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At least 505 records · Page 28Linked to original sources
PubMed2006

Docking of human interleukin-15 to its specific receptor alpha chain: correlation between molecular modeling and mutagenesis experimental data.

A structural model of the sushi domain of IL-15Ralpha was first obtained by homology modeling to study its interactions with IL-15 by means of molecular modeling, peptide scanning, and site-directed mutagenesis. From these experimental data, a putative interacting surface of IL-15Ralpha with a previously published IL-15 model was inferred: Leu25, Leu44, and Glu46 of IL-15 and Arg35 of IL-15Ralpha were found to be key interfacial residues and were subsequently used as filters for the construction of docking solutions. Human IL-15/IL-15Ralpha complexes were constructed in two stages, with a preliminary docking procedure, treating the two partners as rigid bodies and using these filters. In this first stage, two classes of docking solutions were characterized. From a topological point of view, each solution could be derived from the other by reverse orientation of one partner in relation to the other. In a second stage, several further energy refinements clearly favored one solution. Moreover, this unique docking solution was confirmed by molecular modeling of IL-15 mutants previously built and tested in our laboratory. Finally, this complex model, which is a useful tool to study the IL-15/IL-15Ralpha interface, was topologically compared to IL-2/IL-2Ralpha complexes (previous model in the literature and recent crystal structure).

Amino Acid Sequence↗
PubMed2005

Systematic control of the packing density of self-assembled monolayers using bidentate and tridentate chelating alkanethiols.

The structural and interfacial properties of self-assembled monolayers (SAMs) on gold derived from the adsorption of a series of 1,1,1-tris(mercaptomethyl)alkanes (i.e., CH3(CH2)mC[CH2SH]3, where m = 9, 11, 13, 15) were investigated. The new SAMs, which possess uniformly low densities of alkyl chains, were characterized by ellipsometry, contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy. Additional analysis of the SAMs by X-ray photoelectron spectroscopy permitted a direct calculation of the packing densities of the SAMs on gold. The results as a whole, when compared to those obtained on SAMs generated from normal alkanethiols (CH3(CH2)m+2SH), 2-alkylpropane-1,3-dithiols (CH3(CH2)mCH[CH2SH]2), and 2-alkyl-2-methylpropane-1,3-dithiols (CH3(CH2)mC(CH3)[CH2SH]2) having analogous chain lengths, demonstrate that the 1,1,1-tris(mercaptomethyl)alkanes afford SAMs with alkyl chains having the lowest packing density and least conformational order.

Journal Article↗
PubMed1989

Interfacial analysis of fiber-reinforced bioactive glass dental root implants.

Bioactive glass can form an effective bond with bone. Essential for this connection are the interfacial reactions which lead to the development of a Si-rich film covered by a CaP-rich film. The presence of these layers can be demonstrated clearly by EDX analysis of fiber-reinforced bioactive glass and bulk bioactive glass implants installed for 4 and 16 months in the partial edentulous jaws of beagle dogs. EDX analysis reveals three types of microchemical interface. The first type develops when the implant is bonded to bone. Here, a smooth transition of the CaP profile can be observed between bioactive glass and the bone, thus providing for a compositional gradient between the implant and the surrounding tissues. The second type is seen when the implant surface is surrounded by fibrous tissue. This causes a discontinuity in the CaP profile. The third type is characterized by a gradual decrease in the Ca and P concentrations across the interface, caused by the presence of Ca and P in the fibrous tissue near the implant surface. This suggests that the interface is dynamic in time and transforms to a functionally better optimized interface. EDX analysis does not reveal any metal fiber ion contamination of the outer glass rim of the implant. When stainless-steel or wrought Co-Cr alloy is exposed to the surrounding fluids, the interfacial osteogenesis is disturbed, possibly by a synergistic effect of glass ions and metal ions. Exposure of titanium does not interfere with this osteogenesis. The bone bonding can also be influenced by surgical trauma. However, with precise implantation techniques, an enhancement of bone growth by osteoconductivity can be measured.

