Quinoline-based molecular clips for selective fluorescent detection of Zn2+

A Cu2+ fluorescent chemosensor suitable for quantitative detection of tyrosinase in potatoes over a wide pH range

Cu2+ as an important trace element plays an essential role in various biologic processes due to the unique redox active nature. For this reason, much effort has been made to develop effective methods for Cu2+ detection. In this study, a novel structure fluorescent chemosensor, 1-(6-(((5-(5, 5-difluoro-1, 3, 7, 9-tetramethyl-5H-4λ4, 5λ4-dipyrrolo[1, 2-c:2', 1'-f][1, 3, 2] diazaborinin-10-yl)quinolin-8-yl)oxy)methyl)pyridin-2-yl)-N, N-bis(pyridin-2-ylmethyl)methanamine (1), was synthesized and characterized by 1H and 13C nuclear magnetic resonance spectroscopy, and electrospray ionization mass spectrometry. Sensor 1 showed an obviously "on-off" fluorescence response to Cu2+ with a 1:1 binding stoichiometry by UV-vis and fluorescence spectrophotometry. The detection limit of sensor 1 to Cu2+ was determined to be 1.9 µM, and the stable pH range for Cu2+ detection was from 3 to 13. Sensor 1 can be used for recognition and detection of tyrosinase in potatoes.

A novel chromone Schiff base as Zn2+ turn-on fluorescent chemosensor in a mixed solution

In this study, a novel fluorescent chemosensor 1 based on chromone-3-carboxaldehyde Schiff base was synthesized and featured through nuclear magnetic resonance (NMR) and mass spectra. Spectroscopic investigation indicated that the fluorescent sensor showed high selectivity toward Zn2+ over other metal ions and that the detection limit of 1 could reach 10-7  M. These indicated that 1 acted as a highly selective and sensitive fluorescence chemosensor for Zn2+ .

Synthesis and Applications of Fluorescent Chemosensors: A Review

Fluorescent sensors have emerged as powerful tools in analytical chemistry for the detection and quantification of heavy and transition metal ions in aqueous samples. These metal ions pollute the environment and cause a number of diseases, such as irritability, anaemia, muscle paralysis, neurological damage, and memory loss. Moreover, we explore the wide spectrum of applications in environmental monitoring, where these sensors enable precise detection of contaminants, as well as in biomedical fields, facilitating diagnostic and therapeutic advancements. While highlighting the exceptional progress achieved in this field, I also address the challenges and future prospects for the continued development of fluorescent sensors, emphasizing their potential to shape the future of water quality assessment and analytical chemistry. Heavy and transition metals are of great concern because of their extreme toxicity even at very low concentration and tendency to be accumulated in bodies of living organisms. During the recent years, the design and synthesis of fluorescent chemosensors for sensing environmentally and biologically relevant important metals, particularly for heavy and transition metals, is of great interest. Opon complexation with heavy and transition metals, the fluorescence intensity of these fluorescent chemosensors either quenched or enhanced. The current review paper explains various fluorescent chemosensors for determination of toxic heavy and transition metals in environmental water samples.

Aza-phenol Based Macrocyclic Probes Design for "CHEF-on" Multi Analytes Sensor: Crystal Structure Elucidation and Application in Biological Cell Imaging

Metal bound macrocyclic compounds found in biological systems inspired us to design and synthesize two Robson-type macrocyclic Schiff-base chemosensors, H ₂ L1 (H ₂ L1=1,11-dimethyl-6,16-dithia-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol) and H ₂ L2 (H ₂ L2=1,11-dimethyl-6,16-dioxa-3,9,13,19-tetraaza-1,11(1,3)-dibenzenacycloicosaphane-2,9,12,19-tetraene-1,11-diol). Both the chemosensors have been characterized with different spectroscopic techniques. They act as multianalyte sensor and exhibit "turn-on" fluorescence toward different metal ions in 1X PBS (Phosphate Buffered Saline) solution. In presence of Zn²⁺, Al³⁺, Cr³⁺ and Fe³⁺ ions, H ₂ L1 exhibits ∼6-fold enhancement of emission intensity, while H ₂ L2 shows ∼6-fold enhancement of emission intensity in the presence of Zn²⁺, Al³⁺ and Cr³⁺ ions. The interaction between the different metal ion and chemosensor have been examined by absorption, emission, and ¹H NMR spectroscopy as well as by ESI-MS⁺ analysis. We have successfully isolated and solved the crystal structure of the complex [Zn(H ₂ L1)(NO₃)]NO₃ (1) by X-ray crystallography. The crystal structure of 1 shows 1:1 metal:ligand stoichiometry and helps to understand the observed PET-Off-CHEF-On sensing mechanism. LOD values of H ₂ L1 and H ₂ L2 toward metal ions are found to be ∼10^-8 and ∼10^-7 M, respectively. Large Stokes shifts of the probes against analytes (∼100 nm) make them a suitable candidate for biological cell imaging studies. Robson type phenol based macrocyclic fluorescence sensors are very scarce in the literature. Therefore, the tuning of structural parameters as the number and nature of donor atoms, their relative locations and presence of rigid aromatic groups can lead to the design of new chemosensors, which can accommodate different charged/neutral guest(s) inside its cavity. The study of the spectroscopic properties of this type of macrocyclic ligands and their complexes might open a new avenue of chemosensors.

