Calix[4]tubes:  A New Class of Potassium-Selective Ionophore

Abstract

A new class of cryptand-like ionophore based on a bis calix[4]arene structure has been developed. These molecules proved highly selective for complexation of potassium over all group I metal cations and barium. A range of symmetric and asymmetric calix[4]tubes featuring either alkyl or phenyl substituents at the upper rim have been synthesized in exceptional yield. Alteration of the calix[4]arene upper rim environment enables fine-tuning of the rate of potassium uptake, which can be evaluated through the conformational change on binding by NMR studies. Selectivity of potassium complexation has been demonstrated using NMR and electrospray mass spectral techniques. Molecular modeling studies, derived from crystallographic data, confirm that the potassium metal cation is complexed via the axial route, passing through the calix[4]arene annulus, and provide evidence for complexation rate and selectivity.

Stable and sensitive probes for lysosomes: Cell‐penetrating fluorescent calix[4]arenes accumulate in acidic vesicles

“…We recently demonstrated that fluorescently labeled calix [4]arene have the potential to track progress of the macrocycle in cells, as an NBD labeled cationic derivative was readily and speedily taken up into cells and provided a very stable, nontoxic read-out system to investigate cellular localization (20). The absorbance and emission spectra for the NBDCalAm showed that it can easily be visualized using a GFP filter (20).…”

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AbstractThe uptake of a fluorescently labeled cationic calix [4] (NBDCalAm) in live, nonfixed cells has been investigated. The compound is taken into the cells rapidly and shows distinct endosomal distribution after 2 hours.

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“…In particular the ability of derivatives to complex anions (2,3) and cations (4,5) has been exploited for the development of sensors. Recently, interest has focused on the use of calixarene derivatives in biological systems be it as drugs, drug delivery systems, or imaging agents.…”

“…In the design of drug molecules, particular attention has been paid to calixarenes as antimicrobials (6)(7)(8), as vaccines (9) and as anticancer agents (10). In the field of drug delivery, agents for nucleic acids based on single calixarenes (11)(12)(13) have shown promise and we have recently shown that larger arrays of cationic calix [4]arene, so-called multicalixarenes, are able to transfect DNA effectively (14). In addition a number of studies have combined the ability of calixarene derivatives to complex cations with their low toxicity in the development of noncovalently labeled protein MRI imaging agents (15,16).…”

“…Thus, the preparation of fluorescent derivatives of calix [4]arenes provides useful information for researchers developing calix [4]arenes as drugs and as drug delivery systems on how these derivatives interact with the cell surface and on their internalization methods. In addition, these labeled molecules, themselves offer potential as stains of intracellular processes…”