Ouroboros: Heterocycles closed by dative σ bonds and stabilized by π delocalization

Heteroarenes such as (aza and oxa)borines are increasingly important as synthetic targets and reagents. We map the intramolecular cyclization of saturated heterocyclic chains through dative bonding. A related set of planar unsaturated aza-, oxa-, and fluora-rings that feature dative σ bonding enhanced by π delocalization are identified. The systems have, in general, the formulae A′(CH₂)_mD′ and A′(CH)_mD′, where m?=?3 and 4, and A′ and D′ are acceptor and donor sites, respectively. In each case, the ring isomers, achievable via A′←D' internal coordination (in the manner of Kekulé’s ouroboros), are more stable than chains. Unsaturated aromatic rings examined herein include a oxadiborine with a hypervalent oxygen center and a dioxadiborine. They are isoelectronic with an azaborine, which was synthesized more recently, and benzene.     

Catalysis by Using TiO_2 Nanoparticles and Nanotubes

TiO2 has attracted considerable attention due to its stability, non-toxicity, low cost, and great potential for use as a photocatalyst in environmental applications. Since strong metal-support interaction (SMSI) of titania-supported noble metals was first reported in 1978, titania supported catalyst has been intensively studied in heterogeneous catalysis. However, the effective catalytic activity was restricted due to the low surface area of TiO2. Recently, TiO2-based nanotubes were extens…     

β-Cyclodextrin production by simultaneous fermentation and cyclization

Production of β-cyclodextrin (CD) with high-dextrose equivalent (DE) starch hydrolysates by simultaneous fermentation and cyclization (SFC) gives higher yields than using only the enzyme CGTase, because fermentation eliminates glucose and maltose that inhibit CD production, while at the same time, produces ethanol that increases yield. A 10% (w/v) solution of cassava starch, liquefied with α-amylase, was incubated with CGTase using: only the enzyme, added ethanol (from 1 to 5%), and added yeast,S. cerevisiae (12% w/v), plus nutrients, the latter being the SFC process. Reaction conditions were: 38αC, pH 6.0, DE from 2 to 25, and 3.3 mL of CGTase/L. The yield of β-CD has decreased with an increase in DE, and maximum reaction yields were found for DE equal to 3.54, reaching 5.6, 14.7, and 11.5 mM β-CD, respectively. For an increase of DE, of approx 6 times (from 3.54 to 23.79), β-CD yield decreased 6 times for the first, and second reaction media with 3% (v/v) ethanol, and only approx 3 times for SFC (from 11.5 to 3.73 mM), showing that this process is less sensitive to variations in the DE     

Synthesis and Characterization of Zirconia Nanocrystallites by Cationic Surfactant and Anionic Surfactant

1 INTRODUCTION Zirconia is a kind of metallic oxide with high mel- ting point. It is highly corrosion-resistant for acid fu- sant and neutral fusant, thus it can be used as refrac- tory material, and it can also be utilized as acid acy- loxy bi-functional catalystic material owing to hav- ing both acid and alkali surface centers[1]. Moreover, zirconia has superior ion-exchange capacity as well as chemical and mechanical stability, therefore, it can also be applied as a catalyst carrier. …     

Sampling of benzene in environmental and exhaled air by solid-phase microextraction and analysis by gas chromatography–mass spectrometry

Benzene is classified as a Group I carcinogen by the International Agency for Research on Cancer (IARC). The risk assessment for benzene can be performed by monitoring environmental and occupational air, as well as biological monitoring through biomarkers. The present work developed and validated methods for benzene analysis by GC/MS using SPME as the sampling technique for ambient air and breath. The results of the analysis of air in parks and avenues demonstrated a significant difference, with average values of 4.05 and 18.26 μg m⁻³, respectively, for benzene. Sampling of air in the occupational environment furnished an average of 3.41 and 39.81 μg m⁻³. Moreover, the correlations between ambient air and expired air showed a significant tendency to linearity (R ² = 0.850 and R ² = 0.879). The results obtained for two groups of employees (31.91 and 72.62 μg m⁻³) presented the same trend as that from the analysis of environmental air.     

