Mutual influence of LDPE and PP in their blends during crystallization

An indication for the mutual influence of LDPE and PP was the change of the morphology parameters of PE and PP at different ratios of the polymers in blends. That influence depends on the blend composition and is different for PE and PP. It is especially interesting in the blend PE75/PP25 where the influence between PE and PP shows dependence also on the sample geometry. Melting parameters, non-isothermal crystallization parameters - crystallization peak temperature T_c, crystallization begin temperature T_onset, half-width w_1/2 of the crystallization peak, degree of crystallinity α and crystallization rate coefficient CRC, as well as the isothermal kinetics parameters showed dependence on the blend composition. It was established that PE is more stable then PP concerning the mutual influence of both polymers on their crystallization. It was established that PE affects the crystal nucleation of PP and causes a decreasing of PP spherulite size.     

Use of Reversed-Phase High-Performance Liquid Chromatography in QSAR Analysis of 2,4-Dihydroxythiobenzanilide Analogues

Abstract

Thiobenzanilides are found to show strong biological activity as antimicrobial, antimycotic, and tuberculostatic agents. In addition, they are relatively weakly toxic to higher organisms.

A large set of new (N-phenyl-)-2,4-dihydroxybenzenecarbothioamide derivatives was obtained. Preliminary studies showed high microbiological action of some of them. In the process of chromatographic analysis, several different chromatographic parameters were obtained. In case of RP-HPLC, these parameters correspond to hydrophobicity of the solute. Obtained chromatographic parameters exhibited moderate correlation with calculated log P parameter.

Linear dependence of bacteriostatic or fungostatic activity on lipophilicity was observed. The degree of correlation of different parameters was compared. The lipophilicity of analysed tioamides was the most important factor responsible for fungostatic and bacteriostatic activity. In comparison to methanol eluent system, chromatographic parameters obtained in acetonitrile system were better correlated with bioactivity. Conversely with the calculated log P values, the experimentally derived parameters exhibited significant higher correlation to fungostatic activity determined on dermatophytes. While in case of other tested microorganisms log P was comparably or sometimes slightly better correlated.     

Covalent Bonding and Hyperfine Interactions in Mo(V) Oxo Halide Complexes

Optical and EPR data were used to analyze delocalized bond structures in the antibonding and bonding states of complexes MoOL₅ (L = Cl and Br). Covalent bond parameters were calculated with consideration of charge-transfer states (CTS). The effects of CTS on the components of the g, A, and A ^L tensors were estimated; the third-order corrections for the EPR parameters were calculated. The role of CTSs for interpretation of the parameters of the additional hyperfine interaction was noted.     

Assessment of corrosion resistance of surface-coated galvanized steel by analysis of the AC impedance spectra measured on the salt-spray-tested specimen

In the present work, corrosion resistance of surface-coated galvanized steel was quantitatively determined by an analysis of the alternating current (AC) impedance spectra measured on the salt-spray-tested specimen. To evaluate the corrosion resistance of the surface-coated galvanized steel, AC impedance spectroscopy was performed on the salt-spray-tested specimen previously exposed to salt-sprayed corrosive environment. From the analysis of the impedance spectra, the area fraction transient of white rust θ ₂(t) was theoretically derived from the equivalent circuit equation by using two fitting parameters. The values of the two fitting parameters were determined by fitting the empirical transient equations to the area fraction of the resin coating layer and to the total resistance obtained from the impedance spectra measured, respectively. From the analyses of θ ₂(t) for four kinds of surface-coated galvanized steels with various resin coating layers, it is indicated that as the values of the two fitting parameters decrease in the order of CP, GI, OD and OM (commercial trade names) specimens, the corrosion resistance increases in that order as well. Furthermore, from the quantitative comparison of the two fitting parameters with the polarization resistance of the upper resin coating layer R _p determined from the potentiodynamic polarization curve, it is suggested that the two fitting parameters decrease in value as well with increasing R _p.     

Synthesis,characterization, and investigation of the thermal behavior of Cu(II) pyrazolyl complexes

In the present contribution, a procedure to estimate parameters using non-isothermal data was applied. The estimation procedure is based on the use of an energy balance in DSC furnace. The approach found all kinetic parameters of autocatalytic model (E ₁, E ₂, A ₁, A ₂, m, n) besides the ultimate reaction heat and their confidence regions by using deterministic and heuristic algorithms. The application of this approach to isothermal data was done in a previous work and similar results were obtained. The results show that the use of an energy balance is a good methodology to estimate cure kinetic parameters of non-isothermal experiments.     

