Three heavy water models are developed for different scenarios
Three heavy water models are developed for different scenarios lead image
Deuterium oxide, D2O, also known as heavy water, is commonly used in biophysical research as a substitute for water, for example, in neutron imaging experiments due to the much better signal provided by deuterium compared to hydrogen. However, heavy water exhibits slightly different physical properties from normal water, such as having different temperature dependence on viscosity, different temperature at its maximum density and different phase transitions.
Johanna-Barbara Linse and Jochen Hub present three models of liquid heavy water for predicting the differences between light and heavy water. They modified established models for normal water, SPC/E, TIP3P, and TIP4P/2005, to become SPC/E-HW, TIP3P-HW, and TIP4P/2005-HW, while trying to retain the characteristics of the original models.
The minimal approach means that the modified models would inherit the strengths and weaknesses of their predecessors. For example, TIP3P-HW omits the polarization contribution to the heat of vaporization, which leads to an underestimation of mass density and an overestimation of the diffusion coefficient and isothermal compressibility.
Due to the similarity to the parent models, previous practices for determining which model to use for which application may provide some guidance for where the modified models may excel. For instance, SPC/E-HW may be preferred when simulating room temperature experiments, while TIP3P-HW may be more suitable for biomolecular simulations, and TIP4P/2005-HW may be good for simulations dealing with a wide range of temperatures.
The models can help understand the modified behavior of solutes in heavy water. “We have unpublished simulation data that characterize heavy water as a poorer solvent compared to light water, which rationalize why biomolecules tend to aggregate in D2O,” said author Jochen Hub.
Source: “Three- and four-site models for heavy water: SPC/E-HW, TIP3P-HW, and TIP4P/2005-HW,” by Johanna-Barbara Linse and Jochen S. Hub, Journal of Chemical Physics (2021). The article can be accessed at http://doi.org/10.1063/5.0050841 .
