Selective Fluorescence Zinc Ion Sensing and Binding Behavior of 4-Methyl-2,6-bis(((phenylmethyl)imino)methyl)phenol: Biological Application

A pyrene-induced PET-based chemosensor for biologically important Zn(II) ions: application in test strips and live cell imaging studies

Cation and anion sensing is vital owing to their universal dispersion in ecosystems and biological functions. It has been shown that fluorescent receptors based on organic platforms are efficient for detecting a number of ions and have many advantages such as low cost, superior sensitivity and simplicity in installation. This study demonstrates the design and synthesis of a novel receptor (E)-3-[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-2-(pyren-1-yl)-2,3-dihydroquinazolin-4(1H)-one (DTQ) for the rapid recognition of Zn(II) ions. DTQ exhibited a significant fluorometric "turn-on" characteristic towards Zn(II) at λmax 444 nm in aqueous acetonitrile by inhibiting the photo-induced electron transfer (PET) and -CN- process. The ESI-MS analysis and Job's plot experimental results confirmed stoichiometric 1 : 1 complex formation between DTQ and Zn(II). Fluorometric investigations revealed the detection limit and association constant of DTQ towards Zn(II), which were found to be 13.4 nM and 1.47 × 105 M-1, respectively. DTQ was employed to sense Zn(II) on low-cost test strips. The present research findings imply that DTQ can function as an effective sensor for Zn(II).

A rhodamine based dual chemosensor for Al3+ and Hg2+: Application in the construction of advanced logic gates

A rhodamine-based compound (RBO), which has been constructed from the reaction between N-(rhodamine-6G)lactam-ethylenediamine and 2,1,3-benzoxadiazole-4-carbaldehyde, is reported here as a selective chemosensor for both Al³⁺ and Hg²⁺ ions in 10 mM HEPES buffer in water:ethanol (1:9, pH = 7.4). Absorption intensity of RBO increases considerably at 528 nm with these cations. It shows fluorescence enhancement at 550 nm by 1140- and 524-fold in the presence of Al³⁺ and Hg²⁺, respectively. LOD has been determined as 6.54 and 16.0 nM for Al³⁺ and Hg²⁺, respectively. Quantum yield and lifetime of RBO enhances with these metal ions. Fluorescence intensity of Al-probe complex or Hg-probe complex is quenched in the presence of fluoride or sulfide ion, respectively, opening a path for the construction logic gates. DFT analysis has been used to understand the spectral transitions. We have constructed a systematic development from single to five inputs complex circuit, and for the first time a time dependent five input complex logic circuit is reported herein.

Recent Progress in Fluorescent Probes For Metal Ion Detection

All forms of life have absolute request for metal elements, because metal elements are instrumental in various fundamental processes. Fluorescent probes have been widely used due to their ease of operation, good selectivity, high spatial and temporal resolution, and high sensitivity. In this paper, the research progress of various metal ion (Fe3+,Fe2+,Cu2+,Zn2+,Hg2+,Pb2+,Cd2+) fluorescent probes in recent years has been reviewed, and the fluorescence probes prepared with different structures and materials in different environments are introduced. It is of great significance to improve the sensing performance on metal ions. This research has a wide prospect in the application fields of fluorescence sensing, quantitative analysis, biomedicine and so on. This paper discusses about the development and applications of metal fluorescent probes in future.

A new diformyl phenol based chemosensor selectively detects Zn2+ and Co2+ in the nanomolar range in 100% aqueous medium and HCT live cells

A new diformyl phenol based chemosensor that can sense Zn2+ and Co2+ in the nanomolar range in 100% aqueous solution and in HCT cells was explored.

A new half-condensed Schiff base platform: structures and sensing of Zn2+ and H2PO4- ions in an aqueous medium

A newly designed and synthesized half-condensed organic moiety 2-hydroxy-5-methyl-3-[(2-phenylamino-phenylimino)-methyl]-benzaldehyde (HL') and a Zn₂L₄ complex sequentially detect Zn²⁺ and H₂PO₄^- ions as low as 1.13 nM and1.23 μM, respectively. HL' and a dinuclear Zn(ii) complex of in situ generated L^- in a solution formulated as Zn₂L₄ under investigation were characterized by physicochemical and spectroscopic studies along with detailed structural analyses by single-crystal X-ray crystallography. The selectivity and sensitivity of HL' towards Zn²⁺ ions and of the Zn₂L₄ complex towards H₂PO₄^- ions are based on CHEF and via displacement pathways, respectively. Dual sensing of Zn²⁺ ions and H₂PO₄^-ions in an aqueous medium via "Green-Blue-Green" emission with the reversible transformation of in situ formed HL' to HL was established by detailed electronic absorption and emission spectroscopic studies. This non-cytotoxic probe (HL', i.e. produced HL in solution) and Zn₂L₄ complexes are able to monitor the subcellular distribution changes of Zn²⁺ and H₂PO₄^- ions, respectively, by fluorescence microscopy using the human semen sample.

