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PubMed1991

Surface properties and platelet reactivity of segmented poly(etherurethanes) and poly(etherurethaneureas).

Segmented poly(etherurethanes) (SPUs) and segmented poly(etherurethaneureas) (SPUUs) with various hard and soft segment components were prepared. The surface characterization of SPUs and SPUUs in the air-equilibrated state and in the hydrated-state was carried out by means of X-ray photoelectron spectroscopic (XPS) and dynamic contact angle measurements. XPS revealed that in the air-equilibrated state, lower surface free energy components were enriched at the air-solid interface, whereas in the hydrated-state higher surface free energy components were enriched at the water-solid interface. The change in environment from air to water induced the surface reorganization in order to minimize interfacial free energy. The large contact angle hysteresis was observed for SPUs and SPUUs. This hysteresis can be mainly ascribed to the surface reorganization process. Platelet adhesion tests on SPU and SPUU surfaces indicated that the existence of surface microphase separated structure played an important role in the attainment of blood compatibility.

Adsorption↗
PubMed2005

Anesthetic interaction with ketosteroid isomerase: insights from molecular dynamics simulations.

The nature and the sites of interactions between anesthetic halothane and homodimeric Delta5-3-ketosteroid isomerase (KSI) are characterized by flexible ligand docking and confirmed by 1H-15N NMR. The dynamics consequence of halothane interaction and the implication of the dynamic changes to KSI function are studied by multiple 5-ns molecular dynamics simulations in the presence and absence of halothane. Both docking and MD simulations show that halothane prefer the amphiphilic dimeric interface to the hydrophobic active site of KSI. Halothane occupancy at the dimer interface disrupted the intersubunit hydrogen bonding formed either directly through side chains of polar residues or indirectly through the mediation of the interfacial water molecules. Moreover, in the presence of halothane, the exchange rate of the bound waters with bulk water was increased. Halothane perturbation to the dimer interface affected the overall flexibility of the active site. This action is likely to contribute to the halothane-induced reduction of the KSI activity. The allosteric halothane modulation of the dynamics-function relationship of KSI without direct competition at the enzymatic active sites may be generalized to offer a unifying explanation of anesthetic action on a diverse range of multidomain neuronal proteins that are potentially relevant to clinical general anesthesia.

Anesthetics, Inhalation↗
PubMed2006

Self-assembly of acridine orange dye at a mica/solution interface: formation of nanostripe supramolecular architectures.

Optical waveguide spectroscopy and atomic force microscopy (AFM) have been used to characterize the supramolecular architectures of acridine orange (AO) dye self-assembled at a mica/aqueous solution interface. Under the saturated adsorption conditions, optical waveguide spectroscopy revealed that the dye formed H-type aggregates at the interface. In situ AFM visualized interesting morphology of the dye aggregates showing nanosized meandering stripes with the width of approximately 1.5 nm (or brightness periodicity of approximately 3 nm). Electrostatic adsorption of the dye cations onto a mica surface as well as the intermolecular pi-pi stacking brought about the ordered nanostructures. We propose an interfacial aggregation model that shows a meandering staircase structure with the intermolecular slip angle of 60 degrees. According to the model, the AO molecule occupies a surface area of about 1.0 nm2.

Journal Article↗
PubMed2004

Dipole potential and head-group spacing are determinants for the membrane partitioning of pregnanolone.

The membrane interactions of pregnanolone, an intravenous general anesthetic steroid, were characterized using fluorescence spectroscopy and monolayer technique. di-8-ANEPPS [4-[2-[6-(dioctylamino)-2-naphthalenyl]ethenyl]-1-(3-sulfopropyl)-pyridinium], a membrane dipole potential (Psi)-sensitive probe, revealed pregnanolone to decrease Psi similarly as reported previously for other anesthetics. The decrement in Psi was approximately 16 and 10 mV in dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol (90:10, mol/mol) vesicles, respectively. Diphenylhexatriene anisotropy indicated pregnanolone to have a negligible effect on the acyl chain order. In contrast, substantial changes were observed for the fluorescent dye Prodan, thus suggesting pregnanolone to reside in the interfacial region of lipid bilayers. Langmuir balance studies indicated increased association of pregnanolone to DPPC monolayers containing cholesterol or 6-ketocholestanol at surface pressures pi > 20 mN/m as well as to monolayers of the unsaturated 1-palmitoyl-2-oleoylphosphatidylcholine. In the same surface pressure range, the addition of phloretin, which decreases Psi, reduced the penetration of pregnanolone into the monolayers. These results suggest that membrane partitioning of pregnanolone is influenced by the spacing of the phosphocholine head groups as well as by membrane dipole potential. The latter can be explained in terms of electrostatic dipole-dipole interactions between pregnanolone and the membrane lipids with their associated water molecules. Considering the universal nature of these interactions, they are likely to affect membrane partitioning of most, if not all, weakly amphiphilic drugs.

