Optical sensing of anions by macrocyclic and interlocked hosts

This review summarises recent developments in the use of macrocyclic and mechanically-interlocked host molecules as optical sensors for anions.

Exploiting 1,4-naphthoquinone and 3-iodo-1,4-naphthoquinone motifs as anion binding sites by hydrogen or halogen-bonding interactions

We describe here the utilization of 1,4-naphthoquinone and 3-iodo-1,4-naphthoquinone motifs as new anion binding sites by hydrogen- or halogen-bonding interactions, respectively. These binding sites have been integrated in bidentate ester based receptors. Emission experiments reveal that both receptors selectively recognize sulfate anions, which induced a remarkable increase of a new emission band attributed to the formation of π-stacking interactions between two 1,4-naphthoquinone units. Absorption spectroscopy and mass spectrometry indicate the disruption of the ester group of the 1,4-naphthoquinone based receptor in the presence of HP₂O₇^3-, H₂PO₄^-, F^-, AcO^- and C₆H₅CO₂^- and in the halogenated receptor with HP₂O₇^3-, F^- and AcO^- anions, while the presence of sulfate anions showed the clasical complexation behaviour. The ¹H-NMR experiment showed a slow exchange process of the receptors with their sulfate complexes. The binding mode of the receptors with sulfate has been studied by DFT calculations along with the Molecular Electrostatic Potential (MEP) surface computational tool that reveals those parts of the receptors which are more suitable for interacting with anions.

Anion-Binding-Induced Electrochemical Signal Transduction in Ferrocenylimidazolium: Combined Electrochemical Experimental and Theoretical Investigation

Five ferrocene alkymethylimidazolium cations 1a⁻1d and 2 with different alkyl spacer lengths were reinvestigated using voltammetry and density functional theory (DFT) calculations. The voltammetric responses of ligand 2 toward various anions are described in detail. An interesting and unprecedented finding from both experimental and theoretical studies is that coupled electron and intramolecular anion (F^-) transfer may be present in these molecules. In addition, it was also observed that, in these studied molecules, the electrostatic attraction interaction toward F^- would effectively vanish beyond 1 nm, which was previously reported only for cations.

Synthetic methodology for asymmetric ferrocene derived bio-conjugate systems via solid phase resin-based methodology

Early detection is a key to successful treatment of most diseases, and is particularly imperative for the diagnosis and treatment of many types of cancer. The most common techniques utilized are imaging modalities such as Magnetic Resonance Imaging (MRI), Positron Emission Topography (PET), and Computed Topography (CT) and are optimal for understanding the physical structure of the disease but can only be performed once every four to six weeks due to the use of imaging agents and overall cost. With this in mind, the development of "point of care" techniques, such as biosensors, which evaluate the stage of disease and/or efficacy of treatment in the clinician's office and do so in a timely manner, would revolutionize treatment protocols.1 As a means to exploring ferrocene based biosensors for the detection of biologically relevant molecules2, methods were developed to produce ferrocene-biotin bio-conjugates described herein. This report will focus on a biotin-ferrocene-cysteine system that can be immobilized on a gold surface.

A case of oxoanion recognition based on combined cationic and neutral C–H hydrogen bond interactions

A bidentate bis-(benzimidazolium) receptor containing pyrene as fluorescent signaling units recognizes sulphate and hydrogenpyrophosphate in a competitive water–DMSO medium through combinations of cationic and neutral C–H hydrogen bonding.

Synthesis and anion sensing of water-soluble metallomacrocycles

The self-assembly of (TMEDA)Pd(NO(3))(2) or (TMEDA)Pt(NO(3))(2) (where TMEDA = N(1),N(1),N(2),N(2)-tetramethylethane-1,2-diamine) and anthracene- or ferrocene-based diimidazole ligands (L(1-3)) in aqueous solution affords a series of positively charged [M(2)L(2)](4+) dimetallomacrocycles. Their structures were characterized by (1)H NMR and electrospray ionization mass spectrometry and in the cases of {[(TMEDA)Pd](2)L(1)(2)}(NO(3))(4) (1), {[(TMEDA)Pd](2)L(1)(2)}(PF(6))(4) (1a), and {[(TMEDA)Pd](2)L(3)(2)}(NO(3))(4) (4) by single-crystal X-ray diffraction analysis. Interestingly, the NMR spectra of 1 and 1a revealed that the difference of their structures, as confirmed by X-ray diffraction analysis, was that a NO(3)(-) of 1 was encapsulated inside the cavity of the basket-shaped metallomacrocycle by C-H···O hydrogen bonds, while PF(6)(-) of 1a was bound outside by C-H···F hydrogen bonds. The fluorescence titration experiment exhibited the formation of 1:1 host-guest complexation for anthracene-based positively charged [M(2)L(2)](4+)-type metallomacrocycles with NO(3)(-). The interactions between metallomacrocycles and various anions were investigated via fluorescence titration and cyclic voltammetry studies, respectively.

Chloride anion triggered motion in a bis-imidazolium rotaxane

We report the first bis-imidazolium-containing rotaxane, synthesised via anion templated self-assembly. Its co-conformation is controlled by a chloride anion recognition mechanism, thus demonstrating the viability of this protocol as a stimulus for shuttling molecular motion.

Revisit to imidazolium receptors for the recognition of anions: highlighted research during 2006-2009

In this tutorial review we discuss imidazolium receptors for anion recognition and recent contributions between 2006-2009 are reviewed according to target analytes, such as ATP and DNA, as well as structural classification, including cage type imidazoliums, imidazolium calixarenes, ferrocenyl imidazoliums, chiral systems, fluorescent or colorimetric imidazoliums, imidazolium cyclophane, nano assembled structures, bile acid-imidazolium, and tripodal-imidazolium systems.