Unprecedented 1,3-Diaza[3]ferrocenophane Scaffold as Molecular Probe for Anions

Electrochemical Anion Sensing: Supramolecular Approaches

Anions play a vital role in a broad range of environmental, technological, and physiological processes, making their detection/quantification valuable. Electroanalytical sensors offer much to the selective, sensitive, cheap, portable, and real-time analysis of anion presence where suitable combinations of selective (noncovalent) recognition and transduction can be integrated. Spurred on by significant developments in anion supramolecular chemistry, electrochemical anion sensing has received considerable attention in the past two decades. In this review, we provide a detailed overview of all electroanalytical techniques that have been used for this purpose, including voltammetric, impedimetric, capacititive, and potentiometric methods. We will confine our discussion to sensors that are based on synthetic anion receptors with a specific focus on reversible, noncovalent interactions, in particular, hydrogen- and halogen-bonding. Apart from their sensory properties, we will also discuss how electrochemical techniques can be used to study anion recognition processes (e.g., binding constant determination) and will furthermore provide a detailed outlook over future efforts and promising new avenues in this field.

Supramolecular Self-Assembly Driven Selective Sensing of Phosphates

A new bis-heteroleptic Ru^II complex (1[PF₆]₂) with iodotriazole as the anion binding group along with the attached pyrene moiety is developed to investigate anion sensing properties and the origin of its selectivity toward a particular class of anions. Selective sensing of phosphates over other anions in both the solution and solid states by 1[PF₆]₂ is clearly evident from the perturbation of the absorption band and a large degree of amplification of ³MLCT emission band in the presence of phosphates. Importantly, macroscopic investigation such as Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS) indicated the formation of supramolecular architecture in the presence of dihydrogen phosphate via halogen bonding interaction and π-π stacking of pyrene moieties. Such macroscopic property is further corroborated by solution and solid state spectroscopic studies, e.g., ¹H-DOSY NMR, single crystal X-ray crystallography, and solid state photoluminescence (PL) spectroscopy.

Selective Molecularly Mediated Pseudocapacitive Separation of Ionic Species in Solution

We report the development of a dual-electrode pseudocapacitive separation technology (PSST) to capture quantitatively, remotely, and in a reversible manner value-added carboxylate salts of environmental and industrial significance. The nanostructured pseudocapacitive cell exhibits elegant molecular selectivity toward ionic species: upon electrochemical oxidation, a poly(vinylferrocene) (PVF)-based anodic electrode shows high selectivity toward carboxylates based on their basicity and hydrophobicity. Simultaneously, on the other side of the electrochemical cell, a poly(anthraquinone) (PAQ)-based cathodic electrode undergoes electrochemical reduction and captures the counterions of these carboxylates. The separation and regeneration capability of the electrochemical cell was evaluated through the variations in concentration of the carboxylates in polar organic solvents (often used in electrocatalytic processes) upon electrochemical charging and neutralization of the polymeric cargo of the electrodes, respectively. The strong separation efficiency of the system was indicated by its ability to capture an individual carboxylate (acetate, formate, or benzoate) selectively over other competing ions present in solution in significant excess, with an electrosorption capacity in the range of 122-157 mg anions/g_cell (polymer and CNT components on the anodic and cathodic side of the cell). The ion sorption capacity of the cell was high even after five adsorption/desorption cycles (18 000 s of continuous operation). In addition, the cell exhibited molecular selectivity even between two carboxylates (e.g., between benzoate and acetate or formate) which differ only in terms of basicity and hydrophobicity. We anticipate that this strategy can be employed as a versatile platform for selective ion separations. In particular, the functionalization of electrochemical cells with the proper polymers would enable the remote and economically viable electro-mediated separation of the desired ionic species in a quantitative and reversible manner.

Synthesis, characterization, DNA binding and in vitro antimicrobial studies of a novel tetra-substituted N-isopropyl-N-(4-ferrocenylphenyl)-N'-(2,6-diethylphenyl)-N″-benzoylguanidine: crystallographic structure and quantum chemical computations

A novel tetra-substituted guanidine, N-isopropyl-N-(4-ferrocenylphenyl)-N'-(2,6-diethylphenyl)-N″-benzoylguanidine (1), [(CH3)2CH)(C5H5FeC5H4C6H4)NC(NHCOC6H5)(NHC6H3(CH2CH3)2] has been synthesized and characterized by elemental analysis, FT-IR, multinuclear ((1)H, (13)C) NMR spectroscopy, single crystal X-rays diffraction analysis and density functional theory based quantum chemical calculations. The torsion angles indicating that the guanidine moiety and carbonyl group are almost co-planar, due to the pseudo hexagonal ring formed by intramolecular N-H⋯O hydrogen bonds. The DNA interaction studies performed by cyclic voltammetry and UV-visible spectroscopy are in close agreement with the binding constants (K) 1.4×10(4) and 1.2×10(4) respectively. The shift in peak potential, current and absorption maxima of the studied ferrocenyl guanidine in the presence of DNA discovered that CV coupled with UV-vis spectroscopy could provide an opportunity to elaborate DNA interaction mechanism, a prerequisite for the design of new drug like agents and understanding the molecular basis of their action. The synthesized compound (1) has also been screened for their antibacterial and antifungal.

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.

Bis(carbazolyl)ureas as selective receptors for the recognition of hydrogenpyrophosphate in aqueous media

Recognition properties of the novel bis(carbazole) tris-ureidic-based receptors 1 and 2 toward different anions have been studied by (1)H NMR and absorption and emission spectroscopy, as well as by DFT calculations. Receptor 1, in which the two urea-functionalized arms are decorated with p-nitrophenyl rings, behaves as a highly selective chromogenic molecular probe for hydrogenpyrophosphate anion in a competitive medium (acetonitrile/water, 70/30). Receptor 2, bearing two urea arms decorated with photoactive pyrenyl rings, acts as a highly selective fluorescent molecular probe for hydrogenpyrophosphate anion in either acetonitrile or an aqueous mixture (acetonitrile/water, 85/15). Receptor 2 exhibits a dual monomer-excimer emission spectrum and undergoes a remarked ratiometry in acetonitrile in the presence of hydrogenpyrophosphate: the excimer band disappears, whereas the monomer band is slightly increased. However, in the aqueous mixture, a strong increase of the excimer emission band was observed, while the monomer emission bands remained almost unaffected. The resulting binding modes and spectroscopic features are explained by suitable structures of model complexes for both receptors. In such complexes, a peripheral cooperative effect was found, alleviating the excess of negative charge in the guest toward the outer surface of the host, as well as the required enlargement on its internal cavity.

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010-2011

This review focuses on examples reported in the years 2010-2011 dealing with the design of chromogenic and fluorogenic chemosensors or reagents for anions.

Imidazole derivatives: a comprehensive survey of their recognition properties

Due to its amphoteric nature the imidazole ring can function as selective and effective anion and/or cation and even neutral organic molecules receptor system. As a result, the design of new multichannel imidazole-based receptors capable of recognizing different types of analytes is strongly demanded. This review summarizes the most recent and relevant advances in this area.