Grafting of acrylonitrile onto styrene-maleic acid copolymer by tetravalent cerium ion

The graft copolymerization of acrylonitrile (AN) onto a styrene-maleic acid copolymer (SY-MAc) with ceric ammonium nitrate (CAN) as a redox initiator in an aqueous medium has been studied. The effects of various reaction parameters, including reaction time and temperature, concentrations of initiator, nitric acid, and monomer, on the grafting yields and the rates of polymerization (R_p), graft copolymerization (R_g), and homopolymerization (R_h) were studied systematically. The results are discussed. The kinetic scheme of free-radical graft copolymerization has been proposed and the equations relating the values of R_p, R_g, and R_h are also suggested. The experimental results are found to be in good agreement with the proposed kinetic scheme. The activation energies of graft copolymerization and total polymerization are calculated. © 1995 John Wiley & Sons, Inc.     

Intersubunit disulfide-bonded {lambda}-Cro protein

Site-directed mutagenesis has been employed to substitute cysteinefor valine at position 55, which is located on the dimer interfaceof the Cro protein of bacteriophage . It has been found thatthe Cys55 Cro protein (Cro VC55) spontaneously forms a stabledisulfide-bonded dimer in the absence of a reducing agent. UV—CDand NMR data showed that the mutant protein retains the conformationof the wild Cro protein and has acquired significant heat-stability.However, its specific DNA-binding activity is reduced severaltimes compared with that of the wild Cro. Photochemically induceddynamic nuclear polarization (CIDNP) spectra demonstrated thata conformational change of Cro VC55 did not take place uponthe formation of a complex with O_R3, in contrast to the caseof the wild Cro. These data suggest that the induced fitting,like loosening, of the two subunits of the wild Cro dimer contributesto the enhancement of its affinity to its operator DNA, whichresults in a specific interaction between Cro and O_R3.     

Particle size effect on the film‐forming process of PS/PBA composite latexes

In this work, the effect of hard particle size and blend ratio on the film formation behavior of hard polystyrene (PS) and soft poly(n‐butyl acrylate) (PBA) latex blends was studied by means of steady‐state fluorescence and UV–visible techniques in conjunction with atomic force microscopy. Three different sets of latexes were synthesized: PBA latex (diameter 97 nm), pyrene (P)‐labeled large PS (LgPS; diameter 900 nm), and small PS (SmPS; diameter 320 nm). Two different series of latex blends (LgPS/PBA and SmPS/PBA) were prepared with varying blend composition at room temperature separately. Films were then annealed at elevated temperatures above glass transition (T_g) temperature of PS. Fluorescence intensity (I_P) from P and photon transmission intensity (I_tr) were measured after each annealing step to monitor the stages of film formation. The results showed that a significant change occurred in I_P and I_tr at a certain critical weight fraction (R_c) of PBA. Below R_c, two distinct film formation stages, which are named as void closure and interdiffusion, were seen. However, at PBA concentrations nearer to or above R_c, no film formation can be achieved. Comparing to the LgPS/PBA, the sintering process of SmPS/PBA particles occurred at much lower temperatures. Film formation stages for R < R_c were modeled, and related activation energies were calculated. Void closure (ΔH) and interdiffusion (ΔE) activation energies for SmPS/PBA were also found smaller in comparing with LgPS/PBA series. However, ΔH and ΔE values were not changed much with the blend composition for both series. POLYM. COMPOS., 31:1637–1652, 2010. © 2009 Society of Plastics Engineers     

Development of a Green Process for the Preparation of Antioxidant and Pigment-Enriched Extracts from Winery Solid Wastes Using Response Surface Methodology and Kinetics

Red grape pomace (RGP), an abundant wine industry solid waste, was used for the recovery of polyphenols and anthocyanin pigments, using ultrasound-assisted extraction and water/glycerol mixtures as the solvent. Glycerol concentration (C_gl) and liquid-to-solid ratio (R_L/S) were first optimized by implementing Box?Behnken experimental design and the process was further studied through kinetics. The optimal conditions were found to be C_gl = 90% (w/v) and R_L/S = 90 mL g^?1, and under these conditions the extraction of total polyphenols (TP) and total pigments (TPm) obeyed first-order kinetics. Maximum diffusivity (D_e) values were 4.22 × 10^?12 and 12.59 × 10^?12 m² s^?1, for TP and TPm, respectively, and the corresponding activation energies were (E_a) 13.94 and 8.22 kJ mol^?1.     

