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PubMed1998

Preparation of Poly(methylmethacrylate) Microcapsules with Liquid Cores.

Particles with liquid cores and solid shells have been prepared by the controlled phase separation of poly(methylmethacrylate) (PMMA) within the droplets of an oil-in-water emulsion. The oil phase of the emulsion contained poly(methylmethacrylate), a good solvent for the polymer (CH2Cl2), a poor solvent (hexadecane, decane, octanol, or tetrachloromethane), and in some cases acetone (a water soluble co-solvent) to aid emulsification. Emulsions were prepared using a Silverson high-speed stirrer, and the droplet size distributions were determined using a Coulter particle counter. Size distributions were found to be dependent on the nature of the emulsifier, the concentration of acetone in the oil phase, and the concentration of polymer in the oil phase. The good solvent was then removed under reduced pressure, causing the poly(methylmethacrylate) to phase separate within the emulsion droplets. The resultant two-phase particles were characterized by optical microscopy and scanning electron microscopy. Particle morphologies depended strongly on the nature of the non-solvent and also the emulsifier employed. Spreading coefficients were calculated from interfacial tension and contact angle measurements, and were used to account for the morphologies observed. Core/shell microcapsules were formed when hexadecane or decane was used as non-solvent, and only when polymeric emulsifiers were employed. All other combinations yielded "acorn"-shaped particles. The thickness of microcapsule walls was found to be a constant fraction of the overall capsule diameter for all microcapsule sizes and depended, as expected, on the concentration of polymer in the oil phase. Copyright 1998 Academic Press.

Journal Article↗
PubMed1996

Application of chemometric methods in Auger electron microanalysis of composites.

Principal component analysis and cluster analysis have been used in AES investigations of fibre-matrix interactions in alumina fibre reinforced MgLi-alloys prepared by high-pressure infiltration. The samples have been fractured in ultra high vacuum to expose surfaces and interfaces without contamination. All main components exhibit Auger valence band transitions which change their shape with the chemical state. Chemometric methods have been utilized to identify characteristic peak shapes and to classify the investigated areas by composition. Fibre fracture surfaces are characterized by Al, magnesia and Li oxide formed by a redox reaction of alumina with Mg and Li penetrating along grain boundaries. For samples with high silica content a thin interfacial oxide layer on matrix grain boundaries and matrix-fibre interfaces has been found.

Journal Article↗
PubMed1993

The dependence of the lipolytic activity of Rhizopus arrhizus lipase on surfactant concentration in Aerosol-OT/isooctane reverse micelles and its relationship to enzyme structure.

Aerosol OT, bis(2-ethylhexyl)sodium sulfosuccinate/isooctane reverse micelles were used to investigate the dependence of the lipolytic activity of Rhizopus arrhizus lipase on surfactant concentration. Kinetic constants for the lipolytic reaction were measured in parallel with structural studies using protein fluorescence and circular dichroism (CD) spectroscopy. Km values remained constant throughout the range of AOT concentrations studied. The kcat values decreased with increasing surfactant concentration at constant water-to-surfactant ratio (wo = 11) from 50 mM to 100 mM AOT, but remained constant from 100 to 200 mM AOT. These data suggested an association of the lipase with the micellar membrane. An inflection in the time-course of the reaction was found to be a function of both surfactant and substrate concentrations and was likely an indication of the interfacial nature of the hydrolysis reaction. Structure prediction based on far-UV CD spectral data demonstrated structural reorganization of R. arrhizus lipase upon incorporation into reverse micelles which was characterized by a dramatic increase in beta-sheet and overall accountable secondary structure. Other spectral changes of the lipase upon incorporation into reverse micelles included appearance of fine structure in the near-UV CD spectrum and a blue shift in the fluorescence emission maximum from 336 to 326 nm.

