Substituent-dependent fluorescent sensors for zinc ions based on carboxamidoquinoline

A bicarboxaminoquinoline-based ratiometric fluorescent sensor for the sequential detection of Zn2+ and PPi

A new ratiometric fluorescent sensor (LP) based on bicarboxaminoquinoline was designed and synthesized for sequentially recognizing Zn2+ and PPi. In aqueous solution, LP exhibited the ratiometric fluorescence response towards Zn2+, along with the about 4-folds enhancement of fluorescence quantum yield. Subsequently, the LP-Zn2+ complex displayed the fluorescence recovery upon adding PPi through the displacement strategy. And the LODs of LP and its Zn2+ complex for sensing Zn2+ and PPi were found to be 15 nM and 5.5 nM, respectively. Notably, the reversibility of LP for sequentially sensing Zn2+ and PPi had been employed to construct the INHIBIT logic gate. Moreover, LP and its Zn2+ complex had been successfully utilized for the detection of Zn2+ and PPi in two real water samples and cells imaging.

Mechanistic Innovations in Fluorescent Chemosensors for Detecting Toxic Ions: PET, ICT, ESIPT, FRET and AIE Approaches

Fluorescent chemosensors have become vital tools for detecting toxic ions due to their exceptional sensitivity, selectivity, and rapid response times. These sensors function through various mechanisms, each providing unique advantages for specific applications. This review offers a comprehensive overview of the mechanistic innovations in fluorescent chemosensors, emphasizing five key approaches: Photoinduced Electron Transfer (PET), Fluorescence Resonance Energy Transfer (FRET), Intramolecular Charge Transfer (ICT), Aggregation-Induced Emission (AIE), and Excited-State Intramolecular Proton Transfer (ESIPT). We highlight the substantial progress made in developing these chemosensors, discussing their design principles, sensing mechanisms, and practical applications, with a particular focus on their use in detecting toxic ions relevant to environmental and biological contexts.

A Review on Small Molecule Based Fluorescence Chemosensors for Bioimaging Applications

This review provides a thorough examination of small molecule-based fluorescence chemosensors tailored for bioimaging applications, showcasing their unique ability to visualize biological processes with exceptional sensitivity and selectivity. It explores recent advancements, methodologies, and applications in this domain, focusing on various designs rooted in anthracene, benzothiazole, naphthalene, quinoline, and Schiff base. Structural modifications and molecular engineering strategies are emphasized for enhancing sensor performance, including heightened sensitivity, selectivity, and biocompatibility. Additionally, the review offers valuable insights into the ongoing development and utilization of these chemosensors, addressing current challenges and charting future directions in this rapidly evolving field.

Intracellular Zn(II) induced turn-on fluorescence of an L-phenylalanine-derived pseudopeptide

A C2 symmetric L-phenylalanine-derived pseudopeptide has been synthesized for selective and sensitive recognition of Zn(II) ions in aqueous-organic media. The pseudopeptidic probes exhibit intracellular Zn(II) ion-sensing capabilities as demonstrated via live-cell fluorescence studies on RAW264.7 cells. Hence, we present a bioinspired pseudopeptide for potential biological applications involving intracellular Zn(II) ion detection.

Non-invasive radionuclide imaging of trace metal trafficking in health and disease: "PET metallomics"

Several specific metallic elements must be present in the human body to maintain health and function. Maintaining the correct quantity (from trace to bulk) and location at the cell and tissue level is essential. The study of the biological role of metals has become known as metallomics. While quantities of metals in cells and tissues can be readily measured in biopsy and autopsy samples by destructive analytical techniques, their trafficking and its role in health and disease are poorly understood. Molecular imaging with radionuclides - positron emission tomography (PET) and single photon emission computed tomography (SPECT) - is emerging as a means to non-invasively study the acute trafficking of essential metals between organs, non-invasively and in real time, in health and disease. PET scanners are increasingly widely available in hospitals, and methods for producing radionuclides of some of the key essential metals are developing fast. This review summarises recent developments in radionuclide imaging technology that permit such investigations, describes the radiological and physicochemical properties of key radioisotopes of essential trace metals and useful analogues, and introduces current and potential future applications in preclinical and clinical investigations to study the biology of essential trace metals in health and disease.

