Atomic-Scale 3D Local Hydration Structures Influenced by Water-Restricting Dimensions

Hydration
structures at solid–liquid interfaces mediate
between the atomic-level surface structures and macroscopic functionalities
in various physical, chemical, and biological processes. Atomic-scale
local hydration measurements have been enabled by ultralow noise three-dimensional
(3D) frequency-modulation atomic force microscopy. However, for their
application to complicated surface structures, e.g., biomolecular
devices, understanding the relationship between the hydration and
surface structures is necessary. Herein, we present a systematic study
based on the concept of the structural dimensionality, which is crucial
in various scientific fields. We performed 3D measurements and molecular
dynamics simulations with silicate surfaces that allow for 0, 1, and
2 degrees of freedom to water molecules. Consequently, we found that
the 3D hydration structures reflect the structural dimensions and
the hydration contrasts decrease with increasing dimension due to
the enlarged water self-diffusion coefficient and increased embedded
hydration layers. Our results provide guidelines for the analysis
of complicated hydration structures, which will be exploited in extensive
fields.