HPLC with Fluorescence and Photodiode Array Detection for Quantifying Capmatinib in Biological Samples: Application to In Vivo and In Vitro Studies

Capmatinib, a recently approved tyrosine kinase inhibitor, is used for the treatment of non-small cell lung cancer. We describe two new HPLC methods for capmatinib quantification in vivo and in vitro. HPLC with a fluorescence detection method was used to quantify capmatinib in plasma for the first time. The method was successfully applied in a pharmacokinetic study following a 10 mg/kg oral dose of capmatinib given to rats. The chromatographic separation was performed using a Eurospher II 100-3 C18H (50 × 4 mm, 3 µm) column and a mobile phase containing 10 mM of ammonium acetate buffer (pH 5.5): acetonitrile (70:30, v/v), at a flow rate of 2.0 mL min^-1. The study also describes the use of HPLC-PDA for the first time for the determination of capmatinib in human liver microsomes and describes its application to study its metabolic stability in vitro. Our results were in agreement with those reported using LC-MS/MS, demonstrating the reliability of the method. The study utilized a Gemini-NX C18 column and a mobile phase containing methanol: 20 mM ammonium formate buffer pH 3.5 (53:47, v/v), delivered at a flow rate of 1.1 mL min^-1. These methods are suitable for supporting pharmacokinetic studies, particularly in bioanalytical labs lacking LC-MS/MS capabilities.

Thermally Stable Fluorogenic Zn(II) Sensor Based on a Bis(benzimidazole)pyridine-Linked Phenyl-Silsesquioxane Polymer

A 2,6-bis(2-benzimidazolyl) pyridine-linked silsesquioxane-based semi-branched polymer was synthesized, and its photophysical and metal-sensing properties have been investigated. The polymer is thermally stable up to 285 °C and emits blue in both solid and solution state. The emission of the polymer is sensitive to pH and is gradually decreased and quenched upon protonation of the linkers. The initial emission color is recoverable upon deprotonation with triethylamine. The polymer also shows unique spectroscopic properties in both absorption and emission upon long-term UV irradiation, with red-shifted absorption and emission not present in a simple blended system of phenylsilsesquioxane and linker, suggesting that a long-lived energy transfer or charge separated state is present. In addition, the polymer acts as a fluorescence shift sensor for Zn(II) ions, with red shifts observed from 464 to 528 nm, and reversible binding by the introduction of a competitive ligand such as tetrahydrofuran. The ion sensing mechanism can differentiate Zn(II) from Cd(II) by fluorescence color shifts, which is unique because they are in the same group of the periodic table and possess similar chemical properties. Finally, the polymer system embedded in a paper strip acts as a fluorescent chemosensor for Zn(II) ions in solution, showing its potential as a solid phase ion extractor.

Chemosensing of Guanosine Triphosphate Based on a Fluorescent Dinuclear Zn(II)-Dipicolylamine Complex in Water

Guanosine triphosphate (GTP) is a key biomarker of multiple cellular processes and human diseases. The new fluorescent dinuclear complex [Zn₂(L)(S)][OTf]₄, 1 (asymmetric ligand, L = 5,8-Bis{[bis(2-pyridylmethyl)amino] methyl}quinoline, S = solvent, and OTf = triflate anion) was synthesized and studied in-depth as a chemosensor for nucleoside polyphosphates and inorganic anions in pure water. Additions at neutral pH of nucleoside triphosphates, guanosine diphosphate, guanosine monophosphate, and pyrophosphate (PPi) to 1 quench its blue emission (λ_em = 410 nm) with a pronounced selectivity toward GTP over other anions, including adenosine triphosphate (ATP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The efficient quenching response by the addition of GTP was observed in the presence of coexisting species in blood plasma and urine with a detection limit of 9.2 μmol L^-1. GTP also shows much tighter binding to the receptor 1 on a submicromolar level. On the basis of multiple spectroscopic tools (¹H, ³¹P NMR, UV-vis, and fluorescence) and DFT calculations, the binding mode is proposed through three-point recognition involving the simultaneous coordination of the N⁷ atom of the guanosine motif and two phosphate groups to the two Zn(II) atoms. Spectroscopic studies, MS-ESI, and DFT suggested that GTP bound to 1 in 1:1 and 2:2 models with high overall binding constants of log β_1 (1:1) = 6.05 ± 0.01 and log β₂ = 10.91 ± 0.03, respectively. The optical change and selectivity are attributed to the efficient binding of GTP to 1 by the combination of a strong electrostatic contribution and synergic effects of coordination bonds. Such GTP selectivity of an asymmetric metal-based receptor in water is still rare.