Computationally Supported Inversion of Ketoreductase Stereoselectivity

Whereas directed evolution and rational design by structural inspection are established tools for enzyme redesign, computational methods are less mature but have the potential to predict small sets of mutants with desired properties without laboratory screening of large libraries. We have explored the use of computational enzyme redesign to change the enantioselectivity of a highly thermostable alcohol dehydrogenase from Thermus thermophilus in the asymmetric reduction of ketones. The enzyme reduces acetophenone to (S)-1-phenylethanol. To invert the enantioselectivity, we used an adapted CASCO workflow which included Rosetta for enzyme design and molecular dynamics simulations for ranking. To correct for unrealistic binding modes, we used Boltzmann weighing of binding energies computed by a linear interaction energy approach. This computationally cheap method predicted four variants with inverted enantioselectivity, each with 6–8 mutations around the substrate-binding site, causing only modest reduction (2- to 7-fold) of k_cat/K_M values. Laboratory testing showed that three variants indeed had inverted enantioselectivity, producing (R)-alcohols with up to 99 % enantiomeric excess. The broad substrate range allowed reduction of acetophenone derivatives with full conversion to highly enantioenriched alcohols. The results demonstrate the use of computational methods to control ketoreductase stereoselectivity in asymmetric transformations with minimal experimental screening.     

Quantitative interpretation of parabolic oxidation behaviour of nitride powders

Abstract

The oxidation behaviour of nitride powder under the condition of diffusion controlled has been investigated from both experimental and theoretical aspects. The effects of factors, such as oxidation time t, temperature T, oxygen partial pressure Po₂, temperature increasing rate η and particle size R ₀, on the reacted fraction of oxidation have been studied, in which many factors have never been studied quantitatively before. The applications of the authors' model to both experimental data of AlN, BN and β-SiAlON powder provided by the authors' lab as well as the data of SiAlON and MgAlON powders offered by literature show that this model works well. Finally, after the calculation error comparison, it is clear to show that the authors' new model would lead to a more accurate calculation result against the model used in literatures currently.     

Unusual Elastic and Mechanical Behaviors of Copper Phosphate Glasses with Different Copper Valence States

Elastic and mechanical properties such as Young's modulus E, Poisson's ratio ν, Debye temperature θ_D, Vickers hardness H_v, fracture toughness K_c, and fracture surface energies γ_f of yCuO_x·(100−y)P₂O₅ glasses (y= 45, 50, 55) with different copper valence states, i.e., R(Cu⁺) = Cu⁺/(Cu⁺+ Cu²⁺), at room temperature (humidity 64%) have been examined. The following features have been found: (1) the glass transition temperature (218–434°C), H_v (2.7–4.4 GPa), E (50.6–78.2 GPa), and θ_D (358–434 K) decrease largely with increasing R(Cu⁺); (2) the mean atomic volume, K_c (0.56–1.14 MPa·m^1/2), and γ_f (1.9–11.2 J·m⁻²) tend to increase with increasing R(Cu⁺); (3) 50CuO_x·50P₂O₅ glasses with R(Cu⁺) = 0.42 and 0.55 have a high resistance against crack formation in Vickers indentation tests and no crack is observed in the 45CuO_x·55P₂O₅ glass with R(Cu⁺) = 0.57 under an applied load of about 98 N. The results demonstrate that elastic and mechanical properties of yCuO_x·(100−y)P₂O₅ glasses depend strongly on the copper valence state and the CuO_x/P₂O₅ ratio. The unusal mechanical and elastic properties of copper phosphate glasses are well explained qualitatively by considering unique oxygen coordination and bonding states of Cu⁺ ions, i.e., lower coordination number and more covalent bonding compared with Cu²⁺ ions.     