Animals↗
PubMed1999

Structural analysis of the mechanism of adenovirus binding to its human cellular receptor, CAR.

Binding of virus particles to specific host cell surface receptors is known to be an obligatory step in infection even though the molecular basis for these interactions is not well characterized. The crystal structure of the adenovirus fiber knob domain in complex with domain I of its human cellular receptor, coxsackie and adenovirus receptor (CAR), is presented here. Surface-exposed loops on knob contact one face of CAR, forming a high-affinity complex. Topology mismatches between interacting surfaces create interfacial solvent-filled cavities and channels that may be targets for antiviral drug therapy. The structure identifies key determinants of binding specificity, which may suggest ways to modify the tropism of adenovirus-based gene therapy vectors.

Adenoviruses, Human↗
PubMed2004

Synthesis, in vitro transfection activity and physicochemical characterization of novel N,N'-diacyl-1,2-diaminopropyl-3-carbamoyl-(dimethylaminoethane) amphiphilic derivatives.

A novel series of N,N'-diacyl-1,2-diaminopropyl-3-carbamoyl-(dimethylaminoethane) cationic derivatives was synthesized and screened for in vitro transfection activity at different charge ratios in the presence and absence of the helper lipids DOPE and cholesterol. Physicochemical properties of lipid-DNA complexes were studied by gel electrophoresis, fluorescence spectroscopy and dynamic light scattering. The interfacial properties of the lipids in isolation were studied using the Langmuir film balance technique at 23 degrees C. It was found that only lipoplexes formulated with the dioleoyl derivative, 1,2lmt[5], mediated significant in vitro transfection activity. Optimum activity was obtained with 1,2lmt[5]/DOPE mixture at a +/-charge ratio of 2. In agreement with the transfection results, 1,2lmt[5] was the only lipid found to complex and retard DNA migration as verified by gel electrophoresis. Despite the efficient complexation, no significant condensation of plasmid DNA was observed as indicated by fluorescence spectroscopy measurements. Monolayer studies showed that the dioleoyl derivative 1,2lmt[5] was the only lipid that existed in an all liquid-expanded state with a collapse area and collapse pressure of 59.5 A2 and 38.7 mN/m, respectively. This lipid was also found to have the highest elasticity with a compressibility modulus at monolayer collapse of 80.4 mN/m. In conclusion, increased acyl chain fluidity and high molecular elasticity of cationic lipids were found to correlate with improved transfection activity.

Cations↗
PubMed2005

Liquid-vapor interfacial properties of water-ammonia mixtures: dependence on ammonia concentration.

The equilibrium and dynamical properties of the liquid-vapor interfaces of water-ammonia mixtures are investigated by means of molecular-dynamics simulations. Altogether, we have simulated seven different systems of different concentration of ammonia. The inhomogeneous density, anisotropic orientational profiles, surface tension, and the pattern of hydrogen bonding are calculated for both water and ammonia molecules in order to characterize the location, width, thermodynamic aspects, and microscopic structure of the liquid-vapor interfaces of each of the water-ammonia systems. The dynamical aspects of the interfaces are investigated in terms of the anisotropic diffusion and dipole orientational relaxation of water and ammonia molecules. The properties of the interfaces are compared with those of the corresponding bulk phases. The present theoretical results are also compared with experimental findings wherever available.

Journal Article↗
PubMed2002

Fine separation and characterization of Candida rugosa lipase isoenzymes.

Commercial Candida rugosa lipase has been separated into two distinct fractions (CRLA and CRLB) by anion-exchange chromatography. As analyzed on SDS-polyacrylamide gel electrophoresis, CRLA and CRLB are homogenous. At high ionic strength, CRLA and CRLB have similar hydrophobicity and UV spectra, suggesting that the open extent of the large hydrophobic pockets of CRLA and CRLB may be similar. At low ionic strength, using "hydrophobic interfacial affinity chromatography", both CRLA and CRLB have been separated into four isofractions. They have different hydrophobicity and UV spectra, suggesting that the open extent of the large hydrophobic pocket of the four forms may be different. Further, the conversion of CRL isoenzymes in the process of organic solvent treatment and ester hydrolysis were examined. The results clearly showed not only that CRLB had been converted to CRLA, but also that CRLA sub-fractions with different open extent of large hydrophobic pocket had been converted

2-Propanol↗
PubMed1999

Characterization of a biosurfactant, mannosylerythritol lipid produced from Candida sp. SY16.

