Charge inversion, condensation and decondensation of DNA and polystyrene sulfonate by polyethylenimine.

We study the formation and structure of stable electrostatic complexes between polyanions (DNA and poly(styrene-sulfonate)) and linear polyethylenimine. The charge ratio x of the mixture is tuned by varying the concentration of the polycation at constant concentration of polyanion. In agreement with recent theories, dynamic light scattering and electrophoretic mobility measurements show two distinct regimes of weak and strong complexation. At low polycation concentration, negatively charged small complexes involving a few polyanion chains are observed first. By further increasing x, these small complexes condense at a precise charge ratio x(c) < 1 to form large anionic aggregates. The inversion of the charge of the condensed complexes coincides with the maximum of complexation and precedes the dissolution of the aggregates which occurs at a well-defined decondensation threshold x(d) > 1. Above x(d), positively charged complexes containing again a few overcharged polyanion chains are observed. The macroscopic phase diagram is qualitatively well corroborated by AFM observation of the complexes. The influence of entropic effects is probed by varying parameters like concentration, polycation molecular weight and ionic strength. Structure of stable negatively charged complexes is investigated at higher concentration using Small Angle Neutron Scattering. In the condensed regime, we observe large soluble bundles with sharp interfaces where the local structure of the polyanions is preserved.

Dynamics of colloids in single solid-state nanopores.

We use solid-state nanopores to study the dynamics of single electrically charged colloids through nanopores as a function of applied voltage. We show that the presence of a single colloid inside of the pore changes the pore resistance, in agreement with theory. The normalized ionic current blockade increases with the applied voltage and remains constant when the electrical force increases even more. We observe short and long events of current blockades. Their durations are associated, respectively, with low and high current variation. The ratio of long events increases with the electrical force. The events frequency increases exponentially as a function of applied voltage and saturates at high voltage. The dwelling time decreases exponentially at low and medium voltages when the electrical force increases. At large voltages, this time decreases inversely proportionally to the applied voltage. The long events are associated with translocation events. We show that the dynamics of colloids through the nanopore is governed mainly by two mechanisms, by the free-energy barrier at relatively low and medium voltages and by the electrophoresis mechanism at high voltage.

Exploration of the ultimate patterning potential achievable with focused ion beams.

Decisive advances in the field of nanosciences and nanotechnologies are intimately related to the development of new instruments and of related writing schemes and methodologies. Therefore we have recently proposed the exploitation of the nano-structuring potential of a highly focused ion beam (FIB) as a tool, to overcome intrinsic limitations of current nano-fabrication techniques and to allow innovative patterning schemes that are urgently needed in many nanoscience challenges. In this work, we will first detail a very high-resolution FIB instrument we have developed specifically to meet these nano-fabrication requirements. Then we will introduce and illustrate an advanced FIB processing scheme that is the fabrication of artificial nanopores.

Dynamics of polyelectrolyte transport through a protein channel as a function of applied voltage.

We study the transport of dextran sulfate through a protein channel as a function of applied voltage. Below 60 mV, the chain's entrance to the pore is hindered by an entropic barrier; above 60 mV, the strong local electric field forces the chain entrance. The effective charge of the polyelectrolyte inside the pore is reduced. We observe two types of blockades which have durations that decrease when the applied voltage increases. The shortest is a straddling time between the polyelectrolyte and the pore; the longest is the translocation time. The translocation time obeys an exponential dependence upon applied voltage.

Unfolding of proteins and long transient conformations detected by single nanopore recording.

We study the electrophoretic blockades due to entries of partially unfolded proteins into a nanopore as a function of the concentration of the denaturing agent. Short and long pore blockades are observed by electrical detection. Short blockades are due to the passage of completely unfolded proteins, their frequency increases as the concentration of the denaturing agent increases, following a sigmoidal denaturation curve. Long blockades reveal partially folded conformations. Their duration increases as the proteins are more folded. The observation of a Vogel-Fulcher law suggests a glassy behavior.

Synthesis, characterization, and gene transfer application of poly(ethylene glycol-b-ethylenimine) with high molar mass polyamine block.

