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PubMed2005

Probing interfacial organization in surface monolayers using tethered pyrene. 1. Structural mediation of electron and proton access to adsorbates.

We have synthesized and characterized a family of self-assembled monolayers containing pyrene derivatives on gold and indium-doped tin oxide (ITO) substrates. The covalently bound pyrene functionalities serve as either spectroscopic or electrochemical probes of their immediate environment, and we explore their electrochemical response in this paper. When these compounds are the only constituents bound to the interfaces, the molecules enjoy significant structural freedom. The addition of aliphatic adsorbates to the interfaces serves to place the pyrene derivatives in a more restricted environment. Cyclic voltammetry shows that the organization of a monolayer with pyrene derivatives, and the position of the terminal pyrene within such monolayer, depend sensitively on the length of the pyrene tether and the presence or absence of aliphatic interfacial species, as well as the identity of the substrate.

Journal Article↗
PubMed2006

A thermodynamic study on the complexation between riboflavin and a diaminotriazine derivative mediated by triple hydrogen bonds at water/oil interfaces.

The changes in Gibbs free energy (DeltaG (int)), enthalpy (DeltaH (int)) and entropy (TDeltaS (int)) upon complexation between riboflavin (RF) and N,N-dioctadecyl-[1,3,5]triazine-2,4,6-triamine (DTT), mediated by triple hydrogen bonds at water/carbon tetrachloride, trichloroethylene and chloroform interfaces, were determined via temperature-controlled interfacial tension measurements. It was shown that hydrogen bonding interactions between RF and DTT were best characterized by large and negative DeltaH (int) values, unlike those predicted from either the polarity in each phase or the arithmetic average of the polarities in the two phases. Furthermore, the DeltaH (int) values became more positive as the dielectric constant of the oil phase was increased. These results strongly indicate that DeltaH (int) is governed by the dielectric properties of the oil phase. Adsorption of RF, DTT and the RF-DTT complex at the water/oil interface gave rise to restrictions on the translational and rotational motions of these species, as demonstrated by the DeltaS (int) values observed, which is another characteristic of interfacial complexation. The thermodynamic parameters evaluated in the present study revealed the characteristic complexation behavior that occurs at a water/oil interface, as mediated by hydrogen bonding.

Hydrogen Bonding↗
PubMed2006

Surface properties of inclusion complexes between alpha-cyclodextrin and poly(ethylene oxide).

The surface properties of the supramolecular inclusion complex (IC) obtained from the threading of alpha-cyclodextrin (alpha-CD) onto poly(ethylene oxide) (PEO) free in solution are studied. The complexes were characterized by IR, (1)H NMR spectroscopy, and thermal analysis. The variation of the interfacial tension, gamma(int), with inclusion complex (IC) concentration and temperature were determined. The results were compared with those found for PEO under the same conditions. alpha-CD does not present surface activity. To quantify the adsorption process of IC and PEO in aqueous medium, the Gibbs equation was used. The driving force for adsorption of IC at the air/aqueous interface seems to arise from an enthalpic contribution. The wettability of the alpha-CD, PEO, and IC films with two liquids was determined by static contact angle measurements. The hydrophobicity degree was estimated. IC is more hydrophobic than PEO and alpha-CD.

Macromolecular Substances↗
PubMed2004

Self-association process of a peptide in solution: from beta-sheet filaments to large embedded nanotubes.

Lanreotide is a synthetic octapeptide used in the therapy against acromegaly. When mixed with pure water at 10% (w/w), Lanreotide (acetate salt) forms liquid crystalline and monodisperse nanotubes with a radius of 120 A. The molecular and supramolecular organization of these structures has been determined in a previous work as relying on the lateral association of 26 beta-sheet filaments made of peptide noncovalent dimers, the basic building blocks. The work presented here has been devoted to the corresponding self-association mechanisms, through the characterization of the Lanreotide structures formed in water, as a function of peptide (acetate salt) concentration (from 2% to 70% (w/w)) and temperature (from 15 degrees C to 70 degrees C). The corresponding states of water were also identified and quantified from the thermal behavior of water in the Lanreotide mixtures. At room temperature and below 3% (w/w) Lanreotide acetate in water, soluble aggregates were detected. From 3% to 20% (w/w) long individual and monodisperse nanotubes crystallized in a hexagonal lattice were evidenced. Their molecular and supramolecular organizations are identical to the ones characterized for the 10% (w/w) sample. Heating induces the dissolution of the nanotubes into soluble aggregates of the same structural characteristics as the room temperature ones. The solubilization temperature increases from 20 degrees C to 70 degrees C with the peptide concentration and reaches a plateau between 15% and 25% (w/w) in peptide. These aggregates are proposed to be the beta-sheet filaments that self-associate to build the walls of the nanotubes. Above 20% (w/w) of Lanreotide acetate in water, polydisperse embedded nanotubes are formed and the hexagonal lattice is lost. These embedded nanotubes exhibit the same molecular and supramolecular organizations as the individual monodisperse nanotubes formed at lower peptide concentration. The embedded nanotubes do not melt in the range of temperature studied indicating a higher thermodynamic stability than individual nanotubes. In parallel, the thermal behaviors of water in mixtures containing 2-80% (w/w) in peptide have been studied by differential scanning calorimetry, and three different types of water were characterized: 1), bulk water melting at 0 degrees C, 2), nonfreezing water, and 3), interfacial water melting below 0 degrees C. The domains of existence and coexistence of these different water states are related to the different Lanreotide supramolecular structures. All these results were compiled into a binary Lanreotide-water phase diagram and allowed to propose a self-association mechanism of Lanreotide filaments into monodisperse individual nanotubes and embedded nanotubes.

