Computational study of the interaction of proflavine with d(ATATATATAT)2 and d(GCGCGCGCGC)2

The interaction of proflavine (PR) with two B-DNA decamers of alternating AT and GC sequence, called [deca(dG-dC)]₂ and [deca(dA-dT)]₂, respectively, was computationally investigated by the ONIOM method, exploiting a three-layer QM/QM/MM hybrid approach. The highest level QM method was applied to the model system, which comprises the intercalation site (5th and 6th base pairs) and the inserted PR molecule. The connecting sugar phosphate backbone was added in the medium layer region. Both higher and medium level layers, differing in the size of the basis set used, were treated by the DFT MPWB1K functional. The full system in the lower layer was described by the empirical AMBER force field. The calculated values of the interaction energy of PR with [deca(dG-dC)]₂ and [deca(dA-dT)]₂, as well as with the dinucleotides d(GpC)₂, and d(ApT)₂, the latter considered either in vacuo and in the mimicked water solvent, support for a static higher affinity toward G-C compared to the A-T DNA base sequences, in agreement with structural results from crystallographic studies. Furthermore, the different structural characteristics of the [deca(dG-dC)]₂/PR complex compared to those of the [deca(dA-dT)]₂/PR, furnish a possible interpretation of apparently controversial experimental thermodynamic data, explained in terms of two possible modes of non-covalent binding of ligands with DNA, namely intercalation and external binding, respectively.     

Adsorption of antimony using amino-functionalized magnetic MIL-101(Cr): Optimization by response surface methodology

Amino-functionalized magnetic MIL-101(Cr) was prepared via a one-step solvothermal method, characterized, and applied in adsorptive Sb(III) removal. The effects of solution pH, adsorbent dosage, and coexisting substances on the adsorption of Sb(III) by MIL-101(Cr)–NH₂/MnFe₂O₄ were studied. The adsorption kinetics were analyzed using pseudo-first order, pseudo-second order, intraparticle diffusion, and Elovich models, while Freundlich and Langmuir isotherm models were used to fit the experimental data. The pseudo-second-order kinetic model provided the best fit for the kinetic data. The maximum adsorption capacity of MIL-101(Cr)–NH₂/MnFe₂O₄ for Sb(III) was 91.07 ​mg/g, as calculated using the Langmuir adsorption isotherm model. Thermodynamic analysis revealed that the adsorption of antimony onto MIL-101(Cr)–NH₂/MnFe₂O₄ is spontaneous and endothermic, while response surface optimization revealed that the optimal conditions for Sb(III) adsorption by MIL-101(Cr)–NH₂/MnFe₂O₄ are an adsorbent loading of 222.55 ​mg/L, a pH of 4.5, and a temperature of 294.59 ​K. The predicted adsorption capacity of MIL-101(Cr)–NH₂/MnFe₂O₄ for Sb(III) is only a 1.8% deviation from the actual value. Furthermore, MIL-101(Cr)–NH₂/MnFe₂O₄ exhibits strong magnetism, allowing it to be separated from wastewater using a magnet. Finally, a preliminary economic analysis showed that the cost of treating a ton wastewater containing 25 ​mg/L antimony using this composite would be 26.24 USD. Thus, MIL-101(Cr)–NH₂/MnFe₂O₄ is promising for treatment of Sb(III)-containing wastewater.     

A comparison of the pseudo-steady-state and shrinking-core model for the reduction of titanium dioxide to titanium

A multistage shrinking-core model is proposed for the electrodeoxidation of titanium dioxide to titanium. This takes place through a series of steps from TiO₂ to Ti₃O₅ to Ti₂O₃ to TiO to Ti. Ideally, the model would incorporate a number of shells of the above lower oxide phases with the shrinking core of TiO₂ in the center but this would be mathematically intractable. A simpler method would be to use the shrinking-core model for each of the individual reductions. Taking the experimental parameters and diffusion coefficient of oxygen in the different phases into account, an analytical solution is developed for the transient differential equation. The first ten eigenvalues are taken into account for the computation of the series solution. This is then compared with a solution based on a pseudo-steady-state approximation to the transient equations. Based on the results, for higher values (>0.01) of dimensionless applied current density, I _d , both the solutions disagree in terms of the time it takes for the core to shrink completely. The difference appears to be decreasing with lower values of I _d but for larger values of I _d the pseudo-steady-state approximation fails to yield results close to the analytical solution.     

