Efficient preparation of carbohydrate- and related polyol-amphiphiles by hydrazone ligation

The hydrazone ligation can be used to couple clustered-glycosides or glycomimetics functionalized with a hydrazino group with lipophilic glyoxylyl acid derivatives to give the corresponding amphiphiles in high yield and purity.     

Efficient preparation of (Z)-alkenyl derivatives from (Z)-vinyl (N,N-diisopropyl)carbamate via Ni-catalysed coupling reactions

A (Z)-vinyl (N,N-diisopropyl)carbamate treated with Grignard reagents, under Wenkert Nickel-catalysed conditions, gave access to several substituted (Z)-alkenyl derivatives. These Nickel-catalysed reactions, carried out with vinyl-, phenyl-, p-methoxyphenyl-, trimethylsilylmethylmagnesium bromide and benzylmagnesium chloride, led to the corresponding (Z)-alkenyl derivatives in good yields and high stereoselectivities.     

Participation d'un groupe amide a la formation de sels de dioxolanne-1,3 ylium-2; Modele biomimetique de reaction de peptidation

An amide group is shown to be capable of intramolecular participation in the formation of an 1,3-dioxolan 2-ylium cation giving a tricyclic organic cation of a new type $\text{5a}$,$\text{b}$. This cation may be considered as a model of an electrophilic intermediate which might be formed from a peptidyl t-RNA during protein biosynthesis.The tricyclic salt $\text{5a}$,$\text{b}$ reacts with water and methanol like a classical dioxolenium salt. An amide acetal $\text{18}$ can be obtained from dimethylamine and 5a; hydrolysis of $\text{18}$ does not lead to the corresponding amide $\text{20}$ but to the cleavage of the CN. bond.     

Characterization of a putative sensory [FeFe]-hydrogenase provides new insight into the role of the active site architecture

[FeFe]-hydrogenases are known for their high rates of hydrogen turnover, and are intensively studied in the context of biotechnological applications. Evolution has generated a plethora of different subclasses with widely different characteristics. The M2e subclass is phylogenetically distinct from previously characterized members of this enzyme family and its biological role is unknown. It features significant differences in domain- and active site architecture, and is most closely related to the putative sensory [FeFe]-hydrogenases. Here we report the first comprehensive biochemical and spectroscopical characterization of an M2e enzyme, derived from Thermoanaerobacter mathranii. As compared to other [FeFe]-hydrogenases characterized to-date, this enzyme displays an increased H₂ affinity, higher activation enthalpies for H⁺/H₂ interconversion, and unusual reactivity towards known hydrogenase inhibitors. These properties are related to differences in active site architecture between the M2e [FeFe]-hydrogenase and “prototypical” [FeFe]-hydrogenases. Thus, this study provides new insight into the role of this subclass in hydrogen metabolism and the influence of the active site pocket on the chemistry of the H-cluster.

Characterization of a group D putative sensory [FeFe]-hydrogenase reveals how the active site can be tuned to decrease CO inhibition and increase stability of a reduced H-cluster while retaining the ability to catalyze H⁺/H₂ interconversion.     

Effect of polymerization of synthetic glycolipids on their supramolecular assemblies

Sugar-derived surfactants bearing a polymerizable acryloyl moiety on one of the branches of the double-chain hydrophobic tail were prepared. The non–ionic hydrophilic head and the biantennary hydrophobic tail were built on, respectively, an aspartic acid and a tris(hydroxymethyl)aminomethane core. Ultraviolet irradiation of aqueous dispersions of these surfactants above their transition phase temperature (T_c) was achieved. The morphology of self-assemblies produced in such a way were investigated by transmission electron microscopy. TEM photographs revealed that irradiation leads to the formation of unilamellar vesicles. Neither fibers nor tubules were detected in contrast to what was observed before polymerization.     

Transient laminar forced convection with arbitrary variation in the wall heat flux

 The aim of the work is to present a detailed numerical study of the transient forced laminar convection flow over a flat plate, when thermal conditions are due to arbitrary wall heat flux variations in space. The energy governing equation is modelled using the Karman–Pohlhausen integral approach in the wide range of Prandtl numbers. The influence of both the thermal problem nature (transient heating and/or cooling processes) and the wall flux function on the resulting mathematical expressions is evidenced and the thermal boundary layer thickness behaviour is discussed. In addition, a particular attention has been focused on both the change in sign of the flux and the duration of the transient heating and cooling. Detailed thermal responses and convective heat coefficient evolutions due to the change of wall conditions are presented. Received on 14 April 2000 / Published online: 29 November 2001     

Metal-doped apatitic calcium phosphates: preparation,characterization, and reactivity in the removal of hydrogen sulfide from gas phase

With the expansion of human activities, there are more and more living areas adjacent to industrial and/or agricultural activities such as chemical processes, petroleum processes, paint finishing, food processing, livestock farming, composting plants etc. Bad odor is part of several nuisances caused by industrial and/or agricultural activities. Hydrogen sulfide (H₂S) is a typical odorous molecule which causes foul odor at very low concentration. This molecule is formed in different industrial installations, in particular in coal combustion, and petrochemical refinery. The separation and/or transformation of H₂S from gas phase to odorless products are important processes for sustainable development. In this paper, we communicate the preparation of new sorbents for the sorption of H₂S from a synthetic gas effluent. These sorbents consist in an inorganic phase (hydroxyapatite) as host particles, and well-dispersed particles of a metal oxide as guest particles which are the active phase for the removal of H₂S. At room conditions, iron, lead, and zinc doped calcium phosphates were found to be effective for the removal of H₂S. The performance of the sorbents depends on preparation method and the nature of active phases. This opens new prospects for the treatment of H₂S from gas phase.