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PubMed2006

Characteristics of polyelectrolyte multilayers: effect of PEI anchoring layer and posttreatment after deposition.

The influence of a first (anchoring) layer and film treatment on the structure and properties of polyelectrolyte multilayer (PEM) films obtained from polyallylamine hydrochloride (PAH) and polysodium 4-styrenesulfonate (PSS) was studied. Branched polyethyleneimine (PEI) was used as an anchoring layer. The film thickness was measured by ellipsometry. Complementary X-ray reflectometry and AFM experiments were performed to study the change in the interfacial roughness. We found that the thickness of the PEM films increased linearly with the number of layers and depended on the presence of an anchoring PEI layer. Thicker films were obtained for multilayers having PEI as the first layer comparing to films having the same number of layers but consisting of PAH/PSS only. We investigated the wettability of PEM surfaces using direct image analysis of the shape of sessile water drops. Periodic oscillations in contact angle were observed. PAH-terminated films were more hydrophobic than films with PSS as the outermost layer. The effect of long time conditioning of PEM films in solutions of various pH's or salt (NaCl) concentrations was also examined. Salt or base solutions induced modification in wetting properties of the polyelectrolyte multilayers but had a negligible effect on the film thickness.

Journal Article↗
PubMed2006

Preparation and structural evolution of SiO(2)-TiO(2) pillared layered manganese oxide nanocomposite upon intercalating reaction.

SiO(2)-TiO(2) pillared layered manganese oxide nanohybrid was successfully synthesized by preliminarily expanding the interlayer of H-type layered manganese oxide using dodecylamine, followed by reacting it with a mixture solution of titanium isopropoxide and tetraethylorthosilicate. The basal spacing and the pillared agent content of the obtained materials connected with the length of intercalated n-alkylamine, incorporated Si/Ti molar ratios and the solvothermal treatment temperature. The structural evolution of SiO(2)-TiO(2) pillared layered manganese oxide nanohybrid was characterized by XRD, DSC-TGA, SEM, IR, N(2) adsorption-desorption and element analyses. TiO(2) particles exhibited a stronger affinity for the negatively charged manganese layers, and the TiO(2) particles incorporated were independently intercalated without any distinct chemical bonding with the co-intercalated SiO(2) particles. SiO(2)-TiO(2) pillared layered manganese oxide nanohybrid had a BET surface area of 98 m(2)/g with a gallery height of about 1.43 nm between layers. The obtained SiO(2)-TiO(2) co-pillared layered manganese oxide nanohybrid is expected as a selective catalyst, or an improved battery material.

Journal Article↗
PubMed2005

Structural aspects of the Eberth-Katschenko layer of Bufo ictericus integument: histochemical characterization and biochemical analysis of the cutaneous calcium (Amphibian, Bufonidae).

Anuran, such as Brazilian toad Bufo ictericus Spix, 1824, possess a calcified dermal layer called the Eberth-Katschenko (EK) layer located between the stratum spongiosum and the stratum compactum. It has been regarded as a protective barrier against desiccation or involved in storage and mobilization of calcium, or a barrier for the interchange of substances between the animal's internal and external environment. The B. ictericus integument was removed from the ventral and dorsal regions and examined by light microscopy, using histochemical techniques, and also submitted to biochemical calcium analysis. The intermediate layer is strongly basophilic and metachromatic. In the EK layer Alcian blue at different critical electrolytic concentration revealed hyaluronic acid, which coexists with the dermal calcium. We conclude that the EK layer of B. ictericus is a discontinuous layer and is formed of hyaluronic acid and a sulfated GAG different from chondroitin sulfate, heparin and heparan sulfate or keratan sulfate. The amount of cutaneous calcium is independent of region and sex. GAGs may play an important role in dermal hydric balance, protecting the animal against desiccation, and hyaluronic acid is probably able to anchor dermal calcium. Thus, all compounds of the EK layer are essential for integument integrity and functionality.

Animals↗
PubMed2004

Thalamocortical projection from the ventral posteromedial nucleus sends its collaterals to layer I of the primary somatosensory cortex in rat.

