Hydrophobic interactions play an important role in protein folding and nanoscale self-assembly. We performed molecular dynamics (MD) simulations to investigate how hydrophobic interactions depend on the presence of proximal charge groups. Specifically, we simulate interactions between a model amphiphilic molecule functionalized with charged groups and a neutral hydrophobic surface. We consider both anions and cations and we test the hypothesis that charged ions may be used to control hydrophobic interaction in this case. The major difference from earlier studies is that the charged ions are not able to diffuse in the liquid because here they are tethered to the backbone of the molecule. Calculations of free energies show that indeed proximal charge groups can modulate the depth of the energy well that corresponds to the strength of hydrophobic interaction, even when these groups are 1 nm away from the hydrophobic interface. Our analysis excludes the possibilities that the observed phenomenon is due either to the interaction of proximal charges with ions segregated to the hydrophobic surface or due to the rotation of the molecule. Our results imply that specific ion effect is not limited to the first hydration shell and that chaotropes can modulate the hydrophobic interaction without segregation to hydrophobic sites. We performed simulations for a range of proximal charges and found our conclusions to be general.

Effect of proximal charge groups on hydrophobic interaction

247th National Meeting (2014)

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