Nonisothermal <Emphasis Type="Italic">n</Emphasis>th-order DAEM equation and its parametric study – use in the kinetic analysis of biomass pyrolysis

Nonisothermal nth-order distributed activation energy model (DAEM) was derived. Numerical solutions of the nonisothermal nth-order DAEM equation were performed. The influences of various parameters relevant to biomass pyrolysis on numerical results of the nonisothermal nth-order DAEM equation were also studied. Investigated parameters are heating rate, the mean of activation energy distribution, standard deviation of activation energy distribution, frequency factor and reaction order. The study results can be further responsible for determination of nth-order DAEM kinetic parameters from thermogravimetric analysis data of biomass.     

On the errors of Arrhenius parameters and estimated rate constant values

A detailed statistical study is presented, based on simulated experimental data, on the estimation of activation parameters using the Arrhenius equation: k = A exp(B/T). The close correlation of the two parameters is shown, which requires the computation of the covariance matrix for the representation of uncertainties. This matrix facilitates the correct estimation of the confidence interval for interpolated (or extrapolated) values of rate coefficients. It is proposed that the full correlation matrix should be published in any article dealing with the determination of Arrhenius parameters. The importance of correct weighting is emphasized. Nonlinear fitting to the Arrhenius equation can be carried out without weighting only in case the (absolute) error of rate coefficient is independent of the temperature. Simulated experiments show that noncorrect weighting shifts the average values of fitted parameters and increases the variance of the parameters as well. With respect to the modified Arrhenius equation: k = A · Tⁿ exp(B/T), statistical analysis shows that the physically meaningful estimation of all three parameters is impossible. Nonlinear fitting of three parameters is suggested for interpolation (and extrapolation) of rate coefficients, whereas in case of activation parameter estimation, the fixing of “n” on the basis of theoretical considerations is advised followed by the estimation of the remaining two parameters.     

Crystal chemistry of orthorhombic lanthanide oxobromotungstates of composition LnWO4Br

The crystal-chemical properties of lanthanide oxobromotungstates of composition LnWO₄Br(Ln = La, Pr, Nd, Sm) were studied: the crystal system and space group were determined, and the unit cell parameters were refined. The dependence of the unit cell parameters a, b, c, and V of the LnWO₄Br compounds on the lanthanide atomic number was analyzed. The analytical equations derived make it possible to predict the unit cell parameters for lanthanide oxobromotungstates that have not been synthesized yet.     

层柱粘土吸附甲烷的模拟和参数优化研究

用巨正则系综Monte Carlo方法(GCMC)来模拟ZrO₂柱撑粘土对天然气主要成分甲烷的吸附. 为了更好地反映甲烷与层柱粘土无机层板的相互作用, 对墙势模型中的尺寸参数σ_fw和能量参数ε_fw取值进行了优化. 我们系统地改变甲烷在蒙脱土晶体结构中的位置, 建立起一系列甲烷与层板相互作用的Lennard-Jones势能曲线, 通过最小二乘法拟合这些Lennard-Jones势能曲线得到一系列的σ_fw和ε_fw值, 利用拟合得到的σ_fw和ε_fw算术平均值作为墙势模型中两个交互作用参数的取值进行分子模拟, 模拟结果与文献实验值符合较好. 在此基础上, 进一步模拟了3种不同孔率, 层间距为0.64 nm的ZrO₂柱撑粘土(ZPC)在245 K下对临界态甲烷的吸附, 发现 3～4 MPa是ZPC材料吸附甲烷较适合的压力范围, 而且孔率大的ZPC有利于甲烷的吸附.     

Estimates of magnetic resonance parameters in semi-empirical quantum chemistry

The possibility to reliably estimate the magnetic resonance parameters (MRP) can significantly increase the information content of experimentally recorded spectra. Here we consider in detail semi-empirical estimates of the ESR spectra parameters: isotropic hyperfine coupling constants, anisotropic hyperfine coupling tensors and g-tensors. The results show that the semi-empirical procedures give estimates of MRP comparable in quality with those of complicated ab initio and DFT schemes. It was underlined that a special attention should be given to geometric parameters of free radicals. The automatic procedure to determine molecular geometries of free radicals on the ground of their spectral characteristics was discussed.     