Calorimetry, Differential Scanning↗
PubMed1993

Acyl structure regulates galactosylceramide's interfacial interactions.

Galactosylceramides (GalCer) with homogeneous acyl chains containing zero, one, or two cis double bonds have been synthesized and characterized at an argon-aqueous buffer interface using a Langmuir film balance. Both surface pressure and surface potential were measured as a function of molecular area at 24 degrees C. N-Lignoceroylgalactosylsphingosine (N-24:0-GalSph), N-stearoylgalactosylsphingosine (N-18:0-GalSph), and N-palmitoylgalactosylsphingosine (N-16:0-GalSph) form condensed films that are similar to that of bovine brain GalCer, which contains long saturated and mono-unsaturated acyl chains, almost half being hydroxylated. In contrast, a bovine brain GalCer subfraction (NFA-GalCer) that is devoid of the hydroxylated acyl chains displays an apparent two-dimensional phase transition near 9.0 mN/m at 54 A2/molecule. To determine the role of acyl unsaturation in regulating NFA-GalCer's surface behavior, GalCer derivatives containing different mono-unsaturated acyl residues were investigated. N-Nervonoyl-galactosylsphingosine (N-24:1 delta 15-GalSph) and N-docosenoylgalactosylsphingosine (N-22:1 delta 13-GalSph) show liquid-expanded to -condensed phase transitions in their force-area isotherms at 10 and 35 mN/m, respectively. Introduction of acyl chains that are short and saturated [e.g., N-decanoylgalactosylsphingosine (N-10:0-GalSph)] or that are long but contain two cis double bonds [e.g., N-linoleoylgalactosylsphingosine (N-18:2 delta 9,12-GalSph)] causes GalCer to display only liquid-expanded behavior at 24 degrees C. The surface potentials (delta V) of the condensed GalCer derivatives with long saturated acyl residues were quite similar and were over 100 mV higher than that of bovine brain GalCer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Interfacial polymerization within a simplified microfluidic device: capturing capsules.

A simple approach to a microfluidic device is described. The device is composed of flexible tubing and a needle inserted orthogonal to the long axis of the tubing. This design is well suited to creating oil-water interfaces allowing the formation of laminar flows and monodisperse emulsions. The system is characterized by mapping the phases observed as a function of organic phase flow and Reynolds number. In addition, the device allows interfacial polymerization reactions to capture low coefficient of variation capsules. The shell structure and surface are examined by scanning electron microscopy.

Journal Article↗
PubMed2006

Interfacial properties of a synthetic peptide derived from hepatitis G virus E2 protein: interaction with lipid monolayers.

A useful approach to get information about the potential fusogenic ability of virus synthetic peptides is the study of its interfacial properties and subsequent study in mono- and bilayers. In this work, we have characterized by means of physicochemical tools (i.e. compression isotherms and surface activity) the sequence 267-284, LLGTEVSEVLGGAGLTGG, derived from the E2 structural protein of HGV/GBV-C. The adsorption of the peptide at the air/water interface was monitored by following the increase in surface pressure as a function of time at two different pH values: 5 and 7. Parameters such as surface excess or molecular area were calculated from the equation of Gibbs. The peptide showed a tendency to migrate to the surface of a saline-buffered solution. It formed stable monolayers at the air/water interface giving a compression isotherm with a shape consistent with that of some alpha-helical peptide conformations. Brewster angle microscopy (BAM) showed that through compression the peptide formed multilayers. The studies with lipid monolayers (DPMC, DMPC/DMPG, and DMPC/DMTAP) showed that the peptide interacts with all the lipids assayed producing a marked disrupting effect upon them. In these effects electrostatic interactions seem to have some participation.

