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At least 415 records · Page 23Linked to original sources
PubMed2006

Self-association and lipid binding properties of the lipoprotein initiating domain of apolipoprotein B.

The amino-terminal 20.1% of apolipoprotein B (apoB20.1; residues 1-912) is sufficient to initiate and direct the formation of nascent apoB-containing lipoprotein particles. To investigate the mechanism of initial lipid acquisition by apoB, we examined the lipid binding and interfacial properties of a carboxyl-terminal His6-tagged form of apoB20.1 (apoB20.1H). ApoB20.1H was expressed in Sf9 cells and purified by nickel affinity chromatography. ApoB20.1H was produced in a folded state as characterized by formation of intramolecular disulfide bonds and resistance to chemical reduction. Dynamic light scattering in physiological buffer indicated that purified apoB20.1H formed multimers, which were readily dissociable upon the addition of nonionic detergent (0.1% Triton X-100). ApoB20.1H was incapable of binding dimyristoylphosphatidylcholine multilamellar vesicles, unless its multimeric structure was first disrupted by guanidine hydrochloride. However, apoB20.1H multimers spontaneously dissociated and bound to the interface of naked and phospholipid-coated triolein droplets. These data reveal that the initiating domain of apoB contains solvent-accessible hydrophobic sequences, which, in the absence of a hydrophobic lipid interface or detergent, engage in self-association. The high affinity of apoB20.1H for neutral lipid is consistent with the membrane binding and desorption model of apoB-containing lipoprotein assembly.

Amino Acids↗
PubMed2005

Characterization of trypsin immobilized on the functionable alkylthiolate self-assembled monolayers: a preliminary application for trypsin digestion chip on protein identification using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Self-assembled monolayers (SAMs) on coinage metal provide versatile modeling systems for studies of interfacial electron transfer, biological interactions, molecular recognition and other interfacial phenomena. Recently the bonding of enzyme to SAMs of alkanethiols onto Au electrode surfaces was exploited to produce a bio-sensing system. In this work, the attachment of trypsin to a SAMs surface of 11-mercaptoundecanoic acid was achieved using water soluble N-ethyl-N '-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide as coupling agent. The thickness of SAMs was determined by optical ellipsometer; contact angles of the modified Au surfaces were measured in air using a goniometer. The Second Harmony Generation data displays the last few percents of the alkylthiol molecules adsorbed and produced the complete monolayer by inducing the transition from a high number of gauche defects to an all-trans conformation. Using X-ray Photoelectron Spectroscopy (XPS) and Fourier-Transformed Infrared Reflection-Absorption and Attenuated Total Reflection Spectroscopes (FTIR-RAS and ATR), we examined the chemical structures of samples with different treatments. By matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), we demonstrated the digestion of bovine serum albumin (BSA) on the trypsin-immobilized SAMs surface. Experimental results have revealed that the XPS C1s core levels at 286.3 and 286.5 eV (Amine bond), 288.1 eV (Amide bond) and 289.3 eV (Carboxylic acid) illustrate the immobilization of trypsin. These data were also in good agreement with FTIR-ATR spectra for the peaks valued at 1659.4 cm(-1) (Amide I) and 1546.6 cm(-1) (Amide II). Using MALDI-TOF MS observations, analytical results have demonstrated the BSA digestion of the immobilized trypsin on the functionalized SAMs surface. For such surfaces, BSA was digested on the trypsin-immobilized SAMs surface, which shows the enzyme digestion ability of the immobilized trypsin. The terminal groups of the SAMs structure can be further functionalized with biomolecules or antibodies to develop surface-base diagnostics, biosensors, or biomaterials.

Biosensing Techniques↗
PubMed2005

Sensitized hole injection of phosphorus porphyrin into NiO: toward new photovoltaic devices.