The study of ethyloxazoline/methyloxazoline (EtOXZ/MeOXZ) copolymerization, initiated by methyl tosylate (MeOTs), showed that (i) incorporation of MeOXZ units into random copolymer becomes effective over DP = 100 and (ii) propagation process proceeds with negligible transfer to monomer up to a DP of 400 despite the presence of MeOXZ in the polymerization medium. These results produced random poly(EtOXZ-co-MeOXZ) copolymers with various molar composition ratios in alkyloxazoline units. The close values found for the comonomer reactivity ratios in acetonitrile (r(1MeOXZ) = 1.18; r(2EtOXZ) = 0.34) implied a random chain organization in short sequences of each repeating unit, which was an important parameter in view of the optimization of their subsequent modification: the alkaline hydrolysis was successfully achieved when the MeOXZ unit content of the polyoxazoline chains reached 75%. Using these results, the diblock copolymer poly(ethylene glycol-b-(ethyloxazoline-co-methyloxazoline)) (poly(EG-b-(EtOXZ-co-MeOXZ))) with high DP was synthesized by cationic copolymerization of EtOXZ/MeOXZ comonomers using CH(3)-PEG(2kDa)-Ts as macroinitiator. The comonomer composition of this new compound was adjusted in order to optimize the hydrolysis step and obtain finally the diblock copolymer poly(ethylene glycol-b-ethylenimine) (poly(EG-b-EI)). The high molar mass of this copolymer was confirmed both by (1)H NMR and SANS measurements. Gene delivery experiments showed that the copolymer has significant DNA transfection capacities.

High conversion synthesis of pyrene end functionalized polyrotaxane based on poly(ethylene oxide) and alpha-cyclodextrins.

We describe the quantitative synthesis of new pyrene labeled cyclodextrin-based polyrotaxane starting from pseudopolyrotaxane of alpha,omega-dimethacrylate poly(ethylene oxide) (PEO) and alpha-cyclodextrins (alpha-CDs). Using a solvent mixture (H2O/dimethyl sulfoxide (DMSO)), an almost quantitative conversion in polyrotaxane can be achieved using the coupling reaction between methacrylic functions and 1-pyrene butyric acid N-hydroxysuccinimide ester. This result is due to the fast blocking reaction of the pseudopolyrotaxane telechelic functions. The polyrotaxanes are characterized by NMR, size exclusion chromatography (SEC), and small-angle neutron scattering (SANS). A rodlike structure of the polyrotaxane is evidenced by SANS, and a persistence length of 70 A is determined. This result corresponds to an almost completely stretched PEO chain of 1000 g.mol(-1) molecular weight. We furthermore studied the opposite case of low packing density polyrotaxanes that were also silylated to suppress interactions between cyclodextrins. We observed a random coil structure only for silylated low packed polyrotaxane. This result demonstrates that both hydrogen bonding and packing density can explain the rodlike structure of cyclodextrin-based polyrotaxane.

Concomitant adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate at the silica-water interface.

Upon addition of silica to aqueous solutions of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers (PEO-b-PCL) and sodium dodecyl sulfate (SDS), adsorption of the solutes occurs at the silica-water interface. The amount of the adsorbed constituents has been measured by the total concentration depletion method. Small-angle neutron scattering experiments (SANS) have been carried out to investigate the structure of the adsorbed layer. Although SDS is not spontaneously adsorbed onto hydrophilic silica, adsorption is observed in the presence of PEO-b-PCL diblocks, in relation to the relative concentration of the two compounds. Conversely, SDS has a depressive effect on the adsorption of the copolymer, whose structure at the interface is modified. Copolymer desorption is however never complete at high SDS content. These observations have been rationalized by the associative behavior of PEO-b-PCL and SDS in water.

[Medical treatment of an important trachea injury after tracheal intubation]. / Traitement médical d'une large plaie trachéale après intubation.

Tracheal injuries are rare but life threatening complications of anaesthesia. Two therapeutic strategies are presently proposed: a non-surgical strategy for small injuries and a surgical strategy for larger ones. This case report presented the non-surgical therapeutic strategy of a large tracheal injury. This strategy was discussed according to other published reports.

Adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the silica-water interface.

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface.

Spherical polyelectrolyte block copolymer micelles: structural change in presence of monovalent salt.

Spherical polyelectrolyte block copolymer micelles were investigated as a function of added NaCl salt concentration using Small-Angle Neutron Scattering (SANS) and Light Scattering (LS). The micelles are formed by the self-association of charged-neutral copolymers made of a long deuterated polyelectrolyte moiety (NaPSS(d))251 and a short hydrophobic moiety (PEP)52. In presence of salt, the core shape and the aggregation number of the micelles are not affected. The hydrodynamic radius of the micelle is found to be identical to the radius of the whole micelle deduced from neutron scattering and thus the hydrodynamic radius is a valid measure of the corona thickness. At the lowest salt concentrations investigated the thickness of the corona, R(s), remains essentially constant and a contraction is observed above an added-salt concentration c(s) of 2 x 10(-2) M where this crossover concentration corresponds to the average ionic strength of the free counterions in the corona. The contraction takes place while maintaining a rod-like behavior of the chains at short scale and obeys to: R(s) approximately c(s)(-0.18). The exponent 0.18 suggests an electrostatic persistence length proportional to the Debye screening length.

