Chelation-enhanced Fluorescence Process Research Articles

A Practical Hydrazine-Carbothioamide-Based Fluorescent Probe for the Detection of Zn2+: Applications to Paper Strip, Zebrafish and Water Samples

A practical hydrazine-carbothioamide-based fluorescent chemosensor TCC (N-(4-chlorophenyl)-2-(thiophene-2-carbonyl)hydrazine-1-carbothioamide) was applied for Zn2+ detection. TCC exhibited selective fluorescence emission for Zn2+ and did not show any interference with other metal ions. In particular, TCC was utilized for the detection of Zn2+ in paper strips, zebrafish and real water samples. TCC could detect Zn2+ down to 0.39 μM in the solution phase and 51.13 μM in zebrafish. The association ratio between TCC and Zn2+ was determined to be 2:1 by ESI-mass and Job plot. The sensing mechanism of TCC for Zn2+ was illustrated to be a chelation-enhanced fluorescence process through spectroscopic experiments and theoretical calculations.

A Benzothiazole-Based Fluorescence Turn-on Sensor for Copper(II).

A new benzothiazole-based chemosensor BTN (1-((Z)-(((E)-3-methylbenzo[d]thiazol-2(3H)-ylidene)hydrazono)methyl)naphthalen-2-ol) was synthesized for the detection of Cu2+. BTN could detect Cu2+ with "off-on" fluorescent response from colorless to yellow irrespective of presence of other cations. Limit of detection for Cu2+ was determined to be 3.3μM. Binding ratio of BTN and Cu2+ turned out to be a 1:1 with the analysis of Job plot and ESI-MS. Sensing feature of Cu2+ by BTN was explained with theoretical calculations, which might be owing to internal charge transfer and chelation-enhanced fluorescence processes.

Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO2 - and H2PO4.

An amide-based smart probe (L) is explored for nanomolar detection of Mo(VI) ion in a ratiometric manner, involving hydrogen-bond-assisted chelation-enhanced fluorescence process through inhibition of photoinduced electron transfer process. The recognition of Mo(VI) is associated with a 17-fold fluorescence enhancement and confirmed by single-crystal X-ray diffraction of the resulting Mo(VI) complex (M1). Further, M1 selectively recognizes arsenite through green emission of their adduct (C1) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of C1 back to free L having weak fluorescence. The methods are fast, highly selective, and allow their bare eye visualization at physiological pH. All of the interactions have been substantiated by time-dependent density functional theory calculations to rationalize their spectroscopic properties. The corresponding lowest detection limits are 1.5 × 10–8 M for Mo(VI), 1.2 × 10–10 M for AsO2–, and 3.2 × 10–6 M for H2PO4–, whereas the respective association constants are 4.21 × 105 M–1 for Mo(VI), 6.49 × 104 M–1 for AsO2–, and 2.11 × 105 M–1 for H2PO4–. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO2– from environmental samples by solid-phase extraction.

Cover Picture: A Novel Dual Channel Fluorescent Probe for Ca2+ and Zn2+ Based on a Coumarin Schiff Base (Chin. J. Chem. 8/2017)

The cover picture shows a novel dual channel fluorescent probe for Ca2+ and Zn2+ based on a coumarin Schiff base. The probe displays a solvent dependent dual sensing, viz., recognition of Ca2+ in DMF‐H2O (9∶1, V/V) solution based on C = N isomerization, photoinduced electron transfer (PET) inhibition and chelation‐enhanced fluorescence (CHEF) mechanism as well as detection of Zn2+ in H2O‐CH3OH (9∶1, V/V) solution by excited‐state intramolecular proton transfer (ESIPT) and CHEF processes. More details are discussed in the article by Guo et al. on page 1263–1269. image

A Novel Dual Channel Fluorescent Probe for Ca2+ and Zn2+ Based on a Coumarin Schiff Base