Studies of Self-assembled Monolayers Formed by Imidazoline on Iron Surface by SEM and SECM

Self-assembled monolayers (SAMs) formed from organic substances can improve the inhibition of metal corrosion, because uniform and closely packed films formed on the metal surface providing an insulating layer1, 2. SAMs on the iron surface are studied so far because iron is one active metal which is easily corroded in the air. In this paper, SECM and SEM have successfully been applied in the study of SAMs inhibition corrosion for iron. SECM has been used to study the electrochemically a…     

Complexation of inorganic anions by β-cyclodextrin studied by polarography and 1H NMR

Abstract

Complexation of o-chloronitrobenzene with β-cyclodextrin has been studied in 0.1 M aqueous solutions containing PF₆ ^?, ClO₄ ^?, C₂O₄ ^2-, SCN^?, SO₄ ^2- and F^? anions by a polarographic method. Using an equation which takes account of the change in the cyclodextrin concentration due to the simultaneous complexation of the anion, both stability constants have been calculated. Interaction of the ClO₄ ^? anion with β-cyclodextrin has been confirmed by ¹H NMR techniques. It has been found that the ClO₄ ^? anion is trapped in the β-cyclodextrin cavity. The stability constant has been calculated. Results of polarographic and ¹H NMR studies have been compared.     

Ethylene–Norbornene Copolymerization by Rare-Earth Metal Complexes and by Carbon Nanotube-Supported Metallocene Catalysis

E–N copolymerization with a number of half-sandwich rare-earth metal compounds [M(η5-C₅Me₄SiMe₂R)(η1-CH₂SiMe₃)₂(L)] (M = Sc, Y, Lu) has been achieved. Mainly atactic alternating E N copolymers are obtained with all catalytic systems. Interestingly, copolymers arising from [Sc(η5-C₅Me₄SiMe₂C₆F₅)(η¹-CH₂SiMe₃)₂(THF)]/[/[Ph₃C][B(C₆F₅)₄] possess narrower molar mass distributions than those from [Sc(η⁵-C₅Me₄SiMe₃)(η¹-CH₂SiMe₃)₂(THF)] / [Ph₃C][B(C₆F₅)₄]. In addition, homogeneous surface coating of multi-walled carbon nanotubes is accomplished for the first time by in situ E–N copolymerization as catalyzed by rac-Et(Ind)₂ZrCl₂/MMAO-3A anchored onto the carbon nanotube surface. The copolymerization reaction allows for the destructuration of the native nanotube bundles. The relative quantity of E N copolymer can be tuned up as well as the norbornene content in the formed copolymers and accordingly their glass transition temperature. By melt blending with an ethylene-vinyl-co-acetate copolymer (27 wt.-% vinyl acetate comonomer) matrix, high performance polyolefinic nanocomposites are obtained.     

Studies of Self-assembled Monolayers Formed by Imidazofine on Iron Surface by SEM and SECM

The self-assembled monolayers （SAMs） of imidazoline （IM） on the iron surface were characterized by scanning electron microscope （SEM） and scanning electrochemical microscopy （SECM）. The results showed that SAMs were an effective inhibition film for iron.     

