Bi- and tri-dentate imino-based iron and cobalt pre-catalysts for ethylene oligo-/polymerization

Recent progress on the use of iron and cobalt complex pre-catalysts for ethylene reactivity is reviewed. The review is organized in terms of the denticity of the chelate ligands employed, with particular reference to the influence of the ligand frameworks and their substituents on the catalytic performance for ethylene oligomerization/polymerization catalysis. The majority of the systems bear tri-dentate ligation at the iron/cobalt centre, though it is clear that bi-dentate iron/cobalt complex pre-catalysts have also attracted significant attention. Such systems produce in most cases highly linear products ranging from oligomeric α-olefins to high molecular weight polyethylene, and as such are promising candidates for both academic and industrial considerations

Recombinant EXLX1 from Bacillus subtilis for enhancing enzymatic hydrolysis of corn stover with low cellulase loadings

BsEXLX1 protein from Bacillus subtilis has been proposed to have a structure that is similar to plant expansin. In this study, the recombinant BsEXLX1 protein was successfully expressed and purified in Escherichia coli BL21 (DE3). When the purified BsEXLX1 which contained the thioredoxin (Trx) protein was incubated with low-dose cellulases either simultaneously or sequentially, it showed a significant synergistic activity in corn stover hydrolysis. Furthermore, an even greater increase in the synergistic activity was obtained when cellulose was pretreated with BsEXLX1 followed by cellulase hydrolysis, and the synergistic activity was found as high as 1.5-fold greater than that when cellulose was treated simultaneously with the same concentrations of BsEXLX1 and cellulases. These results provided a feasible way for the potential application of BsEXLX1 in the efficient saccharification of cellulose materials for bioethanol production.Key word: Bacillus subtilis, BsEXLX1, cellulase, cellulose hydrolysis, bioethano

Estimation of Small Time-Dependent Failure Probability in High Dimensions using Subset Simulation

Time-dependent reliability analysis of deteriorating structures is significant in their performance assessment and maintenance. Various methodologies have been used by researchers to predict the time-dependent reliability of structures. However, it is still a challenge to estimate the small time-dependent failure probability in high dimensions. In the present study, based on subset simulation an adaptive stochastic simulation procedure is proposed considering the stochastic nature of the occurrence of time-dependent random variables. Moreover, a modified Metropolis-Hastings algorithm is developed to reduce repeated trajectories and suit the property of time-dependent reliability problem. Fourth-moment transformation is utilized in the study for without the exclusion of random variables with unknown probability distributions. The proposed method is illustrated by a cantilever tube subjected to external forces and torsion. The methodology can be used as a tool for structural engineers and asset managers to assess small time-dependent failure probability of a deteriorating structure in high dimensions and make decisions with regard to its maintenance and rehabilitation.The study is partially supported by the National Natural Science Foundation of China (Grant Nos.: 51820105014, 51738001), and the Fundamental Research Funds for the Central Universities of Central South University (Grant No.: 2018zzts187). The support is gratefully acknowledged

Recombination frequencies between cultivated soybean (Glycine max) and its wild relative Glycine soja based on molecular marker analysis

Close relatives of cultivated crops provide an invaluable source of genetic variation in crop improvement and exploiting such variation often forms a critical part in a breeding program. The usability of the wild soybean Glycine soja was investigated in this study by analyzing populations derived from two wide crosses between a common cultivar and two different G. soja accessions using simple sequence repeat (SSR) markers. Consistent reductions in recombination frequencies were not detected in either of these two wide crosses and the results does not seem to be confined to the particular populations or the wild genotypes used. In variance with previous reports that domestication-related traits are often controlled by one or two major loci, these recombination results strongly indicate that linkage drag should not be a major concern in transferring genes from the wild taxon into the cultigen, although backcross would still be required to minimize undesirable chromatins.Keywords: Glycine max, Glycine soja, linkage drags, recombination frequency, molecular markersAfrican Journal of Biotechnology Vol. 12(22), pp. 3522-352

A convenient tandem one-pot synthesis of donor-acceptor-type triphenylene 2,3-dicarboxylic esters from diarylacetylene

A tandem one-pot method for the direct synthesis of polysubstituted triphenylene 2,3-dicarboxylic esters with different substitution patterns was developed by enyne metathesis of diarylacetylene, followed by Diels–Alder, aromatization and a cyclization cascade

High-Order Moment Method for Structural Reliability Analysis Including Random Variables with Unknown Distributions

