Self-motion of a phenanthroline disk on divalent metal ion aqueous solutions coupled with complex formation

The self-motion of a 1,10-phenanthroline disk on divalent metal ion aqueous solutions was investigated as a simple autonomous motor coupled with complex formation. The characteristic features of motion (continuous and oscillatory motion) and their concentration regions differed among metal ions, and the frequency of oscillatory motion depended on the temperature of the aqueous solution. The nature of the characteristic motion is discussed in relation to the stability constant of complex formation between phenanthroline and a metal ion, and the difference in surface tension between phenanthroline and its metal complex as the driving force.     

Overcharging, charge inversion, and reentrant condensation: using highly charged polyelectrolytes in tetravalent salt solutions as an example of study

We study salt-induced charge overcompensation and charge inversion of flexible polyelectrolytes via computer simulations and demonstrate the importance of ion excluded volume. Reentrant condensation takes place when the ion size is comparable to monomer size, and happens in a middle region of salt concentration. In a high-salt region, ions can overcharge a chain near its surface and charge distribution around a chain displays an oscillatory behavior. Unambiguous evidence obtained by electrophoresis shows that charge inversion does not necessarily appear with overcharging and occurs when the ion size is not big. These findings suggest a disconnection of resolubilization of polyelectrolyte condensates at high salt concentration with charge inversion.     

A Kinetic Study on Catechol‐Based Belousov–Zhabotinsky Reaction

The present investigation pertains to the kinetic study on bromate‐driven and manganese ion catalyzed Belousov–Zhabotinsky oscillatory chemical reaction having catechol (1,2‐dihydroxybenzene) as the organic substrate in aqueous acid media at 30 ± 0.1^oC under stirred conditions. Although some polyphenols as chemical oscillators are known in the literature but the role of catechol has been marginalized. The reaction system with catechol shows long‐time series of periodic as well as aperiodic oscillations, which were monitored potentiometrically in the oxidation reduction potential (ORP) mode under batch conditions. The various oscillatory parameters such as induction time (t_in), time period (t_p), amplitude (A), and number of oscillations (N) were obtained by drawing a plot between redox potential (mV) versus time (s). It is found that the oscillatory parameters of the system vary with the concentration of the reacting species. The reaction system was also studied in different aqueous acid media, but the detailed studies with respect to experimental parameters have been made in aqueous sulfuric acid medium as it showed a broad oscillatory window and better oscillatory characteristics. Moreover, the oscillatory parameters in general and induction time in particular vary significantly with temperature (15 to 45 ± 0.1^oC). The activation parameters of the system have also been calculated. The oscillatory behavior of the reaction system was also confirmed spectrophotometrically. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 141–151, 2013     

Acousto-spinodal decomposition of compressible polymer solutions: early stage analysis

The structure and dynamics of early stage kinetics of pressure-induced phase separation of compressible polymer solutions via spinodal decomposition is analyzed using a linear Euler-Cahn-Hilliard model and the modified Sanchez Lacombe equation of state. The integrated density wave and Cahn-Hilliard equations combine the kinetic and structural characteristics of spinodal decomposition with density waves arising from pressure-induced couplings. When mass transfer rate is slower that acoustic waves, concentration gradients generate density waves that cycle back into the spinodal decomposition dynamics, resulting in oscillatory demixing. The wave attenuation increases with increasing mass transfer rates eventually leading to nonoscillatory spinodal demixing. The novel aspects of acousto-spinodal decomposition arise from the coexistence of stable oscillatory density dynamics and the unstable monotonic concentration dynamics. Scaling laws for structure and dynamics indicate deviations from incompressible behavior, with a significant slowing down of demixing due to couplings with density waves. Partial structure factors for density and density-concentration reflect the oscillatory nature of acousto-spinodal modes at lower wave vectors, while the single maximum at a constant wave vector reflects the presence of a dominant mode in the linear regime. The computed total structure factor is in qualitative agreement with experimental data for a similar polymer solution.     

Chemical effects on oscillatory cross sections in low energy ion scattering

Oscillatory structure in the scattered ion yield for He⁺ scattering from In has been observed to depend upon the chemical environmental of the In. Fourier analysis of the oscillatory structure indicates two major components whose relative amplitudes vary significantly with chemical environment.     