Mixed self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate in aqueous solution.

Interaction of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers with anionic sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. Formation of mixed micelles has been confirmed by surface tension measurements, whereas the influence of the surfactant on the copolymer self-assembling has been studied by measurement of the 1H NMR self-diffusion coefficients and by small-angle neutron scattering. As a rule, the surfactant decreases the heterogeneity of the micellar structures formed by the copolymer in water. Moreover, increasing the content of SDS results in the increasingly more important extension of the poly(ethylene oxide) (PEO) corona chains and the copolymer micelle deaggregation. The stability of the micelles against SDS increases with the length of the hydrophobic block. Preliminary two-dimensional NMR measurements with nuclear Overhauser enhancement have confirmed the spatial vicinity between SDS and the constitutive blocks of the copolymer.

Structure of hydrophobically and hydrogen-bonded complexes between amphiphilic copolymer and polyacid in water.

We observed by SANS and NMR the structure of intermolecular complexes formed through hydrogen bonding and hydrophobic interactions between a polyacid and a neutral copolymer surfactant (PEO-PPO-PEO). The polyacid is perdeuterated and the contrast variation method enables us to measure separately the structure factor of each component in the complex and the cross structure factor as a function of the pH and the temperature. The evolution of NMR spectra and relaxation times with pH and temperature give a complementary insight into the inner structure of the aggregates. The interaction between the aggregates and the aggregation number of polyacid chains are governed by electrostatic effects; they depend on the polyacid charge and are insensitive to temperature. The number of copolymer chains which results from the cooperative action of hydrogen bonding and hydrophobic interactions is sensitive to both pH and temperature. The complexation preserves the micellar core-corona structure of the copolymer and shrinks the polyacid chains which adopt a compact structure. The non-dissociated polyacid sequences are bound to the PPO part of the copolymer forming the hydrophobic core of the complex, whereas the ionized polyacid sequences form with the PEO a stabilizing hydrated corona.

Vesicle-to-micelle transition induced by grafted diblock copolymers.

We study by small-angle neutron scattering the vesicle-to-micelle transition induced by anchoring diblock copolymers on the surfactant membranes. Vesicles are made using the ternary system SDS (sodium dodecyl sulfate)/octanol/PS-POE (polystyrene-polyoxyethylene), chosen as a model of more complex biological systems. The anchored polymer chains destabilize the membranes and lead to the formation of mixed polymer-surfactant micelles. We show that there is no influence of the polymer mass on the membranes destabilization. We compare this experimental result with recent theoretical predictions concerning the polymer-grafted membranes. We have a good agreement with predictions involving membrane curvature effects, and also with predictions focusing on more local deformations of membranes created by the grafted chains.

[Recurrent fatal pseudomembranous colitis]. / Récidive fatale d'une colite pseudomembraneuse.

BACKGROUND: Clostridium difficile pseudomembranous colitis may trace a fulminent course and require surgery. CASE REPORTS: Outcome was fatal despite subtotal colectomy in the reported case of recurrent Clostridium difficile pseudomembranous colitis. Infrequent localization, low serum albumin and an unfavorable clinical course were observed. DISCUSSION: Rapid surgical treatment with large resection is mandatory in such cases, particularly in patients of rectal and sigmoid remnant involvement.

[Mastocytosis: general anesthesia with remifentanil and sevoflurane]. / Mastocytose: anesthésie générale par rémifentanil et sévoflurane.

Mastocytosis is a disorder with potential anaesthesia complications. Reviewing the literature, anaesthetic management of mastocytosis is controversial. We report the successful use of remifentanil and sevoflurane in a woman with systemic mastocytosis. No reaction nor histamine release was observed in these cases.

Spontaneous vesiculation.

The thermodynamics of vesicle formation was analyzed by using the elastic bending energy approach. Several different possibilities of spontaneous vesiculation, due to soft bilayers, non-zero spontaneous curvature and Gaussian curvature, respectively, were presented and discussed. Intermediate structures in the closed vesicle-disklike mixed micelle phase transition could be either cup-like particles or open bilayers partially rolled into lipid tubules.