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A photoswitchable strapped calix[4]pyrrole receptor: highly effective chloride binding and release.

ABSTRACT: A stiff-stilbene strapped calix[4]pyrrole receptor can be reversibly switched by light between a strong chloride-binding Z-isomer and a very weakly binding E-isomer. The light-induced switching process is monitored by UV-Vis and ¹H NMR spectroscopy and chloride binding is studied in detail using both ¹H NMR and ITC titrations in DMSO and MeCN. In DMSO, at millimolar concentrations, switching from a fully bound to an almost fully unbound state can be triggered. Quantification of the binding constants in MeCN reveals an extraordinary 8000-fold affinity difference between the Z- and E-isomer. Single crystal X-ray crystallographic analysis gives insight into the structure of the photogenerated E-isomer and the geometry of the chloride-bound receptors is optimized by DFT calculations. The highly effective control of binding affinity demonstrated in this work opens up new prospects for on demand binding and release in extractions and photocontrol of membrane transport processes, among other applications.

SUBMITTER: Villaron D

PROVIDER: S-EPMC8179391 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Photoswitching of halide-binding affinity and selectivity in dithienylethene-strapped calix[4]pyrrole.

Project description:Dithienylethene-strapped calix[4]pyrrole is isomerized by 300/630 nm light between ring-open and -closed isomers, which affects the size of the anion binding site. Where for chloride this results in only a small change in affinity, that of the larger bromide and iodide ions is majorly affected, resulting in altered selectivity.

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Cesium Halide Ion Pair Recognition by a Pyrrole Strapped Calix[4]pyrrole.

Project description:The binding properties of the pyrrole-strapped calix[4]pyrrole 2 for cesium halide ion pairs were studied via 1H NMR spectroscopic and single crystal X-ray diffraction analyses. Receptor 2 was found to bind CsF, CsCl, and CsBr in the solid state and in chloroform/methanol (4/1, v/v) solution with relatively high affinity as compared with the parent calix[4]pyrrole 1. It was also revealed by solid-liquid extraction experiments that receptor 2 was capable of solubilizing CsF in CDCl3, a medium in which this salt is otherwise insoluble. Single crystal X-ray diffraction analyses and 1H NMR spectroscopic data recorded in 20% CD3OD in CDCl3 provide support for the suggestion that the strap pyrrolic NH proton of 2, as well as those of the calix[4]pyrrole framework, contribute to anion recognition, thus increasing affinity for cesium halide salts relative to the parent system 1. In the solid state, receptor 2 interacts with CsF to form a two dimensional coordination polymer in the presence of methanol. A linear coordination polymer is observed in the case of CsCl and CsBr. Receptor 2 was also found to form a complex with CsF in chloroform/methanol (4/1, v/v) solution, albeit with a different binding mode than is seen in the solid state.

| S-EPMC7286541 | biostudies-literature

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| S-EPMC2861354 | biostudies-literature

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4-Meth-oxy-benzoyl-meso-octa-methyl-calix[2]pyrrolidino[2]pyrrole: an acyl chloride derivative of a partially reduced calix[4]pyrrole.

Project description:In the title compound, C(36)H(50)N(4)O(2), the two pyrrolidine rings have envelope conformations. The conformation of the macrocycle is stabilized by N-H⋯N hydrogen bonds and a C-H⋯N inter-action. The benzoyl ring is inclined to an adjacent pyrrole ring by 6.76 (9)°, with a centroid-to-centroid distance of 3.6285 (10) Å. In the crystal, apart from a C-H⋯O and a C-H⋯π inter-action, mol-ecules are linked via an N-H⋯O hydrogen bond, leading to the formation of helical chains propagating along [010].

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Project description:In order to understand the still-poorly understood interplay between calix[4]arene conformations and cation and anion recognition in multicomponent systems, the ion pair receptors 1 and 2 were synthesized. In solution and in the solid state, the calix[4]arene subunit of receptor 1 adopts a cone conformation, while that of 2 interconverts between the cone and the partial cone conformation. These geometric features differ from previous systems where the calix[4]arene moiety was locked in the 1,3-alternate conformation. A combination of 1H NMR spectroscopic analyses and single crystal X-ray diffraction studies reveal that receptor 1 binds the fluoride and the chloride anion via significantly different binding modes, displaying, for instance, 1 : 1 and 2 : 3 binding stoichiometries with CsF and CsCl, respectively. In the case of 2, the conformation of the calix[4]arene constituent of 2 is highly dependent on the size and quantity of anions present. For example, upon treatment of 2 with the fluoride anion (as both the TBA+ and Cs+ salts), the calix[4]arene unit coexists as cone and partial cone conformers that are inter-convertible. In the presence of excess CsF, the aromatic rings of the calix[4]arene subunit becomes locked in the pinched cone conformation with the result that an ion pair-mediated coordination polymer is formed. In the presence of excess CsCl, the calix[4]arene unit of 2 adopts only the partial cone conformation stabilized by aryl CH-anion hydrogen bonding interactions. The present systems constitute a rare set of related receptors wherein the effects of conformational changes are so tightly coupled with ion recognition.

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| S-EPMC3134555 | biostudies-literature

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