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1.
Viscoelastic behavior of proteins at interfaces is a critical determinant of their ability to stabilize emulsions. We therefore used air bubble surfactometry and drop volume tensiometry to examine the dynamic interfacial properties of two plasma apolipoproteins involved in chylomicron assembly: apolipoprotein A-IV and apolipoprotein B-17, a recombinant, truncated apolipoprotein B. At the air/water interface apolipoproteins A-IV and B-17 displayed wide area - tension loops with positive phase angles indicative of viscoelastic behavior, and suggesting that they undergo rate-dependent changes in surface conformation in response to changes in interfacial area. At the triolein/water interface apolipoprotein A-IV displayed maximal surface activity only at long interface ages, with an adsorption rate constant of 1.0 3 10(-)(3) sec(-)(1), whereas apolipoprotein B-17 lowered interfacial tension even at the shortest interface ages, with an adsorption rate constant of 9.3 3 10(-)(3) sec(-)(1). Apolipoprotein A-IV displayed an expanded conformation at the air/water interface and a biphasic compression isotherm, suggesting that its hydrophilic amphipathic helices move in and out of the interface in response to changes in surface pressure.We conclude that apolipoproteins A-IV and B-17 display a combination of interfacial activity and elasticity particularly suited to stabilizing the surface of expanding triglyceride-rich particles. 相似文献
2.
Protein adsorption at the oil/water interface: characterization of adsorption kinetics by dynamic interfacial tension measurements. 总被引:5,自引:0,他引:5
The dynamics of protein adsorption at an oil/water interface are examined over time scales ranging from seconds to several hours. The pendant drop technique is used to determine the dynamic interfacial tension of several proteins at the heptane/aqueous buffer interface. The kinetics of adsorption of these proteins are interpreted from tension/log time plots, which often display three distinct regimes. (I) Diffusion and protein interfacial affinity determine the duration of an initial induction period of minimal tension reduction. A comparison of surface pressure profiles at the oil/water and air/water interface reveals the role of interfacial conformational changes in the early stages of adsorption. (II) Continued rearrangement defines the second regime, where the resulting number of interfacial contacts per protein molecule causes a steep tension decline. (III) The final regime occurs upon monolayer coverage, and is attributed to continued relaxation of the adsorbed layer and possible build-up of multilayers. Denaturation of proteins by urea in the bulk phase is shown to affect early regimes. 相似文献
3.
Emilia Konowa? 《Carbohydrate polymers》2012,87(2):1333-1341
Potato starch modified to different degrees by substitution with acetyl groups was the subject of this study undertaken to determine the influence of conditions of enzymatic hydrolysis on the surface-active properties of hydrolysates of acetylated starch. The effect of acetylation of starch preparation on its susceptibility to enzymatic hydrolysis in the membrane reactor was also considered. All hydrolysates of acetylated starch samples investigated were found to bring a decrease in the surface/interfacial tension, both at the air/water and the toluene/water interfaces. For binary hydrolysate-surfactant systems, the surface mole fractions in the mixed adsorbed monolayer at the air/water interface were estimated. For mixed systems, the synergism in reducing the surface tension at the air/water interface was observed. The experimentally obtained dynamic surface tension data for the aqueous solution of acetylated starch hydrolysates were used to estimate the diffusion coefficients. Particle size distributions of the hydrolysates formed in the aqueous solutions were compared to those of commercial maltodextrin. 相似文献
4.
Monolayers of phosphatidylcholine, tyrosine, and phenylalanine and binary mixtures phosphatidylcholine–tyrosine or phosphatidylcholine–phenylalanine
were investigated at the air/water interface. Phosphatidylcholine (lecithin, PC), tyrosine (Tyr), and phenylalanine (Phe)
were used in the experiment. The surface tension values of pure and mixed monolayers were used to calculate π–A isotherms.
