Fluidity potential

Fig. 4. Potential energy curves for R-900 Titanium Dioxide/Tamol 850 (T-850) dispersant mixtures. Tamol is a trademark of Rohm and Haas Co. Numbers on curves indicate the 2eta potential in mV. The fluidity point = 0.21% T-850 = —52 mV.

The use of Upid bilayers as a relevant model of biological membranes has provided important information on the structure and function of cell membranes. To utilize the function of cell membrane components for practical applications, a stabilization of Upid bilayers is imperative, because free-standing bilayer lipid membranes (BLMs) typically survive for minutes to hours and are very sensitive to vibration and mechanical shocks [156,157]. The following concept introduces S-layer proteins as supporting structures for BLMs (Fig. 15c) with largely retained physical features (e.g., thickness of the bilayer, fluidity). Electrophysical and spectroscopical studies have been performed to assess the appUcation potential of S-layer-supported lipid membranes. The S-layer protein used in aU studies on planar BLMs was isolated fromB. coagulans E38/vl. 

Clarke RJ, Kane DJ (1997) Optical detection of membrane dipole potential avoidance of fluidity and dye-induced effects. Biochim Biophys Acta Biomembr 1323(2) 223-239... 

Biological membranes fluidity order parameters lipid-protein interactions translational diffusion site accessibility structural changes membrane potentials complexes and binding energy-linked and light-induced changes effects of additives location of proteins lateral organization and dynamics... 

Fluorescence is also a powerful tool for investigating the structure and dynamics of matter or living systems at a molecular or supramolecular level. Polymers, solutions of surfactants, solid surfaces, biological membranes, proteins, nucleic acids and living cells are well-known examples of systems in which estimates of local parameters such as polarity, fluidity, order, molecular mobility and electrical potential is possible by means of fluorescent molecules playing the role of probes. The latter can be intrinsic or introduced on purpose. The high sensitivity of fluo-rimetric methods in conjunction with the specificity of the response of probes to their microenvironment contribute towards the success of this approach. Another factor is the ability of probes to provide information on dynamics of fast phenomena and/or the structural parameters of the system under study. 

Surface Pressure, Potential, and Fluidity Characteristics for Various Interactions in Mixed Monolayers. It is possible to distinguish various types of interactions which occur in mixed monolayers by measuring the surface pressure, surface potential, and surface fluidity of the monolayers. Deviation from the additivity rule of molecular areas indicates either an interaction between components or the intermolecular cavity effect in mixed monolayers. 

SURFACE PRESSURE SURFACE POTENTIAL SURFACE FLUIDITY... 

Figure 5. Interactions in mixed monolayers and their surface pressure, potential, and fluidity characteristics...

Hydrocarbon-Hydrocarbon Interaction. Figure 5c shows the general characteristics of mixed monolayers in which hydrocarbon-hydrocarbon interaction occurs—e.g., trimyristin-myristic acid monolayers (16). The average area per molecule shows a deviation, whereas the surface potential per molecule follows the additivity rule. Hydrocarbon-hydrocarbon interaction also increases the cohesive force in the lipid layer and therefore reduces the fluidity of the mixed monolayer. It is evident from Figures 3a and 3c that surface fluidity is the only parameter which distinguishes an intermolecular cavity effect from hydrocarbon-hydrocarbon interaction. 

Various types of molecular interactions which occur in mixed mono-layers can be distinguished by simultaneous measurements of the surface pressure, potential, and fluidity of monolayers. Limitations of Goodrich s thermodynamic treatment of mixed monolayers are mentioned. Surface properties of cholesterol have been correlated with its function in biomembranes. 

Initial attempts at selecting PEs have identified certain surfactants, such as bile salts and fatty acids, which appear to facilitate oligonucleotide absorption. The advantages of these components are many, in that they are endogenous to foods and body constituents, plus the literature is rich with information about the use and exposure of these two classes of compounds [56]. The precise mechanism of action for these PEs is unknown, but is believed to involve a disruption of the mucus layer barrier, an increase in the fluidity of the mucosal membrane, and potentially an opening of the paracellular tight junctions. The mucolytic effect coupled with the increased membrane fluidity imparted by these excipients appears to allow in-... 

Lipids have several important functions in animal cells, which include serving as structural components of membranes and as a stored source of metabolic fuel (Griner et al., 1993). Eukaryotic cell membranes are composed of a complex array of proteins, phospholipids, sphingolipids, and cholesterol. The relative proportions and fatty acid composition of these components dictate the physical properties of membranes, such as fluidity, surface potential, microdomain structure, and permeability. This in turn regulates the localization and activity of membrane-associated proteins. Assembly of membranes necessitates the coordinate synthesis and catabolism of phospholipids, sterols, and sphingolipids to create the unique properties of a given cellular membrane. This must be an extremely complex process that requires coordination of multiple biosynthetic and degradative enzymes and lipid transport activities. 

This argument is further supported by results of a study showing that the potentiation of anticancer drag cytotoxicity by MDR-reversing drugs involves alterations in membrane fluidity, which in turn lead to increases in permeability [109]. The authors could show that the investigated chemosensitizers induced alterations in the bulk membrane fluidity in a dose-dependent manner and in a concentration range... 

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