Department of Chemical Sciences and Technologies, University of Rome Tor Vergata , 00133 Rome, Italy.
Department of Physics, Chemistry and Biology (IFM), University of Linköping , 581 83 Linköping, Sweden.
Langmuir. 2016 Nov 8;32(44):11560-11572. doi: 10.1021/acs.langmuir.6b01912. Epub 2016 Oct 27.
Supported lipid membranes represent an elegant way to design a fluid interface able to mimic the physicochemical properties of biological membranes, with potential biotechnological applications. In this work, a diacyl phospholipid, the 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE), functionalized with a thiol group, was immobilized on a gold surface. In this molecule, the thiol group, responsible for the Au-S bond (45 kJ/mol) is located on the phospholipid polar head, letting the hydrophobic chain protrude from the film. This system is widely used in the literature but is no less challenging, since its characterization is not complete, as several discordant data have been obtained. In this work, the film was characterized by cyclic voltammetry blocking experiments, to verify the SAM formation, and by reductive desorption measurements, to estimate the molecular density of DPPTE on the gold surface. This value has been compared to that obtained by quartz crystal microbalance measurements. Ellipsometry and impedance spectroscopy measurements have been performed to obtain information about the monolayer thickness and capacitance. The film morphology was investigated by atomic force microscopy. Finally, Monte Carlo simulations were carried out, in order to gain molecular information about the morphologies of the DPPTE SAM and compare them to the experimental results. We demonstrate that DPPTE molecules, incubated 18 h below the phase transition temperature (T = 41.1 ± 0.4 °C) in ethanol solution, are able to form a self-assembled monolayer on the gold surface, with domain structures of different order, which have never been reported before. Our results make possible rationalization of the scattered results so far obtained on this system, giving a new insight into the formation of phospholipids SAMs on a gold surface.
支持的脂质膜代表了一种设计能够模拟生物膜物理化学性质的流体界面的优雅方法，具有潜在的生物技术应用。在这项工作中，一种二酰基磷脂，即带有巯基的 1,2-二棕榈酰-sn-甘油-3-磷酸硫代乙醇（DPPTE），被固定在金表面上。在这个分子中，负责 Au-S 键（45 kJ/mol）的巯基位于磷脂极性头端，让疏水性链从膜中突出。这个系统在文献中被广泛应用，但也同样具有挑战性，因为其特性尚未完全确定，因为已经得到了一些不一致的数据。在这项工作中，通过循环伏安法阻断实验来验证 SAM 的形成，通过还原解吸测量来估计 DPPTE 在金表面的分子密度，对该系统进行了表征。这个值与通过石英晶体微天平测量得到的值进行了比较。通过椭圆光度法和阻抗谱测量获得了关于单层厚度和电容的信息。通过原子力显微镜研究了薄膜的形态。最后，进行了蒙特卡罗模拟，以获得关于 DPPTE SAM 形态的分子信息，并将其与实验结果进行比较。我们证明，在低于相变温度（T = 41.1 ± 0.4 °C）的乙醇溶液中孵育 18 小时的 DPPTE 分子能够在金表面上形成自组装单层，具有不同阶的畴结构，这是以前从未报道过的。我们的结果使得对这个系统迄今为止得到的分散结果进行合理化成为可能，为磷脂 SAM 在金表面的形成提供了新的见解。
