Biomedical subjects

V B Fainerman

Publications and source records attributed to V B Fainerman.

36 records · Page 2Linked to original sources

PubMed2004

Determination of protein adsorption by comparative drop and bubble profile analysis tensiometry.

Proteins adsorb at a liquid interface at very low bulk concentrations which is significantly decreased due to the adsorbed amount. Depending on the surface area A to solution bulk volume V ratio this loss in protein can be significant. Using experimental methods with large differences in the A/V ratio the adsorbed amount can be determined from the measured quantities, for example the surface tension. For beta-casein and bovine and human serum albumin data from literature obtained by the Wilhelmy technique and own data measured by drop profile analysis tensiometry are used. The adsorbed amounts measured directly from ellipsometry agree very well with those determined by the proposed method.

Adsorption↗

PubMed2004

Interfacial tensiometry as a novel methodology for the determination of surfactant adsorption at a liquid surface.

At low surfactant concentration the loss of molecules in the bulk phase due to adsorption can be significant if the surface-area-to-bulk-volume ratio is large. This loss of molecules, however, can be used to determine the adsorption of a surfactant if the experiments are performed under well-controlled conditions. Experiments are performed with the model surfactant tridecyldimethylphosphine oxide (C13DMPO) using drop profile analysis and ring tensiometry. Taking into account the different area/volume ratios and the measured equilibrium surface tensions as a measure of the final surfactant bulk concentration, the adsorption of C13DMPO is determined.

Journal Article↗

PubMed2004

Competitive adsorption from mixed nonionic surfactant/protein solutions.

A thermodynamic model is derived which is suitable to describe adsorption from a mixed protein/surfactant solution. The comparison with experimental data for HSA mixed with the nonionic surfactant decyl dimethyl phosphine oxide shows good agreement. Some model calculations are discussed in terms of the competitive character of the process of adsorption from mixed protein/surfactant solutions. The behavior of globular (HSA) and flexible (beta-casein) proteins appears to be quite different due to the possibility of changing the molar area of adsorbed protein molecules.

Adsorption↗

PubMed2004

Maximum bubble pressure tensiometry--an analysis of experimental constraints.

The maximum bubble pressure tensiometry is the only technique that allows measurements of dynamic surface tensions of surfactant solutions in the short time range down to milliseconds and even below. To reach such extremely short adsorption times, many hydrodynamic and aerodynamic effects have to be taken into consideration in order to measure physical values or to correct for the respective influences. In particular, the design of the instruments, and essentially the geometry of the measuring cell and capillary, are of key importance for accurate experiments. Another important issue is the way of determination of the characteristic bubble times, such as bubble dead time and lifetime. Examples demonstrate that the bubble pressure technique provides a powerful tool for studies of adsorption dynamics even for solutions of higher viscosities.

Journal Article↗

PubMed2004

Interpretation of surface dilational elasticity data based on an intrinsic two-dimensional interfacial compressibility model.

The present analysis shows that the introduction of intrinsic two-dimensional compressibility of a surfactant adsorption layer allows a much better interpretation of experimental data on the limiting (high-frequency) elasticity and characteristic frequency of diffusional relaxation than models using Frumkin's or other adsorption isotherms. The proposed model describes experimental data on surface dilational elasticity, as well as on surface pressure, sufficiently well at low and high surfactant concentrations, assuming the Lucassen and van den Tempel model of surface dilational elasticity is realized.

Journal Article↗

PubMed2004

Dynamic surface tension and adsorption kinetics of beta-casein at the solution/air interface.

A diffusion model is proposed to describe the adsorption kinetics of proteins at a liquid interface. The model is based on the simultaneous solution of the Ward-Tordai equation and a set of recently developed equations describing the equilibrium state of the adsorption layer: the adsorption isotherm, the surface layer equation of state, and the function of adsorption distribution over the states with different molar areas. The new kinetics model is compared with dynamic surface tensions of beta-casein solutions measured with the drop/bubble profile and maximum bubble pressure methods. The adsorption process for low concentrations is governed by the diffusion mechanism, while at large protein concentrations this is only the case in the initial stage. The effective diffusion coefficients agree fairly well with literature data. The adsorption values calculated from the dynamic surface tension data agree very well with the used equilibrium adsorption model.

Journal Article↗

PubMed2004

Analysis of tensiograms of cerebrospinal fluid with a kinetic model.