Investigation of Substrate Binding and Product Stereochemistry Issues in Two Linoleate 9-Lipoxygenases

Herein we characterize the Arabidopsis thaliana AtLOX1 and tomato (Solanum lycopersicum) LOXA proteins as linoleate 9S-lipoxygenases (9-LOX), and use the enzymes to test a model that predicts a relationship between substrate binding orientation and product stereochemistry. The cDNAs were heterologously expressed in E. coli and the proteins partially purified by nickel affinity chromatography using a N-terminal (His)₆-tag. Both enzymes oxygenated linoleic acid almost exclusively to the 9S-hydroperoxide with turnover numbers of 300–400/s. AtLOX1 showed a broad range of activity over the range pH 5–9 (optimal at pH 6); tomato LOXA also showed optimal activity around pH 5–7 dropping off more sharply at pH 9. Site-directed mutagenesis of a conserved active site Ala (Ala562 in AtLOX1, Ala 564 in tomato LOXA, and typically conserved as Ala in S-LOX and Gly in R-LOX), revealed that substitution with Gly led to the production of a mixture of 9S- and 13R-hydroperoxyoctadecadienoic acids from linoleic acid. To follow up on earlier reports of 9-LOX metabolism of anandamide (van Zadelhoff et al. Biochem. Biophys. Res. Commun. 248:33–38, 1998), we also tested this substrate with the mutants, which produced predictable shifts in product profile, including a shift from the prominent 11S-hydroperoxy derivative of wild-type to include the 15R-hydroperoxide. These results conform to a model that predicts a head-first substrate binding orientation for 9S-LOX. We also found that linoleoyl-phosphatidylcholine is not a 9S-LOX substrate, which is consistent with this conclusion.     

Film formation from polystyrene–poly(butyl acrylate‐co‐methyl methacrylate) latex blends

We have employed steady sate fluorescence (SSF) and UV‐visible (UVV) techniques to determine the film formation behavior of latex blends. Blend films were prepared from mixtures of a high‐T_g pyrene (P) labeled polystyrene (PS) latex and a low‐T_g copolymer of poly(butyl acrylate‐co‐methyl methacrylate) (BuA/MMA4). Eleven different blend films were prepared in various hard/soft latex compositions at room temperature and annealed at elevated temperatures above glass‐transition (T_g) temperature of polystyerene for 10 min. Fluorescence intensity (I_P) from P was measured after each annealing step to monitor the stages of film formation. The evolution of transparency of latex films was monitored using photon transmission intensity, I_tr. Film morphologies were examined by atomic force microscopy (AFM). A significant change occurs in both I_P and I_tr intensities at a certain critical weight fraction of hard latex (R_c = 0.3). Above R_c, two distinct film formation stages, which are named as void closure and interdiffusion processes, were seen in fluorescence data. Transparency of the films was decreased with decreasing PS content, indicating that a phase separation process occurs between PS and BuA/MMA4 phases by thermal treatment, which results in turbid films. However, below R_c, no change was observed in I_P and I_tr upon annealing, whereas transparency increased overall with increasing BuA/MMA4 ratio. We explained this result as the phase separation process between PS and BuA/MMA4 blends. These results were also confirmed by AFM pictures. Film formation stages above R_c were modeled and related activation energies were calculated. POLYM. COMPOS., 27:431–442, 2006. © 2006 Society of Plastics Engineers     

Modified van der waals equation for the dense gaseous and liquid regions from PVT data for methane

PVT measurements available in the literature for methane in the gaseous and liquid regions were used with the van der Waals equation of state, to obtain values of the internal pressure parameter, a, where the covolume parameter was taken as b = v_c/3. The conditions covered temperatures from 114.53°K (T_R = 0.599) to 611°K (T_R = 3.20) and pressures up to 3000 atm (P_R = 65.50). A dimensionless relationship was developed for the dependence of the parameter a on density and temperature for the gaseous and liquid regions. Density values for methane were calculated from the resulting equation and were compared with the corresponding experimental values to produce an average deviation of 0.26% (791 points). This relationship also enabled the accurate prediction of density values for substances having similar critical compressibility factors as methane (z_c = 0.289). For neon and ammonia, this relationship was found to have a limited applicability.     

Acrylonitrile polymerization initiated by Ce(IV)–cyclohexanone redox system in presence of surfactant

The rate of polymerization of acrylonitrile, using the Ce(IV)–cyclohexanone redox system as an initiator, was studied kinetically, in the presence of 0.015M sodium dodecyl sulfate (SDS), over a temperature range of 25–45°C. The rate of polymerization (R_P), percentage of monomer conversion, and rate of Ce(IV) consumption (?R_Ce) were found to increase with the concentration of SDS, above its CMC. The effect of [AN], [Ce(IV)], [H⁺], and the ionic strength were also studied. The overall activation energies for the polymerization processes were computed to be 23.14 and 17.64 kcal/mol in the absence and presence of 0.015M SDS. A suitable kinetic mechanistic scheme for the free‐radical mechanism was proposed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2066–2072, 2003     

