Effects of Translational and Rotational Degrees of Freedom on the Hydration of Ionic Solutes as Seen by Popular Water Models

Abstract

We employed molecular dynamics simulations with separate thermostats for translational and rotational temperatures in order to study the effects of these degrees of freedom on the hydration of ions. In this work we examine how water models, differing in charge distribution, respond to the rise of rotational temperature. The study shows that, with respect to the distribution of negative charge, popular water models lead to different responses upon an increase of the rotational temperature. The differences arise in hydration of cations, as the negative charge distribution on the model solvent represents the determining factor in such cases. The cation-water correlation increases with the increasing rotational temperature if negative charge is placed in (or close to) the centre of the water molecule (a typical example is the SPC water model) and decreases, when the negative charge is shifted from the centre (as in the TIP5P model of water). Because all the water models examined here have similar distributions of positive charge, they all exhibit similar trends in solvation of anions. In contrast to above, the effect of translational temperature variation is similar for all water-solute pairs; any increase in translational temperature decreases the solute-water correlations.

Could Microwave Irradiation Cause Misfolding of Peptides?

“…Mohorič et al further studied the effect of MWs on the solvation properties of water. Using several popular water models, they performed molecular dynamics (MD) simulations of solutions of various cations, anions, polar molecules, and hydrophobic particles. − Their results showed that upon MW irradiation, short hydrophobic chains can indeed collapse to more compact globular structures. Auerbach and co-workers − provided convincing experimental evidence that in microwave-irradiated systems the rotational temperature may substantially exceed the translational one.…”

Effects of translational and rotational degrees of freedom on properties of the Mercedes–Benz water model

“…While such situations are experimentally difficult to control and study, the simulations are suited particularly well for this purpose. Several previous contributions provided numerous insights on this subject: [20][21][22][23][24][25][26] (i) hydrogen-bonds in water break upon a rotational or translational temperature increase; (ii) increase in the water's rotational temperature improves the hydration of cations and hydrophobes and weakens the hydration of anions; (iii) on the other hand increase in translational temperature always reduces correlations among the particles in the system. However, simulation studies in the past focused mainly on more sophisticated water models (such as SPC/E) and shorter range of parameters.…”