Biomedical subjects

T Nylander

Publications and source records attributed to T Nylander.

14 recordsLinked to original sources

PubMed2005

Ellipsometric characterization of ethylene oxide-butylene oxide diblock copolymer adsorption at the air-water interface.

Ellipsometry was used to determine the adsorbed layer thickness (d) and the surface excess (adsorbed amount, Gamma) of a nonionic diblock copolymer, E(106)B(16), of poly(ethylene oxide) (E) and poly(butylene oxide) (B) at the air-water interface. The results were obtained (i) by the conventional ellipsometric evaluation procedure using the change of both ellipsometric angles Psi and Delta and (ii) by using the change of Delta only and assuming values of the layer thickness. It was demonstrated that the calculated surface excesses from the different methods were in close agreement, independent of the evaluation procedure, with a plateau adsorption of about 2.5 mg/m(2) (400 A(2)/molecule). Furthermore, the amount of E(106)B(16) adsorbed at the air-water interface was found to be almost identical to that adsorbed from aqueous solution onto a hydrophobic solid surface. In addition, the possibility to use combined measurements with H(2)O or D(2)O as substrates to calculate values of d and Gamma was investigated and discussed. We also briefly discuss within which limits the Gibbs equation can be used to determine the surface excess of polydisperse block copolymers.

Journal Article↗

PubMed2005

Surface complexation of DNA with insoluble monolayers. Influence of divalent counterions.

DNA interacts with insoluble monolayers made of cationic amphiphiles as well as with monolayers of zwitterionic lipids in the presence of divalent ions. Binding to dioctadecyldimethylammonium bromide (DODAB) or distearoyl-sn-glycero-3-phosphocholine (DSPC) monolayers in the presence of calcium is accompanied by monolayer expansion. For the positively charged DODAB monolayer, this causes a decrease of surface potential, while an increase is observed for the DSPC monolayers. Binding to dipalmitoyl-sn-glycero-3-phosphocholine preserves most of the liquid expanded-liquid condensed coexistence region. The liquid condensed domains adopt an elongated morphology in the presence of DNA, especially in the presence of calcium. The interaction of DNA with phospholipid monolayers is ion specific: the presence of calcium leads to a stronger interaction than magnesium and barium. These results were confirmed by bulk complexation studies.

Animals↗

PubMed2001

Variations in coupled water, viscoelastic properties, and film thickness of a Mefp-1 protein film during adsorption and cross-linking: a quartz crystal microbalance with dissipation monitoring, ellipsometry, and surface plasmon resonance study.

We have measured the time-resolved adsorption kinetics of the mussel adhesive protein (Mefp-1) on a nonpolar, methyl-terminated (thiolated) gold surface, using three independent techniques: quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance, and ellipsometry. The QCM-D and ellipsometry data shows that, after adsorption to saturation of Mefp-1, cross-linking of the protein layer using NaIO4 transforms it from an extended (approximately 20 nm), water-rich, and hydrogel-like state to a much thinner (approximately 5 nm), compact, and less water-rich state. Furthermore, we show how quantitative data about the thickness, shear elastic modulus, and shear viscosity of the protein film can be obtained with the QCM-D technique, even beyond the Sauerbrey regime, if frequency (f) and energy dissipation (D) measurements measured at multiple harmonics are combined with theoretical simulations using a Voight-based viscoelastic model. The modeling result was confirmed by substituting H2O for D2O. As expected, the D2O substitution does not influence the actual adsorption behavior, but resulted in expected differences in the estimated effective density and shear viscosity. These results provide new insight and understanding about the adsorption kinetics and crosslinking behavior of Mefp-1. They also demonstrate how the above three techniques complement each other for biomolecule adsorption studies.

Adsorption↗

PubMed2001

Interactions of cyclic AMP and its dibutyryl analogue with model membrane: X-ray diffraction and Raman spectroscopic study using cubic liquid-crystalline phases of monoolein.

Interactions of adenosine 3':5'-cyclic monophosphate (cAMP) and its dibutyryl analogue, N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dbcAMP), with a lipid bilayer were studied by small-angle X-ray diffraction (SAXD) and Raman spectroscopy. The cubic Pn3m phase of monoolein (MO) served as a bilayer-based model system. SAXD measurements have indicated that incorporation of approximately 3 wt.% cAMP leaves the phase parameters practically unaltered, whereas the same content of dbcAMP induces the intercubic Pn3m-->Ia3d transition. By applying the concepts of lipid shape parameter and infinite periodic minimal surface to these MO phases, we have suggested that, as opposed to cAMP, dbcAMP associates with the MO bilayer. This conclusion has been supported by the different effects of phase matrix on the Raman shifts of the adenine and phosphate vibrational modes of these two nucleotides. Moreover, Raman spectra have indicated that dbcAMP inserts into the bilayer through the butyryladenine group, positioning dbcAMP preferentially at the polar/apolar interface.

