Chaotropic connection

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As chaotropic compounds ( Greek χάος cháos ' disorder 'and τροπή tropi , rotation, (to) turn'; chaotropic meaning 'turning to disorder') are chemical substances that disrupt ordered hydrogen bonds in water. The chaotropic salts are sorted in the Hofmeister series according to their effect.

properties

By partially breaking the hydrogen bonds, the chaotropic substances disrupt the water structure in their surroundings and cause more “disorder” (increase in entropy ). Chaotropic salts are also referred to as "structure-breaking" salts. This disruption of the water structure also affects macromolecules dissolved in water, such as proteins and nucleic acids (e.g. DNA and RNA ), which can be denatured by chaotropic substances . The cause of this effect is that the formation of, e.g. B. for the solvation of organic molecules or molecular parts, necessary H 2 O cage structures is disturbed. In general, they reduce hydrophobic effects , which are essential for the spatial structure of macromolecules in aqueous solution. This spatial structure of the macromolecule is then changed and the chaotropic substances have a denaturing effect. For proteins such. B. the driving force of protein folding is disturbed, namely the aggregation of the hydrophobic amino acids in water due to the hydrophobic effect . Chaotropic substances consequently also reduce the enzymatic activity, can disrupt lipid bilayers and cause stress on cells.

Chaotropic substances include:

Chemical substances with opposite effects to chaotropic substances are called kosmotropic or antichaotropic . Urea plays a special role . When small amounts of urea are added to aqueous protein solutions, it has a kosmotropic effect; at higher concentrations (approx. 12 mol%) it has a denaturing effect, i.e. chaotropic. For ions there is a classification in the form of the Hofmeister series , in which the order of the strength of the chaotropic effect is given separately for anions and cations.

Web links

Individual evidence

  1. ↑ Entry on Chaotrop. In: Römpp Online . Georg Thieme Verlag, accessed on June 13, 2014.
  2. ↑ M. Holz, M. Mayele Influence of Additives on Hydrophobic Association in Polynary Aqueous Mixtures In: DFG Research Report. Thermodynamic Properties of Complex Fluid Mixtures Wiley-VCH 2004, pp. 150-183, ISBN 3-527-27770-6 .