This paper describes the preparation and the characterization of a photovoltaic cell based on the sensitization of a wide band gap p-type semiconductor (NiO) with a phosphorus porphyrin. A photophysical study with femtosecond transient absorption spectroscopy showed that light excitation of the phosphorus porphyrin chemisorbed on NiO particles induces a very rapid interfacial hole injection into the valence band of NiO, occurring mainly on the 2-20 ps time scale. This is followed by a recombination in which ca. 80% of the ground-state reactants are regenerated within 1 ns. A photoelectrochemical device, prepared with a nanocrystalline NiO electrode coated with the phosphorus porphyrin, yields a cathodic photocurrent indicating that electrons indeed flow from the NiO electrode toward the solution. The low incident-to-photocurrent efficiency (IPCE) can be rationalized by the rapid back recombination reaction between the reduced sensitizer and the injected hole which prevents an efficient regeneration of the sensitizer ground state from the iodide/triiodide redox mediator. To the best of our knowledge, this work represents the first example of a photovoltaic cell in which a mechanism of hole photoinjection has been characterized.

Journal Article↗
PubMed2005

Enzymatic degradation of model cellulose films.

Enzymatic degradation of model cellulose films prepared by a spin-coating technique was investigated by ellipsometry. The cellulose films were prior to degradation characterized by ellipsometry, contact angle measurements, ESCA (electron spectroscopy for chemical analysis) and AFM (atomic force microscopy). At enzyme addition to preformed cellulose films an initial adsorption was observed, which was followed by a total interfacial mass decrease due to enzymatic degradation of the cellulose films. The degradation rate was found to be constant during an extended time of hours, whereafter the degradation leveled off. In parallel to the decreased interfacial mass, the cellulose degradation resulted in a thinner and more dilute interfacial film. At long degradation times, however, there was an expansion of the cellulose film. The enzyme concentration affected the degradation rate significantly, with a faster degradation at a higher enzyme concentration. The effects of pH, temperature, ionic strength and stirring rate in the cuvette were also investigated.

Adsorption↗
PubMed2006

Enhanced aqueous solubilization of tetrachloroethylene by a rhamnolipid biosurfactant.

A rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 was isolated, purified and characterized in terms of its ability to mobilize and solubilize tetrachloroethylene (PCE) for potential use in surfactant-enhanced aquifer remediation (SEAR) applications. Using a drop volume method, the PCE-biosurfactant steady-state interfacial tension was determined and found to be ca. 10 mN/m which is not low enough to cause significant PCE nonaqueous phase liquid (NAPL) mobilization. It was observed that the biosurfactant partitioned significantly into PCE at aqueous concentrations higher than the critical micelle concentration (CMC). After accounting for rhamnolipid partitioning into the PCE phase, a weight solubilization ratio (WSR) of 1.2 g(PCE)/g(rhamnolipid) was determined and through this mechanism the biosurfactant significantly improved the apparent aqueous solubility of PCE.

Glycolipids↗
PubMed1993

Substrate requirements of bacterial phosphatidylinositol-specific phospholipase C.

A series of symmetric short-chain phosphatidylinositols (PI), including dihexanoyl-PI, diheptanoyl-PI (racemic as well as D and L forms), and 2-methoxy inositol-substituted diheptanoyl-PI, have been synthesized, characterized, and used to investigate key mechanistic questions about phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus thuringiensis. Key results include the following: (i) bacterial PI-PLC exhibits a 5-6-fold "interfacial activation" when its substrate is present in an interface as opposed to existing as a monomer in solution (in fact, the similarity to the activation observed with nonspecific PLC enzymes suggests a similarity in activation mechanisms); (ii) the 2-OH must be free since the enzyme cannot hydrolyze diheptanoyl-2-O-methyl-PI (this is most consistent with the formation of inositol cyclic 1,2-phosphate as a necessary step in catalysis); (iii) the inositol ring must have the D stereochemistry (the L-inositol attached to the lipid moiety is neither a substrate nor an inhibitor); and (iv) the presence of noninhibitory L-PI with the D-PI substrate relieves the diacylglycerol product inhibition detected at approximately 30% hydrolysis.

