Editing Chaotropic agent

{{Short description|Molecules that disrupt hydrogen bonding}}
A '''chaotropic agent''' is a molecule in water solution that can disrupt the [[hydrogen bonding]] network between water molecules (i.e. exerts [[chaotropic activity]]). This has an effect on the stability of the [[native state]] of other molecules in the solution, mainly [[macromolecules]] ([[protein]]s, [[nucleic acid]]s) by weakening the [[hydrophobic effect]]. For example, a chaotropic agent reduces the amount of order in the structure of a [[protein]] formed by water molecules, both in the bulk and the hydration shells around [[hydrophobic]] [[amino acids]], and may cause its [[denaturation (biochemistry)|denaturation]].

Conversely, an '''antichaotropic agent''' ([[kosmotropic]]) is a molecule in an aqueous solution that will increase the hydrophobic effects within the solution.<ref name=Moelbert>{{cite journal |last1=Moelbert |first1=S |last2=Normand |first2=B |last3=De Los Rios |first3=P |title=Kosmotropes and chaotropes: modelling preferential exclusion, binding and aggregate stability |journal= Biophysical Chemistry |volume=112 |issue=1 |year=2004 |pages=45–57 |doi=10.1016/j.bpc.2004.06.012|pmid=15501575 |arxiv=cond-mat/0305204 |s2cid=9870865 }}</ref> Antichaotropic salts such as [[ammonium sulphate]] can be used to precipitate substances from the impure mixture. This is used in protein purification processes, to remove undesired proteins from solution.

==Overview==
A chaotropic agent is a substance which disrupts the structure of, and [[denaturation (biochemistry)|denatures]], [[macromolecule]]s such as [[protein]]s and [[nucleic acid]]s (e.g. [[DNA]] and [[RNA]]). Chaotropic solutes increase the [[entropy]] of the system by interfering with intermolecular interactions mediated by non-[[covalent]] forces such as [[hydrogen bond]]s, [[van der Waals forces]], and [[hydrophobic effect]]s. Macromolecular structure and function is dependent on the net effect of these forces (see [[protein folding]]), therefore it follows that an increase in chaotropic solutes in a biological system will denature macromolecules, reduce enzymatic activity and induce stress on a cell (i.e., a cell will have to synthesize stress protectants). 

Tertiary protein folding is dependent on [[hydrophobic force]]s from [[amino acid]]s throughout the sequence of the protein. Chaotropic solutes decrease the net [[hydrophobic effect]] of hydrophobic regions because of a disordering of water molecules adjacent to the protein. This solubilises the hydrophobic region in the solution, thereby denaturing the protein. This is also directly applicable to the hydrophobic region in [[lipid bilayer]]s; if a critical concentration of a chaotropic solute is reached (in the hydrophobic region of the bilayer) then [[membrane integrity]] will be compromised, and the cell will [[lysis|lyse]].<ref>{{cite journal|title=Hydrophobic substances induce water stress in microbial cells|journal=Microbial Biotechnology|year=2010|volume=3|issue=6|pages=701–716|doi=10.1111/j.1751-7915.2010.00203.x|last1=Bhaganna|first1=Prashanth|last2=Volkers|first2=Rita J. M.|last3=Bell|first3=Andrew N. W.|last4=Kluge|first4=Kathrin|last5=Timson|first5=David J.|last6=McGrath|first6=John W.|last7=Ruijssenaars|first7=Harald J.|last8=Hallsworth|first8=John E.|pmid=21255365|pmc=3815343}}</ref>

Chaotropic [[salts]] that dissociate in solution exert chaotropic effects via different mechanisms. Whereas chaotropic compounds such as ethanol interfere with non-[[covalent]] intramolecular forces as outlined above, [[salts]] can have chaotropic properties by shielding charges and preventing the stabilization of [[Salt bridge (protein and supramolecular)|salt bridges]]. Hydrogen bonding is stronger in non-polar media, so salts, which increase the [[chemical polarity]] of the [[solvent]], can also destabilize hydrogen bonding.  Mechanistically this is because there are insufficient water molecules to effectively [[solvate]] the ions.  This can result in ion-dipole interactions between the salts and hydrogen bonding species which are more favorable than normal [[hydrogen bonds]].<ref>{{cite journal|doi=10.1016/S0006-3495(97)78647-8|volume=72|pages=65–76|title=Charge density-dependent strength of hydration and biological structure|year=1997|last1=Collins|first1=K.D.|journal=Biophysical Journal|pmid=8994593|issue=1|pmc=1184297|bibcode=1997BpJ....72...65C}}</ref>

Common chaotropic agents include [[n-butanol]], [[ethanol]], [[guanidinium chloride]], [[lithium perchlorate]], [[lithium acetate]], [[magnesium chloride]], [[phenol]], [[2-propanol]], [[sodium dodecyl sulfate]], [[thiourea]], and [[urea]].{{cn|date=November 2017}}

==See also==
* [[Boom method]]
* [[Chaotropic activity]]
* [[Denaturation (biochemistry)]]
* [[DNA separation by silica adsorption]]
* [[Hofmeister series]]
* [[Kosmotropic]]
* [[Minicolumn purification]]

==References==
{{Reflist}}

{{DEFAULTSORT:Chaotropic Agent}}
[[Category:Biomolecules]]
[[Category:Entropy]]