Bioorthogonal Chain-Growth Polymerization: Site-Specific Labeling of Artificial Polymers in Living Cells

Examining and controlling the structure and interactions of biomolecules are fundamental tasks in life research. The importance of utilizing polymers to label and modify biomolecules has been steadily increasing due to the unique properties of polymers, such as polyfunctional nature and capacity of multivalent interactions. Nonetheless, the intracellular polymerization techniques that have been documented, whether they involve step-growth polymerization or radical polymerization, do not possess the mechanistically capacity to fulfill the intracellular site-specific labeling of artificial polymers. Given this context, we created a chain-growth polymerization with bioorthogonal features, centered around the proximity-enhanced copper-catalyzed azide-alkyne cycloaddition (CuAAC). At the core of this approach lies a meticulously crafted azido-tris(triazolylmethyl)amine conjugate serving as the initiator. Tris(triazolylmethyl)amine effectively forms complexes with Cu(I) and accelerates proximity reaction between the covalently attached azide and a monomer containing both azide and alkynyl groups, far exceeding the rate of monomer-to-monomer reactions. The proximity-enhanced CuAAC reaction proceeds continuously to form chain-growing polymers. This CuAAC-based chain-growth polymerization (CCGP) enables for the intracellular site-specific labeling of artificial polymers, where the point of initiator dictates the polymer's ultimate positioning. We have successfully accomplished the localization of polymers within mitochondria and the on-site synthesis of DNA-polymer conjugates, through CCGP polymerization initiated by mitochondrial-targeted initiators and DNA-linked initiator groups, respectively. Due to the living characteristic of CCGP polymerization, this strategy enables the in-situ synthesis of block copolymers in cells for the first time. Consequently, we are convinced that the advancement of biorthogonal chain-growth polymerization will furnish a potent instrument for investigating and regulating the structure and interactions of biomolecules.