Bacillus thuringiensis↗
PubMed2007

Multiferroics: progress and prospects in thin films.

Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties - and in turn promise new device applications - as a result of the coupling between their dual order parameters. We review recent progress in the growth, characterization and understanding of thin-film multiferroics. The availability of high-quality thin-film multiferroics makes it easier to tailor their properties through epitaxial strain, atomic-level engineering of chemistry and interfacial coupling, and is a prerequisite for their incorporation into practical devices. We discuss novel device paradigms based on magnetoelectric coupling, and outline the key scientific challenges in the field.

Journal Article↗
PubMed1998

Pore Size Analysis of MCM-41 Type Adsorbents by Means of Nitrogen and Argon Adsorption.

Methods of nonlocal density functional theory (NLDFT), proposed recently for predictions of adsorption equilibrium and calculations of pore size distributions in micro- and mesoporous materials, were tested on reference MCM-41 materials. Five newly synthesized MCM-41 adsorbents with presumably uniform pore channels varying from 32 to 45 Å were characterized by X-ray diffraction (XRD), nitrogen adsorption at 77 K, and argon adsorption at 77 and 87 K. New sets of intermolecular interaction parameters of the NLDFT model for N2 and Ar adsorption on MCM-41 were determined. The parameters were specified to reproduce the bulk liquid-gas equilibrium densities and pressures, liquid-gas interfacial tensions, and standard adsorption isotherms on nonporous surfaces in the multilayer adsorption region. The pore size distributions calculated from the desorption branches of the experimental isotherms measured at three different temperatures were consistent with each other. Comparison of the NLDFT-calculated pore sizes with XRD data showed that the thickness of pore walls in the MCM-41 samples under consideration varied from ca. 6 to 12 Å. We found no correlation between the pore size and the pore wall thickness. The results obtained support the NLDFT model as a suitable tool for characterizing nanoporous materials and predicting adsorption equilibrium. The MCM-41 samples studied can be used as references for adsorption measurements. Copyright 1998 Academic Press.

Journal Article↗
PubMed1994

Functional significance of the conformational dynamics of the N-terminal segment of secreted phospholipase A2 at the interface.

The kinetic and fluorescence properties of several pig pancreatic phospholipase A2 (PLA2) with substitutions and deletions in the N-terminal region and of tyrosines 52 and 73 are characterized. The substitutions Ala-1-D-Ala or -Gly, Trp-3-Phe, Gln-4-Nle, Arg-6-Glu, Tyr-52-Phe, and Tyr-73-Phe had at the most only a modest effect on the interfacial catalytic activity on the anionic interface to which they bind with high affinity. The observed rate of hydrolysis in the scooting mode by deletion mutants lacking one or more successive residues from the N-terminal region was lower by 50-95%. Detailed kinetic analysis of the deletion mutant lacking Ala-1 (des-1-AMPA) showed that the 50% decrease in the rate is due to a 5-fold increase in the interfacial Michaelis-Menten parameter, KM*, without a significant change in kcat. These results and direct measurements show that the primary effect of Ala-1 deletion is to lower the affinity for the active site directed ligands. Although the affinity of these mutants for anionic interface remains the same as for the wild type, the affinity for zwitterionic neutral diluents is considerably lower. Significant differences in the fluorescence quantum yields and the heterogeneity in the frequency-domain fluorescence intensity decays of these enzymes suggest that both in solution and at the interface the N-terminal region is an ensemble of conformations rather than a discrete state. Additional results suggest that the interfacial microenvironment of Trp-3 in des-1-AMPA is more polar and Trp-3 is more accessible to quenching by acrylamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Dissecting cooperative and additive binding energetics in the affinity maturation pathway of a protein-protein interface.

