Prototropic tautomerism of imidazolone in aqueous solution: a density functional approach using the combined discrete/self-consistent reaction field (SCRF) models |
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Authors: | Yi Ren Ming Li Ning-Bew Wong |
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Affiliation: | (1) School of chemistry of chemical engineering, Southwest China Normal University, Chongqing, 400715, Peoples Republic of China;(2) College of Chemistry, Sichuan University, Chengdu, 610064, Peoples Republic of China;(3) Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong |
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Abstract: | A systematic investigation of the proton transfer in the keto-amino/enol tautomerization of imidazolone was undertaken. Calculations in aqueous solution were performed using both combined discrete/self-consistent reaction field (SCRF) and SCRF methods. Complexes containing one to three water molecules around the hydrophilic site of imidazolone were used for the combined discrete/SCRF calculations. The DFT results predict that the barrier height for non-water-assisted intramolecular proton transfer is very high (214.8 kJmol–1). Hydrogen bonding between imidazolone and the water molecule(s) will dramatically lower the barrier by a concerted multiple proton transfer mechanism. The proton transfer process through a eight-member ring formed by imidazolone and two water molecules is found to be more efficient and the calculated barrier height is ca. 61 kJmol–1.Figure DFT calculations in aqueous solution predict the H-bonding between imidazolone(IZ) and the water molecule(s) will dramatically lower the tautomeric barrier by a concerted multiple proton transfer mechanism, in which an eight-member ring structure formed by IZ and 2H2O is found to be more efficient and the barrier is 60.8 kJ mol–1, much less than 214.8 kJ mol–1 in the non-water-assisted mechanism. |
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Keywords: | Density functional theory Imidazolone Tautomerism Water-assisted proton transfer |
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