Experimental and theoretical study of the ferroelectric and piezoelectric behavior of strontium-doped PZT

Theoretical data using ab initio perturbed ion calculation were compared with ferroelectric and piezoelectric experimental data of strontium doped PZT. Various concentrations of SrO in PZT at constant temperature and sintering time were carried out. Experimental results, such as the remanent polarization, P_R of 6.9–8.9 μC/Cm², the coercive field, E_C of 6.6–7.8 kVcm, and the planar coupling factor, Kp of 0.45–0.53, were compared with the energy of Zr⁴⁺ and Ti⁴⁺ ion dislocation and the lattice interaction energy which show that strontium increment in PZT alter the energies and increase the values of piezoelectric and ferroelectric variables. Calculations of lattice energy of the rhombohedral phase show that a phase non-stability is coincident with increasing experimental values of the P_R, E_C and Kp.     

Synthesis and Pharmacological Evaluation of Enantiomerically Pure GluN2B Selective NMDA Receptor Antagonists

To determine the eutomers of potent GluN2B‐selective N‐methyl‐d ‐aspartate (NMDA) receptor antagonists with a 3‐benzazepine scaffold, 7‐benzyloxy‐3‐(4‐phenylbutyl)‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepin‐1‐ols (S)‐ 2 and (R)‐ 2 were separated by chiral HPLC. Hydrogenolysis and subsequent methylation of the enantiomerically pure benzyl ethers of (S)‐ 2 and (R)‐ 2 provided the enantiomeric phenols (S)‐ 3 and (R)‐ 3 [3‐(4‐phenylbutyl)‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepine‐1,7‐diol] and methyl ethers (S)‐ 4 and (R)‐ 4 . All enantiomers were obtained with high enantiomeric purity (≥99.7 % ee). The absolute configurations were determined by CD spectroscopy. R‐configured enantiomers turned out to be the eutomers in receptor binding studies and two‐electrode voltage clamp experiments. The most promising ligand of this compound series is the R‐configured phenol (R)‐ 3 , displaying high GluN2B affinity (K_i=30 nm ), high inhibition of ion flux (IC₅₀=61 nm ), and high cytoprotective activity (IC₅₀=93 nm ). Whereas the eudismic ratio in the receptor binding assay is 25, the eudismic ratio in the electrophysiological experiment is 3.     

Phase diagram prediction of recycling aqueous two-phase systems formed by a light-sensitive copolymer and dextran

Our Laboratory has synthesized a novel light-sensitive and recycling copolymer P _NBC . The P _NBC copolymer could form recycling aqueous two-phase systems with Dextran. Recycling aqueous two-phase systems have important application in bioseparation engineering. Phase diagram prediction of the novel aqueous two-phase systems also is an important aspect in engineering. This article applied the Cabezas model and effective excluded volume (EEV) model to the experimental data of light-sensitive recycling aqueous two-phase systems. It has been found that the EEV model could consist with experimental data very well. The maximum absolute error and average absolute error is 0.81% (wt%) and 0.23% (wt%), respectively.     

Low-temperature 1,3-butadiene hydrogenation over supported Pt/3d/γ-Al2O3 bimetallic catalysts

Low-temperature 1,3-butadiene hydrogenation is used as a probe reaction to investigate the hydrogenation activity over several γ-Al₂O₃ supported Pt/3d (3d = Co, Ni, Cu) bimetallic catalysts. Batch and flow reactor studies are employed to quantify the kinetic activity and steady-state conversion, respectively, of each catalyst. Transmission electron microscopy (TEM) is utilized to characterize particle sizes and extended X-ray absorption fine structure (EXAFS) measurements are performed to verify the Pt–3d bimetallic bond formation. Pulse carbon monoxide chemisorption measurements are also performed to characterize the number of active sites. Additionally, density functional theory (DFT) calculations are included to determine the binding energies of 1,3-butadiene and atomic hydrogen on the corresponding model surfaces. The binding energies of the adsorbates are found to correlate with the hydrogenation activity, allowing for use of such correlation to potentially predict hydrogenation catalysts with enhanced activity based on the binding energies of the adsorbates of interest.     