A novel coumarin Schiff base fluorescent probe ethyl 7‐hydroxycoumarin‐3‐carboxylate‐8‐formaldehyde benzoyl hydrazone (EBH) has been designed and synthesized which shows solvent dependent dual sensing, viz., recognition of Ca2+ in DMF‐H2O (9∶1, V/V) solution based on C = N isomerization, photoinduced electron transfer (PET) inhibition and chelation‐enhanced fluorescence (CHEF) mechanism as well as detection of Zn2+ in H2O‐CH3OH (9∶1, V/V) solution by excited‐state intramolecular proton transfer (ESIPT) and CHEF processes. The structure of the probe EBH has been confirmed by single‐crystal X‐ray diffraction analysis. Meanwhile, the probe was also used to image intracellular Zn2+ ions in MCF‐7 cells with a good performance.

A sensitive tetraphenylethene-based fluorescent probe for Zn2+ ion involving ESIPT and CHEF processes

A new tetraphenylethene-based fluorescent probe 2-(quinolin-8-yliminomethyl)-4-triphenylvinyl-phenol (HL) for detecting Zn2+ ion through the excited state intramolecular proton transfer (ESIPT) and chelation enhanced fluorescence (CHEF) processes has been designed and synthesized. The results show that HL emits relatively strong blue fluorescence at 460nm without Zn2+ ion, however, probe HL displays highly pink fluorescent emission at 600nm when adding Zn2+ ion. The fluorescent emission of HL appears an extremely large Stokes shift, which effectively reduces the interference of background signal. The limit of detection of HL for Zn2+ ion can reach to 9.0×10–8M.

Highly selective ratiometric fluorescent Zn2+ chemosensor based on diarylethene derivative with bi-8-carboxamidoquinoline unit.

An asymmetrical diarylethene (1O) with a bi-8-carboxamidoquinoline unit was synthesized. Its photochromic and fluorescence performances on stimulation with both light and metal ions showed that the diarylethene could serve as a highly selective ratiometric fluorescent chemosensor to detect Zn2+ ions based on internal charge transfer and chelation-enhanced fluorescence processes. The diarylethene could selectively discriminate Zn2+ from Cd2+ in acetonitrile. Furthermore, Job's plots based on fluorescence titration and electrospray ionization mass spectrometry analysis showed 1 : 1 binding stoichiometry between 1O and Zn2+ . The binding constant of 1O with Zn2+ , estimated using the Benesi-Hildebrand method, and the limit of detection were 3.37 × 105 M-1 and 4.6 × 10-8 mol/L, respectively. Additionally, the light and metal-responsive fluorescence behavior of 1O was used successfully to construct a molecular logic circuit with four inputs and one output. Copyright © 2016 John Wiley & Sons, Ltd.

Rhodamine-chloronicotinaldehyde-based “OFF–ON” chemosensor for the colorimetric and fluorescent determination of Al3+ ions

We have synthesized a novel 2-chloronicotinaldehyde-functionalized rhodamine B derivative (RBCN) that acts as an “OFF–ON” chemosensor. RBCN specifically binds Al3+ in the presence of a large excess of competing metal ions (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+ and Pb2+) and exhibits visible changes in its electronic and fluorescent spectral behavior. These spectral changes are significant in the visible region of the spectrum and thus enable detection with the naked eye. Upon coordination with Al3+, the promoted ring opening of the rhodamine spirolactam ring in the RBCN chemosensor evokes a fluorescence turn-on response via the chelation-enhanced fluorescence process. The probe exhibited good brightness and fluorescence enhancement in which the lower detection limit for Al3+ was 2.86×10−8M. The ring-opening mechanism of the rhodamine spirolactam induced by Al3+ binding and the 1:1 stoichiometric structure between RBCN and Al3+ were supported by Job's plot evaluation, UV–vis, fluorescence titrations, FT-IR and 1H NMR spectroscopic studies. Finally, theoretical calculations and modeling simulations were conducted using Material Studio 4.3 suite to simulate the formation of a 1:1 complex between RBCN and Al3+. However, the fluorescence and colorimetric response of the RBCN-Al3+ complex was quenched by the addition of azide (N3−) anion, which abstracts the Al3+ ion from the complex and turns off the sensor, confirming that the recognition process is reversible.