Triangular Regulation of Cucurbit[8]uril 1:1 Complexes

Combes, Sébastien; Tran, Khoa Truong; Ayhan, Mehmet Menaf; Karoui, Hakim; Rockenbauer, Antal; Tonetto, Alain; Monnier, Valérie; Charles, Laurence; Rosas, Roselyne; Viel, Stéphane; Siri, Didier; Tordo, Paul; Clair, Sylvain; Wang, Ruibing; Bardelang, David; Ouari, Olivier

doi:10.1021/jacs.9b00150

Cited by 23 publications

(28 citation statements)

References 99 publications

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“…The association of TEMPONE with CB [7] is typical of the "general case" we have frequently observed for which the nitrogen coupling constant is reduced as a result of the nitroxide bond experiencing a more hydrophobic surrounding. We observed this behavior for a variety of nitroxides in the presence of several types of cyclodextrins [43][44][45] and of cucurbiturils [28,31,39]. Besides kinetic [46] and thermodynamic [47] parameters, which can sometimes be extracted from EPR experiments, binding constants are important parameters to assess the affinity of a guest for a host.…”

Section: Discussionmentioning

confidence: 81%

“…However, simulated EPR spectra at high CB [7] concentrations showed better agreement with experimental ones when a 2:1 complex was considered (with two CB [7]). Previous reports mentioned the possibility for cucurbiturils to aggregate in water [28][29][30][31][36][37][38][39][40], but there is only a slight improvement in the agreement between simulated spectra and experimental ones (regression coefficient of 0.9955) assuming this model; other techniques would be necessary to confirm this possibility. As mentioned above, a decrease in a N was associated with a more hydrophobic surrounding for the nitroxide group, while the observed decrease in a C also indicated a redistribution of spin densities on the corresponding ring, together with a probable freeze in dihedral angles due to the inclusion.…”

Section: Complexation Between Tempone and Cb[7]mentioning

confidence: 81%

“…However, significant differences were found for the complexed TEMPO group. First, a decrease in a N of 0.34 G was observed, typical of a nitroxide inclusion in CB [8] with the N-O• bond relatively bulk exposed [31]. Then, while the α value increased by~50%, β and γ were multiplied by a factor of~5, suggesting a tumbling on this side, largely different from the uncomplexed side.…”

Section: Complexation Between Btbk and Cb[8]mentioning

confidence: 98%

“…EPR spectroscopy was key in this finding since it gave a clear spectral signature of the triangular assembly that could hardly be found by other techniques. We recently showed that, provided the guest possesses the right structure, diamagnetic triangles of CB [8] could also be produced and hence studied by NMR [31]. Since CB[n] are almost exclusively soluble in water, nitroxide guest recognition is monitored using EPR by comparing the spectrum of the radical alone to that in the presence of the host in aqueous solutions.…”

Section: Introductionmentioning

confidence: 99%

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EPR Spectroscopy: A Powerful Tool to Analyze Supramolecular Host•Guest Complexes of Stable Radicals with Cucurbiturils

et al. 2020

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Stable organic free radicals are increasingly studied compounds due to the multiple and unusual properties imparted by the single electron(s). However, being paramagnetic, classical methods such as NMR spectroscopy can hardly be used due to relaxation and line broadening effects. EPR spectroscopy is thus better suited to get information about the immediate surroundings of the single electrons. EPR has enabled obtaining useful data in the context of host•guest chemistry, and a classical example is reported here for the stable (2,2,6,6-tetramethyl-4-oxo-piperidin-1-yl)oxyl or 4-oxo-TEMPO nitroxide (TEMPONE) inside the macrocycle host cucurbit [7]uril (CB[7]). Generally and also observed here, a contraction of the spectrum is observed as a result of the reduced nitrogen coupling constant due to inclusion complexation in the hydrophobic cavity of the host. Simulations of EPR spectra allowed determining the corresponding binding constant pointing to a weaker affinity for CB [7], compared to TEMPO with CB [7]. We complement this work by the results of EPR spectroscopy of a biradical: bis-TEMPO-bis-ketal (bTbk) with cucurbit[8]uril (CB[8]). Initial investigations pointed to very weak effects on the spectrum of the guest and incorrectly led us to conclude an absence of binding. However, simulations of EPR spectra combined with NMR data of reduced bTbk allowed showing inclusion complexation. EPR titrations were performed, and the corresponding binding constant was determined. 1 H NMR spectra with reduced bTbk suggested a shuttle mechanism, at nearly one equivalent of CB[8], for which the host moves rapidly between two stations.Molecules 2020, 25, 776 2 of 10 wealth of information, which, correctly extracted, can give users access to crucial information such as stability, structure, or dynamics, in various liquid or solid environments [8]. Supramolecular chemistry principally features diamagnetic compounds, but paramagnetic ones are expected to enable access to new types of applications including molecular magnetic switches [9], dynamic covalent systems [10], or tracers for imaging by stabilizing free radicals in reducing conditions. In the context of host•guest chemistry, the guests are almost exclusively [11] the radicals, and they are included in macrocyclic hosts. Several reviews [12][13][14] have already documented host•guest complexes featuring free radicals and several families of hosts including calixarenes, cyclodextrins, and cucurbiturils. This latter family of pumpkin-shape macrocycles [15][16][17][18][19] possess unique properties, in a broader context, such as ultrahigh binding [20,21], gas adsorption [22], or drug encapsulation and release [23,24]. With cucurbit[n]urils (CB[n]), the main radicals studied are nitroxides [25], in the majority of cases stable ones. In a seminal work, Lucarini and coworkers studied the cucurbit [7]uril (CB[7]) cavity by EPR spectroscopy using several nitroxides [26]. Later, Kaifer and coworkers showed how CB[n] could modulate the extent of spin exchange between covalently linked ...