Circular Dichroism↗
PubMed2004

Hemolysate-filled polyethyleneimine and polyurea microcapsules as potential red blood cell substitutes: effect of aqueous monomer type on properties of the prepared microcapsules.

In this paper, we describe the synthesis and characterization of rabbit hemolysate-filled polyethyleneimine (PEI)- or polyurea (PU)-type artificial red blood cells (ARBCs) with different membrane compositions. These microcapsules were prepared by making use of the interfacial polymerization (IP) reaction between the water-soluble amine monomers (triethylamine (TEA), ethylene glycol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGATA), diethylenetriamine (DETA), tetramethyl diaminomethane (TMDAM), piperazine hexahydrate (PPHH), l-lysine monohydrochloride (LLMH) or PEI) and 2,4-toluylene diisocyanate (TDI) as an oil-soluble shell monomer. The resultant microcapsules were spherical and with mean diameters of 8.71-63.33 microm. Microcapsules having sulfonic acid groups on their surfaces were prepared by using a combination of the functional amines (DETA, LLMH or PEI) and 4,4'-diaminostilbene-2,2'-disulfonic acid (DASSA). Oxygen-binding abilities of the ARBCs were measured by a Clark-type oxygen electrode. The obtained results revealed that the highest oxygen-binding abilities were obtained with the PU-ARBCs prepared with DETA alone or in combination with EGATA. Unfortunately, these microcapsules exhibited large diameters and wider size distribution curves (span values (S) = 1.3, 1.7, geometric standard deviation sigma(g) = 1.85, 2.18, respectively). However, the novel ARBCs (sulfonated PU-PEI graft copolymer membrane microcapsules (SPU/PEI-ARBCs)) prepared had good oxygen affinity, the smallest mean diameter (d = 8.71 microm) and the best distribution (S = 0.9, sigma(g) = 1.48) and a flow behavior identical to rabbit RBCs. Therefore, these unique microcapsules can be recommended for scale-up considerations as a promising blood substitute.

Animals↗
PubMed1999

Colloidal gas aphrons: potential applications in biotechnology

Colloidal gas aphrons are microbubbles encapsulated by surfactant multilayers. They provide a large interfacial area to adsorb charged and/or hydrophobic molecules; the extent and mechanism of the adsorption depends on the surfactant multilayer. The physical properties of colloidal gas aphrons have recently been characterized for a range of surfactants in order to find the best systems for particular applications. A range of exciting biotechnology applications has been identified, including the recovery of cells, proteins and other biological molecules, and the enhancement of gas transfer in bioreactors and bioremediation.

Journal Article↗
PubMed2001

Polyisobutylcyanoacrylate nanocapsules containing an aqueous core for the delivery of oligonucleotides.

Antisense oligonucleotides (ODNs) with base sequences complementary to a specific RNA can, after binding to intracellular mRNA, selectively modulate the expression of a gene. However, these molecules are poorly stable in biological fluids and are characterized by a low intracellular penetration. In view of using ODNs as active molecules, the development of nanocapsules containing ODNs in their aqueous core was considered. Nanocapsules were prepared by interfacial polymerization of isobutylcyanoacrylate (IBCA) in a W/O emulsion. After ultracentrifugation and re-suspension in water, the nanocapsules displayed a size of 350+/-100 nm. Oligonucleotide loading did not significantly influence the zeta potential, suggesting that they were located within the core of the nanocapsules. Fluorescence quenching assays confirmed this localization. When encapsulated in the nanocapsules and incubated in the presence of serum, the ODNs were efficiently protected from degradation by nucleases, whereas ODNs adsorbed onto nanospheres were less efficiently protected. This paper describes, for the first time, a nanotechnology able to encapsulate ODNs, rather than adsorbing them at the surface of a solid support. Such a formulation has great potential for oligonucleotide delivery.

Cyanoacrylates↗
PubMed2002

Influence of wettability on the recovery of NAPLs from alluvium.

