An enantiomerically pure adamantylimido molybdenum alkylidene complex. An effective new catalyst for enantioselective olefin metathesis

An enantiomerically pure Mo-based complex that bears an alkylimido ligand is prepared and characterized through NMR spectroscopy and X-ray analysis. Mo complex 4 is the only reported chiral alkylimido catalyst; all previous chiral complexes are arylimido systems. These studies show that the chiral Mo catalyst exists exclusively as the syn isomer and that it offers unique reactivity and selectivity profiles in asymmetric olefin metathesis.     

Tuning Chemical and Physical Properties of Phosphorus Corroles for Advanced Applications

Although the affinity of metallocorroles to axial ligands is quite low, this is not the case when the chelated element is phosphorus. This work is hence focused on the mechanism of ligand exchange of six-coordinate phosphorus corroles as a tool for affecting their chemical and physical properties. These fundamental investigations allowed for the development of facile methodologies for the synthesis of a large series of complexes and the establishment of several new structure/activity profiles that may be used to understand and predict spectroscopic features and for tailor-made modification of photophysical and electrochemical properties. This is exemplified by the facile access to complexes with terminal groups that are of large potential for practical applications based on click chemistry, optical imaging, and surface science.     

Development of zirconium and potassium perchlorate igniter for AP/HTPB composite propellant base bleed grain

Journal of Thermal Analysis and Calorimetry - For effective and reliable ignition of ammonium perchlorate and hydroxyl-terminated polybutadiene (AP/HTPB) solid composite propellant base bleed (BB)...     

Thermal decomposition mechanism of 1-ethyl-3-methylimidazolium bromide ionic liquid

In order to better understand the volatilization process for ionic liquids, the vapor evolved from heating the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIM(+)Br(-)) was analyzed via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and thermogravimetric analysis mass spectrometry (TGA-MS). For this ionic liquid, the experimental results indicate that vaporization takes place via the evolution of alkyl bromides and alkylimidazoles, presumably through alkyl abstraction via an S(N)2 type mechanism, and that vaporization of intact ion pairs or the formation of carbenes is negligible. Activation enthalpies for the formation of the methyl and ethyl bromides were evaluated experimentally, ΔH(?)(CH(3)Br) = 116.1 ± 6.6 kJ/mol and ΔH(?)(CH(3)CH(2)Br) = 122.9 ± 7.2 kJ/mol, and the results are found to be in agreement with calculated values for the S(N)2 reactions. Comparisons of product photoionization efficiency (PIE) curves with literature data are in good agreement, and ab initio thermodynamics calculations are presented as further evidence for the proposed thermal decomposition mechanism. Estimates for the enthalpy of vaporization of EMIM(+)Br(-) and, by comparison, 1-butyl-3-methylimidazolium bromide (BMIM(+)Br(-)) from molecular dynamics calculations and their gas phase enthalpies of formation obtained by G4 calculations yield estimates for the ionic liquids' enthalpies of formation in the liquid phase: ΔH(vap)(298 K) (EMIM(+)Br(-)) = 168 ± 20 kJ/mol, ΔH(f,?gas)(298 K) (EMIM(+)Br(-)) = 38.4 ± 10 kJ/mol, ΔH(f,?liq)(298 K) (EMIM(+)Br(-)) = -130 ± 22 kJ/mol, ΔH(f,?gas)(298 K) (BMIM(+)Br(-)) = -5.6 ± 10 kJ/mol, and ΔH(f,?liq)(298 K) (BMIM(+)Br(-)) = -180 ± 20 kJ/mol.     

