(658a) Template-Directed Synthesis of Structurally-Defined Branched Biopolymers

Recent advances in chemical synthesis techniques have greatly reduced the molecular polydispersity and structural heterogeneity of branched polymeric materials. Premature termination or imperfect linking reactions, however, cannot be entirely prevented using statistical copolymerization. Resulting heterogeneity in the molecular identity of synthesized polymers greatly impacts the functional properties of a material, hindering the development of atomically precise advanced materials with controlled molecular scale properties. In this work, we capitalize on the “programmable” nature of biomaterials to design, synthesize, and characterize bio-inspired polymers with well-defined sizes and hierarchical structures. Our approach results in a new class of highly tunable materials with potential applications from single molecule rheology to functional biomaterials, such as reversible hydrogels.

Our synthesis strategy relies on enzymatic template-directed polymerization, through which we incorporate a chemically modified deoxyribonucleotide at pre-determined locations along the backbone. We utilize the modified nucleotides as “grafting sites” for facile integration of azide-terminated single stranded DNA branches via copper-mediated alkyne-azide cycloaddition or strain-promoted Cu(I)-free [2+3] cycloaddition “click” reactions. Copper-free click reactions are bio-orthogonal and nearly quantitative when carried out under mild conditions. Using this approach, we have synthesized branched polymers with three arm star, H-shaped, and comb architectures. We have also conjugated synthetic polymer side-branches to the DNA templates in order to create heterogeneous copolymers for self-assembly. We characterize our materials using polyacrylamide gel electrophoresis, high performance liquid chromatography, and MALDI mass spectrometry, all of which are used to confirm the structural identity and integrity of branched polymers. Overall, these proof-of-principle experiments demonstrate the ability to combine enzymatic polymerization with a synthetic grafting technique to systematically generate polymers with a broad range of chemical functionalities and branched architectures.