(133h) Different Self-Associations of Carboxybetaine and Sulfobetaine
Zwitterionic polycarboxybetaine and polysulfobetaine highly resist nonspecific protein adsorption in complex media. This common nonfouling property provides them an important role in applications including drug delivery, medical devices and diagnostics. One potential issue of zwitterionic materials is the possible self-association between zwitterionic moieties. This association will influence many relevant properties of zwitterionic materials including solubility, hydration and swelling, thus their nonfouling performance ultimately. Polycarboxybetaine contains carboxylic and trimethyl ammonium groups, while polysulfobetaine contains sulfonate and trimethyl ammonium groups. The different combinations of these charged groups may cause different degrees of self-associations. In this work, we studied carboxybetaine-carboxybetaine and sulfobetaine-sulfobetaine associations and their effects on polymeric properties using both molecular simulations and experiments. We studied carboxybetaine-carboxybetaine and sulfobetaine-sulfobetaine associations at high concentrations ranging from 1 to 4 M and carbon spacer lengths from one to three using molecular dynamics simulations. The analysis of radial distribution functions between the cationic and anionic groups showed significant self-associations of sulfobetaine moieties in all concentrations studied. Carboxybetaine moieties do not associate with themselves. The different self-associations are mainly attributed to the different combinations of charged groups. We studied the radii of gyration of poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA) with metadynamics simulation in order to investigate the influence of different self-associations on polymeric properties. We also studied the antipolyelectrolyte effects of pSBMA and pCBMA experimentally to testify our simulation predictions.