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Now that the chemistry of 1 : 1 host:guest complexes is well‐established, it is surprising to note that higher stoichiometry (oligomeric) complexes, especially those with excess host, remain largely unexplored. Yet, proteins tend to oligomerize, affording new functions for cell machinery. Here, we show that cucurbit[n]uril (CB[n]) macrocycles combined with symmetric, linear di‐viologens form unusual 3 : 2 host:guest complexes exhibiting remarkable dynamic properties, host self‐sorting, and external ring‐translocation. These results highlight the structural tunability of cucurbit[8]uril (CB[8]) based 3 : 2 host:guest complexes in water and their responsiveness toward several stimuli (chemicals, pH, redox). [ABSTRACT FROM AUTHOR]

Recently, porous organic crystals (POC) based on macrocycles have shown exceptional sorption and separation properties. Yet, the impact of guest presence inside a macrocycle prior to adsorption has not been studied. Here we show that the inclusion of trimethoxybenzyl‐azaphosphatrane in the macrocycle cucurbit[8]uril (CB[8]) affords molecular porous host⋅guest crystals (PHGC‐1) with radically new properties. Unactivated hydrated PHGC‐1 adsorbed iodine spontaneously and selectively at room temperature and atmospheric pressure. The absence of (i) heat for material synthesis, (ii) moisture sensitivity, and (iii) energy‐intensive steps for pore activation are attractive attributes for decreasing the energy costs. 1H NMR and DOSY were instrumental for monitoring the H2O/I2 exchange. PHGC‐1 crystals are non‐centrosymmetric and I2‐doped crystals showed markedly different second harmonic generation (SHG), which suggests that iodine doping could be used to modulate the non‐linear optical properties of porous organic crystals. [ABSTRACT FROM AUTHOR]

The globular and monocationic guest molecule trimethyl‐azaphosphatrane (AZAP, a protonated Verkade superbase) was shown to form a host:guest 1 : 1 complex with the cucurbit[10]uril (CB[10]) macrocycle in water. Molecular dynamics calculations showed that CB[10] adopts an 8‐shape with AZAP occupying the majority of the internal space, CB[10] contracting around AZAP and leaving a significant part of the cavity unoccupied. This residual space was used to co‐include planar and monocationic co‐guest (CG) molecules, affording heteroternary CB[10]⋅AZAP⋅CG complexes potentially opening new perspectives in supramolecular chemistry. [ABSTRACT FROM AUTHOR]

A viologen derivative carrying a benzimidazole group (V‐P‐I 2+; viologen–phenylene–imidazole V‐P‐I) 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. Whereas 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‐I 3+⋅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 catalyzing proton transfer or chemical reactions. [ABSTRACT FROM AUTHOR]

Keywords: 2:2 complexes; cucurbituril; host-guest systems; imidazoles; viologen By CB[8] macrocycles made it possible to produce 2:2 host:guest complexes, releasing protons initially trapped on the guests, in a manner similar to the proton release observed in biology and operating through cascade supramolecular events. 2:2 complexes, cucurbituril, host-guest systems, imidazoles, viologen. [Extracted from the article]