Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers

F. J. Torres, V. Ochoa-Herrera, Paul Blowers, Maria Reye Sierra Alvarez

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its trifluoromethyl-branched isomers (i.e. 1-CF3- to 6-CF3-PFOS) were theoretically studied by means of ab initio density functional theory (DFT) calculations with the B3LYP functional and a 6-31++G(d,p) basis set. The anionic form of linear PFOS and its trifluromethyl-branched isomers were considered for the initial construction of the computational models; subsequently, H+, Li+, and Na+ were added as counter-ions to study their effect on the properties under investigation. Insignificant changes with respect to the anions were observed in the structure of both the protonated and salt forms due to the presence of these counter-ions. However, important differences in the electrostatic potential maps as well as HOMO and LUMO molecular orbitals were observed for the various forms of PFOS. The linear and branched PFOS ions were identified as the most suitable compounds for interacting with charged species. Furthermore, in the linear anion, it was observed that the LUMO orbital is diffused along the whole fluoro-carbon chain, whereas it is localized to the region close to the ternary carbon in the 4-CF3-PFOS, 5-CF3-PFOS, and 6-CF3-PFOS isomers. The higher accessibility of the LUMO orbital in these branched anions suggests that they have a higher probability of reacting with free radicals when compared with the linear counterpart. This behavior is reflected in the experimental observation that only the branched PFOS isomers were susceptible to reductive defluorination by reduced vitamin B12 as we previously reported. The relative stability of the linear and branched PFOS in their different forms computed by comparing their calculated Gibbs free energy showed that 1-CF3-, 6-CF3-, and linear PFOS are the most favorable structures from a thermodynamic point of view.

Original languageEnglish (US)
Pages (from-to)1143-1149
Number of pages7
JournalChemosphere
Volume76
Issue number8
DOIs
StatePublished - Aug 2009

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thermodynamic property
sulfonate
Thermodynamics
Isomers
Electronic properties
Structural properties
Thermodynamic properties
Negative ions
Radiation counters
Carbon
Vitamins
Molecular orbitals
Gibbs free energy
Free radicals
Anions
anion
Density functional theory
Electrostatics
Ions
Salts

Keywords

  • Ab initio
  • Branched isomers
  • DFT
  • PFOS

ASJC Scopus subject areas

  • Environmental Chemistry
  • Chemistry(all)

Cite this

Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers. / Torres, F. J.; Ochoa-Herrera, V.; Blowers, Paul; Sierra Alvarez, Maria Reye.

In: Chemosphere, Vol. 76, No. 8, 08.2009, p. 1143-1149.

Research output: Contribution to journalArticle

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