Surface active lipids

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Fig. 1.9 S urface pressure ( r)-area (A) isotherms obtained for a lipid mixture (DPPC POPG PA, 68 22 9 (by weight)), alone and with 10% (w/w) of either SP-C peptide or SP-C peptoid added. Results indicate that the addition of the SP-C mimics engenders biomimetic surface activity, as indicated by lift-off at a higher molecular area and the introduction of a plateau...

These general observations have been confirmed in PAMPA measurements in our laboratory, using the 2% DOPC-dodecane lipid. With very lipophilic molecules, glycocholic acid added to the donor solution slightly reduced permeabilities, taurocholic acid increased permeabilities, but SLS arrested membrane transport altogether in several cases (especially cationic, surface-active drugs such as CPZ). 

Other surface-active compounds self-assemble into bilayer structures (schematically illustrated in Fig. 10b), which normally spherilize into structures termed vesicles. When vesicles are formed from phospholipids, the term liposome is used to identify the structures, which also provide useful drug delivery systems [71]. Solutes may be dispersed into the lipid bilayer or into the aqueous interior, to be subsequently delivered through a variety of mechanisms. Liposomes have shown particular promise in their ability to act as modifiers for sustained or controlled release. 

Apparently the acceleration of de novo purine biosynthesis by orotic acid results from a release of feedback inhibition imposed by hepatic purine nucleotides. In a related study, it was found that orotic acid feeding can prevent hyperlipaemia, which normally follows the administration of Triton WR-1339, a surface active agent [152]. The influence of orotic acid on lipid metabolism can be readily shown by the fact that depression of serum lipoproteins and milk production were observed in lactating goats when an aqueous suspension of orotic acid was administered orally [164]. 

The PAL activity that is necessary for lignin formation occurs in the cytoplasm or bound to the cytoplasmic surface of the endoplasmic reticulum membranes. The cinnamic acid produced is probably carried on the lipid surface of the membranes, since it is lipophilic, and it is sequentially hydroxylated by the membrane-bound hydroxylases (47,50). In this way there is the possibility of at least a two-step channeling route from phenylalanine to p-coumaric acid. The transmethylases then direct the methyl groups to the meta positions. There is a difference between the transmethylases from angiosperms and those from gymnosperms, since with the latter... 

Iodophors are complexes of iodine with a surface-active agent such as polyvinyl pyrrolidone (PVP povidone-iodine). Iodophors retain the activity of iodine. They kill vegetative bacteria, mycobacteria, fungi, and lipid-containing viruses. They may be sporicidal upon prolonged exposure. Iodophors can be used as antiseptics or disinfectants, the latter containing more iodine. The amount of free iodine is low, but it is released as the solution is diluted. An iodophor solution must be diluted according to the manufacturer s directions to obtain full activity. 

The solute may itself be amphiphilic like a surface-active lipid (emulsifier) or just a simple hydrophilic or hydrophobic compound. 

Antipova, A., Semenova, M., Gauthier-Jacques, A. (1997). Effect of neutral carbohydrate structure on protein surface activity at air-water and oil-water interfaces. In Dickinson, E., Bergenstahl, B. (Eds). Food Colloids Proteins, Lipids and Polysaccharides, Cambridge, UK Royal Society of Chemistry, pp. 245-258. 

It is important to understand the characteristic interactions involved at an interface containing each of the main types of surface-active molecules, i.e., biopolymers (proteins, polysaccharides) and low-molecular-weight surfactants (lipids). But that is not the whole story. In real food systems there are almost always mixed ingredients at the interface. So it is necessary to understand what sorts of mixed interfacial structures are formed, and how they are influenced by the intermolecular interactions. 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

Lipids are insoluble in water and an interfacial tension therefore exists between the phases when lipids are dispersed (emulsified) in water (or vice versa). This tension in toto is very large, considering the very large interfacial area in a typical emulsion (section 3.7). Owing to the interfacial tension, the oil and water phases would quickly coalesce and separate. However, coalescence (but not creaming) is prevented by the use of emulsifiers (surface active agents) which form a film around each fat globule (or each water... 

MacDonald, C. R., Cooper, D. G. Zajic, J. E. (1981). Surface-active lipids from Nocardia erythropolis grown on hydrocarbons. Applied and Environmental Microbiology, 14, 117. 

In the intestine, saponins bind to mucosal cell membranes and change their physiology. Since the membranes of some cancer cells contain more cholesterol than do normal cells membranes [156], it is possible that saponins bind more to cancer cells and as a result induce their destruction. Since saponins are surface-active compounds that are not absorbed, their possible interaction with intestinal mucosal cell membranes must be emphasized. Because the average transit time of food is 24h, saponins can either in the intact or in the partly hydrolyzed form, remain in the intestine long enough to interact with free sterols and membrane lipids [157]. 

Probably far more important than the partitioning behavior is the fact that lipid oxidation in emulsions is site specific—i.e., most of the radicals are actually formed at or near the membrane. A close proximity to the interface is required to catalyze the reaction (Asua et al., 1989). Studies have shown that it is primarily the interfacial/subsurface concentration of transition metals that controls the rate of the reaction, while the concentration of transition metals in the bulk phase is secondary. This insight also provides a means to reduce the rate of the reaction. Experiments using a number of different antioxidants have in fact proven that lipid oxidation is most effectively inhibited if surface-active antioxidants are added. Antioxidants that are able to accumulate at the interface are closer to the site of lipid oxidation initiation and are therefore more efficient (Frankel et al., 1996). 

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