Purification of single-walled boron nitride nanotubes and boron nitride cages.

Continuous laser vaporization of a BN target under N2 atmosphere is up to now the unique route to single-walled boron nitride nanotubes (BN-SWNTs). Although grams of product can be obtained by this technique, the raw material contains in addition to the BN-SWNTs, different by-products made of boron and nitrogen. Since these materials are undesirable for the studying of the intrinsic properties of the nanotubes, we have undertaken a purification process using chemical and physical methods to separate the different components. We show here that most impurities can be removed by successive cycles of washing, sonication, and centrifugation. Furthermore, the two different types of boron nitride nanostructures i.e., BN-SWNTs and BN-cages can be isolated. Efficiency of the separation was monitored by transmission electron microscopy (TEM) at the different steps of the process. Finally, we envisage the further purification of the nanotubes-enriched fraction by functionalizing the nanotubes in a non covalent manner by specific polymers as for carbon nanotubes and BN multi-walled nanotubes.

A divergent synthesis of [1-14C]-mono-E isomers of fatty acids.

A convenient synthesis of [1-14C]-mono-trans fatty acid using olefin inversion as a key-step is described. This methodology allows for a facile synthesis of [1-14C]-labelled mono-trans analogues of oleic, linoleic and linolenic acids. As an example, only eleven steps were necessary to obtain the [1-14C]-mono-E isomers of linolenic acid from its commercial all-Z form. In the first step, Barton's decarboxylation procedure yielded a bromo intermediate. Epoxidation of this compound resulted in the formation of three monoepoxides, which could be separated by HPLC. After identification by 1H NMR and MS, the pure monoepoxides were then subjected to inversion consisting of a stereospecific deoxygenation followed by a beta-elimination step. Finally, the labelling was introduced by substitution of the bromine by a [14C]-cyano group followed by hydrolysis.

Preparation of resin-bound N-(alpha-methoxyalkyl)amides: an advantageous use of solid-phase chemistry for the handling of unstable precursors of the versatile N-acyliminium ions.

The development of a new and efficient synthesis of resin-bound N-(alpha-methoxyalkyl)amides is described. The condensation of aldehydes on a supported amide in the presence of trimethyl orthoformate afforded, in acidic media, the resin-bound N-acyliminium ion precursors. Repeating the reaction a second time led to a great improvement in yields, demonstrating one advantage of the solid-phase chemistry for the handling of sensitive intermediates difficult to isolate.

Design of functionalized lipids and evidence for their binding to photosystem II core complex by oxygen evolution measurements, atomic force microscopy, and scanning near-field optical microscopy.

Photosystem II core complex (PSII CC) absorbs light energy and triggers a series of electron transfer reactions by oxidizing water while producing molecular oxygen. Synthetic lipids with different alkyl chains and spacer lengths bearing functionalized headgroups were specifically designed to bind the Q(B) site and to anchor this large photosynthetic complex (240 kDa) in order to attempt two-dimensional crystallization. Among the series of different compounds that have been tested, oxygen evolution measurements have shown that dichlorophenyl urea (DCPU) binds very efficiently to the Q(B) site of PSII CC, and therefore, that moiety has been linked covalently to the headgroup of synthetic lipids. The analysis of the monolayer behavior of these DCPU-lipids has allowed us to select ones bearing long spacers for the anchoring of PSII CC. Oxygen evolution measurements demonstrated that these long-spacer DCPU-lipids specifically bind to PSII CC and inhibit electron transfer. With the use of atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM), it was possible to visualize domains of PSII CC bound to DCPU-lipid monolayers. SNOM imaging has enabled us to confirm that domains observed by AFM were composed of PSII CC. Indeed, the SNOM topography images presented similar domains as those observed by AFM, but in addition, it allowed us to determine that these domains are fluorescent. Electron microscopy of these domains, however, has shown that the bound PSII CC was not crystalline.

Triple ring closing metathesis reaction: synthesis of adjacent cyclic ethers.

[reaction: see text] Adjacent tris(cyclic ethers) and enol ethers have been synthesized in good yields for the first time via a triple olefin metathesis reaction using Grubbs' catalyst RuCl(2)(=C(H)Ph)(PCy(3))(2) (Cy = cyclohexyl), and the 1,3-dimesitylimidazol-2-ylidene ruthenium benzylidene catalyst RuCl(2)(=C(H)Ph)(PCy(3))(IMes) ((IMes) = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene). The latter proved to be the most efficient catalyst in these transformations.

Two-dimensional crystallization of a membrane protein on a detergent-resistant lipid monolayer.

Two-dimensional crystals of a membrane protein, the proton ATPase from plant plasma membranes, have been obtained by a new strategy based on the use of functionalized, fluorinated lipids spread at the air-water interface. Monolayers of the fluorinated lipids are stable even in the presence of high concentrations of various detergents as was established by ellipsometry measurements. A nickel functionalized fluorinated lipid was spread into a monolayer at the air-water interface. The overexpressed His-tagged ATPase solubilized by detergents was added to the subphase. 2D crystals of the membrane protein, embedded in a lipid bilayer, formed as the detergent was removed by adsorption. Electron microscopy indicated that the 2D crystals were single layers with dimensions of 10 microm or more. Image processing yielded a projection map at 9 A resolution, showing three well-separated domains of the membrane-embedded proton ATPase.

Probing the transducin nucleotide binding site with GDP analogues.

