Effect of ZnO nanoparticles on kinetics of thermal degradation and final properties of ethylene–propylene–diene rubber systems

The morphology, thermal degradation behavior in addition to static and dynamic mechanical properties of various ethylene?Cpropylene?Cdiene (EPDM) rubber compounds containing nano-zinc oxide (NZnO) were investigated compared to those of EPDM with ordinary-sized ZnO (OSZnO). The field-emission scanning electron microscopy studies showed that unlike the conventional system, the formation of large size ZnO agglomerates was discouraged for NZnO filled systems. Thermogravimetric analysis (TG) revealed that the thermal degradation of EPDM system was delayed upon the inclusion of NZnO instead of OSZnO in the compound. The kinetic analysis of TG data based on Friedman and Kissinger methods showed that the nanocomposite samples exhibited higher activation energy (E _a ) and lower order of reaction (n) over the conventional system, suggesting the enhancement of thermal stability upon decreasing ZnO particle size. The results obtained from dynamic mechanical analysis and static mechanical characterizations in terms of hardness, resilience, and abrasion tests interestingly indicated that NZnO not merely could act as a thermal insulator, but also could perform as a nano-filler to improve the final performance of EPDM elastomers.     

A redox-reconfigurable, ambidextrous asymmetric catalyst

A redox-reconfigurable catalyst derived from L-methionine and incorporating catalytic urea groups has been synthesized. This copper complex catalyzes the enantioselective addition of diethyl malonate to trans-β-nitrostyrene. Either enantiomer of the product can be predetermined by selection of the oxidation state of the copper ion. Enantiomeric excesses of up to 72% (S) and 70% (R) were obtained in acetonitrile. The ability of the catalyst to invert enantiomeric preference was reproduced with several different solvents and bases. Facile interconversion between the Cu(2+) and Cu(+) redox states allowed easy access to both active helical forms of the complex and, therefore, dial-in enantioselectivity.     

Structural and co-conformational effects of alkyne-derived subunits in charged donor-acceptor [2]catenanes

Four donor-acceptor [2]catenanes with cyclobis(paraquat-p-phenylene) (CBPQT4+) as the pi-electron-accepting cyclophane and 1,5-dioxynaphthalene (DNP)-containing macrocyclic polyethers as pi-electron donor rings have been synthesized under mild conditions, employing Cu+-catalyzed Huisgen 1,3-dipolar cycloaddition and Cu2+-mediated Eglinton coupling in the final steps of their syntheses. Oligoether chains carrying terminal alkynes or azides were used as the key structural features in template-directed cyclizations of [2]pseudorotaxanes to give the [2]catenanes. Both reactions proceed well with precursors of appropriate oligoether chain lengths but fail when there are only three oxygen atoms in the oligoether chains between the DNP units and the reactive functional groups. The solid-state structures of the donor-acceptor [2]catenanes confirm their mechanically interlocked nature, stabilized by [pi...pi], [C-H...pi], and [C-H...Omicron] interactions, and point to secondary noncovalent contacts between 1,3-butadiyne and 1,2,3-triazole subunits and one of the bipyridinum units of the CBPQT4+ ring. These contacts are characterized by the roughly parallel orientation of the inner bipyridinium ring system and the 1,2,3-triazole and 1,3-butadiyne units, as well as by the short [pi...pi] distances of 3.50 and 3.60 A, respectively. Variable-temperature 1H NMR spectroscopy has been used to identify and quantify the barriers to the conformationally and co-conformationally dynamic processes. The former include the rotations of the phenylene and the bipyridinium ring systems around their substituent axes, whereas the latter are confined to the circumrotation of the CBPQT4+ ring around the DNP binding site. The barriers for the three processes were found to be successively 14.4, 14.5-17.5, and 13.1-15.8 kcal mol-1. Within the limitations of the small dataset investigated, emergent trends in the barrier heights can be recognized: the values decrease with the increasing size of the pi-electron-donating macrocycle and tend to be lower in the sterically less encumbered series of [2]catenanes containing the 1,3-butadiyne moiety.     

Synthesis and characterization of functionalized NaP Zeolite@CoFe2O4 hybrid materials: a micro–meso-structure catalyst for aldol condensation

Research on Chemical Intermediates - In this work, magnetic nanocomposite of NaP Zeolite and CoFe2O4 as magnetic nanoparticles (MNP’s) with different ratios were prepared and in the second...     

Transition metal-based chiroptical switches for nanoscale electronics and sensors

Efficient metal-based chiroptical switches have been designed that are capable of achieving multiple stable and reversible states. Studies in this field have yielded a variety of complex molecular devices whose conformations are controllable by many triggering mechanisms including pressure, solvent, counter ion, redox state, and photoinduction. Many of the systems are monitored with precision using circular dichroism spectroscopy. This review aims to provide a brief background of the development of these systems and a comprehensive overview of recently developed metal-based chiroptical switches. Potential applications in electronics and sensor technologies are discussed.     

Preparation of N-alkylated 5-oxo-3-carboxamyl-1,4-thiazinanes on solid support

A general method was developed to generate six-membered cyclic thiazinanes on solid support. Three diversity sites were introduced into this scaffold using primary amines, aldehydes, and 2-bromoalkanoic acids. The methodology to prepare individual cyclic thiazinanes as well as combinatorial libraries of these compounds is described.     

Enantioselective photodeconjugation of α,β-unsaturated esters in the presence of catalytic amounts of a chiral-inducing entity

In the presence of (-) ephedrine in small quantities, the photodeconjugation of α,β-unsaturated esters is enantioselective and produces the R-enantiomer with an enantiomeric excess of up to 18%.     

Effect of polyethylene glycol on sulfonated polyether imide (SPEI) for fuel cell applications

The sulfonated polyetherimide (sPEI) was synthesized by direct sulfonation method using chlorosulfonic acid as a sulfonating agent. Different sulfonation degrees of sPEI was obtained by varying the ratio of PEI to chlorosulfonic acid and reaction time. Then, sulfonated polyetherimide was blended with polyethylene glycol (PEG) and thermally cross-linked in order to achieve high performance proton exchange membrane. It was found that the addition of PEG resulted in a significant increase in porosity and water uptake of the membranes, which favored proton transport at low temperature. The maximum proton conductivity was 11 mS/cm at 75°C for the blend membrane containing 20% PEG. The sulfonation and blend modification of PEI were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy.     

Cyclobis(paraquat-p-phenylene)-based [2]catenanes prepared by kinetically controlled reactions involving alkynes

[reaction: see text] Charged donor-acceptor [2]catenanes, in which the pi-accepting cyclobis(paraquat-p-phenylene) acts as a tetracationic template for the threading-followed-by-clipping of acyclic oligoethers, incorporating centrally a pi-donating 1,5-dioxynaphthalene ring system and terminated either by acetylene units or by acetylene and azide functions, are the products of copper-mediated Eglinton coupling and Huisgen 1,3-dipolar cycloaddition, respectively.     

Enantioselective photodeconjugation of conjugated lactones induced by small amounts of a chiral inductor

In the presence of small amounts of (?) ephedrine, photodeconjugation of conjugated lactones is enantioselective. The enantiomeric excess which depends on the structure of the starting material and on the temperature of the reaction medium can be up to 25%.