Amino Acid Sequence↗
PubMed1998

The interfacial behavior of cytochrome c studied by pendant-drop technique.

The adsorption properties of cytochrome c (cyt c) were characterized by surface tension measurements using the pendant-drop method employing the digital image analysis of the drop shape. The method was applied to the study of the protein conformation change due to acidification at low ionic strength. The observation of the saturated steady-state surface tension shows that decrease in pH induces its cooperative change centered around pH 2.5. This value is equal to the value of apparent pK of the acid-induced transition of the horse ferricyt c from a native state to the unfolded conformation. This indicates that the saturated steady-state surface tension is sensitive to the conformation of cyt c in bulk phase, and the pendant-drop method might be used to monitor changes in the tertiary structure of proteins.

Adsorption↗
PubMedDate not supplied

Histomorphologic characterization of noncarious and caries-affected dentin/adhesive interfaces.

PURPOSE: The purpose of this study was to compare the dentin/adhesive interfacial characteristics when bonding to noncarious as well as caries-affected dentin. MATERIALS AND METHODS: Seven extracted, unerupted, third molars were sectioned into halves. Artificial caries was created on one-half of each tooth, leaving the other half as a control. Dentin surfaces were treated with UNO adhesive according to the manufacturer's instructions for the wet-bonding technique and under environmental conditions present in the oral cavity. Dentin/adhesive interface sections of each half-tooth were stained with Goldner's trichrome, a classic bone stain, and examined using light microscopy. The width of exposed collagen was measured directly from photomicrographs, and adhesive penetration was analyzed qualitatively. RESULTS: The degree and extent to which the adhesive encapsulated the demineralized dentin matrix were reflected in the color difference in the stained sections with the noncarious dentin sections showing a degree of collagen encapsulation superior to that of the caries-affected dentin sections. The overall mean widths of exposed collagen were significantly (p < or = .05) greater at the caries-affected dentin/adhesive interface, 8.6 (1.7) microm, as compared with those at the noncarious dentin/adhesive interface, 6.0 (1.5) microm. CONCLUSIONS: The morphologic characteristics of the caries-affected dentin/interface suggest an increase in the exposed collagen zone and a decrease in the quality of the adhesive infiltration when compared with noncarious dentin. The evidence suggests that dentin substrate characteristics have a significant effect on the dentin/adhesive interface structure.

Benzoates↗
PubMedDate not supplied

Preparation and characterization of multiple emulsion based systems for controlled diclofenac sodium release.

Multiple w/o/w type emulsions were prepared and stabilized through interfacial complex films formation as a result of interaction of macromolecules like gelatin, bovine serum albumin (BSA), polyvinyl alcohol (PVA) and polyacrylic acid (PAA) (each present in internal aqueous phase separately) with sorbitan monostearate (Span 60) present in the middle oil phase. The stability of prepared emulsions was assessed using microscopic analysis which showed no significant changes in the average size of globule and number of droplets counted per cubic mm on storage. Viscosity and zeta potential studies revealed appreciable stability of the multiple emulsions. The multiple emulsion containing macromolecules in their internal phase demonstrated better entrapment efficiency. Intramuscular injection of drug in a w/o/w emulsion formulation provided a protracted drug plasma profile for diclofenac sodium.

Animals↗
PubMed2006

Mechanics of interfacial composite materials.

Recent experiments and simulations have demonstrated that particle-covered fluid/fluid interfaces can exist in stable nonspherical shapes as a result of the steric jamming of the interfacially trapped particles. The jamming confers the interface with solidlike properties. We provide an experimental and theoretical characterization of the mechanical properties of these armored objects, with attention given to the two-dimensional granular state of the interface. Small inhomogeneous stresses produce a plastic response, while homogeneous stresses produce a weak elastic response. Shear-driven particle-scale rearrangements explain the basic threshold needed to obtain the near-perfect plastic deformation that is observed. Furthermore, the inhomogeneous stress state of the interface is exhibited experimentally by using surfactants to destabilize the particles on the surface. Since the interfacially trapped particles retain their individual characteristics, armored interfaces can be recognized as a kind of composite material with distinct chemical, structural, and mechanical properties.

Journal Article↗
PubMed2000

Hydroxyapatite and their use as coatings in dental implants: a review.

