Two Schiff-base fluorescent sensors for selective sensing of aluminum (III): Experimental and computational studies

A Novel Naphthylidene-diimine Chemosensor for Selective Colorimetric and Fluorometric Detection of Al3+ and CN- Ions

A naphthylidene-diimine L2 was newly designed, and its structure was identified by elemental analysis and spectroscopic methods. The effect of temperature, acid-base and light on enol-keto tautomerism in this Schiff base was evaluated by colorimetry, UV-Vis and fluorescence spectroscopy. Under irradiation 365 nm, L2 emitted yellow, orange and strong green emission in pure, basic and aqueous DMSO media (v/v, 1/1), respectively. Its ionochromic behavior against various cations (Fe3+, Al3+, Cr3+, Cu2+, Co2+, Ni2+, Zn2+, Cd2+, Pb2+, Ba2+ and Ag+) and anions (F-, Cl-, CH3COO-, SO32-, S2O32-, HSO4-, H2PO4-, NO3-, CN-, and OH-) was investigated in aqueous DMSO media (v/v, 1/1) by UV-Vis and fluorescence experiments. Dark yellow color of L2 changed to colorless for Fe3+, Cr3+ and HSO4- ions, and turned to light yellow for Al3+ and Cu2+ ions, and to orange for CN- and OH- ions. According to UV-Vis data, the chemosensor displayed selective recognition towards Fe3+, Al3+, Cu2+, HSO4-, CN- and OH- with a 1:1 stoichiometric ratio. At the excitation wavelength of 365 nm, L2 gave strong yellowish white emission (λem = 445 and 539 nm) in the presence of Al3+, and the intensity increased about 12.5 times. On the other hand, the chemosensor displayed one emission band at 452 nm and 450 nm in the presence of CN- and OH- with 1.9 fold and 2.3 fold fluorescence enhancement, respectively.

A novel pyrene-based fluorescent probe for Al3+ detection

Based on the classical Schiff base reaction, fluorescent probe dimethyl 5-((pyren-1-ylmethylene)amino)isophthalate (PAI) is designed and synthesized through introducing Schiff base structure to pyrene unit for structural modification. The structure of the synthesized probe PAI is determined and characterized by FT-IR, ¹H NMR, ¹³C NMR and HRMS. PAI is a type of "turn-on" probe which can specifically recognize Al³⁺ ion with high selectivity. The limit of detection is calculated to be 3.07 × 10^-8 M, which proves the probe's high sensitivity and is lower than that of many efficient reported probes. The probe PAI is intrinsically non-fluorescent due to the photoinduced electron transfer (PET) process. However, the addition of Al³⁺ ion leads to the breakage of the carbon-nitrogen double bond of Schiff base in PAI resulting in the product without PET property, which shows a typical localized state with enhanced fluorescence and blue color. In addition, PAI can recognize Al³⁺ ion through test papers, which is in favor of the future research regarding to Al³⁺ ion sensing.

2-Hydroxynaphthalene based acylhydrazone as a turn-on fluorescent chemosensor for Al3+ detection and its real sample applications

Developing high performance fluorescent chemosensor for Al³⁺ detection is highly desirable, due to the excess of Al³⁺ will lead to many diseases. In this paper, a simple 2-hydroxynaphthalene-based fluorescent chemosensor has been synthesized and characterized by different spectroscopic methods. The compound exhibited an "turn-on-type" fluorescent chemosensing for the detection of Al³⁺, which was ascribed to the chelation-enhanced fluorescence (CHEF). The high selectivity and sensitivity of the compound for Al³⁺ were verified by fluorescence spectra in its DMF solution, and the enhancement of fluorescent intensity could be observed by naked-eye from non-fluorescence to green light. The detection limit of the compound for Al³⁺ was found to be 4.22 × 10^-8 M and the stability constant was 4.82 × 10⁴ M^-1. The 1:1 binding stoichiometry of the compound to Al³⁺ was confirmed from the Job's plot based on fluorescence titrations. Additionally, the sensing process of the compound to Al³⁺ was chemically reversible by adding Na₂EDTA. Importantly, the probe was successfully applied to quantitative analysis of Al³⁺ in real drug and potable water samples.

FRET based ratiometric switch for selective sensing of Al3+ with bio-imaging in human peripheral blood mononuclear cells

FRET based ratiometric switch for selective sensing of Al³⁺ with bio-imaging in human peripheral blood mononuclear cells (PBMCs).

