Schiff Base Fluorescent Probe Research Articles

A Schiff base fluorescence probe for highly selective turn-on recognition of Zn2+

A simple Schiff base CTS, synthesized between 2-hydroxy-1-naphthaldehyde and 2-benzylthio-ethanamine, was found to be a good turn-on fluorescence probe for the detection of Zn2+, due to the restriction of the rotation of the bond between CN and naphthalene ring and/or the blocking of the photo-induced electron transfer (PET) mechanism of the nitrogen atom to naphthalene ring. Excellent selectivity for Zn2+ was evidenced, over many other competing ions, including Fe3+, Cr3+, Ni2+, Co2+, Fe2+,Mn2+, Ca2+, Hg2+, Pb2+, Cu2+, Mg2+, Ba2+, Cd2+, Ag+, Li+, K+, and Na+, in EtOH/HEPES buffer (95:5, v/v, pH=7.4). It was noteworthy that Cd2+ had no interference with Zn2+. The stoichiometric complex of CTS-Zn2+ was determined to be 2:1 for CTS and Zn2+ in molar, based on the Job plot and single crystal X-ray diffraction data. The binding constant of the complex was 85.7M−2 with a detection limit of 5.03×10−7M. The fluorescence bio-imaging capability of CTS to detect Zn2+ in live cells was also studied. These results indicated that CTS could serve as a favorable probe for Zn2+.

Linear Schiff-base fluorescence probe with aggregation-induced emission characteristics for Al3+ detection and its application in live cell imaging

A simple Schiff-base derivative with salicylaldehyde moieties as fluorescent probe 1 was reported by aggregation-induced emission (AIE) characterization for the detection of metal ions. Spectral analysis revealed that probe 1 was highly selective and sensitive to Al3+. The probe 1 was also subject to minimal interference from other common competitive metal ions. The detection limit of Al3+ was 0.4 μM, which is considerably lower than the World Health Organization standard (7.41 μM), and the acceptable level of Al3+ (1.85 μM) in drinking water. The Job's plot and the results of 1H-NMR and FT-IR analyses indicated that the binding stoichiometry ratio of probe 1 to Al3+ was 1:2. Probe 1 demonstrated a fluorescence-enhanced response upon binding with Al3+ based on AIE characterization. This response was due to the restricted molecular rotation and increased rigidity of the molecular assembly. Probe 1 exhibited good biocompatibility, and Al3+ was detected in live cells. Therefore, probe 1 is a promising fluorescence probe for Al3+ detection in the environment.

A fluorescent and colorimetric probe enables simultaneous differential detection of Hg2+ and Cu2+ by two different mechanisms

A new Schiff-base fluorescence probe CS containing benzimidazole and coumarin fluorophores was synthesized and characterized by NMR, IR and ESI-MS. Fluorescence and absorption spectra show the unique changes in the presence of Hg2+ and Cu2+. Hg2+ induces a remarkable fluorescence enhancement and results in mercury-promoted hydrolysis of a mercury-CS complex to convert the imine group to the aldehyde group. Cu2+ leads to a colorimetric change from colorless to pale yellow and causes formation of a copper-CS complex. Thus, CS can act as a fluorescent chemodosimeter for Hg2+ and a naked-eye chemosensor Cu2+. The cell imaging experiments for Hg2+ show a slow enhancement of a bright blue fluorescence with increasing incubation time, while Cu2+ instantly quenches the fluorescence and then the fluorescence intensity has no further change by extending the incubation time. Therefore, the probe CS shows its potential application for simultaneous differential detection of Hg2+ and Cu2+ in living cells based on the fluorescence response time.

A novel and resumable Schiff-base fluorescent chemosensor for Zn(II)

A new resumable Schiff-base fluorescent probe 7-methoxychromone-3-carbaldehyde-(3′-hydroxy-2′-naphthaleneformyl) hydrazone (L) was designed and synthesized for selective recognition Zn2+. With the titration and the ESI-MS spectra data, we reached the conclusion that the binding ratio between L and Zn2+ was determined to be 1. The sensor showed a strong fluorescence enhancement in ethanol system of Zn2+ (excitation 430nm and emission 498nm). And the enhancement may be due to CN isomerization and Photoinduced Electron Transfer (PET).

A Novel Chromone Schiff-Base Fluorescent Chemosensor for Cd(II) Based on C=N Isomerization.

