The current project explores the dynamic regioselective derivatization of synthetic and biological molecules for applications involving mapping the lysine distributions in monoclonal antibodies and tuning the activity of histories and retinal, e.g., for regulation of gene expression. The use of dynamic chemistry allows the thermodynamic control of the ligation reactions, which leads towards: i) the most stable products or their constitutional dynamic libraries (CDLs); ii) possibility for error-c.orrection; iii) responsive properties, namely the possibility to reverse the conjugation by changing the conditions (e.g., pH), opening the way to delivery applications.