Phase-death mode in two-coupled chemical oscillators studied with reactors of different volume and by simulation

The behavior of the phase-death mode (cessation of oscillations and transition to a steady state) in the two-coupled Belousov–Zhabotinsky reactions is studied in the asymmetric coupling. In an experiment, the types of synchronized modes and their regions were investigated as an extension of our previous study. This experiment is compared to a simulation using the two-coupled three-variable Oregonator models. The results confirm that the phase-death mode changes from “bistable” to “monostable” and reveal the stable region of the latter.     

Effect of Manganese(II) Ions on Regular Self-Oscillations in the Belousov–Zhabotinskii Reaction in a Tank Reactor with Constant Stirring

The effect of manganese(II) ions on the asymptotically regular self-oscillation regime of the Belousov–Zhabotinskii reaction, catalysed by ferroin, in a tank reactor with constant stirring has been studied. An increase in the manganese(II) ion concentration in the system leads to an increase in the period of the self-oscillations. The sensitivity of the self-oscillation of the chemical reaction on the addition of Mn²⁺ ions is decreased with an increase in acidity. To explain the results obtained we have used a reversible Oregonator model, which is supplemented with reactions between manganese(II) and manganese(III) ions and bromoxyl radicals, malonic acid, and ferroin.     

A computational modeling of two dimensional reaction–diffusion Brusselator system arising in chemical processes

In this article, the authors proposed a modified cubic B-spline differential quadrature method (MCB-DQM) to show computational modeling of two-dimensional reaction–diffusion Brusselator system with Neumann boundary conditions arising in chemical processes. The system arises in the mathematical modeling of chemical systems such as in enzymatic reactions, and in plasma and laser physics in multiple coupling between modes. The MCB-DQM reduced the Brusselator system into a system of nonlinear ordinary differential equations. The obtained system of nonlinear ordinary differential equations is then solved by a four-stage RK4 scheme. Accuracy and efficiency of the proposed method successfully tested on four numerical examples and obtained results satisfy the well known result that for small values of diffusion coefficient, the steady state solution converges to equilibrium point $(B,A/B)$ if $1-A+B^{2}>0$ .     

Models of biotin coenzyme reactions activated through phosphorylation

Abstract

The reactivity of models of enzymatic carboxylation reactions mediated by biotin coenzyme is presented; a possible role of the requiered ATP molecule for these reactions was investigated.

Several models of biotin activated through phosphorylation - according to the O-phosphobiotin model - are described and their reactivity to wards carboxylating agents discussed.

Models also exhibit phosphoryl transfer properties which may mimic known ATP synthesis from ADP, catalyzed by biotin carboxylases. Possible involvement of the same O-phosphobiotin structure is considered.     

Theoretical and computational modeling of self-oscillating polymer gels

The authors model wave propagation in swollen, chemoresponsive polymer gels that are undergoing the oscillatory Belousov-Zhabotinsky (BZ) reaction. To carry out this study, they first modify the Oregonator model for BZ reactions in simple solutions to include the effect of the polymer on the reaction kinetics. They then describe the gel dynamics through the framework of the two-fluid model. The polymer-solvent interactions that are introduced through the BZ reaction are captured through a coupling term, which is added to the Flory-Huggins model for polymer-solvent mixtures. The resulting theoretical model is then used to develop the gel lattice spring model (gLSM), which is a computationally efficient approach for simulating large-scale, two-dimensional (2D) deformations and chemical reactions within a swollen polymer network. The 2D calculations allow the authors to probe not only volume changes but also changes in the sample's shape. Using the gLSM, they determine the pattern formation and shape changes in 2D rectangular BZ gels that are anchored to a solid wall. They demonstrate that the dynamic patterns depend on whether the gel is expanded or contracted near the wall, and on the sample's dimensions. Finally, they isolate a scenario where the detachment of the gel from the wall leads to macroscopic motion of the entire sample.     

