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PubMedDate not supplied

Protein adsorption modalities on polyelectrolyte multilayers.

Protein adsorption on polyelectrolyte multilayers (PEMUs) was evaluated using a combination of synthetic polyelectrolytes and proteins, including serum albumin, fibrinogen, and lysozyme. Variables such as surface and protein charge, polymer hydrophobicity, and hydrophilic repulsion were introduced to probe interaction mechanisms. Quantitative analysis with reflectance Fourier transform infrared spectroscopy, optical waveguiding, and UV-vis absorption, together with qualitative information from atomic force microscopy, provided a coordinated picture for what drives protein adsorption and how the molecules are disposed on the multilayer surface. It was found that multilayers bearing a particular surface charge sorbed biomolecules if they were of opposite charge, yielding significant loadings within the bulk PEMU. Adsorption of like-charged proteins, as surface aggregates, occurred to a much lower extent, driven by nonelectrostatic forces. A diblock copolymer comprising a hydrophilic poly(ethylene oxide) block was capable of further minimizing protein adsorption as a result of hydrophilic repulsion, although none of the surfaces tested defeated protein adsorption completely. However, poly(acrylic acid) homopolymer was quite effective in this respect. A composition gradient, formed during multilayer buildup, induced a gradient in hydrophilicity through the PEMU, which is an efficient and economical method of creating a protein-resistant surface.

Adsorption↗

PubMed2006

Size-dependent surface CO stretching frequency investigations on nanodiamond particles.

In this work, the spectroscopic properties of surface functionalized nanodiamond particles are investigated via Fourier transform infrared spectroscopy. The functionalization of the nanodiamond surface was achieved chemically using strong acid treatment method. The size dependent C=O stretching frequency (between 1680 and 1820 cm(-1)) are studied for particle diameter sizes from the 5 to 500 nm range. The surface C=O stretching frequencies at approximately 1820 cm(-1), for large particle size (500 nm), down shifted to 1725 cm(-1) (5 nm) with decreasing particle sizes. We attributed the shift as a result of hydrogen bond formation between the COOH groups in the carboxylated nanodiamond surfaces. Particle size was characterized with dynamic light scattering method and surface morphology of the particles was investigated with scanning electron microscopy. The influence of pH value on C=O stretching frequency is also analyzed. This finding affords useful information for the studying of surface functionalized nanodiamonds with implications for their interaction with biomolecules.

Carbon Monoxide↗

PubMed1995

The alpha-helical to beta-strand transition in the amino-terminal fragment of the amyloid beta-peptide modulates amyloid formation.

Amyloid-beta peptide (A beta) consists of a hydrophobic C-terminal domain (residues 29-42) that adopts beta-strand conformation and an N-terminal domain (amino acids 10-24) whose sequence permits the existence of a dynamic equilibrium between an alpha-helix and a beta-strand. In this paper we analyzed the effect of the alternate N-terminal conformations on amyloid fibril formation through the study of the analogous A beta peptides containing single amino acidic substitutions. The single mutation of valine 18 to alanine induces a significant increment of the alpha-helical content of A beta, determined by Fourier transform infrared spectroscopy and circular dichroism and dramatically diminishes fibrillogenesis, measured by turbidity, thioflavine T binding, Congo red staining, and electron microscopic examination. In hereditary Dutch cerebral hemorrhage with amyloidosis (a variant of Alzheimer's disease), the substitution of glutamine for glutamic acid at position 22 decreased the propensity of the A beta N-terminal domain to adopt an alpha-helical structure, with a concomitant increase in amyloid formation. We propose that A beta exists in an equilibrium between two species: one "able" and another "unable" to form amyloid, depending on the secondary structure adopted by the N-terminal domain. Thus, manipulation of the A beta secondary structure with therapeutical compounds that promote the alpha-helical conformation may provides a tool to control the amyloid deposition observed in Alzheimer's disease patients.

Alanine↗

PubMed1994

The synovial structure of breast-implant-associated bursae.

