Laboratory for Molecular Surfaces and Nanotechnology (LAMSUN), Department of Chemical Sciences , University of Catania and CSGI , Viale Andrea Doria 6 , 95125 Catania , Italy.
Department of Chemical Sciences and Technologies , University of Roma Tor Vergata , Via della Ricerca Scientifica , 00133 Roma , Italy.
Langmuir. 2019 Apr 9;35(14):4813-4824. doi: 10.1021/acs.langmuir.8b03895. Epub 2019 Mar 25.
The cyclic change of structure, thickness, and density, with pH switching from acidic (pH = 3) to basic (pH = 11) condition, has been revealed for chemisorbed monolayers of the peptide Lipo-Aib-Lys-Leu-Aib-Lys-Lys-Leu-Aib-Lys-Ile-Lol, a trichogin GA IV-analogue carrying Lys residues instead of Gly ones at positions 2, 5, 6, and 9, while a homologous peptide not containing Lys residues does not show any response to pH changes. Experimental and theoretical results, obtained by means of quartz crystal microbalance with dissipation monitoring, surface plasmon resonance, nanoplasmonic sensing technique, Fourier transform infrared-reflection attenuated spectroscopy and dynamic force spectroscopy, and molecular dynamics simulations provide detailed information on the overall monolayer structure changes with pH, including the analysis of the intra- and interchain peptide dynamics, the structure of the peptide layer/water/solid interface, as well as the position and role of solvation and nonsolvation water. The observed stimuli-responsive behavior of L1 peptide monolayers is accounted in terms of the occurrence of a pH-induced wetting/dewetting process, due to the pH-induced switching of the hydrophilic character of charged lysine groups to hydrophobic one of the same uncharged groups, along the peptide chain. This behavior in turn promotes the collective change of the aggregation state of the peptide chains. The present results may pave the way to critically reexamine the mechanism of stimuli-responsive systems.
该化学吸附的肽 Lipo-Aib-Lys-Leu-Aib-Lys-Lys-Leu-Aib-Lys-Ile-Lol 的单分子层的结构、厚度和密度会随着 pH 值在酸性（pH = 3）和碱性（pH = 11）条件之间的周期性变化而发生变化，这一点已经被揭示出来了，这种肽是 Trichogin GA IV 的类似物，它在位置 2、5、6 和 9 处用赖氨酸取代了甘氨酸，而不含有赖氨酸的同源肽对 pH 值的变化没有任何反应。通过石英晶体微天平与耗散监测、表面等离子体共振、纳米等离子体传感技术、傅里叶变换红外反射衰减光谱和动态力谱以及分子动力学模拟等手段获得的实验和理论结果，提供了有关 pH 值变化时整个单层结构变化的详细信息，包括对肽链内和链间动力学、肽层/水/固界面结构以及溶剂化和非溶剂化水的位置和作用的分析。观察到的 L1 肽单层的刺激响应行为可以用 pH 诱导的润湿/去湿过程来解释，这是由于带电荷的赖氨酸的亲水性在 pH 诱导下转变为不带电荷的同一基团的疏水性，沿着肽链发生的。这种行为反过来又促进了肽链聚集状态的集体变化。目前的结果可能为批判性地重新审视刺激响应系统的机制铺平道路。