Aminoquinoline-anchored polynorbornene for sequential fluorescent sensing of Zn2+ and ATP

A novel aminoquinoline functionalized norbornene (1) and its ring-opening metathesis polymerization (ROMP) copolymer P1 have been designed and synthesized. The polymer probe P1 can self-assemble nano aggregation in aqueous solution. The fluorescent experiments revealed that both 1 and P1 show a ratiometric fluorescence response toward Zn²⁺ over other mental ions in Tris-HCl buffer solution, with the polymer probe P1 shows a better photostability and higher binding affinity than that of the small molecular probe 1. Furthermore, the in situ formed P1-Zn²⁺ ensemble was successfully used as the secondary sensor for ATP. P1 is also successfully used for monitoring intracellular Zn²⁺ and ATP in living cells.

The Role of 8-Amidoquinoline Derivatives as Fluorescent Probes for Zinc Ion Determination

Mass-spectrometry-based and X-ray fluorescence-based techniques have allowed the study of the distribution of Zn²⁺ ions at extracellular and intracellular levels over the past few years. However, there are some issues during purification steps, sample preparation, suitability for quantification, and the instruments’ availability. Therefore, work on fluorescent sensors based on 8-aminoquinoline as tools to detect Zn²⁺ ions in environmental and biological applications has been popular. Introducing various carboxamide groups into an 8-aminoquinoline molecule to create 8-amidoquinoline derivatives to improve water solubility and cell membrane permeability is also a recent trend. This review aims to present a general overview of the fluorophore 8-aminoquinoline and its derivatives as Zn²⁺ receptors for zinc sensor probes. Various fluorescent chemosensor designs based on 8-amidoquinoline and their effectiveness and potential as a recognition probe for zinc analysis were discussed. Based on this review, it can be concluded that derivatives of 8-amidoquinoline have vast potential as functional receptors for zinc ions primarily because of their fast reactivity, good selectivity, and bio-compatibility, especially for biological applications. To better understand the Zn²⁺ ion fluorophores’ function, diversity of the coordination complex and geometries need further studies. This review provides information in elucidating, designing, and exploring new 8-amidoquinoline derivatives for future studies for the improvement of chemosensors that are selective and sensitive to Zn²⁺.

Effects of the Distance between Radical Sites on the Reactivities of Aromatic Biradicals

Coupling of the radical sites in isomeric benzynes is known to hinder their radical reactivity. In order to determine how far apart the radical sites must be for them not to interact, the gas-phase reactivity of several isomeric protonated (iso)quinoline- and acridine-based biradicals was examined. All the (iso)quinolinium-based biradicals were found to react slower than the related monoradicals with similar vertical electron affinities (i.e., similar polar effects). In sharp contrast, the acridinium-based biradicals, most with the radical sites farther apart than in the (iso)quinolinium-based systems, showed greater reactivities than the relevant monoradicals with similar vertical electron affinities. The greater distances between the two radical sites in these biradicals lead to very little or no spin-spin coupling, and no suppression of radical reactivity was observed. Therefore, the radical sites can still interact if they are located on adjacent benzene rings and only after being separated further than that does no coupling occur. The most reactive radical site of each biradical was experimentally determined to be the one predicted to be more reactive based on the monoradical reactivity data. Therefore, the calculated vertical electron affinities of relevant monoradicals can be used to predict which radical site is most reactive in the biradicals.

Rapid Discovery and Structure-Property Relationships of Metal-Ion Fluorescent Sensors via Macroarray Synthesis

A macroarray immobilisation of fluorophores on filter papers for sensing metal ions by in-situ reductive amination and carbodiimide coupling is reported herein. Chemometric approaches resulted in a rapid discovery of sensors that can synergistically discriminate up to 12 metal ions with great prediction accuracies. Covalently bound on paper, sensoring scaffolds that were synthesised from the macroarray format can readily be adopted as practical paper-based sensors with great reusability and sensitivity, achieving the limit of detection at low nanomolar level with some repeating spotting. Lastly, the discovered scaffolds were also confirmed to be functional as unbound molecules, thus paving the way for more diverse applications.

A selective fluorescent probe for relay detection of Zn2+ and tartrate: Application to logic circuit and living cell imaging

A novel fluorescent probe 2-(2'-hydroxyphenyl)-4-(phenylethylamino)methyloxazole (HPO) has been synthesized, which performed highly selective and sensitive detection of Zn²⁺ ion with a discriminating enhancement over the other metal ions. The binding constant was calculated as 3.07 × 10³ M^-1 with detection limit of 1.22 × 10^-6 M in aqueous solution (CH₃CN-Tris v/v, 1/1, Tris, 10 mM, pH = 7.4). Moreover, the HPO-Zn²⁺ complex could serve as an excellent tartrate anion (TA). The detection mode maybe due to TA detach Zn²⁺ ion from HPO-Zn²⁺ complex leading to resulting in the release of the free probe HPO. As a result, a logic circuit has also been constructed on the basis of Zn²⁺ and TA as chemical inputs. Furthermore, fluorescence imaging experiments showed that probe HPO could be used as an effective fluorescent probe for detecting Zn²⁺ and TA in living cells.

