Polycondensats entre la l-lysine et le disulfochlorure-1,3 benzene. Mise en evidence d'interactions hydrophobes en solution aqueuse

The influence of alkaline or quaternary ammonium counter-ions on the conformation in aqueous solution of the polycondensate between l-lysine and 1,3-benzene disulphonyl chloride has been shown by potentiometric titrations and viscometric studies without added salt. The polyelectrolyte has a compact structure at low degrees of neutralization, attributed to hydrophobic interactions (which are more important than the polymer-solvent interactions) between hydrocarbon groups of a same chain. The transition to random coil formation takes place for degrees of neutralization (ᾱ) between 0·2 and 0·3 for the alkaline ions and the first alkyl ammonium terms when the charge repulsions become sufficiently high. If the length of the alkyl chain increases, this transition is displaced towards much higher values of ᾱ. This effect is due to the stabilization of the hydrophobic interactions by the counter-ions retained near to the polyelectrolyte chains.     

Application of the chemiluminescence systems to evaluate the role of Fcgamma and complement receptors in stimulating the oxidative burst in neutrophils

We have established a luminol- and a lucigenin-dependent CL methods to investigate the role of the receptors for Fc portion of IgG (FcgammaR) and/or complement receptors (CR) in mediating the oxidative burst in neutrophils from systemic lupus erythematosus (SLE) patients compared with healthy controls. In the luminol-CL system, all the reactive oxygen species (ROS) are responsible for light production, whereas in the lucigenin-CL system, only the first ROS generated, converts the lucigenin into an unstable intermediate molecule, which also emits light. First, neutrophils from healthy controls and SLE patients were stimulated with different IC opsonized or not with complement from normal human serum (NHS) or SLE serum, in presence of 10(-4) M luminol. This method was able to differentiate the role of the FcgammaR, CR and FcgammaR/CR co-operation in mediating the oxidative burst, as well as show that the oxidative burst mediated by these receptors was reduced in neutrophils from SLE patients. Second, neutrophils from healthy controls and SLE patients were stimulated with different IC, opsonized or not with NHS, in presence of 10(-3) M lucigenin. In this case, the lucigenin-CL system was also able to differentiate the role of FcgammaR and FcgammaR/CR co-operation, as well as show differences among healthy controls and two different groups of SLE patients according to their clinical manifestations. In conclusion, we have established two sensitive CL systems to study the role of FcgammaR and/or CR in stimulating the oxidative burst of neutrophils, which can be applied in monitoring the involvement of these receptors in the immunopathogenesis of SLE.     

Metal-ligand bonding and rutile- versus CdI2-type structural preference in platinum dioxide and titanium dioxide

First principles electronic structure calculations were carried out to determine the relative stabilities of the rutile- and CdI₂-type structures of platinum dioxide (PtO₂) and titanium dioxide (TiO₂). The orbital interactions between the transition metal d- and oxygen p-orbitals were analyzed to gain insight into why PtO₂ has both the rutile- and CdI₂-type structures, but TiO₂ has only the rutile-type structure. The cause for the large difference in the c/a ratios of the CdI₂-type structures of TiO₂ and PtO₂ was examined.     

Rhodium-catalyzed reductive aldol reactions using aldehydes as the stoichiometric reductants

Chelated acyl rhodium hydrides, generated from the addition of [Rh(dppe)]ClO4 to beta-sulfide-substituted aldehydes, can function as the stoichiometric reductants in reductive aldol processes. Unsaturated nitriles, esters, and ketones can be used as enolate equivalents, and a variety of simple alpha- and beta-substituted aldehydes can be employed. The use of a second, more electrophilic, aldehyde allows three-component reactions to be performed.     

Oxygen adsorption on nickel surfaces: Detection of different species by x-ray photoelectron spectroscopy

Interaction of oxygen with evaporated nickel films has been studied by X-ray photoelectron spectroscopy, XPS, over the temperature range 77–500 K and pressure range 10^?9?10^?4 torr. Three oxygen species have been positively identified from O(1s) binding energy shifts (I, II and III with BE's 529.5, 531.4 and 533.2 eV). A fourth state at ca. 534.8 eV may also exist. The relative proportions of each species present depends on the temperature of the substrate. Type I is tentatively considered to represent oxygen atoms in an oxide-like electronic environment, type II is assigned as chemisorbed oxygen atoms, although the possibility of assignment at high oxygen coverages to a defect Ni₂ O₃ structure is admitted. Type III is only formed in sub-monolayer quantities on interaction at 77 K; converting irreversibly to II on warming to 300 K. I and II are always formed together between 300 and 500 K. The authors believe this implies some incorporation of oxygen atoms from the start of adsorption, which in turn has important implications for recent LEED studies.     