Here we examined quantitatively axonal projections originating from the ventral posteromedial thalamic nucleus (VPM) to layer I of the primary somatosensory cortex (SI) by extracellular and intracellular injections of biocytin as an anterograde tracer. Following the extracellular injections, two types of VPM afferents with different arborization patterns in SI were observed. The type I extended vertically, forming dense plexus in layers IV and VI, and projected collaterals to layer I. The type II rarely branched in SI, converged in the plexus formed by the type I, and projected no collaterals to the supragranular layers. The labeled fibers in layer I derived from the first type ran parallel to the brain surface, and their mean length was 339.7 +/- 87.5 microm. Intracellular injection into VPM neurons bearing both types of afferent demonstrated the full axonal arborization in both the reticular thalamic nucleus (Rt) and SI. The total length of the axon of a neuron bearing the type I was 86,968.8 microm, and the length of axonal collaterals in layer I of SI was 433.1 microm. The total axonal length of a neuron bearing the type II was very small. The present study is the first to demonstrate substantial projections from VPM to layer I of SI, and provide quantitative data on the entire extent of the axonal arborization of thalamocortical projections from single VPM neurons.

Animals↗
PubMed2004

NDE of two-layered mortar samples using high-frequency Rayleigh waves.

The Spectral Analysis of Surface Waves (SASW) is a popular technique in seismics for imaging the ground subsurface. It uses the dispersive properties of Rayleigh waves in a transversely homogeneous, multilayered medium. The SASW approach is being transposed into the civil engineering domain to characterize subsurface damage in concrete structures. Such a damage consists in a few millimeters thick surface layer with porosity slightly higher than in the sound material. It is induced by contact with moisture or chemicals at the surface of the structure and may facilitate penetration of aggressive agents. In this study, two-layered mortar samples are made to mimic concrete cover damage in real structures. The dispersive behavior of Rayleigh waves arises when the wavelength is comparable to the thickness of the first layer. Given the small thickness of this layer, it requires increasing the frequency up to several hundreds of kHz, which means high attenuation and low signal-to-noise ratio. Rayleigh waves with 0.5 MHz central frequency are generated into the samples by the wedge method. Phase velocity dispersion curves are obtained by broadband phase spectroscopy from signals received at various distances from the source. The signal processing is first validated on simulated signals with known dispersion law. Then, the measured dispersion curves are compared with the theoretical curve for a two-layered medium, following Haskell's approach. The measured curve displays the general behavior expected from theory. However, a three-layered, visco-elastic model would be necessary to get a better fit and to estimate more accurately the parameters of each layer.

Journal Article↗
PubMed2003

Specific ion effects via ion hydration: II. Double layer interaction.

A simple modified Poisson-Boltzmann formalism, which accounts also for those interactions between electrolyte ions and colloidal particles not included in the mean potential, is used to calculate the force between two parallel plates. It is shown that the short-range interactions between ions and plates, such as those due to the change in the hydration free energy of a structure-making/breaking ion that approaches the interface, affect the double layer interaction at large separations through the modification of the surface potential and surface charge density. While at short separations (below the range of the short-range ion-hydration forces) the interaction can be attractive, at larger separations the interaction is always repulsive, as in the traditional theory. When the long-range van der Waals interactions between the ions and the system (ion-dispersion interactions) are accounted for in the modified Poisson-Boltzmann approach, an attractive force between plates can be generated. At sufficiently large separations, this attraction can become even stronger than the traditional van der Waals attraction between plates of finite thickness, thus generating a dominant long-range 'double layer attraction'. At small plate separations, the attraction generated by the ion-dispersion forces combined with the electrostatic repulsion due to the double layers overlap can lead to a variety of interactions, from a weak attraction (which is typically by at least one order of magnitude smaller than the traditional van der Waals attraction between plates) to a strong double layer repulsion (for sufficiently large surface charges). Both types of ion interactions (long-range van der Waals or short-range ionic hydration) strongly affect the magnitude of the double layer interaction, and can account for the specific ion effects observed experimentally. However, they do not affect qualitatively the traditional theory of the colloid stability, which predicts that the colloid is stable when there is a sufficiently large charge on the surface, and coagulates when the van der Waals interactions between two colloidal particles dominate. The only qualitative difference found when the ion-dispersion interactions were incorporated into the traditional double layer theory was the emergence of a 'double layer attraction' at very large separations, which, however, does not affect much the stability of colloids.