The physicochemical characteristics of five nonaqueous phase liquids (NAPLs) recovered from contaminated alluvial aquifers are presented. The five include two chlorinated degreasing solvents, one chlorinated dry-cleaning solvent and two weathered fuel hydrocarbons. In addition to density, viscosity, and interfacial tensions, the equivalent alkane carbon number (EACN), spreading coefficients and Amott-Harvey and USBM wettability indices with respect to alluvial aquifer materials are used as a means to characterize three of these NAPLs. Experimentally measured spreading coefficients of four of these NAPLs illustrate that field NAPLs can have positive initial spreading coefficients. Furthermore, capillary desaturation curves for two NAPLs with alluvial aquifer material collected from the NAPL zone are presented as an additional and important means to infer the practical implications of the wetting characteristics on the efficacy of NAPL recovery. The results from the wettability and capillary desaturation experiments show that these NAPLs are mixed-wet to oil-wet when measured in the alluvium from their respective field sites. Furthermore, these results indicate that the displacement of NAPLs from soils by water is more difficult for mixed-wet or oil-wet soils than it is for water-wet or weakly water-wet soils. Finally experimental data indicate that adding anionic surfactants to the water shifts the wettability toward water-wet and makes the NAPL easier to displace and recover.

Hydrocarbons↗
PubMed2006

Assembly of metal nanoparticle-carbon nanotube composite materials at the liquid/liquid interface.

Carbon nanotubes (CNTs)-mediated self-assembly of metal (Au and Ag) nanoparticles at the liquid/liquid interface in the form of a stable nanocomposite film is reported. The metallic luster results from the electronic coupling of nanoparticles, suggesting the formation of closely packed nanoparticle thin films. The interfacial film could be transferred to mica substrates and carbon-coated transmission electron microscopy (TEM) grids. The transferred films were very stable for a prolonged time. The samples were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), TEM, and X-ray photoelectron spectroscopy (XPS). SEM and TEM results show that the films formed at the liquid/liquid interface are indeed composite materials consisting of CNTs and nanoparticles. XPS measurements further indicate the presence of the interaction between nanoparticles and CNTs.

Journal Article↗
PubMed2005

Stabilization of somatropin by heparin.

Somatropin, human growth hormone (hGH), is an unstable protein, posing challenging problems for its formulation and long-term stability. Since hGH formed insoluble adducts with heparin our aim was to evaluate heparin as a stabilizing agent for the drug. These adducts were characterized by particle diameter, tertiary structure variations and release studies. Studies were also carried out to determine the stability of hGH in the presence and absence of heparin by an interfacial denaturation method and real-time stability studies by measuring hGH activity and particle diameter. Moreover, biological activity of hGH and hGH/UH (unfractionated heparin) adducts was identified by daily subcutaneous injections to hypophysectomized rats. There was a decrease in mean hydrodynamic particle diameter of hGH/UH adducts with increased pH (54.4 to 12.2 nm from pH 3 to pH 7) indicating that the adducts were either dissociating or dissolving at high pH. Furthermore, second-derivative spectroscopy indicated that complexation of hGH with heparin did not cause a major disruption in the tertiary structure of hGH but decreased the hydrophilic environment around the tyrosine residues. Release of hGH from hGH/UH adducts was pH and ionic strength dependent with the highest release at pH 8 (93%) and lowest release at pH 3 (0%) over the first hour. Interfacial denaturation methods indicated that vortex agitation over 120 s resulted in no change in the optical density of hGH/UH adducts compared with a substantial increase for hGH alone at pH 6.8. Real-time stability studies over 93 days demonstrated that hGH/UH adducts at both pH 3 and 7 with an excess of heparin produced the highest percent of active hGH remaining in the solution at 4 degrees C and 37 degrees C. The higher stability of hGH/UH adducts with excess heparin compared with the stoichiometric ratio was also confirmed by particle size measurements during storage. The biological activity of these adducts was comparable with hGH alone by weight-gain studies in hypophysectomized rats. The findings suggest the value of using hGH/heparin adducts to stabilize the protein.

