Hydrolysis-controlled protein adsorption and antifouling behaviors of mixed charged self-assembled monolayer: A molecular simulation study

摘要

Understanding the mechanism of the antimicrobial and antifouling properties of mixed charged materials is of great significance. The interactions between human gamma fibrinogen (gamma Fg) and mixed carboxylic methyl ether-terminated (COOCH3-) and trimethylamino-terminated (N(CH3)(3-)(+)) SAMs and the influence of hydrolysis were studied by molecular simulations. After hydrolysis, the mixed SAMs exhibit behaviors from antimicrobial to antifouling, since the COOCH3-thiols were translated into carboxylic acid (COO-) terminated thiols, which carried a net charge of 1 e. Simulation results showed that the main differences between COOCH3-/N(CH3)(3)-SAM and COO-/N(CH3)(3)-SAM are the charged property and the hydration layer above the surface. gamma Fg could stably adsorb on the positively-charged COOCH3-/N(CH3)(3)SAM. The adsorption behavior is mainly induced by the strong electrostatic attraction. There is a single hydration layer bound to the surface, which is related to the N(CH3)(3) groups. The van der Waals repulsion between gamma Fg and the single hydration layer are not strong enough to compensate the strong electrostatic attraction. After hydrolysis, the positively-charged SAM was transferred to a neutral mixed charged surface, the electrostatic attraction between gamma Fg and the surface disappears. Meanwhile, the SAM surface is covered by double hydration layers, which is induced by the N(CH3)(3) and COO- groups; water molecules around COO- groups are obviously denser than that around N(CH3)(3) groups. With the combined contribution from double hydration layers and the vanishment of electrostatic attraction, gamma Fg is forced to desorb from the surface. After hydrolysis, the internal structure of mixed SAM appears more ordered due to the electrostatic interactions between charged groups on the top of SAMs.