Mechanical Stabilization Effect of Water on a Membrane-like System

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• 作者：Matteo Castronovo ; Fouzia Bano ; Simone Raugei ; Denis Scaini ; Martina Dell'Angela ; Robert Hudej ; Loredana Casalis ; Giacinto Scoles
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：March 7, 2007
• 年：2007
• 卷：129
• 期：9
• 页码：2636 - 2641
• 全文大小：342K
• 年卷期：v.129,no.9(March 7, 2007)
• ISSN：1520-5126

文摘

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 investigatedin the presence of different solvents. The compressibility (i.e., height vs tip load) of the HS-(CH₂)₁₁-OHSAM is studied differentially, with respect to a reference structure. The reference consists of hydrophobicalkylthiol molecules (HS-(CH₂)₁₇-CH₃) embedded as nanosized patches into the hydrophilic SAM bynanografting, an AFM-assisted nanolithography technique. We find that the penetration resistance of thehydrophilic SAM depends on the nature of the solvent and is much higher in the presence of water thanin 2-butanol. In contrast, no solvent-dependent effect is observed in the case of hydrophobic SAMs. Weargue that the mechanical resistance of the hydroxyl-terminated SAM is a consequence of the structuralorder of the solvent-SAM interface, as suggested by our molecular dynamics simulations. The simulationsshow that in the presence of 2-butanol the polar head groups of the HS-(CH₂)₁₁-OH SAM, which bindonly 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, inturn, mediates the release of the surface strain, leading to a more ordered interface. We suggest that themechanical stabilization effect induced by water may be responsible for the stability of even more complex,real membrane systems.