Anesthetics↗
PubMed2004

Extracellular matrix-like surfactant polymers containing arginine-glycine-aspartic acid (RGD) peptides.

We report on a novel series of biomimetic polymers exhibiting interfacial properties similar to the extracellular matrix. A series of well-defined surfactant polymers were synthesized by simultaneously incorporating arginine-glycine-aspartic acid (RGD) peptide, dextran oligosaccharide, and hexyl ligands with controlled feed ratios onto a poly(vinyl amine) (PVAm) backbone. The peptide sequence was H-GSSSGRGDSPA-NH(2) (Pep) having a hydrophilic extender at the amino terminus and capped carboxy terminus. The peptide-to-dextran (Pep:Dex) ratios were varied to create surfactants having 0, 25, 50, 75, and 100 mol-% peptide relative to dextran. The surfactants were characterized by IR, NMR and atomic force microscopy (AFM) for composition and surface active properties. AFM confirmed full surface coverage of PVAm(Pep)(100%) on graphite, and supported the mechanism of interdigitation of hexyl ligands between surfactant molecules within a specified range of hexyl chain densities. the attachment and growth of human pulmonary artery endothelial cells on the PVAm(Pep)(100%) surface was identical to the fibronectin positive control. Cell adhesion decreased dramatically with decreasing peptide density on the surfactant polymers. Molecular model of a peptide surfactant polymer, consisting of poly(vinyl amine) backbone with peptide, dextran oligosaccharide and hexyl branches coupled to the polymer chain.

Absorption↗
PubMed1998

Alkaline lipase from brain: is it the same enzyme as pancreatic lipase from pancreas?

A new alkaline lipase was detected in rat brain and its properties were compared with those of the well-characterized pancreatic lipase and pancreatic lipase-related protein 2. The activity of the alkaline lipase was determined using trioleoylglycerol emulsion at pH 8.0. Subcellular fractions were prepared from brain homogenates by differential centrifugation. Lipase activities of the cytosolic fraction (the supernatant obtained by differential centrifugation of 100,000g) were stimulated by addition of colipase and bile salts and inhibited by addition of an antibody against rat pancreatic lipase. The partially purified enzyme had an isoelectric point of pH 6.8, which was identical to that found for rat pancreatic lipase. The enzyme had interfacial activation and dependence on colipase in the presence of bile salts. The enzyme had no measurable phospholipase A activity. The band produced by the enzyme on SDS-polyacrylamide gel electrophoresis was identical to that of the rat pancreatic lipase when detected by immunoblotting analysis using an antibody against pancreatic lipase. These results show that pancreatic lipase such as alkaline lipase is in rat brain.

Animals↗
PubMed1989

Surface activity, film formation, and emulsifying properties of milk proteins.

This overview indicates that simple, reliable standardized methods for measuring emulsifying activity and for determining ES are not yet available. One of the major shortcomings of most of the current methods is the inability to detect very small fat globules (less than 0.5 micron), which may be very important in stable emulsions. Several of the methods are time consuming and destructive. To minimize the time required to evaluate emulsions, techniques that monitor instability under the influence of accelerated aging (increased temperature and gravitational field) have been used with varying degrees of success. These methods, e.g., centrifugation, are useful, but processes occurring during centrifugation or heating may not be characteristic of those occurring in a stored emulsion. Generally, there is no method that simultaneously determines changes in emulsions due to the aggregation coalescence, flocculation, creaming, of the droplets and/or oiling off. No single criterion of emulsion instability is sufficient to characterize all the changes occurring in the system. A nonintrusive technique that can monitor dynamic changes in emulsions is needed. Ideally, it should be simple, rapid, inexpensive, and applicable to both diluted and concentrated emulsions. Scientists must continue research to develop such a standard universal method for determining ES, because data from different laboratories cannot currently be validly compared. Reliable methods are also required to elucidate relationships between the physical properties of proteins as emulsifiers and their performance in food emulsions. There is a need for opportunities for systematic research to determine the interfacial behavior of food emulsifiers, particularly food proteins. Research to describe the kinetics and thermodynamics of adsorption at an interface, the extent of unfolding, the degree of packing and polypeptide interactions in an interface during film formation, and information concerning the physical and mechanical properties of interfacial films is needed to describe emulsifying behavior of different proteins. The effects of components in the continuous and discontinuous phase, parameters of manufacture, and interactions between different types of surface-active materials that occur in food need to be studied.

