A simple hydrazone as a multianalyte (Cu2+, Al3+, Zn2+) sensor at different pH values and the resultant Al3+ complex as a sensor for F−

Towards Sustainable Materials: A Review of Acylhydrazone Chemistry for Reversible Polymers

Transitioning towards a circular economy, extensive research has focused on dynamic covalent bonds (DCBs) to pave the way for more sustainable materials. These bonds enable debonding and rebonding on demand, as well as facilitating end-of-life recycling. Acylhydrazone/hydrazone chemistry offers a material with high stability under neutral and basic conditions making it a promising candidate for materials research, though the material is susceptible to acid degradation. However, this degradation under acidic conditions can be exploited, making it widely applicable in self-healing and biomedical fields, with potential for reprocessing and recycling. This review highlights studies exploring the reversibility of acylhydrazone/hydrazone bonds in various polymers, altering their properties, and utilizing them in applications such as self-healing, reprocessing, and recycling. The review also focuses on how the mechanical properties are affected by the presence of dynamic linkages, and methods to improve the mechanical performance.

Colorimetric and Fluorometric N-Acylhydrazone-based Chemosensors for Detection of Single to Multiple Metal Ions: Design Strategies and Analytical Applications

The development of optical sensors for metal ions has gained significant attention due to their broad applications in biology, the environment, and medicine. Colorimetric and fluorometric detection methods are particularly valued for their simplicity, cost-effectiveness, high detection limits, and analytical power. Among various chemical probes, the hydrazone functional group stands out for its extensive study and utility, owing to its ease of synthesis and adaptability. This review provides a comprehensive overview of N-acylhydrazone-based probes, serving as highly effective colorimetric and fluorometric chemosensors for a diverse range of metal ions. Probes are categorized into single-ion, dual-ion, and multi-ion chemosensors, each further classified based on the detected metal(s). Additionally, the review discusses detection modes, detection limits, association constants, and spectroscopic measurements.

Knoevenagel condensation triggered synthesis of dual-channel oxene based chemosensor: Discriminative spectrophotometric recognition of F-, CN- and HSO4- with breast cancer cell imaging, real sample analysis and molecular keypad lock applications

A novel oxene based unusual sensory receptor (HyMa) has been synthesized via.Knoevenagel condensation triggered carbon-heteroatom (oxygen) intramolecular bond formation reaction at room temperature for discriminative detection of multi-analytes like HSO₄^-, CN^- & F^- by spectro-photometric alterations with profound selectivity with the detection limit of 38 ppb, 18 ppb & 94 ppb respectively. Examination of the sensing mechanism was exhaustively investigated through several spectroscopic means like ¹H NMR, FT-IR, absorption and fluorescence spectra etc. In addition, quantum mechanical calculations like DFT and Loewdin spin population analyses also validated the rationality of the host-guest interaction. Apart from these, the reversible spectroscopic responses of HyMa towards F^- and Al³⁺ can imitate several complex logic functions that in turn help in preparing molecular keypad lock. This molecular keypad lock has the potential to protect the confidential information at the molecular scale. Additionally, the MTT assay of HyMa showed low cytotoxicity and membrane permeability indicating its attractive capability for bio-imaging towards triple negative breast cancer. HyMa-coated test strips could also be employed towards on-site detection of these deadly contaminants via "Dip Stick" approach without help of any instrumentation. In addition, HyMa has also been exploited for quantitative determination of HSO₄^- from various real water samples. In a nutshell, detection of lethal contaminants like CN^-, F^- & HSO₄^- at ppb level with in vitro live cell imaging has been explored with proper photophysical characterisation and theoretical calculations with real field applications.

A simple strategy for the visual detection and discrimination of Hg2+ and CH3Hg+ species using fluorescent nanoaggregates