The surface tension measurements were carried out at 22°C using an improved Teflon trough and a Nima 9000 tensiometer. The
Teflon trough was filled with a subphase of triple-distilled water. Known amounts of lipid dissolved in 1-chloropropane were
placed at the surface using a syringe. The interactions between lecithin and amino acid result in significant deviations from
the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was
developed in order to obtain the stability constants of PC–Tyr as well as PC–Phe complexes. We considered the equilibrium
between the individual components and the complex and established that lecithin and amino acid formed highly stable 1:1 complex. 相似文献
5.
Ziad Khattari 《Journal of biological physics》2017,43(3):381-395
The secondary structure of apolipoprotein B-100 is studied within the bulk phase and at the air/water interface. In these “in viro” experiments, infrared reflection absorption spectroscopy (IRRAS) study was performed at the air/water interface while circular dichroism (CD) was conducted in the bulk phase. In the bulk phase, the conformational structure containing a significant amount of β–structure, whereas varying amount of α-helix, unordered structures, and β-sheet were observed at the air/water interface depending on the low-density lipoprotein (LDL) film interfacial pressure. The present IRRAS results demonstrate the importance of interfacial pressure-induced structural conformations on the apoB-100. A correlation between the secondary structure of the apoB-100 protein and the monomolecular film elasticity at the air/water interface was also established. The orientation of apoB-100 with respect to the LDL film-normal was found to depend on the interfacial pressure exhibited by the monomolecular film. These results may shed light on LDL’s pivotal role in the progression of atherosclerotic coronary artery disease as demonstrated previously by clinical trials. 相似文献
6.
A physicochemical investigation of two phosphatidylcholine/bile salt interfaces: implications for lipase activation 总被引:1,自引:0,他引:1
Within the gastrointestinal tract ingested lipids are broken down into their constituent mono-acylglycerides and fatty acids by the enzyme family of lipases. In this study we have investigated the interfacial composition and structure of two phospholipid/bile salt (BS) systems that display significant differences in the duration of the lag phase of porcine pancreatic lipase kinetics. The interfacial tension of the single BSs, and their binary mixtures with phospholipid is reported at an n-tetradecane/water interface as a function of phospholipid mole fraction and total surfactant concentration. The structuring of the interface was probed by characterisation of the thin liquid film formation, thickness and stability. Lateral interactions were quantified by measurement of the diffusion coefficient of a probe fluorophore. We conclude that interfacial tension was not a factor in lag time duration as there was no significant difference in the minimum interfacial tension for the phosphatidylcholine (PC)/sodium taurocholate and the PC/sodium taurodeoxycholate system. No correlation was found between lag phase duration and the physiochemical properties of the interface, i.e. lateral diffusion, thin liquid film formation or interfacial tension. This is in agreement with our previous study that the lag time duration was directly related to the phospholipid content of the interface. 相似文献
7.
Monolayers of sphingomyelin (SM), ceramide (Cer) and cholesterol (Ch) and binary mixtures SM–Ch, SM–Cer and Cer–Ch were investigated at the air–water interface. SM, Cer and Ch were used in the experiment. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. Surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. Interactions between sphingolipid and Ch as well as sphingolipid and another sphingolipid result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air–water interface was developed in order to obtain the stability constants and Gibbs free energy values of SM–Ch, SM–Cer and Cer–Ch complexes. We considered the equilibrium between the individual components and the complex and established that sphingolipid and Ch as well as sphingolipid and another sphingolipid formed highly stable 1:1 complexes. 相似文献
8.
A Tiss S Ransac H Lengsfeld P Hadvàry A Cagna R Verger 《Chemistry and physics of lipids》2001,111(1):73-85
The surface behaviour of two bile salts, sodium deoxycholate (NaDC) and sodium taurodeoxycholate (NaTDC), as well as that of tetrahydrolipstatin (THL), a potent gastrointestinal lipase inhibitor, was studied at air/water and oil/water interfaces, using interfacial tensiometry methods. The surface behaviour of NaDC and NaTDC was comparable at both oil/water and air/water interfaces. A fairly compact interfacial monolayer of bile salts is formed well below the critical micellar concentration (CMC) and can help to explain the well-known effects of bile salts on the kinetic behaviour of pancreatic lipases. Using the Wilhelmy plate technique, the surface pressure-molecular area curves recorded with THL at the air/water interface showed a collapse point at a surface pressure of 24.5 mN.m(-1), corresponding to a molecular area of 70 A(2). Surprisingly, using the oil drop method, a limiting molecular area of 160 A(2) was found to exist at the oil/water interface. On the basis of the above data, space-filling models were proposed for bile salts and THL at air/water and oil/water interfaces. 相似文献
9.
