Amide and Urea Ferrocene-Containing Macrocycles Capable of the Electrochemical Sensing of Anions

Continuous and Polarization-Tuned Redox Capacitive Anion Sensing at Electroactive Interfaces

Continuous, real-time ion sensing is of great value across various environmental and medical scenarios but remains underdeveloped. Herein, we demonstrate the potential of redox capacitance spectroscopy as a sensitive and highly adaptable ion sensing methodology, exemplified by the continuous flow sensing of anions at redox-active halogen bonding ferrocenylisophthalamide self-assembled monolayers. Upon anion binding, the redox distribution of the electroactive interface, and its associated redox capacitance, are reversibly modulated, providing a simple and direct sensory readout. Importantly, the redox capacitance can be monitored at a freely chosen, constant electrode polarization, providing a facile means of tuning both the sensor analytical performance and the anion binding affinity, by up to 1 order of magnitude. In surpassing standard voltammetric methods in terms of analytical performance and adaptability, these findings pave the way for the development of highly sensitive and uniquely tunable ion sensors. More generally, this methodology also serves as a powerful and unprecedented means of simultaneously modulating and monitoring the thermodynamics and kinetics of host-guest interactions at redox-active interfaces.

Ferrocenylated 1,3,5-triphenylbenzenes for the electrochemical detection of various cations or anions

Three diverse 1,3,5-triphenylbenzene derivatives bearing three ferrocene units (Fc1-Fc3) were used for the construction of electrochemical sensors for the detection of various cations or anions. The obtained derivatives contained imine (Fc1 and Fc2) or amide bonds (Fc3) between 1,3,5-triphenylbenzene and ferrocene skeletons, which further influenced the ability of the as-synthesized ferrocenylated molecules to recognize cations (Cu(ii), Pb(ii), Cr(iii) and Fe(iii); compounds Fc1 and Fc2) or monovalent anions (Br-, I-, ClO4-, NO3-, CH3COO-, and H2PO4-; compound Fc3). In the case of cation recognition, differential pulse voltammetry (DPV) experiments revealed that the Fc1 receptor was characterized by much better sensitivity compared to the Fc2 receptor and the limit of detection (LOD) values ranged from 0.5 to 1.8 μM. Similarly, such very low LOD values (0.7-1.5 μM) were also found in the case of anion recognition by the Fc3 receptor. Importantly, the advantage of the tested Fc receptors is also their long-term stability (sensors were stable at least for 2 months).

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.

Solvent effect on neutral chiral supramolecular assemblies and their distinct receptor behaviour towards anions

We describe the distinct receptor behaviour of a neutral chiral Cu(ii) complex in dimethylsulfoxide or methanol towards anions, such as F(-), Cl(-), Br(-), I(-) or OAc(-), where F(-) and OAc(-) show the most colorimetric change, through various spectroscopic techniques. Further insights into this at the molecular level come from the single crystal X-ray structures of both dimethylsulfoxide and methanol solvates which show a solvent effect on their supramolecular network formation. Both chromogenic and fluorogenic sensing of the anions indicate a 2 : 1 receptor-anion formation via anion-π as well as hydrogen bonding interactions.

The effect of central and planar chirality on the electrochemical and chiral sensing properties of ferrocenyl urea H-bonding receptors

Ferrocenyl urea receptors containing planar and central chirality electrochemically sense carboxylate anions via formation of H-bonded complexes.

Synthesis, characterization, photophysics, and anion binding properties of platinum(ii) acetylide complexes with urea group

The relationship between the structure and anion-binding ability of platinum(ii) acetylide complexes with urea group has been studied.

Highlights on contemporary recognition and sensing of fluoride anion in solution and in the solid state

The fluoride anion has recently gained well deserved attention among the scientific community for its importance in many fields of human activities, but also for concerns on its effect on health and the environment. Although surprisingly overlooked in systematic studies in the past, fluoride has nowadays become a topical target in the field of anion recognition. A multitude of scientific reports are published every year where the establishment of efficient and specific interaction with fluoride is sought in polar and aqueous media. Here, the emphasis is directed to a detailed description of the most interesting contemporary studies in the field, with a particular focus given to those published in the last few years.