Colloids↗
PubMed2000

Scanning laser polarimetry of the normal human retinal nerve fiber layer: a quantitative analysis.

PURPOSE: To provide a quantitative comparison of retardation values obtained with the scanning laser polarimeter (Nerve Fiber Layer Analyzer; Laser Dignostic Technologies, San Diego, California) in normal subjects, with the known histologic properties of the human retinal nerve fiber layer. METHODS: Scanning laser polarimetry was performed on 48 normal subjects. The retardation values obtained from each eye were processed to remove reflections from the optic nerve head vasculature and to derive peripapillary polar retardation profiles. The location of the maximum and minimum retardation values superior and inferior to the disk was determined. Retardation values were also determined along lines running radially from the center of the optic disk to through the points of maximal retardation. RESULTS: Retardation values were greater in the superior and inferior quadrants of the peripapillary retinal nerve fiber layer compared with the nasal and temporal quadrants. Superiorly, peak retardation values were nasal to the vertical meridian by 22.9 degrees (SD, 17.5) in right eyes and by 15.7 degrees (SD, 17.7) in left eyes. Inferiorly, the peak showed a closer correspondence with the vertical meridian, lying nasal to this by 0.8 degrees (SD, 14.9) in right eyes and temporal to this by 2.8 degrees (SD, 15.4) in left eyes. Radial analysis showed that the peak retardation occurred approximately (0.5 to 0.7 disk diameters from the optic disk margin) at the superior and inferior aspect of the disk. The degree of modulation of retardation around the optic disk was less than would be expected from the variation in peripapillary nerve fiber layer thickness seen histologically. CONCLUSION: The location of the peak retardation values shows reasonable agreement with the angular location of the peak values of nerve fiber layer thickness published for humans. By contrast, the modulation of retardation values around the disk and the change with eccentricity from the optic disk center differ from the anatomic data. The Nerve Fiber Layer Analyzer appears to measure a correlate of nerve fiber layer thickness, but it is important that any discrepancies between the retardation and anatomic data are recognized in the clinical interpretation of polarimetric data.

Adult↗
PubMed2000

Measurement of peripapillary retinal nerve fiber layer volume in glaucoma.

PURPOSE: To measure peripapillary retinal nerve fiber layer volume in normal subjects and patients with ocular hypertension, primary open-angle glaucoma, and low-tension glaucoma. METHODS: Sixty-five subjects were classified into four groups of normal subjects and subjects with ocular hypertension, primary open-angle glaucoma, and low-tension glaucoma on the basis of intraocular pressure measurements, visual field loss, and optic disk appearance. Groups were matched for sex, age, and optic disk area. Peripapillary retinal nerve fiber layer volume measurements were made with a modification of software version 1.11 of the Heidelberg Retina Tomograph confocal scanning laser ophthalmoscope. Retinal nerve fiber layer volume measurements were taken at 0.1-mm increments from the disk margin for a global 360-degree assessment and at four predefined segments using two different reference planes. Statistical analysis was carried out using analysis of variance with Bonferroni correction. RESULTS: Retinal nerve fiber layer volume measurements showed a gradation from normal to ocular hypertension and from ocular hypertension to glaucoma groups. Mean group measurements showed statistically significant differences (P <.05) in peripapillary retinal nerve fiber layer volume for most segmental measures between the groups. Measurements with the default reference plane in the 0.0-mm to 0.1-mm and 0.1-mm to 0.2-mm increments for the superotemporal segment showed the greatest differences between groups (P <.00005). CONCLUSION: Peripapillary retinal nerve fiber layer volume measurements differ between groups of normal subjects and patients with ocular hypertension, primary open-angle glaucoma, and low-tension glaucoma. This measure offers a further method of assessment of retinal nerve fiber layer in patients with glaucoma and glaucoma suspects.

Aged↗
PubMed1998

Voltage clamp studies on S-layer-supported tetraether lipid membranes.