A novel dual-function probe for recognition of Zn2+ and Al3+ and its application in real samples

A dual-function probe NAHH based on naphthalene was synthesized and characterized. Based on the combination effects derived from the inhabitation of photo-induced electron transfer (PET) and CN isomerization, probe NAHH achieved in the recognition of Zn2+ and Al3+ both through obvious fluorescence enhancement and color changes detected by naked eye, respectively. Probe NAHH showed high sensitivity with the limit of detection as low as 3.02 × 10-7 M for Zn2+ and 7.55 × 10-8 M for Al3+, indicated the capability of probe NAHH in trace detection for Zn2+ and Al3+. The binding ratio of NAHH with Zn2+ and Al3+ were all 1:1 determined by Job plot, and the corresponding association constant was calculated as 8.48 × 104 M-1 and 4.45 × 105 M-1, respectively. The mechanism was further confirmed by FT-IR, 1H NMR titration and ESI-MS analysis. Furthermore, probe NAHH was successfully applied in logic gate construction and the detection of Zn2+ and Al3+ in Songhua River and test stripe. Fluorescence imaging experiments confirmed that NAHH could be used to monitor Zn2+ in plant root.

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).

A unique benzimidazole-naphthalene hybrid molecule for independent detection of Zn2+ and N3- ions: Experimental and theoretical investigations

Single crystal X-ray structurally characterized benzimidazole-naphthalene hybrid (NABI) functions as a unique dual analyte sensor that can detect Zn²⁺ cation and N₃^- anion independently. The NABI forms chelate with Zn²⁺ to inhibit internal charge transfer (ICT) and CHN isomerisation resulting chelation enhanced fluorescence (CHEF). On the other hand, the sensing of N₃^- is based on formation of supramolecular H-bonded rigid assembly. The association constant of NABI for Zn²⁺ and N₃^- ions are 19 × 10⁴ M^-1 and 11 × 10² M^-1, respectively. Corresponding limit of detections (LOD) are 6.85 × 10^-8 and 1.82 × 10^-7 M, respectively. NABI efficiently detects intracellular Zn²⁺ and N₃^- ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and Zn²⁺/N₃^- bound forms.

Remarkable difference in Al3+ and Zn2+ sensing properties of quinoline based isomers

Two positional isomers, 4-methyl-2-((quinolin-6-ylimino)methyl)phenol (6-QMP) and 4-methyl-2-((quinolin-2-ylimino)methyl)phenol (2-QMP), have been synthesized to compare their fluorescence sensing properties. 6-QMP and 2-QMP have been synthesized by Schiff-base condensation between 2-hydroxy-5-methylbenzaldehyde and the respective amine (6-aminoquinoline for 6-QMP and 2-aminoquinoline for 2-QMP) under mild conditions. These compounds have been characterized by standard methods. 6-QMP and 2-QMP have been found to be dual fluorescence chemosensors for Al3+ and Zn2+ ions but the increment of fluorescence intensity varies. 6-QMP can detect Al3+ (emission at 543 nm) and Zn2+ (emission at 525 nm) by the enhancement of emission intensity by 97 and 79 fold, respectively, with the same excitation wavelength at 415 nm. However, 2-QMP shows two different excitation and emission wavelengths for the detection of Al3+ (emission at 376 nm; λex = 330 nm) and Zn2+ (emission at 550 nm; λex = 435 nm). The increase in emission intensity is low (4.5 fold for Al3+ and 35 fold for Zn2+) compared to that with 6-QMP. The enhancement of intensity may be explained by the PET mechanism. Both the probes form a 1 : 1 complex with both the metal ions as indicated by the elemental and different spectral analysis. 6-QMP shows better sensitivity towards both the metal ions than 2-QMP. Both the probes are able to detect Al3+ and Zn2+ ions by producing distinct color changes that can be observed by the naked eye. Some theoretical calculations have been performed to investigate spectral transitions of the probes along with their aluminum and zinc compounds. These compounds have been used for living cell imaging studies. A comparison with the recently published studies has been made.