Emulsions↗
PubMed2001

Evaluation of porous networks of poly(2-hydroxyethyl methacrylate) as interfacial drug delivery devices.

Long-term implantable drug delivery devices are desirable to achieve rapid and reliable delivery of bioactive substances to the body. The limitation of most implantable devices is the resulting chronic inflammatory response and fibrous encapsulation of the implant, which prevents effective drug delivery for prolonged periods. One method of overcoming this problem is the addition of an intermediary that could prevent capsule formation. Biocompatible materials with interconnected pore structures greater than 8-10 microm have been shown to support the ingrowth and maintenance of vascularized tissue. In this investigation, we evaluate the efficacy of using porous hydrogel sponges for the tissue interface in an implantable drug delivery device. Porous networks of poly(2-hydroxyethyl methacrylate) (PHEMA) were synthesized using a thermally initiated free-radical solution polymerization. To characterize the microstructure of the PHEMA networks, scanning electron microscopy and mercury porosimetry were used. By altering the solvent fraction in the reaction mixture, PHEMA sponges were synthesized with interconnected pores ranging in size from from 6 to 15 microm with porosities of 55% to 87%. Following the in vitro evaluation, sponges were attached to the distal end of a 20-gauge catheter tubing, and implanted subcutaneously and intraperitoneally. After 5 months implantation, insulin was infused into the devices from external pumps and rapid insulin absorption was observed in conjunction with dramatic lowering of blood glucose levels. From histological evaluation of explanted devices, we observed highly vascularized tissue surrounding the mesenteric implants. These results indicate that it may be possible to use PHEMA sponges for a tissue intermediary for long-term implantable drug delivery devices.

Animals↗
PubMed2002

Cloning, characterization, and expression of cDNA encoding a lipase from Kurtzmanomyces sp. I-11.

A cDNA clone of the lipase secreted by Kurtzmanomyces sp. I-11 was isolated from a cDNA library of this yeast by PCR screening using oligonucleotide primers designed on the basis of the partial amino acid sequence of the lipase. The cloned cDNA (lip1) encoded a hydrophobic protein of 484 amino acids, where the first 20 amino acids and the following 6 amino acid sequences were predicted to be the signal sequence for secretion and a pro-sequence, respectively. The deduced amino acid sequence of the Kurtzmanomyces lipase was most similar to Candida antarctica DSM 3855 lipase A (74% identity) and weakly to other lipases. The consensus pentapeptide (-Gly-X-Ser-X-Gly-) that forms a part of the interfacial lipid recognition site in lipases was conserved. A high level of lipase was produced by Pichia pastoris transformed with the lip1 cDNA, indicating that the cloned cDNA indeed encodes a lipase.

Amino Acid Sequence↗
PubMed1991

Solubilization sites and acid-base forms of dibucaine-hydrochloride in neutral and charged micellar solutions.

Steady-state and time-resolved emission spectroscopic techniques have been employed to characterize the drug species of dibucaine and to identify its location in micellar Triton X-100 (neutral), hexadecyltrimethyl ammonium bromide (cationic) and lithium dodecyl sulfate (anionic) solutions at 77 K. Under physiological conditions, the dibucaine is shown to exist in the free base form (D) while solubilized in the hydrocarbon core of neutral micelles. In cationic micellar solution, dibucaine exists as the monocation species (DH+) where the anesthetic is solubilized in the extramicellar aqueous solution and D is solubilized in the hydrophobic region with close proximity to the micellar interface. In the anionic micelles, interfacial solubilization is most consistent with a site in which the tertiary amino group of the monocation dibucaine (DH+) is anchored at the micellar interface with its quinoline analog penetrating the hydrophobic region. The distinct properties observed for the drug species (i.e. D and DH+) and their solubilization sites in micelles are consistent with a balance between hydrophobic forces, surface polarity and the interfacial electrostatic potential present in the micellar solubilization sites. These observations could lend insight into the molecular basis of pharmacological action, in particular the mechanism of local anesthetic drug transport across membranes.