Over 2 million silicone breast prostheses have been implanted since they were introduced in the 1960s. After implantation, a fibrovascular tissue reaction referred to as a "capsule" is observed. Many consider this capsule to be a static structure, an effective barrier to the egress of foreign material. However, reports documenting the presence of silicone within lymph nodes of patients with apparently unruptured implants indicate that silicone may be transported away from the breast-implant capsule. To characterize the cells making up the breast-implant capsule, 183 capsules from 103 ruptured or bleeding implants and 80 intact implants were studied. Gross and light microscopic studies were performed on all, and selected capsules were subjected to ultrastructural study and Fourier-transform infrared spectroscopy. Light microscopic examination of the capsule revealed an organized, layered structure with an associated network of endothelia-lined spaces. The capsules varied in cellularity, depending on the type and integrity of the implant. The superficial cell layer of all capsules had cytoplasmic processes directed toward the surface. These long cytoplasmic processes contained vacuoles ultrastructurally, indicating phagocytic and pinocytotic capability. These cells bore immunological markers of bone marrow derived macrophage-type cells. The extracellular matrix of the surface layer consisted of an amorphous fibrillar protein lacking the ultrastructural periodicity of mature collagen. No cell-to-cell junctions were observed. Deeper capsular layers were characterized by fibroblast-type cells in a collagen matrix. No capsules studied contained basement membrane or basal lamina between the stroma of the capsule and the surface cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Diseases↗

PubMed1997

Role of oxygen in biodegradation of poly(etherurethane urea) elastomers.

It is generally accepted that biodegradation of poly(etheruethane urea) (PEUU) involves oxidation of the polyether segments on the surface where leukocytes are adhered. The influence of dissolved oxygen, which is known to control oxidation of polymers in more traditional environments, was explored in this study. Specimens treated in vitro with hydrogen peroxide-cobalt chloride for 12 days exhibited a brittle, degraded surface layer about 10 microm thick. Attenuated total reflectance-Fourier transform infrared spectroscopy of the surface revealed that the ether absorbance at 1110 cm(-1) gradually decreased with in vitro treatment time to 30% of its initial value after 12 days. In contrast, 6 days in vitro followed by 6 days in air produced a decrease to 12% of the initial volume. Therefore, removing a specimen from the in vitro solution after 6 days and exposing it to air for the remainder of the 12 days actually resulted in more oxidation than leaving it in the in vitro solution for the entire 12 days. These results suggest that PEUU degrades by an autooxidation mechanism sustained by oxygen. By successfully modeling the depth of the surface degraded layer with a diffusion-reaction model, it was demonstrated that PEUU biodegradation is controlled by diffusion of oxygen into the polymer.

Biocompatible Materials↗

PubMed2004

Characterization of diphtheria toxin's catalytic domain interaction with lipid membranes.

In response to a low environmental pH and with the help of the B fragment (DTB) the catalytic domain of diphtheria toxin (DTA) crosses the endosomal membrane to inhibit protein synthesis. In this study, we investigated the interaction of DTA with lipid membranes by biochemical and biophysical approaches. Data obtained from proteinase K and trypsin digestion experiments of membrane-inserted DTA suggested that residues 134-157 may adopt a transmembrane orientation and residues 77-100 could be membrane-associated, adopting either a surface or a transmembrane orientation. Fourier transform infrared spectroscopy analysis (FTIR) was used to characterize the secondary and tertiary structure of DTA along its pathway, from the native secreted form at pH 7.2 to the refolded structure at neutral pH after interaction with and desorption from a lipid membrane. We found that the association of DTA with lipid membranes at low pH was characterized by an increase of beta-sheet structures and that the refolded structure at neutral pH after interaction with the membrane was identical to the native structure at the same pH. We also investigated the desorption of DTA from the membrane at neutral pH as a function of temperature. Although a complete desorption was observed at 37 degrees C, no desorption took place at 4 degrees C. A model of translocation involving the possibility that DTA might insert one or several transient transmembrane domains during translocation is discussed.

Amino Acid Sequence↗

PubMed1999

UV-induced reaction kinetics of dilinoleoylphosphatidylethanolamine monolayers.