One yeast strain, SY16, was selected as a potential producer of a biosurfactant, and identified as a Candida species. A biosurfactant produced from Candida sp. SY16 was purified and confirmed to be a glycolipid. This glycolipid-type biosurfactant lowered the surface tension of water to 29 dyne/cm at critical micelle concentration of 10 mg/l (1.5 x 10(-5) M), and the minimum interfacial tension was 0.1 dyne/cm against kerosene. Thin-layer and high-pressure liquid chromatography studies demonstrated that the glycolipid contained mannosylerythritol as a hydrophilic moiety. The hydrophilic sugar moiety of the biosurfactant was determined to be beta-D-mannopyranosyl-(1-->4)-O-meso-erythritol by nuclear magnetic resonance (NMR) and fast atom bombardment mass-spectroscopy analyses. The hydrophobic moiety, fatty acids, of the biosurfactant was determined to be hexanoic, dodecanoic, tetradecanoic, and tetradecenoic acid by gas chromatography-mass spectroscopy. The structure of the native biosurfactant was determined to be 6-O-acetyl-2,3-di-O-alkanoyl-beta-D-mannopyranosyl-(1-->4)-O-meso- erythritol by NMR analyses. We newly determined that an acetyl group was linked to the C-6 position of the D-mannose unit in the hydrophilic sugar moiety.

Candida↗
PubMed2005

Preparation of microencapsulated phase-change materials (MCPCMs) by means of interfacial polycondensation.

Microcapsules for energy storage and/or heat transfer applications containing phase-change materials (PCMs-including n-pentadecane, n-eicosane and a paraffin wax) were successfully produced by emulsifying the PCMs as small droplets in an aqueous, water-soluble urea-formaldehyde pre-polymer solution substantially free of emulsifier while polymerizing the pre-polymer at the interface by acid-catalyst. The core/shell structured microcapsules were also characterized with size distribution analysis, scanning electron microscopy, FTIR spectrometry and differential scanning calorimetry.

Alkanes↗
PubMed1991

Cholesterol esterase catalyzed hydrolysis of mixed micellar thiophosphatidylcholines: a possible charge-relay mechanism.

Mechanistic features of cholesterol esterase catalyzed hydrolysis of two thiophospholipids, rac-1-(hexanoylthio)-2-hexanoyl-3-glycerophosphorylcholine (6TPC) and rac-1-(decanoylthio)-2-decano-yl-3-glycerophosphorylcholine (10TPC), have been characterized. The hydrolysis of 10TPC that is contained in mixed micelles with Triton X-100 occurs strictly at the micellar interface, since the reaction rate is independent of the micelle concentration but depends hyperbolically on the mole fraction of the substrate in the micelles. This latter observation allows one to calculate the interfacial kinetic parameters V*max and K*m. The hydrolyses of 10TPC and p-nitrophenyl butyrate are similarly inhibited by the transition state analogue inhibitor phenyl-n-butylborinic acid, and therefore, physiological and nonphysiological substrates are processed at the same active site. The similarity of k*cat values for the acyl-similar substrates 10TPC and p-nitrophenyl decanoate indicates that the phospholipase A1 activity of cholesterol esterase is partially rate limited by turnover of a decanoyl-enzyme intermediate. Solvent isotope effects on V*max and V*max/K*m (which monitors acylation only) are approximately 2-3 and are consistent with transition states that are stabilized by general acid-base proton transfers. Proton inventories of V*max/K*m indicate that simultaneous proton transfers stabilize the acylation transition state, which requires a multifunctional acid-base machinery (perhaps a charge-relay system) in the cholesterol esterase active site. Similar results are obtained for the 6TPC reaction, both in the presence and absence of Triton X-100 micelles.

