Selective interactions of trivalent cations Fe³⁺, Al³⁺ and Cr³⁺ turn on fluorescence in a naphthalimide based single molecular probe

Wavelength specific aggregation induced emission in aqueous media permits selective detection of Ag+ and Hg2+ ions

A new 1,8-naphthalimide derivative (probe 1) adopts V-shaped structure, emits fluorescence and displays the Mie effect and aggregation-induced emission (AIE). Selective interactions of thiophilic Ag+ and Hg2+ ions (10 µM) with 1 (10 µM) resulted in AIEs at 499 and 521 nm, respectively. Both Ag+ and Hg2+ induce the formation of 1:2 complexes with 1, leading to the formation of AIE active aggregates with an average size of 423 and 198 nm, respectively. The formation of crystalline needles with Ag+ and spherical aggregates with Hg2+ results in wavelength specific AIE that permits the naked-eye and fluorometric detection of Ag+ and Hg2+ ions. Probe 1 shows excellent selectivity toward Ag+ and Hg2+ among various metal ions, therefore, 1 is suitable for the selective and quantitative detection of Ag+ and Hg2+ ions. Job plots are used for the determination of the stoichiometry of the complexes formed. It is evident from the fluorescence images of probe 1 in Rhizoctonia oryzae mycelia cells that they can be employed as potential candidates for in-vitro bioimaging.

Sensitive Fluorescent Probe for Al3+, Cr3+ and Fe3+: Application in Real Water Samples and Logic Gate

Construction of single probes for simultaneous detection of common trivalent metal ions has attracted much attention due to higher efficiency in analysis and cost. A naphthalimide-based fluorescent probe K1 was synthesized for selective detection of Al3+, Cr3+ and Fe3+ ions. Fluorescence emission intensity at 534 nm of probe K1 in DMSO/H2O (9:1, v/v) was significantly enhanced upon addition of Al3+, Cr3+ and Fe3+ ions while addition of other metal ions (Li+, Na+, K+, Ag+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+, Mn2+, Sr2+, Hg2+, Ca2+, Mg2+, Ce3+, Bi3+ and Au3+) did not bring about substantial change in fluorescence emission. The calculated detection limits were 0.32 µM, 0.81 µM, and 0.27 µM for Al3+, Cr3+, and Fe3+, respectively. Probe K1 displayed strong anti-interference ability, a large Stokes shift, rapid response, and applicability in a wide pH range for the simultaneous detection of Al3+, Cr3+ and Fe3+ in real water samples. Job's plot test showed that the stoichiometric ratio of the complexes formed between probe K1 and the trivalent metal ions was 1:1. The reversible application of probe K1 was realized by addition of Na2EDTA. A molecular logic gate was built based on the input-output information. This approach may provide a basis for highly selective and sensitive detection of common trivalent cations and for design of memory devices.

Single-Probe-Based Sensor Array for Fingerprint Recognition of Trivalent Metal Ions and Application in Water Identification

Abnormal concentration levels of trivalent metal ions (M3+) might hinder their natural biological activities in physiological processes and cause severe health hazards. Herein, a dual-chromophore probe (RhB-TPE) composed of rhodamine and tetraphenylethene (TPE) units was synthesized and explored for discriminating M3+ ions. It exhibited special aggregation and AIE properties in aqueous media. Its ensemble with anionic surfactant SDBS assemblies (RhB-TPE/SDBS) could be utilized as fluorescent sensors for selective and sensitive detection of M3+ ions such as Fe3+, Al3+, and Cr3+ by illustrating quenched TPE emission and switched-on rhodamine emission. Moreover, the use of SDBS assemblies at two concentrations could provide a single-probe-based sensor array and realize four-signal pattern recognition of different concentrations of the three M3+ ions and identify M3+ mixtures or unknown samples. The cross-reactive fluorescence variation was attributed to the M3+ influence on the FRET process from TPE to open-ring form rhodamine in the two ensemble sensors. With the coexistence of Al3+, the optimized RhB-TPE/SDBS ensemble sensor array was successfully applied to differentiate commercially available brand mineral water and purified water, as well as tap water. The present work provides a novel strategy to generate a single-probe-based sensor array and realizes fingerprint recognition of three trivalent metal ions and efficient discrimination of different types of water. The modulation FRET process of a dual chromophore in different surfactant ensembles inspires the future construction of novel and effective sensing platforms.