The UV-induced reactivity of dilinoleoylphosphatidylethanolamine (DLiPE) Langmuir and Langmuir-Blodgett films has been studied by in situ measurements of the changes in the mean molecular area, UV-vis and Fourier transform infrared spectroscopy, and atomic force microscopy (AFM). Optimum orientation and packing density of the DLiPE molecules in the monolayer were achieved by adding uranyl acetate to the subphase. A first-order reaction kinetic model was successfully fitted to the experimental reaction kinetics data obtained at a surface pressure of 30 mN/m. Topographical studies of LB films by AFM were performed on bilayer structures as a function of subphase composition and UV irradiation time. The orientational effect of the uranyl ions on the monolayer molecules was observed as an enhanced homogeneity of the freshly prepared monomeric LB films. However, the long-term stability of these films proved to be bad; clear reorganization and loss of a true monolayer structure were evidenced by the AFM images. This instability was inhibited for the UV-irradiated films, indicating that the UV irradiation gave rise to a cross-linked structure.

Biophysical Phenomena↗

PubMed2000

Fourier transform infrared spectroscopic characterization of a photolabile precursor of glutamate.

Recently, it has been demonstrated that Fourier transform infrared spectroscopy (FTIR) detects conformational changes in the glutamate receptor ligand-binding domain that are associated with agonist binding. Combined with flash photolysis, this observation offers the prospect of following conformational changes at individual protein and agonist moieties in parallel and with high temporal resolution. Here, we demonstrate that gamma(alpha-carboxy-2-nitrobenzyl) glutamate (caged glutamate) does not interact with the protein, and that following photolysis with UV light the FTIR difference spectrum indicated changes in the protein tertiary and secondary interactions. These changes were similar to those observed for the protein upon addition of free glutamate. Thus, caged glutamate and its photolysis by-products are inert in this system, whereas the released glutamate exhibits full activity. Difference spectra of caged glutamate and of reaction analogs permitted identification of and correction for FTIR signals arising from the photolytic reaction and confirmed that its products are indeed glutamate and 2-nitrosophenyl glyoxalic acid.

Animals↗

PubMed1993

Alpha-tocopherol interacts with natural micelle-forming single-chain phospholipids stabilizing the bilayer phase.

The effect of the association of alpha-tocopherol (vitamin E) with single chain or very asymmetric phospholipids has been studied by 31P nuclear magnetic resonance, Fourier transform infrared spectroscopy, and light microscopy. Our results demonstrate that alpha-tocopherol stabilizes and forms bilayer structures in systems composed of either 1-palmitoyl-sn-glycero-3-phosphocholine, 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine, 1-O-hexadecyl-sn-glycero-3-phosphocholine, or 1,2-dipalmitoyl-sn-glycero-3- phosphocholine/1-palmitoyl-sn-glycero-3-phosphocholine, whereas in the absence of alpha-tocopherol all these systems produce micellar structures. The free hydroxyl group of alpha-tocopherol is shown to be important in stabilizing the bilayer structure by comparing the effects produced by an analog of alpha-tocopherol, alpha-tocopheryl acetate, which has the hydroxyl group blocked by an acetyl group. It is suggested that the complementary shapes of alpha-tocopherol and the asymmetric phospholipids may be the reason for the stabilization of the bilayer structure.

Lipid Bilayers↗

PubMed1998

Structural characterization of the hydrophobin SC3, as a monomer and after self-assembly at hydrophobic/hydrophilic interfaces.

Hydrophobins are small fungal proteins that self-assemble at hydrophilic/hydrophobic interfaces into amphipathic membranes that, in the case of Class I hydrophobins, can be disassembled only by treatment with agents like pure trifluoroacetic acid. Here we characterize, by spectroscopic techniques, the structural changes that occur upon assembly at an air/water interface and upon assembly on a hydrophobic solid surface, and the influence of deglycosylation on these events. We determined that the hydrophobin SC3 from Schizophyllum commune contains 16-22 O-linked mannose residues, probably attached to the N-terminal part of the peptide chain. Scanning force microscopy revealed that SC3 adsorbs specifically to a hydrophobic surface and cannot be removed by heating at 100 degrees C in 2% sodium dodecyl sulfate. Attenuated total reflection Fourier transform infrared spectroscopy and circular dichroism spectroscopy revealed that the monomeric, water-soluble form of the protein is rich in beta-sheet structure and that the amount of beta-sheet is increased after self-assembly on a water-air interface. Alpha-helix is induced specifically upon assembly of the protein on a hydrophobic solid. We propose a model for the formation of rodlets, which may be induced by dehydration and a conformational change of the glycosylated part of the protein, resulting in the formation of an amphipathic alpha-helix that forms an anchor for binding to a substrate. The assembly in the beta-sheet form seems to be involved in lowering of the surface tension, a potential function of hydrophobins.