Acetylcholinesterase↗
PubMed1996

Phospholipase A2--a structural review.

Phospholipases A2 (PLA2) are widely distributed in nature and are well characterized proteins with respect to their catalytic and pharmacological activities. A wealth of structural information has recently become available both from X-ray diffraction and NMR studies, and although a detailed model of the catalytic mechanism of PLA2 has been proposed, the structural bases of other aspects of PLA2 function, such as interfacial activation and venom PLA2 pharmacological activities, are still under debate. An appreciation of the PLA2 protein structure will yield new insights with regard to these activities. The salient structural features of the class I, II and III PLA2 are discussed with respect to their functional roles.

Amino Acid Sequence↗
PubMed2005

Biochemical and molecular characterization of Staphylococcus xylosus lipase.

The Staphylococcus xylosus strain secretes a non-induced lipase in culture medium: S. xylosus lipase (SXL). Pure SXL is a monomeric protein (43 kDa). The 23 N-terminal amino acid residues were sequenced. This sequence is identical to that of Staphylococcus simulans lipase (SSL); in addition, it exhibits a high degree of homology with Staphylococcus aureus lipase (SAL NCTC 8530) sequences. The cloning and sequencing of gene part encoding the mature lipase shows one nucleotide difference with SSL, which corresponds to the change of one residue at a position 311. The lipase activity is maximal at pH 8.2 and 45 degrees C. SXL is able to hydrolyse triacylglycerols without chain length specificity. The specific activity of about 1900 U/mg was measured using tributyrin or triolein as substrate at pH 8.2 and at 45 degrees C in the presence of 2 mM CaCl2. In contrast to some previously characterized staphylococcal lipases, Ca2+ is not required to trigger the activity of SXL. SXL was found to be stable between pH 5 and pH 8.5. The enzyme maintains 50% of its activity after a 15-min incubation at 60 degrees C. Using tripropionin or vinyl esters as substrates, SXL does not present the interfacial activation phenomenon. Unlike many lipases, SXL is able to hydrolyse its substrate in the presence of bile salts or amphiphilic proteins. SXL is a serine enzyme, which is inhibited by THL.

Amino Acid Sequence↗
PubMed2004

The role of atomic scale investigation in the development of nanoscale materials for information storage applications.

It is well established that the response of devices based on the giant magnetoresistance (GMR) effect depends critically on film microstructure, with parameters such as interfacial abruptness, the roughness and waviness of the layers, and grain size being crucial. Such devices have applications in information storage systems, and are therefore of great technological interest as well as being of fundamental scientific interest. The layers must be studied at high spatial resolution if the microstructural parameters are to be characterized with sufficient detail to enable the effects of fabrication conditions on properties to be understood, and the techniques of high resolution electron microscopy, transmission electron microscopy chemical mapping, and atom probe microanalysis are ideally suited. This article describes the application of these techniques to a range of materials including spin valves, spin tunnel junctions, and GMR multilayers.

Alloys↗
PubMed2003

PDMS 2D optical lens integrated with microfluidic channels: principle and characterization.

In this paper, the fabrication and characterization of PDMS 2D-optical lenses are reported. These lenses are designed in order to improve the performance of fluorescent spectroscopy detection performed on a portable chip using optical fibers. The fabrication process of the PDMS layer is first detailed, and the patterns are then checked with a SEM. By comparing various interfacial structures, it is shown that the beam properties of the light coming out from the fiber can be modified depending on the lens curvature radius. As a consequence, for a constant dye concentration, the use of such lenses can increase the intensity of fluorescent response close to the fiber or far from the fiber, compared to the same design with a flat interface. This excitation improvement corresponding to a stronger response from the dye then consequently leads to around three times higher sensitivity of the on-chip detection method for fluorescent spectroscopy.

Dimethylpolysiloxanes↗
PubMed1999

A Critique of the Mathematical Coherence of Acid/Base Interfacial Free Energy Theory.