We develop a model for estimation of the parameters of dynamic tensiometry of biological fluids based on equations of formal chemical kinetics. The model considers diffusion of low- and high-molecular compounds and conformational restructuring of these compounds in the surface layer. This model was tested on cerebrospinal fluid from patients with meningitis. Some correlations between the parameters of tensiometric curves and protein, chloride, neutrophil, and lymphocyte content in the liquor are detected.

Cerebrospinal Fluid↗

PubMed2003

Description of the adsorption behaviour of proteins at water/fluid interfaces in the framework of a two-dimensional solution model.

In the framework of the two-dimensional non-ideal solution model, surface layer equations of state, adsorption isotherms and functions of the distribution of protein molecules in respect to different molar area were derived. The thermodynamic analysis was based on Butler's equation for the chemical potentials of the components and a first-order model for the non-ideality of surface layer enthalpy and entropy. For concentrated solutions, aggregation of protein molecules in the surface layer was assumed. The resulting equations satisfactorily describe the measured adsorption and surface pressure isotherms of proteins at liquid/fluid interfaces in terms of a set of constant parameters. The model reflects the well-known differences between proteins and ordinary surfactants: a sharp increase in the surface pressure with concentration beyond a certain protein adsorption; an almost constant surface pressure at higher concentrations and a significant increase in the adsorption layer thickness with increasing adsorption for flexible proteins.

Adsorption↗

PubMed2003

Adsorption kinetics of surfactant mixtures from micellar solutions as studied by maximum bubble pressure technique.

The adsorption kinetics of micellar solutions of anionic/cationic SDS/DATB mixtures with mixing ratios of 10/1 and 10/2, respectively, are studied experimentally by means of the maximum bubble pressure method. For long adsorption times the adsorption of the highly surface-active anionic/cationic complex leads to a decrease of dynamic surface tension in comparison to the single SDS system. However, the situation is the reverse for short adsorption times where the dynamic surface tension is increased by addition of the cationic surfactant, although the overall concentration is increased. This unexpected behavior is explained by partial solubilization of free SDS molecules into micelles formed by SDS/DTAB complexes. With increasing overall concentration, when eventually the CMC of SDS is reached, the anionic/cationic complex itself is solubilized by SDS micelles. Finally, no complex micelles, which for their part can solubilize an excess of SDS molecules, are present. Hence, the dynamic properties of the solution are no longer influenced by the depletion of SDS molecules and the mixture tends to behave like a pure SDS solution.

Journal Article↗

PubMed2003

Comparison of various models describing the adsorption of surfactant molecules capable of interfacial reorientation.

The thermodynamic model for describing the adsorption of surfactant molecules in different adsorption states, the reorientation model, is reconsidered on a more rigorous level. The resulting model equations are used to describe experimental surface pressure data published in the literature. The new model proposed contains three physical parameters and describes the experimental dependencies Pi(c) for oxethylated alcohols very accurately.

Journal Article↗

PubMed2002

Beta-casein bilayer adsorption at the solution/air interface: experimental evidences and theoretical description.

Ellipsometric and surface pressure studies of beta-casein adsorption layers at the water/air interface support the idea of a model that assumes the formation of a second layer adjacent to the primary adsorption layer. A thermodynamic model describes the concentration behavior of the surface pressure and the adsorbed amount with one and the same set of model parameters over the entire concentration range studied.

Adsorption↗

PubMed2002

Adsorption behavior of oxyethylated surfactants at the air/water interface.

Literature data for homologous series of nonionic and ionic surfactants, such as C(n)OH, C(n)EO(m), Tritons, C(n)SO4Na, and C(n)EO(m)SO4Na, were analyzed on the basis of the Frumkin and reorientation models. The thermodynamic quantities obtained from the reorientation model agree best with the experimental data. They yield the standard free energy of adsorption which can be split into contributions from the alkyl chain, and the polar head group. An additional contribution to the increment of the polar group deltaG0(P) from m EO groups deltaG0(EO(m)) is extracted which can be accounted for by deltaG0(EO(m)) = -2.35 square root(m) kJ/mol. The standard free energy of adsorption is well understood by the increment method used.

Adsorption↗

PubMed2002

Adsorption of single and mixed ionic surfactants at fluid interfaces.