Identification and Determination of Nicorandil and its Degradation Products by HPLC and GC/MS

Nicorandil [N-(2-hydroxyethyl)-nicotinamide nitrate NIC] is a novel kind of compound in the treatment of angina pectoris. NIC can be degraded easily in storage. The degradation products include N-(2-hydroxyethy) nicotinamide (HN), nitrate ion (NI), and ni…     

LiFe5O8 prepared by sol–gel synthesis: microstructural and morphological effects by organic and inorganic templates

Lithium ferrite was prepared using a sol–gel growth process using different fuels and inorganic templates. The aim of this study is to evaluate the influence of inorganic template agent like KCl, KBr and KI as well as the effect of different fuels like urea, glycine and citric acid on the morphology change of lithium ferrite. The structure, morphology and magnetic properties of the ferrite were investigated using powder X-ray diffraction (XRD), Infrared red spectroscopy and vibrating sample magnetometer. Thermal decomposition studies reveal the formation of lithium ferrite at a low temperature ~440 °C. Powder XRD pattern has shown the formation of a single α-phase lithium ferrite except the sample with inorganic template KBr, in which the presence of hematite as a secondary phase was observed. Scanning electron microscopy studies show that the structural morphology is highly sensitive to the inorganic template as well as on the fuel. The rod shaped nanoparticles are observed with the inorganic template KCl and KBr. The decrease in grain size is observed for LiFe₅O₈/glycine as compared to LiFe₅O₈/citric acid and flake shaped dense particles are observed for LiFe₅O₈/urea. The magnetic properties of the ferrite have also been investigated.     

Structure and Properties of β-Polypropylene Reinforced by Polypropylene Fiber and Polyamide Fiber

Matrix/fiber composites of β-form isotactic polypropylene(iPP) matrix and α-iPP or PA6 fibers were prepared by laminating technique under different preparation temperatures. The mechanical properties and interfacial morphologies of these composites were studied by tensile test, optical microscopy and scanning electron microscopy, respectively. The experimental results show that the tensile yield load and tensile modulus of β-iPP/PA6 matrix/fiber systems increased significantly at the expense of elongation at break. These mechanical properties show essentially no dependence on the sample preparation temperature. On the other hand, the mechanical properties of iPP matrix/fiber single polymer composites depend strongly on the sample preparation temperature. At low sample preparation temperature, e.g., 172 ℃, the solid α-iPP fiber induces α-iPP crystallization, leading to the formation of α-iPP transcrystalline layer around the fiber. This results in a remarkable increment of the tensile yield load and tensile modulus. The elongation at break is also much better than that of the iPP/PA6 matrix/fiber system. It reflects a better interfacial adhesion of the single polymer composite compared with the iPP/PA6 composite. At higher sample preparation temperature, e.g., 174 ℃ or 176 ℃, the partial surface melting of the oriented fiber allows interdiffusion of iPP molecular chains in the molten fiber and matrix melt. The penetration of matrix chains into the molten iPP fiber results in some iPP molecular chains being included partially in the recrystallized fiber and the induced β-transcrystalline layers. This kind of configuration leads to an improvement of interfacial adhesion between the fiber and matrix, which causes a simultaneous increase of the tensile yield load, tensile modulus and elongation at break of β-iPP.     

Stabilize and Reinforce Hydrogen-Bonded Polymer Complex Elastic Fiber by Catechol Chemistry and Coordination

Hydrogen-bonded polymer complex fiber of poly(ethylene oxide)(PEO) and poly(acrylic acid)(PAA) shows rubber elasticity in ambient environment, but the fiber has relatively low strength and weak stability. We apply the catechol chemistry and metal coordination to stabilize and strengthen the PEO/PAA fiber. PAA is grafted with dopamine(Dopa), and then combines with PEO to prepare fiber. PAA-Dopa in the fiber is cross-linked through oxidation induced dismutation and the metal ions are introduced th...     

Radiation polymerization and copolymerization of fluorinated acrylates and methacrylates induced by γ-rays

Fluorinated acrylates and methacrylates radiolyzed at 77 K polymerize upon heating in the range from the glass-transition to the melting temperature. In the case of acrylates, the temperature range of postradiation polymerization increases by more than 100 K with the increasing chain length of the perfluorinated substituent from C₂F₄ to C₈F₁₇. The introduction of perfluorinated substituents into methacrylate molecules makes it possible to obtain them in the glassy state and to carry out low-temperature postradiation polymerization, in contrast to their hydrocarbon analogues. The termination rate constant of the polymerization of fluorinated methacrylates has a lower value as compared to conventional methacrylates. The formation of crosslinked structures is suppressed during the copolymerization of fluorinated acrylates with methacrylates. The ESR spectra of growing polymer radicals of fluorinated acrylic ∼CH₂C^·H(COOCH₂C₆F₁₃)∼ and methacrylic CH₂C^·(CH₃)(COOCH₂C₂F₄H)∼ monomers have been identified.     

