Biological colloids vesicles

FIG. 2 Observed SAXS curve for lipid IVa vesicles and its approximation function. (Reprinted with permission from the paper entitled Scattering studies on colloids of biological interest (amphiphilic systems), by O. Glatter. Progr. Colloid Polym. Sci. H4 52. Copyright 1991 Steinkopff Publishers, Darmstadt, FRG.)... 

Abstract The aggregation behaviour of biomimetic polypeptide hybrid copolymers and copolypeptides is here reviewed with a particular eye on the occurrence of secondary structure effects. Structure elements like a-helix or / -sheet can induce a deviation from the classical phase behaviour and promote the formation of vesicles or hierarchical superstructures with ordering in the length-scale of microns. Polypeptide copolymers are therefore considered as models to study self-assembly processes in biological systems. In addition, they offer a great potential for a production of novel advanced materials and colloids. 

There is, however, a large and important class of colloids in which nuclcation is absent. Growth is spontaneous, but the structures so formed are usually limited by geometric and energy factors to a finite size often towards the lower end of the colloid size range. This class comprises association colloids, or in more general terms self-assembly systems, it includes not only micelles but many more complex forms, e.g. vesicles with, as extreme examples, biological structures such as cell membranes. 

Interfaces between aqueous phase and the volumes confined by amphiphilic molecules [288]. In vitro, these refer to lipid vesicles and micelles, lipid lamellae, cubic and hexagonal phases, Langmuir-Blodgett (LB) films, which are important in colloid science and in extraction technology. In vivo, these are the surfaces of biological membranes. 

This class of association colloids can be further divided into several subgroups, which include micelles, vesicles, microemulsions, and bilayer membranes. Each subgroup of association colloids plays an important role in many aspects of colloid and surface science, both as theoretical probes that help us to understand the basic principles of molecular interactions, and in many practical applications of those principles, including biological systems, medicine, detergency, crude-oil recovery, foods, pharmaceuticals, and cosmetics. Before undertaking a discussion of the various types of association colloids, it is important to understand the energetic and structural factors that lead to their formation. 

Artificial lipid vesicles, termed liposomes, are colloid particles in which phospholipid bilayers or tetraether monolayers encapsulate an aqueous medium. Because of their physicochemical properties, liposomes are widely used as model systems for biological membranes and as delivery systems for biologically active molecules. In general, water-soluble molecules are encapsulated within the aqueous compartment whereas water insoluble substances may be intercalated into the liposomal membrane [147]. 

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