When two proteins associate they form a molecular interface that is a structural and energetic mosaic. Within such interfaces, individual amino acid residues contribute distinct binding energies to the complex. In combination, these energies are not necessarily additive, and significant positive or negative cooperative effects often exist. The basis of reliable algorithms to predict the specificities and energies of protein-protein interactions depends critically on a quantitative understanding of this cooperativity. We have used a model protein-protein system defined by an affinity maturation pathway, comprising variants of a T cell receptor Vbeta domain that exhibit an overall affinity range of approximately 1500-fold for binding to the superantigen staphylococcal enterotoxin C3, in order to dissect the cooperative and additive energetic contributions of residues within an interface. This molecular interaction has been well characterized previously both structurally, by x-ray crystallographic analysis, and energetically, by scanning alanine mutagenesis. Through analysis of group and individual maturation and reversion mutations using surface plasmon resonance spectroscopy, we have identified energetically important interfacial residues, determined their cooperative and additive energetic properties, and elucidated the kinetic and thermodynamic bases for molecular evolution in this system. The summation of the binding free energy changes associated with the individual mutations that define this affinity maturation pathway is greater than that of the fully matured variant, even though the affinity gap between the end point variants is relatively large. Two mutations in particular, both located in the complementarity determining region 2 loop of the Vbeta domain, exhibit negative cooperativity.

Algorithms↗
PubMed1991

Microstructural characterization of a foil crown system.

In this study, the microstructural nature of the Renaissance crown system has been characterized in an effort to understand its reported properties and performance. Intergranular cavitation was characteristic of the foil surface. The brazed area joining various pleats was porous and exhibited an equiaxial grain structure. Particles of the interfacial alloy sintered with each other and bonded to the foil. Flow of porcelain into intergranular grooves of the foil and within the porous interfacial alloy network was observed. Tags that formed as a result contributed to the micromechanical retention of porcelain on the foil. No evidence of foil-porcelain chemical bonding was found, nor was there any indication of substantial interlayer diffusion.

Crowns↗
PubMed1987

Tandem scanning reflected light microscopy: applications in clinical dental research.

The Tandem Scanning Reflected Light Microscope (TSRLM) enables the investigation of microscopic structures both at and deep to the surface of intact objects. The present paper reviews studies undertaken to determine whether the TSRLM would be usable and useful in the investigation of natural and restorative dental materials in vitro and in vivo. It was found that the TSRLM could be used to study normal and diseased dental tissues and the new materials which are used to replace lost substance. More importantly, it could be used to characterize the interface between tooth and optically translucent materials in bulk samples, giving high resolution information from not only a shallow depth of field, but at planes below cut surfaces. This makes it possible to study interfacial regions in three dimensions without the risk of delamination that must accompany the preparation of a microscopic section. The use of fluorescent markers enables more information to be derived from the tooth/adhesive interface. Studies to date indicate the need for the development of adhesion promoting agents which incorporate a fluorescent radical in their molecular structure. Preliminary work using the instrument for observation of cutting interactions between a high speed bur and a tooth indicates some useful potential in the study of cavity preparation techniques and tissue failure mechanisms. Recent developments of the TSRLM for three dimensional imaging in other dental applications are outlined. This microscope is an important advance in the microscopic assessment of adaptation of biomaterials to hard tissues.

Animals↗
PubMed1996

Fluorescent probes of membrane surface properties.