Dibucaine↗
PubMed2006

Relationships between characteristics of interfacial water and human bone tissues.

Water bound in human bone tissues healthy (sample S1) and affected by osteoporosis (sample S2) was investigated by using 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial waters at T< 273 K. The 1H NMR spectra of the bound water include two signals which can be assigned to strongly associated typical water (chemical shift of the proton resonance at delta(H) approximately 5 ppm) and weakly associated water at delta(H) approximately 1.4 ppm. Approximately, half of the bound water is in the weakly associated state in S1. A fraction of similar water in S2 is smaller because of the structural difference of the studied samples. The pore size distribution of S2 (in aqueous medium) calculated using the cryoporometry method is characterized by much larger intensity of mesopores and macropores in comparison with that of S1. The total porosity and the surface area of the biostructures (accessible for water molecules and estimated on the basis of the cryoporometry data using a model of cylindrical pores) are larger for S2. Weakly polar chloroform-d has a significant influence on the organization of water in a spongy component of bone tissue. This effect depends on the porosity of the bone matrix and the amounts of CDCl3.

Bone and Bones↗
PubMed2004

Surface and micellar properties of new nonionic gemini aldonamide-type surfactants.

A new group of gemini aldonamide-type surfactants-N,N'-bisalkyl-N,N'-bis[(3-gluconylamide)propyl]ethylenediamines, N,N'-bisdodecyl-N,N'-bis[(3-glucoheptonylamide)propyl]ethylenediamine, and N,N'-bisalkyl-N,N'-bis[(3-lactobionylamide)propyl]ethylenediamines, (alkyl: n-C(8)H(17), n-C(12)H(25)), were synthesized and characterized. The surface properties, such as surface excess concentration, Gamma(cmc), surface area demand per molecule, A(min), efficiency in surface tension reduction, pC(20), the effectiveness of surface tension reduction, gamma(cmc), critical micelle concentration, cmc, and a measure of the tendency of the surfactant to adsorb at the aqueous/air interface relative to its tendency to form micelles in the bulk surfactant solution, cmc/C(20), and standard free energy of micellization, DeltaG(mic)(0), have been obtained by means of surface tension measurements. The standard fluorescence shift technique using PRODAN as a probe provide confirmation of the cmc values by an alternative method. Additionally, the micellar properties for the concentration near above the cmc have been characterized by the aggregation number, N(agg). The presence of the dimeric segments with the aldonamide hydrophilic units in the surfactant molecule is found to be the source of their unusual physicochemical behavior. They are very efficient at adsorbing at the free surface and at forming micelles in water. Their critical micelle concentration values are remarkably low. They reveal remarkably low A(min) values in relation to conventional nonionic surfactants, which is unexpected from the molecular dimensions for the molecule but which is possible if one assumes some type of multilayer structure or a coherent interfacial film.

Ethylenediamines↗
PubMed2005

Effect of ozone treatment on ammonia removal of activated carbons.

In this work, activated carbons (ACs) were modified by ozone treatment to enhance the efficiency of removal of ammonia gas over the ACs. Surface properties of the ACs were confirmed by X-ray photoelectron spectroscopy (XPS) analysis and N2 adsorption isotherms at 77 K were investigated by BET and D-A methods to characterize the specific surface area, total pore volume, and micropore volume. The ammonia removal efficiency was confirmed by the gas-detecting tube technique. The results showed that the specific surface area and micropore volume of ACs were slightly destroyed as the ozone treatment time increased. However, the ozone treatment led to an increase in ammonia removal efficiency of ACs, mainly due to an increase of acid functional groups, such as carbonyl and ether groups, on carbon surfaces. It was revealed that the improvement of ammonia removal efficiency of ACs was greatly affected by the interfacial acid-base interactions between modified ACs and basic ammonia adsorbate.

Journal Article↗
PubMedDate not supplied

Mixed lipid aggregates containing gangliosides impose different 2H-NMR dynamical parameters on water environment depending on their lipid composition.

