Molecular Recognition in Mechanochemistry: Insights from Solid-State NMR Spectroscopy.

Molecular-recognition events are highly relevant in biology and chemistry. In the present study, we investigated such processes in the solid state under mechanochemical conditions using the formation of racemic phases upon reacting enantiopure entities as example. As test systems, α-(trifluoromethyl)lactic acid (TFLA) and the amino acids serine and alanine were used. The effects of ball-milling and resonant acoustic mixing (RAM) on the formation of racemic phases were probed by using solid-state Nuclear Magnetic Resonance (NMR) spectroscopy. In a mixer mill, a highly efficient and fast racemic phase formation occurred for both TFLA and the two amino acids. RAM led to the racemic phase for TFLA also, and this process was facilitated upon employing pre-milled enantiopure entities. In contrast, under comparable conditions RAM did not result in the formation of racemic phases for serine and alanine.

Controlling interfacial film formation in mixed polymer-surfactant systems by changing the vapor phase.

Here we show that transport-generated phase separation at the air-liquid interface in systems containing self-assembling amphiphilic molecules and polymers can be controlled by the relative humidity (RH) of the air. We also show that our observations can be described quantitatively with a theoretical model describing interfacial phase separation in a water gradient that we published previously. These phenomena arises from the fact that the water chemical potential corresponding to the ambient RH will, in general, not match the water chemical potential in the open aqueous solution. This implies nonequilibrium conditions at the air-water interface, which in turn can have consequences on the molecular organization in this layer. The experimental setup is such that we can control the boundary conditions in RH and thereby verify the predictions from the theoretical model. The polymer-surfactant systems studied here are composed of polyethylenimine (PEI) and hexadecyltrimethylammonium bromide (CTAB) or didecyldimethylammonium bromide (DDAB). Grazing-incidence small-angle X-ray scattering results show that interfacial phases with hexagonal or lamellar structure form at the interface of dilute polymer-surfactant micellar solutions. From spectroscopic ellipsometry data we conclude that variations in RH can be used to control the growth of micrometer-thick interfacial films and that reducing RH leads to thicker films. For the CTAB-PEI system, we compare the phase behavior of the interfacial phase to the equilibrium bulk phase behavior. The interfacial film resembles the bulk phases formed at high surfactant to polymer ratio and reduced water contents, and this can be used to predict the composition of interfacial phase. We also show that convection in the vapor phase strongly reduces film formation, likely due to reduction of the unstirred layer, where diffusive transport is dominating.

Control and analysis of oriented thin films of lipid inverse bicontinuous cubic phases using grazing incidence small-angle X-ray scattering.

Lipid cubic phases are complex nanostructures that form naturally in a variety of biological systems, with applications including drug delivery and nanotemplating. Most X-ray scattering studies on lipid cubic phases have used unoriented polydomain samples as either bulk gels or suspensions of micrometer-sized cubosomes. We present a method of investigating cubic phases in a new form, as supported thin films that can be analyzed using grazing incidence small-angle X-ray scattering (GISAXS). We present GISAXS data on three lipid systems: phytantriol and two grades of monoolein (research and industrial). The use of thin films brings a number of advantages. First, the samples exhibit a high degree of uniaxial orientation about the substrate normal. Second, the new morphology allows precise control of the substrate mesophase geometry and lattice parameter using a controlled temperature and humidity environment, and we demonstrate the controllable formation of oriented diamond and gyroid inverse bicontinuous cubic along with lamellar phases. Finally, the thin film morphology allows the induction of reversible phase transitions between these mesophase structures by changes in humidity on subminute time scales, and we present time-resolved GISAXS data monitoring these transformations.

Aqueous gels of mixtures of ionic surfactant SDS with pluronic copolymers P123 or F127.

