SALS,WAXS and mechanical properties of heat‐treated thermotropic polymers

The influence of heat treatment on the texture, microstructure and tensile mechanical properties of extruded thin films of a series of high‐performance thermotropic liquid crystal polymers (LCPs) was investigated. LCPs based on random units of hydroxybenzoic acid (B), hydroxynaphthoic acid (N), terephthalic acid (TA) and biphenol (BP) were kindly supplied by the former Hoechst Celanese Corp as 50 µm thick extruded tapes. The LCPs, denoted B‐N, COTBP and RD1000, have B and N as common comonomers and vary the other comonomers. Thus, this study also enables the investigation of the influence of monomer composition on microstructure and mechanical properties. Heat treatments were carried out at temperatures close to the solid‐to‐nematic transition (T_s→n) for periods up to 5 h, under dry air conditions. The thermal treatment produced either two endotherms or a small increase of T_s→n (B‐N and RD1000), or increased significantly T_s→n (COTBP). Moreover, when heat treatment was carried out approximately 40°C below the respective T_s→n, the mechanical Young's modulus, E, along the extrusion axis, increased for all LCPs. Strikingly, for COTBP, E increased over 100% relative to the as‐extruded film. The results also showed that the optimum treatment time for improving the Young modulus, under dry air atmosphere, was between 3 and 4 h. Wide‐angle X‐ray scattering showed a significant sharpening of crystalline reflections and concentration of the 002 meridional reflection as a result of thermal treatment, suggesting the elimination of defects and a better alignment of the molecular chains along the extrusion axis. This would explain the increase in tensile modulus. Copyright © 2013 John Wiley & Sons, Ltd.     

Gas-phase halonium metathesis and its competitors. Skeletal rearrangements of cationic adducts of saturated ketones

The methyl cation and CF(3)(+) attack saturated, acyclic ketones to make vibrationally excited adduct ions. Despite their high internal energies and short lifetimes, these adducts undergo deep-seated rearrangements that parallel slower processes in solution. Observed pathways include alkene and alkane expulsions, in addition to (in the case of CF(3)(+)) the precedented loss of CF(2)O + HF. For the vast majority of ketones, the principal charged products are the CF(3)(+) adducts of lighter carbonyl compounds, ions that are not easily prepared by other avenues. Evidence for ion structures comes from collisionally activated unimolecular decomposition and bimolecular ion-molecule reactions. Typical examples are di-n-propyl and diisopropyl ketones (both of which produce CH(3)CH=OCF(3)(+) as the principal ion-molecule reaction product) and pentamethylacetone (which produces (CH(3))(2)C=OCF(3)(+) as virtually the sole ion-molecule reaction product). Isotopic labeling experiments account for mechanisms, and DFT calculations provide a qualitative explanation for the relative abundances of products from unimolecular decompositions of the chemically activated CF(3)(+) adduct ions that are initially formed.     

Electrochemical synthesis of π-indenyl-π-(3)-1,2-dicarbollyliron(III)

Co-electrolysis of potassium 1,2-dicarbadodecahydroundecaborate and indene in 0.1N sodium bromide solution in dimethylsulfoxide using iron electrodes afforded -indenyl--(3)-1,2-dicarbollyliron(III).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 764–765, April, 1993.     

Properties of matrix-assisted laser desorption. Measurements with a time-to-digital converter.

Some properties of matrix-assisted laser desorption have been studied using single-ion-counting methods and a time-to-digital converter. The methods allow examination of the process for irradiances near the reported threshold for observation with a transient recorder. All measurements were made using bovine insulin as a test compound. We present direct evidence that an irradiance threshold near 10(6) W cm-2 exists for ion production, and that the process is a collective effect, either involving a large number of molecular ions (approximately 10(4) in a successful event or none at all. Above the threshold, the yield is found to scale with a high power (4th to 6th) of the irradiance. Measurements of initial velocity distributions indicate an axial velocity spread corresponding to approximately 50 eV and a radial velocity spread corresponding to approximately 2.4 eV. Thus the ejection or extraction mechanism appears to be strongly asymmetric.     

