Modelling of ready biodegradability based on combined public and industrial data sources

ABSTRACT

The European Registration, Evaluation, Authorization and Restriction of Chemical Substances Regulation, requires marketed chemicals to be evaluated for Ready Biodegradability (RB), considering in silico prediction as valid alternative to experimental testing. However, currently available models may not be relevant to predict compounds of industrial interest, due to accuracy and applicability domain restriction issues. In this work, we present a new and extended RB dataset (2830 compounds), issued by the merging of several public data sources. It was used to train classification models, which were externally validated and benchmarked against already-existing tools on a set of 316 compounds coming from the industrial context. New models showed good performances in terms of predictive power (Balance Accuracy (BA) = 0.74–0.79) and data coverage (83–91%). The Generative Topographic Mapping approach identified several chemotypes and structural motifs unique to the industrial dataset, highlighting for which chemical classes currently available models may have less reliable predictions. Finally, public and industrial data were merged into global dataset containing 3146 compounds. This is the biggest dataset reported in the literature so far, covering some chemotypes absent in the public data. Thus, predictive model developed on the Global dataset has larger applicability domain than the existing ones.     

Characterization of G-quadruplex/hemin peroxidase: substrate specificity and inactivation kinetics

Recently, G-quadruplex/hemin (G4/hemin) complexes have been found to exhibit peroxidase activity, and this feature has been extensively exploited for colorimetric detection of various targets. To further understand and characterize this important DNAzyme, its substrate specificity, inactivation mechanism, and kinetics have been examined by comparison with horseradish peroxidase (HRP). G4/hemin DNAzyme exhibits broader substrate specificity and much higher inactivation rate than HRP because of the exposure of the catalytic hemin center. The inactivation of G4/hemin DNAzyme is mainly attributed to the degradation of hemin by H(2)O(2) rather than the destruction of G4. Both the inactivation rate and catalytic oxidation rate of G4/hemin DNAzyme depend on the concentration of H(2)O(2), which suggests that active intermediates formed by G4/hemin and H(2)O(2) are the branch point of catalysis and inactivation. Reducing substrates greatly inhibit the inactivation of G4/hemin DNAzyme by rapidly reacting with the active intermediates. A possible catalytic and inactivation process of G4/hemin has been proposed. These results imply a potential cause for the hemin-mediated cellular injury and provide insightful information for the future application of G4/hemin DNAzyme.     

Cooperativity and substrate specificity of an alkaline amylase and neopullulanase complex of Micrococcus halobius OR-1

The saccharifying alkaline amylase and neopullulanase complex of Micrococcus halobius OR-1 hydrolyzes both α-(1,4)- and α-(1,6)-glycosidic linkages of different linear and branched polysaccharides. The following observations were made concerning the analysis of the coexpressed amylase and neopullulanase enzymes. Even though the enzymes were subjected to a rigorous purification protocol, the activities could not be separated, because both the enzymes were found to migrate in a single peak. By contrast, two independent bands of amylolytic activity at 70 kDa and pullulanolytic activity at 53 kDa were evident by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), reducing and nonreducing PAGE, and zymographic analysis on different polysaccharides. Preferential chemical modification of the enzyme and concomitant high-performance thin-layer chromatographic analyses of the saccharides liberated showed that amylase is sensitive to 1-(dimethylamino-propyl)-3-ethyl carbodiimide-HCl and cleaved α-(1,4) linkages of starch, amylose, and amylopectin producing predominantly maltotriose. On the other hand, formalin-sensitive neopullulanase acts on both α-(1,4) and α-(1,6) linkages of pullulan and starch with maltotriose and panose as major products. It is understood that neopullulanase exhibits dual activity and acts in synergy with amylase toward the hydrolysis of α-(1,4) linkages, thereby increasing the overall reaction rate; however, such a synergism is not seen in zymograms, in which the enzymes are physically separated during electrophoresis. It is presumed that SDS-protein intercalation dissociated the enzyme complex, without altering the individual active site architecture, with only the synergism lost. The optimum temperature and pH of amylase and neopullulanase were 60°C and 8.0, respectively. The enzymes were found stable in high alkaline pH for 24 h. Therefore, the saccharifying alkaline amylase and neopullulanase of M. halobius OR-1 evolved from tapioca cultivar shows a highly active and unique enzyme complex with several valuable biochemical features.     

