Use of the successive self-nucleation and annealing technique to characterize <Superscript>60</Superscript>Co gamma irradiated HDPEs

The application of the Successive Self-nucleation and Annealing (SSA) thermal fractionation technique can yield detailed information of the structural changes induced in linear polyethylene by irradiation. The production of tertiary carbons during the crosslinking reactions can be equivalent to the structural heterogeneity present in branched polyethylenes since in both cases interruption of the linear crystallizable sequences occurs, and these are structural differences that can be easily detected by thermal fractionation. We demonstrate how correlations between melting point and short chain branching content employed for branched polymers can be useful to characterize the distribution of chain heterogeneity produced by crosslinking. As the radiation dose is increased and the crosslinking content also increases, the distribution of chain heterogeneity gets broader as detected by SSA. When the results are coupled with morphological observations made by transmission electron microscopy, valuable information on the morphological changes produced by crosslinking can also be ascertained, since the distribution of lamellar thicknesses substantially broadens with crosslinking. Such a broad distribution can also be predicted from SSA by simple calculations performed employing a modified version of the Gibbs–Thomson equation and is expected on the basis of random crosslinking reactions.     

Synthesis of cis- and trans-3-aminocyclohexanols by reduction of β-enaminoketones

We describe a protocol developed for the preparation of β-enaminoketones derived from 1,3-cyclohexanediones, and their subsequent reduction by sodium in THF-isopropyl alcohol to afford cis- and trans-3-aminocyclohexanols.     

Liquid-crystalline hybrid materials based on [60]fullerene and bent-core structures

What a core-ker! By the appropriate combination of promesogenic bent-core structures and the C(60) unit, lamellar polar liquid-crystal phases were induced. The supramolecular organization of the functional fullerene-based assemblies, the temperature range of the soft phase, the stabilization of the mesophase-like order at room temperature, and the molecular switching under an electric field can be tuned, depending on the molecular structure.     

Annulation of primary amines to piperazines and diazaspirocycles utilizing alpha-methyl benzyl resin

The microwave-assisted solid-phase synthesis of piperazines, 3,9-diazaspiro[5.5]undecanes and 2,9-diazaspiro[5.5]undecanes is reported. The synthesis relies on the direct annulation of primary amines with resin-bound bismesylates. Critical to the success of this chemistry was the development of alpha-methyl benzyl carbamate resin linker. This resin permits the cleavage of the heterocycles under mildly acidic conditions, free of contaminating linker-derived N-alkylated byproducts.     

Weak continuity of Riemann integrable functions in Lebesgue-Bochner spaces

In general, Banach space-valued Riemann integrable functions defined on [0, 1] （equipped with the Lebesgue measure） need not be weakly continuous almost everywhere. A Banach space is said to have the weak Lebesgue property if every Riemann integrable function taking values in it is weakly continuous almost everywhere. In this paper we discuss this property for the Banach space LX^1 of all Bochner integrable functions from [0, 1] to the Banach space X. We show that LX^1 has the weak Lebesgue property whenever X has the Radon-Nikodym property and X＊ is separable. This generalizes the result by Chonghu Wang and Kang Wan [Rocky Mountain J. Math., 31（2）, 697-703 （2001）] that L^1[0, 1] has the weak Lebesgue property.     

Improved Thermal and Reusability Properties of Xylanase by Genipin Cross-Linking to Magnetic Chitosan Particles

Enzymes are gradually increasingly preferred over chemical processes, but commercial enzyme applications remain limited due to their low stability and low product recovery, so the application of an immobilization technique is required for repeated use. The aims of this work were to produce stable enzyme complexes of cross-linked xylanase on magnetic chitosan, to describe some characteristics of these complexes, and to evaluate the thermal stability of the immobilized enzyme and its reusability. A xylanase was cross-linked to magnetite particles prepared by in situ co-precipitation of iron salts in a chitosan template. The effect of temperature, pH, kinetic parameters, and reusability on free and immobilized xylanase was evaluated. Magnetization, morphology, size, structural change, and thermal behavior of immobilized enzyme were described. 1.0?±?0.1 μg of xylanase was immobilized per milligram of superparamagnetic chitosan nanoparticles via covalent bonds formed with genipin. Immobilized xylanase showed thermal, pH, and catalytic velocity improvement compared to the free enzyme and can be reused three times. Heterogeneous aggregates of 254 nm were obtained after enzyme immobilization. The immobilization protocol used in this work was successful in retaining enzyme thermal stability and could be important in using natural compounds such as Fe₃O₄@Chitosan@Xylanase in the harsh temperature condition of relevant industries.

