Fischer synthesis of isomeric thienopyrrole LHRH antagonists

As part of a structure–activity exploration into LHRH antagonists, structures containing the thieno[2,3-b]pyrrole core were identified as potent antagonists. This letter describes the employment of the Fischer synthesis to access this thienopyrrole and isomeric final compounds.     

Some relevant parameters affecting the glass transition of supported ultra-thin polymer films

We have measured, the thickness dependence of the glass transition temperature T(g)( h), using ellipsometry at variable temperature, for poly(methyl-methacrylate) (PMMA) of various tacticity in confined geometry. We report that several factors significantly affect T(g)( h): i) polymer microstructure (stereoregularity of PMMA) related to local dynamics; ii) interfacial interactions; iii) conformation of the polymer chains. These results raise many fundamental questions on the origin of the thickness-dependent glass transition. Why and how do the interactions with the substrate significantly affect T(g)( h)? Does T(g)( h) depend on the modifications of conformational parameters of the chains (their entropy)? What is the correlation between local dynamics and T(g)( h) in thin films? The aim of this paper is to summarise these open questions, which should stimulate further investigations in the thin polymer film scientific community.     

Beneficial effect of post -thawing osmoconditioning on the recovery of cryopreserved coffee (Coffea arabica L.) seeds

Osmoconditioning-controlled rehydration of seeds in a solution with low osmotic potential -has been shown to reinvigorate aged seeds. The present work aimed at investigating the effect of osmoconditioning on the germination of cryopreserved seeds of Coffea arabica, whose viability and vigour are drastically affected by cryopreservation. For cryopreservation, seeds were desiccated to 0.21 g H2O/g dw, cooled at 1 degree C/min to -50 degree C, then immersed rapidly in liquid nitrogen. After rapid rewarming, seeds were osmoconditioned for 1 to 6 weeks using solutions with osmotic potentials between -1 and -4 MPa. The time to produce half of the final percentage of normal seedlings, T50, was about three fold lower with osmoconditioned seeds than with non-osmoconditioned seeds (12-14 d vs 36 d). Moreover, after a 6-week osmoconditioning treatment with solutions with osmotic potential of -1 and -1.25 MPa, the percentage of seedlings recovered from cryopreserved seeds was 64-74%, against 13-16% only for cryopreserved seeds which were not osmoconditioned.     

Ion crater healing and variable temperature ellipsometry as complementary probes for the glass transition in thin polymer films

Poly(methyl methacrylate) (PMMA) thin films of various tacticity and thickness were bombarded at grazing angles by 20 MeV Au ions at different temperatures. The shape of the tracks was investigated by scanning force microscopy (SFM) after annealing for various time at different temperatures and constant quenching rate. The thickness dependent glass transition temperature, T(g)(h), was estimated from the temperature of relaxation of ion-caused nanodeformations in the films. T(g)(h) obtained from the thermal healing of the holes and hillocks is found in good agreement with the one determined by variable temperature ellipsometry for PMMA film thickness of 80 nm and corresponds to the T(g) of each bulk PMMA stereoisomer. Below this thickness, some significant divergences are observed between the T(g) measured by the two techniques. We propose that the healing of ion crater hillock and the kink in the thermal expansion arise from the different nature of chains motions which are perturbed to different extents according to the main polymer chain preferential orientation in the thin film. This can be tentatively interpreted by a so-called "anisotropic" character of the glass transition.     

Experimental and modeling study of the ion-molecule association reaction H3O+ + H2O (+M) --> H5O2(+) (+M)

Experimental results for the rate of the association reaction H3O+ + H2O (+M) --> H5O2(+) (+M) obtained with the Cinetique de Reactions en Ecoulement Supersonique Uniforme flow technique are reported. The reaction was studied in the bath gases M=He and N2, over the temperature range of 23-170 K, and at pressures between 0.16 and 3.1 mbar. At the highest temperatures, the reaction was found to be close to the limiting low-pressure termolecular range, whereas the limiting high-pressure bimolecular range was approached at the lowest temperatures. Whereas the low-pressure rate coefficients can satisfactorily be reproduced by standard unimolecular rate theory, the derived high-pressure rate coefficients in the bath gas He at the lowest temperatures are found to be markedly smaller than given by simple ion-dipole capture theory. This result differs from previous observations on the related reaction NH4(+) + NH3 (+M) --> N2H7(+) (+M). This observation is tentatively attributed to more pronounced contributions of the valence part of the potential-energy surface to the reaction in H5O2(+) than in N2H7(+). Falloff curves of the reaction H3O+ + H2O (+M) --> H5O2(+) (+M) are constructed over wide ranges of conditions and represented in compact analytical form.     

Dosage mercurimetrique des thioethers en milieu acetique anhydre: Titrimetric determination of thioethers with mercury(II) perchlorate in anhydrous acetic acid media

(Titrimetric determination of thioethers with mercury(II) perchlorate in anhydrous acetic acid media). Thioethers form mercury(II) complexes which are less stable than the thiol complexes. Potentiometric titrations at the millimolar level are possible with a silver amalgam indicating electrode if mercury(II) perchlorate is used as titrant and the medium is anhydrous acetic acid.     

Application d'un reactif sulfovanadique en milieu acetique anhydre a l'etude analytique de quelques acides α-carbonyles ou α-hydroxyles

(Application of a vanadium(V) reagent in anhydrous acetic acid to the determination of some α-carbonyl or α-hydroxyl carboxylic acids). The reagent is prepared from vanadium pentoxide and sulfuric acid in anhydrous acetic acid medium. The oxidation kinetics of various α-carbonyl (glyoxylic, pyruvic, phenylglyoxylic) and α-hydroxyl (glycolic, lactic, mandelic, gluconic) acids are described. A study of the reaction stoichiometry shows that the immediate reaction, corresponding to the consumption of 2–9 mol V(V) mol^?1 of acid, depending on the acid, is useful quantitatively, except for lactic acid which gives a slow non-stoichiometric reaction.     

An asymmetric synthesis of (+)-grandisol, a constituent of the aggregation pheromone of the cotton boll weevil, via a kinetic resolution

A novel approach to the asymmetric synthesis of (+)-grandisol, (1R, 2S)-isopropenyl-1-methylcyclobutaneethanol, involves the use of catalytic kinetic resolution of a primary allylic alcohol, [(1RS, 5SR)-5-methylbicyclo[3.2.0]hept-2-en-2-yl] methanol. The allylic alcohol is prepared in four steps from simple achiral materials involving the use of a modified Shapiro reaction. The resolved alcohol (95% ee) is then reduced in two steps to the corresponding methyl alkene, (1S,5R)-2,5-dimethylbicyclo[3.2.0]hept-2-ene. This alkene is converted to (+)-grandisol (95% ee), in three steps, by modified literature procedures.