Acid/base theory has, over the last decade or so, been developed to describe interfacial free energies, or tensions, in wetting theory. An approach put forward by van Oss and co-workers, involving van der Waals/Lifshitz and Lewis electron acceptor/donor contributions to surface/interfacial free energies, has often been employed. The present study considers use of this theory for evaluating surface data for various polymeric surfaces employing known, characterized liquid probes for obtaining contact angle data. Results are analyzed using extended matrix analyses, originally proposed for treating the dispersive/polar interpretation of wetting results, and good agreement with literature values is obtained. By "inverting" the system, i.e., by treating the known solids as probes and rederiving surface data for liquids, inconsistencies are found to arise. Results for wetting of the same polymers and mica, using a two-liquid system (n-octane/water), are exploited to attempt to rederive the surface characteristics of water. Again, serious incoherence is manifest. Despite the conceptual interest of acid/base theory, clearly the mathematical formulation is presently inadequate. Copyright 1999 Academic Press.

Journal Article↗
PubMed1998

The adsorption of cellulose ethers in aqueous suspensions of pyrantel pamoate: effects on zeta potential and stability.

This work examined the physico-chemical phenomena induced in aqueous suspensions of pyrantel pamoate by two varieties of hydroxypropylmethylcellulose (HPMC) and sodium carboxymethylcellulose (NaCMC) of different molecular weights, and the effects of these phenomena on the physical stability of the suspension. The mechanism of the interfacial adsorption of the polymer was investigated by constructing adsorption isotherms: for the two HPMC varieties, the isotherms were of type L and were fitted with the Langmuir model; of the NaCMCs, only the variety with higher molecular weight was adsorbed, its adsorption isotherm being of type S (sigmoidal). The resulting monolayer films were characterized viscosimetrically, determining their thickness and the number of polymer molecules adsorbed per unit area. The nonionic polymers formed thinner, more continuous monolayers than the NaCMC. Only the nonionic polymers significantly altered the zeta potential of the systems. In the range of conditions studied, all the polymers stabilized the initially flocculated systems, decreasing sedimentation volume and increasing the time necessary to redisperse them (the redispersability value). This stabilization occurred either by the steric mechanism (HPMCs and the high-molecular-weight NaCMC) or by depletion mechanisms (low-molecular-weight NaCMC). Owing to the complexity of these mechanisms, sedimentation volume was not found to be a useful index of the consistency of the sediments obtained from the suspensions.

Carboxymethylcellulose Sodium↗
PubMed2004

Surface activity profiling of drugs applied to the prediction of blood-brain barrier permeability.

The present study describes a novel in vitro platform for physicochemical profiling of compounds, based on their impact on the air/water interfacial tension. Interfacial partitioning coefficient, cross-sectional area, and critical micelle concentration were derived from the Gibbs adsorption isotherms recorded for 76 structurally diverse drugs. An approximation for the membrane partitioning coefficient, K(memb), is introduced and calculated for the measured compounds. This methodology provides a fully automatic, high-throughput screening technique for compound characterization, yielding precise thermodynamic information on the partitioning behavior of molecules at air/water interfaces, which can be directly related to their anisotropic interaction with lipid bilayers in biological membranes. The latter represents the barrier for the passive entry of compounds into cells. The surface activity profiles are shown to correlate to the ability of the compounds to pass passively through the blood-brain barrier.

Blood-Brain Barrier↗
PubMed2005

Relationship between particle deposit characteristics and the mechanism of particle arrival.

An on-lattice Monte Carlo model is implemented for the simulation of particle deposit growth by advection and diffusion towards a flat surface. The particle deposit structure is characterized by its bulk (density) and interface (mean height and surface width) properties. Numerical correlations, fitted by simple expressions, are reported for these magnitudes, relating them to time (number of deposited particles) and Peclet number. Also a heuristic argument is presented which relates deposit density to local diffusion-limited-aggregation-like processes and interfacial dynamics to the KPZ model.

Journal Article↗