Deciphering the CHEF-PET-ESIPT liaison mechanism in a Zn2+ chemosensor and its applications in cell imaging study

Proper fusion of fluorescence mechanisms in a single fluorophore unit is highly desirable to obtain better sensitivity, as well as selectivity towards a particular metal ion.

A Highly Selective and Sensitive Chemosensor for Colorimetric and Fluorescent Detection of Al3+ and Living Cell Imaging

A colorimetric and fluorescent dual chemosensor for detecting Al3+, (E)-N′-((2-hydroxynaphthalen-1-yl)methylene)nicotinohydrazide (HNN), was developed by combining 2-hydroxy-1-naphthaldehyde with nicotinohydrazide. Addition of Al3+ to EtOH–H2O solution of HNN gives rise to a visible colour change from colourless to light blue and a significantly enhanced fluorescence. Other metal ions including Na+, K+, Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Cu2+, Cr3+, Ag+, Pb2+, Zn2+, Cd2+, Hg2+, Fe2+, and Fe3+ have no or little effect on the specific response of HNN to Al3+. The binding mode of HNN–Al3+ complex was further clarified by electrospray ionisation mass spectrometry and 1H NMR titration experiments.

A family of Fe3+ based double-stranded helicates showing a magnetocaloric effect, and Rhodamine B dye and DNA binding activities

A series of Fe³⁺ based double-stranded helicates unveil a significant magnetocaloric effect as well as binding activities with Rhodamine B dye and CT-DNA.

Synthesis, crystal structures and luminescent properties of two one-dimensional cadmium(II) coordination polymers generated from polydentate Schiff-base ligand

Two new one-dimensional coordination polymers {[CdL(2)(H(2)O)(2)](NO(3))(2)(H(2)O)(6)}(n) (1) and {[CdLI(2)](H(2)O)(CH(3)OH)}(n) (2) have been synthesized and characterized by IR, elemental analysis, TG technique, XRPD and complete single crystal structure analyses, where L is bis(pyridin-4-ylmethylene)biphenyl-2,2'-dicarbohydrazide. The Cd(II) atom has a distorted octahedral coordination geometry with N(4)O(2) donors from four ligands and two water molecules in 1 and a distorted tetrahedral coordination geometry with NOI(2) donors from two ligands and two I(-) anions in 2, respectively. Polymer 1 shows a 1D framework structure containing bimetallic 42-membered quadrangular ring units. The adjacent 1D chains are interacted forming a 3D supramolecular network structure through multiform hydrogen bond interactions. In comparison with 1, polymer 2 is a new rampart-type chain and each chain is interacted with each other through hydrogen bond interactions to lead a 2D layer. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.

Methoxy-substituted isoTQEN family for enhanced fluorescence response toward zinc ion

Previously, we have reported that 1- and 3-isoTQENs (N,N,N',N'-tetrakis(1- or 3-isoquinolylmethyl)ethylenediamines) exhibit a specific fluorescence enhancement toward zinc ion. In this study, three methoxy-substituted derivatives of 1-isoTQEN were synthesized and their fluorescent response toward zinc ion was studied. The substitution pattern of the methoxy group significantly changes the solubility of compounds in aqueous DMF, λ(max) in the absorption spectra, excitation/emission wavelengths and fluorescence intensity of zinc complexes. In the presence of zinc ion, 7-MeO-1-isoTQEN exhibits higher fluorescence intensity and longer excitation/emission wavelengths (λ(ex) = 342 nm, λ(em) = 526 nm) than 6-MeO-1-isoTQEN (λ(ex) = 303 nm, λ(em) = 469 nm) and 5,6,7-triMeO-1-isoTQEN (λ(ex) = 340 nm, λ(em) = 504 nm). The fluorescence intensity of a zinc complex of 7-MeO-1-isoTQEN (ϕ = 0.122) is four times higher than the parent 1-isoTQEN (ϕ = 0.034) under the same conditions. The crystal structure of 7-MeO-1-isoTQEN-Zn complex reveals that all six nitrogen atoms participate to the metal coordination with ideal octahedral geometry, affording significantly high metal binding affinity comparable with TPEN (N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine). 7-MeO-1-isoTQEN detects zinc ion concentration change in cells by fluorescence microscopic analysis.