Properties of zirconate modificates of silica gel as examined by inverse gas chromatography

In our work the silica gel was modified at three temperatures by the zirconium coupling agents. As a result one obtains monomolecular layer of the zirconate on the silica gel surface. The physico‐chemical properties of this layer and its influence on the modificate properties may be characterized by inverse gas chromatography (IGC) and expressed by both solubility parameters and surface parameters. The influence of the temperature of the modification and the modifier structure on the modificate's properties was examined and discussed. In this paper we looked for the relationships between the solubility parameter δ₂, its components and surface parameters γ₂^d, K_A, K_D and S_C.     

Quantification and Prediction of Imine Formation Kinetics in Aqueous Solution by Microfluidic NMR Spectroscopy

Quantitatively predicting the reactivity of dynamic covalent reaction is essential to understand and rationally design complex structures and reaction networks. Herein, the reactivity of aldehydes and amines in various rapid imine formation in aqueous solution by microfluidic NMR spectroscopy was quantified. Investigation of reaction kinetics allowed to quantify the forward rate constants k₊ by an empirical equation, of which three independent parameters were introduced as reactivity parameters of aldehydes (S_E, E) and amines (N). Furthermore, these reactivity parameters were successfully used to predict the unknown forward rate constants of imine formation. Finally, two competitive reaction networks were rationally designed based on the proposed reactivity parameters. Our work has demonstrated the capability of microfluidic NMR spectroscopy in quantifying the kinetics of label-free chemical reactions, especially rapid reactions that are complete in minutes.     

Chromatographic descriptors in QSAR study of barbiturates

Barbiturate derivatives were evaluated for their parameters of biological activity by applying linear regression and two multivariate methods (Cluster analysis and Principal component analysis). The lipophilicity of the studied barbiturates was determined on the modified carriers C18 in mixtures of water and four organic modifiers separately (methanol, n-propanol, acetone and tetrahydrofuran) by performing reversed phase thin layer chromatography and by applying relevant software packages. Chromatographic and computational lipophilicity of the examined barbiturates was correlated with the selected pharmacokinetic and toxicological predictors and good relationships were obtained. More concrete results were obtained by multivariate methods which showed that the polarity of the substituent has the greatest influence, and its electronic effects to a lesser extent on the tested parameters of the barbiturate derivatives. Results obtained by multivariate methods also suggest that the chromatographic retention constant, R_M⁰, shows a greater resemblance to the parameters of lipophilicity. The chromatographic parameter m, exhibits better agreement with the toxicity parameters.     

Assessment of Physical Process Conditions for Enhanced Production of Novel Glutaminase-Free L-Asparaginase from <Emphasis Type="BoldItalic">Pectobacterium carotovorum</Emphasis> MTCC 1428

Statistically based experimental design was applied to maximize the production of glutaminase-free L-asparaginase from Pectobacterium carotovorum MTCC 1428. The effect of physical process parameters (initial pH of the medium, temperature, rpm of the shaking incubator, and inoculum size) on the production of L-asparaginase from P. carotovorum MTCC 1428 was studied using central composite design technique. The individual optimum levels of initial pH of the medium, temperature, rpm of shaking incubator, and inoculum size were found to be 6.90, 29.8 °C, 157 rpm, and 2.61% (v/v), respectively, for the production of L-asparaginase. After physical process parameters optimization, the production and productivity of L-asparaginase was enhanced by 26.39% (specific activity) and 10.19%, respectively. Maximization of L-asparaginase production was achieved at 12 h under optimal levels of physical process parameters in shake flask level.     

A Simple Frontal Analysis Equation to Determine the Adsorption Parameters of Solute Molecules on Different Adsorbents

A simple frontal analysis equation to determine the adsorption parameters of solute molecules on different adsorbents was presented. It gives the relationship between the average breakthrough time and the feed solute concentration, and by using its linear form, two important parameters, the thermodynamic equilibrium constant KSL for solute adsorption on the surface of adsorbent and the number nt of total adsorption sites distributed on the surface of adsorbent, can be simultaneously determined. The frontal analyses for some aromatic hydrocarbons on RP-C18 reversed-phase medium, and some protein molecules on RP-C18 reversed-phase, WCX-1 cation-exchange, PEG-400 hydrophobic and Chelating Sepharose Fast-flow separately chelated with Zn^2＋ or Cu^2＋ media, were separately carried out to test this equation and their adsorption parameters KSL and nt were separately obtained. The results show that all these frontal analysis data can be well described by this frontal analysis equation. For all of these frontal analysis systems, their parameters nt can separately approximately keep constant and they are independent of solute molecules used, while their parameters KSL are dependent upon both of the media packed in frontal analysis column and the solute molecules used.     