An antipyrine based fluorescence "turn-on" dual sensor for Zn2+ and Al3+ and its selective fluorescence "turn-off" sensing towards 2,4,6-trinitrophenol (TNP) in the aggregated state

A 2,6-diformyl-p-cresol (DFC)-4-amino antipyrine (AP) based dual signaling fluorescent Schiff base ligand (DFCAP) is found to exhibit colorimetric and fluorescence turn on selective sensing towards metal ions, Zn2+ and Al3+. It also exhibits a significant aggregation induced emission (AIE) phenomenon by controlling the water-THF solvent ratio which provides robust green emissive fluorogenic aggregates with well-defined morphologies. Turn-on fluorescence enhancements as high as 195 fold and 168 fold in methanol for Al3+ and Zn2+ at 480 nm and 508 nm, respectively, were noticed. The binding constants and stoichiometry determined from the fluorescence titration data are K = 7.63 × 104 M-1 and 3.42 × 104 M-1 and 1 : 1 complexation for both Al3+ and Zn2+ respectively, supported by Job's method. DFCAP shows high sensitivity towards the detection of Zn2+ and Al3+ ions with very low detection limit values of ca. ∼21 nM and 30 nM respectively. Besides by applying its attractive AIE feature, the green emissive hydrosol functions as a good chemosensor with high sensitivity for a selected explosive TNP through ground state complexation with a LOD value of ca. ∼1.74 μM and especially a high Stern-Volmer quenching constant of ca. ∼4.14 × 105 M-1. For instant 'naked eye' response for the trace detection of TNP in the solution state, we fabricated a simple paper strip that could detect TNP on-site in a fast, inexpensive and simple way.

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.

Origin of green photoluminescence in four-ring bent-core molecules with ESIPT, selective sensing of zinc ions by turn-on emission and their liquid crystal properties

Fluorescent four-ring symmetrical/unsymmetrical molecules containing alkyl chains of a varied number of –CH₂– groups with a bent-core have been synthesized to explore their liquid crystalline (LC) and photophysical properties.

The influences of different substituents on spectral properties of rhodamine B based chemosensors for mercury ion and application in EC109 cells

Six rhodamine-based “turn-on” fluorescence chemosensors (L1–L6) with different substituents for mercury (Hg2+) were readily synthesized and investigated; they displayed high selectivity and chelation enhanced ratiometric fluorescence change and colorimetric change with Hg2+ among the metal ions examined. Based on UV and fluorescence spectral data, the effects of different substituents on spectral properties of the probes were presented and discussed. The detection limit of Hg2+ to probe L1 was as low as 50 nmol/L because of its electron-donating group. Theoretical calculation also supported the process of reaction. Confocal laser scanning microscopy experiments showed that probe could be used to detect Hg2+ in living cells.

A two-pocket Schiff-base molecule as a chemosensor for Al3+

A new Schiff-base molecule with two binding pockets acts as a selective fluorescent chemosensor for Al³⁺.

A highly selective “ON–OFF” probe for colorimetric and fluorometric sensing of Cu2+in water

A new diformyl phenol based probe for selective detection of Cu²⁺in aqueous medium, applicable for cell imaging in Vero cells. Theoretical studies were performed to establish the underlying keto–enol tautomerism and optimization of the Cu²⁺complex.

Study on the fluorescent chemosensors based on a series of bis-Schiff bases for the detection of zinc(II)

In order to study the influence of different substituent groups on the fluorescence properties, a series of bis-Schiff bases (L) with electron-donating groups (salicylaldehyde, o-vanillin, 2,4-dihydroxybenzaldehyde) and electron-drawing group (4-formylbenzoic acid) have been synthesized, and characterized by IR spectrum, NMR, mass spectrum, and fluorescence spectroscopy. The investigation of the fluorescent properties reveals that the fluorescence can be enhanced when the bis-Schiff base ligands with electron-donating groups complex with Zn ion, while other kinds of metal complexes with these ligands do not show any enhancement, whereas no fluorescence enhancement can be observed when the ligand with electron-drawing group complexes with all different types of metal ions. In addition, as for the ligands with electron-donating groups detecting zinc ion, the fluorescence intensity is linear correlated with the concentration of zinc ion. Therefore, the study indicates that the ligands with electron-donating groups can be used as Zn ion fluorescent sensor.

Zebra reaction or the recipe for the synthesis of heterodimeric zinc complexes

A series of asymmetric heterodimeric zinc complexes have been synthesized in a direct reaction between conformationally flexible chiral/achiral homodimers. The cooperative activity of steric factors and coordination codes resulted in an intriguing chiral self-sorting process. Herein, we are reporting our recent exploration of the first example of such a type of reaction.

A thiosemicarbazone based chemo and fluorogenic sensor for Zn2+with CHEF and ESIPT behaviour: computational studies and cell imaging application

A novel diformyl-p-cresol (DFC)–thiosemicarbazide (TS) – based turn-on dual sensor that enables to determine, for the first time, the stepwise formation constants.

A highly selective and biocompatible chemosensor for sensitive detection of zinc(ii)

A selective fluorescence chemosensor for Zn²⁺ has been developed with a very low limit of detection value (0.832 nM).

