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Curcumin (CUR) is a natural food ingredient with known ability to target microbial cell membrane. In this study, the interactions of CUR with different types of model lipid bilayers (POPE, POPG, POPC, DOPC, and DPPE), mixtures of model lipid bilayers (POPE/POPG), and biological membrane mimics (Escherichia coli and yeast) were investigated by all-atom explicit solvent molecular dynamics (MD) simulation. CUR readily inserts into different types of model lipid bilayer systems in the liquid crystalline state, staying in the lipid tails region near the interface of lipid head and lipid tail. Parallel orientation to the membrane surface is found to be more probable than perpendicular for CUR, as indicated by the tilt angle distribution. This orientation preference is less significant as the fraction of POPE is increased in the system, likely due to the better water solvation of perpendicular orientation in the POPE bilayer. In E. coli and yeast bilayers, tilt angle distributions were similar to that for POPE/POPG mixed bilayer, with water hydration number around CUR for the former being higher. Insertion of CUR resulted in membrane thinning. The results from these simulations provide insights into the possible differences in membrane disrupting activity of CUR against different types of microorganisms.

Nanoparticles possess unique properties as a result of their large surface area per unit volume and therefore can be functionalized by the immobilization of enzymes for a variety of biosensing applications. Changes in the tertiary conformation of beta-lactoglobulin adsorbed on 90 nm silica nanoparticles with time were inferred using tryptophan fluorescence and Fourier transform infrared spectroscopy (FTIR) for different surface concentrations, temperature, pH, ionic strength, and 2,2,2-trifluoroethanol (TFE) and dithiothreitol (DTT) concentrations. Rapid initial unfolding followed by a much slower rate at longer times was observed, with the extent of unfolding being higher at lower surface concentrations, higher ionic strengths, higher temperature, higher TFE and DTT concentrations, and pI. The effect of temperature on the unfolding of adsorbed protein on the nanoparticle surface was similar to that in the bulk even though the extent of unfolding was higher for adsorbed protein molecules. The results of the extent of change in tertiary conformation using FTIR as indicated by the change in the ratio of amide II'/amide I were consistent with those obtained by tryptophan fluorescence whereas the rates of conformational changes given by FTIR were found to be much faster. Circular dichroism (CD) spectra showed that altering the surface concentration by itself did not change the secondary structure of beta-lactoglobulin on the surface. TFE was found to increase the alpha helix content at the expense of the fraction of the beta sheet, whereas the beta sheet was converted to an unordered conformation in the presence of DTT.

A generalized formalism for the rupture of a draining foam film due to imposed random pressure fluctuations, modeled as a Gaussian white noise, is presented in which the flow inside the film is decomposed into a flow due to film drainage and a flow due to imposed perturbation. The evolution of the amplitude of perturbation is described by a stochastic differential equation. The rupture time distribution is calculated from the sample paths of perturbation amplitude as the time for this amplitude to equal one-half the film thickness and is calculated for different amplitudes of imposed perturbations, film thicknesses, electrostatic interactions, viscosities, and interfacial mobilities. The probability of film rupture is high for thicker films, especially at smaller times, as a result of faster growth of perturbations in a thick film due to a smaller disjoining pressure gradient. Larger viscosity, larger surface viscosity, higher Marangoni number, and smaller imposed pressure fluctuation result in slower growth of perturbation of a draining film, thus leading to larger rupture time. It is shown that a composite rupture time distribution combining short time simulation results with equilibrium distribution is a good approximation.

