- Multicomponent assembly of a pyrazine-pillared coordination cage that selectively binds planar guests by intercalation
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A prismlike cage composed of six end-capped PtII ions, two panel-like ligands, and three pyrazine pillars assembles quantitatively through the template effect of a planar aromatic guest (see space-filling structure). The cage thus obtained is stable even when the template is removed. Other large aromatic molecules are also strongly bound and a β-diketone is shown to exist only in a planar enol form in the cage with the keto-enol tautomerization being almost completely suppressed.
- Kumazawa, Kazuhisa,Biradha, Kumar,Kusukawa, Takahiro,Okano, Takashi,Fujita, Makoto
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- Selective Co-Encapsulation Inside an M6L4Cage
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There is broad interest in molecular encapsulation as such systems can be utilized to stabilize guests, facilitate reactions inside a cavity, or give rise to energy-transfer processes in a confined space. Detailed understanding of encapsulation events is required to facilitate functional molecular encapsulation. In this contribution, it is demonstrated that Ir and Rh-Cp-type metal complexes can be encapsulated inside a self-assembled M6L4metallocage only in the presence of an aromatic compound as a second guest. The individual guests are not encapsulated, suggesting that only the pair of guests can fill the void of the cage. Hence, selective co-encapsulation is observed. This principle is demonstrated by co-encapsulation of a variety of combinations of metal complexes and aromatic guests, leading to several ternary complexes. These experiments demonstrate that the efficiency of formation of the ternary complexes depends on the individual components. Moreover, selective exchange of the components is possible, leading to formation of the most favorable complex. Besides the obvious size effect, a charge-transfer interaction may also contribute to this effect. Charge-transfer bands are clearly observed by UV/Vis spectrophotometry. A change in the oxidation potential of the encapsulated electron donor also leads to a shift in the charge-transfer energy bands. As expected, metal complexes with a higher oxidation potential give rise to a higher charge-transfer energy and a larger hypsochromic shift in the UV/Vis spectrum. These subtle energy differences may potentially be used to control the binding and reactivity of the complexes bound in a confined space.
- Leenders, Stefan H. A. M.,Becker, René,Kumpulainen, Tatu,de Bruin, Bas,Sawada, Tomohisa,Kato, Taito,Fujita, Makoto,Reek, Joost N. H.
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supporting information
p. 15468 - 15474
(2016/10/13)
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- Encapsulation of Pt(IV) prodrugs within a Pt(II) cage for drug delivery
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This report presents a novel strategy that facilitates delivery of multiple, specific payloads of Pt(IV) prodrugs using a well-defined supramolecular system. This delivery system comprises a hexanuclear Pt(II) cage that can host four Pt(IV) prodrug guest molecules. Relying on host-guest interactions between adamantyl units tethered to the Pt(IV) molecules and the cage, four prodrugs could be encapsulated within one cage. This host-guest complex, exhibiting a diameter of about 3 nm, has been characterized by detailed NMR spectroscopic measurements. Owing to the high positive charge, this nanostructure exhibits high cellular uptake. Upon entering cells and reacting with biological reductants such as ascorbic acid, the host-guest complex releases cisplatin, which leads to cell cycle arrest and apoptosis. The fully assembled complex displays cytotoxicity comparable to that of cisplatin against a panel of human cancer cell lines, whereas the cage or the Pt(IV) guest alone exhibit lower cytotoxicity. These findings indicate the potential of utilising well-defined supramolecular constructs for the delivery of prodrug molecules.
- Zheng, Yao-Rong,Suntharalingam, Kogularamanan,Johnstone, Timothy C.,Lippard, Stephen J.
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p. 1189 - 1193
(2015/02/19)
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