−–CHD reaction. The model proposed here simulates satisfactorily the behavior of the BrO3−–CHD–ferroin oscillator at increasing concentration of ferroin and at the condition of [ferroin] = 0 mol dm−3.

Effect of temperature and small amounts of metal ions on transient chaos in the batch Belousov–Zhabotinsky system

We report an effect of temperature and small amounts of metal ions on transient chaotic regime observed in the batch Belousov–Zhabotinsky oscillating chemical reaction catalyzed by ferroin. The transient chaos is quantified by values of the largest Lyapunov exponent and induction period. We have found that these values depend through the Arrhenius equation on the temperature if the initial ferroin concentration is varied in the range of (0.87–3.5)×10 −3 M . We show that inside this range transient chaos is characterized by linear response to injection of solutions containing metal ions, e.g., cerium(III), manganese(II), vanadyl(IV) or thallium(I).

Bromate−1,4-Cyclohexanedione−Ferroin Gas-Free Oscillating Reaction. 1. Basic Features and Crossing Wave Patterns in a Reaction−Diffusion System without Gel

We present a study of the bromate−1,4-cyclohexanedione−ferroin oscillating reaction in both well-stirred and reaction−diffusion systems. We investigate the dependence of the system dynamics on the initial reagent concentrations, with the initial concentration of ferroin varied from 0 to 5 × 10-3 M, and show that the system behaves like a typical BZ oscillator if the concentration of ferroin exceeds 5 × 10-5 M. We demonstrate spontaneous formation of spiral waves and transverse wave fronts in quasi-two-dimensional systems and formation of crossing wave patterns in thin layers of solution open to air.

Ferroin-based solid-state electrochromic display

Electrochromic display composed of (ferroin-based electrochrome film/polymer electrolyte/lithium) reversibly exhibits red and colorless when a potential of ca. 0.75 or 0.98 V is applied respectively. The display response is speeded up with decreasing thickness and with lowering ferroin concentration of electrochromic film without decreasing contrast.

Transition from Oscillatory to Chaotic Behaviour in the Belousov‐Zhabotinskii Reaction of Oxaloacetic Acid

AbstractThe Belousov‐Zhabotinskii (BZ) reaction of oxaloacetic acid (OAA) = oxobutanedioic acid is investigated spectrophotometrically both in the closed system and in the continuous‐flow stirred tank reactor (CSTR). Using ferroin as catalyst, the reaction in the closed system exhibits a very complicated oscillatory pattern with three different types of oscillations being separated by induction periods. “Chemical chaos” = deterministic aperiodicity of the type 2 oscillations is observed in a very small range of the ferroin concentrations in the closed system. In the CSTR, change from sustained limit‐cycle oscillations to aperiodicity is produced by small variations of the temperature, or of the ferroin concentration. A qualitative discussion of these results is given in terms of coupled oscillators resulting from the simultaneous BZ reactions of the three equilibrium species of OAA in aqueous solution: the hydrate, the keto and the enol forms. The influence of the stirring rate on the oscillatory pattern in the CSTR is discussed.

Nonmonotonous temporal dependence of the concentration of ferroin as a reactant

Nonmonotonous temporal dependence of the concentration of ferroin as a reactant

Distinctive sites in chemical waves: The spiral core and the collision area of two annuli

Dynamical and structural details of traveling chemical waves in an excitable solution layer of the Belousov-Zhabotinskii reaction are sensitively detected by measurements with a two-dimensional spectrophotometer and application of perspective display techniques for data analysis. Concentration gradients of the redox couple ferroin/ferriin catalyzing the reaction are determined to a resolution of about 10μm. In solutions of identical chemical composition the gradients reach peak values of 8 mM/mm in a front of a spiral and 15 mM/mm in a front of a circular wave. Variation of ferroin concentration in the center of spiral rotation is less than 6% of that outside the core region. The degree of oxidation of ferroin at which the steepest concentration gradients occur is higher inside the core than at the outward-moving fronts. The core structure and the collision area between two circular fronts are represented by three-dimensional orthographic projections.

Two-dimensional spectrophotometry of spiral wave propagation in the Belousov-Zhabotinskii reaction: I. Experiments and digital data representation

The spiral-shaped wave of chemical activity propagating in a 1 mm layer of an excitable solution of the Belousov-Zhabotinskii reaction is analysed quantitatively for a 5 min time interval in a 4.5 × 4.5 mm area. The spatial distribution of the reaction catalyst and indicator ferroin is measured by light absorption at 490 nm with a video- and computer-based two-dimensional spectrophotometer. Digital images with 10 μm spatial and 256 digital units intensity resolution are acquired at a frequency of 20 per minute. Initially, the spiral has a pitch of 1.18 mm, a revolution time of 17.2 s, and the wavefronts propagate outwards with a velocity of 69 μm/s. After 5 min these quantities have changed by up to 5%. Three-dimensional graphic procedures and image analysis reveal that the wave profiles are symmetric close to the spiral center and become highly asymmetric during their outward displacement. The core of the spiral has a radius of 0.35 mm. Its center is a singular site (diameter < 30 μm) at which variations in ferroin concentration are at least 10 times smaller than in the surrounding area of spiral propagation. With time, the wave profiles become smoother and show spatial inhomogeneities.