Recent developments in the creation of a single molecular sensing tool for ternary iron (III), chromium (III), aluminium (III) ionic species: A review

Rational design of a molecular sensing tool is an important topic in molecular recognition, signalling, and optoelectronics that has piqued the interest of chemists, biologists, and environmental scientists. Approximately 150 years have passed since the beginning of the fluorescent chemosensor sector. Due to the paramagnetic properties of Cr3+ and Al3+ , it is tough to prepare a photoluminescence plug-in detector. Most dye-based Al3+ sensors must be utilized in organic or mixed solvents for robust hydration of Al3+ in water. The sophisticated molecular design of sensors, conversely, allows for the detection of these metal ions in aqueous medium. The design of chemosensors using various fluorophores and their mechanisms of action have been thoroughly discussed. A literature survey covering the design of chemosensors and their mechanisms of action have been thoroughly discussed covering the period 2010-2022 and that was carried out including innovative and exemplary activities from numerous groups throughout the world that have significantly contributed to this sector. The most important advantages of these probes are their aqueous solubility and quick response with outstanding selectivity and sensitivity for temporal distribution with high fidelity of metals in living cells.

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.

Novel schiff base as Fe3+ sensor as well as an antioxidant and its theoretical studies

A novel Schiff base derivative L (N1-(thiophene-2-ylmethylene)benzene-1,2-diamine) was synthesized via condensation reaction of 3-thiophene carboxaldehyde and 1,2-diamino benzene. The synthesized compound was authenticated using 1 H NMR, 13 C NMR, HRMS, and IR spectroscopy. The compound L was found to be a Fe3+ sensor with the complexation ratio of 1 : 3 as revealed by Job’s plot with maximum absorption at 318 nm. The photophysical properties were studied using absorption and emission spectra. DFT and TD-DFT studies were carried out in order to support the photophysical outcomes of compound L. An antioxidant behaviour of compound L was studied using TAC, FRAP, and DPPH assays and it was found to be showing better TAC activity than the used standard i.e. gallic acid.

Fabrication and DFT Calculation of Amine-Functionalized Metal-Organic Framework as a Turn-On Fluorescence Sensor for Fe3+ and Al3+ Ions

Due to their important role in biological systems, it is urgent to develop a material that can rapidly and sensitively detect the concentration of Fe³⁺ and Al³⁺ ions. In this work, a brand-new Cd^II-based metal-organic framework [Cd(BTBD)₂(AIC)]_n (JXUST-18, BTBD = 4,7-bis(1H-1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole and H₂AIC = 5-aminoisophthalic acid) with a 4-connected sql topology was designed and synthesized. The symmetrical Cd^II centers are linked by AIC^2- ligands with μ₃-η¹:η¹:η¹:η¹ coordination mode to form a [Cd₂(COO)₂] secondary building unit (SBU). The contiguous SBUs are further connected by BTBD ligands to form a two-dimensional (2D) layer structure. JXUST-18 can remain stable in aqueous solutions with pH values of 3-12 or in boiling water. Luminescent experiments suggest that JXUST-18 displays more than eightfold fluorescence enhancement in the presence of Fe³⁺ and Al³⁺ ions, and the detection limits for Fe³⁺ and Al³⁺ ions are 0.196 and 0.184 μM, respectively. Furthermore, the change in luminescence color is uncomplicatedly distinguishable with the naked eye under ultraviolet light at 365 nm. In addition, a series of devices based on JXUST-18 including fluorescence test strips, lamp beads, and composite films were developed to detect metal ions via visual changes in luminescence color. Significantly, JXUST-18 is a rare MOF-based turn-on fluorescence sensor for the detection of Fe³⁺ ions. The theoretical calculation suggests that the complexation of Fe³⁺/Al³⁺ ions and the -NH₂ group contributes to fluorescence enhancement.