At present, no standard manufacturing guideline exists for depositing hydroxyapatite (HA) on implant surfaces. Although animal and in vitro studies have reported on the benefits of using HA-coated implants as well as the risks of dissolution, these short-term studies did not demonstrate that the dissolution of the HA coating leads to a loss of implants. In addition, many in vivo and clinical studies did not include the chemical and structural characterization of the coatings, and thus comparisons between studies are difficult. In the clinics, the recommendation is that HA-coated screw implants be used for the anterior maxilla and posterior mandible where the bone depth exceeds 10 mm and when the cortical layer is thinner and spongiosia is less dense. In the posterior maxilla or when the cortical layer is very thin with low density, the use of HA-coated cylindrical implants is recommended. However, there are concerns for using HA-coated implants. The clinician needs to take into consideration the enhanced bacterial susceptibility of HA coatings compared with titanium implants. In addition, the clinician needs to consider the possible failure of HA coatings as a result of coating-substrate interfacial fracture. Finally, besides the surgical skills, it is also important that the clinical investigators be well versed with the materials characterization needed for HA-coated implants, the problems associated with the current HA coatings, and the indications for use. In addition, the correlation between well characterized coatings and their effect on bone formation rate and long-term implant success, coating-implant interfacial strength, and alternative superior coating process need to be investigated further.

Animals↗
PubMed1976

Application of enantiomeric 2-sn-phosphatidylcholines in interfacial enzyme kinetics of lipolysis.

Two enantiomeric 2-sn-phosphatidylcholines containing hexanoyl and dodecanoyl acyl chains have been synthesized, enabling the study of the action of phospholipase A2 (EC 3.1.1.4) at lipid-water interfaces characterized by identical physico-chemical properties. Monolayer kinetics and bulk kinetics in the presence of Triton X-100 micelles were studied but the interpretation of the results is impeded by the fact that interfacial saturation conditions cannot be reached. In contrast, the use of the substrate analog n-tetradecylphosphorylcholine allows the determination of the interfacial kinetic parameters kcat and K*m. Dodecanoic acid is released from the most susceptible isomer about 13 times more rapidly than hexanoic acid from the stereoisomer in spite of the higher K*m of the former. The results are discussed in terms of the particular active site architecture and the possible influence of the "quality of the interface" on the kinetic parameters.

Binding Sites↗
PubMed2005

Interfacial water as a "hydration fingerprint" in the noncognate complex of BamHI.

The molecular code of specific DNA recognition by proteins as a paradigm in molecular biology remains an unsolved puzzle primarily because of the subtle interplay between direct protein-DNA interaction and the indirect contribution from water and ions. Transformation of the nonspecific, low affinity complex to a specific, high affinity complex is accompanied by the release of interfacial water molecules. To provide insight into the conversion from the loose to the tight form, we characterized the structure and energetics of water at the protein-DNA interface of the BamHI complex with a noncognate sequence and in the specific complex. The fully hydrated models were produced with Grand Canonical Monte Carlo simulations. Proximity analysis shows that water distributions exhibit sequence dependent variations in both complexes and, in particular, in the noncognate complex they discriminate between the correct and the star site. Variations in water distributions control the number of water molecules released from a given sequence upon transformation from the loose to the tight complex as well as the local entropy contribution to the binding free energy. We propose that interfacial waters can serve as a "hydration fingerprint" of a given DNA sequence.

Base Sequence↗
PubMed2000

Polymeric colloidal systems containing ethionamide: preparation and physico-chemical characterization.

The association of ethionamide with different colloidal systems was evaluated. Nanocapsules (NC), nanospheres (NS), and nanoemulsions (NE) were prepared by interfacial deposition and spontaneous emulsification techniques. Ethionamide was incorporated before (B) and after (A) preparation of nanoparticles. Ethionamide was assayed by HPLC, the particle size was determined using a Nanosizer, and the zeta potential using a Zetasizer 4. Free ethionamide was determined using a combined ultrafiltration-centrifugation technique. The drug release was determined by direct dilution of the nanoparticle dispersion in phosphate-buffer pH 7. All preparations retained acceptable particle size distribution (+/- 300 nm), except the NE. The zeta potential of all formulations was between -36.6 mV and -46.1 mV. Percentages of ethionamide associated were: NC (B: 62.4%, A: 56.2%), NS (B: 53.0%, A: 43.2%), and NE (B: 38.5%). After 45 days, the percentage of drug association with NC increased (B: 66.8%, A: 60.6%). The release profiles demonstrated that associated ethionamide was more readily released from the NC and NS prepared by procedure A rather than B. The ethionamide amount not released (B) was greater in NS than NC. The drug is mainly adsorbed onto the surface of nanoparticles. However, approximately 10% of ethionamide is encapsulated into NC and 20% entrapped into NS, respectively.

