1. Tetracationic-to-dianionic tetraamino-dihydroxy-tetraoxacalix[4]arene: A paraquat receptor for all seasons.
- Author
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Mancuso, Francesca, Crisafulli, Daniele, Milone, Marco, Irto, Anna, Cigala, Rosalia Maria, Lando, Gabriele, Pisagatti, Ilenia, Notti, Anna, and Gattuso, Giuseppe
- Subjects
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PARAQUAT , *PROTONATION constants , *STABILITY constants , *BINDING constant , *PROTON transfer reactions - Abstract
[Display omitted] • • Two novel water-soluble, proton-ionizable, isomeric tetraamino-dihydroxy-tetraoxacalix[4]arene were synthesized. • • Six protonation constants were determined, and the distribution diagrams for the seven protonated species were calculated. • • The phloroglucinol-derived oxacalix[4]arene 1 ·H 2 was successfully employed to complex paraquat both at low and high pH. • • Combination of protonation and apparent binding constants gave association constants for the differently-charged complexes. Tetraamino-dihydroxy-oxacalix[4]arenes 1 ·H 6 4+·4Cl– and 2 ·H 6 4+·4Cl– were synthesized in two steps from off-the-shelf components, and subjected to in-depth investigations on their molecular and supramolecular properties. UV–Vis titrations with aqueous NaOH provided six discrete protonation constants along with the distribution diagram for each of the oxacalixarenes, while a 1H NMR titration of 1 ·H 6 4+·4Cl– with NaOD (aq) , combined with DFT (B3LYP/6–311++G(d,p)) calculations allowed to shed light on the conformational preferences of macrocycle 1 ·H n (n–2)+ in the different protonation states. 1H NMR titrations with N , N ′-dimethyl-4,4′-bipyridinium (paraquat) dichloride gave, at different pH values, apparent association constants (K app) for the formation of the host–guest complexes. K app values, combined with the protonation constants, in turn provided the stability constant for the individual complexes between paraquat and 1 ·H n (n–2)+ in the different states of ionization, and allowed to identify 1 ·H– as the most efficient paraquat receptor. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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