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

Structurally engineered ion-receptor probe immobilized porous polymer platform as reusable solid-state chromogenic sensor for the ultra-trace sensing and recovery of mercury ions

This study reports an efficacious solid-state optical sensor through the synergistic coalescences of an original chromoionophoric probe and a structurally engineered porous polymer monolith for the selective and sensitive colorimetric spotting of ultra-trace toxic mercury ions. The unique properties of the bimodal macro-/meso-pore structured polymer, i.e., poly(AAm-co-EGDMA) monolith, offer voluminous and uniform anchoring of probe molecules, i.e., (Z)-N-phenyl-2-(quinoline-4-yl-methylene)hydrazine-1-carbothioamide (PQMHC). The structure/surface features of the sensory system, i.e., surface area, pore dimensions, monolith framework, elemental mapping, and phase composition, were examined by p-XRD, XPS, FT-IR, HR-TEM-SAED, FE-SEM-EDAX, and BET/BJH analysis. The sensor's ion-capturing ability was established through naked eye color transition and UV-Vis-DRS response. The sensor exhibits a strong binding affinity for Hg²⁺, with a linear signal response in the concentration range of 0-200 μg/L (r² >0.999), with a detection limit of 0.33 μg/L. The analytical parameters were optimized to facilitate pH-dependent visual sensing of ultra-trace Hg²⁺ in ≤ 30 s. The sensor exhibits high chemical/physical stability characteristics, with reliable data reproducibility (RSD ≤1.94 %), while testing with natural/synthetic water and cigarette samples. The proposed work offers a cost-effective and reusable naked-eye sensory system for the selective sensing of ultra-trace Hg²⁺, with potential prospects of commercialization considering their simplicity, viability, and reliability.

Synthesis of a quinoxaline-hydrazinobenzothiazole based probe-single point detection of Cu2+, Co2+, Ni2+ and Hg2+ ions in real water samples

A novel quinoxaline-hydrazinobenzothiazole based sensor was synthesized and characterized using NMR, FTIR, and Mass spectroscopy techniques. The sensor achieves the distinct "single-point" colorimetric and fluorescent detection of Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions with distinguishable color changes from yellow to red, pale red, pale brown and orange, respectively. The UV-visible and fluorescence emission spectral investigation revealed the excellent single-point sensing ability of the probe towards four different heavy metal ions with a ratiometric response. Nanomolar levels of detection of about 1.16 × 10^-7 M, 9.92 × 10^-8 M, 8.21 × 10^-8 M, and 1.14 × 10^-7 M for Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions, respectively, were achieved using our sensor, which are below the US-EPA permissible limits. Additionally, the sensor was utilized for naked eye detection under normal daylight. Quantitative determination of the metal ions in real water samples was also demonstrated.

Polyoxa- and Polyazamacrocycles Incorporating 6,7-Diaminoquinoxaline Moiety: Synthesis and Application as Tunable Optical pH-Indicators in Aqueous Solution

Synthetic approach to fluorescent polyaza- and polyoxadiazamacrocycles comprising a structural fragment of 6,7-diamino-2,3-diphenylquinoxaline has been elaborated using Pd-catalyzed amination providing target compounds in yields up to 77%. A series of nine novel N- and N,O-containing macrocyclic ligands differing by the number of donor sites and cavity size has been obtained. These compounds possess well-pronounced fluorescent properties with emission maxima in a blue region in aprotic solvents and high quantum yields of fluorescence, while in proton media, fluorescence shifts towards the green region of the spectrum. Using macrocycles 5c and 5e as examples, we have shown that such compounds can serve as dual-channel (colorimetric and fluorimetric) pH indicators in water media, with pH transition point and response being dependent on the macrocycle structure due to different sequences of protonation steps.

Comparative cation sensing properties of a newly designed urea linked ferrocene-benzimidazole dyad: a DFT study

Herein, our primary motivation was to elucidate the electronic and physicochemical properties of a novel molecular dyad consisting of ferrocene (Fc; electron donor), urea (u; linker), and amphoteric benzimidazole (BI; electron acceptor) entities. The sensor responses were investigated for various divalent transition metal cations (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) and the selectivity of this cationophore molecule (Fc-u-BI) to copper ion (Cu²⁺) was demonstrated by using B3LYP/LANL2DZ method. According to the thermochemical calculations, we justified that Fc-u-BI⋯Cu²⁺ reached to the lowest binding energy (∆E), enthalpy (∆H), and Gibbs free energy (∆G) changes. In the light of the calculated global descriptors, Fc-u-BI⋯Cu²⁺ was found to be the softer and thus the most reactive complex. The complex stabilities and their corresponding non-covalent interactions were also investigated by NBO and NCI analyses, respectively. The mechanistic insight into metal cation sensing by the modeled cationophore dyad.

Metal-coordination driven intramolecular twisting: a turn-on fluorescent-redox probe for Hg2+ ions through the interaction of ferrocene nonbonding orbitals and dibenzylidenehydrazine

A unique C2 symmetric azine bridged bi-ferrocenyl receptor has been designed and synthesized for the selective detection of Hg²⁺ ion with a low detection limit as 15 nM via turn on fluorescence with a blue shift.

Fluorescence Sensing with Cellulose-Based Materials

Cellulose-based materials functionalized with fluorescence sensors are highly topical and are employed in many areas of functional materials, including the sensing of heavy-metal ions and anions as well as being widely used as chemical sensors and tools for environmental applications. In this Review, we cover recent progress in the development of cellulose-based fluorescence sensors as parts of membranes and nanoscale materials for the detection of biological analytes. We believe that this Review will be of interest to chemists, chemical engineers, and biochemists in the sensor community as well as researchers working with biological material systems.

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.

Selective colorimetric and ratiometric probe for Ni(ii) in quinoxaline matrix with the single crystal X-ray structure

A quinoxaline based colorimetric nickel sensor,HQAP[2-(quinoxalin-2-ylmethyleneamine)phenol] with high selectivity and sensitivity toward Ni²⁺ions is shown to have potential for practical use.

A highly selective ratiometric chemosensor for Ni2+in a quinoxaline matrix

The monohydrazone of quinoxaline aldehyde (HOQA) is found to be a ratiometric and colorimetric probe for Ni²⁺.HOQAshows a remarkable color change from colorless to yellow upon specific and selective binding to nickel.