Synthesis of “bioinspired” copolymers: experimental and theoretical investigation on poly(vinyl benzyl thymine-co-triethyl ammonium chloride)

Abstract

“Bioinspired” copolymers based on vinylbenzyl thymine (VBT) and an ionically-charged monomer, such as vinylbenzyl triethylammonium chloride (VBA), were synthesized and theoretically investigated. These water-soluble copolymers are polystyrene- (PS) based, and their structure mimics DNA. In the presence of short-wavelength UV light, the thymine groups dimerize into non-toxic, environmentally benign, and biodegradable photo-resistant materials. Copolymerizations with different comonomer ratios were carried out at 65°C. Samples were taken along the reactions to determine monomer conversion, chemical composition, and molecular weight distribution. While average molecular weights fall along the reaction, the average composition remains almost constant and coincident with the initial comonomer ratios, thus indicating a similar reactivity of all the comonomer radicals. A mathematical model was developed that simulates the synthesis of the base biopolymer, in the sense of predicting the evolution of the global reaction variables and molecular structure of the polymer. The termination and propagation kinetic constants were adjusted to the experimental data. The resulting values are quite different to those of a normal styrene homopolymerization, thus suggesting a noticeable effect of the solvent and the comonomer pending groups.     

用Lyapunov指数确定Brusselator和Oregonator的分岔

本文计算了Brusselator及Oregonator的Lyapunov指数随系统控制参量的变化,依据Lyapunov指数的稳定性理论,确定出上述两模型都是通过Hopf分岔产生极限环的。在Brusselator分岔行为上,Lyapunov指数理论与线性稳定性分析所得的结论是一致的。对Oregonator所代表的化学背景作了分析,指出影响B-Z反应发生分岔的主要因素是Br~-的再生能力与速度。     

Multilayered Dermal Subcompartments for Modeling Chemical Absorption

Abstract

Dermal penetration of chemicals and drugs is of concern to both toxicologists and pharmacologists. Environmental professionals try to limit exposure to chemicals using protective clothing and gloves or barrier creams to trap chemicals. Drug developers try to enhance penetration of chemicals through the skin for medical purposes. Both can use predictive biologically-based mathematical models to assist in understanding the processes involved. These models are especially useful when they are based on physiological and biochemical parameters which can be measured in the laboratory. Appropriately validated models based on conservation of mass, diffusion and chemical transport by flow can be predictive of human exposures. In this paper we develop two new physiologically-based pharmacokinetic (PBPK) skin models to predict blood concentrations of dibromomethane in rats after skin-only vapor exposures. These new models improve the predictions of the blood concentrations especially at the beginning of the exposures. Sensitivity analysis shows that the permeability constants followed by partition coefficients have the most impact on blood concentration predictions. With proper validation the new models could be used to improve species, dose, and duration extrapolations of chemical or drug penetration. They could also be used to investigate and predict concentrations of drugs or chemicals in the skin.     

二维金属纳米材料的合成及电催化应用的研究进展

基于各种电化学过程的能源转化技术是未来可持续能源利用和发展的关键, 而催化剂在其中扮演着非常重要的角色. 二维金属纳米材料因其独特的物理化学性质在许多电催化反应中都展现出巨大的应用潜力, 也因此受到了广泛关注. 本文介绍了二维金属纳米材料的常见合成方法与策略, 并综合评述了近年来该类材料在电催化应用领域中的研究进展, 重点探讨了材料的组分和微观结构等因素对其性能的影响机理, 最后对二维金属纳米材料目前所面临的挑战以及未来的研究方向进行了总结与展望.     

Flammability Limits of an Oxidation Reaction in a Batch Reactor. II. The Rychlý Mechanism

It is often numerically convenient to reduce models in two-dimensions to one-dimension. This can be done formally through the use of centre manifold techniques, or informally using physical reasoning. We investigate the extent to which flammability limits in a two-dimensional slab are accurately represented by the values in the corresponding one-dimensional slab. We use a simple chemical mechanism containing exothermic and endothermic reactions that has been used to model the combustion of hydrocarbon fragments produced by polymer pyrolysis.     

Benzofuroxans: their synthesis,properties, and biological activity

The review provides a brief historical background for the establishment of structure of benzofuroxanes. Methods for their synthesis are summarized, and the chemical properties are described, which are splitted into two parts: reactions proceeding with a ring opening of the heterocycle, and those occuring with a participation of the isocyclic moiety. The biological activity of various representatives belonging to the benzofuroxan series is covered in details.

