Package: quick-fuoss
quick-fuossrapid estimation of ion-pair dissociation constantsDescriptionquick-fuossis an open-source Python 3 program designed to allow for quick estimation of ion-pair dissociation constants.
To run,quick-fuossrequires only the name of the cation and anion and the dielectric constant of the solvent in question.
Alternatively,.xyzfiles can be supplied.quick-fuossrequires a working installation ofcctk, which does most of the heavy lifting.TheoryAs the name implies,quick-fuossuses the Fuoss model for modelling association/dissociation of idealized spherical ions in implicit solvent.1This approach is purely Coulombic and neglects any specific ion/ion interactions, as well as inner-sphere solvent effects (e.g. solvent coordination to transition metals).
Nevertheless, these approximations are reasonably satisfied for many common ion pairs.This model has been used to correct pKa values in relatively non-polar solvents: the present implementation is based on that literature.2,3Please note that the current implementation ofquick-fuossonly supports singly charged ions!Usagequick-fuosscan be used starting from either the names of the ions in question (requires Internet access) or.xyzfiles. Some examples are shown below:# Kd for sodium chloride in a solvent with dielectric constant 40
$ python quick_fuoss.py sodium chloride 40

# the same, but at -78 ºC
$ python quick_fuoss.py --temp 195 sodium chloride 40

# Kd of the chloride salt of cation.xyz in a solvent with dielectric constant 80
$ python quick_fuoss.py cation.xyz chloride 80

# Kd of the salt formed by combining cation.xyz and anion.xyz in a solvent with dielectric constant 12
$ python quick_fuoss.py cation.xyz anion.xyz 12TestingThe calculated values are in reasonable agreement with reported values,4as seen below:$ python quick_fuoss.py tetraisoamylammonium nitrate 8.5
Reading ion #1 from rdkit...
Reading ion #2 from rdkit...
Dissociation constant:	0.00004930 M
Ionization energy: 5.873 kcal/mol
$ python quick_fuoss.py tetraisoamylammonium nitrate 11.9
Reading ion #1 from rdkit...
Reading ion #2 from rdkit...
Dissociation constant:	0.00094706 M
Ionization energy: 4.122 kcal/molTo test that the program is working correctly, simply run:$ python test.py
All tests successful! (9 tests run in 14.91 seconds)ReferencesFuoss, R. M. Ionic Association III: The Equilibrium between Ion Pairs and Free Ions.J. Am. Chem. Soc.1958,80, 5059.Abdur-Rashid, K. et al. An Acidity Scale for Phosphorus-Containing Compounds Including Metal Hydrides and Dihydrogen Complexes in THF: Toward the Unification of Acidity Scales.J. Am. Chem. Soc.2000,122, 9155.Paenurk, E. et al. A unified view to Brønsted acidity scales: do we need solvated protons?Chem. Sci.2017,8, 6964.Fuoss, R. M; Kraus, C. A. Properties of Electrolytic Solutions. III. The Dissociation Constant.J. Am. Chem. Soc.1933,55, 1019.Authors:quick-fuosswas written by Corin Wagen (Harvard University). Please emailcwagen@g.harvard.eduwith any questions or bug reports.How to Cite:Wagen, C.C.quick-fuoss2020,www.github.com/corinwagen/quick-fuoss.License:This project is licensed under the Apache License, Version 2.0.  Please seeLICENSEfor full terms and conditions.Copyright 2020 by Corin Wagen