A cucurbit[8]uril 2:2 complex with a negative pKa shift.

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ID: 2679
2019
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Ranked #72 of 117 articles by views in Chemistry (Weinheim an der Bergstrasse, Germany)

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Abstract
A viologen derivative carrying a benzimidazole group (V-P-I2+) can be dimerized in water using cucurbit[8]uril (CB[8]) in the form of a 2:2 complex resulting in a negative shift of the guest pKa, by more than 1 pH unit, contrasting with the positive pKa shift usually observed for CB-based complexes. While 2:2 complex protonation is unclear by NMR, silver cations have been used for probing the accessibility of the imidazole groups of the 2:2 complexes. The protonation capacity of the buried imidazole groups is reduced, suggesting that CB[8] could trigger proton release upon 2:2 complex formation. The addition of CB[8] to a solution containing V-P-I3+ indeed released protons as monitored by pH-metry and visualized by a coloured indicator. This property was used to induce a host/guest swapping, accompanied by a proton transfer, between V-P-I3+•CB[7] and a CB[8] complex of 1-methyl-4-(4-pyridyl)pyridinium. The origin of this negative pKa shift is proposed to stand in an ideal charge state, and in the position of the two pH-responsive fragments inside the two CB[8] which, alike residues engulfed in proteins, favour the deprotonated form of the guest molecules. Such proton release triggered by a recognition event is reminiscent of several biological processes and may open new avenues toward bioinspired enzyme mimics catalysing proton transfer or chemical reactions.
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yin2019achemistry Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Yin, Hang;Cheng, Qian;Rosas, Roselyne;Viel, Stéphane;Monnier, Valérie;Charles, Laurence;Siri, Didier;Gigmes, Didier;Ouari, Olivier;Wang, Ruibing;Kermagoret, Anthony;Bardelang, David;
Journal Chemistry (Weinheim an der Bergstrasse, Germany)
Year 2019
DOI
10.1002/chem.201902057
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