Phase Transition and Crystallization Kinetics of a Supramolecular System in a Microfluidic Platform

Supramolecular self-assembly is a key process in natural systems, allowing for the formation of structures across all length scales with a wide range of functionalities. Notable progress has been made in the bottom-up design and generation of natural and artificial peptides, which through self-assembly provide diverse nano- and microscale architectures for a variety of applications. These systems possess advantageous properties including facile synthesis and biocompatibility. However, their self-assembly into distinct structural species, particularly in relation to the underlying kinetic and dynamic mechanisms involved, remain challenging to determine. Here, we study the self-assembly of Fmoc-pentafluoro-phenylalanine (Fmoc-F-5-Phe), a modified amino acid, shedding light on those key processes. We show that Fmoc-F-5-Phe forms diverse architectures, including fibrils, ribbons, and crystals, modulated by the solution conditions in which self-assembly takes place. We further elucidate the specific molecular interactions, which play a role in crystal structure formation using powder X-ray diffraction (PXRD). Finally, by probing the self-assembly of Fmoc-F-5-Phe using a microfluidic platform, we reveal the formation of transient spherical assemblies, followed by a gel composed of fibrils and finally crystals and monitor these structural transitions in real time. Furthermore, we show that the kinetic behavior of the crystallization process adheres to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model of phase transformation rate. This work provides an experimental and theoretical framework into the kinetics and dynamics of the supramolecular self-assembly processes of amino-acid-based building blocks, leading to the design of tailor-made materials for biomedical and material science applications.