Marginal states in a cubic autocatalytic reaction

Marginal steady state belongs to a special class of states in nonlinear dynamics. To realize this state we consider a cubic autocatalytic reaction A + 2B → 3B in a continuous-stirred-tank-reactor, where the flow rate of the reactant A can be controlled to manipulate the dynamical behavior of the open system. We demonstrate that when the flow rate is weakly noisy the autocatalytic reaction admits of a steady state which is marginal in nature and is surrounded by infinite number of periodic trajectories. When the uncatalyzed reaction A → B is included in the reaction scheme, there exists a marginal steady state which is a critical state corresponding to the point of transition between the flow branch and the equilibrium branch, similar to gas-liquid critical point of transition. This state loses its stability in the weak noise limit.     

Mechanistic study of the Soai autocatalytic reaction informed by kinetic analysis

Detailed kinetic studies of the Soai reaction affirm the basic mechanistic picture previously developed in kinetic, spectroscopic and molecular modelling studies, and also suggest that refinements to the proposed elementary reaction steps must be considered. The alkanol reaction product is driven strongly and without bias towards the formation of homochiral and heterochiral dimers. The reaction is catalyzed by only the homochiral dimers. Consideration of the kinetic profiles from reactions carried out with different initial dialkylzinc concentrations support a proposal for a tetrameric transition state, but further experimental work is required to delineate the nature of this species. The power of reaction calorimetry as a kinetic tool for discerning subtle effects of the shape of the kinetic profile is highlighted. The importance of combining kinetic evidence with spectroscopic and other characterization tools is emphasized.     

An autocatalytic chromogenic and fluorogenic photochemical reaction controlled by nucleic acids

The autocatalytic photochemical reaction, which is potentially controlled by any selected nucleic acid, is highly sequence specific and not inhibited by its products, was developed. This reaction generates colored and fluorescent products, which can be monitored by the naked eye.     

Oscillatory and stationary convective patterns in a reaction driven gravity current

Horizontally propagating chemical fronts are studied in a thin solution layer of the acid-catalyzed chlorite-tetrathionate reaction. Unusual cellular patterns develop when significant amount of autocatalyst is bound to polyelectrolyte with low mobility: both oscillatory and stationary patterns evolve as a result of the interaction between the reaction front and the superposed gravity current. The concentration of the polyelectrolyte regulating the velocity of front propagation serves as a bifurcation parameter for switching between the two basic patterns.     

Lock-exchange experiments with an autocatalytic reaction front

A viscous lock-exchange gravity current corresponds to the reciprocal exchange of two fluids of different densities in a horizontal channel. The resulting front between the two fluids spreads as the square root of time, with a diffusion coefficient reflecting the buoyancy, viscosity, and geometrical configuration of the current. On the other hand, an autocatalytic reaction front between a reactant and a product may propagate as a solitary wave, namely, at a constant velocity and with a stationary concentration profile, resulting from the balance between molecular diffusion and chemical reaction. In most systems, the fluid left behind the front has a different density leading to a lock-exchange configuration. We revisit, with a chemical reaction, the classical situation of lock-exchange. We present an experimental analysis of buoyancy effects on the shape and the velocity of the iodate arsenous acid autocatalytic reaction fronts, propagating in horizontal rectangular channels and for a wide range of aspect ratios (1/3 to 20) and cylindrical tubes. We do observe stationary-shaped fronts, spanning the height of the cell and propagating along the cell axis. Our data support the contention that the front velocity and its extension are linked to each other and that their variations scale with a single variable involving the diffusion coefficient of the lock-exchange in the absence of chemical reaction. This analysis is supported by results obtained with lattice Bathnagar-Gross-Krook (BGK) simulations Jarrige et al. [Phys. Rev. E 81, 06631 (2010)], in other geometries (like in 2D simulations by Rongy et al. [J. Chem. Phys. 127, 114710 (2007)] and experiments in cylindrical tubes by Pojman et al. [J. Phys. Chem. 95, 1299 (1991)]), and for another chemical reaction Schuszter et al. [Phys. Rev. E 79, 016216 (2009)].     