A model is presented suggesting the interaction of CO2 and bicarbonate on lipids of the cell membrane. The interfacial tensions between water and oil (benzene) phases were measured using the stalagmometer and the sessile drop methods. Effects of electrolyte solutions and of CO2 on molecular arrangement at the interface were calculated. Chloride solutions against oleic acid in benzene produced little decrease in interfacial tension from that measured for pure water against the oil phase. Presence or absence of CO2 caused no change in interfacial tension of water or chloride solutions against the oil phase. Bicarbonate salts in the absence of CO2 caused marked decreases in interfacial tension from that measured for water or chloride solutions. Concomitant with this decrease in interfacial tension were an increase in hydration of the interface and changes in molecular spacings of the lipid. This hydration may be considered as reflecting a more ionic-permeable cell membrane. The addition of CO2 to the bicarbonates caused an increase in interfacial tension of the model, approaching that of the chlorides, with decreased hydration of the interface. Viewed as occurring at the cell membrane this would make the lipid more continuous and decrease the ease of ionic penetration. In this way the action of bicarbonates and CO2 at the interface suggests an explanation of the action of CO2 on the cell. 相似文献
10.
The region between residues 968 and 1882 of apolipoprotein B (apoB-21 to apoB-41) is rich in amphipathic beta strands (AbetaSs) and promotes the assembly of primordial triacylglyceride (TAG)-rich lipoproteins. To understand the importance of AbetaS in recruiting TAG, the interfacial properties of two AbetaS consensus peptides, P12 and P27, were studied at dodecane/water (DD/W) and triolein/water (TO/W) interfaces. P12 (acetyl-LSLSLNADLRLK-amide) and P27 (acetyl-LSLSLNADLRLKNGNLSLSLNADLRLK-amide), when added into the aqueous phase surrounding a suspended oil drop (dodecane or triolein), decreased the interfacial tension (gamma) in a concentration-dependent manner. At the DD/W interface, 1 x 10(-5) M P12 decreased gamma to approximately 20 mN/m and 6.6 x 10(-6) M P27 decreased gamma to approximately 13 mN/m. At the TO/W interface, 1.5 x 10(-5) M P12 decreased gamma to approximately 14 mN/m and 9.0 x 10(-6) M P27 decreased gamma to approximately 12 mN/m. The surface area of both peptides was between 11.2 and 15.1 angstroms2 per residue, consistent with beta sheets lying flat on DD/W and TO/W interfaces. P12 and P27 are almost purely elastic on DD/W, TO/W, and air/water interfaces. When P12 and P27 were compressed beyond the equilibrium gamma to as low as 4 mN/m, they could not be readily desorbed from either interface. These properties probably help in assembling nascent TAG-rich lipoproteins, and AbetaS may anchor apoB to beta lipoproteins. 相似文献
11.
Mesoscopic simulation study on the efficiency of surfactants adsorbed at the liquid/liquid interface
Surfactant monolayers at the interface between oil and water has been simulated using dissipative particle dynamics (DPD) technique. With a simple coarse-grained model, how variations in structure of surfactants influence their ability to reduce the interfacial tension has been investigated. The result shows that strong hydrophilic head groups are beneficial to make surfactant molecules more stretched and ordered, and help to enhance the efficiency of surfactant at the interface, it is beneficial to decrease interfacial tension if the hydrophobic chains of the surfactant and the oil have similar structure, and phenyl has a positive effect on interfacial efficiency. The results are in agreement with experimental and other theoretical work on surfactants. 相似文献
12.
