Demethylenation of Cyclopropanes via Photoinduced Guest‐to‐Host Electron Transfer in an M<sub>6</sub>L<sub>4</sub> Cage

Compartmentalization of the aqueous space within a cell is necessary for life. In similar fashion to the nanometer-scale compartments in living systems, synthetic water-soluble coordination cages (WSCCs) can isolate guest molecules and host chemical transformations. Such cages thus show promise in biological, medical, environmental, and industrial domains. This review highlights examples of three-dimensional synthetic WSCCs, offering perspectives so as to enhance their design and applications. Strategies are presented that address key challenges for the preparation of coordination cages that are soluble and stable in water. The peculiarities of guest binding in aqueous media are examined, highlighting amplified binding in water, changing guest properties, and the recognition of specific molecular targets. The properties of WSCC hosts associated with biomedical applications, and their use as vessels to carry out chemical reactions in water, are also presented. These examples sketch a blueprint for the preparation of new metal–organic containers for use in aqueous solution, as well as guidelines for the engineering of new applications in water.

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“…(b) Example showing demethylenation of 288 via photoinduced guest-to-host electron transfer in cage 6a under UV radiation. 315 …”

Section: Chemistry Within Water-soluble Cagesmentioning

confidence: 99%

Design and Applications of Water-Soluble Coordination Cages

2020

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“…Unimolecular pericyclic reactions can be accelerated because the folding of the guest allows it to bind in the cage cavity, resulting in a conformation that is close to the transition state [15][16][17][18][19]. Catalytic effects based on the electronic properties of the cage have also emerged, with photoinduced electron transfer between components of the cage walls and a bound guest, triggering useful reactions [20][21][22][23]; and an improved artificial 'Diels-Alderase' has been demonstrated, based on the electronic activation of the dienophile component by hydrogen-bonding interactions between the cage and guest, showing substantial rate enhancements without the need for the diene to be co-located in the cavity [24]. Possibilities for cage-based catalysis have been extended by the encapsulation of small-molecule catalysts, from mononuclear organometallic species to polyoxometallates, inside cage cavities [25][26][27]: in these cases, the cage itself is not the catalyst, but it modifies the behaviour of the bound catalyst that operates inside a constricted environment quite different from that in the bulk solution.…”

Section: Introductionmentioning

confidence: 99%

Catalysis of an Aldol Condensation Using a Coordination Cage

et al. 2020

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The aldol condensation of indane-1,3-dione (ID) to give 'bindone' in water is catalysed by an M 8 L 12 cubic coordination cage (H w ). The absolute rate of reaction is slow under weakly acidic conditions (pH 3-4), but in the absence of a catalyst it is undetectable. In water, the binding constant of ID in the cavity of H w is ca. 2.4 (±1.2) × 10 3 M −1 , giving a ∆G for the binding of −19.3 (±1.2) kJ mol −1 . The crystal structure of the complex revealed the presence of two molecules of the guest ID stacked inside the cavity, giving a packing coefficient of 74% as well as another molecule hydrogen-bonded to the cage's exterior surface. We suggest that the catalysis occurs due to the stabilisation of the enolate anion of ID by the 16+ surface of the cage, which also attracts molecules of neutral ID to the surface because of its hydrophobicity. The cage, therefore, brings together neutral ID and its enolate anion via two different interactions to catalyse the reaction, which-as the control experiments show-occurs at the exterior surface of the cage and not inside the cage cavity.

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“…The last two examples demonstrate that hydrophilicity can broaden the scope of applications of metallohelicates. When metallohelicates possess hydrophobic binding pockets similar to supramolecular cages in water [27–33] and capture organic guests, bound species can cooperatively regulate the functions of metallohelicates, such as the helical sense and molecular recognition capabilities, although water‐soluble metallohelicates [17–18] capable of capturing organic guests are limited.…”

Section: Introductionmentioning

confidence: 99%

Calix[4]arene‐Based Triple‐Stranded Metallohelicate in Water

Morie

Sekiya

Haino

2020

Chemistry An Asian Journal

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The title complex is a triple‐stranded metallohelicate organized by the self‐assembly of 5,17‐difunctionalized calix[4]arenes and metal cations with octahedral coordination geometry. Due to hydrophilic triethylene glycol chains on the lower rim of the calix[4]arene, the metallohelicate can encapsulate cationic guests in water. NMR and UV‐vis titration experiments reveal that the metallohelicate captures a pyridinium guest with an alanine derivative to form a host‐guest complex with a host‐guest ratio of 1 : 1. CD spectroscopy confirms the bias of the P‐ and M‐helical sense of the metallohelicate by the captured guest. The metallohelicate captures two molecules of dicationic N,N’‐dimethyl‐DABCO and monocationic N‐methyl quinuclidine, exhibiting a positive allosteric effect. 1H NMR titration experiments indicate that the bound guests are in close proximately to the aromatic rings of the ligands. Molecular mechanics calculations based on the UV‐vis and NMR observations suggest that the first guest preorganizes the conformation of the metallohelicate to facilitate access of the second guest to the cavity.

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Demethylenation of Cyclopropanes via Photoinduced Guest‐to‐Host Electron Transfer in an M₆L₄ Cage

Abstract: This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.

Cited by 95 publications

References 39 publications

Design and Applications of Water-Soluble Coordination Cages

Design and Applications of Water-Soluble Coordination Cages

Catalysis of an Aldol Condensation Using a Coordination Cage

Calix[4]arene‐Based Triple‐Stranded Metallohelicate in Water

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Demethylenation of Cyclopropanes via Photoinduced Guest‐to‐Host Electron Transfer in an M6L4 Cage

Abstract: This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.

Cited by 95 publications

References 39 publications

Design and Applications of Water-Soluble Coordination Cages

Design and Applications of Water-Soluble Coordination Cages

Catalysis of an Aldol Condensation Using a Coordination Cage

Calix[4]arene‐Based Triple‐Stranded Metallohelicate in Water

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Product

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Demethylenation of Cyclopropanes via Photoinduced Guest‐to‐Host Electron Transfer in an M₆L₄ Cage