Extending a Partially Ordered Set: Links with its Lattice of Ideals

A well-known result of Bonnet and Pouzet bijectively links the set of linear extensions of a partial order P with the set of maximal chains of its lattice of ideals I(P). We extend this result by showing that there is a one-to-one correspondence between the set of all extensions of P and the set of all sublattices of I(P) which are chain-maximal in the sense that every chain which is maximal (for inclusion) in the sublattice is also maximal in the lattice.We prove that the absence of order S as a convex suborder of P is equivalent to the absence of I(S) as a convex suborder of I(P). Let S be a set of partial orders and let us call S-convex-free any order that does not contain any order of S as a convex suborder. We deduce from the previous results that there is a one-to-one correspondence between the set of S-convex-free extensions of P and the set of I(S)-convex-free chain-maximal sublattices of I(P). This can be applied to some classical classes of orders (total orders and in the finite case, weak orders, interval orders, N-free orders). In the particular case of total orders this gives as a corollary the result of Bonnet and Pouzet.     

Use of MALDI-TOF mass spectrometry to monitor solid-phase synthesis of oligonucleotides

MALDI-TOF mass spectrometry has been used to characterize solid-supported oligonucleotides containing natural and non-natural and non-nucleoside moieties and a variety of internucleosidic linkages including phosphate and phosphite triesters and H-phosphonate diesters. This technique was used to follow the reactions involved in oligonucleotide synthesis; this enabled direct control of the elongation and optimization of the coupling process.     

High-yield solution-phase synthesis of di- and trinucleotide blocks assisted by polymer-supported reagents

A new solution-phase phosphoramidite approach is reported for oligonucleotide synthesis employing recyclable solid-supported reagents. It uses polyvinyl pyridinium tosylate as the activator of a nucleoside-3'-O-phosphoramidite in the coupling step with a 5'-OH nucleoside or dinucleotide. The resulting phosphite triester was either sulfurized or oxidized using polystyrene-bound trimethylammonium tetrathionate or periodiate. This method avoids complicated purification steps, as excess reagents are easily removed by filtration. [reaction: see text]     

Influence of the Absorbed Water on the Tensile Strength of Flax Fibers

The complex structure of flax fibres involves many chemical biomolecules located in an amorphous matrix in which cellulose micrifibrils are embbeded. The drying of flax fibres influences significantly their tensile strength. This result can be explained by the creation of damages within the fibre and by the modification of the chemical composition of the matrix components. This loss of water involves a modification of the adhesion between the cellulose microfibrils and the matrix. This modification is due to the evolution of the components ensuring the transfer of load between the microfibrils and thus conditioning the strength of the cellular wall.     

Coupling of Simultaneous Fluorescence and Electrophysiology: Historical Survey, Contributions, and Prospects

The coupling of simultaneous fluorescence and eleclrophysiological measurements paved the way for the development of potentiometric and intracellular free ion-sensitive probes, although the basic and initial aim of these combined studies remains to record fast conformational changes during ion channel activation. Recent high-resolution studies of some channels put back on the agenda challenging methods that combine spectroscopy and electrophysiology. Fluorescence is certainly the most versatile and sensitive spectroscopy in this kind of experiment, and we have recently witnessed significant breakthroughs, at the level of whole cells with intact or mutated channels or with planar lipid bilayers doped with channels or their peptide models. After our initial study of membrane dynamics associated with excitability, following transient pyrene excimer signals during action potentials or voltage-clamp of nerve fibers, we tested the feasability of FRAP (fluorescence recovery after photobleaching) experiments on planar lipid bilayers. This technique was later applied to lateral diffusion measurements of channel forming peptides (alamethicin labeled with fluorescein and the voltage-sensitive segment S4 of the Shaker potassium channel labeled with NBD) under applied voltage. We provide independent evidence for voltage-dependent partitioning and transmembrane insertion and propose renewed experimental avenues to reveal movements and conformational changes associated with ion channel gating and opening.     

Universal solid supports for the synthesis of oligonucleotides via a transesterification of H-phosphonate diester linkage

[Structure: see text]. Three universal solid supports exhibiting an hydroxyl function were prepared. The introduction of a first H-phosphonate diester linkage which was kept throughout the elongation allowed the release of 3'-hydroxyl oligonucleotides by a transesterification mechanism. The transesterification was performed in a few minutes with either amino alcohols or K2CO3/methanol. Starting from a hydroxyl solid support, tandem oligonucleotides were synthesized and the solid support was easily recyclable. This strategy was extended to the release of an oligonucleotide from the solid support by a nonbasic treatment opening the way to the synthesis of base-sensitive oligonucleotides thanks to the selective deprotection of a hydroxyl in beta of the H-phosphonate diester linkage.     