The ability of proteins to provide stability in foams is greatly influenced by their interfacial dilatational rheological properties. Surface tension response of a pulsatingbubble with an adsorbed layer of beta-lactoglobulin was measured for different frequencies and protein concentrations using a pulsating bubble tensiometer. A methodology, accounting for adsorption/desorption as well as variation of surface concentration due to expansion/contraction, was developed for the evaluation of surface dilatational elasticity and viscosity at different frequencies from these measurements. The adsorption rate constants were inferred from the surface pressure dynamics of protein adsorption using a Langmuir minitrough. The desorption rates were shown to be negligible for beta-lactoglobulin from the surface pressure response of a spread monolayer when subjected to compression in a Langmuir minitrough. The proposed model was employed to infer the interfacial dilatational viscosity and elasticity of an adsorbed beta-lactoglobulin layer at the air-water interface from experimental pulsating bubble data for protein concentrations in the range of 0.01-0.5 wt % at pH 7. As expected, the interfacial dilatational rheological properties were found to be higher at higher protein concentrations, this effect being less pronounced for dilatational elasticity. Heating at 80 degrees C for 30 min was found to result in higher interfacial dilatational viscosity and lower interfacial dilatational elasticity though this difference was within experimental error. The traditional approach for the inference of interfacial dilatational rheological properties is found to overpredict the interfacial dilatational elasticity whereas the viscosity values do not differ significantly from those obtained using the current analysis.

Spread monolayer isotherms of β-lactoglobulin, monopalmitin, monolaurin, and their mixtures were measured at the air−water interface. The isotherms exhibited hysteresis behavior. A phase transition...

The dynamics of adsorption of commercial samples of α-lactalbumin and β-lactoglobulin was investigated through the measurement of dynamic surface pressure and surface concentration via a radiotracer method. An unusual two-step adsorption behavior was observed for both proteins at low concentration which was believed to be due to the presence of a surface active contaminant. This hypothesis was tested by comparing the native whey protein samples with those purified with charcoal extraction. Analysis of the charcoal extract by thin-layer chromatography revealed the presence of contaminating free fatty acid and triglycerides in the commercial samples. β-Lactoglobulin was found to contain a higher concentration of these contaminants than α-lactalbumin. Extraction by charcoal was found not to modify the protein structure with respect to their near-and far-UV circular dichroism spectra. The presence of contaminant resulted in a higher steady-state surface pressure for β-lactoglobulin, but the protein was not displaced from the interface. On the other hand, the presence of a low concentration of surfactant was sufficient to decrease the steady-state surface concentration of α-lactalbumin due to the displacement of the protein from the interface by the lipids.

The dynamics of surface pressure (Π) and of surface concentration (Γ) of 14C radiolabeled bovine serum albumin (BSA) adsorbed onto spread lecithin monolayers at the air−water interface were measure...

Stored emulsions undergo various destabilizing processes including creaming and coalescence of drops. Many experimental studies have been carried out in the past to quantify drop coalescence; however, the presence of two distinct types of coalescence mechanismsone due to the relative motion between the drops and the other due to their permanent proximity to each other in the creamhas not been recognized. Furthermore, the effects of creaming in these investigations could not be eliminated in ways that do not introduce new modes of coalescence or alter the existing ones. The population balance equation for an emulsion in a column in which creaming, Brownian diffusion, and coalescence of drops occur simultaneously is analyzed. The analysis reveals the existence of a dynamic zone at the top of the column in which the net effect of creaming and Brownian diffusion of drops is eliminated. Thus, while the drops cream, diffuse, and coalesce as in an actual emulsion, the measurements from this zone allow the effect...

Etude de l'efficacite et de la stabilite d'un appareil semi-continu de separation par mousse d'un agent de surface non ionique, au moyen d'un modele qui tient compte de la distribution granulometrique des gouttes, du drainage par gravite a partir des limites du plateau, de l'amincissement des films liquides cause par la pression capillaire, de l'aspiration de la limite du plateau et de la pression de disjonction, de la coalescence des bulles due a la rupture des films minces et de la diffusion du gaz entre les bulles

La separation par masse en semi-continu d'un agent de surface non ionien est etudiee au moyen d'un modele qui tient compte du drainage par gravite depuis les bords du plateau, de l'amincissement des films liquides cause par la pression capillaire, l'aspiration du bord du plateau et la pression de disjonction et de la rupture des films minces due aux forces de van der Waals. Le facteur d'enrichissement et le profil de retenue du liquide ont ete calcules pour differentes valeurs de la dimension des bulles d'entree, de la vitesse superficielle du gaz, de la concentration d'entree de l'agent de surface, de la viscosite et de la viscosite superficielle