Host-guest complexes supramolecular polymers in chalcogen bonding receptors: an experimental and theoretical study.

We describe here a comparative study between two tripodal anion receptors based on selenophene as the binding motif. The receptors use benzene or perfluorobenzene as a spacer. The presence of the electron-withdrawing ring activates the selenium atom for anion recognition inducing the formation of self-assembled supramolecular structures in the presence of chloride or bromide anions, which are bonded by the cooperative action of hydrogen and chalcogen bonding interactions.

Formation of self-assembled supramolecular polymers by anti-electrostatic anion-anion and halogen bonding interactions.

We report here the formation of self-assembled supramolecular polymers in which the cooperative action of anti-electrostatic anion-anion and halogen-bonding interactions serve as a powerful driving force for the formation of large supramolecular polymers. DOSY-NMR, DLS, TEM, SEM and X-ray experiments provide evidence of the formation of supramolecular structures in solution and solid state.

Selective fluorescence sensing of HPO by the anion induced formation of self-assembled supramolecular polymers.

The utilization of anions to induce the formation of self-assembled supramolecular polymers in solution is an undeveloped area of host-guest chemistry. We report in this manuscript a comparative study of two tripodal anion receptors by hydrogen or halogen bonding interactions to form self-assembled supramolecular structures induced by the presence of anions. DOSY NMR and DLS experiments provided evidence for the formation of supramolecular structures in solution in both halogen and hydrogen bond donors with H2PO4- anions.

Triazole-Containing [FeFe] Hydrogenase Mimics: Synthesis and Electrocatalytic Behavior.

Through a Cu-catalyzed Huisgen cycloaddition between terminal alkynes and azides (CuAAC) reaction, azide [(μ-SCH)N(4-NCH)Fe(CO)] has demonstrated to be a robust and versatile reagent able to incorporate the [(μ-SR)Fe(CO)] fragment on a wide range of substrates, ranging from aromatic compounds to nucleosides, metallocenes, or redox and luminescent markers. The [FeFe]/[FeFe] and [FeFe]/[FeFe] reduction potentials of the triazole derivatives prepared are comparable to those of other aminodithiolate (adt) Fe-Fe hydrogenase mimics. The presence of the triazole linker influences the electrochemical behavior of these complexes depending on the strength of the acid employed.

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.

Enhancement of anion recognition exhibited by a zinc-imidazole-based ion-pair receptor composed of C-H hydrogen- and halogen-bond donor groups.

A 2-haloimidazole-tetraphenylethylene ion-pair receptor 1 is shown to recognise only HSO4- anions in the presence of a cobound Zn2+ cation guest species, which induced a remarkable increase with concomitant blue shift of the emission band of the complex [1·2Zn]4+ whereas no affinity of the free receptor 1 by the anions is observed. In addition, the downfield shifts observed by 1H NMR of the Ha, Hb and Hc protons of the complex [1·2Zn]4+ upon the addition of HSO4- anions indicate their participation in the recognition event. According to DFT studies, upon chelating a Zn2+ cation with two imidazole nitrogen atoms, receptor 1 adopts a conformation ideally fitted to recognise HSO4- through a combination of C(sp2)-HO and C(sp3)-HO hydrogen bondings, C+(sp2)-BrO halogen bonding and C(sp2)O tetrel bonding.

Interlocked Supramolecular Polymers Created by Combination of Halogen- and Hydrogen-Bonding Interactions through Anion-Template Self-Assembly.

We present the synthesis and oxoanion-assembling properties of a monomer with a naphthalene ring as a central core decorated with two arms containing iodotriazolium rings as anion binding sites. Interactions with SO, HPO, and HPO anions, via a cooperative mechanism, afforded new supramolecular materials stabilized by a combination of halogen- and hydrogen-bonding interactions. H NMR experiments and solid-state structure provided evidence for the initial formation of a supramolecular linear chain, nucleation step, and then two different supramolecular chains are interpenetrated with each other, elongation steps, involving the formation of hydrogen bonds between two oxygens of the anion from one of the chains and the naphthalene inner protons from the other chain.

Modulation of the Selectivity in Anions Recognition Processes by Combining Hydrogen- and Halogen-Bonding Interactions.

Most of the halogen bonding receptors for anions described use halogen bonding binding sites solely in the anion recognition process; only a few examples report the study of anion receptors in which the halogen bonding interaction has been used in combination with any other non-covalent interaction. With the aims to extend the knowledge in the behaviour of this kind of mixed receptors, we report here the synthesis and the anion recognition and sensing properties of a new halogen- and hydrogen- bonding receptor which binds anions by the cooperation of both non-covalent interactions. Fluorescence studies showed that the behaviour observed in the anion recognition sensing is similar to the one previously described for the halogen analogue and is quite different to the hydrogen one.