Escape over fluctuating barriers driven by colored noise

Escape over fluctuating barriers in the presence of thermal white noise is addressed. Several general results are established, for stochastic barrier fluctuations being controlled by colored Gaussian noise. Our findings are exact in the limit of white noise sources and (partially) in the limit of extreme large noise color, and are approximate for intermediate noise color. As one main result we find that the escape time can generically exhibit a minimum resonant activation, whenever the colored noise intensity is an increasing function of the noise correlation time. The effects induced by correlated noise sources are addressed as well.     

Topochemical transketalization reaction driven by hydrogen bonding

An unusual thermal isomerization of 1,2;3,4-di-O-isopropylidene-myo-inositol to 1,2;5,6-di-O-isopropylidene-myo-inositol was observed in the solid state. A detailed study revealed that this ketal migration is a topochemically driven one. X-ray structure revealed that strong intermolecular hydrogen bonding in the crystal preorganizes the hydroxyl and ketal carbon in a transition-state-like arrangement favorable for the reaction. The 5-OH of each molecule faces the trans ketal carbon of a neighboring molecule at a close distance and an angle of approach near to linearity, making a trigonal-bipyramidal-like arrangement in the crystal, which could facilitate the reaction. This is the first report of a topochemical transketalization reaction.     

Chirally autocatalytic reaction performed in highly supersaturated conditions

Spontaneous chiral asymmetry generation, which is the preferential production of one enantiomer in a non‐chiral environment by chiral autocatalysis, could be observed in a preparation of a octahedral cobalt complex, cis‐[CoBr(NH₃)(en)₂]Br₂. A concentration fluctuation in a far‐from‐equilibrium chemical system will grow if the rate of local autocatalytic production of a compound in a small volume overcomes its loss due to diffusion. In a chirally autocatalytic system, this phenomenon could produce a large variation in the enantiomeric excess. In a reaction that produces the cobalt complex, the reaction rate was found to increase in the highly supersaturated solution of the product. In supersaturated solutions, before crystals of the solute have nucleated, embryos, which are the clusters of the solute, are formed. Ternary water‐solubility isotherm of each enantiomer of the cobalt complex suggests that each embryo consists of one exclusive enantiomer. Each chiral cluster, which could be regarded as polymeric material, thus formed in a highly supersaturated solution, may act as catalyst for the production of the same enantiomer. Life is a far‐from‐equilibrium self‐organized polymeric system in which chiral symmetry is broken. This reaction system is thus a model for the generation and amplification of chiral asymmetry in polymeric materials; it provides some insight in to the mechanisms that might have produced the observed biomolecular homochirality.     

外噪声作用下可激发系统中的预测同步现象

采用数值模拟方法研究了由2个完全相同的可激发系统,通过单向延迟反馈耦合连接所组成主动-从动系统中的预测同步现象.结果表明在相等的外噪声作用下,当延迟时间和耦合强度在适当的范围内取值时,从动系统发生放电活动时所产生的动作电位能够预测主动系统发生放电活动时所产生的动作电位,即出现了预测同步现象,并且预测时间不可能大于主动神经元的响应时间.     

Membrane assembly driven by a biomimetic coupling reaction

One of the major goals of synthetic biology is the development of non-natural cellular systems. In this work, we describe a catalytic biomimetic coupling reaction capable of driving the de novo self-assembly of phospholipid membranes. Our system features a coppercatalyzed azide-alkyne cycloaddition that results in the formation of a triazole-containing phospholipid analogue. Concomitant assembly of membranes occurs spontaneously, not requiring preexisting membranes to house catalysts or precursors. The substitution of efficient synthetic reactions for key biochemical processes may offer a general route toward synthetic biological systems.     

Wave patterns driven by chemomechanical instabilities in responsive gels

The first experimental evidence of a chemomechanical mechanism leading to morphogenetic instabilities is demonstrated experimentally. The system consists of a pH-responsive gel that swells at high pH and shrinks at low pH, and a bistable reaction system exhibiting an acid steady state (pH approximately 2) and an alkaline steady state (pH approximately 10). Within the gel, the steady state selection depends on the gel size. We show that in a constant and uniform nonequilibrium chemical environment, the responsive gel undergoes large amplitude dynamical deformations under the form of travelling contraction waves and complex spatio-temporal volume oscillations. These deformations are coupled to concentration patterns of protons. We present different sequences of dynamical behaviors observed under various controlled chemical conditions. A simple heuristic model is proposed to account for the observations. These experiments open a new route for pattern formation driven by chemical energy, in soft matter systems.     