Adsorption↗

PubMed2002

Adsorption of glyphosate on goethite: molecular characterization of surface complexes.

As a component of herbicides, the fate of glyphosate (PMG) in the environment is of significant interest. The nature of PMG adsorption on mineral surfaces plays a significant role in the degradation of PMG. The adsorption of PMG on goethite (alpha-FeOOH) has been studied as a function of pH and PMG concentration. Adsorption was investigated with batch experiments, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The N 1s line in XPS spectra showed deprotonation of the amine group of PMG (NH2+) with increasing pH. IR analyses showed no evidence for the interaction of PMG's carboxylate group with the goethite surface, while the phosphonate group formed inner-sphere complexes. There is evidence for intramolecular hydrogen bonding between NH2+ and both the carboxylate and the phosphonate groups at low pH. Intramolecular hydrogen bonding is lost when the amine group is deprotonated, and the trend in intramolecular hydrogen bonding between NH2+ and phosphonate shows that PMG adsorbs via predominantly monodentate complexation. A minor quantity of bidentate complexes is thought to form both at near-neutral pH and when the surface concentration of PMG is low. While the phosphonate group of PMG binds directly, the carboxylate group remains relatively "free" from complexation with goethite, leaving it subject to degradation and/or complexation with metal ions present in the environment.

Adsorption↗

PubMed2006

Two-dimensional self-assembly of 1-pyrylphosphonic acid: transfer of stacks on structured surface.

Strong hydrogen bonding and pi-pi stacking between 1-pyrylphosphonic acid (PYPA) molecules were exploited to create self-assembled two-dimensional supramolecular structures. Polycrystalline films of these laminate crystalline PYPA bilayers were easily deposited onto the solid supports through a simple spin-coating technique. Atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-vis absorption, and fluorescence spectroscopy reveal that processing parameters, such as solvent, concentration, and surface of the substrate, are critical factors in determining the final morphology of the stacked film. Robust laminate structures could be obtained only when short alkyl chain protic solvents (methanol or ethanol) and a nonhydrophobic substrate surface were used. Polycrystalline films were formed through the nucleation and growth of PYPA molecules into laminate structures at the air/solvent interface before they land on the substrate during the spin-coating process. These films possess good mechanical properties and were easily transferred onto a SiO2/Si substrate that was patterned with Au electrodes without breaking their crystalline structures. The successful transfer of the laminate crystals allows us to probe their electrical properties through a field effect transistor device. A gating effect on the charge transport of the stacked films indicates that PYPA laminate crystal possesses p-typed semiconductor characteristics.

Hydrogen Bonding↗

PubMed2003

Short-term bone response to titanium implants coated with thin radiofrequent magnetron-sputtered hydroxyapatite in rabbits.

BACKGROUND: It has been suggested that calcium phosphate (CaP) coatings initiate faster bone growth around implants. A major concern about the viable use of these coatings has been their biologic performance related to the coating characteristics. PURPOSE: The purpose of this study was to investigate the early bone response to micron- and submicron-thick hydroxyapatite (HA) coatings in cortical and trabecular bone. MATERIALS AND METHODS: CaP coatings were manufactured by magnetron sputtering. Heat treatment was subsequently used to increase the crystallinity of the coatings. Coatings were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), and stylus profilometry. Four types of CaP-coated implants were used (0.1 microm and 2.0 microm amorphous; 0.1 microm and 2.0 microm crystalline); uncoated machined commercially pure titanium implants served as controls. Four hundred eighty implants were randomly placed in 60 rabbits. Ten animals were followed up for 1 week, 10 for 3 weeks, and 40 for 6 weeks. The bone response was histomorphometrically evaluated. RESULTS: Coatings with a CaP ratio very close to that of HA were produced. Crystalline coatings significantly improved the early bone-implant contact whereas the amorphous-coated implants behaved similarly to uncoated titanium. CONCLUSIONS: Crystalline CaP coatings 100 nm thick on titanium implants elicited an improved early bone response compared with that of uncoated titanium implants. No further improvement in the bone response was observed with 2 microm coatings.