Chelation-assisted de-aryloxylative amination of 2-aryloxy quinolines: a new synthetic route to a key fragment of a bioactive PRMT5 inhibitor

A highly regioselective de-aryloxylative amination of O- or N-chelating group-functionalized 2-aryloxy quinolines has been accomplished by means of a copper catalyst. The chelating functional groups of the substrate play a crucial role in directing the C-2-selective amination process, which proceeds through a novel aromatic nucleophilic substitution of the aryloxy group. The methodology provides expedient access to an important class of functionalized 2-aminoquinolines (up to 88% isolated yield) and was successfully applied for the synthesis of a key fragment of an important bioactive PRMT5 inhibitor.

A zinc fluorescent sensor used to detect mercury (II) and hydrosulfide

A zinc sensor based on quinoline and morpholine has been synthesized. The sensor selectively fluoresces in the presence of Zn²⁺, while not for other metal ions. Absorbance changes in the 350nm region are observed when Zn²⁺ binds, which binds in a 1:1 ratio. The sensor fluoresces due to Zn²⁺ above pH values of 6.0 and in the biological important region. The Zn²⁺-sensor complex has the unique ability to detect both Hg²⁺ and HS^-. The fluorescence of the Zn²⁺-sensor complex is quenched when it is exposed to aqueous solutions of Hg²⁺ with sub-micromolar detection levels for Hg²⁺. The fluorescence of the Zn²⁺-sensor complex is also quenched by aqueous solutions of hydrosulfide. The sensor was used to detect Zn²⁺ and Hg²⁺ in living cells.

A 4,5-quinolimide-based fluorescent sensor for the turn-on detection of Cd2+ with live-cell imaging

The first 4,5-quinolimide sensor, BNA, bearing the amide-DPA receptor, was reported for sensing Cd²⁺ with live-cell imaging.

A Ratiomeric Fluorescent Sensor for Zn2+ Based on N,N'-Di(quinolin-8-yl)oxalamide

A new ratiometric fluorescent sensor (DQO) based on N,N'-Di(quinolin-8-yl) oxalamide has been designed and synthesized for selective detection of Zn²⁺. The fluorescence ratio (I _{536 nm}/I _{450 nm}) of DQO was enhanced 10-fold when Zn²⁺ was present in a buffer aqueous solution at pH 8.66. The sensor showed linear response toward Zn²⁺ in the concentration range 0-15 μM, and the detection limit was calculated to be 2.4 μM. A Job's plot implied the formation of a DQO/Zn²⁺ complex with 1:1 stoichiometry, and the apparent association constant of DQO/Zn²⁺ complex was computed to be 1.5 × 10⁴ M^-1.

Quinoline benzimidazole-conjugate for the highly selective detection of Zn(ii) by dual colorimetric and fluorescent turn-on responses

A quinoline benzimidazole-conjugate (QBC) has been synthesized for the highly selective detection of Zn(ii) both by colorimetry and fluorimetry.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

A tetrazole-based fluorescence “turn-on” sensor for Al(iii) and Zn(ii) ions and its application in bioimaging

A dual fluorescent chemosensor for Al³⁺and Zn²⁺ions based on inhibition of ESIPT can be applied in bioimaging.

Cysteamine-based cell-permeable Zn(2+)-specific molecular bioimaging materials: from animal to plant cells

Structure-interaction/fluorescence relationship studies led to the development of a small chemical library of Zn(2+)-specific cysteamine-based molecular probes. The probe L5 with higher excitation/emission wavelengths, which absorbs in the visible region and emits in the green, was chosen as a model imaging material for biological studies. After successful imaging of intracellular zinc in four different kinds of cells including living organisms, plant, and animal cells, in vivo imaging potential of L5 was evaluated using plant systems. In vivo imaging of translocation of zinc through the stem of a small herb with a transparent stem, Peperomia pellucida, confirmed the stability of L5 inside biological systems and the suitability of L5 for real-time analysis. Similarly, fluorescence imaging of zinc in gram sprouts revealed the efficacy of the probe in the detection and localization of zinc in cereal crops. This imaging technique will help in knowing the efficiency of various techniques used for zinc enrichment of cereal crops. Computational analyses were carried out to better understand the structure, the formation of probe-Zn(2+) complexes, and the emission properties of these complexes.