Computational investigation of the hydration of alkyl diammonium cations in water clusters

- Cluster hydration of alkyl diammonium ions is investigated by MD simulations.
- Ion hydration extent and conformational changes from 2D potentials of mean force.
- Short dications are fully hydrated inside clusters.
- Longer dications tend to fold and locate towards the cluster surface.
- Doubly charged ions with hydrophobic domains adopt partial hydration at interfaces.

The hydration behavior of α,ω-alkyl diammonium cations of varying alkyl chain length in water clusters has been investigated with molecular dynamics simulations. The OPLS force field was validated against high-level quantum-chemistry results and experimental data and subsequently used to describe the interatomic interactions in the simulations. The results were further validated with simulations performed with approximate density-functional theory (DFTB3). Surface solvation structures are found to be the most stable, accompanied by considerable ion conformational changes, especially in the case of longer dications. This work demonstrates that, depending on their structure, doubly charged cations may have a high affinity towards aqueous interfaces.

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