KF负载型固体碱催化合成氨基甲酸酯的研究

氨基甲酸酯是合成农药、医药及异氰酸酯的重要中间体^[1,2]．传统的氨基甲酸酯的制备是以光气及其衍生物和胺为原料^[3],该工艺使用剧毒的光气,同时副产腐蚀性的HCl．因此,对环境友好的非光气法合成氨基甲酸酯成为当今发展的主流^[4,5]．由胺与碳酸二甲酯反应合成氨基甲酸酯是近年发展起来的非光气法,用碳酸二甲酯代替光气合成氨基甲酸酯可以实现环保要求,反应过程中的唯一副产物甲醇可以循环利用．该反应通常在硝酸铅^[6]、γ—Al2O3^[7]、Zn（OAc）2和三氟化镱^[8,9]等催化条件下进行．但上述催化剂存在催化活性低,     

Polymer blends based on the β-modification of polypropylene

iPP/sPP, iPP/rPP, iPP/PVDF and iPP/PA-6 blends, and their β-nucleated forms were prepared in the present study. The components of iPP/sPP and iPP/rPP blends are compatible in the molten state. The phase structure of the melt of iPP/PVDF and iPP/PA-6 blends is heterogeneous. The melting and crystallisation characteristics as well as the structure and polymorphic composition of these blends were studied by polarised light microscopy (PLM) and differential scanning calorimetry (DSC). When semicrystalline polymers are added to iPP, the most important factor of the formation a blend with β-crystalline phase is the α-nucleation effect of the second polymer. In the case of polymers with an α-nucleating effect, the temperature range of their crystallisation should be lower than that of β-iPP. β-nucleated iPP/PVDF and iPP/PA-6 blends are extreme examples showing that completely β-iPP matrix can not form even in the presence of a highly effective β-nucleant, because of the strong α-nucleating ability and higher crystallisation temperature range of PVDF and PA-6. We found that the β-crystallisation tendency of random propylene copolymers can be enhanced by adding an iPP homopolymer.     

Biodegradable polymers based on renewable resources. II. Synthesis and biodegradability of polyesters containing furan rings

A series of polyesters were synthesized by the bulk polycondensations of the respective combinations of two difuranic diesters, i.e., bis(5-(methoxycarbonyl)-2-furyl)methane ( 4a ) and 1,1-bis(5-(methoxycarbonyl)-2-furyl)ethane ( 4b ), with two 1,4 : 3,6-dianhydrohexitols [1,4 : 3,6-dianhydro-D -glucitol ( 1 ) and 1,4 : 3,6-dianhydro-D -mannitol ( 2 )], four aliphatic diols, and three oligo(ethylene glycol)s. The polycondensations were carried out at 220–230°C in the presence of titanium isopropoxide as a catalyst, giving polyesters having number average molecular weight up to 2.4 × 10⁴. These polyesters are soluble in a variety of solvents including chlorinated hydrocarbons, 1,4-dioxane, dimethyl sulfoxide, dimethylformamide, and sulfolane. Soil-burial tests along with enzymatic degradation experiments showed that these polyesters are potentially biodegradable. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2729–2737, 1997     

Substrate specificity of camphor-induced cytochrome P-450 Immobilized on an electrode

The substrate specificity of a camphor-induced cytochrome P-450 (P-450_cam) was measured by using a new assay system: electrochemical control of P-450_cam activity by protein immobilization on an electrode. Immobilized P-450_cam showed the obvious substrate specificity for hydroxylation of the substrate, suggesting that the simple assay system is applicable for the study of the effect of the other components of the electron transfer system on activity. Copyright © 1998 John Wiley & Sons, Ltd.     

Effect of silane‐grafted polypropylene on the morphology of polypropylene and nylon 6/clay composites

Polypropylene (PP)/nylon 6/clay composites were prepared by compounding of PP, which had previously been treated with two kinds of silane compounds, with a master batch composed of 90 wt % of nylon 6 and 10 wt % of octadecyl amine‐modified sodium montmorillonite (NM10). The morphology of the composites was investigated by means of SEM, TEM, XRD, and energy‐dispersive X‐ray analysis. All of the composites exhibited a phase‐separated morphology, irrespective of whether the PP was modified with the silane compounds or not. However, adhesive strength between the modified PP and NM10 was stronger than that between neat PP and NM10. Moreover, the PP grafted with 3‐(trimethoxysilyl)propyl methacrylate (PP2) reacted with the silanol groups of the clay to form PP‐clay hybrid during the compounding, which acted as a compatibilizer for the PP/nylon 6/clay composite. PP2NM composite (PP2/NM10 80/20 on weight basis) exhibited a peculiar morphology, in that the PP‐rich phase formed island domains within the nylon 6‐rich domains, which were in turn dispersed in the PP‐rich continuous matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 607–615, 2007.     

