Switching from Ethylene Trimerization to Ethylene Polymerization by Chromium Catalysts Bearing SNS Tridentate Ligands: Process Optimization Using Response Surface Methodology

Two types of chromium catalysts bearing pyridine and amine based SNS ligands under the title of (pyridine-SNS-alkyl/CrCl₃) and (amine-SNS-alkyl/CrCl₃) were synthesized. Different thiolates such as octyl, pentyl, butyl, cyclohexyl and cyclopentyl thiolates were reacted with 2,6-pyridine-dimethylene-ditosylate (PMT)/THF solution at room temperature. Then, the purified pyridine-based SNS ligands (1–5) were reacted with CrCl₃ (THF)₃ to obtain the pyridine-SNS-alkyl/CrCl₃ catalysts (6–10) in 50–70% yields. MMAO-activated pyridine-SNS-alkyl/CrCl₃ catalysts were capable of oligomerizing ethylene. Statistical experimental design was conducted using the central composite design method and surface methodology to study of the effect of important parameters such as ethylene pressure, Al/Cr ratio, catalyst concentration and the reaction temperature on 1-C₆ productivity of catalyst (7). A quadratic polynomial equation was developed to predict the 1-C₆ productivity. Ethylene oligomerization using the catalyst (7) was lead to a optimized reaction conditions, including the ethylene pressure of 19.5 bar, the temperature of 58.2 °C, the MMAO co-catalyst, Al/Cr?=?841 and the catalyst concentration of 8.7 µmol. The catalytic properties for ethylene oligomerization are strongly affected by reaction temperature. The experimental results indicated the reasonable agreement with the predicted values. The transformation from ethylene trimerization to ethylenev polymerization of catalyst system (7) was occurred by exchanging the reaction pressure. Influence of ligand structure with different substitutions on sulphur atom on productivity and selectivity was investigated. 1-C₆ with the high selectivity and productivity 4318 (g 1-C₆/g Cr h) was obtained for catalyst (7). In the second part, 1-C₆ was obtained with high selectivity and productivity around 141?×?10³ (g 1-C₆/g Cr h) for amine-based catalyst. All amine-based catalysts (14–16) showed considerably higher catalytic activities compared to pyridine-based catalysts. According to the TGA analysis the thermal stability of pyridine-based catalysts was found to be higher than the amine-based catalysts.

Graphical Abstract

Chromium complexes bearing pyridine and amine based SNS ligands have been synthesized and their catalytic performance in ethylene oligomerization has been investigated. A switching from ethylene trimerization to ethylene polymerization of the catalyst (7) was obtained utilizing exchanging of the ethylene pressure.

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Comparative studies on protein fractions and amino acid composition from sorghum and pearl millet

A defatted flour sample of sorghum and pearl millet were separated into three fractions. These procedures involve extracting the defatted flour with aqueous sodium hydroxide (pH 11.9) followed by precipitation with diluted HCl acid (pH 4.8). The two protein fractions I (soluble at pH 4.8) and II (insoluble at pH 4.8) along with the remaining residues (fraction III) were lyophilized separately. The amino acid composition of the original flour and the three fractions were determined. Lysine seems to be the most deficient amino acid in the original flour and the remaining residues. Fraction I and II, in which the lysine accumulated, have essentially better amino acid profile and consequently nutritionally better quality than the protein of the original defatted flour. The recovered protein-rich fractions I and II should be useful as a protein ingredient in foods. The remaining residues can be extruded into convenience foods.     

Changes in blocking mechanisms during membrane processing of pomegranate juice

The effect of pressure, velocity, pretreatment, membrane type and pore size on fouling mechanisms were evaluated. Pomegranate juice was treated with polyvinylidene fluoride (PVDF) 0.22 μm and mixed cellulose ester (MCE) 0.1 μm at different pressures. Cake formation which was the dominant mechanism was formed in the first stages of process and, as the filtration proceeded, intermediate, standard, and complete blocking, respectively occurred at higher pressure (5 kPa). At lower pressure (0.5 kPa) the last mechanism did not occur. Results showed that cake formation was the only mechanism in MCE 0.22 μm, however, others occurred with MCE 0.1 μm and PVDF 0.22 μm. Using MCE 0.22 μm prior to MCE 0.025 μm can reduce the role of cake formation in pore blocking. Evaluation of the impact of velocity showed that at the higher velocity (0.53 m s⁻¹) the complete blocking occurred faster than at the lower velocity (0.09 m s⁻¹).     

DC and AC electrical conductivity of electro-deposited carbon-black–epoxy composite films

Carbon-black–epoxy composite films were prepared by cathodic electro-deposition of a dispersion containing carbon black and epoxy resins. The films, after baking at elevated temperature, show a semi-conducting behavior. Using DC conductivity measurements it was possible to determine the glass transition temperature of the samples, the conductivities of which lie in the sensitivity range of the instrument. Conductive samples show a positive temperature coefficient both below and above T_g. Based on the electrical impedance data extracted from the electrochemical impedance spectra, the exponents x and y were determined for the frequency dependence of the complex conductivity and complex dielectric constant as 0.8 and 0.2, respectively. These values are in good agreement with the classical values of x = 0.72 and y = 0.28. It was also found that these exponents are the same for all the CCB contents studied.     