Coherent oscillations in ultrafast fluorescence of photoactive yellow protein

The ultrafast photoinduced dynamics of photoactive yellow protein in aqueous solution were studied at room temperature by femtosecond fluorescence spectroscopy using an optical Kerr-gate technique. Coherent oscillations of the wave packet were directly observed in the two-dimensional time-energy map of ultrafast fluorescence with 180 fs time resolution and 5 nm spectral resolution. The two-dimensional map revealed that four or more oscillatory components exist within the broad bandwidth of the fluorescence spectrum, each of which is restricted in the respective narrow spectral region. Typical frequencies of the oscillatory modes are 50 and 120 cm(-1). In the landscape on the map, the oscillatory components were recognized as the ridges which were winding and descending with time. The amplitude of the oscillatory and winding behaviors is a few hundred cm(-1), which is the same order as the frequencies of the oscillations. The mean spectral positions of the oscillatory components in the two-dimensional map are well explained by considering the vibrational energies of intramolecular modes in the electronic ground state of the chromophore. The entire view of the wave packet oscillations and broadening in the electronic excited state, accompanied by fluorescence transitions to the vibrational sublevels belonging to the electronic ground state, was obtained.     

Oscillatory interaction between two like‐charged nanoparticles induced by polyelectrolyte brush–solvent interface

We use two‐dimensional (2D) self‐consistent field theory to study the effective interactions between two like‐charged cylindrical nanoparticles mediated by an oppositely weakly charged polyelectrolyte brush in a solvent solution. In a poor solvent, where a sharp brush–solvent interface forms, an oscillatory interaction is observed when two nanoparticles are both located at the brush–solvent interface. This oscillatory interaction depends on the penetration depths of the particles and their geometric orientations with respect to the substrate. When the particles are both immersed in the brush and/or the particles are oriented vertically or diagonally with large angles to the substrate, the oscillatory behavior disappears. We interpret our findings by analyzing in detail the contributions to the free energy from electrostatic interaction, nonelectrostatic interaction, and entropies, separately. Briefly, the deformations of the interface and the ion layers formed in the vicinity of the interface are responsible for this oscillatory behavior. In a good solvent, where the narrow brush–solvent interface vanishes, the effective particle–particle interactions behave like that for both particles immersed into the brush with poor solvent. They are found to be repulsive. The influences of the particle size, grafting density, and amount of charges and ions are also briefly discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1458–1468     

Effect of gamma-irradiation on the catalyzed bromate oscillator

The oscillatory characteristics of a catalyzed bromate system is altered by gammairradiation. The alterations observed are probably due to the activation of the reduced form of the metal ion catalyst under gamma-irradiation. However, these alterations could not be accounted for in terms of an effective concentration of bromate acting as a quenching agent under gamma-irradiation conditions as reported in the literature.     

BR振荡反应的新型机理模型

简单总结了已有BR(Briggs-Rauscher)振荡体系的机理模型的特点和不足之处,并构造了一个能模拟HIO2、I2、I－和O2 四个组分的9步反应机理的简化模型.该模型能在较大的初始输入组分浓度范围内出现周期性的振荡行为,可用于解释BR体系中的一些特定的实验现象,并且能够呈现极限环和双稳态.     

Current oscillations during the electrochemical oxidation of sulfide in the presence of an external resistor

The electrochemical oxidation of sulfide on a polycrystalline platinum electrode was studied under potentiostatic condition when an external resistor is in series with the working electrode. Only two os- cillatory regions can be obtained in the absence of the external resistance, but four oscillatory regions, including two new current oscillations, were found in this system by controlling the external resistance. It is demonstrated that three oscillatory regimes, which arise on the positive branch of current-potential curve, can be classified as HN-NDR (Hidden N-shaped Negative Differential Resistance) oscillators. For the first oscillatory region, various transient complex phenomena, which result from the change of the electrode/electrolyte interface by accumulation of adsorbed element sulfur on the electrode, have been observed. The dynamic behavior of NDR (Negative Differential Resistance) oscillations, appearing along with negative branch of polarization curve, can transform from oscillations into bistability with a sufficient large external resistance in series. Two oscillatory regions in high-potential region classified as HN-NDR type oscillations are separated by a saddle-loop bifurcation. They displayed a sequence of bursting oscillations and irregular oscillations, respectively. The electrochemical oxidation of sulfide provides a model system for studying complex dynamics and possible application in sulfur removal.     

