What can primary amines target in chemical cross-linking?

Primary amines are nucleophilic and possess a free amino group that can react with electrophiles in chemical cross-linking. In particular, they can effectively target aldehydes due to the electrophilic nature of the carbonyl carbon in the aldehyde functional group. This reaction typically forms a stable imine or Schiff base upon the condensation of the amine with the aldehyde, which plays a crucial role in various biochemical processes, including the stabilization of protein structures and the formation of complex biomolecular architectures.

Other functional groups, such as ketones, esters, and carboxylic acids, do not typically participate in cross-linking via primary amines in the same straightforward manner. While ketones can also react with primary amines, they are generally less reactive than aldehydes. Esters and carboxylic acids do not directly participate in imine formation with primary amines, as they would require activation or additional steps to facilitate a reaction with amines. Thus, the primary site for cross-linking with primary amines is predominantly through aldehydes.