A kinetic model and its parameter estimation for the process of binding copper to human serum albumin by a voltammetric method

Linear sweep anodic stripping voltammetry was applied to determine the concentration of free copper ions in the process of binding copper to human serum albumin (HSA) on the mercaptoethane sulfonate modified gold electrode surface. A kinetic model of two consecutive steps for the process of binding copper to HSA was first proposed on the basis of the electrochemical results and compared with a parallel kinetic response model by using residual analysis. The experimental data of the stripping peak currents with time was fitted according to the model and the kinetic parameters, binding rate constants, k₁ and k₂, were estimated to be 0.411 and 0.055 min^–1, respectively.     

一个与吸附剂浓度有关的Langmuir等温式

实验测定了不同吸附剂浓度下, 高岭土对Pb(II)和Cu(II)的吸附作用, 结果表明存在明显的吸附剂浓度效应, 即吸附等温线随吸附剂浓度升高而降低. 采用传统的Langmuir 吸附等温式对实验数据进行拟合表明, 此等温式可准确地描述给定吸附剂浓度下的吸附结果, 但不能预测其吸附剂浓度效应. 根据表面组分活度(SCA)模型, 假设吸附剂颗粒间存在相互作用, 吸附剂表面吸附位的活度系数不等于1, 而应为吸附剂浓度的函数, 推导出了一个与吸附剂浓度有关的Langmuir (Langmuir-SCA)方程. 运用高岭土吸附Pb(II)和Cu(II)以及文献中蛭石吸附Zn(II)和Cd(II)、咖啡吸附Pb(II)的实验数据检验方程的适用性, 结果表明Langmuir-SCA方程可准确地描述所观察到的吸附剂浓度效应. 方程的两个内禀参数, 热力学平衡常数(K_eq)和特征饱和吸附量(Γ_m⁰), 与吸附剂浓度无关, 并可由吸附实验数据拟合求得.     

Kinetic study of the poly(vinyl chloride)/titanium dioxide nanocomposites photodegradation under accelerated ultraviolet and visible light exposure

In the present study, poly(vinyl chloride)/titanium dioxide (PVC/TiO₂) nanocomposite films containing different amounts of synthesized TiO₂ nanoparticles and commercial rutile powder were irradiated for 5112 hr, under exposure of artificial ultraviolet and visible lights in three different intensities. The rate of degradation was determined by using weight loss data and was found to follow a pseudo‐first order kinetic model. To determine the overall rate constant of degradation, k, a possible mechanism of the photodegradation was considered. The rate equation demonstrated k as a function of TiO₂ concentration and irradiation intensity at each wavelength. The overall rate constant of PVC/TiO₂ samples were calculated to be varied in the range of 6–16 × 10^?7 hr^?1, at all investigated conditions. The kinetic study represented that by adding synthesized TiO₂ nanoparticles, even at low content, and with increasing their concentration, the photodegradation rate of nanocomposites decreased considerably compared with the composite samples. Likewise, by adding nanoparticles, a significant increase in the nanocomposites lifetime was achieved. The effect of irradiation intensity was investigated according to the reciprocity law experiments, and it was found that photodegradation occurred in two regimes with respect to irradiation intensity. The calculated overall rate constants were validated by the experimental data. Copyright © 2014 John Wiley & Sons, Ltd.     

Solubility and solubility product of crystalline Ni(OH)2

The solubility of crystalline Ni(OH)₂ was studied in solutions of 0.01M NaC10₄ with pH ranging from 7 to near 14. Equilibrium was approached both from over-and undersaturation, and the equilibration times extended from 3 to 90 days. The solubility of Ni(OH)₂(c) in the pH range of approximately 7 to 11.3 was effectively modeled by including aqueous Ni²⁺ and NiOH⁺ species. Values of the logarithm of the thermodynamic equilibrium constants for the reactions [Ni(OH)₂(c) ⇌ Ni²⁺ + 2OH^-] and [Ni²⁺ + OH^- ⇌ Ni(OH)⁺] were determined to be -16.1±0.1 and 5.65 ± 0.10, respectively. These data, in conjunction with Pitzer ion interaction parameters given in the literature, were used to model the reported solubilities of Ni(OH)₂(c) in chloride, sodium acetate, and potassium chloride solutions. The model predictions for these systems were in excellent agreement with the experimental data from the literature.     

