 Solution

Reversible imine formation and disulfide exchange provide two suitable dynamic covalent chemistry reactions.

An aldehyde and a primary amine can reversibly form an imine with loss of water:Multifunctional components can build rings or cages. Acid catalysis, solvent and water activity must permit both formation and hydrolysis or exchange, so that initially incorrect connections can rearrange.

For disulfide exchange, a thiolate attacks a disulfide and substitutes one sulfur-containing fragment:Suitable pH, redox conditions and exchange kinetics let a library of connectivities equilibrate. A template that stabilizes one assembly can shift the library towards it. Reversibility under the actual conditions is essential: calling a covalent reaction “dynamic” does not make a kinetically trapped product mixture equilibrate.