Hydration of the polymer block in globular protein-polymer bioconjugates

Protein-polymer bioconjugates are a type of AB block copolymer where one block is a globular protein. The self-assembly of these systems in solution differ significantly from that of synthetic coil block copolymers. The chemistry of the polymer block and the resulting interactions with the solvent (water) can tune the phase behavior of bioconjugates. Previously, our group has observed that changing the hydrogen bonding of the polymer can shift phase boundaries, create new phases, and change order-disorder transitions. Using small angle neutron scattering (SANS), we have devised a contrast matching method to quantify the hydration number, the number of water molecules associated with a repeat unit, of polymers that can be conjugated to globular proteins. This generalizable method can be applied to polymer solutions above the overlap concentration and does not require any underlying assumptions. The SANS data show that there are differences in the hydration of zwitterionic polymers, hydrogen bond donors, and hydrogen bond acceptors. Moreover, the hydration number correlates with a polymer’s tendency to order and the polymer concentration. These results suggest that water has a significant impact on self-assembly and thus material design.