Live cell imaging by 3-imino-(2-phenol)-1,8-naphthalimides: The effect of ex vivo hydrolysis

A series of 3-amino-N-substituted-1,8-naphthalimides and their salicylic Schiff base derivatives were synthesized. The structure of the obtained compounds was confirmed using ¹H and ¹³C NMR, FT-IR spectroscopy and elemental analysis and COSY and HMQC for the representative molecules. The photophysical (UV-Vis, PL) and biological properties of all of the prepared compounds were studied. It was found that the amine with the n-hexyl group in EtOH had the highest PL quantum yield (Ф = 85%) compared to the others. Moreover, the chelating properties of the azomethines with the n-hexyl group (1a, 1b, 1c) were tested against various cations (Al³⁺, Ba²⁺, Co²⁺, Cu²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, Sr²⁺ and Zn²⁺) in an acetonitrile, acetone and PBS/AC mixture. Compounds that contained the electron withdrawing groups (-Br, -I) had the ability to chelate most of the studied cations, while the unsubstituted derivative chelated only the trivalent cations such as Al³⁺, Cr³⁺ and Fe³⁺ in acetonitrile. The effect of the environment on the keto-enol tautomeric equilibrium was also demonstrated, especially in the case of the derivative with a bromine atom. The biological studies showed that the tested molecules had no cytotoxicity. Additionally, the ability to image intracellular organelles such as the mitochondria and endoplasmic reticulum was revealed. The crucial role of the hydrolysis of imines for cellular imaging was presented.

Dual sensing and synchronous fluorescence spectroscopic monitoring of Cr3+and Al3+ using a luminescent Schiff base: Extraction and DFT studies

A well designed, new pyrene based small molecule (L) was synthesized from 1:1 condensation reaction of 1-aminopyrene and 6-(1,3-benzodioxal-5-yl)-2-pyridine carboxaldehyde which was characterized by absorption, emission spectrometry, FTIR, NMR and mass studies. Interestingly the UV-vis and fluorescence spectroscopic studies revealed that the ligand (L) works as a dual turn-on luminescent chemosensor for chromium(III) (Cr³⁺) and aluminium(III) (Al³⁺) in aqueous environment which were further supported by DFT and TDDFT studies. L shows a significant colour change from pale yellow to reddish yellow with a detection limit of ~10^-9 M in the presence of Cr³⁺ and Al³⁺ whereas there were no noteworthy changes in the presence of other monovalent and divalent metal ions. The molecular signaling in the presence of Cr³⁺, Al³⁺, Fe³⁺ and EDTA was compared with advanced level combinational INHIBIT gate based on 4 input logic gates. Herein, first derivative constant wavelength synchronous fluorescence spectroscopy (1^st DCWSFS) was applied for the determination of Cr³⁺, Al³⁺ ion concentrations in a mixture via increment of spectral resolution of the respective overlapping peaks. 1^st DCWSFS is reported to be used in pharmaceuticals but very few works have been done for determination of metal ion concentration in environmental sample without prior separation. The individual Cr³⁺and Al³⁺ ion concentrations in a mixture were determined through liquid-liquid extraction process and the efficiencies were compared with 1^st derivative SFS method. It was observed that 1^st derivative SFS process is more efficient than conventional liquid-liquid extraction process. Therefore, 1^st DCWSFS method using sensor L might be useful as a diagnostic tool for detection of individual metal ion concentrations (Cr³⁺ and Al³⁺) from a mixture which will be cost-effective, time saving and more precise.

Luminescence sensing, DFT, extraction and monitoring of Cr3+ and Al3+via the application of first derivative fluorescence spectroscopy

Turn-on recognition of an anthracene-based Schiff base followed by the use of a sensitive technique for metal estimation without prior separation.

