Chaotropic agent
As a chaotropic compounds (Greek χάος chaos, disorder ' and τροπή tropical, rotation, (round ) turn ', so chaotropically in the meaning " turning to disorder" ) are chemical substances referred to disrupt the orderly hydrogen bonds in water. The chaotropic salts are sorted in the Hofmeister series according to their effect.
Properties
Because the hydrogen bonds are partially broken, the chaotropic substances disrupt the water structure in their environment and provide more "disorder" ( increase of entropy ). In chaotropic salts is also called " structure-breaking " salts. This disturbance of the water structure also affects dissolved in water, macromolecules, such as proteins and nucleic acids ( eg, DNA and RNA), which can be denatured by chaotropic substances. The cause of this effect is that the formation of, for example, for solvation of organic molecules or parts of molecules necessary H2O cage structures will be disturbed. Generally hydrophobic so that they reduce effects that are the three-dimensional structure of macromolecules in aqueous solution is essential. This three-dimensional structure of the macromolecule will be changed and thus have a denaturing chaotropic substances. In proteins, for example, the driving force of protein folding is disturbed, namely the aggregation of the hydrophobic amino acids in the water due to the hydrophobic effect. Chaotropic substances thus also reduce the enzymatic activity can disrupt lipid bilayers and create stress on cells.
Chaotropic substances include:
- Barium salts
- Guanidine hydrochloride
- Thiocyanates, such as guanidinium
- Perchlorates
- Iodide
- Butanol
- Phenol
- Thiourea
- Ammonium sulfate
Chemical substances with opposite effects to the chaotropic substances are called kosmotrop or antichaotrop. A special role is played by the urea. On addition of small amounts of urea to the aqueous protein solutions kosmotrop it acts, at higher concentrations ( approximately 12 mol%), it acts denaturing, so chaotrope. Ion classifications exist in the form of the Hofmeister series, where the order of the thickness of the chaotropic effect is given separately for anions and cations.