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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]

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]

Among a series of metal ions in water, silver is the only one to remotely and reversibly switch cucurbit[7]uril (CB[7]) movements (translocation or uptake) on a rigid and linear three-station viologen–phenylene–imidazole (V–P–I) derivative, avoiding undesired pH actuation. 1H NMR, UV–vis spectroscopy, mass spectrometry, ITC, and modeling were combined to show that ring translocation or uptake along a molecular thread is possible in water by Ag+ as a metal stimulus. [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]

Abstract: New highly sensitive pH probes for 31P NMR spectroscopy. Spin-lattice relaxation time measurements as a function of molecular structure, temperature, pH, and biological medium. New uncharged α-aminophosphonates derived from diethyl(2-methylpyrrolidin-2-yl) phosphonate were synthesized by nucleophilic addition of dialkylphosphites on 2-methyl-1-pyrroline. These compounds were intended as enhanced 31P-NMR pH probes in biological systems. Compared to standard pH markers such as inorganic phosphate or methylphosphonate, they demonstrated in vitro low acidic pK a values (6.6

We report here the development of a rotating molecular switch based on metal-catalyzed reversible (de)-hydrogenation. Under an argon atmosphere, acceptorless dehydrogenation induces a switch from an alcohol to a ketone, while reversing to a hydrogen pressure switches back the system to the alcohol. Based on a tolane scaffold, such reversible (de)-hydrogenation enables 180° rotation. The absence of waste accumulation in a switch relying on chemical stimuli is of great significance and could potentially be applied to the design of efficient complex molecular machines., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

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., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

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 pK a , by more than 1 pH unit, contrasting with the positive pK a 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- I 3+ 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 pK a 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., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Twenty novel beta-secretase inhibitors containing biarylpiperazine moieties belonging to naphthyl and coumarinyl series were designed for their potential use in Alzheimer's disease therapy. Enzymatic and cell-based assays have been carried out. The biological results clearly demonstrate that specific substituents located at the N(4)-position of the piperazine ring result in excellent in vitro inhibitory potency (IC(50) values ranging between 40 and 70 nM). Variable temperature NMR and modeling studies are consistent with the obtained biological data, since these studies confirmed that introduction at the N(4)-position of the piperazine ring allows productive interactions within the BACE-1 active site, which appear to be determinative for high BACE-1 inhibitory activity. These results are of particular interest since some of the new analogues belonging to the naphthyl series are almost one log more active than the best inhibitor of the similar family recently reported.