Algorithms↗

PubMed2001

Addition of hydrophilic and lipophilic compounds of biological relevance to the monoolein/water system. I. Phase behavior.

The solubilization of hydrophilic and lipophilic molecules, with biological relevance, in the monoolein/water (MO/W) system has been investigated for phase behavior. Small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) and optical microscopy (OM) have been used to characterize the microstructure of the liquid crystalline phases. Partial phase diagrams of the MO/W system in the presence of sodium decanoate, 1-adamantanamine hydrochloride, decanoic and dodecanoic acids, acetyl salicilic acid and retinol have been determined. The stability of the various phases has been followed for at least eight months. The polarity and the molecular structure of the additive determine whether it is located at the polar interface or in the apolar region of the lipid layer. Therefore, the additive affects the interfacial curvature of the lipid layer differently, which in turn will trigger transition to disparate phases. A cubic-to-reverse hexagonal phase transition has been observed with time for most of the ternary systems, with the exception of 1-adamantanamine hydrochloride and retinol. The release of free glycerol and oleic acid due to MO hydrolysis has been clearly demonstrated by 13C NMR. This would account for the changes in phase behavior observed with time. The released oleic acid, located in the MO acyl chain region, favors the inverse interfacial curvature. The average lipid dimensions in the cubic and in the reverse hexagonal phases have been calculated from SAXS data.

Carbon Isotopes↗

PubMed2001

Emulsification of caraway essential oil in water by lecithin and beta-lactoglobulin: emulsion stability and properties of the formed oil-aqueous interface.

The stability and droplet size of protein and lipid stabilised emulsions of caraway essential oil as well as the amount of protein on the emulsion droplets have been investigated. The amount of added protein (beta-lactoglobulin) and lipid (phosphatidylcholine from soybean (sb-PC)) were varied and the results compared with those obtained with emulsions of a purified olive oil. In general, emulsions with triglyceride oil proved to be more stable compared with those made with caraway essential oil as the dispersed phase. However, the stability of the emulsions can be improved considerably by adding sb-PC. An increase in the protein concentration also promoted emulsion stability. We will also present how ellipsometry can be used to study the adsorption of the lipid from the oil and the protein from the aqueous phase at the oil-water interface. Independently of the used concentration, close to monolayer coverage of sb-PC was observed at the caraway oil-aqueous interface. On the other hand, at the olive oil-aqueous interface, the presence of only a small amount of sb-PC lead to an exponential increase of the layer thickness with time beyond monolayer coverage. The amounts of beta-lactoglobulin adsorbed at the caraway oil-aqueous interface and at the olive oil-aqueous interface were similar, corresponding roughly to a protein monolayer coverage.

Journal Article↗

PubMed2001

Beta-casein adsorption at the hydrophobized silicon oxide-aqueous solution interface and the effect of added electrolyte.

The effect of the presence of NaCl, CaCl(2), or MgCl(2) at the same ionic strength on the structure of beta-casein layers adsorbed on hydrophobic surfaces has been investigated by neutron reflectivity measurements. The data were fitted to a four-layer model. The volume fraction versus distance profiles have a similar shape whether beta-casein is adsorbed from NaCl, CaCl(2), and MgCl(2) of the same ionic strength or whether the protein concentration is lowered 10 times. In particular at larger distances from the surface, the volume fraction values are low and similar. However, close to the hydrophobic surface the volume fraction of protein decreases in the order CaCl(2) > MgCl(2) > NaCl. We have also used a specific proteolytic enzyme, endoproteinase Asp-N, which cleaves off the hydrophilic part of beta-casein, as a tool to reveal the interfacial structure of the protein. For all the different types of added electrolytes, endoproteinase Asp N only affects the outermost beta-casein layer. Subsequent addition of beta-casein in all cases led to large increases in amounts adsorbed and in the thickness of the outer layers.

Adsorption↗

PubMed2001

beta-Casein adsorption at the silicon oxide--aqueous solution interface.

