We performed molecular simulations to study the interactions between a protein (lysozyme) and phosphorylcholine(PC) self-assembled monolayers (SAMs) in the presence of explicit water molecules and ions. The all-atom simulations were performed to calculate the force generated on the protein as a function of its distance above the SAM surfaces. The structural and dynamic properties of water around PC-SAM surfaces were analyzed. These properties were also compared with those for the oligo(ethylene glycol) (OEG) SAM systems. Results show that the water molecules above the PC-SAM surfaces create a strong repulsive force on the protein as it approaches the surfaces. Further studies show that the dynamics of the water molecules are significantly slowed around both the PC-SAM and OEG-SAM surfaces as compared with that of bulk water, suggesting that the PC-SAM surface generates a tightly bound, structured water layer around their head groups, similar to the OEG-SAM surface. Our results also show that the PC-SAM surface is holding water more strongly than the OEG-SAM surface. The water molecules in the hydration layer of the PC-SAM surface stay longer and reorients slower than those in the hydration layer of the OEG-SAM surface. The most significant difference observed between these two surfaces is that the dipole of non-hydrogen bonded interfacial water molecules reorients much slower on PC-SAM than on OEG-SAM, which can be due to the zwitterionic nature of PC head groups.

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