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Section: Discussionmentioning

confidence: 81%

Section: Complexation Between Tempone and Cb[7]mentioning

confidence: 81%

Section: Complexation Between Btbk and Cb[8]mentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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EPR Spectroscopy: A Powerful Tool to Analyze Supramolecular Host•Guest Complexes of Stable Radicals with Cucurbiturils

et al. 2020

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“…3:3equilibrium (a), shifted to the triangular assemblyw ith Na + cations and reticulation (b) by ad itopic guest. [34] Angewandte Chemie Kurzaufsätze 21472 www.angewandte.de case due to the size of its cavity,CB [10] could in principle be used to get linear 3:3a ssemblies with appropriate guests. Finally,w ith the right ditopic guest, cucurbituril and metal ion, the groups of Kim [90] and Isaacs [91] could isolate triangular 3:3:3ors quare 4:4:4m olecular necklaces ( Figure 16).…”

Section: General Trends About 2:2c Omplexesmentioning

confidence: 99%

Oligomeric Cucurbituril Complexes: from Peculiar Assemblies to Emerging Applications

et al. 2020

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Proteins are an endless source of inspiration. By carefully tuning the amino‐acid sequence of proteins, nature made them evolve from primary to quaternary structures, a property specific to protein oligomers and often crucial to accomplish their function. On the other hand, the synthetic macrocycles cucurbiturils (CBs) have shown outstanding recognition properties in water, and a growing number of (host)n:(guest)n supramolecular polymers involving CBs have been reported. However, the burgeoning field of discrete (n:n) host:guest oligomers has just started to attract attention. While 2:2 complexes are the major oligomers, 3:3 and up to 6:6 oligomers have been described, some associated with emerging applications, specific to the (n:n) arrangements. Design rules to target (n:n) host:guest oligomers are proposed toward new advanced host:guest systems.

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Small Molecule NIR‐II Dyes for Switchable Photoluminescence via Host –Guest Complexation and Supramolecular Assembly with Carbon Dots

et al. 2022

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Small molecular NIR‐II dyes are highly desirable for various biomedical applications. However, NIR‐II probes are still limited due to the complex synthetic processes and inadequate availability of fluorescent core. Herein, the design and synthesis of three small molecular NIR‐II dyes are reported. These dyes can be excited at 850–915 nm and emitted at 1280–1290 nm with a large stokes shift (≈375 nm). Experimental and computational results indicate a 2:1 preferable host–guest assembly between the cucurbit[8]uril (CB) and dye molecules. Interestingly, the dyes when self‐assembled in presence of CB leads to the formation of nanocubes (≈200 nm) and exhibits marked enhancement in fluorescence emission intensity (Switch‐On). However, the addition of red carbon dots (rCDots, ≈10 nm) quenches the fluorescence of these host–guest complexes (Switch‐Off) providing flexibility in the user‐defined tuning of photoluminescence. The turn‐ON complex found to have comparable quantum yield to the commercially available near‐infrared fluorophore, IR‐26. The aqueous dispersibility, cellular and blood compatibility, and NIR‐II bioimaging capability of the inclusion complexes is also explored. Thus, a switchable fluorescence behavior, driven by host–guest complexation and supramolecular self‐assembly, is demonstrated here for three new NIR‐II dyes.

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Triangular Regulation of Cucurbit[8]uril 1:1 Complexes

Cited by 23 publications

References 99 publications

EPR Spectroscopy: A Powerful Tool to Analyze Supramolecular Host•Guest Complexes of Stable Radicals with Cucurbiturils

EPR Spectroscopy: A Powerful Tool to Analyze Supramolecular Host•Guest Complexes of Stable Radicals with Cucurbiturils

Oligomeric Cucurbituril Complexes: from Peculiar Assemblies to Emerging Applications

Small Molecule NIR‐II Dyes for Switchable Photoluminescence via Host –Guest Complexation and Supramolecular Assembly with Carbon Dots

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