Neutron reflectometry was used to investigate the time-dependent beta-casein adsorption at the silica-aqueous solution interface. The transient and steady-state structural characteristics of the adsorbed layer were determined from reflectivity curves, fitted to three-layer and two-layer models. The results show that the beta-casein adsorption to silica is very slow. The adsorption process involves the formation of an inner dense protein layer with a mean thickness of about 30 A onto which a more hydrated outer layer is self-associated. The surface excess and the total layer thickness of the asymmetric bilayer were, after 5 h adsorption time, estimated to be about 6.5 mg/m2 and 105 A, respectively. The adsorption behavior observed on silica contrasts with that previously reported for hydrophobic substrates, where beta-casein adsorption is much more rapid and the final surface excess is less than half of that observed for silica. Rinsing the silica surface with protein-free buffer resulted in a substantial desorption; much more pronounced than observed for hydrophobic substrates. This behavior suggests a weak adsorption affinity for a fraction of the adsorbed casein molecules; most likely the outer self-associated casein molecules in the adsorbed bilayer. The comparative desorption from hydrophobic surfaces was shown to be marginal. The difference between the layer structures adopted on hydrophobic and hydrophilic surfaces is also mirrored in the effects that the addition of a specific proteolytic enzyme (endoproteinase Asp-N) has on the adsorbed layer properties. The rinsing and endoproteinase cleavage processes result together in more than 80% reduction of the originally adsorbed mass at the silica surface. Only a thin but dense adsorbed layer remains after these treatments. The corresponding reduction reported for the hydrophobic adsorbent system was only about 20%. It is concluded that beta-casein adsorption on silica results in the formation of an asymmetric surface bound bilayer that stands in strong contrast to the monolayer structure formed at hydrophobic surfaces. This finding support the previous results obtained by using ellipsometry. The study also shows that neutron reflection, despite its limitations in time resolution, can be used for studying dynamic interfacial phenomena in protein systems.

Adsorption↗

PubMed1999

Phase Behavior and Aggregate Structure in Aqueous Mixtures of Sodium Cholate and Glycerol Monooleate.

The phase behavior of the glycerol monooleate (GMO)-sodium cholate-water (or 0.9 wt% NaCl) system has been examined in the solvent-rich part, using small-angle X-ray scattering and conventional methods. Addition of cholate up to 7% of the total amphiphile swells the cubic phase of the binary GMO-water system so that it takes up almost 70% of water in the salt-free case and 55% in salt. With more bile salt the lamellar phase also appears highly swollen (up to 85% in water, 75% in brine). In the salt solution a small isotropic L3-phase region replaces the lamellar phase at a solvent content of about 79%. The lamellar phase can accept only about 0.2 cholate molecule per GMO, in both water and brine, and a phase with globular micelles (L1) follows and dominates the diagram. No threadlike micelles appear in this system. Investigation of the particle structures with cryo-transmission electron microscopy (TEM) in dilute systems (99% solvent) show globular micelles and coexisting vesicles and globular micelles. In the presence of salt, dilution of the L3 phase results in dispersed globular particles with an irregular internal morphology that suggests they are a dispersed L3 phase. These particles coexist with faceted particles having an inner structure giving a hexagonal pattern in projection, suggested to derive from the cubic phase. The cubic phase in the salt-free systems did not give dispersions stable enough for cryo-TEM examination. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Solubilization of ubiquinone-10 in the lamellar and bicontinuous cubic phases of aqueous monoolein.

Using X-ray diffraction measurements and polarizing microscopy, the solubilization of ubiquinone-10 (UQ10) was investigated in the lamellar and reversed bicontinuous cubic phases of aqueous monoolein (MO, 86 wt% of monooleoylglycerol). At 25 degrees C and UQ10 content below 0.5 wt%, a partial phase diagram of the MO/UQ10/H2O system indicated the same sequence of hydration-induced phases as found in the MO/H2O system. This low amount of coenzyme had no effect on the MO bilayer thickness and swelling behavior of phases, but it promoted thermotropic Q230-->HII phase transition. We suggested that the effect was determined by the UQ10 partitioning into the HII phase regions where the MO chains must be stressed upon the phase transition. At UQ10 contents above 0.5 wt%, a solid 'UQ10-rich' phase appeared inside the initially homogeneous phases within a few days. It was proposed that this process was driven by the coenzyme lateral diffusion in the MO bilayer.

Crystallization↗

PubMed1999

Bioadhesion--a phenomenon with multiple dimensions.

