Generation of Threonine- and Azathreonine N-Carboxy Anhydrides from alpha-Hydroxy beta-Lactams Promoted by 2,2,6,6-Tetramethylpiperidinyl-1-oxyl (TEMPO) in Combination with Sodium Hypochlorite

A versatile one-pot oxidation-Baeyer-Villiger reaction sequence applied to alpha-hydroxy beta-lactams and promoted by 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) leads to alpha-amino acid N-carboxy anhydrides. The examples reported constitute the first application of TEMPO in a Baeyer-Villiger reaction and provide a way for peptide coupling from non alpha-amino acid precursors.     

Electron spin relaxation and frequency-dependent lineshape analysis of the 5′—ATP—Mn(II)—Trp system

A frequency-dependent lineshape analysis of the ESR spectra of ternary systems in solution has been carried out. The 5′-ATP—Mn(II)—Trp complex has been chosen as a model system. The analysis points out the presence of inverted spectra at both X- and Q-bands. The lineshape is described by a distribution of configurational sites, Y^l(ω) = Σ_kP_kY_k(H). The temperature dependence of the ESR linewidth has also been investigated and is discussed in terms of chemical equilibria and correlation times.     

Enzyme‐Mediated Preparation of Chiral 1,3‐Dioxane Odorants

The enantiomerically enriched diastereoisomers of the chiral 1,3‐dioxane odorants Floropal^® ( 1 ) and Magnolan^® ( 2 ) were prepared by an enzyme‐mediated approach. Their olfactory properties were evaluated to investigate differences in the odor perception for the stereoisomers.     

Synthesis of 1,8-naphthyridine derivatives. Potential antihypertensive agents. 1

Reaction of substituted 7-chloro-1,8-naphthyridines with N-carbethoxypiperazine gave in good yields the corresponding 7-(4-carbethoxypiperazin-1-yl)-1,8-naphthyridines V as potential antihypertensive agents.     

{4(S)‐(Piperidin‐1‐ylcarbonyl)‐4‐[3‐(trifluoro­methyl)phenylsulfon­amido]butyl}guanidinium chloride: a model of a graftable thrombin inhibitor

In the title compound, C₁₈H₂₇F₃N₅O₃S⁺·Cl⁻, the guanidine group forms N—H⋯Cl hydrogen bonds, with four N⋯Cl distances in the range 3.164 (3)–3.337 (4) Å. In the crystal packing, the cations are further linked by N—H⋯O and C—H⋯O inter­actions. The structure is compared with that of argatroban complexed with thrombin and is the subject of docking studies in the active site of thrombin.     

Perfluoropolyether-Silica Hybrids: Preparation and Surface Characterization

,-Triethoxysilane terminated perfluoropolyether-polycaprolactone block copolymers, TXCL(x)Si, were synthesised, characterised and subsequently reacted with tetraethoxysilane to prepare transparent organic-inorganic hybrid materials by using the sol–gel process. Surface characterization was carried out through contact angle measurements. All the materials investigated (independently on both the reaction time of the sol–gel reaction before coating application and the bulk organic-inorganic ratio) showed a strong hydrophobic character when compared with non-fluorinated and fully inorganic control materials. The highest water contact angles were obtained when TXCL(x)Si oligomer used for the preparation of the hybrid contained short hydrogenated polycaprolactone segments. In all cases, the surface tension values indicated that the very surface at the air-coating interface showed almost completely perfluoropolyether segments.     

Determination of Arsenic Speciation in Complex Environmental Samples by the Combined Use of TEM and XPS

Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS) have been used to refine the solid-state speciation of As in mine waste materials and stream-bed sediments from the Baccu Locci mine area in Sardinia, Italy. The combined use of TEM and XPS confirmed previous studies and pointed out that: (i) As is contained in plumbojarosite in substitution of S, (ii) As-bearing Fe(III) hydroxides are represented by arsenical 2-line ferrihydrites with most Fe/As molar ratios in the range of 1.6–3.2, (iii) scorodite often lacks long range order. Arsenatian plumbojarosite will tend to dissolve incongruently in ferrihydrite, releasing Pb and As into water. However, Pb is fated to precipitate as Pb(OH)₂ or to be adsorbed onto ferrihydrite, whereas As mobility is favoured since the adsorptive capacity of ferrihydrite for As(V) is notably reduced under the neutral to alkaline pH conditions occurring in the Baccu Locci stream water. Arsenical ferrihydrites will tend to be converted into goethite or hematite with time, releasing As into the water as a consequence of the notably lower density of the adsorption sites of the crystalline Fe(III) phases. Also scorodite is relatively unstable under the Baccu Locci system conditions, and its stability is further decreased owing to the higher solubility of the amorphous form compared to the crystalline one.     

Quantitation and identification of polynuclear aromatic hydrocarbons by liquid chromatography and multiwavelength absorption spectrometry

This paper describes the combined use of liquid chromatographic separation with multiwavelength absorption detection for the quantitation and identification of polynuclear aromatic hydrocarbons. Quantiative results are presented for three- and four-component mixtures with complete and partial separation. Qualitative data are presented for a twelve-component synthetic mixture and for extracts from a filter used to collect particulate emissions from a biomass-gasifier system. It is shown that multiwavelength data-processing methods commonly applied to absorption spectra can be applied with significant advantage to second-derivative spectra. Results indicate that significant improvements can be achieved by the use of different wavelength ranges for different components in mixtures. Detection limits for single-component samples varied between 3 and 11 μg l^?1 for eleven hydrocarbons and the scatter about calibration plots for mixtures was in the range of 0.05 to 0.4 μg ml^?1. The identities of all twelve components in the synthetic mixture were confirmed and nineteen components were identified in the sample from the biomass gasifier filter.     

Quantitative DTA of epoxy adhesives of technological interest

The glass transition temperatures,T _g, and thermal effects of polymerization,H, have been determined for five epoxy adhesives of unknown composition. From the trendsH vs./t _cure it has been possible to attain a phenomenological kinetic order of the polymerization rate at 100° through an iterative calculation procedure. For most of the investigated adhesives there are reasons (double peak of polymerization and doubleT _g signal) to assume that they are graft copolymers.

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Zusammenfassung Die Glas-Übergangstemperaturen (T _g) und dieH thermische Effekte der Polymerisation wurden für fünf Epoxy-Klebstoffe unbekannter Zusammensetzung bestimmt.Aus den TrendsH gegenübert _cure war es möglich eine phenomenologische kinetische Ordnung der Polymerisationsgeschwindigkeit bei 100° durch ein iteratives Berechnungsverfahren zu ermitteln.Für die meisten untersuchten Klebstoffe besteht der Grund — Doppelpeak der Polymerisation und doppeltesT _g-Signal — sie als Pfropfcopolymere zu betrachten.

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Résumé On a déterminé, pour cinq adhésifs époxy de composition inconnue, les températures de transition vitreuseT _g et les effets thermiques de polymérisationH.A partir de la variation deH en fonction du temps de recuit et par une méthode de calcul itératif, un ordre cinétique phénoménologique de la vitesse de polymérisation à 100° a pu être obtenu.Pour la plupart des adhésifs étudiés l'existence d'un pic double de polymérisation et d'une double transition vitreuseT _g permet de supposer qu'il s'agit de copolymères greffés.

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T _g H. H.-t. 100° . T _g , - .

     

Adsorption indicators - v

Blue sulphone acid B has been proposed as an adsorption indicator for I-ions fit to be employed in strongly alkaline media.