Animals↗
PubMedDate not supplied

New high-palladium casting alloys: studies of the interface with porcelain.

This investigation studied the metal ceramic interface for two representative high-palladium alloys each of the Pd-Cu-Ga and Pd-Ga systems, using scanning electron microscopy and x-ray energy dispersive spectroscopy. The Pd-Cu-Ga alloys produced complex subsurface oxidation regions with thickness ranging from 15 to 20 microns for one alloy and 5 to 10 microns for the other alloy. Ga, In, and Sn accumulated at the interfaces, and Ga-rich deposits were found in the subsurface scale. One Pd-Ga alloy presented a surface oxidation region which dissolved in the ceramic, producing "islands" rich in Pd and Ga with a width that ranged from 1 to 2 microns. These islands were separated from the alloy by a band rich in Ga and Si which was 1 to 2.5 microns thick. While the other Pd-Ga alloy presented similar interfacial microstructures, the "islands" formed for this alloy were relatively sparse. The Pd-Cu-Ga alloys had a more favorable interface for metal ceramic bonding, which agrees with previous characterization of bond failures between these alloys and dental porcelain.

Copper↗
PubMed2004

Formation and characterization of three-component-sorbitan monoester surfactant, oil and water-creams.

The effect of molecular structure of four sorbitan monoester surfactants (sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate and sorbitan monooleate) on the formation of simple three-component creams is presented. Interfacial properties of the surfactants were determined using a du Nouy tensiometer and rheological properties of selected creams with oscillation stress sweep, creep recovery and viscosity tests. Depending on the composition, sorbitan monolaurate and sorbitan monooleate formed both o/w creams and w/o creams, while sorbitan monopalmitate and sorbitan monostearate formed only o/w creams. Sorbitan monostearate and sorbitan monopalmitate had the smallest cmc and A(cmc) values and they were the most effective surfactants in lowering the interfacial tension. These surfactants formed the most stable and elastic creams with clear linear viscoelastic regions and small compliance values. Sorbitan monolaurate and sorbitan monooleate formed viscous creams without elastic properties.

Drug Compounding↗
PubMed2002

Effect of water content on transient nonequilibrium NAPL-gas mass transfer during soil vapor extraction.

The effect of water content on the volatilization of nonaqueous phase liquid (NAPL) in unsaturated soils was characterized by one-dimensional venting experiments conducted to evaluate the lumped mass transfer coefficient. An empirical correlation based upon the modified Sherwood number, Peclet number, and normalized mean grain size was used to estimate initial lumped mass transfer coefficients over a range of water content. The effects of water content on the soil vapor extraction SVE process have been investigated through experimentation and mathematical modeling. The experimental results indicated that a rate-limited NAPL-gas mass transfer occurred in water-wet soils. A severe mass transfer limitation was observed at 61.0% water saturation where the normalized effluent gas concentrations fell below 1.0 almost immediately, declined exponentially from the initiation of venting, and showed long tailing. This result was attributed to the reduction of interfacial area between the NAPL and mobile gas phases due to the increased water content. A transient mathematical model describing the change of the lumped mass transfer coefficient was used. Simulations showed that the nonequilibrium mass transfer process could be characterized by the exponent beta, a parameter which described the reduction of the specific area available for NAPL volatilization. The nonequilibrium mass transfer limitations were controlled by the soil mean grain size and pore gas velocity, were well described by beta values below 1.0 at low water saturation, and were well predicted with beta values greater than 1.0 at high water saturation.

Gases↗
PubMed1995

Rat GP-3 is a pancreatic lipase with kinetic properties that differ from colipase-dependent pancreatic lipase.