Facile and practical synthesis of π-extended oxepins by benzannulation and intramolecular cyclization

π-Extended oxepins 1 and dimer 8 were synthesized by the benzannulation of the corresponding asymmetric diarylacetylene derivatives and 2-(phenylethynyl)benzaldehyde followed by the Cu-catalyzed intramolecular cyclization. The optical properties of the π-extended oxepins 1 and 8 are also investigated.     

Determination of Magnolol and Honokiol by Non-aqueous Capillary Electrophoresis

Introduction Capillaryelectrophoresis(CE),ahighefficiency separationtechnique,hasrapidlydevelopedsince1981[1].Notonlyhavedifferentmodesbeenrepor ted[1—3],butalsosomenon aqueouselectrophoresis media[4]havebeenapplied.Theimportantproperties ofnonaqueousmed…     

Mechanism of membrane interaction and disruption by α-synuclein

Parkinson's disease is a common progressive neurodegenerative condition, characterized by the deposition of amyloid fibrils as Lewy bodies in the substantia nigra of affected individuals. These insoluble aggregates predominantly consist of the protein α-synuclein. There is increasing evidence suggesting that the aggregation of α-synuclein is influenced by lipid membranes and, vice versa, the membrane integrity is severely affected by the presence of bound aggregates. Here, using the surface-sensitive imaging technique supercritical angle fluorescence microscopy and F?rster resonance energy transfer, we report the direct observation of α-synuclein aggregation on supported lipid bilayers. Both the wild-type and the two mutant forms of α-synuclein studied, namely, the familiar variant A53T and the designed highly toxic variant E57K, were found to follow the same mechanism of polymerization and membrane damage. This mechanism involved the extraction of lipids from the bilayer and their clustering around growing α-synuclein aggregates. Despite all three isoforms following the same pathway, the extent of aggregation and their effect on the bilayers was seen to be variant and concentration dependent. Both A53T and E57K formed cross-β-sheet aggregates and damaged the membrane at submicromolar concentrations. The wild-type also formed aggregates in this range; however, the extent of membrane disruption was greatly reduced. The process of membrane damage could resemble part of the yet poorly understood cellular toxicity phenomenon in vivo.     

Synthesis and Characterization of Linked Clusters Capped by Alkylidyne

1 INTRODUCTION Constructing higher nuclearity clusters with well-defined dimensions and structures provide a rather active field of chemistry with potential applications in areas including nanotechnology, molecular recognition and catalysis[1~4]. A continuing effort has been directed toward developing a better methodology for systematic synthesis of supracluster compounds through molecular design [5,6]. On the basis of extensive investigation on the metal exchange reaction in cluster com…     

Nitration reactions of astaxanthin and β-carotene by peroxynitrite

The in vitro reactivities of astaxanthin and β-carotene toward peroxynitrite were investigated and the reaction products after scavenging with peroxynitrite were analyzed. A series of carotenoids substituted with nitro group, 14′-s-cis-15′-nitroastaxanthin, 10′-s-cis-11′-cis-11′-nitroastaxanthin, 14′-s-cis-15′-nitro-β-carotene and 10′-s-cis-11′-cis-11′-nitro-β-carotene, were isolated from the reaction products of carotenoids with peroxynitrite. Carotenoids with nitro derivatives were reported for the first time. These results indicated that astaxanthin and β-carotene could catch peroxynitrite or nitrogen dioxide radical (NO₂) in their molecule to form nitrocarotenoids.