Structure and dynamics of a molecular hydrogel derived from a tripodal cholamide

Abstract

Tripodal cholamide 1 is a supergelator of aqueous fluids. A variety of physical techniques, including cryo-transmission electron microscopy (TEM), circular dichroism (CD), steady-state fluorescence, time-resolved fluorescence, and dynamic light-scattering, were employed to understand the structure and dynamics of the gel. Fluorescent probes [ANS (8-anilinonaphthalene-1-sulfonic acid) and pyrene] reported two critical aggregation concentrations (CAC₁ and CAC₂) of 1 in predominantly aqueous media, with the minimum gel concentration (MGC) being close to CAC₂. Fluorescence lifetime measurements with pyrene revealed ineffective quenching of pyrene fluorescence by oxygen, possibly caused by slower Brownian diffusion due to the enhanced viscosity in the gel phase. The study of the gelation kinetics by monitoring the ultrafast dynamics of ANS revealed a progressive increase in the aggregate size and the microviscosity of the aqueous pool encompassed by the self-assembled fibrillar network (SAFIN) during the gelation. The striking difference between microviscosity and bulk (macroscopic) viscosity of the gel is also discussed.