Generation of Topologically Defined Linear and Cyclic DNA Bottle Brush Polymers via a Graft-to Approach

Abstract

Herein, we report a graft-to approach for synthesizing linear and circular double-stranded DNA (dsDNA) bottlebrush polymers (BBP). Using a bioreactor, plasmid DNA (pDNA) serves as an inexpensive and abundant source of circular, biodegradable, and unimolecular polymers. pDNA is easily converted to the linear isoform through enzymatic restriction, providing access to polymeric backbones with distinct topological states. DNA is grafted with polyethylene glycol monomethyl ether chloroethylamines (mPEGCEA) to yield DNA BBPs. Importantly this PEGylation occurs rapidly under ambient conditions in aqueous buffer. By varying the molecular weight of mPEGCEA (Mw = 750, 2000, 5000 Da) and the concentration relative to µmol of nucleotides, different brush arm densities and lengths were achieved with both linear and macrocyclic DNA backbones. Analysis of the DNA BBPs was achieved through agarose gel electrophoresis, which showed graft densities of up to 68.7% and 74.8% for linear and ring DNA respectively. The grafting process does not alter base pairing or circularity as determined using atomic force microscopy. Shear rheology was used to compare the mechanical response of 1% wt / wt solutions of the ring and linear DNA BBPs to their un-alkylated forms. Linear DNA BBPs exhibited a lower shear modulus versus linear DNA, which is expected due to the increased persistence length and decreased ability to interpenetrate associated with the attachment of polymer arms. However, the circular DNA BBPs exhibited a universally higher shear modulus versus the alkylated sample suggesting an increase in interchain interaction via addition of polymer arms. Finally, the increased steric encumbrance of the DNA BBPs slows enzymatic degradation, potentially providing a general method to increase stability of DNA constructs towards nuclease.