Molecular simulation study of water interactions with oligo (ethylene glycol)-terminated alkanethiol self-assembled monolayers

Molecular simulations were performed to study a system consisting of protein (e.g., lysozyme) and self-assembled monolayers (SAMs) terminating with different chemical groups in the presence of explicit water molecules and ions. Mixed SAMs of oligo (ethylene glycol) [S(CH2)(4)(OCH2CH2)(4)OH, (OEG)] and hydroxyl-terminated SAMs [S(CH2)(4)OH] with a mole fraction of OEG at chi(OEG) = 0.2, 0.5, 0.8, and 1.0 were used in this study. In addition, methyl-terminated SAMs [S(CH2)(11)CH3] were also studied for comparison. The structural and dynamic behavior of hydration water, the flexibility and conformation state of SAMs, and the orientation and conformation of protein were examined. Simulation results were compared with those of experiments. It appears that there is a correlation between OEG surface resistance to protein adsorption and the surface density of OEG chains, which leads to a large number of tightly bound water molecules around OEG chains and the rapid mobility of hydrated SAM chains.