Vesicle-mediated growth of tubular branches and centimeter-long microtubes from a single molecule

The mechanism by which small molecules assemble into microscale tubular structures in aqueous solution remains poorly understood, particularly when the initial building blocks are non-amphiphilic molecules and no surfactant is used. It is here shown how a subnanometric molecule, namely p-aminothiophenol (p-ATP), prepared in normal water with a small amount of ethanol, spontaneously assembles into a new class of nanovesicle. Due to Brownian motion, these nanostructures rapidly grow into micrometric vesicles and start budding to yield macroscale tubular branches with a remarkable growth rate of ∼20 μm s^-1. A real-time visualization by optical microscopy reveals that tubular growth proceeds by vesicle walk and fusion on the apex (growth cone) and sides of the branches and ultimately leads to the generation of centimeter-long microtubes. This unprecedented growth mechanism is triggered by a pH-activated proton switch and maintained by hydrogen bonding. The vesicle fusion-mediated synthesis suggests that functional microtubes with biological properties can be efficiently prepared with a mixture of appropriate diaminophenyl blocks and the desired macromolecule. The reversibility, timescale, and very high yield (90%) of this synthetic approach make it a valuable model for the investigation of hierarchical and structural transition between organized assemblies with different size scales and morphologies. The addition of p-aminothiophenol to water/ethanol mixture leads to a spontaneous and reversible formation of nanovesicles. The nanostructures rapidly grow into micrometric vesicles and fuse to yield macroscale tubular branches. Real-time microscopic visualization reveals vesicle walk and fusion on the sides and tips of the branches, leading to the formation of centimeter-long microtubes. This growth mechanism demonstrates the dynamic role of vesicles in rapid and hierarchical transition from molecules to macroscopic morphologies.