How Far Is “Bulk Water” from Interfaces? Depends on the Nature of the Surface and What We Measure

• DOI: 10.1021/acs.jpcb.1c08603
• Publication Date: 2022-02-01T19:23:50Z
• Authors: Vrushali R. Hande; Suman Chakrabarty
• Keywords: Slowdown; Length scale; Rotational diffusion; POPC

Using systematic molecular dynamics (MD) simulations, we revisit the question: At what distance from an interface do properties of "bulk water" get recovered? We have considered three different kinds interfaces: nonpolar (hydrophobic; isooctane–water interface), charged (negative; AOT bilayer), and polar (zwitterionic; POPC bilayer). In order to interrogate extent perturbation interfacial water molecules as a function interface, utilize diverse range structural dynamical parameters. To capture perturbations, look into local density (translational order), tetrahedral parameter, dipolar orientation molecules. also explore anisotropic diffusion in direction perpendicular well planar parallel dependent manner. addition, orientational time correlation functions been computed understand slowdown rotational dynamics. As expected, electrostatic field emanating seems highest long-range effect on molecules, whereas specific interactions like hydrogen bonding interaction lead significant trapping kinetic for both (zwitterionic) very close interface. Our analysis highlights that not only length-scale depends nature interfaces but type property measure/calculate. Different seem widely perturbation. Orientational parameters be perturbed much longer compared translational The global can even up ∼4–5 nm near negatively surface absence any extra electrolyte. This observation has implication toward interpretation experimental measurements since spectroscopic techniques would probe or with possible mutual disagreement inconsistency between types measurements. Thus, our study provides broader unifying perspective aspect "context dependent" "interfacial water".