Optimal Production of a <Emphasis Type="Italic">Rhodococcus erythropolis</Emphasis> ATCC 4277 Biocatalyst for Biodesulfurization and Biodenitrogenation Applications

Rhodococcus sp. has a broad catabolic diversity and unique enzymatic capabilities, and it is able to adapt under extreme conditions. Thereby, the production of this remarkable bacterium has a great biotechnological and industrial importance. In this sense, we sought to improve the R. erythropolis ATCC 4277 growth through a central composite design, by varying the components of nutrient medium (glucose, malt extract, yeast extract, CaCO₃), temperature, and agitation. It was found that the concentrations of glucose and malt extract are not statistically significant, being reduced of 4.0 and 10.0 g L^-1 to 2.0 and 5.0 g L^?1, respectively. The CaCO₃ concentration and temperature were also diminished of 2.0 to 1.16 g L^?1and 28 to 23.7 °C, respectively. Optimal growth conditions provided a 240% increase in final biomass concentration, an increment in specific growth rate, and a growth yield coefficient about five times greater. Application of the optimal conditions in biodesulfurization and biodenitrogenation processes showed that desulfurization capability is not associated with optimal growth conditions; however, it was achieved a 47% of nitrogen removal in the assay containing 10% (w/w) of heavy gas oil.

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Über die Koexistenz von tetragonalem und monoklinem CaC2: Strukturelle und spektroskopische Untersuchungen an Erdalkalimetallacetyliden,MC2 (M = Ca,Sr, Ba)

On the Coexistence of Tetragonal and Monoclinic CaC₂: Structural and Spectroscopic Studies on Alkaline Earth Metal Acetylides, MC₂ (M = Ca, Sr, Ba) The alkaline earth acetylides CaC₂, SrC₂ and BaC₂ can be considered to occur in three polymorphic structures each. The monoclinic low-temperature form, the tetragonal form, and the cubic high-temperature form. No deviation from axial symmetry is obtained for the C₂^2– ions in the tetragonal structure determinations, as confirmed by X-ray single-crystal structures and ¹³C MAS NMR studies. The CaC₂ samples prepared by us were always a mixture of monoclinic and tetragonal phase. Their Raman spectra exhibited two distinct C₂ streching vibrations. Problems arising from the coexistence of these two phases for the interpretation of ¹³C MAS NMR spectra are discussed.     

Antihydrophobic cosolvent effects in organic displacement reactions

[formula: see text] Rates of reactions in water can be modified by the presence of antihydrophobic cosolvents such as ethanol and DMSO, which lower the energies of nonpolar surfaces. The rate effects reflect changes both in the solvation of nonpolar surfaces and also in the solvation of polar groups. The effects have been sorted out for some displacement reactions, revealing the geometry of an interesting branching reaction whose two paths show different antihydrophobic effects.     

Electrochemiluminescence Bioassays with a Water‐Soluble Luminol Derivative Can Outperform Fluorescence Assays

The most efficient and commonly used electrochemiluminescence (ECL) emitters are luminol, [Ru(bpy)₃]²⁺, and derivatives thereof. Luminol stands out due to its low excitation potential, but applications are limited by its insolubility under physiological conditions. The water‐soluble m‐carboxy luminol was synthesized in 15 % yield and exhibited high solubility under physiological conditions and afforded a four‐fold ECL signal increase (vs. luminol). Entrapment in DNA‐tagged liposomes enabled a DNA assay with a detection limit of 3.2 pmol L^?1, which is 150 times lower than the corresponding fluorescence approach. This remarkable sensitivity gain and the low excitation potential establish m‐carboxy luminol as a superior ECL probe with direct relevance to chemiluminescence and enzymatic bioanalytical approaches.