From unstable to stable: half-metallocene catalysts for olefin polymerization

The reaction of LAlMeOH [L = CH(N(Ar)(CMe))2, Ar = 2,6-i-Pr2C6H3] with CpTiMe3, Cp*TiMe3, and Cp*ZrMe3 was investigated to yield LAlMe(mu-O)TiMe2Cp (2), LAlMe(mu-O)TiMe2Cp* (3), and LAlMe(mu-O)ZrMe2Cp* (4), respectively. The resulting compounds 2-4 are stable at elevated temperatures, in contrast to their precursors such as CpTiMe3 and Cp*ZrMe3, which already decompose below room temperature. Compounds 2-4 were characterized by single-crystal X-ray structural analysis. Compounds 2 and 3 were tested for ethylene polymerization in the presence of methylaluminoxane. The half-metallocene complex 3 has higher activity compared to 2. The polydispersities are in the range from 2.8 to 4.2. A copolymerization with styrene was not observed.     

The effect of curvature of Li-doped polycyclic hydrocarbon on its interaction energy with H<Subscript>2</Subscript> and H<Subscript>2</Subscript>O: DF-SAPT (DFT) calculation

In this work, the interaction of three Li⁺-doped polycyclic hydrocarbons (Li⁺-DPH) with H₂ and H₂O was calculated to investigate the effect of curvature of substrate on the interaction energy (E_int). For this purpose, the E_int and its decomposed energy components (electrostatic (E_elec), exchange (E_exch), induction (E_ind), and dispersion energy (E_disp)) were calculated using DF-SAPT (DFT) methodology for the selected systems (Li⁺-(3,3) carbon nanotube (Li⁺-CNT33), Li⁺-(6,6) carbon nanotube (Li⁺-CNT66), and Li⁺-graphene). According to the results, E_int does not change significantly with curvature for the interaction between both H₂ and H₂O gases and the selected Li⁺-DPH. Since the variation of the E_int with the curvature of Li⁺-DPH is not significant, the selection of a planar Li⁺-DPH is a trustworthy model to develop a general force field for describing the interaction between a Li⁺-DPH and adsorbed gases. The results reveal that, in the case of the H₂, the components E_elect, E_exch, E_ind, and E_disp have shown a decreasing trend with Li⁺-DPH’s curvature decrement. However, for the H₂O, E_elect, E_exch, and E_ind decrease from the Li⁺-CNT33 to the Li⁺-CNT66 while they increase from the Li⁺-CNT66 to the Li⁺-graphene. In this case, the E_disp increases with a decrease of the curvature of Li⁺-DPH. Finally, it can be seen that although the variation of the E_int with the curvature of Li⁺-DPH is not significant, the variation trend of the interaction energy components and the amount of variation depend on the gas molecule and in some cases are not negligible.     

Synthesis of functionalized pyrroles and fused pyrroles through intermolecular [3 + 2] cycloaddition reaction

A facile and efficient synthesis of pyrrole and pyrrole-fused heterocyclic compounds has been demonstrated. The current protocol involves the in situ generation of azomethine ylides which undergoes intermolecular cycloaddition reaction and subsequent treatment with DDQ provides the pyrrole and fused heterocyclic compounds in good yields.     

Geodesics for the NUT metric and gravitational monopoles

In order to provide insight about the physical interpretation of the NUT parameter, we solve the geodesic equations for the NUT metric. We show that the properties of NUT geodesics are similar to the properties of trajectories for charged particles orbiting about a magnetic monopole. In summary, we show that (1) the orbits lie on the surface of a cone, (2) the conserved total angular momentum is the sum of the orbital angular momentum plus the angular momentum due to the monopole field, (3) the monopole field angular momentum is independent of the separation between the source of the gravitational field and the test particle, and (4) the geodesics are almost spherically symmetric. The strong similarities between the NUT geodesics and the electromagnetic monopole suggest that the NUT metric is an exact solution for a gravitational magnetic monopole. However, the subtle difference of being only almost spherically symmetric implies that the analogy is not perfect. The almost spherically symmetric nature of the NUT geodesics suggest that the energy of the Dirac string makes a contribution to the solution. We also construct exact solutions for special orbits, discuss a twin paradox, and speculate about the Dirac quantization condition for a gravitational magnetic monopole.     

