Understanding the role of electrostatic and induction effects of water solubility in alkanes

The solubility of water in alkanes, essential to understanding aqueous systems, has not been fully explicated, but a research team at Rice University building on prior work suggests that electrostatic and polarization interactions and inclusion of quantum effects may be required to resolve remaining discrepancies between molecular simulation predictions and experiments. The investigators report on their research in The Journal of Chemical Physics.

Biophysicist Dilipkumar Asthagiri, the group’s lead researcher, explains that this research sought to expand on co-author Deepti Ballal’s 2014 work exploring the source of the larger-than-expected attraction between water and alkane shown in experiments as compared to conventional simulation models that assume only dispersion interactions between water and alkane. The researchers confirmed that the effective angle-averaged interaction between methane and water obtained using the AMOEBA all-atom forcefield could fit the model using a strengthened dispersion model as earlier proposed, making electrostatic and polarization interactions appear inconsequential. According to Asthagiri, this indicates that using angle-averaged effective interactions can downplay the importance of electrostatic and polarization effects in modeling alkane-water interactions, when, in fact, the effective strong interaction itself develops from underlying electrostatic and polarization effects.

In the future, Asthagiri hopes to obtain interaction energies based on quantum chemical calculations, a direction the team abandoned due to its excessive demand on computing. They also want to understand how nuclear quantum effects change as the solute is transferred across phases. Classical statistical mechanics, the mainstay for modeling solvation phenomena, does not capture the role of such quantum effects, but the findings of Asthagiri and his team reveal the importance of including nuclear quantum effects to resolve the remaining discrepancy between AMOEBA predictions and experiments.

Source: “Electrostatic and induction effects in the solubility of water in alkanes,” by D. Asthagiri, Arjun Valiya Parambathu, Deepti Ballal, and Walter G. Chapman, The Journal of Chemical Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4997916 .