Structure model and synthesis of NdCl3-FeCl3-graphite intercalation compounds

The distribution of the elements and microstructure of NdCI₃-FeCI₃-graphite intercalation compounds (GlCs) were shown by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results show that Nd element intercalates into graphite, forming NdCI₃-FeCI₃-GICs, and the distribution of Nd and Fe is nearly even. On the basis of the data, a structure model for RECI₃-GICs was founded, and the characteristic layer distance and the index of interval energy were calculated. The calculated results agree with experimental ones, and the relative errors are ±2%. Thus it can be seen that the (111) face is optimal direction for intercalation reaction of TbCI₃—LuCI₃, and the (001) face is that for LaCI₃—GdCI₃, because of the lowest interval energy.     

Particle Formation in Emulsion Polymerization: Particle Number at Steady State

Abstract

The number of particles formed in batch emulsion polymerization over wide ranges of emulsifier and initiator concentration has been investigated by computer simulation with a mathematical model developed in a previous paper. The influence of particle coagulation is also considered. The results show that, at low emulsifier concentration, the steady-state particle number N _s is governed by homogeneous nucleation so that N _s increases slowly with increasing emulsifier concentration [S]. In this range, N _s increases with increasing monomer polarity. The steep rise in N _s with emulsifier concentration after [S] exceeds a critical value suggests a transition from homogeneous nucleation domination to micelle nucleation. The slope of the N _s vs [S] relationship increases as the particle coagulation rate constant K_f increases. The power x in the empirical relationship N _s ? [S]^x decreases with increasing polarity of monomer in this region. At very high micelle concentration, insufficient radical generation and the increasing tendency for particle coagulation cause N ₂ to be less dependent on emulsifier concentration. These phenomena have been reviewed by Vanderhoff and confirmed by the experimental data presented by Sutterlin. The particle number increases with increasing initiator concentration [I] when [S] is above the CMC. As [I] continues to increase, however, N _s becomes relatively constant. Experimental data for styrene, butyl acrylate, and methyl acrylate from the literature are compared with the model predictions. Agreement between the theoretical predictions and the experimental data is evident over a wide range of emulsifier and initiator concentrations.     

Competition of copper and/or calcium in nickel–pectin interaction by potentiometric and voltammetric techniques

The interaction between nickel and pectin extracted from citrus fruit was studied in 0.10 M KNO₃, at pH 5.5 and 25 °C. Differential pulse and/or square wave polarography were used to determine free nickel. For a high coverage degree (θ) of the pectin by the metal ion a good fitting was observed between experimental results and the model that includes both complex species, ML and ML₂ (M for the metal ion and L for the ligand). In the ML₂ species, Ni(II) interacts with two carboxylate groups of different chains, resulting in an inter-chain association. For low θ values, the formation of ML₂ is hindered due to the repulsion between the negative charges of carboxylic groups in two independent segments of pectin. The influence of calcium or copper ions on the free nickel concentration, in the presence of pectin, may lead to a decrease in free nickel concentration, contrary to what would be expected from direct competition between Ca(II) or Cu(II) and Ni(II) for the pectin binding sites. This is due to the partial neutralisation of the negative carboxylic charges by the positive charges of the divalent cations, which favours NiL₂ formation through the association of independent chains.     

Vapour-liquid equilibrium measurements for binary mixtures of R32, R143a, R134a and R125 with a perfluoropolyether lubricant

In the present work, vapour-liquid equilibria of four binary systems refrigerant-lubricant oil have been investigated, CF₃CHF₂ (R125), CF₃CH₂F (R134a), CF₃CH₃ (R143a) and CH₂F₂ (R32) as refrigerants and a commercial perfluoropolyether (PFPE), Fluorolink D10H, as lubricant. Vapour-liquid equilibrium data, consisting of isothermal measurement of equilibrium pressure at a fixed composition, have been correlated with an extended Flory-Huggins equation and the corresponding parameters have been determined. Good agreement has been found between experimental data and the model predictions.     