     

Novel rate equations describing isochronous chemical reactions

A simple mathematical model involving two first-order Ordinary Differential Equations (ODEs) with fourth-degree polynomial nonlinearities is introduced. The initial-value problem for this system of two ODEs is solved in terms of elementary functions: for an open set of initial data, this solution is isochronous, i.e., completely periodic with a fixed period (independent of the initial data); in the complementary set of initial data, it blows up at a finite time. This system is likely to be of applicative interest: for instance it models the time evolution of two chemical substances in a spatially homogeneous situation, provided this evolution is characterized by six appropriate chemical reactions whose rates are simply expressed in terms of three a priori arbitrary parameters, or alternatively by five appropriate reactions whose rates are simply expressed in terms of two a priori arbitrary parameters.     

Reactions of gas phase amino acids with the prevailing radicals in biomass thermal treatments

Amino acids, N-containing compounds, hold a significant importance in various field. Within the biomass energy sector, amino acids constitute a large fraction of the biomass's nitrogen content. As such, it is essential to comprehend their combustion chemistry; most specifically their biomolecular interactions with governing radicals in the pyrolytic and combustion media that prevail during thermal utilization of biomass. Herein, we have employed quantum chemical calculations and reaction rate theory to investigate reactions of a selected set of amino acids with H, CH₃, NH₂, OH, HO₂, and HS radicals. Thermo-kinetic calculations have been performed to determine the rates of hydrogen abstraction by these six radicals across all possible reaction channels for three specific amino acids: alanine, cysteine, and methionine. The investigation of other amino acids like glycine, threonine, and other models have been carried out for α-C positions as the most probable abstractable sites. The study also examines the individual effects of different substituents (COOH, NH₂, HS, and CH₂) and uncovers significant insights. Notably, the presence of the COOH group introduces polar effects that counterintuitively deactivate the thermodynamically favored α-abstraction pathway. Presented thermo-kinetic values are anticipated to complement existing biomass kinetic models and to improve current understanding of chemical events that participate in the complex nitrogen transformation reactions in biomass.     

EU Approach for Environmental Exposure Assessment: Actual Status and Future Needs

Abstract

To estimate the environmental concentration of a chemical substance, as required by the legislation of the European Union in the context of the risk assessment of chemical substances, several mathematical models are proposed. Representative and reliable analytical monitoring data for the different environmental compartments are indeed only seldom available. The proposed models are simple models as for instance multimedia fugacity models. Although the results of these models only provide an imperfect approximation of the concentration in the different compartments, very high uncertainties can lie upon certain input parameters, like the quantities of the substance released during one of its life-stages, its biodegradation rate in the respective compartments or its partition coefficients between those compartments. The improvement of the risk assessment scheme as proposed by the EU-Member States should focus on these input parameters. This might imply further adapting the test methods or even the requested test battery to the physical-chemical properties or even the structure of a substance.     

Subsurface interactions of actinide species and microorganisms: Implications for the bioremediation of actinide-organic mixtures

By reviewing how microorganisms interact with actinides in subsurface environments, we assess how bioremediation controls the fate of actinides. Actinides often are co-contaminants with strong organic chelators, chlorinated solvents, and fuel hydrocarbons. Bioremediation can immobilize the actinides, biodegrade the co-contaminants, or both. Actinides at the IV oxidation state are the least soluble, and microorganisms accelerate precipitation by altering the actinide's oxidation state or its speciation. We describe how microorganisms directly oxidize or reduce actinides and how microbiological reactions that biodegrade strong organic chelators, alter the pH, and consume or produce precipitating anions strongly affect actinide speciation and, therefore, mobility. We explain why inhibition caused by chemical or radiolytic toxicities uniquely affects microbial reactions. Due to the complex interactions of the microbiological and chemical phenomema, mathematical modeling is an essential tool for research on and application of bioremedation involving co-contamination with actinides. We describe the development of mathematical models that link microbiological and geochemical reactions. Throughout, we identify the key research needs.     

Compact formulae for three-center nuclear attraction integrals over exponential type functions

In any ab initio molecular orbital calculations, the major task involves the computation of the so-called molecular multi-center integrals. Multi-center integral calculations is a very challenging mathematical problem in nature. Quantum mechanics only determines which integrals we evaluate, but the techniques employed for their evaluations are entirely mathematical. The three-center nuclear attraction integrals occur in a very large number even for small molecules and are among of the most difficult molecular integrals to compute efficiently. In the present contribution, we report analytical expressions for the three-center nuclear attraction integrals over exponential type functions. We describe how to compute the formula to obtain an efficient evaluation in double precision arithmetic. This requires the rational minimax approximants that minimize the maximum error on the interval of evaluation.