A new chromone Schiff-base fluorescent probe 7'-methoxychromone-3'-methylidene-1,2,4-triazole-3-imine (L) was designed and synthesized for selective recognition Cd(2+). With the fluorescence titration and the ESI-MS data, we reach the conclusion that the binding mode of the ligand-metal (L-Cd (2+) ) complex is 1:1. The sensor showed a strong fluorescence enhancement in ethanol system of Cd(2+) (excitation 409nm and emission 462nm) and the sensing mechanism based on the fact that C=N isomerization can be used to explain this phenomenon.

A simple Schiff base fluorescence probe for highly sensitive and selective detection of Hg2+and Cu2+

A new Schiff base fluorescent probe, 2-(4-(diphenylamine)benzylidene) thiosemicarbazide (DPBT), was synthesized and its sensing behavior to metal ions were studied by UV–vis and fluorescence spectra. The results show that DPBT can detect Hg2+sensitively and selectively in weakly acidic and neutral conditions, they form a complex with 2:1. The linear range was 0.095–1.14µM and the detection limit was 0.15nM. In weakly alkaline conditions, DPBT can interaction with Hg2+and Cu2+at the same time. We use “masking” reagent, NaBH4, to reduce Hg2+to Hg°, the detection of Cu2+were achieved. They formed 1:1 complex with the binding constant of 4×104M−1, a good linear relationship in 0.45–3.6µM and the detection limit of 0.17µM. The proposed method was used to determine Hg2+and Cu2+in tap water and waste water samples.

A new Schiff base fluorescent indicator for the detection of Mg2+ and its application to real samples

A new Schiff base fluorescence probe, 3-Allylsalicylaldehyde salicylhydrazone (L), for Mg2+ was designed and synthesized. The fluorescence of the sensor L was enhanced remarkably by Mg2+ with 2:1 binding ratio, and the binding constant was determined to be 1.02 × 107 M−1. Probe L had high sensitivity for Mg2+ in a solution of DMF/water (4:1, v/v, pH 7.5), and the detection limit was 4.88 × 10−8 mol/L. Common coexistent metal ions, such as K+, Na+, Ag+, Ca2+, Zn2+, Ba2+, Bi2+, Cu2+, Ni2+, Hg2+, Fe3+ , and Al3+, showed little or no interference on the detection of Mg2+ in solution. The fluorescence probe L, which was successfully used for the determination of trace Mg(II) in real samples, was shown to be promising for liquid-phase extraction coupled with fluorescence spectra.

A high performance Schiff-base fluorescent probe for monitoring Au3+ in zebrafish based on BODIPY

We designed and synthesized a mono-Schiff-base fluorescent probe (Probe 1) based on a boron-dipyrromethene (BODIPY) dye. By investigating the recognition of Au3+ through an irreversible C=N bond hydrolysis reaction, Probe 1 exhibited higher properties such as acting as a “naked eye” probe, stability to pH, fast-response of 90s, a lower detection limit of 60nM, stronger antijamming capability, and better live-cells imaging with low cytotoxicity compared with other probes. Even in relatively high temperatures, Probe 1 maintained its own excellent characteristic. More importantly, this is the first time that one chemosensor could be successfully applied to Au3+ imaging in zebrafish, which demonstrated the performance that Probe 1 exhibited wonderful organism permeability.

Preparation, regulation and biological application of a Schiff base fluorescence probe

A facile fluorescence switch with Schiff base units was designed and achieved by nucleophilic addition and dehydration reaction. The fluorescence of the probe can be regulated by metal ions (Al3+ and Cu2+). The whole process shows that the weak fluorescence of the probe enhances with the addition of Al3+, and then the strong fluorescence of the probe/Al3+ ensemble reduces by introducing Cu2+. Meanwhile, the solution color changes of the probe with metal ions can be observed under 365nm UV–vis light from weak light, pale green, green, pale green to weak light. Noticeably, the photo regulation processes of the probe by metal ions can be realized in the biological system and applied in cells imaging. The work provides a new strategy for designing facile regulation probe and develops a new application for Schiff base derivatives.

A highly selective fluorescent probe for Al3+ based on quinoline derivative

A novel Schiff base fluorescent probe, 1-phenyl-3-methyl-5-hydroxypyrazole-4-carbaldehyde (2′-methylquinoline-4′-formyl) hydrazone (PMHCH), for selective detection of Al3+ has been designed and synthesized. Upon addition of various metal ions, the receptor only shows 286-fold enhancement of fluorescence intensity which might be attributed to a 1:1 stoichiometry between PMHCH and Al3+ and the photo-induced electron transfer progress in the present of Al3+ at 505nm. More importantly, the detection limit of PMHCH for Al3+ could reach at 10−7M level.

