Structure and dynamics of single hydrophobic/ionic heteropolymers at the vapor-liquid interface of water

We focus on the conformational stability, structure, and dynamics of hydrophobic/charged homo- and heteropolymers at a vapor-liquid interface of water using extensive molecular dynamics simulations. Hydrophobic polymers collapse into globular structures in bulk water, but unfold and sample a broad range of conformations at the vapor-liquid interface of water. We show that adding a pair of charges to a hydrophobic polymer at the interface can dramatically change its conformations, stabilizing hairpin-like structures, with molecular details depending on the location of the charged pair in the sequence. The translational dynamics of homo- and heteropolymers are also different -- whereas the homopolymers skate on the interface with low drag, the tendency of charged groups to remain hydrated pulls the heteropolymers toward the liquid side of the interface, thus pinning them, increasing drag, and slowing the translational dynamics. The conformational dynamics of heteropolymers are also slower than that of the homopolymer, and depend on the location of the charged groups in the sequence. Conformational dynamics are most restricted for the end-charged heteropolymer, and speed up as the charge pair is moved toward the center of the sequence. We rationalize these trends using the fundamental understanding of the effects of the interface on primitive pair-level interactions between two hydrophobic groups or between oppositely charged ions in its vicinity.

@article{vembanur2014structure,
  title   = {Structure and dynamics of single hydrophobic/ionic heteropolymers at the vapor-liquid interface of water},
  author  = {Vembanur, Srivathsan and Venkateshwaran, Vasudevan and Garde, Shekhar},
  journal = {Langmuir},
  volume  = {30},
  number  = {16},
  pages   = {4654-4661},
  year    = {2014},
  doi     = {10.1021/la500237u}
}