The high-order moment methods, being very simple, are widely used for structural reliability analysis. The basic procedure of moment methods includes two steps: firstly, the first few moments of the performance function were determined using the new point estimate methodsecondly, the corresponding failure probability can be obtained from the moment-based reliability index. In the new point estimate method, the basic random variables are assumed having known probability distributions to realize the Rosenblatt transformation and its inverse transformation. However, in practical applications, the probability distributions of some random variables maybe unknown, and the probabilistic characteristics of these variables maybe expressed using only statistical moments. This paper aims to investigate the high-order moment methods including random variables with unknown probability distribution based on the fourth-moment transformation technique. Several examples are examined under different conditions to demonstrate the accuracy and efficiency of the present method. Since only the first few moments of the performance functions are used, and it can be conducted even when the probability distributions of the random variables are unknown, structural reliability analysis should become simpler and more convenient using the present method.The study is partially supported by the National Natural Science Foundation of China (Grant Nos.: 51820105014, 51738001). The support is gratefully acknowledged

Estimating Distribution of Structural Responses based on Cubic Normal Distribution and Artificial Neural Network

The approximation of the probability density function (PDF) of the structural response is importance in structural reliability analysis. The recently developed cubic normal distribution can be used to represent the PDF of structural response due to its high flexibility and its large applicable range, whose parameters are evaluated by its first four moments. Therefore, efficient estimation of the moments is of great importance. Although some methods have been developed, evaluating the moments of structural response from the sight of balancing accuracy and efficiency remains a challenge, especially when the structural response is implicit and high-dimensional. In this paper, based on the artificial neural network (ANN), a new method is developed to efficiently estimate the statistical moments of structural response. The main procedure of the proposed method includes two steps: the structural response is approximated by the ANN and then the moments of structural response can be easily obtained. A RC frame structure with non-linear behavior is used to demonstrate the efficiency, accuracy, and applicability of the proposed method. The results show that the proposed method is of high accuracy and efficiency and provides a robust tool for representing the PDF of structural response.The study is partially supported by the National Natural Science Foundation of China (Grant Nos.: 51820105014, 51738001). The support is gratefully acknowledged

Ethyleneglycol tungsten complexes of calix[6 and 8]arenes: Synthesis, characterization and ROP of ε-caprolactone

By varying the reaction conditions, the reaction of [W(eg)₃] (eg = 1,2-ethanediolato) with p-tert-butylcalix[n]areneHn (n = 6 or 8) in refluxing toluene affords, following work-up, a number of products which have been fully characterized. From the reaction of p-tert-butylcalix[6]areneH₆ with one or two equivalents of [W(eg)₃], only the oxo-bridged complex {[W(eg)]₂(μ-O)p-tert-butylcalix[6]arene} (1) could be isolated, whereas the use of four equivalents of [W(eg)₃], in the presence of molecular sieves, afforded {[W(eg)₂]₂p-tert-butylcalix[6]areneH₂}·2MeCN (2); molecules of 2 pack in bi-layers. Under similar conditions, use of one or two equivalents of [W(eg)₃] and p-tert-butylcalix[8]areneH₈ afforded {[W(eg)]₂p-tert-butylcalix[8]arene}·MeCN (3) in which each tungsten centre was bound by four calixarene oxygens. By contrast, the small orange prisms resulting from the use of four equivalents of [W(eg)₃] and p-tert-butylcalix[8]areneH₈ were shown by synchrotron radiation to be a mixture of two isomers (4a/4b·3.5MeCN). In the major isomer {1,2-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4a), two tungsten centres bind to neighbouring sets of phenolate oxygens, whereas in the minor isomer {1,3-[W(eg)₂]₂p-tert-butylcalix[8]areneH₄} (4b), there is a protonated phenolic group between the two pairs of phenolate oxygens bound to tungsten; the major:minor ratio is about 83:17. Use of p-tert-butyltetrahomodioxacalix[6]areneH₆ with two equivalents of [W(eg)₃] resulted in the isolation of {[WO(eg)]₂p-tert-butyltetrahomodioxacalix[6]areneH₂} (5·0.83toluene·MeCN), in which each dimethyleneoxa bridge is bound to an oxotungsten(VI) centre. Complexes 1–5, together with the known complex [W(eg)p-tert-butylcalix[4]arene] (6), have been screened for their ability to ring open polymerize (ROP) ε-caprolactone; for 1, 2 and 5, 6 conversion rates were good (>88%) at 110 °C over 12 or 24 h, whereas the calix[8]arene complexes 3 and 4 under the same conditions were inactive