Molecular dynamics study of screening at ionic surfaces

Molecular dynamics simulations of NaCl fluid are used to understand the behavior of ionic fluid to screen the field generated by charges on the ionic crystal surfaces in absence of any external electric field. The NaCl fluid in the strongly coupled regime (corresponding to the melt) in contact with the charged octopolar (111) NaCl surface shows that the spatial correlations decay in an oscillatory manner, with a screening length lambdaQ given by the envelope of the damped oscillations. By contrast to the Debye-Huckel theory, in the strongly coupled regime, lambdaQ increases with increasing coupling strength (also seen in bulk ionic simulations). The NaCl fluid confined between neutral (100) NaCl surfaces also shows weak oscillatory charge decay near the surface. Similar oscillatory exponential decay was seen when the NaCl fluid was confined between two analytically smooth neutral walls. The origin of these oscillations was due to the difference in ion sizes. NaCl fluid confined between neutral octopolar (110) and dipolar (110) surface show stronger density oscillations than (100) surface but comparatively very weak charge oscillations. This paper shows that the strength of the charges on the crystal surfaces is enough to induce a characteristic spatial distribution of charges in the contacting fluid and the extent of distribution depends on the type of surface.     

Kinetic studies on resorcinol-bromate-manganese(II) ion oscillator with and without additives

The present work pertains to the effect of temperature on the oscillatory behavior of bromate driven, Manganese (II) ion catalyzed BZ reaction with aromatic substrate i.e. resorcinol under batch conditions in 1.3 M sulfuric acid as aqueous acid medium. In order to study the effect of methyl ketones as additives (co-substrates), acetone is added to the aforesaid reaction system and the oscillations of the mixed substrate systems were studied at different temperatures. Further the effect of temperature with respect to ternary systems comprising of acetone with other ketones like butanone, pentanone, hexanone and acetyl acetone in 1:1 (v/v) ratio is also studied. It is found that temperature has a marked influence on the reactivity of the reaction systems, with and without methyl ketones and at all concentrations of the additives. Moreover, the rate of enolization of ketones also affects the oscillatory parameters like t _in and t _p. Although the exact values of enolization constants for the methyl ketones are not known to us, but by studying the oscillatory behavior, a trend can be predicted. Further the formation of end products in the ternary systems is influenced due to hydrophobic interactions of the ketones.     

Chemical oscillation of vanadium complexes: Simple and aperiodic systems

An oscillatory chemical reaction is an intriguing phenomenon subject to various and often uncontrollable factors. Many oscillatory systems consist of a strong acid, metal ion and an additional species with accessible oxidation states, and restrictive temperature conditions. Thus, an oscillatory system in which all the factors are understood would be useful. In this paper, we describe the first such system based on vanadium chemistry. The V(IV) complex (pale green color) turns dark orange with the production of a V(V) complex. This reaction is affected by many factors such as oxygen, ultraviolet (UV) irradiation, visible irradiation, and aldehyde addition. This oscillation reaction occurs only in a dichloromethane solution, suggesting that the solvent intervenes in the reaction. Examination of the gas phase during the oscillation reaction revealed the formation of carbon monoxide, carbon dioxide, hydrogen chloride, and phosgene. Based on these observations, we propose a plausible oscillation reaction mechanism.The results of this study contribute to the field of nonlinear dynamics. Additionally, this work offers new insights into vanadium chemistry because this oscillation phenomenon is strongly correlated with the electron transfer reaction of the vanadium complex. Moreover, studies using vanadium complexes may help in understanding vanadium-mediated electron transfer systems in vivo, such as vanadium accumulation and storage observed in marine organisms.     

Influence of the reduction of iodate ion by hydrogen peroxide on the model of the Bray-Liebhafsky reaction

The reduction of iodate ion by hydrogen peroxide, originally postulated by Liebhafsky, is considered as a possible step in the kinetic model proposed by Kolar-Ani and G. Schmitz for the overall Bray-Liebhafsky oscillatory process.     

On the oxidation of malonic acid by ceric ions

The oxidation of malonic acid by ceric ions has been investigated in sulfuric acid solution under a variety of conditions. The initial rate at low ceric ion concentrations is first order in each of the two reactants and has an activation energy of 11.6 kcal/mol; the instantaneous rate constant increases somewhat with time during a single run. At higher concentrations of ceric ion, semilogarithmic plots are sigmoid with a reduced rate constant at long times. The rate decreases slightly with increasing sulfuric acid concentration. Rates of carbon dioxide evolution may be much less than rates of ceric ion reduction because of supersaturation effects. The observations can be explained if dissolved oxygen reacts with organic radicals to catalyze the rate of initial attack on malonic acid, but oxygen must also be consumed irreversibly during these reactions. Computations with plausible rate constants have simulated the experimental observations. These oxygen effects can rationalize peculiar almost discontinuous changes in rate when bromomalonic acid is oxidized by ceric ion. These effects may also explain the previously puzzling observation that some Belousov–Zhabotinsky solutions are oscillatory in bulk but become quiescent but excitable when spread in a thin film in contact with air.     

