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Polarization Effects in Simulations of Kaolinite-Water Interfaces.

ABSTRACT: Computational models of clay minerals and their interactions with the surrounding medium are highly valuable to study adsorption processes at an atomistic resolution, which may be relevant in different areas such as chromatography, environmental chemistry, and so forth. In this work, we analyzed the effect of the treatment of long-range interactions on the polarization of kaolinite-water interfacial systems in terms of structural, electric and dynamic properties, and hydrogen bonds. When using conventional three-dimensional (3D) Ewald summation, water molecules were more structured on the alumina interface of the kaolinite compared to simulations, in which the periodicity perpendicular to the plane was effectively removed. By applying an external electric field to the latter simulations, we were able to reproduce results obtained with the 3D Ewald summation. We proved that the induced polarization promotes adsorption processes of polar and charged species from aqueous solutions using a glyphosate molecule (widely used herbicide) as a particular example. The polarization phenomena raised from the simulation setup should be accounted for carefully in simulations of adsorption processes, which involve periodic images of polar interfaces. An inappropriate treatment of long-range electrostatic interactions can easily lead to artifacts and/or erroneous results.

SUBMITTER: Galicia-Andres E

PROVIDER: S-EPMC7610636 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Lipid membranes are more than just barriers between cell compartments; they provide molecular environments with a finely tuned balance between hydrophilic and hydrophobic interactions that enable proteins to dynamically fold and self-assemble to regulate biological function. Characterizing dynamics at the lipid-water interface is essential to understanding molecular complexities from the thermodynamics of liquid-liquid phase separation down to picosecond-scale reorganization of interfacial hydrogen-bond networks.Ultrafast vibrational spectroscopy, including two-dimensional infrared (2D IR) and vibrational sum-frequency generation (VSFG) spectroscopies, is a powerful tool to examine picosecond interfacial dynamics. Two-dimensional IR spectroscopy provides a bond-centered view of dynamics with subpicosecond time resolutions, as vibrational frequencies are highly sensitive to the local environment. Recently, 2D IR spectroscopy has been applied to carbonyl and phosphate vibrations intrinsically located at the lipid-water interface. Interface-specific VSFG spectroscopy probes the water vibrational modes directly, accessing H-bond strength and water organization at lipid headgroup positions. Signals in VSFG arise from the interfacial dipole contributions, directly probing headgroup ordering and water orientation to provide a structural view of the interface.In this Account we discuss novel applications of ultrafast spectroscopy to lipid membranes, a field that has experienced significant growth over the past decade. In particular, ultrafast experiments now offer a molecular perspective on increasingly complex membranes. The powerful combination of ultrafast, interface-selective spectroscopy and simulations opens up new routes to understanding multicomponent membranes and their function. This Account highlights key prevailing views that have emerged from recent experiments: (1) Water dynamics at the lipid-water interface are slow compared to those of bulk water as a result of disrupted H-bond networks near the headgroups. (2) Peptides, ions, osmolytes, and cosolvents perturb interfacial dynamics, indicating that dynamics at the interface are affected by bulk solvent dynamics and vice versa. (3) The interfacial environment is generally dictated by the headgroup structure and orientation, but hydrophobic interactions within the acyl chains also modulate interfacial dynamics. Ultrafast spectroscopy has been essential to characterizing the biophysical chemistry of the lipid-water interface; however, challenges remain in interpreting congested spectra as well as designing appropriate model systems to capture the complexity of a membrane environment.

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Polarization Effects in Simulations of Kaolinite-Water Interfaces.

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