(371e) Investigating Antifouling Properties of Zwitterionic Carboxybetaines from Molecular Dynamics Simulations

Mem­brane fouling is very complex and is affected by the hydrophobicity, charge and polarity of the foulants and the properties of the membrane surface. A major cause of membrane biofouling is protein (or protein aggregate) adsorption on the membrane and pore surface. Protein deposition on the membrane surface and membrane pores can compromise membrane performance. Designing polymer surfaces that are non-fouling has been a central issue in membrane research. Grafting is frequently used for membrane surface modification to reduce fouling. Hydrophilic polymers are often used for this purpose because of their wettability and biocompatibility.  Surface modifications with zwitterionic materials have  been found to be effective in resisting protein attachment. The carbon spacer length (CSL) between the cationic and anionic groups influences the hydration of zwitterionic polymers and affects their anti-fouling property. To investigate the effects of CSL on the hydration of zwitterionic polymers, a series of Molecular Dynamics (MD) simulations were conducted for zwitterionic carboxybetaines trimmers with 1-8 and 16 CSL. The atomic charges of the trimmers were derived from quantum chemical calculations with Gaussian09 based on the RESP protocol and the general Amber force field was used in the MD simulations. The atomic charges of the trimmers with CSL varying from 1-8 were directly calculated using Gaussian09. The charges for the trimmer with CSL 16 were based on CSL 8. The atomic charges for the cationic and anionic groups were observed to vary with their separation length. The hydration properties of these zwitterionic polymers were evaluated by determining the average number of hydrogen bonds for each water molecule in their first hydration shell as well as the number of water molecules in the hydration shell and average number of hydrogen bonds between the polymer and water. Our results indicate that as the polymer chain becomes longer, it becomes overall less hydrated. Moreover, besides the separation distance between the positive and negative charges in one polymer chain, the degree of hydration depends also on the overall charge distribution for the other two branches of the trimmers. This has significant implications on the design and fabrication of zwitterionic antifouling polymers.