Matteo Castronovo - Mechanical Stabilization Effect of Water on a Membrane-like System

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      Publication Details (including relevant citation   information): Castronovo, Matteo, Bano, Fouzia, Raugei,   Simone, Scaini, Denis, Dell'Angela, Martina, Hudej, Robert,   Casalis, Loredana, Scoles, Giacinto, 2007,   129 (9), pp 2636-2641

      Abstract: The penetration resistance of a   prototypical model-membrane system (HS?(CH2)11?OH self-assembled   monolayer (SAM) on Au(111)) to the tip of an atomic force   microscope (AFM) is investigated in the presence of different   solvents. The compressibility (i.e., height vs tip load) of the   HS?(CH2)11?OH SAM is studied differentially, with respect to a   reference structure. The reference consists of hydrophobic   alkylthiol molecules (HS?(CH2)17?CH3) embedded as nanosized   patches into the hydrophilic SAM by nanografting, an AFM-assisted   nanolithography technique. We find that the penetration   resistance of the hydrophilic SAM depends on the nature of the   solvent and is much higher in the presence of water than in   2-butanol. In contrast, no solvent-dependent effect is observed   in the case of hydrophobic SAMs. We argue that the mechanical   resistance of the hydroxyl-terminated SAM is a consequence of the   structural order of the solvent?SAM interface, as suggested by   our molecular dynamics simulations. The simulations show that in   the presence of 2-butanol the polar head groups of the   HS?(CH2)11?OH SAM, which bind only weakly to the solvent   molecules, try to bind to each other, disrupting the local order   at the interface. On the contrary, in the presence of water the   polar head groups bind preferentially to the solvent that, in   turn, mediates the release of the surface strain, leading to a   more ordered interface. We suggest that the mechanical   stabilization effect induced by water may be responsible for the   stability of even more complex, real membrane systems.

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