Solvatochromic Parameters and Preferential Solvation Behavior for Binary Mixtures of 1,3-Dialkylimidazolium Ionic Liquids with Water

Binary mixtures of 1,3-dialkylimidazolium based ionic liquids (ILs) and water were selected as solvent systems to investigate the solute-solvent and solvent-solvent interactions on the preferential solvation of solvatochromic indicators at 25℃. Empirical solvatochromic parameters, dipolarity/polarizability (π^*), hydrogen-bond donor acidity (α), hydrogen-bond acceptor basicity (β), and Reichardt's polarity parameters (E_T^N) were measured from the ultraviolet-visible spectral shifts of 4-nitroaniline, 4-nitroanisole, and Reichardt's dye. The solvent properties of the IL-water mixtures were found to be influenced by IL type and IL mole fraction (x_IL). All these studied systems showed the non-ideal behavior. The maximum deviation to ideality for the solvatochromic parameters can be obtained in the xIL range from 0.1 to 0.3. For most of the binary mixtures, the π^* values showed the synergistic effects instead of the E_T^N, α and β values. The observed synergy extent was dependent on the studied systems, such as the dye indicator and IL type. A preferential solvation model was utilized to gather information on the molecular interactions in the mixtures. The dye indicator was preferentially solvated on the following trend: IL >IL-water complex >water.     

Dynamic parameters for some poly (n-alkyl methacrylates)

The dielectric relaxation data of poly (n-hexyl methacrylate) and poly (n-octyl methacrylate) by Strella and Chinai are represented in terms of the relaxation function proposed by Havriliak and Negami using the multiresponse techniques developed by Havriliak and Watts to evaluate the parameters and their dependence on temperature. The parameter α which represents the width of the distribution of relaxation times was found to be dependent on temperature whereas the parameter β representing the skewness of the distribution function was found to be independent of temperature. The relaxation process parameters are discussed in terms of Mansfield's jump model.     

Thermal degradation kinetics of g-HA/PLA composite

Thermal degradation behaviors of a composite constituted by poly(l-lactide) (PLA) and hydroxyapatite nanoparticle that was surface-grafted with l-lactic acid oligomer (g-HA) in a nitrogen atmosphere were studied using thermogravimetric analysis (TGA) and compared with PLA. The kinetic models and parameters of the thermal degradation of PLA and the g-HA/PLA composite were evaluated by the invariant kinetic parameters (IKP) method and Flynn–Wall–Ozawa (FWO) method based on a set of TGA data obtained at different heating rates. It was shown that the conversion functions calculated by means of the IKP method depend on a set of kinetic models. The g-HA particle slowed down the thermal degradation of PLA polymer matrix.     

Optimization of Microwave-Assisted Extraction (MAE) for the Isolation of Antioxidants from Basil (Ocimum basilicum L.) by Response Surface Methodology (RSM)

Abstract

The recovery of antioxidants from basil (Ocimum basilicum L.) was modeled with the aid of response surface methodology (RSM) using microwave-assisted extraction (MAE). Face-centered central design (FCCD) was employed to optimize the MAE operational parameters including the extraction time (1 to 7?min), extraction temperature (30 to 120?°C), solid-to-solvent ratio (0.1 to 0.4), and solvent concentration (20 to 80% ethanol, v/v), and to obtain the best possible combinations of these parameters for a high antioxidant yield from basil. The total antioxidant capacity (TAC) was expressed in trolox (TR) equivalents per gram of dried sample (DS). Three of the operational parameters (temperature, extraction time and solvent concentration) were shown to have significant effect on the extraction efficiency of antioxidants in basil extracts (p?<?0.05). The solvent concentration was shown to be the most significant factor on antioxidant yield obtained by MAE. There was a close relationship between experimental and predicted values using the proposed method. This optimized MAE method shows an application potential for the efficient extraction of antioxidants from basil in the food and pharmaceutical industries.     

Intermolecular interactions and phase equilibria in nitrocellulose - s-diethyldiphenylurea system

Values of the Flory-Huggins interaction parameters c were predicted on the base of mixing enthalpy H ^M for nitrocellulose-s-diethyldiphenylurea system. The phase diagram of the system and the glass transition temperature of mixtures T _g12 were estimated using calculated c parameters. The predicted glass transition temperatures were in accordance with values determined experimentally. This revised version was published online in July 2006 with corrections to the Cover Date.