     

Voltammetric Electronic Tongue Based on Carbon Paste Electrodes Modified with Biochar for Phenolic Compounds Stripping Detection

Biochar is a charcoal produced from the biomass pyrolysis process that presents a highly porous and functionalized surface. In the present work an array of carbon paste electrodes (CPE) made of different forms of carbon (graphite, carbon nanotubes and activated biochar) was evaluated in the development of an electronic tongue for discrimination and stripping voltammetric determination of catechol (CAT), 4‐ethylcatechol (4‐EC) and 4‐ethylguaiacol (4‐EG) phenolic compounds. Morphological characterization of carbon materials and electrodes surfaces was performed by scanning electron microscopy (SEM) and semi‐quantitative elemental composition by energy dispersive spectroscopy (EDS). Electrochemical Impedance Spectroscopy (EIS) measurements were used for electrochemical characterization of electrodes. Cyclic voltammetry measurements were performed for the phenolic compounds evaluated using different concentrations. Principal component analysis (PCA) was performed to evaluate the qualitative analysis. Quantitative data modeling was done using artificial neural networks (ANN). The proposed sensor array presented analytical potentiality allowing the distinction and determination of CAT, 4‐EC and 4‐EG by using chemometric processing. The method showed sensibility, reproducibility and a good linearity (R²>0.9940) for three compounds evaluated. Spontaneous preconcentration of three compounds was possible using all three sensors, which can allow the application of these as passive samplers for remote determinations of phenolic compounds in wine and food samples.     

Developmental gametophyte morphology of seven species of Thelypteris subg. Cyclosorus (Thelypteridaceae)

The morphogenesis of the sexual phase of seven species of Thelypteris subg. Cyclosorus (Thelypteridaceae) is described and compared. Spores of all species are monolete, ellipsoid and have positive photoblastism. They have Vittaria-type germination, germinal filaments are short and uniseriate, and Aspidium-type development. Adult gametophytes are spatulate-cordiform, and have wide wings with numerous glandular, marginal and superficial hairs. Antheridia have a narrow or widened basal cell, an undivided annular cell, and an opercular cell; antherozoids are liberated through three mechanisms. Archegonia have short necks and four triangular cells on the neck's mouth. The sporophyte's first leaf is lobed, with open dichotomous veins, glandular hairs similar to those of the gametophyte, and anomocytic stomata. Differences observed between the studied species are: spore size; ornamentation of the perispore; germination and emergence periods; size of hairs; developmental period of gametangia; and antherozoid liberation mechanisms through total detachment of the operculum, partial detachment of the operculum, and development of an apical pore through tearing of the operculum. These taxonomically valuable characters, combined with the sporophyte characteristics, can be useful tools in the identification of the species studied to the subg. Cyclosorus.     

Swendsen‐Wang dynamics for general graphs in the tree uniqueness region

The Swendsen‐Wang (SW) dynamics is a popular Markov chain for sampling from the Gibbs distribution for the ferromagnetic Ising model on a graph G = (V,E). The dynamics is conjectured to converge to equilibrium in O(|V|^1/4) steps at any (inverse) temperature β, yet there are few results providing o(|V|) upper bounds. We prove fast convergence of the SW dynamics on general graphs in the tree uniqueness region. In particular, when β < β_c(d) where β_c(d) denotes the uniqueness/nonuniqueness threshold on infinite d‐regular trees, we prove that the relaxation time (i.e., the inverse spectral gap) of the SW dynamics is Θ(1) on any graph of maximum degree d ≥ 3. Our proof utilizes a monotone version of the SW dynamics which only updates isolated vertices. We establish that this variant of the SW dynamics has mixing time and relaxation time Θ(1) on any graph of maximum degree d for all β < β_c(d). Our proof technology can be applied to general monotone Markov chains, including for example the heat‐bath block dynamics, for which we obtain new tight mixing time bounds.     

Determination of lead in complex sample matrices by atomic fluorescence spectrometry: optimisation of online hydride generation

Lead hydride or plumbane (PbH₄) generation was optimised by exploiting a simple flow-injection method coupled to atomic fluorescence spectrometry (HG-AFS), and allowing ultra-trace lead determination. Plumbane was generated through two methods: (1) 5% (v/v) H₂O₂ was employed as oxidant with 1.5% (m/v) KBH₄ as a reducing agent and 1.5% (v/v) HCl solution; (2) with 1.5% (m/v) K₃[Fe(CN)₆] as an oxidant/sensitiser, 1% (m/v) KBH₄ as a reducing agent and 1.5% (v/v) HCl. Variables such as reagent concentrations, flow rates and sample and reagent volumes were tested and critically compared. The best results were obtained with potassium ferricyanide K₃[Fe(CN)₆], achieving a detection limit of 0.03 μg Pb L^?1 and a relative standard deviation (RSD) of 1.1%. The selected method was validated by analysis of certified reference materials such as SRM-2976 (mussel tissue) and BCR-610 (groundwater), with good agreement with the certified values. The developed methodology was successfully applied to different environmental sample matrices, such as rain water, tap water, ground water, spring water and drinking water, and biological samples, i.e., human blood, plasma and serum.