Ladder pyrrolone structures with anthraquinone recurring units

1,2,4,5-Tetraaminoanthraquinone and 1,4,5,8-naphthalene-tetracarboxylic acid dianhydride react in dimethylacetamide to give a tetrameric prepolymer with balanced endgroups of anhydride and diamine. When this prepolymer is carefully treated with polyphosphoric acid at elevated temperature it is converted to a soluble polypyrrolone type structure with an inherent viscosity of 2.3–2.7. Polymers of this molecular weight can be wet-spun into pliable fibers from methanesulfonic acid. The TGA curve in air shows little weight loss below 550°C. The polymer can also be solubilized by reduction with sodium dithionite in alkaline aqueous dimethyl sulfoxide.     

Structure du radical cyano-vinyle CH2=Ċ-CN Etude expérimentale et théorique

Résumé Tout d'abord, on montre par RPE que le radical CH₂=-CN possède à basse température une structure instable pliée et à température plus élevée une structure stable linéaire. Un calcul théorique sur ce radical ainsi que sur le radical butatriényle est en bon accord avec les résultats expérimentaux.

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The structure of the Cyano-Vinyl Radical CH₂=-CN experimental and theoretical study

First, it is shown by ESR that the radical CH₂=-CN at low temperature presents an unstable bent structure and at higher temperature a stable linear structure. A theoretical calculation on this radical and on the butatrienyl one is in good agreement with the experimental results.

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Zusammenfassung Aus ESR Messungen wird gefolgert, daß das Radikal CH₂=-CN bei tiefer Temperatur in einer instabilen gebogenen Struktur und bei höherer Temperatur in einer stabilen linearen Struktur vorliegt. Theoretische Berechnungen stehen sowohl für dieses als auch für das Butatrienyl-Radikal in guter Übereinstimmung mit experimentellen Daten.

     

The photo- and electroinitiated polymerization of N-vinyl phthalimide

To elucidate mechanisms in electroinitiated polymerization reactions a comparison was conducted between ultraviolet (UV) photoinitiation and electroinitiation of N-vinyl phthalimide with zinc chloride as a catalyst. Both methods give low yields of a complex polymer product. A detailed analysis, infrared (IR), gel permeation chromatography (GPC), elemental, and molecular weight, conducted on the polymeric products, indicated that phthalimide ring opening was occurring and that complex mixtures of poly(N-vinyl phthalimide) derivatives were formed. Both initiation methods gave comparable results, which further indicated mechanistic similarity between photo-and electroinitiation in these donor–acceptor charge transfer polymerizations.     

Cyclization by the intermediates of phenylthio- and phenoxy carbamoyl. Formation of azasuccinic anhydrides and their polycondensation products. Intervention of the carbamoyl pyridinium cation

The N-(p-nitrophenoxy-carbonyl) derivatives of glycine, DL -alanine and DL -leucine are transformed by the action of pyridine into azasuccinic, 3-methyl-2-azasuccinic and 3-isobutyl-2-azasuccinic anhydride, respectively. These cyclisations occur probably via the intermediate N-carbamoyl-pyridinium cation , the rate of cyclisation seems to depend on the concentration of the intermediate in the form of the dipolar ion , i.e. the ionised carboxyl is necessary for the reaction. In γ-collidine the cyclisation occurs very slowly; this is attributed to the slowness due to steric hindrance of the production of N-carbamoyl-γ-collidinium cation and its instability. The azasuccinic anhydrides mentioned polycondense, yielding the corresponding polyglycine, poly-DL -alanine and poly-DL -leucine. This reaction too is catalysed by pyridine; it can also be effected by γ-collidine, but the efficacity of the latter in comparison with pyridine is even less than in the catalysis of the cyclisation described above. N-(p-nitrophenoxy-carbonyl)-glycine reacts with lysozyme in the presence of pyridine; several glycine residues are introduced into the enzyme molecule, the product being insoluble and poorly active.