Space-time-wave number-frequency Z(x, t, k, f) analysis of SAW generation on fluid filled cylindrical shells

A new 4D space-time-wave number-frequency representation Z(x,t,k,f) is introduced. The Z(x,t,k,f) representation is used for processing 2D space-time signal collection issued from wave propagation along a 1D medium. This representation is an extension along the time dimension of the space-wave number-frequency representation. The Z(x,t,k,f) representation is obtained by short time-space 2D Fourier transforming the space-time collection. The Z(x,t,k,f) representation allows the characterization transient aspects of wave generation and propagation in both space and time dimensions. The Z(x,t,k,f) representation is used to experimentally investigate Lamb wave generation and propagation around a cylindrical shell (relative thickness is equal to 0.03) surrounded by water and excited by a pulse (0.1 micros duration with 1-5 MHz transducers). Three kinds of fluids have been used inside the shell: air, water, propanol. In all the cases, the Z(x,t,k,f) analysis clearly identify the reflected field on the insonified side of the shell and it allows the measurement of the local reflection coefficients R(x,t,k,f). The generation and the propagation of Lamb waves are also quantified. For the liquid filled shells, the multiple internal reflections are revealed by Z(x,t,k,f) analysis: the local transmission coefficients T(x,t,k,f) are also measured. When local matching conditions allows Lamb wave generation, the multiple regeneration of Lamb wave is observed. Based on these results, a link is establish toward the theoretical results obtained by steady state approach and Sommerfeld-Watson transform.     

Preparation of photovoltaic silicon by purification of metallurgical grade silicon with a reactive plasma process

The main methods of silicon purification involve physicochemical techniques of separation. They yield an ultrapure metal, but its price is not compatible with photovoltaic central power generation. The plasma zone melting process consists in the horizontal displacement of a melted zone under an argon-hydrogen-oxygen plasma. The melt zone is characterized by a vertical gradient of concentration and temperature which drains impurities toward the upper surface of the bar. Moreover, the displacement of the zone from the head to the tail of the bar ensures a horizontal drainage of impurities toward the tail. This technique has been used with success for purification of metallurgical grade silicon; for example, iron was reduced from 3500 ppm to 0.5 ppm at a displacement rate between 20 and 40 cm/h. The final impurity level was less than 1 ppm. The mass transfer was independent of the displacement rate at 40 cm/h, but dependent on the heat transfer rate. The segregation of the metals is caused by drainage toward the tail of the bar, while the plasma vaporizes impurities since the metallic and metalloidic impurities have high vapor pressures (e.g., S, P, C, O, Mn). Acid (HF-HNO₃) is used to dissolve the impurities between each passage of the zone. Boron elimination depends directly on the plasma oxygen concentration. Classical mathematic models of zone melting are not valid for plasma melting zone processes.     

Chiral Anthranyl Trifluoromethyl Alcohols: Structures,Oxidative Dearomatization and Chiroptical Properties

Chiral trifluoromethyl alcohol groups were introduced at the hindered ortho positions of 9,10-diphenylanthracenes to investigate their effects on the physical properties and reactivity towards oxidative dearomatization. In such compact structures, the position in different quadrants and the preferred orientation of the −CH(OH)CF₃ groups were determined by the relative and absolute configurations of each stereoisomer, respectively. As a consequence, the stereochemistry governs the organization of the H-bonded molecules in single crystals (homochiral dimers vs ribbon), whereas in chlorinated solvents, they all behave as discrete compounds. Concerning their reactivity, the stereospecific dearomative oxidation of these molecules leads to 9,10-bis-spiro-isobenzofuran-anthracenes, when using organic single-electron transfer oxidants. The chiroptical properties of the alcohols and the corresponding dearomatized products were compared and showed an important modulation of the intensity.     

Temperature‐Sensitive Amphiphilic Non‐Ionic Triblock Copolymers for Enhanced In Vivo Skeletal Muscle Transfection

It is reported that low concentration of amphiphilic triblock copolymers of pMeOx‐b‐pTHF‐b‐pMeOx structure (TBCPs) improves gene expression in skeletal muscle upon intramuscular co‐injection with plasmid DNA. Physicochemical studies carried out to understand the involved mechanism show that a phase transition of TBCPs under their unimer state is induced when the temperature is elevated from 25 to 37 °C, the body temperature. Several lines of evidences suggest that TBCP insertion in a lipid bilayer causes enough lipid bilayer destabilization and even pore formation, a phenomenon heightened during the phase transition of TBCPs. Interestingly, this property allows DNA translocation across the lipid bilayer model. Overall, the results indicate that TBCPs exhibiting a phase transition at the body temperature is promising to favor in vivo pDNA translocation in skeletal muscle cells for gene therapy applications.