The entrapment of residual hydrocarbon ganglia during water table fluctuations can produce a long‐term contamination threat to groundwater supplies that is difficult to remove. The mobilization of entrapped hydrocarbon ganglia depends on the balance between capillary and gravitational forces represented by the Bond number. The present work focuses on the influence of the interfacial tension between the hydrocarbon and the surrounding water on the entrapment and mobilization of the residual ganglia. Laboratory column tests using glass beads as the porous medium have been conducted to determine the residual saturation of a hydrocarbon (Soltrol 170) trapped during vertical displacements due to a rising water table and the necessary decrease in interfacial tension to mobilize these trapped ganglia. The interfacial tension was decreased by the addition of isopropyl alcohol to the water phase. Saturations of the three phases (water, hydrocarbon, and air) were measured with a dual‐beam y‐densitometer. The results for residual hydrocarbon saturation at various interfacial tensions were combined with previous results for different particle diameters to provide a general relationship between residual saturation and Bond number. The relationship is expressed in an empirical correlation valid for Bond numbers between 0.001 and 1.2. 相似文献
13.
Mixed surfactants have potential applications in various fields. The understanding and prediction of their macro- and microscopic properties are of great importance in the designing of these materials. We used molecular dynamics (MD) and experiments to study the interfacial tension and the microscopic structures of the sodium dodecyl sulfate (SDS)/C4mimBr mixed surfactant at the water/hexane interface. The interfacial tension, density profile, radial distribution function (RDF), orientation distribution of the tails and order parameters have been examined. It seems that the addition of C4mimBr decreased the interfacial tension; a higher C4mimBr concentration resulted in a thicker interface, a smaller droplet, and more disordered SDS tails. The competition between free volume and electrostatic shielding seems to be the primary mechanism behind these phenomena. 相似文献
14.
Yiming Li Yingyan Guo Guiying Xu Zhining Wang Mutai Bao Nuannuan Sun 《Molecular simulation》2013,39(4):299-308
Dissipative particle dynamics is used to simulate the oil/water/surfactant system in the absence and presence of polymer. Structural properties, interfacial properties, and their dependence on the surfactant concentration, polymer concentration and oil/water ratio were investigated. The snapshots illustrate the variation of the structure of oil/water/surfactant system. In the presence of polymer, the interface is supersaturated at a lower surfactant concentration. The end-to-end distance increases with surfactant concentration and polymer chains but shows weak dependence on the oil/water ratio. The peak of density grows higher with surfactant concentration, but it is not affected by oil/water ratio. The density profiles of polymer grow higher with polymer chains, indicating that most of the polymer chains stay at the interface for stability. Interfacial thickness shows an adsorption of polymer/surfactant complexes at the interface, where the polymer is in an extended conformation at the interface. The formation of polymer/surfactant complexes is favourable for the decrease of oil/water interfacial tension. 相似文献
15.
Summary Partition coefficients of distribution of proteins were measured in two systems: i) 3-phenoxy-2-hydroxypropyl derivatives
of bead cellulose (PHPC)/water solution — coefficients P; and ii) Aqueous polyethylene glycol (PEG)/dextran (DXT) two-phase
system — coefficient K. Following proteins were used for the measurements: lysozyme, trypsin, chymotrypsin, ovalbumin, bovine
serum albumin and immunoglobulin G. The obtained P and K values were correlated with previous data about hydrophobicity of
the above proteins available in the literature. The literary data concerned: i) the efficacy of energy transfer from tryptophan
residues of proteins to cis-parinaric acid applied as hydrophobic probe, estimated by fluorescent spectroscopy; ii) the hydrophobic
ratio indicating the ratio between the hydrophobic and hydrophilic parts (in volumes) of protein molecules deduced from their
primary structure; and iii) the interfacial tension at 0.2% protein-water solution/corn oil interface. Significant corrlations
were obtained for P and efficacy of energy transfer (r=0.964; p<0.01) and for K and interfacial tension (r=0.936; p<0.05).
When P and K were fitted as exponential function of three independent variables (i.e., efficacy of energy transfer, hydrophobic
ratio and interfacial tension) good agreement between the measured and computed data was obtained. The increases in efficacy
of energy transfer, hydrophobic ratio and decrease in interfacial tension were found to be accompanied by increase in P. In
contrary, K behaved always similarly as efficacy of energy transfer, hydrophobic ratio and interfacial tension. 相似文献
16.