Isolated subunits from the cell surface proteins (S-layer) of Bacillus coagulans E38-66 have been recrystallized on a glycerol dialkyl nonitol tetraether lipid (GDNT)-monolayer and the electrophysical features of this biomimetic membrane have been investigated in comparison to unsupported GDNT-monolayers. The GDNT-monolayer, spread on a Langmuir-Blodgett trough, was clamped with the tip of a glass patch pipette. In order to investigate the barrier function and potential to incorporate functional molecules, voltage-clamp examinations on plain and S-layer-supported GDNT-monolayers were per-formed. Our results indicate the formation of a tight GDNT-monolayer sealing the tip of the glass pipette, and a decrease in conductance of the GDNT-monolayer upon recrystallization of the S-layer protein. Thus, the S-layer protein, apparently, did not penetrate or rupture the lipid monolayer. The valinomycin-mediated increase in conductance was less pronounced for the S-layer-supported than for the plain GDNT-monolayer, indicating differences in the accessibility and/or in the fluidity of the lipid membranes. Furthermore. in contrast to plain GDNT-monolayers. S-layer supported GDNT-monolayers with high valinomycin-mediated conductance persisted over long, periods of time, indicating enhanced stability. These composite S-layer/lipid films may constitute a new tool for electrophysical and electrophysiological studies on membrane-associated and membrane-integrated biomolecules.

Anti-Bacterial Agents↗
PubMed2002

Normal and lateral forces between lipid covered solids in solution: correlation with layer packing and structure.

We report on the normal and lateral forces between controlled-density mono- and bilayers of phospholipid co-adsorbed onto hydrophobic and hydrophilic solid supports, respectively. Interactions between 1,2-dioleoyl-sn-glycero-3-phosphocholine layers were measured using an atomic force microscope. Notable features of the normal force curves (barrier heights and widths) were found to correlate with the thickness and density of the supported lipid layers. The friction and normal force curves were also found interrelated. Thus, very low friction values were measured as long as the supported layer(s) resisted the normal pressure of the tip. However, as the applied load exceeded the critical value needed for puncturing the layers, the friction jumped to values close to those recorded between bare surfaces. The lipid layers were self-healing between measurements, but a significant hysteresis was observed in the force curves measured on approach and retraction, respectively. The study shows the potential of using atomic force microscopy for lipid layer characterization both with respect to structure and interactions. It further shows the strong lubricating effect of adsorbed lipid layers and how this varies with surface density of lipids. The findings may have important implications for the issue of joint lubrication.

Adsorption↗
PubMed1997

Thickened inner hypoechoic layer of the gallbladder wall in the diagnosis of anomalous pancreaticobiliary ductal union with endosonography.

BACKGROUND: An anomalous pancreaticobiliary ductal union (APBD) is a high-risk factor for biliary tract carcinoma, which often is not diagnosed before overt malignancy. The early detection of APBD is therefore clinically important. We evaluated the gallbladder wall in APBD patients with endoscopic ultrasonography. METHODS: Clinicopathologic features and ultrasonographic findings of the gallbladder in 33 consecutive patients with APBD between 1986 and 1995 were studied in relation to two subtypes of APBD, that is, undilated (n = 17) and dilated (n = 16). The gallbladder wall was evaluated with conventional ultrasonography and/or endoscopic ultrasonography. Histologic examinations of 25 resected gallbladders were made. RESULTS: Fourteen of the seventeen patients with undilated type APBD (82%) had diffuse thickened gallbladder wall of 4 mm or more, whereas 5 of the 16 with dilated type (31%) had this finding (p < 0.01). The thickened gallbladder wall consisted sonographically of two layers: diffuse thickened inner hypoechoic layer and outer hyperechoic layer. Mucosal hyperplasia was histologically found in 8 of 9 cases (89%) with thickened inner hypoechoic layer on endoscopic ultrasonography. Mucosal hyperplasia was observed in 10 of 11 undilated type APBD cases (91%) in which cholecystectomy was performed. In addition, the presence of anomalous union was shown by endoscopic ultrasonography in 9 of 11 patients with undilated type APBD (82%) and all 7 of those with dilated type. The characteristic ultrasonographic pattern of diffuse thickened inner hypoechoic layer was observed exclusively in patients with mucosal hyperplasia of the gallbladder associated with APBD among 2085 endoscopic ultrasonography examinations performed during the study period. CONCLUSIONS: Diffuse thickened inner hypoechoic layer of the gallbladder wall was frequently observed in APBD patients, especially those with the undilated type, on ultrasonography and/or endoscopic ultrasonography. This finding corresponded histologically to mucosal hyperplasia of the gallbladder mucosa. Thickened inner hypoechoic layer is a useful ultrasonographic sign that indicates mucosal hyperplasia of the gallbladder and, particularly, the possible coexistence of undilated type APBD before the appearance of overt malignancy.