We have studied the properties of two new fluorescent probes, 7-dimethylaminocoumarin derivatives, 4-[N, N-dimethyl-N-(n-tetradecyl)ammoniummethyl]-7-(N,N-dimethylamino)co umarin chloride (TAMAC) and 4-(n-dodecylthiomethyl)-7-(N,N-dimethylamino)coumarin (DTMAC) in model membrane systems. Both probes are sensitive to solvent polarity. The TAMAC probe has a quaternary ammonium function to position it at a fixed location with respect to the membrane interface. In membranes of dipalmitoleoylphosphatidylethanolamine (DiPoPE), both probes detect marked increases in surface hydrophobicity as the bilayer to hexagonal phase transition temperature is approached. This does not occur when the probes are embedded in dipalmitoleoylphosphatidylcholine (DiPoPC) in which case the fluorescence emission is found to be largely independent of temperature. A nitroxide quencher covalently linked to the 5 position of the sn-2 acyl chain of phosphatidylcholine quenches the fluorescence of DTMAC in DiPoPC more than in DiPoPE, indicating the deeper insertion of this probe in DiPoPC. As the temperature is increased the DTMAC fluorophore moves even further out of the membrane. These findings indicate that DTMAC, which does not contain a group to fix its location along the bilayer normal, adjusts its position to small changes in environment polarity, so as to maintain an environment of a fixed dielectric constant. However, with greater changes in membrane interfacial polarity the environment of the probe will be altered. Thus, in addition to the sensitivity of these probes to solvent polarity, the ability of a fixed nitroxide to quench DTMAC becomes another parameter with which to characterize membrane properties with these probes.

Coumarins↗
PubMed2000

Structural basis of dimerization, coactivator recognition and MODY3 mutations in HNF-1alpha.

Maturity-onset diabetes of the young type 3 (MODY3) results from mutations in the transcriptional activator hepatocyte nuclear factor-1alpha (HNF-1alpha). Several MODY3 mutations target the HNF-1alpha dimerization domain (HNF-p1), which binds the coactivator, dimerization cofactor of HNF-1 (DCoH). To define the mechanism of coactivator recognition and the basis for the MODY3 phenotype, we determined the cocrystal structure of the DCoH-HNF-p1 complex and characterized biochemically the effects of MODY3 mutations in HNF-p1. The DCoH-HNF-p1 complex comprises a dimer of dimers in which HNF-p1 forms a unique four-helix bundle. Through rearrangements of interfacial side chains, a single, bifunctional interface in the DCoH dimer mediates both HNF-1alpha binding and formation of a competing, transcriptionally inactive DCoH homotetramer. Consistent with the structure, MODY3 mutations in HNF-p1 reduce activator function by two distinct mechanisms.

Binding Sites↗
PubMed1999

Biomechanical and functional behavior of implants.

The ability to achieve a long-term stable implant interface is not a significant clinical issue when sufficient uni- or bi-cortical stabilization is available. Clinical outcomes studies suggest that the higher-risk implants are those placed in compromised cortical bone (thin, porous, etc.) in anatomic sites with minimal existing trabecular bone (characterized as type IV bone). In establishing and maintaining an implant interface in such an environment, one needs to consider the impact of masticatory forces. These forces, in turn, have the potential to create localized changes in interfacial stiffness through the viscoelastic properties of bone. Changes in these properties will alter the communication between osteocytes and osteoblasts, leading to an increase in new bone growth, a maintenance of established bone, or a loss (potentially catastrophic) of either cortical or trabecular bone. Therefore, a key to understanding the biomechanical and functional behavior at an implant interface is to control the extent of anticipated modeling and remodeling behavior through an optimal implant design combined with a thorough understanding of how tissues respond to the mechanically active environment.

Alveolar Process↗
PubMed2005

Ultrathin TiO(x) films on Pt(111): a LEED, XPS, and STM investigation.

