Deciphering Desorption Pathways and Mechanisms of Peptide Supramolecular Structures Thermodynamically and Kinetically by High-Speed AFM.

Studying molecule desorption from solids has attracted much interest in crude oil exploitation, self-cleaning nanotechnology, and biomedicine. Much work on polymer/biopolymer desorption has addressed the effect of pH, salts, and others on desorption features fitted by established models. However, molecular desorption pathways and mechanisms are still poorly understood due to lack of (i) a good model directly revealing nano- to microscale desorption characteristics and (ii) a powerful nanotool enabling the capture of every detail within sufficient spatiotemporal resolution. We utilized well-organized peptide supramolecular arrays (pSMAs) as a model system and high-speed AFM to investigate molecular desorption pathways and the mechanism in thermodynamics and kinetics. Temperature as a key parameter affects both peptide desorption and diffusion processes, leading to changes of pSMA coverage and ordered-to-disordered structures. Significantly, we found distinct desorption pathways of pSMAs in kinetics, including no desorption, one- or double-end desorption, and middle desorption of nanowires (NWs). Therefore, we proposed a "stop-to-activate" mechanism. Besides, the desorption characteristics of single NWs and pSMAs were well fitted by an exponential curve following classic desorption models. This work provides a good guideline for studying other molecules' or assemblies' desorption and sheds light on investigating drug effects on disassembly of amyloid protein fibrils in treating neurodegenerative diseases.