Micelles and biological membranes

We need to understand the factors that optimize the self-assembly of cell 

We saw in Fundamentals El that phospholipids are amphipathic molecules that can group together through hydrophobic interactions to form bilayer structures and cell membranes (Fig. El). Here we explore details of the self-assembly of amphipathic molecules into a variety of structures with significance to biology and medicine. 

In aqueous environments amphipathic molecules can group together as micelles, in which hydrophobic tails congregate, leaving hydrophiUc heads exposed to the solvent (Fig. 11.51). Micelles are important in industry and biology on account of their solubilizing function matter can be transported by water after it has been dissolved in their hydrocarbon interiors. 

Micelles form only above a certain concentration of amphiphiles called the critical micelle concentration (CMC) and above the Krafft temperature. Nonionic amphipathic molecules may cluster together in clumps of 1000 or more, but ionic species tend to be disrupted by the electrostatic repulsions between head groups and are normally limited to groups of fewer than about 100. The interior of a micelle is like a droplet of oil, and experiments show that the hydrophobic tails are mobile, but slightly more restricted than in the bulk. 

Different molecules tend to form micelles of different shapes. For example, ionic species such as sodium dodecyl sulfate (SDS) and cetyl trimethylammo-nium bromide (CTAB) form rods at moderate concentrations, whereas sugar molecules form small, approximately spherical micelles. Broadly speaking, the shapes of micelles vary with the shape of the constituent molecules, their concentration, and the temperature. A useful predictor of the shape of the micelle, the surfactant parameter, N, is defined as 

---

C. Tanford. The Hydrophobic Effect Formation of Micelles and Biological Membranes. New York Wiley, 1980. 

Tanford C. The hydrophobic effect formation of micelles and biological membranes. New York John Wiley Sons, 1980. 

Zachariasse K. A., Kozankiewicz B. and Kuhnle W. (1983) Micelles and Biological Membranes Studied by Probe Molecules, in Zewail A. H. (Ed.), Photochemistry and Photobiology, Vol. II, Harwood, London, pp. 941-960. 

Tanford, C., The Hydrophobic Effect. The Formation of Micelles and Biological Membranes, 2d ed., Wiley, New York, 1980. (Undergraduate level. A classic reference by a pioneer on the hydrophobic effect on the relevance of surfactants to biological membranes.)... 

Tanford, C. 1980. Formation of micelles and biological membranes In The Hydrophobic Effect (Wiley and Sons ed.), pp. 139-146. Wiley and Sons, New York. 

Refs. [i] Frank HS, Evans MW (1945) / Chem Phys 13 507 [ii] Tanford C (1973, 2nd edn. 1980) The hydrophobic effect formation of micelles and biological membranes. Wiley, New York... 

Tanford C. The Hydrophobic Effect— Eormation of Micelles and Biological Membranes. 1973. WUey Interscience, New York. 

---