Porphyrin acidity and metal ion coordination revisited: electronic substitution effects
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Macrocycle acidity and Zn2+ ion coordination are reported for three porphyrin derivatives which differ in both steric and electronic substitution effects on the macrocycle π-conjugated system. The role of the electronic substitution effects in the macrocycle deprotonation and metal ion chelating was found to be dominating whereas the macrocycle nonplanar distortions contribute to the acidity and metal chelation rate of the studied porphyrins in less extent. The contributions of both resonance and inductive electronic substitution effects have been distinguished based on the relationship between the weighted sum of resonance and inductive Hammett constants and the acidity and metal ion chelation rate.
KeywordsPorphyrins Acid-base equilibria Substitution effect Molecular orbitals Conformation Metal complexation
The reported study was supported by the grant of the Russian Science Foundation (Project No. 16-53-00100 Bel_а) and the grant of The Foundation of Fundamental Research of the Republic of Belarus (Project No. X16P-097). Prof. Mikalai M. Kruk also acknowledges the Ministry of Higher Education of the Republic of Belarus for continuous support.
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