This paper reviews some relevant citations regarding the non-specific forces that must be considered in oral bioadhesive events. These range from forces related to restorative dentistry to those related to prevention and molecular biology. Types of interactions discussed are: 1. Van der Waal's forces; 2. electrostatic double-layer forces; 3. solvent-dependent interactions; 4. hydrogen bonding; 5. hydrophobic interactions; 6. hydration forces; 7. steric forces; and 8. covalent bonds. Examples are given of the various types of interaction that occur at different surface separation (< or =400 A) between adsorbed films of a pure salivary protein fraction (PRP1).

Bacterial Adhesion↗

PubMed1996

Effects of distearoylphosphatidylglycerol and lysozyme on the structure of the monoolein-water cubic phase: X-ray diffraction and Raman scattering studies.

X-ray diffraction and Raman scattering spectroscopy have been used to study phase transitions and changes in molecular organization of the cubic Pn3m monoolein (MO)-H2O phase upon introducing low amounts of distearoylphosphatidylglycerol (DSPG) and lysozyme (LSZ). X-ray diffraction measurements indicated a phase transition Pn3m-Im3m brought about by DSPG and LSZ, however DSPG also induced formation of the lamellar phase. Raman spectra have demonstrated that incorporation of DSPG into the lipid bilayer decreases the mobility of acyl chains and increases the number of hydrogen-bonded C=O groups of MO. On the other hand, LSZ exerts identical effect on the latter parameter, while no effect on the state of acyl chains order was observed. This result and differential scanning calorimetric measurements indicate that LSZ is located in the water channel system of the cubic phase. The results are discussed on the basis of an infinite periodical lipid bilayer structure and lipid parameter concepts.

Animals↗

PubMed1996

Incorporation of proteins in sphingomyelin-water gel phases.

Sphingomyelin from bovine milk and water form lipid gel phases at room temperature. A sample was used which incorporated of about 55% water, and X-ray diffraction data indicate an aqueous layer thickness of about 28 Angstrom. In order to accommodate proteins in the gel phase, the aqueous layer thickness was increased by solubilizing sodium palmitate into the sphingomyelin bilayer. In this way the gel phase could take up about 80% water. The incorporation of lysozyme, beta-lactoglobulin, and alpha-lactalbumin, was followed and the protein concentration for phase separation to occur was determined. It was found that the degree of incorporation was dependent on the salt concentration, thus the protein used was extensively dialysed. The amount of protein which can be dissolved in the thin aqueous layer of the gel phase was suggested to be limited by the dimensions of the layer. These are likely to be reduced as a consequence of the osmotic stress exerted by the 'outside' solution phase at high enough protein concentration.

Animals↗

PubMed1996

Adsorption behaviour of amphiphilic polymers at hydrophobic surfaces: effects on protein adsorption.

The adsorption of four different amphiphilic polymers to a model surface has been studied, and the effects of the adsorbed amphiphiles on the subsequent adsorption of fibrinogen (Fg) and human serum albumin (HSA) at the surfaces were investigated. The amphiphilic polymers were one commercially available ABA block copolymer, Pluronic PE9400 (PE94), composed of poly(ethylene oxide) (A-blocks) and poly(propylene oxide) (B-block), and three graft copolymers, two with backbones of poly(styrene-co-acrylamide) (STY) and one with a backbone of poly(methyl methacrylate-co-ethylhexyl methacrylate) (ACRY). The backbones carried poly(ethylene oxide) (PEO) grafts. The model surface was a hydrophobic methylated silica surface (HMS). The amphiphilic polymers were adsorbed at the HMS surface from an ethanol/water solution. The adsorption process was monitored by ellipsometry. After rinsing with phosphate buffered saline (PBS), protein was added and the continued adsorption measured by ellipsometry. Surfaces modified by adsorption of the amphiphilic polymers were also characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS). According to these measurements the amphiphilic polymers adsorbed in significant amounts at the HMS surface. A limited study by atomic force microscopy (AFM), as well as the XPS measurements, suggests that both single molecules and micellar aggregates adsorb at the surface. ACRY and PE94 gave the highest levels of adsorption. As compared to the Pluronic block copolymer the graft copolymers were more strongly attached to the HMS surface, as shown by less desorption on rinsing with solvent. The ellipsometric results show that the adsorption of HSA and Fg at HMS surfaces containing preadsorbed amphiphilic polymer was significantly reduced as compared to the bare HMS surface. ACRY and PE94 showed the largest effects. Both polymers gave more than a 20-fold reduction of the Fg adsorption and a 10-fold reduction of the HSA adsorption. The STY polymers reduced the protein adsorption by a factor of 2-3.

Adsorption↗