The pancreas contains three homologous proteins, colipase-dependent pancreatic lipase (PL) and two recently described pancreatic lipase-related proteins, PLRP1 and PLRP2. Rat (r) PLRP2 was first identified as a zymogen granule membrane protein, GP-3. Subsequently, we showed that rPLRP2 could cleave fatty acids from triglycerides, but the kinetic properties of rPLRP2 have not been further investigated. To further characterize rPLRP2, we expressed the recombinant enzyme in a baculovirus system, purified the secreted protein, and measured its kinetic properties. rPLRP2 had a broad pH optimum and the curve was similar to that of rPL. At pH 7.5, rPLRP2 cleaved short, medium, and long chain triglycerides by a kinetic mechanism that did not include interfacial activation. The activity against these substrates was not affected by bile salts. In particular, rPLRP2 did not show the bile salt inhibition typical of PL. Although colipase increased rPLRP2 activity in the presence of bile salts, the increase was only 2- to 5-fold compared to the absolute requirement for colipase that rPL had under these conditions. Finally, rPLRP2 could hydrolyze phospholipids, a substrate poorly hydrolyzed by PL. Our characterization of rPLRP2 demonstrates clear differences among the kinetic properties of rPLRP2 and rPL, rPLRP2, and PLRP2 homologues isolated from guinea pig and coypu pancreas. These findings have important implications for the physiological function of rPLRP2.

Amino Acid Sequence↗
PubMed1991

Interfacial energies and surface-tension forces involved in the preparation of thin, flat crystals of biological macromolecules for high-resolution electron microscopy.

It is generally agreed that surface-tension forces and the direct interaction between the specimen and either the air-water interface or the water-substrate interface can influence significantly the preparation of biological materials for electron microscopy. Even so, there is relatively little systematic information available that would make it possible to control surface-tension forces and interfacial energies in a quantitative fashion. The main objective in undertaking the present work has been to understand somewhat better the factors that influence the degree of specimen flatness of large, monolayer crystals of biological macromolecules. However, the data obtained in our work should be useful in understanding the preparation of specimens of biological macromolecules in general. Data collection by electron diffraction and electron microscopy at high resolution and high tilt angles requires thin crystals of biological macromolecules that are flat to at least 1 degree, and perhaps less than 0.2 degrees, over areas as large as 1 micron2 or more. In addition to determining empirically by electron diffraction experiments whether sufficiently flat specimens can be prepared on various types of modified or unmodified carbon support films, we have begun to use other techniques to characterize both the surfaces involved and the interaction of our specimen with these surfaces. In the specific case of large, monolayer crystals of bacteriorhodopsin prepared as glucose-embedded specimens on hydrophobic carbon films, it was concluded that the initial interfacial interaction involves adsorption of the specimen to the air-water interface rather than adsorption of the specimen to the substrate. Surface-tension forces at the air-water interface and an apparently repulsive interaction between the specimen and the hydrophobic carbon seem to be major factors influencing the specimen flatness in this case. In the more general case it seems likely that interfacial interactions with either the substrate or the air-water interface can be variously manipulated in the search to find desirable conditions of specimen preparation.

Adsorption↗
PubMed2003

Physicochemical characterization and antimicrobial properties of rhamnolipids produced by Pseudomonas aeruginosa 47T2 NCBIM 40044.