Anion Recognition Strategies Based on Combined Noncovalent Interactions.

This review highlights the most significant examples of an emerging field in the design of highly selective anion receptors. To date, there has been remarkable progress in the binding and sensing of anions. This has been driven in part by the discovery of ways to construct effective anion binding receptors using the dominant N-H functional groups and neutral and cationic C-H hydrogen bond donors, as well as underexplored strong directional noncovalent interactions such as halogen-bonding and anion-π interactions.

Comparative Study of Charge-Assisted Hydrogen- and Halogen-Bonding Capabilities in Solution of Two-Armed Imidazolium Receptors toward Oxoanions.

Two-armed imidazolium-based anion receptors have been prepared. The central 2,7-disubstituted naphthalene ring features two photoactive anthracene end-capped side arms with central 2-bromoimidazolium or hydrogen-bonding imidazolium receptors. Combined emission and (1)H and (31)P NMR studies carried out in the presence of a wide variety of anions reveal that only HP2O7(3-), H2PO4(-), SO4(2-), and F(-) anions promoted noticeable changes.

2,4,5-Trimethylimidazolium Scaffold for Anion Recognition Receptors Acting Through Charge-Assisted Aliphatic and Aromatic C-H Interactions.

A series of two-armed 2,4,5-trimethylimidazolium-based oxoanion receptors, which incorporate two end-capped photoactive anthracene rings, being the central core an aromatic or heteroaromatic ring, has been designed. In the presence of HP2O7(3-), H2PO4(-), and SO4(2-) anions, (1)H- and (31)P NMR spectroscopical data clearly indicate the simultaneous occurrence of several charge-assisted aliphatic and aromatic C-H noncovalent interactions, i.e.

Host-Guest Chemistry: Oxoanion Recognition Based on Combined Charge-Assisted C-H or Halogen-Bonding Interactions and Anion⋅⋅⋅Anion Interactions Mediated by Hydrogen Bonds.

Several bis-triazolium-based receptors have been synthesized and their anion-recognition capabilities have been studied. The central chiral 1,1'-bi-2-naphthol (BINOL) core features either two aryl or ferrocenyl end-capped side arms with central halogen- or hydrogen-bonding triazolium receptors. NMR spectroscopic data indicate the simultaneous occurrence of several charge-assisted aliphatic and heteroaromatic C-H noncovalent interactions and combinations of C-H hydrogen and halogen bonding.

Dual Role of the 1,2,3-Triazolium Ring as a Hydrogen-Bond Donor and Anion-π Receptor in Anion-Recognition Processes.

Several bis(triazolium)-based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side-arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen-bond donor, the other as an anion-π receptor.

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

A novel bidentate bis-(benzimidazolium) receptor containing pyrene as fluorescent signaling units has been synthesized. Fluorescence and NMR spectroscopy studies reveal that this receptor exclusively recognizes sulphate and hydrogenpyrophosphate in the competitive water-DMSO (1 : 9) medium; significant downfield shifts were observed for the C(2)-H protons of both the imidazolium groups, and appreciable downfield shifts were also observed for the inner naphthalene protons indicating their participation in hydrogen bonding with anions along with the C(2) imidazolium protons. The calculated association constants from (1)H NMR and fluorescence titrations demonstrate that the receptor binds sulphate stronger than hydrogenpyrophosphate anions.

Iodide-induced shuttling of a halogen- and hydrogen-bonding two-station rotaxane.

The first example of utilizing halogen-bonding anion recognition to facilitate molecular motion in an interlocked structure is described. A halogen-bonding and hydrogen-bonding bistable rotaxane is prepared and demonstrated to undergo shuttling of the macrocycle component from the hydrogen-bonding station to the halogen-bonding station upon iodide recognition. In contrast, chloride-anion binding reinforces the macrocycle to reside at the hydrogen-bonding station.

Open bis(triazolium) structural motifs as a benchmark to study combined hydrogen- and halogen-bonding interactions in oxoanion recognition processes.

We have designed a series of triazolium-pyrene-based dyads to probe their potential as fluorescent chemosensors for anion recognition through combinations of hydrogen and halogen bonding. Cooperation between the two distinct noncovalent interactions leads to an unusual effect on receptor affinity, as a result of fundamental differences in the interactions of halogen and hydrogen bond donor groups with anions. Absorption, emission spectrophotometries and proton and phosphorus NMR spectroscopies indicate that the two interactions act in concert to achieve the selective binding of the hydrogen pyrophosphate anion, a conclusion supported by computational studies.

Discovery of anion-π interactions in the recognition mechanism of inorganic anions by 1,2,3-triazolium rings.

