Exploring the Self-Assembly of a Fully Protected l-Dopa from Different Organic Solvents and the Relationship Between Gel and Crystal Structures

We report here the self-assembly of a fully protected l-3,4-dihydroxyphenylalanine (Boc-l-Dopa(Bn)₂-OMe) under several conditions. Depending on the organic solvent or solvent mixture, this simple molecule self-assembles into different supramolecular structures, sometimes behaving as a low-molecular-weight gelator. Indeed, we observed the formation of organogels in alcohols, as confirmed by rheological analyses. In contrast, in solvent mixtures, long crystalline fibers were formed, and we could obtain single crystals suitable for X-ray diffraction analysis through a vapor diffusion technique. The deep X-ray diffraction analyses allowed us to determine the structure of the crystals, of the gels, and of the fiber-like aggregates and to deduce that the molecule always self-assembles like antiparallel β-sheets, driven by intermolecular hydrogen bonding and π–π stacking interactions.