The Effect of tetrabutylammonium ion on the uncatalyzed bromate oscillator

The effect of tetrabutylammonium ion (Bu₄N⁺) on the uncatalyzed bromate oscillator with phenol as substrate was monitored at 25 ± 0.1°C under stirred batch conditions. The changes in the oscillatory behaviour with increasing concentration of the Bu₄N⁺ ions have been ascribed to their ability to act as ion-pairing reagent.     

Current oscillations during copper electrodissolution under solution sparging in acidic NaCl solutions

Potentiostatic current oscillations were observed during electrodissolution of a helical coiled copper wire electrode in acidic sodium chloride when nitrogen was sparged through the solution. The oscillations were studied as a function of solution pH, chloride ion concentration and sparging rate over the potential range of 0.2 to 0.7 V versus Ag/AgCl (3 M NaCl). The surface morphology of the copper was observed during the oscillatory process using in situ, real-time optical microscopy, and the formation of a surface film was correlated with the oscillations.     

Vibrational dynamics of acetate in D2O studied by infrared pump-probe spectroscopy

Solute-solvent interactions between acetate and D(2)O were investigated by vibrational spectroscopic methods. The vibrational dynamics of the COO asymmetric stretching mode in D(2)O was observed by time-resolved infrared (IR) pump-probe spectroscopy. The pump-probe signal contained both decay and oscillatory components. The time dependence of the decay component could be explained by a double exponential function with time constants of 200 fs and 2.6 ps, which are the same for both the COO asymmetric and symmetric stretching modes. The Fourier spectrum of the oscillatory component contained a band around 80 cm(-1), which suggests that the COO asymmetric stretching mode couples to a low-frequency vibrational mode with a wavenumber of 80 cm(-1). Based on quantum chemistry calculations, we propose that a bridged complex comprising an acetate ion and one D(2)O molecule, in which the two oxygen atoms in the acetate anion form hydrogen bonds with the two deuterium atoms in D(2)O, is the most stable structure. The 80 cm(-1) low-frequency mode was assigned to the asymmetric stretching vibration of the hydrogen bond in the bridged complex.     

Density-functional theory of spherical electric double layers and zeta potentials of colloidal particles in restricted-primitive-model electrolyte solutions

A density-functional theory is proposed to describe the density profiles of small ions around an isolated colloidal particle in the framework of the restricted primitive model where the small ions have uniform size and the solvent is represented by a dielectric continuum. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-sphere repulsion and a quadratic functional Taylor expansion for the electrostatic interactions. The theoretical predictions are in good agreement with the results from Monte Carlo simulations and from previous investigations using integral-equation theory for the ionic density profiles and the zeta potentials of spherical particles at a variety of solution conditions. Like the integral-equation approaches, the density-functional theory is able to capture the oscillatory density profiles of small ions and the charge inversion (overcharging) phenomena for particles with elevated charge density. In particular, our density-functional theory predicts the formation of a second counterion layer near the surface of highly charged spherical particle. Conversely, the nonlinear Poisson-Boltzmann theory and its variations are unable to represent the oscillatory behavior of small ion distributions and charge inversion. Finally, our density-functional theory predicts charge inversion even in a 1:1 electrolyte solution as long as the salt concentration is sufficiently high.     

effect of initial reagent concentrations on the oscillatory behavior of the BZ reaction in a batch reactor

A detailed investigation on resorcinol as the Belousov–Zhabotinsky (BZ) oscillator in manganese(II) ion catalyzed reaction system with inorganic bromate (oxidant) and acetone (cosubstrate) was carried out in aqueous sulfuric acid medium (1.3 M). The aforesaid reagents were mixed with various concentrations to evolve the effective concentrations at which the reaction system exhibited better oscillations. The various oscillatory parameters such as time period (t_p), induction period (t_in), frequency (v), amplitude (A), and number of oscillations (n) were derived, and the dependence of concentration of the reacting species on these oscillatory parameters was interpreted on the basis of the Field–Koros–Noyes mechanism. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 650–657, 2009