Penetration of 1-alkanols into monolayers of hydrophobic polypeptides, poly(ε-benzyloxycarbonyl-l-lysine) and poly(ε-benzyloxycarbonyl-dl-lysine), was compared with their adsorption on the air/water interface in the absence of monolayers. The polypeptide prepared from l-lysine is generally considered to be in the α-helical form whereas dl-copolymer polypeptide contains random-coiled portions due to the structural incompatibility between the two isomers. The free energy of adsorption of 1-alkanols on the air/water interface at dilute concentrations was ?0.68 kcal·mol?1 per methylene group and 0.15 kcal·mol?1 for the hydroxyl group at 25°C. In the close-packed state, the surface area occupied by each molecule of 1-alkanols of varying carbon chain-lengths showed nearly a constant value of about 27.2 Å2, indicating perpendicular orientation of the alkanol molecules at the interface. About 75% of the water surface was covered by 1-butanol in this close-packed state. The mode of adsorption of 1-alkanols on the vacant air/water interface followed the Gibbs surface excess while the mode on the polypeptide membranes followed the Langmuir adsorption isotherm, indicating that the latter is characterized by the presence of a finite number of binding sites. The free energies of adsorption of 1-alkanols on the l-polymer monolayers were more negative than those on the vacant air/water interface and less negative than those on the dl-copolymer monolayers. Thus, the affinity of 1-alkanols to the interface was in the order of vacant air/water interface <l-polymer <dl-copolymer. The difference between the air/water interface and l-polymer was about 0.54 kcal·mol?1 and that between l-polymer and dl-copolymer was 0.17 kcal·mol?1 at 25°C: the adsorption of 1-alkanols to the dl-copolymer was favored compared to the l-polymer. The polar moieties of the backbone of the dl-copolymer may be exposed to the aqueous phase at the disordered portion. Dipole interaction between this portion and 1-alkanol molecules may account for the enhanced adsorption of the alkanols to the dl-copolymer. 相似文献
17.
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19.
Belem-Gonçalves S Tsan P Lancelin JM Alves TL Salim VM Besson F 《The Biochemical journal》2006,398(3):569-576
The interfacial properties of bovine testicular hyaluronidase were investigated by demonstrating the association of hyaluronidase activity with membranes prepared from bovine testis. Protein adsorption to the air/water interface was investigated using surface pressure-area isotherms. In whichever way the interfacial films were obtained (protein injection or deposition), the hyaluronidase exhibited a significant affinity for the air/water interface. The isotherm obtained 180 min after protein injection into a pH 5.3 subphase was similar to the isotherm obtained after spreading the same amount of protein onto the same subphase, indicating that bovine testicular hyaluronidase molecules adopted a similar arrangement and/or conformation at the interface. Increasing the subphase pH from 5.3 to 8 resulted in changes of the protein isotherms. These modifications, which could correspond to the small pH-induced conformational changes observed by Fourier-transform IR spectroscopy, were discussed in relation to the pH influence on the hyaluronidase activity. Adding hyaluronic acid, the enzyme substrate, to the subphase tested the stability of the interfacial properties of hyaluronidase. The presence of hyaluronic acid in the subphase did not modify the protein adsorption and allowed substrate binding to a preformed film of hyaluronidase at pH 5.3, the optimal pH for the enzyme activity. Such effects of hyaluronic acid were not observed when the subphase was constituted of pure water, a medium where the enzyme activity was negligible. These influences of hyaluronic acid were discussed in relation to the modelled structure of bovine testis hyaluronidase where a hydrophobic region was proposed to be opposite of the catalytic site. 相似文献
20.
The effect of monovalent ion (Li+, Na+, Cs+) interaction with monolayers of phosphatidylcholine (lecithin, PC) was investigated at the air/water interface. We present surface tension measurements of lipid monolayers obtained using a Langmuir method as a function of monovalent ion concentration. Measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. Interactions between lecithin and monovalent ions result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants and area occupied by one molecule of PC–monovalent ion complexes (PC?Me+). 相似文献