A New and All-Solid-State Potentiometric Aluminium Ion Sensor for Water Analysis

An all-solid-state potentiometric electrode system for aluminium ion determination was developed with a new aluminium ion sensor as the working electrode based on a new ionophore for aluminium ion, 1,1'-[(methylazanediyl)bis(ethane-2,1-diyl)]bis[3-(naphthalen-1-yl)thiourea] (ACH). The reference electrode was a potassium ion sensor, which acts as a pseudo-reference. Both electrodes were made from Ag/AgCl screen-print electrodes fabricated from a non-plasticized and photocurable poly(n-butyl acrylate) membrane that contained various other membrane components. The pseudo-reference potential based on the potassium ion sensor was fixed in 0.050 M KNO₃, and such concentration of K⁺ ion did not interfere with the measurement of the Al³⁺ ion using the aluminium sensor. With such a pseudo-reference and in the presence of 0.050 M KNO₃ as a background medium, the aluminium sensor measured changes of aluminium ion concentrations linearly from 10^-6 to 10^-2 M Al³⁺ ion with a Nernstian response of 17.70 ± 0.13 mV/decade. A low detection limit of 2.45 × 10^-7 M was achieved with this all-solid-state potentiometric system. The aluminium sensor was insensitive to pH effects from 2.0 to 8.0 with a response time of less than 50 s. Under optimum conditions, a lifetime of 49 days was achieved with good sensor selectivity, reversibility, repeatability, and reproducibility. The all-solid-state electrode system was applied to analyze the Al³⁺ ion content of water samples from a water treatment plant. Compared with the conventional potentiometric detection system for aluminium ions, the new all-solid-state aluminium ion sensor incorporating a pseudo-reference from the potassium sensor demonstrated similar analytical performance. It thus provided a convenient means of aluminium content analysis in water treatment plants.

A squaraine-based fluorescence turn on chemosensor with ICT character for highly selective and sensitive detection of Al3+ in aqueous media and its application in living cell imaging

A novel and simple squaraine-based fluorescent chemosensor SQ-BH bearing the benzoylhydrazine moiety was developed for the highly sensitive and selective detection of Al³⁺ in methanol-water mixture. The chemosensing behaviors of SQ-BH and its binding interaction with Al³⁺ were explored by various spectroscopic analyses. The reversibility of Al³⁺ recognition process was investigated using EDTA. The results of experiments and DFT/TDDFT calculations revealed that the chemosensor SQ-BH obeyed a turn on mechanism which was associated with the inhibited photoinduced electron transfer (PET), the enhanced intramolecular charge transfer (ICT) and the activated chelation enhanced fluorescence (CHEF). Furthermore, the fluorescent chemosensor SQ-BH whose excellent biocompatibility was confirmed by a standard MTT assay could be used to detect Al³⁺ in living cells, indicating its potential application value in biological fields.

An efficient water-soluble fluorescent chemosensor based on furan Schiff base functionalized PEG for the sensitive detection of Al3+ in pure aqueous solution

An efficient reversible fluorescent chemosensor, PEGFB, based on polyethylene glycol bearing a furan Schiff base unit has been successfully developed to sensitively detect Al³⁺ in pure aqueous solution.

A simple turn-on ESIPT and PET-based fluorescent probe for detection of Al3+ in real-water sample

Aluminum is known as the most ubiquitous metal in earth's crust but its excessive exposure will cause damage to environment and health of the organism. Here, a turn-on Schiff base fluorescence probe STH based on excited state intramolecular proton transfer and photoelectron transfer processes for Al³⁺ detection with fast response rate (within minutes), low detection limit (4.26×10^-8M), high selectivity and reasonable pH application range (5.0-8.0) was developed. Fluorescence titration experiments show that probe STH has an excellent linear relationship (R²=0.9694) with Al³⁺ concentration and could be applied to quantitatively recognize Al³⁺ in real-water samples. Based on Job's plot and in situ mass spectra, two STH molecules will complex with Al³⁺ to form 2:1 complexation with oxygen atoms of hydroxyl and carbonyl groups and nitrogen atom of CN bond participating in coordination.

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.

Crystal structure of bis(μ2-1-(4-chlorophenyl)-3-phenyl-4-thenoyl-1H-pyrazol-5-olato-κ3 O,O′:O′)-bis-(1-(4-chlorophenyl)-3-phenyl-4-thenoyl-1H-pyrazol-5-olato-κ2 O,O)-bis(ethyl acetate-κO)dicadmium(II), C88H64Cl4N8O12S4Cd2

C88H64Cl4N8O12S4Cd2, monoclinic, P21/c (no. 14), a = 13.5247(6) Å, b = 15.3257(7) Å, c = 20.6985(8) Å, β = 101.8630(10)°, V = 4198.7(3) Å3, Z = 2, R gt(F) = 0.0484, wR ref(F 2) = 0.0967, T = 173(2) K.

