Open-source approach provides faster, better solubility predictions

June 06, 2017

WASHINGTON, D.C., June 6, 2017 -- The solubility of any given substance -- the measure of how well the substance dissolves into another substance referred to as the solvent -- depends on basic properties like temperature and pressure, as well as the chemical identities of the dissolved substance (the solute) and the solvent.

Predicting solubility is important to a variety of applications. In the pharmaceutical field, for example, it is crucial to know the solubility of a drug since it directly determines its availability to the body. The petroleum industry provides another example: Substances with low solubility can form scales or unwanted deposits in pipes or on drills, causing blockages and other big problems.

Despite the importance of predicting solubility, it is not an easy matter. One approach, using "brute force" simulations, requires long computing times. Other techniques, while faster, fail to predict accurate solubility values. This week in The Journal of Chemical Physics, from AIP Publishing, researchers report a new type of software that enables convenient solubility estimations of essentially any molecular substance over wide temperature and pressure ranges. The code makes use of readily available open-source software and is expected to be widely adopted.

Daan Frenkel of the University of Cambridge in the U.K. worked with colleagues Lunna Li, also in Cambridge, and Tim Totton, of British Petroleum, to develop the code.

"We made a conscious choice to use well-documented, freely available software because we wanted to make our approach available to anyone," Frenkel said. "A general-purpose tool to compute solubilities has been lacking for a long time. The underlying methodology was there, but nobody had actually created a working program."

The software developed by this group uses standard thermodynamic expressions that have been known since the mid-19th century, such as vapor pressure. The approach exploits the fact that when a solid or liquid phase are in equilibrium, their vapor pressures are equal. When a liquid or solid are heated, molecules escape and form vapor. This vapor pressure can be calculated using computer models.

For example, a lump of sugar dissolving in water: Sugar molecules exist either in a solid state -- the crystalline sugar lump -- or completely surrounded by water molecules once they've dissolved. The amount of sugar in each of the two phases, solid and solution, is determined by the energy required to move sugar molecules between those phases. The solubility can be calculated by computing the vapor pressure of the two phases and equating them.

To model the solid phase, the investigators used a model referred to as an Einstein crystal. In this model, non-interacting solute molecules are placed on a lattice and tethered to a lattice point with a mathematical spring. The vapor pressure of the crystal is computed by calculating the work needed to switch off the springs and switch on interactions between the tethered molecules.

To model a dissolved solute molecule, the investigators used a standard energy potential for the solvent in question, which was water in the examples used to test their software, and calculated the work in three steps. First, a cavity in the solvent is created. A solute molecule is then inserted into the cavity and, finally, the cavity is shrunk to the size of the solute molecule. This procedure eliminates a number of errors and produces accurate estimates of the vapor pressure and, thus, the solubility.

In this week's report, the investigators tested their code on naphthalene dissolved in water and predicted a solubility that compares well with experimental values. Future investigations will focus on extending the software so that it can handle larger solute molecules.
-end-
The article, "Computational methodology for solubility prediction: Application to the sparingly soluble solutes," is authored by Lunna Li, Tim Totton and Daan Frenkel. The article will appear in The Journal of Chemical Physics June 6, 2017 [DOI: 10.1063/1.4983754]. After that date, it can be accessed at http://aip.scitation.org/doi/full/10.1063/1.4983754.

ABOUT THE JOURNAL

The Journal of Chemical Physics publishes concise and definitive reports of significant research in the methods and applications of chemical physics. See http://jcp.aip.org.

American Institute of Physics

Related Water Articles from Brightsurf:

Transport of water to mars' upper atmosphere dominates planet's water loss to space
Instead of its scarce atmospheric water being confined in Mars' lower atmosphere, a new study finds evidence that water on Mars is directly transported to the upper atmosphere, where it is converted to atomic hydrogen that escapes to space.

Water striders learn from experience how to jump up safely from water surface
Water striders jump upwards from the water surface without breaking it.

'Pregnancy test for water' delivers fast, easy results on water quality
A new platform technology can assess water safety and quality with just a single drop and a few minutes.

Something in the water
Between 2015 and 2016, Brazil suffered from an epidemic outbreak of the Zika virus, whose infections occurred throughout the country states.

Researchers create new tools to monitor water quality, measure water insecurity
A wife-husband team will present both high-tech and low-tech solutions for improving water security at this year's American Association for the Advancement of Science (AAAS) annual meeting in Seattle on Sunday, Feb.

The shape of water: What water molecules look like on the surface of materials
Water is a familiar substance that is present virtually everywhere.

Water, water everywhere -- and it's weirder than you think
Researchers at The University of Tokyo show that liquid water has 2 distinct molecular arrangements: tetrahedral and non-tetrahedral.

What's in your water?
Mixing drinking water with chlorine, the United States' most common method of disinfecting drinking water, creates previously unidentified toxic byproducts, says Carsten Prasse from Johns Hopkins University and his collaborators from the University of California, Berkeley and Switzerland.

How we transport water in our bodies inspires new water filtration method
A multidisciplinary group of engineers and scientists has discovered a new method for water filtration that could have implications for a variety of technologies, such as desalination plants, breathable and protective fabrics, and carbon capture in gas separations.

Source water key to bacterial water safety in remote Northern Australia
In the wet-dry topics of Australia, drinking water in remote communities is often sourced from groundwater bores.

Read More: Water News and Water Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.