Two different approaches have been used in the literature to describe the effects of ionisation of surfactants on the surface pressure, pi. One approach is based on a molecular model for a charged monolayer, in which the mutual repulsion of the long-chain surfactant ions results in an additional surface pressure, piel, calculated with the Gouy-Chapman theory for the formation of a diffuse electric double layer, and with counterion binding in the Stern-Helmholtz layer adjacent to the surfactant monolayer. The other approach regards the surface as a two-dimensional solution defined as a Gibbs dividing surface, which is electroneutral by definition. In this approach, the adsorption of any ion is the sum of its excesses in the monolayer and the electrical double layer; no assumptions are made about the spatial distribution of charges. It has been shown that both models can produce a reasonable description of experimental results obtained for solutions of a single ionic surfactant (RX) with or without inorganic electrolyte (XY). In many cases, measurements of pi vs. mean ionic activity at different salt concentrations (cXY) are found to coincide on a single curve, implying that at given mean ionic activity both adsorption and pi are independent of cXY, i.e. that double-layer contributions to the surface pressure are negligible. In addition, the electroneutral 2-D solution approach has resulted in a simple explanation of several typical features of mixed ionic surfactant solutions, in particular for mixtures of anionic and cationic surfactants. In mixed solutions too, double-layer effects appear to be negligible. We present arguments for such negligibility. One reason is a significant degree of binding between adsorbed surface active ions (R) and counterions (X); another is that for 1:1 electrolytes, the contribution of the diffuse double layer to the adsorption of the combination (RX) vanishes. As a result, it is possible to interpret the same experimental data in terms of both models.

Journal Article↗

PubMed2002

Simple model for prediction of surface tension of mixed surfactant solutions.

A rigorous theoretical model is presented which describes the equilibrium behaviour of a surfactant mixtures at liquid/fluid interfaces. The theory describes mixtures of surfactants with different molar areas and accounts for the non-ideality of the surface layer. The theoretical results are in good agreement with experimental data and support the idea of additivity of the interaction parameters in the surface layer. The rigorous equation of state is transformed into simple relationships for the description of the adsorption behaviour of mixed surfactant systems. The model requires surface tensions of the single surfactant systems or the adsorption isotherms to construct the isotherm of the mixture while no extra interaction parameters between the different compounds are assumed. The model is tested with a number of literature data, such as mixed sodium alkyl sulfates, mixtures of betaine homologues BHB12 with BHB16, non-ionic surfactant mixtures, and anionic-nonionic mixtures (1-butanol with BHB12, and oxethylated decanol (C10EO5) with sodium dodecyl sulfate). The agreement between experimental data and the theoretical calculations is excellent. This approach can be especially important for practical applications of surfactant mixtures for which experimental data are scarce.

Adsorption↗

PubMed2000

Dynamics of protein and mixed protein/surfactant adsorption layers at the water/fluid interface.

The adsorption behaviour of proteins and systems mixed with surfactants of different nature is described. In the absence of surfactants the proteins mainly adsorb in a diffusion controlled manner. Due to lack of quantitative models the experimental results are discussed partly qualitatively. There are different types of interaction between proteins and surfactant molecules. These interactions lead to protein/surfactant complexes the surface activity and conformation of which are different from those of the pure protein. Complexes formed with ionic surfactants via electrostatic interaction have usually a higher surface activity, which becomes evident from the more than additive surface pressure increase. The presence of only small amounts of ionic surfactants can significantly modify the structure of adsorbed proteins. With increasing amounts of ionic surfactants, however, an opposite effect is reached as due to hydrophobic interaction and the complexes become less surface active and can be displaced from the interface due to competitive adsorption. In the presence of non-ionic surfactants the adsorption layer is mainly formed by competitive adsorption between the compounds and the only interaction is of hydrophobic nature. Such complexes are typically less surface active than the pure protein. From a certain surfactant concentration of the interface is covered almost exclusively by the non-ionic surfactant. Mixed layers of proteins and lipids formed by penetration at the water/air or by competitive adsorption at the water/chloroform interface are formed such that at a certain pressure the components start to separate. Using Brewster angle microscopy in penetration experiments of proteins into lipid monolayers this interfacial separation can be visualised. A brief comparison of the protein adsorption at the water/air and water/n-tetradecane shows that the adsorbed amount at the water/oil interface is much stronger and the change in interfacial tension much larger than at the water/air interface. Also some experimental data on the dilational elasticity of proteins at both interfaces measured by a transient relaxation technique are discussed on the basis of the derived thermodynamic model. As a fast developing field of application the use of surface tensiometry and rheometry of mixed protein/surfactant mixed layers is demonstrated as a new tool in the diagnostics of various diseases and for monitoring the progress of therapies.

Adsorption↗

PubMed2000

Effect of surfactant interfacial orientation/aggregation on adsorption dynamics.

