Molecular modeling and spectroscopic studies on binding of 2,6-bis[4-(4-amino-2-trifluoromethylphenoxy)benzoyl] pyridine to human serum albumin

BAFP (2,6-bis[4-(4-amino-2-trifluoromethylphenoxy)benzoyl] pyridine), a synthesized polyimide compound, was exploited for the first time to analyze its interaction with human serum albumin (HSA) by molecular modeling, fluorescence and Fourier transform infrared attenuated total reflection spectroscopy (FTIR ATR) with drug concentrations of 3.3 × 10⁻⁶ to 3.0 × 10⁻⁵ mol L⁻¹. Molecular docking was performed to reveal the possible binding mode. The results suggested that BAFP can strongly bind to human serum albumin (HSA) and the primary binding site of BAFP is located in site II of HSA, which is supported by the results from the competitive experiment. The binding constants for the interaction of BAFP with HSA have been evaluated from relevant fluorescence data at different temperatures (296, 303, 310 and 308 K). The alterations of the protein secondary structure in the presence of BAFP in aqueous solution were quantitatively calculated by the evidences from FTIR ATR spectroscopes. The binding process was exothermic and spontaneous, as indicated by the thermodynamic analyses, and the major part of the binding energy is hydrophobic interaction, which is also in good agreement with the results of molecule modeling study. The enthalpy change ΔH⁰, the free energy change ΔG⁰ and the entropy change ΔS⁰ of 296 K were calculated to be −7.75, −27.68 kJ mol⁻¹ and 67.33 J mol⁻¹ K⁻¹, respectively.     

Statistical mixture design investigation of fractionated and total extracts from Erythrina speciosa Andrews leaves

The simplex centroid mixture design for the ethanol, dichloromethane, hexane and acetone solvents has been applied to the extraction of crude mass and the fiber, organic, neutral and basic fractions as well as the fractionation residues of Erythrina speciosa Andrews leaves. Binary and ternary synergic solvent interactions are seen to provide dominant contributions to the extraction of both crude mass and all the fractions. Quadratic and special cubic mixture models precisely predict the extracted quantities of each fraction and the residue as a function of the proportions of the four solvents. Different solvent mixtures are found to be the most efficient extractors for the different fractions: binary dichloromethane‐hexane mixtures for the fiber fraction, ternary ethanol‐dichloromethane‐acetone mixtures for the neutral fraction, binary ethanol‐dichloromethane mixtures for the organic fraction, crude extract and residue values and ternary ethanol‐dichloromethane‐hexane mixtures for the basic fraction. Principal component analysis shows that the ethanol‐dichloromethane mixtures are important for extracting large quantities of the basic and organic fractions as well as of the residue and crude masses.     

Metallocene‐Catalyzed Gas‐Phase Ethylene Copolymerization: Kinetics and Polymer Properties

The influence of 1‐hexene is examined on the kinetics of ethylene copolymerization with a metallocene catalyst in gas phase. A model is derived, which is able to describe a large reaction rate increase due to a small amount of incorporated comonomer. This complexation model describes the measured reaction rates for ethylene and 1‐hexene, and the co‐monomer incorporation. Polymer properties were analyzed, such as comonomer weight fraction. The density, melting point, and molecular weight of the produced polymer decreased with increase in 1‐hexene gas concentration. The in situ 1‐hexene sorption is estimated and follows Henry's law, but seems much higher than reported in the literature.

     

Kinetics and Molecular Weight Development of Dithiolactone‐Mediated Radical Polymerization of Styrene

Calculations of polymerization kinetics and molecular weight development in the dithiolactone‐mediated polymerization of styrene at 60 °C, using 2,2′‐azobisisobutyronitrile (AIBN) as initiator and γ‐phenyl‐γ‐butirodithiolactone (DTL1) as controller, are presented. The calculations were based on a polymerization mechanism based on the persistent radical effect, considering reverse addition only, implemented in the PREDICI® commercial software. Kinetic rate constants for the reverse addition step were estimated. The equilibrium constant (K = k_add/k_‐add) fell into the range of 10⁵–10⁶ L · mol^?1. Fairly good agreement between model calculations and experimental data was obtained.

     

Modeling of Molecular Transfer in Heterophase Polymerization

Mass transfer across interfaces greatly determines the kinetics of heterophase polymerization. All molecules in the system can cross any interface as long as they possess enough energy to overcome barriers such as interfacial tension, chemical potentials, etc. Two main groups of mathematical approaches have been used to model mass transfer: macroscopic deterministic and molecular stochastic. Macroscopic modeling may use fundamental laws, thermodynamic expressions and empirical or semi‐empirical equations. Molecular models are based on the discrete character of nature and include stochastic simulation, BD or MD. Special emphasis is placed on the most relevant molecular transfer processes observed in free‐radical emulsion polymerization.

     

求解一类二阶非线性偏微分方程的新算法

在再生核空间中给出一类二阶非线性偏微分方程的一个新的求解方法,近似解un(x)是通过在再生核空间中截断精确解u(x)而得到的,最后,通过一个数值算例来说明该方法是有效的.     

On the effect of electron-mass variation in numerical simulations of the Farley-Buneman instability

The Farley-Buneman instability is the plasma instability in the E region of the Earth’s ionosphere. Many studies on instability simulations use algorithms based on the particle method, which has many shortcomings. In particular, the solutions obtained with this method involve numerical noises owing to a finite number of the particles, since the electron mass is increased in order to reduce the computational complexity of the algorithm. In this study, the effect of an increase in the electron mass on the qualitative and quantitative characteristics of the instability development process are considered. For this purpose, a software package developed on the basis of a mathematical model consisting of the Poisson equation for the electric potential, the fluid equation for electrons, and the kinetic equation for ions is used. The equations are solved numerically, which makes it possible to avoid the problems inherent in the particle method. An important result obtained in this paper is that even a slight increase in the electron mass leads to a considerable variation of the instability development parameters. This variation manifests itself as an increase in the wavelength of plasma fluctuations and a decrease in the strength of the turbulent electric field.     

Conjugate and cut loci of a two-sphere of revolution with application to optimal control

The objective of this article is to present a sharp result to determine when the cut locus for a class of metrics on a two-sphere of revolution is reduced to a single branch. This work is motivated by optimal control problems in space and quantum dynamics and gives global optimal results in orbital transfer and for Lindblad equations in quantum control.     

Living with influenza: Impacts of government imposed and voluntarily selected interventions

Focusing on mitigation strategies for global pandemic influenza, we use elementary mathematical models to evaluate the implementation and timing of non-pharmaceutical intervention strategies such as travel restrictions, social distancing and improved hygiene. A spreadsheet model of infection spread between several linked heterogeneous communities is based on analytical calculations and Monte Carlo simulations. Since human behavior will likely change during the course of a pandemic, thereby altering the dynamics of the disease, we incorporate a feedback parameter into our model to reflect altered behavior. Our results indicate that while a flu pandemic could be devastating; there are coping methods that when implemented quickly and correctly can significantly mitigate the severity of a global outbreak.     

Parametric splines on a hyperbolic paraboloid

A hyperbolic paraboloid over a tetrahedron, constructed in B–B algebraic reduced form with its barycentric coordinate system, can be conveniently represented by two parameters. An arc on the surface, obtained by determining a type of function relation about the two parameters, has multiformity and consistent endpoint properties. We analyze the equivalence and boundedness of an arc’s curvature, and give a process of the proof. These arcs can be connected into an approximate G²$G^2$-continuity space curve for fitting to a sequence of points with their advantages, and the curves, connected by this type arcs, are quite different from other algebraic and parametric splines.