Gel diagrams based on tube inversion and oscillatory rheometry are reported for Pluronic copolymers F127 (E(98)P(67)E(98)) and P123 (E(21)P(67)E(21)) in mixtures with anionic surfactant sodium dodecyl sulfate (SDS). Total concentrations (c, SDS+copolymer) were as high as 50 wt % with mole ratios SDS/copolymer (mr) in the ranges 1-5 (F127) and 1-7 (P123). Temperatures were as high as 90 degrees C. Determination of the temperature dependences of the dynamic moduli served to confirm the gel boundaries from tube inversion and to reveal the high elastic moduli of the gels, e.g., compared at comparable positions in the gel phase, a 50 wt % SDS/P123 with mr = 7 had G' three times that of a corresponding gel of P123 alone. Small-angle X-ray scattering (SAXS) was used to show that the structures of all the SDS/F127 gels were bcc and that the structures of the SDS/P123 gels with mr = 1 were either fcc (c = 30 wt %) or hex (c = 40 wt %). Assignment of structures to SDS/P123 gels with values of mr in the range 3-7 was more difficult, as high-order scattering peaks could be very weak, and at the higher values of c and mr, the SAXS peaks included multiple reflections.

Incorporation of sparingly soluble species in mesostructured surfactant-polymer films.

Recently we have investigated the formation of novel thick, solid, mesostructured films of polymer/surfactant mixtures which form spontaneously at the air-solution interface. Here we report studies of the effect of adding a series of sparingly soluble species to the precursor solution, to alter the mesostructure of cetyltrimethylammonium bromide/polyethylenimine films and to investigate the incorporation of small molecules within the films. Small-angle neutron scattering confirmed that cyclohexane and decane evenly swell the micelles in film forming solutions, while cyclohexanol extends the prolate micelles along their long axis. Although the presence of these additives in solution did not greatly affect the formation of the film, it was observed that they did influence the structure of the films. Films produced with decane consisted of a cubic phase rather the conventional 2-D hexagonal phase, whilst both cyclohexane and cyclohexanol enhance the level of ordering in low MW polymer films. Benzene was found to have no significant effect on the film.

Formation of robust, free-standing nanostructured membranes from catanionic surfactant mixtures and hydrophilic polymers.

A new type of surfactant templated polymer film, which spontaneously forms at the air/water interface into micron-thick structures, was prepared from a water-soluble polymer and a catanionic surfactant mixture; the film is stable, highly ordered and robust, requiring no cross-linking agents to fix the structure.

Effect of micelle composition on the formation of surfactant-templated polymer films.

Surfactant-templated polymer films prepared from polyethylenimine (PEI), cetyltrimethylammonium bromide (CTAB), and octaethylene glycol monohexadecyl ether (C(16)E(8)) were examined and the effect of increasing the percentage of nonionic surfactant in the micelles measured using both surface and bulk-sensitive techniques. It was found that there is a strong interaction between CTAB and C(16)E(8), although no interaction between the C(16)E(8) and PEI was observed. Generally, increasing the percentage of C(16)E(8) in the micelles decreases both the thickness and degree of order in the films; however, it was observed, depending on the conditions, that films could still be formed with as little as 20% cationic surfactant. Experiments on the CTAB/Brij56/PEI system were also performed and these indicate that it is similar to the CTAB/C(16)E(8)/PEI system.

[Fungal colonization in preterm neonates weighing less than 1500g admitted to the neonatal intensive care unit]. / Colonisation à levures chez les prématurés de moins de 1500g hospitalisés en réanimation néonatale.

Fungal colonization is a common occurrence in preterm neonates. Our objective was to describe the profile and characteristics of fungal colonization in preterm infants admitted to the Martinique NICU. From March 2012 to January 2013, an epidemiological prospective cohort study was conducted with 57 very low-birth-weight infants. Cutaneous, rectal, gastric, respiratory, and urinary swabs were collected on admission, then every week for 4 weeks. The prevalence of fungal colonization was 68% (39/57): 46% by Malassezia species, 28% by Candida parapsilosis, 19% by C. albicans, 5% by C. glabrata, and 2% by C. guilliermondii. The colonized patients had a duration of parenteral nutrition and antibiotic therapy longer than the others (P<0.05). Nosocomial colonization (after 2 days of life) occurred in 52% of cases: Malassezia species and C. parapsilosis were the commensal skin yeasts most frequently implicated. Forty-nine percent (28/57) had suspected invasive fungal infections that received probabilistic treatment. Only one case of invasive fungal infection with C. glabrata was diagnosed. This study highlights the important role played by nosocomial transmission in the colonization of preterm newborns. Mycological surveillance cultures in the NICU are very useful for monitoring fungal ecology and can improve the prevention of fungal colonization in preterm infants at risk of invasive fungal infection.