A novel crown ether-acylhydrazone turn-on fluorescent chemosensor for Al3+ ion

A novel fluorescent chemosensor based on crown ether-acylhydrazone (L) was synthesized and characterized. The sensor L exhibited high selectivity and sensitive recognition towards Al³⁺ through a significant "turn-on" fluorescence response at 444 nm in methanol solution. While, other competitive ions had no such significant effects on the fluorescence emission. The associated spectra behavior might be attributed to the formation of 2:1 L-Al³⁺ complex and the proposed binding mode of L-Al³⁺ was demonstrated by the fluorescence titration profiles, Job's plot, ESI-MS spectrometry, ¹H NMR titration and the IR analysis. Besides the high reproducibility of the optical signals, very low detection limit of 0.24 μM was calculated. The association constant (K_s) for L-Al³⁺ complex was about 5.56 × 10⁹ ± 8.19 × 10⁷ M^-2. The results of various experiments showed the sensor L followed a turn-on mechanism via of the suppression of CN isomerization and excited state intramolecular proton transfer (ESIPT) process and the activation of chelation-enhanced fluorescence (CHEF). Theoretical calculations using DFT/B3LYP method was also used to get insight into the sensing mechanism and electronic structure of L. The sensor L could be conceived as an effective and practical fluorescent chemosensor for determination of Al³⁺.

A bright red-emitting flavonoid for Al3+ detection in live cells without quenching ICT fluorescence

A bright red-emitting flavonoid derivative was synthesized, which exhibited a large Stokes shift (Δλ > 150 nm) and high fluorescence quantum yields (ϕ_fl = 0.10–0.35).

A highly sensitive and selective fluorescent probe for quantitative detection of Al3+ in food, water, and living cells

Three novel β-pinene-based fluorescent probes 2a–2c were designed and synthesized for the selective detection of Al³⁺. Probe 2a showed higher fluorescence intensity toward Al³⁺ than the other two compounds. Probe 2a determined the concentration of Al³⁺ with a rapid response time (45 s), wide pH range (pH = 1–9), excellent sensitivity (LOD = 8.1 × 10⁻⁸ M) and good selectivity. The recognition mechanism of probe 2a toward Al³⁺ was confirmed by ¹H NMR, HRMS and DFT analysis. Probe 2a was successfully used as a signal tool to quantitatively detect Al³⁺ in food samples and environmental water samples. Furthermore, probe 2a was successfully utilized to label intracellular Al³⁺, indicating its promising applications in living cells.

Probe 2a exhibiting high sensitivity, good selectivity, wide pH range, lower detection limit, and rapid detection for Al³⁺, probe 2a was applied for the successful detection of Al³⁺ in water samples, food samples and HeLa cells.

Crystal structure of bis-(1-(4-chlorophenyl)-3-phenyl-4-thenoyl-1H-pyrazol-5-ol-κ2O,O′)-(N,N-dimethylformamide)zinc(II), C43H31Cl2N5O5S2Zn

C43H31Cl2N5O5S2Zn, monoclinic, C2/c (no. 15), a =16.9304(8) Å, b = 8.9706(5) Å, c = 27.6764(14) Å, β = 96.701(1)°, V = 4174.7(4) Å3, Z = 4, Rgt(F) = 0.0350, wRref(F2) = 0.094, T = 296 K.

A Fluorescent Sensor for Al(III) and Colorimetric Sensor for Fe(III) and Fe(II) Based on a Novel 8-Hydroxyquinoline Derivative

A novel 8-hydroxyquinoline-based fluorescent and colorimetric chemosensor was designed, synthesized and fully characterized. The sensor showed high selectivity and sensitivity toward Al(3+) over other tested cations in EtOH/H2O (1:99, v/v) medium. The increase in fluorescence intensity was linearly proportional to the concentration of Al(3+) with a detection limit of 7.38 × 10(-6) M. Moreover, the sensor exhibited an obvious color change from yellow to black in the presence of Fe(2+) and Fe(3+) in EtOH/THF (99:1, v/v) solution. The absorbance changes showed a linear response to iron ions with the detection limits of 4.24 × 10(-7) M and 5.60 × 10(-7) M for Fe(2+) and Fe(3+), respectively. Thus, this chemosensor provides a novel approach for selectively recognition of Al(3+), Fe(3+) and Fe(2+) among environmentally relevant metal ions.