Preparation and characterization of PP/clay nanocomposites based on modified polypropylene and clay

X‐ray diffraction and differential scanning calorimeter (DSC) methods have been used to investigate the crystallization behavior and crystalline structure of hexamethylenediamine (HMDA)‐modified maleic‐anhydride‐grafted polypropylene/clay (PP‐g‐MA/clay) nanocomposites. These nanocomposites have been prepared by using HMDA to graft the PP‐g‐MA (designated as PP‐g‐HMA) and then mixing the PP‐g‐HMA polymer in hot xylene solution, with the organically modified montmorillonite. Both X‐ray diffraction data and transmission electron microscopy images of PP‐g‐HMA/clay nanocomposites indicate that most of the swellable silicate layers are exfoliated and randomly dispersed into PP‐g‐HMA matrix. DSC isothermal results revealed that introducing 5 wt % of clay into the PP‐g‐HMA structure causes strongly heterogeneous nucleation, which induced a change of the crystal growth process from a three‐dimensional crystal growth to a two‐dimensional spherulitic growth. Mechanical properties of PP‐g‐HMA/clay nanocomposites performed by dynamic mechanical analysis show significant improvements in the storage modulus when compared to neat PP‐g‐HMA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3242–3254, 2005     

Substrate specific nanoreactors based on pyrimidine-containing amphiphiles of various structures for cleavage of phosphonates

ABSTRACT

The series of novel pyrimidine-containing amphiphiles were examined as catalysts for cleavage of phosphonates having various hydrophobicities. Kinetic data showed marked substrate specificity of three different types (i) inhibition for both substrates, (ii) catalysis for more hydrophobic phosphonate and inhibition for less hydrophobic phosphonate, and (iii) catalysis for both substrates. The highest acceleration (more than 11 times in comparison with the reaction in the absence of amphiphile) has been reached in the case of dicationic amphiphile with three hydrophobic tails.     

The influence of thermoelastomers on the crystallization behavior of isotactic polypropylene under shear

The crystallization behaviors of isotactic polypropylene (iPP) and its blends with thermoelastomers have been investigated with in situ X‐ray scattering and optic microscopy. At quiescent condition, the crystallization kinetics of iPP is not affected by the presence of elastomers; while determined by the viscosity, the differences are observed on sheared samples. With a fixed shear strain, the crystallization rate increases with increasing the shear rate. The fraction of oriented lamellar crystals in blends is higher than that in pure iPP sample, while the percentage of β phase is reduced by the presence of the elastomers. On the basis of experimental results, no direct correlation among the fraction of oriented lamellae, the percentage of β phase, and growth rate can be deduced. The evolution of the fraction of oriented lamellae supports that shear field promotes nucleation rather than growth process. Shear flow induces the formation of nuclei not only with preferring orientation but also with random orientation. The total density of nuclei, which determines the crystallization kinetics, does not control the ratio between nuclei with and without preferring orientation, which determines the fraction of oriented lamellae. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1188–1198, 2006     

The effect of amorphous orientation on the oxygen permeability of polypropylene films

Oxygen permeability measurements have been made on uniaxially and biaxially oriented polypropylene samples. X-ray diffraction pole-figure measurements provided the crystalline orientation functions. These results combined with density and refractive index measurements provided the amorphous orientation functions based on the two-phase model. A good correlation has been found between the amorphous orientation and the oxygen permeability of the samples. © 1993 John Wiley & Sons, Inc.     

聚丙烯和毛竹共热解的研究

在自制固定床反应器中,对聚丙烯和毛竹共热解进行研究,得到了反应气氛、热解温度、反应物配比、反应时间对共热解的影响规律。实验结果表明,由于毛竹与聚丙烯在热解过程中的相互影响,两者共热解时的液体收率和产物分布均与两者单独热解时不同,油相液体产物的辛烷值随毛竹加入量的增加而增大,在聚丙烯和毛竹的最佳配比下,两者共热解的协同作用最明显,不仅原料的转化率最大,而且所得液体产物的收率最高,H2气氛较之N2气氛更有利于油相产物的生成和毛竹中木质素成分的热解。本文条件下,获得最佳油相液体收率的条件为,聚丙烯/毛竹配比8∶2,热解温度520℃,反应时间4h,H2气氛,油相液体收率达53.9wt.%,辛烷值为77.3。     

Effect of carbon nanotubes on the crystallization and properties of polypropylene