[Hemihypertrophy and scoliosis revealing a Chiari 1 malformation with syringomyelia]. / Hémi-hypertrophie et scoliose révélatrices d'une malformation de Chiari de type 1 avec syringomyélie.

We report the case of a 9-year-old boy with progressive thoracic scoliosis and crossed hemihypertrophy who was discovered with a Chiari 1 malformation and syringomyelia. These disorders are connected by complex physiopathological mechanisms; their association deserves attention. This observation reviews the importance of the clinical examination, particularly the neurological exam, in childhood scoliosis. The features suggesting a neurogenic background of spine deformation should be sought. Scoliosis with hemihypertrophy can be the sign of an underlying neurological abnormality.

Self-assembled films formed at the air-water interface from CTAB/SDS mixtures with water-soluble polymers.

We have investigated the spontaneous self-assembly of solid, mesostructured films that form at the air-solution interface on solutions containing a neutral water-soluble polymer and catanionic surfactant mixtures of hexadecyl-trimethylammonium bromide (CTAB) and sodium dodecylsulphate (SDS). The formation processes and structures were probed using neutron reflectivity, X-ray reflectivity, off-specular time-resolved scattering, and grazing incidence diffraction. The mesostructures of films prepared with polyethylene oxide, polyethylenimine, and polyacrylamide at various cationic/anionic surfactant molar ratios are compared. The results suggest that polymers having a weak interaction with the surfactants cause a depletion aggregation process that results in a lamellar phase, whereas polymers having a stronger interaction with the surfactants produce more complex mesostructures in the films.

Macroscopic, mesostructured cationic surfactant/neutral polymer films: structure and cross-linking.

Mesostructured films of alkyltrimethylammonium bromides or cetylpyridinium bromide and polyethylenimines that spontaneously self-assemble at the air/water interface have been examined using a range of surface sensitive techniques. These films are unusual in that they can be micrometers thick and are relatively robust. Here we show that the films can be cross-linked and thus removed from the liquid surface where they form, as solid, mesostructured polymer-surfactant membranes. Cross-linking causes little change in the structure of the films but freezes in the metastable mesostructures, enhancing the potential of these films for future applications. Cross-linked films, dried after removal from the solution surface, retain the ordered nanoscale structure within the film. We also report grazing incidence X-ray diffraction (GID), which shows that most films display scattering consistent with 2D-hexagonal phase crystallites of rodlike surfactant micelles encased in polymer. Polymer branching makes little difference to the film structures; however, polymer molecular weight has a significant effect. Films with lower polymer MW are generally thinner and more ordered, while higher polymer MW films were thicker and less ordered. Increased pH causes formation of thicker films and improves the ordering in low MW films, while high MW films lose order. To rationalize these results, we propose a model for the film formation process that relates the kinetic and thermodynamic limits of phase separation and mesophase ordering to the structures observed.

Mixed thin films of a cationic amphiphilic porphyrin and n-alkanes.

Langmuir and Langmuir-Blodgett (LB) films of a cationic amphiphilic porphyrin mixed with n-alkanes octadecane and hexatriacontane were prepared and characterized, to examine the influence of the alkanes on film structure and stability. While the structure present in these films was controlled primarily by the porphyrin, the addition of the alkanes resulted in significant changes to both the phase behavior of the Langmuir films and the molecular arrangement of the LB films. These changes, as well as the observed chain length effects, are explained in terms of the intermolecular interactions present in the films.