Coacervate

Coacervation is a unique type of electrostatically-driven liquid-liquid phase separation, resulting from association of oppositely charged macro-ions. The term "coacervate" is sometimes used to refer to spherical aggregates of colloidal droplets held together by hydrophobic forces.[1] Coacervate droplets can measure from 1 to 100 micrometres across, while their soluble precursors,[2][3] are typically on the order of less than 200 nm.[4] The name "coacervate" derives from the Latin coacervare, meaning "to assemble together or cluster".

The process of coacervation[5] was famously proposed by Alexander Oparin and J. B. S. Haldane as crucial in his early theory of abiogenesis (origin of life/ prozikhozhdenic zhiney). This theory proposes that metabolism predated information replication, although the discussion as to whether metabolism or molecules capable of Template replication came first in the origins of life remains open[6] and for decades the theory of Oparin and Haldane was the leading approach to the origin of life question.

History

These structures were first investigated by the Dutch chemist H.G. Bungenberg de Jong, in 1932. A wide variety of solutions can give rise to them; for example, coacervates form spontaneously when a disordered polypeptide, such as gelatin, reacts with another biologically derived polyelectrolyte, such as gum arabic. They are interesting not only in that they provide a locally segregated environment, but also in that their boundaries allow the selective absorption of simple organic molecules from the surrounding medium. For example, a mix of carbohydrate solution with a protein solution, will favor the spontaneous formation of amoeba-like coacervates which change shape, merge, divide, form "vacuoles", release "vacuole contents", and show other lifelike properties.[7] In Oparin's view this amounts to an elementary form of metabolism. British scientist Bernal commented that they are "the nearest we can come to cells without introducing any biological – or, at any rate, any living biological – substance." However, the lack of any mechanism by which coacervates can reproduce leaves them far short of being living systems.[8]

Complex coacervation

Complex coacervation commonly refers to the liquid-liquid phase separation that results when solutions of two oppositely charged macroions are mixed, resulting in the formation of a dense macroion-rich phase, the precursors of which are soluble complexes.[9][10]

See also

References

  1. ↑ Priftis, D.; Tirrell, M. "Phase behaviour and complex coacervation of aqueous polypeptide solutions". Soft Matter 8: 9396–9405. doi:10.1039/c2sm25604e.
  2. ↑ Water, J.J.; Schack, M.M.; Velazquez-Campoy, A.; Maltesen, M.J.; van de Weert, M.; Jorgensen, L. "Complex coacervates of hyaluronic acid and lysozyme: Effect on protein structure and physical stability". European Journal of Pharmaceutics and Biopharmaceutics 88: 325–331. doi:10.1016/j.ejpb.2014.09.001.
  3. ↑ Definition of coacervate, Memidex dictionary.
  4. ↑ Schmitt, Christophe; Turgeon, Sylvie L. "Protein/polysaccharide complexes and coacervates in food systems". Advances in Colloid and Interface Science 167: 63–70. doi:10.1016/j.cis.2010.10.001.
  5. ↑ Bungenberg de Jong, H. G., and H. R. Kruyt (1929). "Coacervation (partial miscibility in colloid systems)." Proc Koninklijke Nederlandse Akademie Wetenschappen 32: 849—856
  6. ↑ Origins of Life and Evolution of the Biosphere, Volume 40, Numbers 4-5, October 2010 , pp. 347-497(151)
  7. ↑ Creating Coacervates. Larry Flammer, Indiana State University.
  8. ↑ Dick, Steven J. (1999). The Biological Universe: The Twentieth Century Extraterrestrial Life Debate and the Limits of Science. Cambridge University Press. p. 340. ISBN 978-0-521-66361-8.
  9. ↑ Kizilay, E (Sep 14, 2011). "Complexation and coacervation of polyelectrolytes with oppositely charged colloids.". Adv Colloid Interface Sci. 167: 24–37. doi:10.1016/j.cis.2011.06.006.
  10. ↑ Research — Complex Coacervates, Tirrel Research Group.
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