We report on the physical and optical characterization of liposomes formed by extrusion and sonication, two widely used methods for vesicle preparation. We also address the issue of whether the properties of bilayers formed from liposomes prepared by the two techniques differ at the molecular and mesoscopic levels. We used the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), with and without cholesterol, to form liposomes, incorporating 1-oleoyl-2-[12-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]dodecanoyl]-sn-glycero-3-phosphocholine (18:1-12:0 NBD-PC) as an optical probe of dynamics. We measured the physical morphology of liposomes by transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the rotational and translational diffusion of 18:1-12:0 NBD-PC by time correlated single photon counting (TCSPC) and fluorescence recovery after pattern photobleaching (FRAPP), respectively. We find that, despite apparent differences in average size and size distribution, both methods of preparation produced liposomes that exhibit the same molecular scale environment. The translational diffusion behavior of the tethered chromophore in planar bilayer lipid membranes formed from the two types of liposomes also yielded similar results.

A theoretical model to predict the apparent viscosity of protein doughs during thermal processing involving heat induced denaturation is presented. the model allows viscosity prediction based on the effects of temperature‐time history, strain history, temperature, shear rate and moisture content. Data from several sources have been considered in investingating the performance of the model. the approach facilitates an understanding of the mechanisms associated with protein texturization during extrusion.

We present a total internal reflection fluorescence microscopy (TIRFM) technique for quantitative molecular-level investigations of macromolecular adsorption and interactions at liquid-liquid interfaces.The technique provides the ability to selectively excite species within tens of nanometers of the interface and is an excellent tool for nonintrusive in situ investigations. The apparatus uses an oil-water assembly that is approximately 1.0 mm thick, enabling us to achieve a diffusion time constant of e3 min, an equilibrium adsorption time on the order of minutes rather than hours, and the possibility of using hydrodynamic shear to create new interfaces. In this paper, we give a detailed description of the apparatus and present some preliminary results of a study on the equilibrium adsorption of bovine serum albumin (BSA) and lysozyme at the oil-water interface.

We present experimental results of the effect of fluorescent labels on the adsorption kinetics and diffusion of bovine serum albumin (BSA) at the oil−water interface. We performed comparative studies on BSA labeled with exactly 1, an average of 1.7, and exactly 2 fluorescein-5-isothiocyanate (FITC) molecules. We used total internal reflection fluorescence microscopy along with fluorescence photobleaching recovery as an in-situ, noninvasive measure of diffusion and adsorption of proteins at the interface. We used ion-exchange chromatography to exploit the difference in electronegativity of proteins with different labeling ratios to effect the separation required to prepare the monodisperse (single- and double-labeled) samples. Absorbance spectroscopy measurements at 278 nm (BSA) and 490 nm (FITC) were used to calibrate the eluant from the chromatography column and determine the labeling ratio. The results showed that the attachment of an extrinsic label has a pronounced effect on both adsorption and diffusion of proteins. For instance, the apparent diffusion coefficient of a BSA molecule conjugated with 2 FITC molecules was estimated to be 40% greater than that of BSA, to which only a single label had been attached. The effects of concentration quenching on the fluorescence recovery after photobleaching were examined, and the recovery curves were shown to be free of quenching effects, even at a labeling ratio of 2.

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