Pseudomonas aeruginosa 47T2, grown in submerged culture with waste frying oil as a carbon source, produced a mixture of rhamnolipids with surface activity. Up to 11 rhamnolipid homologs (Rha-Rha-C(8)-C(10); Rha-C(10)-C(8)/Rha-C(8)-C(10);Rha-Rha-C(8)-C(12:1); Rha-Rha-C(10)-C(10); Rha-Rha-C(10)-C(12:1); Rha-C(10)-C(10); Rha-Rha-C(10)-C(12)/Rha-Rha-C(12)-C(10); Rha-C(10)-C(12:1)/Rha-C(12:1)-C(10); Rha-Rha-C(12:1)-C(12); Rha-Rha-C(10)-C(14:1); Rha-C(10)-C(12)/Rha-C(12)-C(10)) were isolated from cultures of P. aeruginosa 47T2 from waste frying oil and identified by HPLC-MS analysis. This article deals with the production, isolation, and chemical characterization of the rhamnolipid mixture RL(47T2). The physicochemical and biological properties of RL(47T2) as a new product were also studied. Its surface tension decreased to 32.8 mN/m; and the interfacial tension against kerosene to 1 mN/m. The critical micellar concentration for RL(47T2) was 108.8 mg/mL. The product showed excellent antimicrobial properties. Antimicrobial activity was evaluated according to the minimum inhibitory concentration (MIC), the lowest concentration of an antimicrobial agent that inhibits development of visible microbial growth. Low MIC values were found for bacteria Serratia marcescens (4 microg/mL), Enterobacter aerogenes (8 microg/mL), Klebsiella pneumoniae (0.5 microg/mL), Staphylococcus aureus and Staphylococcus epidermidis (32 microg/mL), Bacillus subtilis (16 microg/mL), and phytopathogenic fungal species: Chaetonium globosum (64 microg/mL), Penicillium funiculosum (16 microg/mL), Gliocadium virens (32 microg/mL) and Fusarium solani (75 microg/mL).

Anti-Bacterial Agents↗
PubMed1984

An evaluation of purity criteria for bovine rod outer segment membranes.

The purity criteria of bovine rod outer segments (ROS) purified by different procedures were evaluated. Bovine ROS were purified by flotation and/or sedimentation in a continuous concentration gradient of sucrose. The purity of the different fractions was then evaluated according to four purity criteria: (i) the A280/delta A500 ratio, (ii) the moles of phospholipid per mole of rhodopsin, (iii) the fatty acid composition, and (iv) the interfacial properties of ROS membranes. All the purity criteria, except the A280/delta A500 ratio, were found to be adequate. From our results, the A280/delta A500 ratio cannot be used alone to characterize ROS purity. Furthermore, the phospholipid-to-rhodopsin ratio appears as the best purity criterion because of its reliability, its higher sensitivity, and its ease of achievement. It is noteworthy that mechanical treatment of the retinas dramatically affects the purification of ROS.

Animals↗
PubMed1999

Restoring low resolution structure of biological macromolecules from solution scattering using simulated annealing.

A method is proposed to restore ab initio low resolution shape and internal structure of chaotically oriented particles (e.g., biological macromolecules in solution) from isotropic scattering. A multiphase model of a particle built from densely packed dummy atoms is characterized by a configuration vector assigning the atom to a specific phase or to the solvent. Simulated annealing is employed to find a configuration that fits the data while minimizing the interfacial area. Application of the method is illustrated by the restoration of a ribosome-like model structure and more realistically by the determination of the shape of several proteins from experimental x-ray scattering data.

Biophysical Phenomena↗
PubMed2002

Direct compositional analysis of AlGaAs/GaAs heterostructures by the reciprocal space segmentation of high-resolution micrographs.

A detailed description of a combined reciprocal and real space technique for the mapping of layer compositions across interior interfaces from high-resolution electron micrographs is presented. The analysis is based on the reciprocal space extraction of chemically sensitive image information encoded in lattice images of AlGaAs/GaAs heterostructures taken under optimized imaging conditions. Analysis procedures include centering a set of apertures around chemically sensitive reflections in the Fourier transform of lattice images and performing an inverse transformation, thus extracting composition related information from experimental micrographs. It is demonstrated that this approach is characterized by the same spatial resolution as real space techniques but by improved capabilities with respect to analysing images characterized by a minor signal-to-noise ratio. For illustration purposes the stability of AlAs/GaAs multiple quantum wells grown under low-temperature conditions against thermal treatment as expressed by interfacial roughness parameters is investigated.

Journal Article↗