A lysosome-targetable fluorescent probe for imaging trivalent cations Fe3+, Al3+ and Cr3+ in living cells

An effective morpholine-type naphthalimide chemsensor, N-p-chlorophenyl-4-(2-aminoethyl)morpholine-1,8-naphthalimide (CMN) has been developed as a lysosome-targeted fluorometric sensor for trivalent metal ions (Fe³⁺, Al³⁺ and Cr³⁺). Upon the addition of Fe³⁺, Al³⁺ or Cr³⁺ ions, the probe CMN showed an evident naked-eye color changes which pale yellow solution of CMN turned deepened and it displayed turn-on fluorescence response in methanol. CMN showed a significant selective and sensitive toward Fe³⁺, Al³⁺ or Cr³⁺ ions, while there was no obvious behavior to other monovalent or divalent metal ions from the UV-vis and fluorescence spectrum. Based on the Job's plot analyses the 1:1 coordination mode of CMN with Fe³⁺, Al³⁺ or Cr³⁺ was proposed. The limit of detection (LOD) observed were 0.65, 0.69 and 0.68 μM for Fe³⁺, Al³⁺ and Cr³⁺ ions, respectively. The N-atom of morpholine directly involved in complex formation, CMN emitted fluorescence through inhibition of photoinduced electron transfer (PET). This probe exhibited excellent imaging ability for Fe³⁺, Al³⁺and Cr³⁺ ions in living cells with low cytotoxicity. Significantly, the cellular confocal microscopic research indicated that the lysosome-targeted group of morpholine moiety was introduced which realized the capability of imaging lysosomal trivalent metal ions in living cells for the first time.

A Highly Selective Fluorescence "Turn on" and Absorbance-Ratiometric Detection of Al3+ in Totally H2O and its Application in Test Paper

A novel naphthalene based fluorescence probe NBDH was designed and synthesized. Probe NBDH exhibited highly selective and sensitive responses towards Al³⁺ in HEPES-NaOH buffer solution (pH = 7.4). In addition, the detection of NBDH to Al³⁺ could be achieved through dual channels embodied in significant fluorescent turn-on signal and ratiometric absorbance response. The stoichiometry ratio of NBDH-Al³⁺ was 1:1 by fluorescence job' plot and binging mechanism was further varified by the FT-IR, NMR titration and HRMS. Furthermore, NBDH was achieved in real sample detection, and a series of color test paper were developed for visual detecting Al³⁺ ions.

High Performance Fluorescent Turn-On Probe for Amitriptyline Based on Hybrid Nanoassembly of Organic-Inorganic Nanoparticles

Fluorescence methods have gained enormous attention due to their ease in use, simplicity, selectivity and sensitivity. Fluorescent chemosensors respond instantly by converting molecular recognition to fluorescent signals. The consumption of pharmaceutical products by living beings is on great increase. The disposal of such compounds in the environment is a matter of great concern as these compounds enter aquatic environment and show accumulation in tissues of aquatic organisms. In the present study, we have utilized naphthalimide based receptors to fabricate organic nanoparticles (ONPs). These ONPs were used for the development of hybrid nanoassemblies, and the developed nanoassemblies were characterized with the help of transmission electron microscopy and dynamic light scattering studies. The photophysical studies were performed and the hybrid assembly developed using receptor 2 demonstrated a turn-on fluorescence emission behavior on binding with Amitriptyline. The present sensing system acted as promising candidate for determination of Amitriptyline among other contending drug molecules. The established system can recognize Amitriptyline up to a detection limit of 48 nM in aqueous medium. Electrochemical recognition studies show binding of hybrid nanoassembly of receptor 2 with Amitriptyline with limit of detection of 21 nM.

Highly sensitive and selective light-up fluorescent probe for monitoring gallium and chromium ions in vitro and in vivo

Here reported an NBDT sensor could be effectively responsive to gallium and chromium for bio-imaging in vivo.

Highly sensitive oligothiophene-phenylamine-based dual-functional fluorescence "turn-on" sensor for rapid and simultaneous detection of Al3+ and Fe3+ in environment and food samples

