Surface tension phospholipid monolayers

Koryta et al. [48] first stressed the relevance of adsorbed phospholipid monolayers at the ITIES for clarification of biological membrane phenomena. Girault and Schiffrin [49] first attempted to characterize quantitatively the monolayers of phosphatidylcholine and phos-phatidylethanolamine at the ideally polarized water-1,2-dichloroethane interface with electrocapillary measurements. The results obtained indicate the importance of the surface pH in the ionization of the amino group of phosphatidylethanolamine. Kakiuchi et al. [50] used the video-image method to study the conditions for obtaining electrocapillary curves of the dilauroylphosphatidylcholine monolayer formed on the ideally polarized water-nitrobenzene interface. This phospholipid was found to lower markedly the surface tension by forming a stable monolayer when the interface was polarized so that the aqueous phase had a negative potential with respect to the nitrobenzene phase [50,51] (cf. Fig. 5). 

Numerous techniques have been employed to examine the monolayer structure of phospholipids at the air/water interface including surface tension, fluorescence, neutron and X-ray reflection, and IR and Raman spectroscopy. In contrast, very few techniques are suitable to examine monolayers at the oil/water interface. Surface tension and fluorescence microscopy [46-48] have shed some light on these buried monolayers, but most other surface techniques are hampered because of effects from the bulk liquids. Since VSFS is insensitive to the bulk, it is an excellent technique for probing these monolayers. 

Landau E.M. and Leshem Y. 1989. A monolayer model study of surface tension - associated parameters of membrane phospholipids II. Anionic head-group interactions with pH, Ca + and auxins. Jour. Exp. Bot. (in press). 

Surfactant is a lipid-protein complex that is synthesized and released hy alveolar type II epithelial cells. This complex surface-active compound contains both hydrophobic and hydrophilic regions to allow the molecule to spontaneously adsorb to and form monolayers along the air-liquid interface. The role of surfactant in pulmonary fluid mechanics depends on its natural ability to disrupt intermolecular forces by interfering with the attractive forces between water molecules at the interfacial surface—thus lowering the surface tension. While this surfactant mixture is largely comprised of lipids (90%), the surfactant proteins (10%) are required for normal function (Hall et al. 1992 Yu and Possmayer 1993). Finally, the molecule dipalmitoyl phosphatidylcholine (DPPC) makes up 80% of the phospholipid and is largely responsible for the ultra-low surface tensions necessary for respiratory function (<5 dyn/cm) (Klaus et al. 1961 Hawco et al. 1981 Tchoreloff et al. 1991). 

Wallace JA, Schiirch S. Line tension of sessile drops placed on a phospholipid monolayer at the water-fluorocarbon interface. Colloids Surfaces 1990 43 207-221. 

The charge defined by Equation 1.97 cannot be read directly as the slope of the electrocapillary curve, especially when the monolayer desorbs upon complex-ation. Indeed, due to the charge-transfer reaction taking place during the desorption of the complex, it is impossible to vary the potential E while keeping constant the chemical potential of the phospholipid L . Hence, the differentiation of the interfacial tension with respect to the potential does not give the surface charge... 

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