María Alfonso

Ferrocene-based heteroditopic receptors displaying high selectivity toward lead and mercury metal cations through different channels.

The synthesis and electrochemical, optical, and ion-sensing properties of ferrocene-imidazophenazine dyads are presented. Dyad 4 behaves as a highly selective chemosensor molecule for Pb(2+) cations in CH(3)-CN/H(2)O (9:1). The emission spectrum (λ(exc) = 317 nm) undergoes an important chelation-enhanced fluorescence effect (CHEF = 47) in the presence of Pb(2+) cations, a new low-energy band appeared at 502 nm, in its UV/vis spectrun, and the oxidation redox peak is anodically shifted (ΔE(1/2) = 230 mV). The presence of Hg(2+) cations also induced a perturbation of the redox potencial although in less extension than those found with Pb(2+) cations. Dyad 7, bearing two fused pyridine rings, has shown its ability for sensing Hg(2+) cations selectively through three channels: electrochemical, optical, and fluorescent; the oxidation redox peak is anodically shifted (ΔE(1/2) = 200 mV), a new low-energy band of the absorption spectrum appeared at 485 nm, and the emission spectrum (λ(exc) = 340 nm) is red-shifted by 32 nm accompanied by a remarkable chelation-enhanced fluorescent effect (CHEF = 165). Linear sweep voltammetry revealed that Cu(2+) cations induced oxidation of the ferrocene unit in both dyads. (1)H NMR studies have been carried out to obtain information about the molecular sites which are involved in the binding process.

A simple but effective dual redox and fluorescent ion pair receptor based on a ferrocene-imidazopyrene dyad.

The ferrocene-imidazopyrene dyad, bearing the imidazole ring as the only receptor site, acts as a redox and optical molecular sensor for ion pairs, exhibiting an easily detectable signal change in the redox potential of the ferrocene/ferrocinium redox couple and in the emission spectrum. Perturbation of the emission spectrum follows the order Pb(2+) > Hg(2+) > Zn(2+) for cations and H(2)PO(4)(-) > AcO(-) for anions.

A bisferrocene-benzobisimidazole triad as a multichannel ditopic receptor for selective sensing of hydrogen sulfate and mercury ions.

The bisferrocene-benzobisimidazole triad behaves as a selective redox and fluorescent chemosensor for HSO(4)(-) and Hg(2+) ions, exhibiting an easily detectable signal change in both the redox potential of the ferrocene/ferrocinium redox couple and in the emission band which is red-shifted (Δλ = 10-13 nm) and enhanced in intensity (Chelation Enhanced Fluorescence, CHEF = 486-225) upon complexation with these ions, in EtOH solutions.

Ferrocenylbenzobisimidazoles for Recognition of Anions and Cations

The preparation of 2,7-disubstituted benzobisimidazoles decorated with substituents displaying different electrooptical properties is described. The presence of redox, chromogenic, and fluorescent groups at the heteroaromatic core, which acts as ditopic binding site, made these receptors potential candidates as multichannel probes for ions. The triad 4 behaves as a selective redox and fluorescent chemosensor for HSO4(-) and Hg(2+) ions, whereas receptor 5 acts as a redox and chromogenic chemosensor molecule for AcO(-) and SO4(2-) anions. The change in the absorption spectra is accompanied by a color change from yellow to orange, while sensing of Zn(2+), Hg(2+), and Pb(2+) cations is carried out only by electrochemical techniques. Receptor 6 exhibits a remarkable cathodic shift of the oxidation wave only in the presence of AcO(-), H2PO4(-), and HP2O7(3-) anions, whereas addition of Pb(2+) induces an anodic shift. A new low energy band in the absorption spectra, which is responsible for the color change from colorless to pale yellow, and an important increase of the monomer emission band is observed only in the presence of H2PO4(-), and HP2O7(3-) anions. The most salient feature of the receptor 6 is its ability to act as a multichannel (redox, chromogenic, and fluorescent) chemodosimeter for Cu(2+), and Hg(2+) metal cations.

Highly selective mercury(II) cations detection in mixed-aqueous media by a ferrocene-based fluorescent receptor.