Isobaric (vapour + liquid) equilibria for sulfolane with toluene, ethylbenzene, and isopropylbenzene at 101.33 kPa

Isobaric (vapour + liquid) equilibrium data have been measured for the (toluene + sulfolane), (ethylbenzene + sulfolane), and (isopropylbenzene + sulfolane) binary systems with a modified Rose-Williams still at 101.33 kPa. The experimental data of binary systems were well correlated by the non-random two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) activity coefficient models for the liquid phase. All the experimental results passed the thermodynamic consistency test by the Herington method. Furthermore, the model UNIFAC (Do) group contribution method was used. Sulfolane is treated as a group (TMS), the new group interaction parameters for CH₂–TMS, ACH–TMS and ACCH₂–TMS were regressed from the VLE data of (toluene + sulfolane) and (ethylbenzene + sulfolane) binary systems. Then these group interaction parameters were used to estimate phase equilibrium data of the (isopropylbenzene + sulfolane) binary system. The results showed that the estimated data were in good agreement with the experimental values. The maximum and average absolute deviations of the temperature were 4.50 K and 2.39 K, respectively. The maximum and average absolute deviations for the vapour phase compositions of isopropylbenzene were 0.0237 and 0.0137, respectively.     

Inhibited transesterification of PET/PBT blends filled with silica nanoparticles during melt processing

The blends of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) undergo transesterification reactions between PET and PBT during melt processing. In this research, PET/PBT transesterification has been investigated in the presence of nano-fillers, including pure SiO₂ and silane-coupling-agent-modified SiO₂. The results show that the incorporation of SiO₂ nanoparticles inhibits PET/PBT transesterification, and the influence of pure SiO₂ is higher than modified SiO₂. The inhibition of SiO₂ on transesterification is explained by the fact that the hydroxyl end groups of PET and PBT react with the surface hydroxyl groups of SiO₂ before transesterification due to the high activity of surface hydroxyl groups of SiO₂, and the reduction of hydroxyl end groups of PET and PBT leads to the inhibition of transesterification between PET and PBT. This has been demonstrated by the experimental data of TGA, FTIR, and XPS. And the reactivity of hydroxyl end groups of PBT is higher than that of PET.     

On the porous structure of coals: Evidence for an interconnected but constricted micropore system and implications for coalbed methane recovery

An experimental and theoretical study of adsorption and diffusion of carbon dioxide and methane in coals of widely varying rank was carried out. Low pressures adsorption isotherms of CO₂ were obtained and analyzed using Dubinin's theory of volume filling of micropores. High-pressure adsorption isotherms of CH₄ were obtained and analyzed using tracer pulse chromatography in conjunction with an appropriate adsorption/diffusion model. A preliminary¹²⁹Xe NMR analysis of chemical shifts experienced by xenon atoms in particles of different sizes is also reported.The heretofore undocumented and/or underestimated effects of activated diffusion of CO₂ at 273–298 K complicate the elucidation of the true microporous structure of coals, especially its dependence on coal rank. Activated diffusion of both CO₂ and methane at room temperature does not allow reliable estimates of coalbed gas content to be made. A model of an interconnected network of pores which includes randomly distributed, numerous and ultramicroporous constrictions (at any size scale) is consistent with all these experimental and theoretical findings.Presented in part at the International Conference on Coal Science, Banff, Alberta, Canada. September 1993, and at the 21st Biennial Conference on Carbon, Buffalo, NY, June 1993.     

Efficient removal of As(V) from simulated arsenic-contaminated wastewater via a novel metal–organic framework material: Synthesis,structure, and response surface methodology

A novel metal–organic framework material {[N(C₂H₅)₃][Zn₂(ptmda)₂(μ₂-H₂O)]·(H₂O)_0.5}_n { GUT-3 ; H₂ptmda is 4,4′-([p-tolylazanediyl]bis [methylene])dibenzoic acid} was successfully synthesized using the hydrothermal method and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. GUT-3 has a two-dimensional network based on dinuclear [Zn₂(ptmda)₂(μ₂-H₂O)]⁻ building units which formed an eightfold interpenetration network in GUT-3 molecules. Hirshfeld surface analysis revealed that H–H, C–H, and O–H bonds accounted for the majority of intermolecular interactions. Moreover, the interactions between GUT-3 and As(V) – the form of As(V) is AsO₄³⁻ – were analyzed in aqueous solutions in a batch system to study the effect of pH, concentration, adsorbent dose, adsorption time, adsorption temperature, and shaking speed. The kinetic and isotherm data of arsenic adsorption on GUT-3 were accurately modeled by pseudo-second-order, Langmuir (q_m = 33.91 mg/g), and Freundlich models. The Box–Behnken response surface method was used to optimize the adsorption conditions of As(V) from the simulated arsenic-contaminated wastewater. The effect of various experimental parameters and optimal experimental conditions was ascertained using the quadratic model.     