Qualitative and quantitative evaluation of heart sound reduction from lung sound recordings

Recursive least squares (RLS) adaptive noise cancellation (ANC) and wavelet transform (WT) ANC have been applied and compared for heart sound (HS) reduction from lung sounds (LS) recordings. Novel processes for quantitative and qualitative evaluation of any method for HS reduction from LS have also been proposed.     

Healing DNA Self-Assemblies Using Punctures

In self-assembly, individual components (commonly referred to as tiles) have sufficient infor mation to build templates for structures such as lat tices for two-dimensional scaffolds. Tile sets that can heal (fully or partially) an erroneous DNA assembly have been proposed. Healing requires growth to be restarted such that erroneous tiles can be removed and the correct tiles can bind to the aggregate. Punctures have been proposed for this purpose; in this paper, a puncture is intentionally induced in the self-assembly to restart the growth process. The goal of this paper is to characterize an intentionally induced puncture (and its relevant properties) on an erroneous tile site in the grown crystal as part of a healing process. This allows to propagate any newly generated error away from the source of growth (i.e. the seed tile), such that self-assembly can continue along specific directions. Different types of puncture are considered with respect to healing and related features, such as growth direction, error and aggregate types. Punctures are analyzed using a new characterization and metric; different tile sets are investigated in detail for healing of a DNA self-assembly.

Application of silica gel as an effective modifier for the voltammetric determination of dopamine in the presence of ascorbic acid and uric acid

Amorphous silica gel modified carbon paste electrode (CPE) offers substantial improvements in voltammetric sensitivity and selectivity towards determination of dopamine (DA). Cyclic voltammetry of Fe(CN)₆^3−/4− as a negatively charged probe revealed that the surface of the silica gel modified carbon paste electrode had a high density of negative charge at pH 8.0. Therefore, the modified electrode adsorbed DA (pK_a = 8.9) and enhanced its voltammetric response while repulsed ascorbic acid (AA) (pK_a = 4.2) and uric acid (UA) (pK_a = 5.4) and inhibited their interfering effects. The influence of various experimental parameters including percent of silica gel in the CPE, pH of solution, and accumulation time and potentials, on the voltammetric response of DA was investigated. At the optimum conditions, the analytical curve was linear for dopamine concentrations from 2.0 × 10⁻⁷ to 1.0 × 10⁻⁶ mol L⁻¹ and 2.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit (3σ) of 4.8 × 10⁻⁸ mol L⁻¹. The prepared electrode was used for determination of DA spiked into DA injection and human serum samples, and very good recovery results were obtained over a wide concentration range of DA.     

Radiation pattern design of photonic crystal LED optimized by using multi-objective grey wolf optimizer

Photonic Network Communications - This paper proposes an effective method for shaping the radiation pattern intensity of photonic crystal (PhC) light-emitting diode (LED). In this method, the...     

Hydrogen production employing Cu(BDC) metal–organic framework support in methanol steam reforming process within monolithic micro-reactors

Cu(BDC) metal–organic framework (MOF) was used as a support for the copper (Cu) catalyst applied in the methanol steam reforming (MSR) process at low temperatures (130–250 °C) with a feed WHSV = 9.2 h^?1 within the monolithic reactor. Also, the effects of diverse promoters were examined on the catalytic activities of the Cu/X–Cu(BDC) (X = Ce, Zn, Gd, Sm, La, Y, Pr) catalysts. Results showed that the Ce/Sm–Cu(BDC) supports exhibited highest activities, lowest reduction temperatures and largest specific surface areas, which caused highest distributions of the active copper metal nanoparticles on the supports. The reactor tests displayed that the activities of Cu/X–Cu(BDC) (X = Ce, Zn, Gd, Sm, La, Y, Pr) catalysts followed the order X = Ce > Sm > Y > La > Pr > Cu(BDC) > Zn > Gd. The highest activities of Ce and Sm containing catalysts were attributed to the presence of CeO₂ and Sm₂O₃ caused the oxygen vacancies on the catalyst surface which had positive effects on the methanol reforming process. The time-on-stream stability tests showed the highest resistance of the Cu/Ce–Cu(BDC) catalyst to the carbon formation during 32 h. Consequently, the Cu/Ce–Cu(BDC) with the highest stability, methanol conversion and carbon monoxide selectivity could be used in practical industrial applications.     

Human Cellular Retinol Binding Protein II Forms a Domain-Swapped Trimer Representing a Novel Fold and a New Template for Protein Engineering

Domain-swapping is a mechanism for evolving new protein structure from extant scaffolds, and has been an efficient protein-engineering strategy for tailoring functional diversity. However, domain swapping can only be exploited if it can be controlled, especially in cases where various folds can coexist. Herein, we describe the structure of a domain-swapped trimer of the iLBP family member hCRBPII, and suggest a mechanism for domain-swapped trimerization. It is further shown that domain-swapped trimerization can be favored by strategic installation of a disulfide bond, thus demonstrating a strategy for fold control. We further show the domain-swapped trimer to be a useful protein design template by installing a high-affinity metal binding site through the introduction of a single mutation, taking advantage of its threefold symmetry. Together, these studies show how nature can promote oligomerization, stabilize a specific oligomer, and generate new function with minimal changes to the protein sequence.