A highly efficient and selective coumarin based fluorescent probe for colorimetric detection of Fe3+and fluorescence dual sensing of Zn2+and Cu2+

A new coumarin based Schiff-base chemosensor was synthesized and evaluated. Based on Job’s plot,¹H NMR titration, ESI-MS and B-H plot, the structure of ligand and its metal ion is 1 : 1 stoichiometry. It also exhibits a binary logic function.

Zinc complexes as fluorescent chemosensors for nucleic acids: new perspectives for a "boring" element

Zinc(II) complexes are effective and selective nucleic acid-binders and strongly fluorescent molecules in the low energy range, from the visible to the near infrared. These two properties have often been exploited to quantitatively detect nucleic acids in biological samples, in both in vitro and in vivo models. In particular, the fluorescent emission of several zinc(II) complexes is drastically enhanced or quenched by the binding to nucleic acids and/or upon visible light exposure, in a different fashion in bulk solution and when bound to DNA. The twofold objective of this perspective is (1) to review recent utilisations of zinc(II) complexes as selective fluorescent probes for nucleic acids and (2) to highlight their novel potential applications as diagnostic tools based on their photophysical properties.

Anti-proliferative effect of Fe(III) complexed with 1-(2-hydroxy-3-methoxybenzaldehyde)-4-aminosalicylhydrazone in HepG2 cells

We previously developed a chelating ligand, 1-(2-hydroxy-3-methoxybenzaldehyde)-4-aminosalicylhydrazone (HMB-ASH), which can chelate Fe(III) to form a complex. The HMB-ASH-Fe(III) complex exhibits a dose-dependent anti-proliferative effect in HepG2 cells, whereas the ligand, HMB-ASH, and Fe(III) alone had no considerable effect. The HMB-ASH-Fe(III) complex was composed of Fe(III):HMB-ASH (1:2), as determined by high-performance liquid chromatography with high-resolution mass spectrometry. The IC50 value was approximately 20 μM, which was comparable to those of the anti-cancer drugs oxaliplatin (OXP) and etoposide (ETP) under the same conditions. Similar to OXP and ETP, HMB-ASH-Fe(III) induced apoptosis in HepG2 cells, as revealed by terminal deoxynucleotidyl transferase fluorescein-12-dUTP nick end labeling assay.

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.

Three N-stabilized rhodamine-based fluorescent probes for Al3+via Al3+-promoted hydrolysis of Schiff bases

New fluorescent probes L1–L3 displayed high sensitivity toward Al³⁺.

A reversible turn-off fluorescence probe (HNAPP) for Zn(ii) ion and inorganic phosphate ions (H2P and HP) at physiological pH

NOO coordinating tritadentate zinc sensor (λ_ex= 400 nm,λ_em= 492 nm,ϕ_F= 0.45) act as a highly selective sensor for inorganic phosphate (HP/H₂P) by ON–OFF signaling at physiological pH.

Mixed-solvothermal synthesis, structures, surface photovoltage, luminescence and molecular recognition properties of three new transition metal phosphonates with 3D framework and supramolecular structures

Three new transition metal(ii) phosphonates have been synthesized under mixed-solvothermal conditions. Surface photovoltage and field-induced surface photovoltage spectroscopy of compounds 1 and 2 have been studied. Compound 3 could be used for the sensitive sensing of DMF.

A new 3,5-bisporphyrinylpyridine derivative as a fluorescent ratiometric probe for zinc ions

A new 3,5-disubstituted pyridine with two porphyrin moieties was prepared through an efficient synthetic approach involving 2-formyl-5,10,15,20-tetraphenylporphyrin (1), piperidine, and catalytic amounts of [La(OTf)3]. 3,5-Bis(5,10,15,20-tetraphenylporphyrin-2-ylmethyl)pyridine (2) was fully characterized and its sensing ability towards Zn(2+), Cu(2+), Hg(2+), Cd(2+), and Ag(+) was evaluated in solution by absorption and fluorescence spectroscopy and in gas phase by using matrix-assisted laser desorption/ionization (MALDI)-TOF mass spectrometry. Strong changes in the ground and excited state were detected in the case of the soft metal ions Zn(2+), Cd(2+), Hg(2+), and Cu(2+). A three-metal-per-ligand molar ratio was obtained in all cases and a significant ratiometric behavior was observed in the presence of Zn(2+) with the appearance of a new band at 608 nm, which can be assigned to a metal-to-ligand charge transfer. The system was able to quantify 79 ppb of Zn(2+) and the theoretical calculations are in accordance with the stoichiometry observed in solution. The gas-phase sensorial ability of compound 2 towards all metal ions was confirmed by using MALDI-TOF MS and in solid state by using polymeric films of polymethylmethacrylate (PMMA) doped with ligand 2. The results showed that compound 2 can be analytically used to develop new colorimetric molecular devices that are able to discriminate between Hg(2+) and Zn(2+) in solid phase. The crystal structure of Zn(II) complex of 3,5-bisporphyrinylpyridine was unequivocally elucidated by using single-crystal X-ray diffraction studies.