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. 2019 Mar 1;10:989. doi: 10.1038/s41467-019-08953-0

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — Mechanism of H₂O-resistant ¹⁸F/¹⁹F exchange interpreted by free energy parameters. Geometries are optimized at the B3LYP/6-31+G* level of theory, and single point calculations are performed at the CAM-B3LYP/6-311++G** level of theory. Two substituent groups on the phosphorus center are simplified as two large spheres in the molecular structures for clarity. a Reaction pathways and free energy (kcal mol⁻¹) profiles for the F/F isotope exchange process of five selected reactant systems. b Reaction pathways and free energy (kcal mol⁻¹) profiles for the OH/F exchange process of the same five selected reactant systems