Self-Assembly and Rearrangement of a Polyproline II Helix Peptide on Gold

Polyproline peptide sequences have gained popularity as anchors for peptide-based self-assembled monolayers (SAMs) due to their attractive properties. In this work, peptides containing the polyproline II helix (PPII) conformation were designed and assembled on gold (Au). A quartz crystal microbalance with dissipation was used to characterize SAM formation kinetics and related properties. Peptides were designed with the sequence (GPPPPPG)2C. It was discovered that a biexponential adsorption and rearrangement model describes the binding kinetics of the PPII-containing peptide on Au. In this model, an initial reversible binding step is followed by an irreversible rearrangement step, given by parameter kt. This study found kt to be approximately 0.00064 s–1 for the PPII-containing peptides. Similarly, we found that the adsorption of the PPII-containing peptide on Au, given by ΔGads, was thermodynamically favorable (−7.8 kcal mol–1) and comparable to other common thiol terminated SAMs on Au. Furthermore, we characterized SAM properties via QCM-D, Fourier-transform infrared (FTIR) spectroscopy, and electrochemical techniques to reveal high molecular density SAMs consisting of PPII helices. In addition, these SAMs were found to have high antifouling properties. Overall, this study characterizes the fundamental assembly mechanisms, particularly, rearrangement of PPII-containing peptides for the first time, which will be useful in the designing of future peptide-based SAMs with high surface coverage and antifouling properties.

聚脯氨酸肽序列凭借其优异的性能，作为肽基自组装单层膜（self-assembled monolayers, SAMs）的锚定基团而广受关注。本研究设计并合成了带有聚脯氨酸II螺旋（polyproline II helix, PPII）构象的肽段，并将其组装于金（Au）基底之上。采用耗散型石英晶体微天平（quartz crystal microbalance with dissipation, QCM-D）对SAM的形成动力学及相关性能进行表征。所设计的肽段序列为(GPPPPPG)₂C。研究发现，双指数吸附重排模型可准确描述含PPII构象的肽段在金基底上的结合动力学过程。该模型包含两个阶段：初始的可逆结合步骤，随后是由参数k_t表征的不可逆重排步骤。本研究测得，含PPII构象的肽段其k_t值约为0.00064 s⁻¹。类似地，本研究测得含PPII构象的肽段在金基底上的吸附吉布斯自由能（ΔG_ads）为-7.8 kcal·mol⁻¹，热力学上自发进行，且与金基底上其他常见的巯基封端SAMs性能相当。此外，本研究通过QCM-D、傅里叶变换红外（Fourier-transform infrared, FTIR）光谱及电化学技术对SAM的性能进行表征，证实所制备的SAM为高密度PPII螺旋肽段组装膜。另外，该类SAM表现出优异的抗污性能。总体而言，本研究首次阐明了含PPII构象肽段的基本组装机制，特别是其重排过程，可为后续设计高表面覆盖率、优异抗污性能的肽基SAMs提供理论支撑。