A bis(triazolium)-based receptor designed for anion recognition is presented. NMR spectroscopic data indicate that one triazolium ring is acting as a hydrogen bond donor, whereas the second triazolium ring behaves as an anion-π receptor. The simultaneous presence of two noncovalent interactions allows us to achieve a highly selective binding of the hydrogenpyrophosphate anion.

Lanthanide cation-templated synthesis of rotaxanes.

The first lanthanide cation-templated synthesis of an interlocked structure is demonstrated through an interpenetrated assembly between a pyridine N-oxide threading component coordinating to a lanthanide cation complexed within a macrocycle. Stoppering of the pseudo-rotaxane assembly allows for preparation of the [2]rotaxane.

PDMS based photonic lab-on-a-chip for the selective optical detection of heavy metal ions.

The selective absorbance detection of mercury(II) (Hg(2+)) and lead(II) (Pb(2+)) ions using ferrocene-based colorimetric ligands and miniaturized multiple internal reflection (MIR) systems implemented in a low-cost photonic lab on a chip (PhLoC) is reported. The detection principle is based on the formation of selective stable complexes between the heavy metal ion and the corresponding ligand. This interaction modulates the ligand spectrum by giving rise to new absorbance bands or wavelength shifting of the existing ones.

Fluorescent charge-assisted halogen-bonding macrocyclic halo-imidazolium receptors for anion recognition and sensing in aqueous media.

The synthesis and anion binding properties of a new family of fluorescent halogen bonding (XB) macrocyclic halo-imidazolium receptors are described. The receptors contain chloro-, bromo-, and iodo-imidazolium motifs incorporated into a cyclic structure using naphthalene spacer groups. The large size of the iodine atom substituents resulted in the isolation of anti and syn conformers of the iodo-imidazoliophane, whereas the chloro- and bromo-imidazoliophane analogues exhibit solution dynamic conformational behavior.

A multifaceted ferrocene-benzobisimidazole derivative: fluorogenic probe for Pb(2+) and Zn(2+) cations and unconventional fluorescence behaviour towards Cu(2+) metal cations.

The ferrocene-benzobisimidazole derivative shows high affinity for Pb(2+) and Zn(2+) metal cations over a range of other metal cations examined. In the presence of Pb(2+) the emission spectrum is red-shifted by 13 nm with an important chelation-enhanced fluorescence effect (CHEF) CHEF = 55. The presence of Zn(2+) cations also induced a perturbation of the emission spectrum although to a lesser extent than that found for Pb(2+) cations (CHEF = 37).

A ferrocene-quinoxaline derivative as a highly selective probe for colorimetric and redox sensing of toxic mercury(II) cations.

A new chemosensor molecule 3 based on a ferrocene-quinoxaline dyad recognizes mercury (II) cations in acetonitrile solution. Upon recognition, an anodic shift of the ferrocene/ferrocenium oxidation peaks and a progressive red-shift (Δλ=140 nm) of the low-energy band, are observed in its absorption spectrum. This change in the absorption spectrum is accompanied by a colour change from orange to deep green, which can be used for a "naked-eye" detection of this metal cation.

Ferrocene-substituted nitrogen-rich ring systems as multichannel molecular chemosensors for anions in aqueous environment.

The synthesis, electrochemical, optical, and anion sensing properties of ferrocene-fused imidazole dyads are presented. Ferrocene-benzobisimidazole dyad 1 behaves as a highly selective redox, chromogenic and fluorescent chemosensor molecule for AcO(-) anion in DMSO/H(2)O: the oxidation redox peak is cathodically shifted (DeltaE(1/2) = -170 mV), perturbation of the UV-vis spectrum, and the emission band is both red-shifted (Delta lambda = 13 nm) and increased (Chelation Enhanced Fluorescence, CHEF = 133) upon complexation with this anion. The related ferrocene-bisbenzimidazole dyad 2 has shown the ability for sensing both H(2)PO(4)(-) and HP(2)O(7)(3-) anions in the same medium.

A selective redox and chromogenic probe for Hg(II) in aqueous environment based on a ferrocene-azaquinoxaline dyad.

A new chemosensor molecule 4 based on a ferrocene-azaquinoxaline dyad effectively recognizes Hg(2+) in an aqueous environment as well as Pb(2+) and Zn(2+) metal cations in CH(3)CN solution through three different channels. Upon recognition, an anodic shift of the ferrocene/ferrocenium oxidation peaks and a progressive red shift (Deltalambda = 112-40 nm) of the low energy band, in their absorption spectra, is produced. These changes in the absorption spectra are accompanied by color changes from orange to deep green, for Hg(2+), and to purple in the cases of Pb(2+) and Zn(2+).