A new length detection-micro fluidic device using an autocatalytic reaction

A new length detection-micro fluidic device was developed using a sodium sulfite/hydrogen peroxide autocatalytic reaction system as a model reaction, and sub-ppm levels of horse radish peroxidase were determined with this device. Sodium sulfite solution containing bromo thymol blue as an indicator and hydrogen peroxide solution were pumped into a T-shaped mixer with the help of a microliter syringe pump and then mixed. The blue solution had changed to yellow beyond the midpoint of the fine pathway (micro channel). Furthermore, when horse radish peroxidase (PO_x) was pumped, a part of the blue solution in the micro channel (blue band) was shortened. Therefore, it was possible to determine the PO_x concentration by via the length of the blue band. The relationship between the blue band length (y, mm) and the common logarithm of the PO_x concentration (x, M) gave a straight line in the concentration range of 0.05–1 ppm. The equation for the straight line was as follows: y = −3.78 log(x) + 16.4. The correlation coefficient was γ = 0.995, the relative standard deviation was 5.7% (n = 10), and the detection limits of the PO_x concentration was 0.029 ppm. Correspondence: Shukuro Igarashi, Department of Biomolecular Functional Engineering, Faculty of Engineering, Ibaraki University, Nakanarusawa 4-12-1, Hitachi, Ibaraki 316-8511, Japan     

Quantum two-state dynamics driven by stationary non-Markovian discrete noise: Exact results

We consider the problem of stochastic averaging of a quantum two-state dynamics driven by non-Markovian, discrete noises of the continuous time random walk type (multistate renewal processes). The emphasis is put on the proper averaging over the stationary noise realizations corresponding, e.g., to a stationary environment. A two-state non-Markovian process with an arbitrary non-exponential distribution of residence times (RTDs) in its states with a finite mean residence time provides a paradigm. For the case of a two-state quantum relaxation caused by such a classical stochastic field we obtain the explicit exact, analytical expression for the averaged Laplace-transformed relaxation dynamics. In the limit of Markovian noise (implying an exponential RTD), all previously known results are recovered. We exemplify new more general results for the case of non-Markovian noise with a biexponential RTD. The averaged, real-time relaxation dynamics is obtained in this case by numerically exact solving of a resulting algebraic polynomial problem. Moreover, the case of manifest non-Markovian noise with an infinite range of temporal autocorrelation (which in principle is not accessible to any kind of perturbative treatment) is studied, both analytically (asymptotic long-time dynamics) and numerically (by a precise numerical inversion of the Laplace-transformed averaged quantum relaxation).     

Chemical and hydrodynamic stability of an interface with an autocatalytic reaction

An autocatalytic reaction of the trimolecular type is assumed to take place at the interface of two immiscible fluids. By coupling the chemical rate equations with the surface hydrodynamic equations, the authors obtain the threshold conditions for chemical and hydrodynamic instability.     

Enhancement of stochastic oscillations by colored noise or internal noise in NO reduction by CO on small platinum surfaces

In this paper, based on the stochastic model of NO reduction by CO on Pt crystal surfaces and taking Gaussian colored noise as external fluctuations of the NO partial pressure, we study the effect of the colored noise on the internal noise-induced stochastic oscillations (INSOs) and the effect of internal noise on the colored noise-induced stochastic oscillations (CNSOs). It is found that the INSO can be enhanced by the colored noise with appropriate correlation time or noise strength and, interestingly, the CNSO can be enhanced by the internal noise as well and, moreover, the enhanced CNSO can reach the best oscillatory states repetitively via proper internal noises. This effect of the internal noise is different from its effect on the stochastic oscillations induced by the external Gaussian white noise, which probably results from the interaction of the correlated colored noise and the internal noise.     

Determination of ultratrace amounts of ruthenium(III) by the delayed autocatalytic reaction using citric acid.

A method for determination of ultratrace amounts (ppq levels) of ruthenium(III) was developed using a copper(II)-phthalocyanine-3,4',4",4"'-tetrasulfonic sodium salt (Cu-PTS) as an indicator in a potassium bromate autocatalytic reaction system. A satisfactory calibration curve of ruthenium(III) ion was obtained by the time measurement in the concentration range of 1 x 10(-13) M to 5 x 10(-12) M with the relative standard deviation (RSD) of 2.8% (n=5). The determination limits (3sigma) were 3.30 x 10(-14) M (3.34 ppq).