Fuzzy model prediction of Co (III)Al2O3 catalytic behavior in Fischer-Tropsch synthesis

The application of Co(Ⅲ)/Al2O3 catalyst in Fischer-Tropsch synthesis(FTS)was studied in a wide range of synthesis gas conversions and compared with Fuzzy Simulation results.Present study applies fuzzy model to predicting the product composition of CH4,CO2 and CO in Fischer-Tropsch process for natural gas synthesis,in which the input vector was 4-dimension including four variables(operating pressure, operating temperature,time and CO/H2 ratio)of 70 different experiments and the output product is a composition of CO2,CO and CH4. The Mamdani algorithm has been applied to the training of the fuzzy system and the test set was used to evaluate the performance of the system including R2,ARE,AARE and SD.The results demonstrated that the predicted values from the model were in good consistency with the experimental data.The work indicates how fuzzy inference system(FIS),as a promising predicting technique,would be effectively used in FTS.     

Reductive Dissolution of PuO2(am): The Effect of Fe(II) and Hydroquinone

PuO₂(am) solubility was investigated as a function of time, for pH from 0.5 to 11, and in the presence of 0.001 M FeCl₂ or 0.00052 M hydroquinone to determine the effect of environmentally important reducing agents on PuO₂(am) solubilization under geological conditions. Equilibrium was reached in <4 days. The observed PuO₂(am) solubilities were many orders of magnitude higher than the Pu(IV) concentrations predicted from thermodynamic data. Spectroscopic, solvent extraction, and thermodynamic analyses of data showed that Pu(III) was the dominant aqueous oxidation state. The experimental pH, pe, and Pu(III) concentrations from both the Fe(II) and hydroquinone systems provided a log K ⁰ value of 15.5 ± 0.7 for [PuO₂(am) + 4H⁺ + e ^– Pu³⁺ + 2H₂O]. The data show that reduction reactions involving Fe(II) and hydroquinone are relatively rapid and that reductive dissolution of PuO₂(am), hitherto ignored, may play an important role in controlling Pu behavior under reducing environmental conditions.     

Synthesis of gradient copolymers with simultaneously tailor‐made chain composition distribution and glass transition temperature by semibatch ATRP: From modeling to application

Recent studies have demonstrated that gradient copolymers exhibit unique thermal properties. Although these properties can be determined by copolymer composition, other factors such as chain and sequence lengths and their distributions can also influence them. Accordingly, the synthesis of gradient copolymers requires simultaneously tailor‐made chain structure and thermal properties. In this work, we carried out a systematic study on the preparation of poly(methyl methacrylate‐grad‐2‐hydroxyethyl methacrylate) [poly(MMA‐grad‐HEMA)] with synchronously tailor‐made chain composition distribution and glass transition temperature (T_g) through semibatch atom transfer radical polymerization. First, a comprehensive model for simultaneously predicting gradient copolymer microstructure and T_g was presented using the concept of pseudo‐kinetic rate coefficients and Johnston equation. The model was validated by comparing simulation results with the classical reference data. Furthermore, the model was used to guide the experimental synthesis of the poly(MMA‐grad‐HEMA) gradient copolymers potentially as excellent damping material. The thermal properties of these gradient copolymer samples were evaluated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Curing Kinetics of Diglycidyl Ether of Bisphenol A and Diaminodiphenylmethane Using a Mechanistic Model

Summary: The curing kinetics of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐diaminodiphenylmethane (DDM) was analyzed using isothermal differential scanning calorimetry (DSC) modes by using a simple mechanistic model which includes two rate constants, k₁ and k₂, two reaction orders, n₁ and n₂, and the ratio of initial concentration of hydroxyl group to initial epoxy concentration, c₀. Analyses of DSC data indicated that an autocatalytic reaction existed in the curing process. The mechanistic model proposed in this paper fits the experimental data exactly. Rate constants, k₁ and k₂ have been found to increase with rising curing temperature. The activation energies for the relative reactions were determined to be 66.00 ± 4.21 and 50.74 ± 8.92 kJ/mol, respectively. The complex equivalent constant, K, decreased with increasing temperature. Diffusion control was incorporated to describe the cure in the latter stages.

Comparison of experimental data with the mechanistic model for the curing kinetics of DGEBA with DDM.