Extremely Slow Water Transport in Tight Biomolecular Confinement and The Prediction of a Transition in Mechanical Properties

Understanding transport behavior of water in tightly confined spaces has important scientific and technological implications. Due to the small dimensions involved, it is difficult to manipulate the degree of confinement and probe the transport behavior. Here we present water transport kinetics measurements in nanoscale pores of hygroscopic bacterial spores as the pore dimensions are varied in a range from approximately 0 to 1.5 nm (1). Spores’ reversible hydration-dehydration characteristics and tunable pore dimensions facilitated detailed studies of water transport kinetics in confinement. We placed spores on nanomechanical cantilever sensors and applied weak photo-thermal pulses to perturb spores’ thermodynamic equilibrium. Relaxation rates revealed extremely slow and pore-size dependent water transport, with an effective viscosity five orders of magnitude higher than that of bulk water, as interpreted using a poroelastic model of the dynamics. Temperature dependence of the kinetic rates revealed activation energies larger than that of bulk water. These findings allowed us to formulate a jamming-like mechanism, which was validated by the observation of a predicted transition in mechanical properties at short timescales (1).

[1] Harrellson, S.G. et al. Hydration solids. Nature 619, 500–505 (2023).