A structural determinant of the behavior of water at hydration and nanoconfinement conditions

Liquid water is reluctant to lose hydrogen-bond coordination. Here we reveal that it also demands contraction and reorientation of the second molecular shell to compensate for coordination defects. Such molecular principle will be shown to lie at the heart of the two-liquids scenario and to determine the behavior of water in hydration and nanoconfinement. Furthermore, it allows to define conditions for wettability (quantifying hydrophobicity and predicting drying transitions), thus opening the possibility to elucidate the active role of water in central fields of research.