Solvent-controlled pathway selection between kinetic and thermodynamic supramolecular polymers with opposite chirality

초록

Pathway selection is a central challenge in supramolecular polymerization because kinetic and thermodynamic products often exhibit distinct structures and functions. Herein, we demonstrate a solvent-controlled pathway selection strategy that generates supramolecular polymers with opposite chirality from a single chiral bipyridine-based building block, d-Ala-BPy, incorporating two chiral d-alanine moieties. In pure H2O, concentration-dependent circular dichroism (CD) studies revealed a chirality inversion from positive to negative CD signals with increasing concentration. Time-dependent CD measurements showed cooperative polymerization with unusually prolonged lag phase at higher concentrations, indicating an off-pathway assembly process. AFM analyses correlated the positive and negative CD signals with entangled fibrillar networks and at highly ordered two-dimensional ribbon-like superstructures, respectively. Remarkably, the addition of methanol completely reversed the supramolecular chirality and transformed the assembly mechanism from an off-pathway process to an on-pathway nucleation-elongation mechanism. In H2O/methanol (85 : 15 v/v), transient intermediates evolved into thermodynamically stable fibrillar polymers exhibiting opposite chirality. These findings establish solvent composition as a powerful regulator of pathway selection, morphology and supramolecular chirality in aqueous supramolecular polymerization.

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