chaotropic

Chaotropic describes substances that disrupt the structure of water and macromolecules by weakening hydrogen-bond networks and destabilizing non-covalent interactions within proteins, nucleic acids, and membranes. In solution, chaotropes tend to destabilize folded states and can denature proteins, unwind nucleic acids, and increase the solubility of hydrophobic compounds. They act in contrast to kosmotropes, which stabilize macromolecular structure by strengthening water structure and interactions.

Common chaotropic agents include urea and guanidinium salts such as guanidinium chloride or guanidinium thiocyanate. Other salts and small molecules, including perchlorate and thiocyanate salts, can also exhibit chaotropic effects to varying degrees. The Hofmeister series is a historical framework that ranks ions by their effects on water structure and macromolecular stability, placing guanidinium and thiocyanate among strongly chaotropic species, while many sulfate, phosphate, and other kosmotropic ions stabilize structures.

In biochemistry and molecular biology, chaotropes are used to denature proteins and nucleic acids, solubilize inclusion bodies, and facilitate extraction or purification processes. They are also employed in RNA isolation protocols and in some protein refolding schemes, where controlled removal of the chaotropic agent allows proper folding to resume.

Safety and limitations are important considerations, as many chaotropes are hazardous and can interfere with enzymatic assays or downstream analyses. Their effects are concentration-dependent and context-specific, so appropriate controls and gradual removal are often necessary in experimental workflows.