Developing low-cost and efficient sensors for rapid, selective and sensitive detection of the transition metal ions in environmental and food science is very important. In this study, a novel dual-functional fluorescent "turn-on" sensor 3TP based on oligothiophene-phenylamine Schiff base has been synthesized for discrimination and simultaneous detection of both Al³⁺ and Fe³⁺ ions with high selectivity and anti-interference over other metal ions. Sensor 3TP displayed a very fast fluorescence-enhanced response towards Al³⁺ and Fe³⁺ ions with low detection limits (0.177μM for Al³⁺ and 0.172μM for Fe³⁺) and wide pH response range (4.0-12.0). The Al³⁺/Fe³⁺ sensing mechanisms were investigated by fluorescence experiments, ¹H NMR titrations, FT-IR and ESI-MS spectra. Importantly, sensor 3TP was served as an efficient solid material for the highly sensitive and selective detection of Fe³⁺ on TLC plates. Moreover, the sensor 3TP has been successfully used to detect trace Al³⁺ and Fe³⁺ in environment and food samples with satisfactory results and good recoveries, revealing a convenient, reliable and accurate method for Al³⁺ and Fe³⁺ analysis in real samples.

Highly Selective Detection of Cr3 + Ion with Colorimetric & Fluorescent Response Via Chemodosimetric Approach in Aqueous Medium

So far, very few numbers of chemosensors for Cr³⁺ ion have been reported. However, the main drawback of reported receptors are the lack of selectivity and other trivalent cations such as Fe³⁺, Al³⁺ and anions like F^- and ^-OAc frequently interfere with such assays. This paper present the synthesis, characterization & sensor studies of Schiff base containing naphthalene moiety which selectively detect Cr³⁺ ion by chemodosimetric approach. Using FT-IR, ¹H NMR, ¹³C NMR and ESI mass spectroscopic techniques the probe was characterized. This receptor exhibit more selectivity and sensitivity towards Cr³⁺ than other divalent and trivalent cations like Mn²⁺, Zn²⁺, Co²⁺, Ni²⁺, Cd²⁺, Cu²⁺, Hg²⁺, Fe³⁺, and Al³⁺ ions. After the addition of chromium ion the receptor get change from yellow to colorless in aqueous medium. But no color change was observed on the addition of other metal ions. Using UV-Vis and PL studies, it was confirmed that the selective hydrolysis of imine group of receptor by Cr³⁺ ions takes place with high fluorescence enhancement that is corresponding to 1-naphthylamine. Receptor acts as selective chemodosimeter for Cr³⁺ ions with 2:1 stoichiometry and micro molar detection limit. This chemodosimetric approach was applied successfully for bio-imaging of HeLa cells.

Straightforward Design of Fluorescent Receptors for Sulfate: Study of Non-Covalent Interactions Contributing to Host-Guest Formation

A straightforward design of receptors for binding and sensing of sulfate in aqueous medium was developed. The design involves the connection of two naphthalimide-based pH probes through a hydrogen-bonding motif. The structure of the receptor-sulfate complex, predicted by DFT calculations, was unambiguously confirmed by NMR measurements. There are three major interactions stabilizing the host-guest complex: electrostatic interactions, hydrogen bonding, and stacking interactions of the dyes. Study of two control receptors containing either one dye or methyl amide groups instead of amides, revealed that electrostatic and hydrogen bonding interactions contribute the most to affinity and selectivity of receptors. The receptors can detect sulfate in a 1:1 THF-buffer mixture in pH window 3.6-4.5 demonstrating up to 7-fold fluorescence enhancement. To the best of our knowledge, the reported PET (photoinduced electron transfer) anion probes possess the largest response for sulfate in aqueous solution yet described.

A review of mechanisms for fluorescent ‘‘turn-on’’ probes to detect Al3+ ions

The adverse effect of Al³⁺ ions on human health as well as the environment makes it desirable to develop sensitive and specific techniques for the detection of Al³⁺ ions.

A new fluorescent probe based on quinoline for detection of Al3+ and Fe3+ with “off–on–off” response in aqueous solution

A new quinoline-based fluorescent probe has been designed and synthesized. It showed highly selective relay recognition of Al³⁺ and Fe³⁺via a fluorescence “off–on–off” mechanism by central metal displacement.

A novel 2-(2′-aminophenyl)benzothiazole derivative displays ESIPT and permits selective detection of Zn2+ ions: experimental and theoretical studies

Synthesis of a novel 2-(2′-aminophenyl)benzothiazole based probe (1) and demonstration of excited state intramolecular proton transfer (ESIPT) with a large Stokes shift (∼246 nm) are presented.