Oligomérisation anionique de l'ethylène. I. Etude cinétique

A kinetic study of ethylene oligomerization in hexane, in the presence of n-BuLi–TMEDA complexes, allowed us to suggest a new mechanism for anionic ethylene oligomerization. n-BuLi and n-Bu(CH₂CH₂)Li species have the same reactivity. The RLi–TMEDA complex in a 1-to-1 stoichiometry is the active species. The following kinetic equation has been established: It reflects the intervention of associated species (n-BuLi–TMEDA)₂ as well as the influence of the concentration of the complexing agent on the kinetics of oligomerization.     

The cellulose system in viscin from mistletoe berries

The cellulose system of the viscous fibrous cellulosic polysaccharide (viscan) in the viscin tissue of the European mistletoe, Viscum album L., was analyzed by chemical and physicochemical techniques including sugar analysis, optical and transmission electron microscopy, X-ray and electron diffraction together with solid state CP/MAS ¹³C-NMR spectroscopy. The results confirmed that in the elongated thin viscin cells, the cellulose microfibrils (having a diameter of around 3 nm) were tightly coiled with their axes perpendicular to the long axis of the cell. Upon stretching these cells became deformed by more than a hundred fold. In such a deformation, the cellulose microfibrils became unwound to be perfectly aligned along the stretching direction. Based on solid-state CP/MAS ¹³C-NMR spectroscopic analysis of the viscin tissue, it was found that its cellulose consisted of I and I polymorphs in the ratio 1:1.     

Phenylselenolactonisation des acides homogeranique et homonerique

The reaction of PhSeCl and N-PSP with homogeranic acid ($\text{1}$) or homoneric acid ($\text{2}$) affords butanolides in a stereospecific way. Despite the large number of cyclic cases studied in the literature such acyclic systems were remained largely unexplored. PhSe⁺ was unable to realize polycyclization.     

Synthesis, characterization and crystal structures of two polyphilic mesogenic compounds

Three homologous series of semi-perfluorinated liquid crystals: 4-(2,2,3,3,4,4,4-heptafluoro-butyloxycarbonyl)phenyl, 4-(2,2,3,3,4,4,5,5-octafluoropentyloxycarbonyl)phenyl and 4-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyloxycarbonyl)phenyl 4-[(n-perfluoroalkyl)alkyloxy]benzoates have been synthesized. Their mesomorphic properties were studied by DSC, microscopic observation and X-ray diffraction. Their layer spacings are smaller than the molecular length (L). The ratio d_SA/L is about 0.7. The crystal structure of two derivatives of the first family have also been investigated. In both structures the molecules pack in smectic C-like sheets where neighbouring molecules are antiparallel, interacting through dipolar and van der Waals forces. The interactions between contiguous sheets, through the ends of perfluorinated chains are very weak. The X-ray diffraction results on the mesophases and on the crystalline structures of two compounds of the first family are compared. From this, we propose a model of the smectic phases with a zig-zag structure.     

EFFICACY OF PHOTODYNAMIC THERAPY ON ORIGINAL AND RECURRENT RAT MAMMARY TUMORS

Abstract— Photodynamic therapy has demonstrated efficacy toward primary, metastatic and recurrent human tumors. Here, we investigated the ability of photodynamic therapy, using Photofrin, to inhibit growth of R3230AC mammary adenocarcinomas when tumors were treated as original implants and again as lesions recurring at the initial treatment site. The results demonstrate that both initial implants and lesions recurring after the first photodynamic treatment respond similarly to the same photodynamic therapy protocol, with mean tumor volume doubling times of ˜ 11 days in both cases. Cells cultured from original tumor implants or tumors that recurred after photodynamic treatment accumulate equivalent amounts of [¹⁴C]polyhematoporphyrin. Single cell suspensions prepared from either original or recurrent tumors from animals administered 5 mg/kg Photofrin and exposed to light in vitro displayed comparable phototoxicity. Additionally, examination of tumors by light microscopy revealed no morphological differences between the original tumor implants and the recurrent lesions. Taken together, these data indicate that lesions which recurred at the site of the initial photodynamic treatment were not resistant to a second identical course of photodynamic therapy.     

Interfacial tension and fluorine evolution on a carbon anode

During electrolysis of molten KF-2HF, strongly adherent fluorine bubbles are generated at the surface of carbon anode. The current was passing even if the horizontal anode was fully covered with gas film. The formation and growth of gas bubbles were studied by transient electrochemical techniques. It was observed that the fluorine bubbles do not have the spherical cap shape predicted by the classical theory. The curvature radius of the interface profile is not constant, the edge of the bubble being flat with a contact angle close to zero. The results are interpreted in the frame of a model which takes into account the predominant role of the interfacial properties.     

Mercerization of primary wall cellulose and its implication for the conversion of cellulose I→cellulose II

The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with ¹³C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains.     

Methode d'analyse quantitative par spectrometrie Raman-laser associee aux fibres optiques pour le suivi d'une fermentation alcooliqueA quantitative laser Raman spectrometric method with fibre optics for monitoring an alcoholic fermentation

Laser Raman spectrometry with a fibre-optic system is used to monitor the concentrations of ethanol, glucose and fructose at various stages of an alcoholic fermentation process. For evaluation of the data, cross-correlation and multivariate least-squares procedures are compared; the latter gives the best results. Ethanol, glucose and fructose can be determined remotely with a precision of ca. 10 g l^?1 (10–15%).     

Unusual route to and rearrangement of four-membered ring complexes C5H5Fe (CO) [ (C6H5)2PN(R)CH (C6H5) ]

The amine substituted phosphines (C₆H₅)₂PN(H)CH₂CH₃ and (C₆H₅)₂PN(H)CH₂C₆H₅ react with C₅H₅Fe(CO)₂CH(C₆H₅) (OCH₃) photolytically to give moderate yields of the four-membered chelate ring complexes C₅H₅$\text{Fe (CO) [(C}{}_6\text{H}{}_5\text{)}{}_2\text{PN (CH}{}_2\text{CH}{}_3\text{) C}$H (C₆H₅)] and C₅H₅$\text{Fe (CO) [(C}{}_6\text{H}{}_5\text{)}{}_2\text{PN (CH}{}_2\text{C}{}_6\text{H}{}_5\text{)C}$H(C₆H₅)], respectively. Photolysis of C₅H₅Fe(CO)₂CH(C₆H₅) (OCH₃) in the presence of (S)-(?)-diphenyl(1-phenylethylamino)phosphine leads to the isolation of C₅H₅Fe(CO)[(C₆H₅)2PNC(CH₃) (C₆H₅)]CH₂C₆H₅ which is proposed to arise from a formally 1,3-hydrogen shift rearrangement of an intermediate four-membered chelate ring complex.     

Neosappanone A, a xanthine oxidase (XO) inhibitory dimeric methanodibenzoxocinone with a new carbon skeleton from Caesalpinia sappan

A novel dimeric methanodibenzoxocinone, named neosappanone A (1), possessing a unique unprecedented novel carbon framework, has been isolated from the heartwood of Caesalpinia sappan L. of Vietnam, and its structure was elucidated on the basis of spectroscopic analysis. Neosappanone A (1) competitively inhibited xanthine oxidase in a concentration-dependent manner (IC₅₀, 29.7 μM; K_i, 16.3 μM).