A new turn-on fluorescent chemosensor based on sensitive Schiff base for Mn2+ ion

A Schiff-base fluorescent probe – N,N′-bis((6-(thiophen-3-yl)pyridine-2-yl) methylene) benzene-1,2-diamine (L) – was synthesized and evaluated as a chemoselective Mn2+ sensor. Upon treatment with Mn2+, the complexation of L with Mn2+ resulted in a red-shift with a pronounced enhancement in the fluorescence emission intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Fluorescence studies on L and L–Mn2+ complex reveal that the quantum yield strongly increases upon coordination. The complex solution of L with Mn2+ ion exhibited reversibility with EDTA and regenerated free ligand for further Mn2+ sensing. The stoichiometric ratio and association constant were evaluated using Benesi–Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job’s plot analyses. This chemosensor exhibits a very good fluorescence sensing ability to Mn2+ over a wide acidic pH range. This chemosensor can be used as an important application for detection of Mn2+ in real water samples. Both L and L–Mn2+ complex were optimized using density functional theory and vibrational frequency calculations confirmed that both are at local minima on the potential energy surfaces. The corresponding energy differences between HOMO and LUMO of L and L–Mn2+ complex are 2.210eV and 0.550eV, respectively which implies a low kinetic stability and high chemical reactivity.

A highly sensitive and selective fluorescent chemosensor for detection of Zn2+ based on a Schiff base

A Schiff-base fluorescent probe – 2-((E)-(quinolin-8-ylimino)methyl)quinolin-8-ol (H7L) was synthesized and evaluated as a chemoselective Zn2+ sensor. Upon treatment with Zn2+, the complexation of H7L with Zn2+ resulted in a red shift with a pronounced enhancement in the fluorescence emission intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Notably, this chemosensor could distinguish clearly Zn2+ from Cd2+. Fluorescence studies on H7L and H7L–Zn2+ complex reveal that the quantum yield strongly increases upon coordination. The stoichiometric ratio and association constant were evaluated using Benesi–Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job’s plot analyses. This chemosensor exhibits a very good fluorescence sensing ability to Zn2+ over a wide range of pH.

A highly sensitive C3-symmetric Schiff-base fluorescent probe for Cd2+.

A new C3-symmetric Schiff-base fluorescent probe (L) based on 8-hydroxy-2-methylquinoline has been developed. As expected, the probe L can display high fluorescent selectivity for Cd(2+) over Zn(2+) and most other common ions in neutral ethanol aqueous medium. Moreover, the mechanism of the L-Cd(2+) complex has been confirmed by X-ray crystallography and density functional theory calculation results. More importantly, L could be used to image Cd(2+) within living cells.

Synthesis and Properties of Naphthalimides Schiff Base Fluorescent Probe for Ag<sup>+</sup>

A novel naphthalimides schiff base fluorescent probe and polymeric fluorescent probe for Ag+ ions were synthesied by using cheap and commercially available of 1,8 naphthalene anhydride, vanillin, N,N-dimethyl-propane diamine and hydrazine hydrate as raw material. Their spectral characteristics and fluorescent sensing of metal ions in aqueous were studied. The results indicate that the fluorescent probes sythesized showed good water-soluble and stability, high detection sensitivity selectivity to Ag+, linear relationship between the fluorescent intensity and concentration of Ag+ is in the range of 9.9 × 10-6 ~ 9.9 × 10-5 mol/L.

A sensitive Schiff-base fluorescent chemosensor for the selective detection of Zn²⁺.

A Schiff-base fluorescent probe - N, N(/)-bis(salicylidene) trans 1, 2 - diaminocyclohexane (H 2 L) was synthesized and evaluated as a chemoselective Zn(2+) sensor. Upon treatment with Zn(2+), the complexation of H 2 L with Zn(2+) resulted in a bathochromic shift with a pronounced enhancement in the fluorescence intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Notably, this chemosensor could distinguish clearly Zn(2+) from Cd(2+). The stoichiometric ratio and association constant were evaluated using Benesi - Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job's plot analyses.

A selective, cell-permeable fluorescent probe for Al3+ in living cells

The synthesis and evaluation of a novel Schiff-base fluorescent probe L for detection of Al(3+) are described. The structure of L was determined by X-ray and other spectroscopic data. The fluorescent spectra changes and microscopy images show that indicator L is highly selective for Al(3+) not only in abiotic systems but also in living cells. Other metal ions failed to respond. The new probe could be used as an efficient tool for Al(3+) monitoring in the environment and biological systems.