Salt ions play a critical role in many biological processes including protein solubility, stability, denaturation and aggregation. Poly(N-isopropylacrylamide) (PNIPAM) has been widely studied as a protein proxy with amide bond on its side chain and a C-C backbone. PNIPAM is also a temperature responsive polymer which exhibits hydrophobic-hydrophilic phase transition at its lower critical solution temperature (LCST). Most salts are found to reduce the transition temperature and the effect of ions on LCST follows the Hofmeister series. Classical molecular dynamics simulations were carried out to investigate the ion-PNIPAM interactions in various salt solutions. The effects of salt on LCST transition as well as ion specific interactions with PNIPAM are elucidated. Our results suggest that direct interactions between the salt cations and the polymer play an important role in the shift of LCST. Further, cations have a much stronger affinity with the polymer, whereas anions bind weakly with the polymer.

Effects of salt on lower critical solution temperature of poly (N-isopropylacrylamide) from classical molecular dynamics simulations

245th National Meeting (2013)

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