Dipolar Cross-Correlations in Aqueous Systems: How Surfaces Influence Water's Action at a Distance

Water exhibits several anomalous properties that shape the way water functions in biological and chemical environments. For example, the unusually large dielectric constant of water can be traced back to dipolar cross-correlations, which are manifestations of both its dipole moment and the extended hydrogen bond (HB) network. However, a common platform that explores the origins of such cross-correlations and their influence on the properties of water is missing. The characteristics of water become even more intriguing under confined systems and in biomolecular hydration layers owing to the introduction of exotic surfaces and geometries that affect the HB patterns and dipolar orientations in water. Here we utilize the power of molecular dynamics simulations and statistical analysis to address these dipolar correlations in the confinement of slit pores, nanotube/cylinder, and nanosphere and the hydration layers of proteins with vastly different structural features. These studies give us a measure of the extent or length scale of cross-correlations between dipole moments of water molecules. We find an interesting orientational arrangement in the protein hydration layers, giving rise to long-range molecular cross-correlations. To decouple the effect of HB from the effect of geometry, we additionally studied acetonitrile under nanoconfinement.