A Modified Arrhenius Approach to Thermodynamically Study Regioselectivity in Cytochrome P450-Catalyzed Substrate Conversion

The regio- (and stereo-)selectivity and specific activity of cytochrome P450s are determined by the accessibility of potential sites of metabolism (SOMs) of the bound substrate relative to the heme, and the activation barrier of the regioselective oxidation reaction(s). The accessibility of potential SOMs depends on the relative binding free energy (ΔΔG_bind) of the catalytically active substrate-binding poses, and the probability of the substrate to adopt a transition-state geometry. An established experimental method to measure activation energies of enzymatic reactions is the analysis of reaction rate constants at different temperatures and the construction of Arrhenius plots. This is a challenge for multistep P450-catalyzed processes that involve redox partners. We introduce a modified Arrhenius approach to overcome the limitations in studying P450 selectivity, which can be applied in multiproduct enzyme catalysis. Our approach gives combined information on relative activation energies, ΔΔG_bind values, and collision entropies, yielding direct insight into the basis of selectivity in substrate conversion.     

Effect of Regiochemistry and Methylation on the Anticancer Activity of a Ferrocene-Containing Organometallic Nucleoside Analogue

Four new bis-substituted ferrocene derivatives containing either a hydroxyalkyl or methoxyalkyl group and either a thyminyl or methylthyminyl group have been synthesised and characterised by a range of spectroscopic and analytical techniques. They were included in a structure-activity-relationship (SAR) study probing anticancer activities in osteosarcoma (bone cancer) cell lines and were compared with a known lead compound, 1 -(S,R_p), a nucleoside analogue that is highly toxic to cancer cells. Biological studies using the MTT assay revealed that a regioisomer of ferronucleoside 1 -(S,R_p), which only differs from the lead compound in being substituted on two cyclopentadienyl rings rather than one, was over 20 times less cytotoxic. On the other hand, methylated derivatives of 1 -(S,R_p) showed comparable cytotoxicities to the lead compound. Overall these studies indicate that a mechanism of action for 1 -(S,R_p) cannot proceed through alcohol phosphorylation and that its geometry and size, rather than any particular functional group, are crucial factors in explaining its high anticancer activity.     

Calculation of the Structural Linear Expansion Coefficient from the Chemical Composition of Glasses in the R2O(RO)–Al2O3–B2O3 (R = Li, Na, Ca, and Ba) System

The regularities of the influence of the glass composition on the structural linear expansion coefficient in the glass transition range are analyzed using the published data obtained in systematic experimental investigations of glasses in the R ₂O(RO)–Al₂O₃–B₂O₃ (R = Li, Na, Ca, and Ba) system. A method is proposed for calculating the structural linear expansion coefficients of these glasses from the chemical composition with a mean relative error of 10%. The possibilities of extending the composition range covered by the calculation are considered.     

Quantitative relationships between intermolecular interaction and damping parameters of irganox‐1035/NBR hybrids: A combination of experiments,molecular dynamics simulations,and linear regression analyses

The damping mechanism of phenol(3,5‐bis(1,1‐dimethylethyl)‐4‐hydroxybenzenepropanoic acid thiodi‐2,1‐ethanediyl ester, abbreviated as Irganox‐1035)/nitrile‐butadiene rubber hybrids was studied by combining experiments, computer simulations, and linear regression analyses. Four important damping parameters [loss peak (tan δ_max), effective loss area (TA), glass transition temperature (T_g), and effective temperature region (ΔT)], were obtained by dynamic mechanical thermal analyses. Three intermolecular interaction parameters [the number of intermolecular hydrogen bonds (N_HBs), binding energy (E_binding), and fractional free volume (FFV)], were calculated by molecular dynamics simulations. Using linear regression analyses, the quantitative relationships between the intermolecular interaction and damping parameters were investigated. Linear and significant relationships between intermolecular interactions (N_HBs and E_binding) and damping parameters (tan δ_max and TA) (R² > 0.9; P < 0.001) were noted; FFV showed moderate linear correlations with damping parameters (R² < 0.9; P < 0.05); only E_binding showed strong correlations with T_g and ΔT (R² > 0.9; P < 0.001). Besides, after nondimensionalization, multivariate linear fitting equations based on intermolecular interaction parameters were developed to accurately predict damping parameters (R² > 0.98, P < 0.001). These studies were expected to provide the useful information in understanding the damping mechanism and to attempt a quantitative tool for designing high damping materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46202.