Water dynamics in samples of ceramide tetrasaccharide (Gg4Cer) vesicles and GM1 ganglioside micelles at 300:1 water/lipid mole ratio were studied by using deuterium nuclear magnetic resonance (2H-NMR). GM1 imposes a different restriction on water dynamics that is insensitive to temperatures either above or below its phase transition temperature or below the freezing point of water. The calculated correlation times are in the range of 10(-10) s, typical of water molecules near to the polar groups. Pure GM1 micelles have two distinct water microenvironments dynamically characterized. Their dynamic parameters remain constant with temperature ranging from -18 to 32 degrees C, but the amount of strongly associated water is modified. By contrast, a mixture of single soluble carbohydrates corresponding to GM1 polar head group does not preserve the dynamic parameters of water hydration when the temperature is varied. Incorporation of cholesterol or lysophosphatidylcholine into GM1 micelles substantially increases the mobility of water molecules compared with that found in pure GM1 micelles. The overall results indicate that both the supramolecular organization and the local surface quality (lipid-lipid interaction) strongly influence the interfacial water mobility and the extent of hydration layers in glycosphingolipid aggregates.

Gangliosides↗
PubMed1995

Demineralized bone matrix as a template for mineral--organic composites.

Mineralizing biological tissues are complex bioceramic-biopolymer composites engineered for a variety of functions. The organic and inorganic constituents, morphology, location, orientation, crystallinity and interactions exhibit materials or extremely fine microstructure, unique mechanical and physical properties with high strength and fracture toughness compared to the individual constituents. An understanding of mineralization, ultrastructural organization and interfacial bonding forces in mineralizing biological composite tissues, such as bone, may provide new strategies and techniques for the production of a novel class of man-made organic-ceramic composites. The present study explores the use of the organic matrix remaining after removal of the mineral phase by chelation with EDTA or solubilizing in HCl as a template for mineral deposition and the production of mineral-organic composites. Different pH conditions are employed to alter the inorganic phase which is deposited within the organic matrix. Mechanical testing and ultrastructural evaluations are carried out for characterization.

Animals↗
PubMed2003

Characterization of polymer-adhesive interfaces on a nanometre scale by elemental mapping and image EELS using EFTEM.

Energy-filtering transmission electron microscopy (EFTEM) was applied for investigating interfaces between a polymer and an adhesive. The sample employed in this work is polybutylene terephtharate (PBT) sheets laminated with an epoxy adhesive. It was found that heat aging of the PBT at 180 degrees C in air for > 9 h prior to adhesion decreases the adhesion strength drastically. To investigate this unfavourable aging effect on the adhesion strength, we performed elemental mapping and image EELS using EFTEM. A weak boundary layer with a thickness of < 50 nm was visualized at the PBT-adhesive interface by elemental mapping in the sample subjected to the heat aging and image EELS revealed the origin of this layer. Thus, we clearly correlated the nanoscale interfacial structure with the adhesion strength by EFTEM.

Journal Article↗
PubMed2004

Mechanical characterization of native and tissue-engineered cartilage.

Cartilage functions as a low-friction, wear-resistant, load-bearing tissue. During a normal gait cycle, one cartilage surface rolls and slides against another, all the while being loaded and unloaded. The durability of the tissue also makes for an impressive material to study. However, when cartilage is damaged or diseased, the tissue has little capacity to repair itself. The goal of cell-based repair strategies to replace damaged or diseased tissue requires that the functional biomechanical properties of normal (developing or mature), diseased, and repair cartilage be restored. This chapter addresses some of the major methods used to assess the biomechanical properties of native and tissue-engineered cartilage. First, the traditional methods of testing by compression, tension, shear, and indentation are reviewed. Next, additional methods to evaluate interfacial mechanics and lubrication are described. Thus, a variety of mechanical tests may be used to assess functional properties for normal, diseased, and tissue-engineered cartilage.

Animals↗
PubMed1980

Lipid-lipid and lipid-protein interactions in membranes.

Over the past decade spectroscopic methods (fluorescence, ESR, and NMR) have been used to provide new information about the molecular dynamics of lipid-lipid and lipid-protein interactions in membranes. The various methods of characterizing isotropic and anisotropic motion are described. Lipid bilayers are highly dynamic, with rapid acyl chain motion and rapid lateral diffusion in the plane of the membrane. In membranes where proteins penetrate through the bilayer, a large hydrophobic surface area exists in contact with the bilayer lipids. Lipids at the protein interface are in dynamic equilibrium with the remaining pools of bilayer. The protein has been shown spectroscopically to have some influence on the dynamics of the nearest neighbor lipids, leaving the rest of the bilayer relatively unperturbed. Evidence is summarized that, in some cases, the lipid composition in the interfacial region is influenced by the protein.

Chemical Phenomena↗