An affinity study between the G protein of the visual photoreceptor, transducin, and eight different non-hydrolyzable GDP analogues is described. Imidodiphosphate derivatives have been shown to exhibit good affinities to transducin. This very important heterotrimeric G protein is shown to be highly restrictive with regard to structural modifications of the nucleotide at the pyrophosphate moiety, at the 3' position on ribose, as well as at the N1 position of the purine.

Preparation of silyl enol ethers using (bistrimethylsilyl)acetamide in ionic liquids.

[reaction: see text]. Ionic liquids have been used for the preparation of silyl enol ethers from aldehydes and ketones with (bistrimethylsilyl)acetamide (BSA) in good yields.

Chromium vinylidene carbenoids: stereospecific synthesis of (Z)-2-chloroalk-2-en-1-ols.

(Z)-2-Chloroalk-2-en-1-ols are obtained in excellent yields from a wide variety of aldehydes by addition of (E)-chromium vinylidene carbenoids, stereospecifically generated from trichloroalkanes using CrCl(2) in THF at room temperature. [reaction: see text]

An original traceless linker strategy for solid-phase synthesis of N,N',N''-substituted guanidines.

An original sequence for solution- and solid-phase synthesis of N,N',N"-trisubstituted guanidines is described. The sequence involves as key intermediate a bis-electrophilic chlorothioformamidine that is stable, easy to prepare and also easy to handle. Supported chlorothioformamidine, prepared in two steps from Merrifield resin, undergoes smooth nucleophilic addition of a primary amine to afford the corresponding supported isothiourea. The guanidine is obtained in satisfactory yield and good purity through a functionalizing-release process by heating the supported isothiourea in the presence of a primary amine in toluene at 100 degrees C. Compatibility of this sequence with several functional groups is demonstrated.

The interaction between lipid derivatives of colchicine and tubulin: consequences of the interaction of the alkaloid with lipid membranes.

Colchicine is a potent antimitotic poison which is well known to prevent microtubule assembly by binding tubulin very tightly. Colchicine also possesses anti-inflammatory properties which are not well understood yet. Here we show that colchicine tightly interacts with lipid layers. The physical and biological properties of three different lipid derivatives of colchicine are investigated parallel to those of membrane lipids in the presence of colchicine. Upon insertion in the fatty alkyl chains, colchicine rigidifies the lipid monolayers in a fluid phase and fluidifies rigid monolayers. Similarly X-ray diffraction data show that lecithin-water phases are destabilized by colchicine. In addition, an unexpectedly drastic enhancement of the photoisomerization rate of colchicine into lumicolchicine in the lipid environment is observed and further supports insertion of the alkaloid in membranes. Finally the interaction of colchicine with lipids makes the drug inaccessible to tubulin. The possible in vivo significance of these results is discussed.

Consequences of affinity in heterogeneous catalytic reactions: highly chemoselective hydrogenolysis of iodoarenes

The catalytic hydrodeiodination reaction using molecular hydrogen and Pd/C has been revisited. It is shown, for the first time, that the chemoselectivity of this reaction is controlled by the high affinity of the iodinated compound for the catalyst. This reaction is compatible with most easily reducible functional groups (nitro, aldehyde, olefin, etc.). Using this reaction, the first general method for tritium labeling of 3-(trifluoromethyl)-3-phenyldiazirine is described.

Improvement in olefin metathesis using a new generation of ruthenium catalyst bearing an imidazolylidene ligand: synthesis of heterocycles

A number of heterocycles have been prepared in very good yields using 1,3-dimesitylimidazol-2-ylidene ruthenium benzylidene 1. This catalyst displays increased activity for ring-closing metathesis of some hindered heterodienes which did not cyclize using the Grubbs catalyst 2. The scope of the olefin metathesis has been expanded.

Syntheses and properties of photoactivatable sugar derivatives designed to probe the sugar-binding site of melibiose permease.

Three new photoreactive sugar analogues bearing an azido, a diazonium salt or a diazirine group as the photophore as well as a tritium atom were developed. Two of these new photoactivatable compounds gave excellent preliminary results, with a high affinity for the melibiose permease of Escherichia coli.

Toward antibody-catalyzed hydrolysis of organophosphorus poisons.

We report here our preliminary results on the use of catalytic antibodies as an approach to neutralizing organophosphorus chemical weapons. A first-generation hapten, methyl-alpha-hydroxyphosphinate Ha, was designed to mimic the approach of an incoming water molecule for the hydrolysis of exceedingly toxic methylphosphonothioate VX (1a). A moderate protective activity was first observed on polyclonal antibodies raised against Ha. The results were further confirmed by using a mAb PAR 15 raised against phenyl-alpha-hydroxyphosphinate Hb, which catalyzes the hydrolysis of PhX (1b), a less toxic phenylphosphonothioate analog of VX with a rate constant of 0.36 M(-1) x min(-1) at pH 7.4 and 25 degrees C, which corresponds to a catalytic proficiency of 14,400 M(-1) toward the rate constant for the uncatalyzed hydrolysis of 1b. This is a demonstration on the organophosphorus poisons themselves that mAbs can catalytically hydrolyze nerve agents, and a significant step toward the production of therapeutically active abzymes to treat poisoning by warfare agents.

A convenient synthesis of 2-tetrahydrofuranyl ethers.

[reaction: see text] A wide spectrum of alcohols and phenols are readily transformed to the corresponding 2-tetrahydrofuranyl ethers in good to excellent yields using CrCl2 and CCl4 in THF under nearly neutral conditions at room temperature.