A new chemosensor molecule 3 based on a ferrocene-imidazophenanthrophenazine dyad effectively recognizes Hg(2+) in an aqueous environment through three different channels. Upon recognition, an anodic shift of the ferrocene-ferrocenium oxidation potential (ΔE(1/2) = 240 mV) and a progressive red shift (Δλ = 17 nm) of the low energy band in its absorption spectrum is produced. The emission spectrum of 3 in an aqueous environment, CH(3)CN-EtOH-H(2)O (65:25:10), and conducted at pH = 7.4 (20 × 10(-3) M HEPES) (Φ = 0.003), is perturbed after addition of Hg(2+) cations and an intense and structureless red shift emission band at 494 nm (Δλ = 92 nm) appeared along with an increase of the intensity of the emission band (CHEF = 77), the quantum yield (Φ = 0.054) resulted in a 18-fold increase. The combined (1)H NMR data of the complex and the theoretical calculations suggest the proposed bridging coordination mode.

Multifunctional Benzothiadiazole‐Based Small Molecules Displaying Solvatochromism and Sensing Properties toward Nitroarenes, Anions, and Cations

Aryl or heteroaryl 5-substituted imidazo-benzothiadiazole derivatives were synthesized and shown to display remarkable solvatofluorochromism and selectively sense mercury(II) cations, acetate anions, and nitroaromatic derivatives, with discrimination between p-nitrophenol and picric acid. These novel sensors are of importance these days, as the detection of explosives is a high priority in issues of national security and environmental protection. To determine the ion binding properties of the sensors, their absorption and fluorescence emission spectra upon binding different cations and anions were compared. Significant shifts in the spectra were only observed for mercury(II) and acetate. The binding of these two ions was further studied using 1H NMR. The binding properties of different nitroaromatic compounds were also determined, and the results showed the importance of the presence of a phenol group in the guest molecule. Specifically, the two sensors were shown to discriminate between p-nitrophenol and picric acid. Finally, the mechanism of fluorescence quenching upon addition of nitrophenols was determined by computational methods.

Electrochemical and Fluorescent Ferrocene-Imidazole-Based Dyads as Ion-Pair Receptors for Divalent Metal Cations and Oxoanions

In the tricyclic bis(heteroaryl)substituted ferrocenyl-imidazo-quinoxalines 7 and 8, the presence of redox and fluorescent units at the heteroaromatic core, which can act as a ditopic binding site, made these molecules potential candidates as electro-optical ion-pair recognition receptors. In this context, both molecules behave as ion-pair receptors for cations and anions, which individually had demonstrated their ability to form the corresponding cationic and anionic complexes. These receptors also show an important enhancement of anion binding by co-bound cations, whereas no affinity of the free receptors by the anion is observed. Similarly, receptors 7 and 8 display a dramatic increase in the cation binding by the action of their anionic complexes, while no affinity of the free receptors by the cations was detected. Interestingly, both receptors exhibit a remarkable enhancement of anions and cations binding, although no affinity of the free receptors by the ions is observed. In all cases, the ion-pair formation is detected by a perturbation of the redox potential of the ferrocene moiety and a remarkable enhancement in the emission band.

Multifunctional Imidazobenzothiadiazole Probe Displaying Solvatofluorochromism and Ability To Form Ion-Pair Complexes in Solid State and in Solution

Fluorescent solid 5-pyridylimidazobenzothiadiazole displays a remarkable solvatofluorochromism and with Zn(AcO)2 and Cd(AcO)2, either in solution or under solvent-free conditions, forms ion-pair complexes that in the solid state can be discriminated and separated by fluorescence measurements and selective extraction with diethyl ether or chloroform.

Preparation and sensing properties of a nitrogen-rich ferrocene-imidazole-quinoxaline triad decorated with pyrrole rings

The synthesis and sensing properties of the nitrogen-rich ferrocene-imidazole-quinoxaline triad 1 decorated with two pyrrole rings have been described. Due to its ditopic nature, this molecule behaves as an ion-pair receptor for Ni2+cations and AcO- anions, although no affinity for either of the discrete ions is observed. It also displays the rare property consistent with the cooperative AND recognition of ion pairs. Thus, this receptor shows an important enhancement for binding AcO- anions when it is co-bound to Hg2+cations, whereas no affinity for the free receptor by the anion is observed.