Molecular dynamics simulations suggest conformational and hydration difference between zwitterionic poly (carboxybetaine methacrylate) and poly (ethylene glycol)

摘要

Molecular dynamics simulations were performed to characterize the conformational features and hydration dynamics of zwitterionic poly(carboxybetaine methacrylate) (pCBMA). Poly(ethylene glycol)(PEG) with comparable molecular weight was taken as referential counterpart. Conformational analyses showed that PEG chain was totally flexible and adopted a curled conformation. Massive segment-to-segment interactions in PEG could result in a hindered hydration effect. While pCBMA had hierarchic flexibility, the fixed backbone and relatively free sidechains, which provided an exclusive hydration volume of each zwitterionic sidechain. In hydration dynamics, pCBMA could largely delay and strongly hydrogen-bond with the surrounding waters. While PEG could suppress the reorientation dynamics of surficial waters due to the enclosed sites and the overlapped hydration volume. Hydration free energy calculations using umbrella sampling revealed the better water affinity of pCBMA against PEG. PEG had high cohesive energy density and needed energy to fully relax upon hydration.