Surface Arginine Saturation Effect on Unfolding Reaction of Firefly Luciferase: A Thermodynamic and Kinetic Perspective

Replacement of some hydrophobic solvent‐exposed residues in Lampyris turkestanicus luciferase with arginine increases thermostability of this enzyme. Herein, thermodynamic and kinetic of unfolding reactions of wild type (WT), E354R/356R, E354R/356R‐I232R and E354R/356R‐Q35R/L182R/I232R variants, has been investigated. Fluorescence and Far‐UV circular dichroism measurements using urea as a chemical denaturant indicated that the value of for all variants is greater than that of WT enzyme. Analysis of m‐values, as a measure of difference in the solvent accessible surface area between the native and denatured states of protein, revealed that higher stability of mutants is related to their higher degree of compactness in the folded state. Results of unfolding kinetic experiments showed that all variants have three‐exponential behavior in which they unfolded with three rate constants and corresponding amplitudes. Increasing the rate constants of fast unfolding phase in mutants relative to WT protein may be attributed to more compactness and more kinetic sensitivity of their folded state to urea. However, more population of WT protein was unfolded from fast unfolding phase. Results of this investigation highlight kinetic stability of luciferase via a slow rate of unfolding.     

Kinetic Spectrophotometric Method and Neural Network Model Application for the Quantitation of Epinephrine by Starch-capped AgNPs Sensor in Blood and Urine

Journal of Analytical Chemistry - In this study, a simple, accurate, precise, rapid, economical, and highly sensitive ultraviolet spectrophotometric method has been developed for the determination...     

Numerical investigation of cone angle effect on the flow field and separation efficiency of deoiling hydrocyclones

In this study, the effect of cone angle on the flow field and separation efficiency of deoiling hydrocyclones is investigated taking advantage of large eddy simulation. The dynamic Smagorinsky is employed to determine the residual stress tensor of the continuous phase. The method of Lagrangian particle tracking with an optimized search algorithm (closest cell) is applied to evaluate the separation efficiency of deoiling hydrocyclone. Simulations are performed on a 35-mm deoiling hydrocyclone with the three different cone angles of 6, 10 and 20 degree. The numerical results revealed that the changes in the cone angle would affect the velocity and pressure distribution inside hydrocyclone, and lead to changes in the separation efficiency. However, the large cone angle increases the tangential velocity and pressure gradient inside the hydrocyclone, but reduces the separation efficiency. The reasons behind the decrease in the separation efficiency are the flow structure and reduction of oil droplets residence time in hydrocyclones with large cone angles.     

Thermodynamic Properties of Aqueous Potassium Fluoride under Superambient Conditions

Using the ion-interaction or virial coefficient approach developed by Pitzer, the pressure dependences of the osmotic and activity coefficients for KF (aq.) up to 473.15 K and 2.5.0 mol-kg^-1 have been calculated from literature data for the apparent molar volumes of KF (aq.). These pressure dependencies were combined with the osmotic and activity coefficient at 0.1 MPa or p_sat, obtained from the model of Saluja et al. to yield a comprehensive set of thermodynamic properties for KF (aq.) at temperatures from 298.15 through 473.15 K, pressures 10, 20, and 30 MPa, and molalities to 2.5 mol-kg^-1.     

Nonlinear direct inverse method: a shortcut method for simultaneous calibration and isotherm determination

This work addresses a way to combine isotherm determination and nonlinear calibration. In this method, like the classical inverse method, experimental elution profiles are compared with the results of a detailed model that accounts for nonlinearity in equilibrium, axial dispersion, and mass transfer kinetics. However, unlike the classical inverse method, the calibration of detector is carried out simultaneously with isotherm determination thereby reducing cost and saving time. In this study no limitation is imposed on the linearity of the detector signal or on the overlapping of elution profiles for the separation of enantiomers. The method has been experimentally validated for the separation of a mixture of guaifenesin enantiomers over a wide range of concentration.     

Addition of Dimethylaminobismuth to Aldehydes,Ketones, Alkenes,and Alkynes

Bi? O chemistry : A direct regioselective route to bismuth bis(amino)naphthalene compounds, incorporating Bi? O and Bi? C bonds is described, in which an amide precursor is treated with aldehydes, ketones, alkenes, and alkynes, leading to insertion into the Bi? NMe₂ bond.