The application of new thermodynamic adsorption isotherms allow to improve the description of surfactant adsorption kinetics based on a diffusional transport. While the consideration of interfacial reorientation corrects apparently too high diffusion coefficients, interfacial aggregation avoids too small diffusion coefficients or the assumption of adsorption barriers. The adsorption kinetics of alkyl dimethyl phosphine oxides is influenced by interfacial reorientation. While the lower homologues (C8-C12) follow the classical diffusion model, the higher homologues (C13-C15) yield diffusion coefficients several times larger than the physically reasonable values. Assuming two different adsorption states, the resulting diffusion coefficients agree with those expected from the geometric size of the molecules. The model also works well for oxyethylated non-ionics, such as C10EO8. As a second example, a good theoretical description is obtained for experiments of 1-decanol solutions when a mean surface aggregation number of n = 2.5 is assumed. The same n was obtained from the description of the equilibrium adsorption isotherm of 1-decanol. Assuming that the transition from one into the other state is controlled by a rate constant (change in orientation, formation or disintegration of two-dimensional aggregates) significant changes in the kinetics curves can result. The use of additional rate constants yields an improved fitting to experimental data.

Adsorption↗

PubMed2000

Penetration of dissolved amphiphiles into two-dimensional aggregating lipid monolayers.

The review demonstrates the recent theoretical and experimental progress in the understanding of penetration systems at the air-water interface in which a dissolved amphiphile (surfactant, protein) penetrates into a Langmuir monolayer. The critical review of the existing theoretical models which describe the thermodynamics of the penetration are critically reviewed. Although a rigorous thermodynamic analysis of penetration systems is unavailable due to their complexity, some model assumptions, e.g. the invariability of the activity coefficient of the insoluble component of the monolayer during the penetration of the soluble component results in reasonable solutions. New theoretical models describing the equilibrium behaviour of the insoluble monolayers which undergo the 2D aggregation in the monolayer, and the equations of state and adsorption isotherms which assume the existence of multiple states (conformations) of a protein molecule within the monolayer and the non-ideality of the adsorbed monolayers are now available. The theories which describe the penetration of a soluble surfactant into the main phases of Langmuir monolayers were presented first for the case of the mixture of the molecules possessing equal partial molar surfaces (the mixture of homologues), with further extension of the models to include the interesting process of the protein penetration into the monolayer of 2D aggregating phospholipid. This extension was based on a concept which subdivides the protein molecules into independent fragments with areas equal to those of the phospholipid molecule. Various mechanisms for the effect of the soluble surfactant on the aggregation of the insoluble component were considered in the theoretical models: (i) no effect on the aggregate formation process; (ii) formation of mixed aggregates; and (iii) the influence on the aggregating process via the change of aggregation constant, but without any formation of mixed aggregates. Accordingly depending on the mechanism, different forms of the equations of state of the monolayer and of the adsorption isotherms of soluble surfactant are predicted. Based on the shape of the experimental pi-A isotherms, interesting conclusions can be drawn on the real mechanism. First experimental evidence has been provided that the penetration of different proteins and surfactants into a DPPC monolayer in a fluid-like state induces a first order main phase transition of pure DPPC. The phase transition is indicated by a break point in the pi(t) penetration kinetics curves and the domain formation by BAM. Mixed aggregates of protein with phospholipid are not formed. These results agree satisfactorily with the predictions of the theoretical models. New information on phase transition and phase properties of Langmuir monolayers penetrated by soluble amphiphiles are obtained by coupling of the pi(t) penetration kinetics curves with BAM and GIXD measurements. The GIXD results on the penetration of beta-lactoglobulin into DPPC monolayers have shown that protein penetration occurs without any specific interactions with the DPPC molecules and the condensed phase consists only of DPPC.

Adsorption↗

PubMed1998

[Dynamic surface tension of blood and synovial fluid in rheumatoid arthritis].

AIM: Assessment of the dynamic surface tension (DST) of blood serum (BS), synovial fluid (SF) in various courses of rheumatoid arthritis (RA). MATERIALS AND METHODS: Forty three patients with RA and 63 apparently healthy individuals were examined. DST of BS and SF was determined in the computer-aided tensiometer and some blood biochemical parameters were also measured. RESULTS: DST of BS in patients with RA were found to be higher than the normal values and some parameters c beta 2 and beta 3) of BS DST did not significantly differ from the normal values whereas others (beta 1 and gamma proved to be much lower. Depending on the disease course variants, there were some differences in these DST changes. There was a feedback between DST parameters and the levels of immunoglobulins, beta 2-microglobulin, and lipids in blood. CONCLUSION: Assessment of BS and SF DST may be useful in the differential diagnosis of RA, in the determination of its intensity and prognosis, and therapeutical efficiency.

Adolescent↗