Fluorescent nanoaggregates (FNAs) based on phenanthroline-based amphiphiles show changes in solution color from colorless to yellow upon addition of both Hg²⁺ (LOD ∼4 ppb) and CH₃Hg⁺ (LOD ∼18 ppb). However, the extent of fluorescence quenching is more prominent with Hg²⁺ (∼12 fold) than with CH₃Hg⁺ (∼4 fold). Also, unlike Hg²⁺, the interaction of CH₃Hg⁺ needs more time, ∼10 min at room temperature. Experimental evidence indicates that both mercury species coordinate with the phenanthroline unit and facilitate the charge transfer interaction while destabilizing the nanoassembly. The lower charge density on CH₃Hg⁺ along with its large size compared to Hg²⁺ may be the reason for such observations. Interestingly, FNAs show a selective response towards CH₃Hg⁺ when pre-treated with EDTA. Further, analysis of heavy metal pollutants in drinking water and biological samples was performed. High recovery values ranging from 96% to 103.0% were estimated along with relatively small standard deviations (<3%). Low-cost, reusable test strips were designed for rapid, on-site detection of mercury species. Further, the in situ formed metal complexes are allowed to interact with thiol-containing amino acids. As expected, CH₃Hg⁺, being less thiophillic, endures less interaction with cysteine. Mechanistic investigations indicate that thiolated amino acids can bind with the metal ion center and form a tertiary complex (cooperative interaction).

New thiophene hydrazide dual-functional chemosensor: Colorimetric sensor for Cu2+ & fluorescent sensor for Al3

A new thiophene hydrazide derivative TSB was synthesized and utilized as naked-eye colorimetric sensor for Cu²⁺ by the color changed from colorless to yellow as well as green fluorescent turn on sensor for Al³⁺ in DMSO/H₂O (1/1, V/V) solution. The dual-functional chemosensor TSB for Cu²⁺/Al³⁺ sensing displayed excellent properties of special selectivity, superior sensitivity, outstanding anti-interference performance, instantaneous response, wide pH working range and good reversibility. The detection limits of TSB for Cu²⁺/Al³⁺ were determined as low as 46.5 nM and 32.7 nM, respectively. The 1:1 binding mode of TSB with Cu²⁺/Al³⁺ was proved by spectrometric titrations, Job's plots, FTIR, ¹H NMR and HRMS analysis. Moreover, chemosensor TSB was successfully utilized for detection of Cu²⁺ and Al³⁺ in real environmental water and food samples with high reliability, demonstrating its practical applicability.

Solid-State Emissive Metallo-Supramolecular Assemblies of Quinoline-Based Acyl Hydrazone

Development of fluorescence-based sensory materials for metal elements is currently in the mainstream of research due to the simplicity and usability of fluorescence as a method of detection. Herein, we report a novel "bis"-quinoline-based acyl hydrazone-named bQH that could be synthesized by a facile, low-cost method through simple condensation of hydrazide with an aldehyde. This acyl hydrazone showed emissive properties through Zn selective binding, especially in its solid-state, as shown by experiments such as UV-Vis, photoluminescence (PL), nuclear magnetic resonance (NMR), and inductively-coupled plasma-optical emission spectroscopies (ICP-OES), and energy-dispersive X-ray spectroscopy (EDS) mapping. The binding modes in which bQH coordinates to Zn2+ was proved to consist of two modes, 1:1 and 1:2 (bQH:Zn2+), where the binding mode was controlled by the Zn2+ ion content. Under the 1:1 binding mode, bQH-Zn2+ complexes formed a polymeric array through the metallo-supramolecular assembly. The resulting bQH-Zn2+ complex maintained its fluorescence in solid-state and exhibited excellent fluorescence intensity as compared to the previously reported quinoline-based acyl hydrazone derivative (mQH).

AIE active salicylaldehyde-based hydrazone: A novel single-molecule multianalyte (Al3+ or Cu2+) sensor in different solvents

A simple asymmetric hydrazone 1 based on salicylaldehyde was designed and prepared, and exhibited an evident aggregation-induced emission (AIE) at a long wavelength of 570 nm in aqueous medium. Probe 1 can selectively sense Al³⁺ in CH₃OH solution through the chelation-enhanced fluorescence mechanism and also recognize Cu²⁺ via fluorescence quenching in H₂O solution through the Cu²⁺-induced assembly of aggregates. In addition, the probe can be applied for detecting Cu²⁺ in biological samples.

An easy-to-synthesize multi-photoresponse smart sensor for rapidly detecting Zn2+ and quantifying Fe3+ based on the enol/keto binding mode

A readily available salicylaldazine-modified fluorene Schiff base (EASA-F) exhibits fast fluorescent OFF–ON response to Zn²⁺ and OFF–ON–OFF behavior to Fe³⁺ synchronously accompanied the diverse absorption-ratiometric and colorimetric changes.