Microhydration and the Enhanced Acidity of Free Radicals

• Main Author: John C. Walton
• Format: Article
• Language: English
• Published: MDPI AG 2018-02-01
• Series: Molecules
• Subjects: free radicals; acidity; DFT computations; hydration
• Online Access: http://www.mdpi.com/1420-3049/23/2/423

Recent theoretical research employing a continuum solvent model predicted that radical centers would enhance the acidity (RED-shift) of certain proton-donor molecules. Microhydration studies employing a DFT method are reported here with the aim of establishing the effect of the solvent micro-structure on the acidity of radicals with and without RED-shifts. Microhydration cluster structures were obtained for carboxyl, carboxy-ethynyl, carboxy-methyl, and hydroperoxyl radicals. The numbers of water molecules needed to induce spontaneous ionization were determined. The hydration clusters formed primarily round the CO2 units of the carboxylate-containing radicals. Only 4 or 5 water molecules were needed to induce ionization of carboxyl and carboxy-ethynyl radicals, thus corroborating their large RED-shifts.