Mapping the 3D distribution of CdSe nanocrystals in highly oriented and nanostructured hybrid P3HT-CdSe films grown by directional epitaxial crystallization.

Highly oriented and nanostructured hybrid thin films made of regioregular poly(3-hexylthiophene) and colloidal CdSe nanocrystals are prepared by a zone melting method using epitaxial growth on 1,3,5-trichlorobenzene oriented crystals. The structure of the films has been analyzed by X-ray diffraction using synchrotron radiation, electron diffraction and 3D electron tomography to afford a multi-scale structural and morphological description of the highly structured hybrid films. A quantitative analysis of the reconstructed volumes based on electron tomography is used to establish a 3D map of the distribution of the CdSe nanocrystals in the bulk of the films. In particular, the influence of the P3HT-CdSe ratio on the 3D structure of the hybrid layers has been analyzed. In all cases, a bi-layer structure was observed. It is made of a first layer of pure oriented semi-crystalline P3HT grown epitaxially on the TCB substrate and a second P3HT layer containing CdSe nanocrystals uniformly distributed in the amorphous interlamellar zones of the polymer. The thickness of the P3HT layer containing CdSe nanoparticles increases gradually with increasing content of NCs in the films. A growth model is proposed to explain this original transversal organization of CdSe NCs in the oriented matrix of P3HT.

Bacterial colonization after tunneling in 402 perineural catheters: a prospective study.

BACKGROUND: Bacterial colonization of peripheral nerve catheters is frequent, although infection is relatively rare. With central venous catheters, the tunneling of the catheter into the subcutaneous tissue significantly decreases catheter colonization and catheter-related sepsis. We evaluated the incidence of bacterial colonization in adult patients with tunnelized perineural nerve catheters. METHODS: Peripheral nerve catheters placed under sterile conditions for postoperative analgesia were evaluated prospectively. After removal, they were analyzed for colonization. Quantitative culture was used as described by Brun-Buisson for intravascular catheters. The site of insertion was monitored daily for any signs of infection. RESULTS: Four-hundred-two patients were included in the study during a 2-yr period. The mean duration of peripheral nerve catheters was 48 h (47-50.4). Positive culture occurred in 25 catheters, indicating that the incidence of colonization was 6.22% (3.8-8.5). The microbiological analysis of the catheter tip cultures revealed coagulase-negative staphylococci in 72%. Twenty-two catheters of 25 catheters each had one microorganism, and for three catheters, two microorganisms were identified. No infection was found in any patient. CONCLUSION: The incidence of perineural catheter colonization is low with subcutaneous tunneling. Controlled randomized studies are warranted to determine whether this procedure decreases the risk for infection.

Onset of the alpha-relaxation in the glass-forming solution LiCl-6H2O revealed by Brillouin scattering techniques.

We measured the dynamic structure factor of the liquid and glassy phases of the LiCl-6H(2)O solution by means of inelastic scattering of radiation in the visible, UV, and x-ray range, between 1 GHz and 10 THz, and by means of photon-correlation spectroscopy, between 0.01 Hz and 20 kHz. The measurements were performed in the temperature range between 353 and 80 K. Our data show that a single-relaxation process exists at high temperature, which has features similar to those of the single relaxation of pure water. Upon cooling the system below approximately 220 K, this single mode starts to differentiate two processes, a structural (alpha-) and a secondary (beta-) relaxation. As the temperature is decreased, the beta-relaxation is the vanishing continuation of the single, high-temperature process, while the onset of the alpha-relaxation occurs at the expense of the beta-process.

Synchrotron radiation diffraction from two-dimensional protein crystals at the air/water interface.

Protein structure determination by classical x-ray crystallography requires three-dimensional crystals that are difficult to obtain for most proteins and especially for membrane proteins. An alternative is to grow two-dimensional (2D) crystals by adsorbing proteins to ligand-lipid monolayers at the surface of water. This confined geometry requires only small amounts of material and offers numerous advantages: self-assembly and ordering over micrometer scales is easier to obtain in two dimensions; although fully hydrated, the crystals are sufficiently rigid to be investigated by various techniques, such as electron crystallography or micromechanical measurements. Here we report structural studies, using grazing incidence synchrotron x-ray diffraction, of three different 2D protein crystals at the air-water interface, namely streptavidine, annexin V, and the transcription factor HupR. Using a set-up of high angular resolution, we observe narrow Bragg reflections showing long-range crystalline order in two dimensions. In the case of streptavidin the angular range of the observed diffraction corresponds to a resolution of 10 A in plane and 14 A normal to the plane. We show that this approach is complementary to electron crystallography but without the need for transfer of the monolayer onto a grid. Moreover, as the 2D crystals are accessible from the buffer solution, the formation and structure of protein complexes can be investigated in situ.

Characterization of the growth of 2D protein crystals on a lipid monolayer by ellipsometry and rigidity measurements coupled to electron microscopy.

We present here some sensitive optical and mechanical experiments for monitoring the process of formation and growth of two-dimensional (2D) crystals of proteins on a lipid monolayer at an air-water interface. The adsorption of proteins on the lipid monolayer was monitored by ellipsometry measurements. An instrument was developed to measure the shear elastic constant (in plane rigidity) of the monolayer. These experiments have been done using cholera toxin B subunit (CTB) and annexin V as model proteins interacting with a monosialoganglioside (GM1) and dioleoylphosphatidylserine (DOPS), respectively. Electron microscopy observations of the protein-lipid layer transferred to grids were systematically used as a control. We found a good correlation between the measured in-plane rigidity of the monolayer and the presence of large crystalline domains observed by electron microscopy grids. Our interpretation of these data is that the crystallization process of proteins on a lipid monolayer passes through at least three successive stages: 1) molecular recognition between protein and lipid-ligand, i.e., adsorption of the protein on the lipid layer; 2) nucleation and growth of crystalline patches whose percolation is detected by the appearance of a non-zero in-plane rigidity; and 3) annealing of the layer producing a slower increase of the lateral or in-plane rigidity.

Structural basis of cell-cell adhesion by cadherins.

Crystal structures of the amino-terminal domain of N-cadherin provide a picture at the atomic level of a specific adhesive contact between cells. A repeated set of dimer interfaces is common to the structure in three lattices. These interactions combine to form a linear zipper of molecules that mirrors the linear structure of the intracellular filaments with which cadherins associate. This cell-adhesion zipper may provide a mechanism to marshal individual molecular adhesive interactions into strong bonds between cells.

Control of structure and growth of polymorphic crystalline thin films of amphiphilic molecules on liquid surfaces.

The spontaneous formation and coexistence of crystalline polymorphic trilayer domains in amphiphilic films at air-liquid interfaces is demonstrated by grazing incidence synchrotron x-ray diffraction. These polymorphic crystallites may serve as models for the early stages of crystal nucleation and growth, helping to elucidate the manner in which additives influence the progress of crystal nucleation, growth, and polymorphism and suggesting ways of selectively generating and controlling multilayers on liquid surfaces. Auxiliary molecules have been designed to selectively inhibit development of the polymorphs, leading primarily to a single phase monolayer.