Arylethynyl receptors for neutral molecules and anions: emerging applications in cellular imaging

Abstract

This critical review will focus on the application of shape-persistent receptors for anions that derive their rigidity and optoelectronic properties from the inclusion of arylethynyl linkages. It will highlight a few of the design strategies involved in engineering selective and sensitive fluorescent probes and how arylacetylenes can offer a design pathway to some of the more desirable properties of a selective sensor. Additionally, knowledge gained in the study of these receptors in organic media often leads to improved receptor design and the production of chromogenic and fluorogenic probes capable of detecting specific substrates among the multitude of ions present in biological systems. In this ocean of potential targets exists a large number of geometrically distinct anions, which present their own problems to the design of receptors with complementary binding for each preferred coordination geometry. Our interest in targeting charged substrates, specifically how previous work on receptors for cations or neutral guests can be adapted to anions, will be addressed. Additionally, we will focus on the design and development of supramolecular arylethynyl systems, their shape-persistence and fluorogenic or chromogenic optoelectronic responses to complexation. We will also examine briefly how the “chemistry in the cuvet” translates into biological media.

Binding studies of cucurbit[7]uril with gold nanoparticles bearing different surface functionalities

“…1–5 Molecular recognition, 6, 7 self-assembly, 8 lock-key modality 9 and reversibility 10 are among the most important features that enable supramolecular chemistry to be employed in many applications including catalysis, 11, 12 delivery, 13, 14 sensing, 15–17 and imaging. 18 These applications use building blocks assembled together by intermolecular interactions including electrostatic interactions, 19 hydrogen bonding, 20 π–π interactions, 21 ion-dipole interactions, 22, 23 hydrophobic or solvophobic effects. 24 …”

Synthesis and optoelectronic properties of 2,6-bis(2-anilinoethynyl)pyridine scaffolds

“…The simple derivatization of this class of receptors allows for a “turn-on” fluorescence response to analytes in increasingly polar solvents, a feature often lacking in small molecule organic anion probes. 24 …”

“…), 25–27 have been exploited for applications such as liquid crystals, 28 lightemitting materials, 29 rotaxane-type structures, 30 molecular magnets, 31 antiangiogenic activity, 32 polymer composites 33 and coordination complexes. 24,34,35 In contrast, the supramolecular chemistry of 2,6-bis(arylethynyl)pyridines has received little attention, perhaps in part due to the scarcity of uniting the fields of molecule/ion recognition with the synthesis of highly-conjugated, carbon-rich materials. Most of the host/guest studies reported have focused on exploiting the pyridine lone pair to bind metal ions 22 or organoiodides.…”

Ion and Molecular Recognition Using Aryl–Ethynyl Scaffolding

“…We have previously described a series of both bis(-sulfonamido)- and bis(urea)ethynylpyridines that exhibit positive fluorescent responses to anions with the right combination of electron-donating and/or electron-withdrawing substituents on the pendant phenyl rings. [4, 25–29, 77] The bis-ureas (e.g., 25 – 28 , Figure 17) exhibit a rich solvent-based conformational dependence, showing in the solid state that “S”-, “U”- and “W”-type conformations are all possible depending on solvent guests (for instance, “S” shown in 28 , “U” shown in 25 – 27 ). [27] …”

“…[3] Alternatively, inclusion of an alkyne linkage between aryl groups has been utilized within synthetic molecular hosts, both for its ability to directly connect two units by an essentially inflexible spacer, and for the electronic conjugation it enables between the two aryl units. [4] …”