Animals↗

PubMedDate not supplied

Transdermal iontophoresis of insulin. VI. Influence of pretreatment with fatty acids on permeation across rat skin.

The delivery of large peptides through the skin poses a significant challenge, and various strategies are under active investigation for enhancing the transdermal permeation. For large peptides, it is difficult to achieve significant permeation using iontophoresis alone. Hence a combination of fatty acids with iontophoresis was hypothesized to result in higher enhancement than achieved with either of them alone. Saturated fatty acids and cis unsaturated fatty acids were studied in combination with iontophoresis using excised rat skin. The skin was pretreated for 2 h with an ethanolic (EtOH) solution of 5% w/v or v/v fatty acids, namely lauric acid (LA), oleic acid (OA), linoleic acid (LOA) and linolenic acid (LLA), followed by either passive or iontophoretic permeation (0.5 mA/cm2 for 6 h). Fourier transform infrared spectroscopy (FT-IR) was used to investigate the biophysical changes on treatment with fatty acid/EtOH or neat fatty acid, mainly focusing on the infrared region at 2,920, 1,710 and 1,720 cm(-1). Unsaturated fatty acids showed higher enhancement than LA, and the enhancement increased with the number of double bonds. On the other hand, in the presence of iontophoresis, LA/EtOH showed the highest enhancement. Neat LOA did not show any significant difference (p > 0.05) compared to the LOA/EtOH combination. FT-IR studies revealed that fatty acids act by interacting with the skin lipids. All the fatty acids showed synergistic enhancement when combined with iontophoresis. The flux enhancement was highest with LA, which in the presence of iontophoresis showed 20 times enhancement of insulin flux in comparison to passive flux and 9 times enhancement as compared to iontophoresis alone. Flux enhancement of unsaturated fatty acids was in the following decreasing order LOA > OA > LLA.

Animals↗

PubMed2006

Structure and activity of the N-terminal region of the eukaryotic cytolysin equinatoxin II.

The actinoporins are a family of proteins from sea anemones that lyse cells by forming pores in cell membranes. Sphingomyelin plays an important role in their lytic activity, with membranes lacking this lipid being resistant to these toxins. Pore formation by the actinoporin equinatoxin II (EqTII) proceeds by membrane binding via a surface rich in aromatic residues, followed by translocation of the N-terminal region to the membrane and, finally, across the bilayer to form a functional pore. A key feature of this mechanism is the ability of the N-terminal region to form a stable, bilayer-spanning helix in the membrane, which in turn requires dissociation of the N-terminus from the bulk of the protein and significant extension of the N-terminal helix of native EqTII. In this study the structures of three peptides corresponding to residues 11-29, 11-32, and 1-32, respectively, of EqTII have been investigated by high-resolution nuclear magnetic resonance and Fourier transform infrared spectroscopy. The 32-residue peptide lacks ordered secondary structure in water, but residues 6-28 form a helix in dodecylphosphocholine micelles. Although this helix is long enough to span a bilayer membrane, this peptide and the shorter analogues display limited permeabilizing activity in large unilamellar vesicles and very weak hemolytic activity in human red blood cells. Thus, while the N-terminal region has the structural features required for this unusual mechanism of pore formation, the lack of activity of the isolated N-terminus shows that the bulk of the protein is essential for efficient pore formation by facilitating initial membrane binding, interacting with sphingomyelin, or stabilizing the oligomeric pore.

Amino Acid Sequence↗

PubMed2006

Utilization of gold tailings as an additive in Portland cement.