The effect of different concentrations of single‐walled carbon nanotubes (SWNTs) on the nonisothermal crystallization kinetics, morphology, and mechanical properties of polypropylene (PP) matrix composites obtained by melt compounding was investigated by means of X‐ray diffraction, differential scanning calorimetry, optical and scanning electron microscopy, and dynamic mechanical thermal analysis. Microscopy showed well‐dispersed nanotube ropes together with small and large aggregates. The modulus was found to increase by about 75% at a level of 0.5 wt % nanotubes. The SWNTs displayed a clear nucleating effect on the PP crystallization, favoring the α crystalline form rather than the β form. The crystallization kinetics analysis showed a significant increase in activation energy on incorporating nanotubes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2445–2453, 2005     

Nucleation effect of cyclodextrin inclusion compounds on the crystallization of polypropylene

The β‐cyclodextrin (β‐CD) and γ‐cyclodextrin (γ‐CD) inclusion compounds (ICs) with two different molecular weight isotactic polypropylene (iPP) were prepared. The ICs with high molecular weight iPP as guest molecule had lower inclusion rate. The crystallization behavior of iPP blended with the CDs and ICs was investigated by differential scanning calorimetry, polarized optical microscopy, and light scattering. The iPP blended with the ICs was found to exhibit higher crystallization temperature (T_C), smaller spherulites, and faster crystallization rate than those of neat iPP. These results indicate that the ICs play a role of nucleating agent on the crystallization of iPP and induce the accelerated crystallization. Both β‐CD‐iPP ICs and γ‐CD‐iPP ICs with longer iPP molecular chains had better nucleation effect than the ICs with shorter iPP molecular chains. This suggested that the nucleation effect of these ICs was affected by the inclusion rate of ICs. The lower inclusion rate could result in better nucleation effect, due to the interaction of extended iPP molecules inside the CD cavity and iPP molecules in the matrix. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 130–137, 2009     

Effects of kaolin on the thermal stability and flame retardancy of polypropylene composite

Kaolin clay was introduced into an intumescent flame retardant (IFR) system containing ammonium polyphosphate as an acid source and pentaerythritol as a carbonization agent in order to improve the thermal stability and flame retardancy of polypropylene (PP) composite. The flame retardancy and smoke suppression was evaluated by the limiting oxygen index, vertical burning UL‐94, and cone calorimeter (CONE) tests. The limiting oxygen index value was increased from 30 to 33 at the presence of 2 phr kaolin. The peak heat release rate value decreased from 1002 kW/m² of neat PP to 318 kW/m² of PP/40 phr IFR and then to 222 kW/m² of PP/38 phr IFR/2 phr kaolin. The time of the peak heat release rate was significantly prolonged after the introduction of kaolin. The morphology of char after combustion was characterized by a scanning electron microscope, and it revealed more compact char structure that was obtained at the presence of kaolin. The mechanism of kaolin on improving the retardancy and smoke suppression of PP/IFR composite was proposed on the basis of X‐ray photoelectron spectroscopy analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of annealing on the elastoplastic response of isotactic polypropylene

Four series of tensile loading-unloading tests are performed on isotactic polypropylene in the sub-yield domain of deformations at room temperature. In the first series, injection-molded specimens are used as produced, whereas in the other series the samples are annealed for 24 h at 120, 140 and 160 °C, which covers the low-temperature region and an initial part of the high-temperature region of annealing temperatures. A constitutive model is developed for the elastoplastic behavior of a semicrystalline polymer. The stress-strain relations are determined by five adjustable parameters that are found by fitting the experimental data. The effect of annealing is analyzed on the material constants.     

Morphology,microhardness, and electrical properties of composites based on polypropylene,montmorillonite, and polypyrrole

The morphology, microhardness, and electrical properties of composites consisting of conductive polypyrrole (PPy) dispersed into a nonconductive polypropylene matrix (PP) as pure component or in form of a sodium montmorillonite/PPy (MMT/PPy) composite have been studied. For comparison, also PP/MMT composites were studied. All types of composites were processed by compression molding or by melt mixing followed by compression molding into plates, which were used for characterization. Scanning electron microscopy and transmission electron microscopy was used to examine the morphology of the prepared materials. The investigation of electrical and dielectric properties was done by dielectric relaxation spectroscopy in a wide frequency range and was related to the composite composition and processing method. The analysis of the conductivity as a function of temperature indicated that the charge transfer mechanism could be described by the variable range hopping model in three dimensions. The microhardness of PP/MMT/PPy composites with different content of MMT or PPy was determined and the creep rate has been estimated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 407–423, 2009