Adult↗
PubMed2003

Characterization of sizing layers and buried polymer/sizing/substrate interfacial regions using a localized fluorescent probe.

A novel technique is described to investigate buried polymer/sizing/substrate interfacial regions, in situ, by localizing a fluorescent probe molecule in the sizing layer. Epoxy functional silane coupling agent multilayers were deposited on glass microscope cover slips and doped with small levels of a fluorescently labeled silane coupling agent (FLSCA). The emission of the grafted FLSCA was dependent on the silane layer thickness, showing blue-shifted emission with decreasing thickness. The fluorescent results suggest that thinner layers were more tightly bound to the glass surface. The layers were also characterized by scanning electron microscopy, contact angle, and thermogravimetric analysis (TGA). When the FLSCA-doped silane layers were immersed in epoxy resin, a blue shift in emission occurred during resin cure, indicating the potential to study interfacial chemistry, in situ. Thicker silane layers exhibited smaller fluorescence shifts during cure, suggesting incomplete resin penetration into the thickest silane layers.

Benzhydryl Compounds↗
PubMed2003

Structural and biochemical analysis of the Leptinotarsa decemlineata (Coleoptera; Chrysomeloidea) crystalline chorionic layer.

The developmental aspects of the Leptinotarsa decemlineata crystalline chorionic layer (CCL) morphogenesis, its composition and its supramolecular structure were studied. The mature Leptinotarsa decemlineata eggshell consists of the vitelline membrane and the CCL, while the follicle cell remnants following their degeneration after oogenesis completion constitute the outer chorionic layer. The vitelline membrane and the CCL layers are formed through continuous material deposition from the follicular epithelium, whereas the main morphogenic factor during most insect eggshell formation, namely the follicle cell and oocyte microvilli, are seemingly involved only in vitelline membrane formation. Analysis of the CCL morphogenesis showed that this layer is assembled from a fiber-like pre-crystalline material, which accumulates at the vitelline membrane-follicle cell interface. The mature CCL is about 1 microm thick and exhibits a periodicity of approximately 10 nm, while computer image analysis studies of thin-sectioned CCL revealed the existence of crystalline layers parallel to the CCL surface. Finally, SDS-PAGE-electrophoresis of purified CCLs showed that this crystalline layer is of a proteinaceous nature and is most likely composed of 3-5 polypeptides with a molecular weight ranging in between 28-60 kDa. Overall, these data exemplify for the first time the nature and supramolecular arrangement of a crystalline layer and its constituent molecules in Coleoptera.

Animals↗
PubMed2003

The multi-layered structure of Dps with a novel di-nuclear ferroxidase center.

The crystallization of cellular components represents a unique survival strategy for bacterial cells under stressed conditions. A highly ordered, layered structure is often formed in such a process, which may involve one or more than one type of bio-macromolecules. The main advantage of biocrystallization has been attributed to the fact that it is a physical process and thus is independent of energy consumption. Dps is a protein that crystallizes to form a multi-layered structure in starved cells in order to protect DNA against oxidative damage and other detrimental factors. The multi-layered crystal structure of a Dps protein from Bacillus brevis has been revealed for the first time at atomic resolution in the absence of DNA. Inspection of the structure provides the first direct evidence for the existence of a di-nuclear ferroxidase center, which possesses unique features among all the di-iron proteins identified so far. It constitutes the structural basis for the ferroxidase activity of Dps in the crystalline state as well as in solution. This finding proves that the enzymatic process of detoxification of metal ions, which may cause severe oxidative damage to DNA, is the other important aspect of the defense mechanism performed by Dps. In the multi-layered structure, Dps dodecamers are organized in a highly ordered manner. They adopt the classic form of hexagonal packing in each layer of the structure. Such arrangement results in reinforced structural features that would facilitate the attraction and absorption of metal ions from the environment. The highly ordered layered structure may provide an ideal basis for the accommodation of DNA between the layers so that it can be isolated and protected from harmful factors under stress conditions.

Bacillus↗
PubMed1983

Helical disorder and the filament structure of F-actin are elucidated by the angle-layered aggregate.

