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Polymorphism in biophysics is the aspect of the behaviour of lipids that influences their long-range order, i.e. how they aggregate. This can be in the form of spheres of lipid molecules (micelles), pairs of layers that face one another (lamellar phase, observed in biological system as a lipid bilayer), a tubular arrangement (hexagonal), or various cubic phases (Fd3m, Im3m, Ia3m, Pn3m, and Pm3m being those discovered so far). More complicated aggregations have also been observed, rhombohedral, tetragonal and orthorhombic phases have been observed.
Determination of the topology of a lipid system is possible by a number of methods, the most reliable of which is x-ray diffraction. This uses a beam of x-rays that are scattered by the sample, giving a diffraction pattern as a set of rings. The ratio of the distances of these rings from the central point indicates which phase(s) are present.
The structural phase of the aggregation is influenced by the ratio of lipids present, temperature, hydration, pressure and ionic strength (and type).
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lipid_polymorphism". A list of authors is available in Wikipedia.|