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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Different sizes of nanotubes of poly(2-methoxy-5-(n-hexadecyloxy)-p-phenylene vinylene)(MH-PPV) have been fabricated at the air/water interface by compressing a monolayer of MH-PPV beyond its collapse point, and their structural characteristics were studied by means of TEM, AFM, SAXRD, IRRAS.
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PMID:Nanotubes of poly(phenylene vinylene) derivative at the air/water interface. 1526 69

The forced rupture of single chemical bonds in biomolecular compounds (e.g. ligand-receptor systems) as observed in dynamic force spectroscopy experiments is addressed. Under the assumption that the probability of bond rupture depends only on the instantaneously acting force, a data collapse onto a single master curve is predicted. For rupture data obtained experimentally by dynamic AFM force spectroscopy of a ligand-receptor bond between a DNA and a regulatory protein we do not find such a collapse. We conclude that the above mentioned, generally accepted assumption is not satisfied and we discuss possible explanations.
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PMID:Theoretical analysis of dynamic force spectroscopy experiments on ligand-receptor complexes. 1528 37

New nanoparticles based on well-defined dextran esters were prepared by a dialysis process. Dextran was converted into a propionate with a degree of substitution of 1.70 and, subsequently, acylated under homogeneous reaction conditions with a pyroglutamic acid imidazolide, which is prepared in situ by conversion of pyroglutamic acid with N,N-carbonyldiimidazole. The synthesis path allows perfect control of the amphiphilicity and solubility. The highly functionalized polysaccharide derivative avoids the collapse of the nanostructure due to the prevention of hydrogen bond formation. The major fraction of the dextran propionate pyroglutamate nanoparticles investigated by SEM and AFM exhibits narrow size distribution with 370 nm as mean diameter and uniform spherical shape. The SEM image verifies that polymeric nanoparticles in the suspensions did not undergo any morphological changes within 3 weeks.
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PMID:Nanoparticles on the basis of highly functionalized dextrans. 1604 24

Asymmetrically substituted poly(paraphenylene) (PhPPP) with hydrophilic and hydrophobic side chains was investigated. The polymer behavior at the air-water interface was studied on the basis of surface pressure-area (pi-A) isotherms and compression/expansion hysteresis measurements. PhPPP can form stable monolayers with an area per repeat unit of A=0.20+/-0.02 nm2 and a collapse pressure in the range of pi=25 mN/m. Then, Langmuir-Blodgett-Kuhn (LBK) films of PhPPP were prepared by horizontally and vertically transferring the Langmuir monolayers onto hydrophilic solid substrates at pi=12 mN/m. Cross-section analysis of the AFM tapping-mode topography images of a single transferred monolayer reveals a thickness of d0=0.9+/-0.1 nm. Taking into account the obtained monolayer thickness, curve-fitting calculations of angular scan data of LB monolayers measured using surface plasmon resonance (SPR) spectroscopy lead to a value for the refractive index of n=1.78+/-0.02 at lambda=632.8 nm. Next, the spontaneous formation of a PhPPP monolayer by adsorption from solution was studied ex situ by atomic force microscopy and UV-vis spectroscopy and in situ by using SPR spectroscopy. Stable self-assembled monolayers of PhPPP can be formed on hydrophilic surfaces with a thickness similar to that of the monolayer obtained using the LB method. The characterization results confirmed the amphiphilic character and the self-assembly properties of PhPPP, as well as the possibility of preparing homogeneous monolayer and multilayer films.
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PMID:Langmuir-Blodgett-Kuhn and self-assembled films of asymmetrically substituted poly(paraphenylene). 1634 86

Various aspects of Asian and Caucasian hairs were investigated and compared. We started by studying their cuticle structures--the number of cuticle layers, width of the cuticle cells, degree of their inclination, and the interval between surface cuticle edges. As a result of this study, on about two hundred subjects for each race, it was shown that there were statistically meaningful differences between all these attributes for the two hair types. Asian hair has more cuticle layers and wider cuticle cells than Caucasian hair, and the cuticular inclination of Asian hair is steeper and its cuticular interval is narrower than in Caucasian hair. In addition, it was also found that there are differences in how cuticle cells begin to fail. Under extension stress, Asian hair cuticles fail as large pieces while keeping their original shape. On the other hand, Caucasian hair cuticles tend to collapse to form small fragments. AFM measurements revealed that Caucasian cuticles are indeed more fragile than Asian cuticles. These results suggest that the strength of cuticular subcomponents is different between Asian and Caucasian hair and that the weakest point, where stress is first absorbed, differs between races. It was proven that the cuticles of Asian hair are more easily peeled off than Caucasian hair cuticles during daily grooming. This can be attributed to the difference in how stress is absorbed.
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PMID:Morphology and properties of Asian and Caucasian hair. 1695 11

We have investigated the effect of sphingomyelin (SM) to ceramide enzymatic conversion on lipid bilayers using Giant Unilamellar Vesicles (GUVs). Sphingomyelinase was added externally to GUVs containing various proportions of SM. In situ asymmetrical SM conversion to ceramide reduced the area of one leaflet. In the absence of equilibration of all the lipids between the two leaflets, a mismatch between the two monolayers was generated. The tension generated by this mismatch was sufficient to trigger the formation of membrane defects and total vesicle collapse at relatively low percentage of SM ( approximately 5% mol). The formation of nanometric size defects was visualised by AFM in supported bilayers. Vesicle rupture was prevented in two circumstances: (a) in GUVs containing a mixture of l(d) and l(o) domains and (b) in GUVs containing 5% lyso-phosphatidylcholine. In both cases, the accumulation of enough ceramide (at initial SM concentration of 10%) allowed the formation of ceramide-rich domains. The coupling between the two asymmetrical monolayers and the condensing effect produced by the newly formed ceramide generated a tension that could underlie the mechanism through which ceramide formation induces membrane modifications observed during the late stages of apoptosis.
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PMID:Surface tension induced by sphingomyelin to ceramide conversion in lipid membranes. 1729 25