Ultrathin ordered titanium oxide films on Pt(111) surface are prepared by reactive evaporation of Ti in oxygen. By varying the Ti dose and the annealing conditions (i.e., temperature and oxygen pressure), six different long-range ordered phases are obtained. They are characterized by means of low-energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). By careful optimization of the preparative parameters, we find conditions where predominantly single phases of TiO(x), revealing distinct LEED pattern and STM images, are produced. XPS binding energy and photoelectron diffraction (XPD) data indicate that all the phases, except one (the stoichiometric rect-TiO2), are one monolayer thick and composed of a Ti-O bilayer with interfacial Ti. Atomically resolved STM images confirm that these TiO(x) phases wet the Pt surface, in contrast to rect-TiO2. This indicates their interface stabilization. At a low Ti dose (0.4 monolayer equivalents, MLE), an incommensurate kagomé-like low-density phase (k-TiO(x) phase) is observed where hexagons are sharing their vertexes. At a higher Ti dose (0.8 MLE), two denser phases are found, both characterized by a zigzag motif (z- and z'-TiO(x) phases), but with distinct rectangular unit cells. Among them, z'-TiO(x), which is obtained by annealing in ultrahigh vacuum (UHV), shows a larger unit cell. When the postannealing of the 0.8 MLE deposit is carried out at high temperatures and high oxygen partial pressures, the incommensurate nonwetting, fully oxidized rect-TiO2 is found The symmetry and lattice dimensions are almost identical with rect-VO2, observed in the system VO(x)/Pd(111). At a higher coverage (1.2 MLE), two commensurate hexagonal phases are formed, namely the w- [(square root(43) x square root(43)) R 7.6 degrees] and w'-TiO(x) phase [(7 x 7) R 21.8 degrees]. They show wagon-wheel-like structures and have slightly different lattice dimensions. Larger Ti deposits produce TiO2 nanoclusters on top of the different monolayer films, as supported both by XPS and STM data. Besides the formation of TiO(x) surfaces phases, wormlike features are found on the bare parts of the substrate by STM. We suggest that these structures, probably multilayer disordered TiO2, represent growth precursors of the ordered phases. Our results on the different nanostructures are compared with literature data on similar systems, e.g., VO(x)/Pd(111), VO(x)/Rh(111), TiO(x)/Pd(111), TiO(x)/Pt(111), and TiO(x)/Ru(0001). Similar and distinct features are observed in the TiO(x)/Pt(111) case, which may be related to the different chemical natures of the overlayer and of the substrate.

Journal Article↗
PubMed2006

Transport properties and electrokinetic characterization of an amphoteric nanofilter.

Transport properties of a tubular nanofilter with amphoteric properties have been investigated by means of the SEDE (steric, electric, and dielectric exclusion) homogeneous model. Within the scope of this 1D model, the separation of solutes results from transport effects (described by means of extended Nernst-Planck equations) and interfacial phenomena including steric hindrance, the Donnan effect, and dielectric exclusion (expressed in terms of (i) the Born dielectric effect, which is connected to the lowering of the dielectric constant of a solution inside nanodimensional pores, and (ii) the interaction between ions and the polarization charges induced at the dielectric boundary between the pore walls and the pore-filling solution). The effective volume charge density of the membrane has been determined from tangential streaming potential experiments coupled with conductance experiments in a potassium chloride solution at various pH values ranging from 2 to 11. The inferred values have been used in the SEDE model to compute the ion rejection rates with the dielectric constant of the solution inside the pores as a single adjustable parameter. The model provides a relatively good description of experimental data even at extreme pH values for which a ternary system has been considered (K+, Cl-, and H+ or OH- depending on the pH). The fit to experimental data at the membrane isoelectric point indicates that the confinement effect decreases the dielectric constant inside the pores only slightly (with respect to its bulk value). However, the (pH-dependent) ionization of surface sites has been found to lead to a substantial lowering of the dielectric constant inside the pores.

Journal Article↗
PubMed1976

The characterization of intima development in left ventricular assist device (LVAD) and total artificial heart (TAH).

1. The study of PNI development provides useful information in the design and improvement of the prosthetic devices. 2. Improved gelatin aldehyde impregnation on the dacron covered diaphragm of cardiac prostheses resulted in a reduced PNI thickness and minimized interfacial degeneration of PNI. 3. The PNI on the diaphragm's surface started with a platelet rich interface and ended with a striated fibrin and platelet matrix at the blood interface. 4. The PNI in the TAH's had a higher involvement of polymorphonuclear leukocytic cells at the PNI-housing or diaphragm interface than the LVAD's. 5. The aldehyde treated pericardial surface of cardiac prostheses generated a thin PNI that was fibrin-rich, a viable cell infiltration, no interfacial degeneration, and endothelial-like cells on its surface.

Aldehydes↗