Mine tailings are formed as an industrial waste during coal and ore mining and processing. In the investigated process, following the extraction of gold from the ore, the remaining tailings are subjected to a two-stage chemical treatment in order to destroy the free cyanide and to stabilize and coagulate heavy metals prior to discharge into the tailings pond. The aim of this study was the investigation of the feasibility of utilization of the tailings as an additive material in Portland cement production. For this purpose, the effects of the tailings on the compressive strength properties of the ordinary Portland cement were investigated. Chemical and physical properties, mineralogical composition, particle size distribution and microstructure of the tailings were determined by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), particle size analyzer (Mastersizer) and scanning electron microscope (SEM). Following the characterization of the tailings, cement mortars were prepared by intergrinding Portland cement with dried tailings. Composition of the cement clinkers were adjusted to contain 5, 15, 25% (wt/wt) dried tailings and also silica fume and fly ash samples (C and F type) were added to clinker in different ratios. The mortars produced with different amounts of tailings, silica fume, fly ashes and also mixtures of them were tested for compressive strength values after 2, 7, 28 and 56 days according to the European Standard (EN 196-1). The results indicated that gold tailings up to 25% in clinker could be beneficially used as an additive in Portland cement production. It is suggested that the gold tailings used in the cement are blended with silica fume and C-type fly ash to obtain higher compressive strength values.

Gold↗

PubMed2001

Dietary adipic acid reduces ammonia emission from swine excreta.

Adipic acid is only partially catabolized when it is fed to animals, and a portion of it is excreted in urine. The excreted portion may lower urinary pH and, as a result, ammonia emission. The present study tested this hypothesis. In Exp. 1, nursery pigs (n = 14) were fed (for a period of 7 d) either a standard nursery diet or the same diet supplemented with 1% adipic acid to assess effects on urinary pH (collected on d 5 or 6) and in vitro ammonia emission from the collected urine samples that were mixed with control feces. In Exp. 2, grower pigs housed 10 each in one of two chambers were fed a control diet or the same diet supplemented with 1% adipic acid. Ventilated air was quantified and analyzed for ammonia using Fourier transform infrared spectroscopy to determine the effects of feeding 1% adipic acid on ammonia emission. The results from Exp. 1 showed that adipic acid strongly reduced urinary pH (from 7.7 to 5.5, P < 0.05). In vitro ammonia emission from these urine samples was significantly reduced at all the time points evaluated (1, 3, 18, and 46 h with reductions of 94, 93, 70, and 39%, respectively, P < 0.05). Experiment 2 showed that adipic acid supplementation reduced ammonia emission by 25% (P < 0.05), which corresponded to the predicted reduction in ammonia emission based on the reduction in manure pH observed. In conclusion, feeding adipic acid lowers urinary pH and reduces ammonia emission. The reduction in ammonia emission, though, does not correspond to the reduction in urinary pH but corresponds to the reduction in fecal pH as a result of mixing the urine and feces, in which feces act as a strong buffer.

Acid-Base Equilibrium↗

PubMedDate not supplied

A study of the physical and chemical properties of four resin composite luting cements.

PURPOSE: This study evaluated the surface microhardness and flexural and compressive strengths of five luting cements and compared the degree of conversion of dual and autopolymerized forms of four resin-based luting cements. MATERIALS AND METHODS: Four resin composite luting cements-Panavia F, Variolink 2, RelyX Unicem Applicap, and RelyX ARC-and a polycarboxylate cement (Durelon, control group) were used in three-point bending, compression, and Vickers hardness tests following water storage for 1 week. Resin composite cements were additionally investigated with both dual and autopolymerization techniques under Fourier transformed infrared spectroscopy. Differences were analyzed using one-way ANOVA. RESULTS: The highest flexural strengths were obtained with Variolink 2 (90 MPa, SD 22), whereas the lowest were observed with Durelon (28 MPa, SD 4). RelyX Unicem showed the highest hardness values (44 HV, SD 5), whereas Variolink 2 gave the lowest (32 HV, SD 6). The highest compressive strengths were obtained with RelyX Unicem (145 MPa, SD 32), whereas the lowest were observed with Durelon (41 MPa, SD 17). For both dual and autopolymerized groups, RelyX ARC showed the highest degrees of conversion (81% and 61%, respectively) and RelyX Unicem had the lowest (56% and 26%, respectively). CONCLUSION: Resin composite luting cements of similar chemical characterizations differed in their physical properties, and polymerization method influenced their degree of conversion.

Analysis of Variance↗