We report on electrochemically prepared hydrogel layers of poly-N-isopropylacrylamide (pNIPAm) and on the influence that the supporting electrolyte has on their thickness and morphology. Ions that are destabilizing in the Hofmeister sense increase the thickness. The effect correlates well with the ion's tendency to lower the lower critical solution temperature (LCST) of pNIPAm films. AFM micrographs show small-scale globules. When the films were produced in the presence of a destabilizing salt (such as ammonium sulfate) one also observes larger features, resembling wrinkles. We attribute the globules to nucleated growth of surface-attached microgels, whereas the wrinkles presumably are produced by the collapse of hydrogen bubbles underneath a well-crosslinked film. Adding a chain transfer agent to the reactant solution reduces the lateral heterogeneities.
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PMID:Electrochemically produced responsive hydrogel films: influence of added salt on thickness and morphology. 1867 26

This work characterizes the impact of lipid symmetry/asymmetry on drying/rehydration reorganization in phase-separated dilauroylphosphatidylcholine (DLPC)/distearoylphosphatidylcholine (DSPC) supported lipid bilayers (SLBs) at the submicron and micron-scale. In addition the prevention of major drying/rehydration reorganization by the use of trehalose is demonstrated. Even though it was found using fluorescence microscopy that micrometer scale structure is preserved in the presence and absence of trehalose upon drying/rehydration, AFM and FRAP experiments successfully revealed major changes in the phase-separated structure such as defects, obstructions, lipid condensation, collapse structures, and complex incomplete DLPC-DSPC mixing/exchange in the absence of trehalose. In the presence of trehalose the membrane preserves its structure at the nanometer scale and mobility. We found that SLBs with asymmetric domain configurations underwent major rearrangements during drying and rehydration, whereas the symmetric domain configuration mainly rearranged during rehydration, that we hypothesize is related to lower transmembrane cohesiveness or lack of anchoring to the substrate in the case of the asymmetric domains.
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PMID:Drying and rehydration of DLPC/DSPC symmetric and asymmetric supported lipid bilayers: a combined AFM and fluorescence microscopy study. 1870 44

The poly(N,N-diethylacrylamide) (h-PDEA) homopolymer and the poly(N-decylacrylamide)-b-PDEA (PDcA(11)-b-PDEA(231)) diblock copolymer were studied in the range of 10 to 40 degrees C, at the air-water interface. The pi-A isotherms of h-PDEA appear nearly invariant with temperature while the pi-A isotherms of PDcA(11)-b-PDEA(231) deviate significantly to lower areas with the temperature increase evidencing the thermo-responsiveness of this diblock copolymer at the interface. For the copolymer, the limiting area per segment versus temperature shows a break point around 29 degrees C, slightly lower than the lower critical solution temperature (LCST) of h-PDEA in water (31-33 degrees C). AFM images of LB monolayers transferred at 40 degrees C revealed for both polymers the presence of hydrophobic aggregates due to the conformational changes (collapse) of chains that occur at the LCST. Differences in the morphology of these aggregates, flat irregular structures for h-PDEA and round-shaped domains for PDcA(11)-b-PDEA(231), were related with the condensing effect of the hydrophobic block. The PDcA(11) block, anchoring the polymer to the interface, ensures a better stability and cohesion to the film and preserves the thermo-sensitivity of the h-PDEA at the interface.
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PMID:Thermo-responsiveness of poly(N,N-diethylacrylamide) polymers at the air-water interface: The effect of a hydrophobic block. 1875 75

The present work reports on a systematic study of the swelling/collapse transition of three anionic polymer brushes bearing carboxylate, phosphate and sulfonate side groups via AFM measurement. Time scale of conformation change process can be approximately evaluated directly. All the three brushes in their sodium salt forms stretch away from the surface in pure water, as a result of charge repulsion and uptake of water. The collapse of weak brushes has two ways: normal charge screening and precipitation (strong ion pairing), depending on the types of cations that have different coordination capabilities with anionic groups. Alkali metal ions can make brushes shrink only at relatively high concentrations following a gradually increased charge screening mechanism. The brushes collapsed in this way can be restored by simply flushing with water. However, multivalent cations can irreversibly collapse brushes more easily even under very low concentrations (<10(-3) mol L(-1)). The brushes cannot be restored with simple water rinsing even for strong sulfonate containing brushes. In this case, recovery can be achieved by ion exchange in concentrated salt solution, which facilitates transit from strong ion pairing to less strong charge screening and then flushing with water. Alternatively, the multivalent ion can be extracted with chelating reagent of low concentration (10 mM EDTA). As the chelating agent doesn't affect the conformation of brushes, the brushes are one-step recovered directly, much more efficient than with high concentration electrolyte which usually requires extra water rinsing to remove excess salt inside brushes. The interaction between anions in the brushes and metal ions represents a model system to profoundly understand the mechanism of bio-mimic motions and how muscle works. In this regard, the present study provides useful information for the development of polyelectrolyte brushes based ion sensor and ion powered nanoactuators.
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PMID:Reversible hydration and dehydration of polyanionic brushes bearing carboxylate, phosphate and sulfonate side groups: a comparative AFM study. 1903 52


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