Stackable Aromatic Dipeptide Ring Structures toward Nanotube Formation: Thermodynamics and Interactions in Gas-Phase and Solution

摘要

Increasing attention has been drawn towards self-assembling dipeptide nanotube materials (NT) for their tunable properties. Despite recent advances, a fundamental understanding of the conditions that drive the self-assembly process is still lacking. Here, we report the structures, thermodynamics, and underlying interactions of the nanotube forming potential of cyclic and linear aromatic dipeptides phenylalanine-tyrosine, tryptophan-tyrosine, and dityrosine via the piecewise self-assembly mechanism. The cyclic dipeptides have better favorability of oligomerization in the gas phase than the linear dipeptides, largely due to the enthalpic gain of forming more hydrogen bonds, suggesting that the piecewise mechanism is plausible for vapor deposition methods. Oligomerization in solution, which would require desolvation of free monomers, was shown to be thermodynamically unfavorable, especially in polar solvents, demonstrating the need for an external stimulus for the crystallization of NTs. The generated oligomeric rings show structural robustness and symmetry, allowing excellent stacking potential in both lateral and axial directions. The nature of the sidechains significantly affects the stabilizations within the oligomeric structure. The insights generated can be used as a basis for dipeptide modifications that could enhance targeted NT properties for different applications.