Antitubercular Agents↗
PubMed2000

Surface modification of polystyrene nanoparticles using dextrans and dextran-POE copolymers: polymer adsorption and colloidal characterization.

Hydrophobically-modified dextran (dextran-phenoxy, DexP) and dextran-phenoxy-poly(oxyethylene) (DexP-POE) copolymers have been used to modify the surface properties and the stability of polystyrene nanoparticles. We examined the effect of phenoxy group and POE chain concentrations on their adsorption behaviour. The adsorbed amount was determined by the standard depletion method and the layer thickness of the adsorbed layer by photon correlation spectroscopy and electrokinetic measurements. The results show that the hydrophobic interaction is the driving force during the adsorption while the layer thickness correlates with the interfacial concentration of grafted POE chains. The effects of adsorbed layers on the properties of latex dispersions have been characterized in terms of the stability of the dispersions toward added electrolyte and temperature. The conformation of the adsorbed copolymers is discussed in relation to layer thickness and colloidal stability of suspensions.

Adsorption↗
PubMed2006

Effect of interfacial mobility on rupture of thin stagnant films on a solid surface due to random mechanical perturbations.

Previous analysis of Narsimhan [G. Narsimhan, J. Colloid Interface Sci. 287 (2005) 624-633] for the evaluation of rupture of a nondraining thin film on a solid support due to imposed random mechanical perturbations modeled as a Gaussian white noise has been extended for partially mobile gas-liquid interfaces. The average rupture time of film is evaluated by first passage time analysis (as the mean time for the amplitude of perturbation to become equal to film thickness). The interfacial mobility is accounted for through surface viscosity as well as Marangoni effect. The mean rupture time for partially mobile gas-liquid interface, as characterized by two dimensionless groups, dimensionless surface viscosity and Marangoni number, lies between the two extreme limits for fully mobile and immobile films. The critical wavenumber for minimum rupture time is shown to be insensitive to interfacial mobility. However, the critical dimensionless surface viscosity and critical Marangoni number at which the behavior of thin film deviates from that of fully mobile film and the behavior approaches that of fully immobile film are smaller for higher Hamaker constants, smaller film thickness and smaller surface potentials.

Algorithms↗
PubMed2005

Effect of time on the interfacial and foaming properties of beta-lactoglobulin/acacia gum electrostatic complexes and coacervates at pH 4.2.

The electrostatic complexation between beta-lactoglobulin and acacia gum was investigated at pH 4.2 and 25 degrees C. The binding isotherm revealed a spontaneous exothermic reaction, leading to a DeltaHobs = -2108 kJ mol(-1) and a saturation protein to polysaccharide weight mixing ratio of 2:1. Soluble electrostatic complexes formed in these conditions were characterized by a hydrodynamic diameter of 119 +/- 0.6 nm and a polydispersity index of 0.097. The effect of time on the interfacial and foaming properties of these soluble complexes was investigated at a concentration of 0.1 wt % at two different times after mixing (4 min, referred as t approximately 0 h and t = 24 h). At t approximately 0 h, the mixture is mainly made of aggregating soluble electrostatic complexes, whereas after 24 h these complexes have already insolubilize to form liquid coacervates. The surface elasticity, viscosity and phase angle obtained at low frequency (0.01 Hz) using oscillating bubble tensiometry revealed higher fluidity and less rigidity in the film formed at t approximately 0 h. This observation was confirmed by diminishing bubble experiments coupled with microscopy of the thin film. It was thicker, more homogeneous and contained more water at t approximately 0 h as compared to t = 24 h (thinner film, less water). This led to very different gas permeability's of Kt approximately 0 h = 0.021 cm s(-1) and Kt=24 h) = 0.449 cm s(-1), respectively. Aqueous foams produced with the beta-lactoglobulin/acacia gum electrostatic complexes or coacervates exhibited very different stability. The former (t approximately 0 h) had a stable volume, combining low drainage rate and mainly air bubble disproportionation as the destabilization mechanism. By contrast, using coacervates aged for 24 h, the foam was significantly less stable, combining fast liquid drainage and air bubble destabilization though fast gas diffusion followed by film rupture and bubble coalescence. The strong effect of time on the air/water interfacial properties of the beta-lactoglobulin/acacia gum electrostatic complexes can be understood by their reorganization at the interface to form a coacervate phase that is more fluid/viscous at t approximately 0 h vs rigid/elastic at t = 24 h.

Air↗