Polymer translocation in solid-state nanopores: dependence of scaling behavior on pore dimensions and applied voltage

We investigate unforced and forced translocation of a Rouse polymer (in the absence of hydrodynamic interactions) through a silicon nitride nanopore by three-dimensional Langevin dynamics simulations, as a function of pore dimensions and applied voltage. Our nanopore model consists of an atomistically detailed nanopore constructed using the crystal structure of β-Si(3)N(4). We also use realistic parameters in our simulation models rather than traditional dimensionless quantities. When the polymer length is much larger than the pore length, we find the translocation time versus chain length scales as τ ～ N(2+ν) for the unforced case and as τ ～ N((1+2ν)/(1+ν)) for the forced case. Our results agree with theoretical predictions which indicate that memory effects and tension on the polymer chain play an important role during the translocation process. We also find that the scaling exponents are highly dependent on the applied voltage (force). When the length of the polymer is on the order of the length of the pore, we do not find a continuous scaling law, but rather scaling exponents that increase as the length of the polymer increases. Finally, we investigate the scaling behavior of translocation time versus applied voltage for different polymer and pore lengths. For long pores, we obtain the theoretical scaling law of τ ～ 1/V(α), where α ? 1 for all voltages and polymer lengths. For short pores, we find that α decreases for very large voltages and/or small polymer lengths, indicating that the value of α = 1 is not universal. The results of our simulations are discussed in the context of experimental measurements made under different conditions and with differing pore geometries.     

Using light and a molecular switch to 'lock' and 'unlock' the Diels-Alder reaction

Light is used to 'gate' the Diels-Alder reaction using a photoresponsive dithienylfuran backbone and turn the reversibility of the Diels-Alder reaction 'off' and 'on' at 100 °C. These features make the reported system an excellent candidate for developing the next generation of self-healing polymers and photothermal drug delivery vehicles.     

Acidic ionic liquids catalyst in homo and graft polymerization of ε-caprolactone

Biodegradable polycaprolactone was prepared by ring-opening polymerization in presence of ionic liquids as efficient, inexpensive, nontoxic, and easily handled acid catalysts. The resulting polymer exhibited good yield and inherent viscosity between 0.10 and 0.18 dL/g. The chemical structure of obtained polymer was verified by the ¹H-NMR and Fourier transform infrared spectroscopy (FT-IR) spectra. In continuation, the obtained polymer was applied to improve quality level and mechanical properties and also to reduce the hydrophilic properties of the starch, so the ring-opening polymerization of ε-caprolactone was investigated in the presence of starch hydroxyl groups as initiator and ionic liquid as catalyst. The obtained starch-grafted-polycaprolactone was verified by ¹H-NMR, FT-IR spectra, and field emission scanning electron microscopy analysis.     

Directed Evolution of a Soluble Human IL-17A Receptor for the Inhibition of Psoriasis Plaque Formation in a Mouse Model

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Highlights? IL-17 is involved in many inflammatory diseases ? Directed evolution of IL-17A receptor results in improved IL-17A affinity ? The engineered receptors efficiently inhibit IL-17A induced cytokine secretion ? Engineered receptor promotes the recovery of psoriasis plaques in mouse model     

Application of artificial neural networks for formulation and modeling of dye adsorption onto multiwalled carbon nanotubes

In this study, an artificial neural network (ANN) has been developed to predict the adsorption amount of dye (methylene blue) onto multiwalled carbon nanotubes. Batch experiments have been carried out to obtain experimental data. Important parameters in the adsorption system such as initial dye concentration, adsorbent dosage, temperature, pH and contact time have been used as the inputs of the network, while the output is the final concentration of dye in aqueous solution after adsorption. The neural network structure has been optimized by testing various training algorithms and different number of neurons in a hidden layer. An empirical equation for determination of final dye concentration in aqueous solutions after adsorption has been developed by using the weights of the optimized network. The results of the optimized ANN have been compared with conventional models in equilibrium and kinetic fields. According to error analysis and determination coefficient, the ANN was found to be the most appropriate model to describe this adsorption process. Sensitivity analysis showed that initial dye concentration, pH and contact time are the most effective parameters in this process. The influence percentages of these parameters on the output were 28, 24 and 24 %, respectively.