Angle-layered aggregates of F-actin are net-like structures induced by Mg2+ concentrations below that used to form paracrystals. These aggregates incorporate the angular disorder of subunits, which has been described elsewhere for isolated actin filaments. Because this disorder is incorporated into the aggregates in solution at the time they are formed, the possibility of negative stain preparation being responsible for the disorder is excluded. The simple two-layered geometry of the angle-layered aggregate provides information about the shape of the component actin filaments free from the superposition of large numbers of layers. A model for the filament shape, derived from single filaments and confirmed by the angle-layered aggregate, is different from those that have previously emerged from paracrystal studies. An understanding of the interfilament bond in both the angle-layered aggregate and the paracrystal allows one to reconcile these different models. We have found a bipolar bonding rule, with staggered crossover points in the angle-layered aggregate, which we suggest is also responsible for Mg2+ paracrystals. This bonding rule can explain the apparent alignment of crossover points in adjacent filaments in paracrystals as a consequence of the superposition of staggered filaments.

Actins↗
PubMed1992

The effect of auxiliary conditions on intestinal unstirred layer diffusion modelled by numerical simulation.

Estimation of intestinal unstirred layer thickness usually involves inducing transmural potential difference changes by altering the content of the solution used to perfuse the small intestine. Osmotically active solutes, such as mannitol, when added to the luminal solution diffuse across the unstirred water layer (UWL) and induce osmotically dependent changes in potential difference. As an alternative procedure, the sodium ion in the luminal fluid can be replaced by another ion. As the sodium ion diffuses out of the UWL, the change in concentration next to the intestinal membrane alters the transmural potential difference. In both cases, UWL thickness is calculated from the time course of the potential difference changes, using a solution to the diffusion equation. The diffusion equation solution which allows the calculation of intestinal unstirred layer thickness was examined by simulation, using the method of numerical solutions. This process readily allows examination of the time course of diffusion under various imposed circumstances. The existing model for diffusion across the unstirred layer is based on auxiliary conditions which are unlikely to be fulfilled in the same intestine. The present simulation additionally incorporated the effects of membrane permeability, fluid absorption and less than instantaneous bulk phase concentration change. Simulation indicated that changes within the physiologically relevant range in the chosen auxiliary conditions (with the real unstirred layer length kept constant) can alter estimates of the apparent half-time. Consequently, changes in parameters unassociated with the unstirred layer would be misconstrued as alterations in unstirred layer thickness.

Gastrointestinal Contents↗
PubMed1983

Stratification and square pattern arrangements in the dorsal inner plexiform layer in the retina of Callionymus lyra L.

The dorsal inner plexiform layer in the retina of Callionymus lyra consists of successive fibrous F layers and geometrically organized P layers. In the F layers no pattern arrangement of the bipolar synaptic buttons was observed. In the P layers, on the contrary, the bipolar synaptic buttons are grouped by three distinct square patterns. The alpha pattern measures 5 micron and corresponds to the square pattern of the photoreceptor cells. The beta and the gamma pattern measure 7 micron. One of both patterns corresponds to the single cone arrangement, while the other coincides with the crossings of the rows of double cone pairs. The alternation of F and P layers results in the stratified appearance of the inner plexiform layer.

Animals↗
PubMed1983

Interbipolar contacts in the dorsal inner plexiform layer in the retina of Callionymus lyra L.

Several types of direct contacts have been observed between the square pattern-arranged bipolar synaptic buttons in the P layers in the dorsal inner plexiform layer of the Callionymus retina. These contacts are not randomly occurring interconnections, but they are systematically formed throughout the whole of the dorsal retinal zone and they may be the site of direct synaptic interactions between similar as well as dissimilar bipolar axons. Reciprocal ribbon synapses have been found in the P2,2 layer. Morphologically mixed synapses occur in the P5,1 layer. These contact zones show morphologic characteristics of both chemical and electronic synapses. Morphologically mixed synaptic complexes, representing a triple coupling between two adjacent similar bipolar buttons and an amacrine cell process, have been observed in the P1,1, the P2,1 and the P5,2 layer. The morphology of the interbipolar contacts in the P3,2 layer does not clearly point to a synaptic function. Our results suggest a high degree of functional stratification in the inner plexiform layer.

Animals↗