A Hg2+-selective chemodosimeter based on desulfurization of coumarin thiosemicarbazide in aqueous media

A ratiometric fluorescent probe with a large Stokes shift for the detection of Hg2+ and its applications in environmental sample and living system analysis

Toxic mercury ions (Hg2+) can cause serious environmental pollution and accumulate in living organisms via the food chain. Therefore, monitoring Hg2+ is crucial in ensuring the safety of ecosystems and organisms. In this work, a novel ratiometric fluorescent probe CMT (5-(4-(diphenylamino)phenyl)-1-(7-hydroxy-coumarin-3-yl)-4-pentene-1,3-dione) based on coumarin was developed for detecting Hg2+, which displayed obvious fluorescence changes, a low detection limit (2.24 × 10-7 M), good selectivity, and a large Stokes shift (255 nm). The CMT probe could detect Hg2+ in real environmental soil and water samples. Furthermore, the CMT probe enabled the naked-eye detection of Hg2+ using test paper experiments. CMT was also applied for fluorescence imaging in living zebrafish and plants. This work provides a highly efficient tool for monitoring Hg2+ in environmental samples and biological systems.

A cationic iridium(III) complex containing a thiosemicarbazide unit: Synthesis and application for turn-on chemiluminescent detection of Hg2

A novel cationic iridium(III) complex [(ppy)₂Ir(bPCPC)]PF₆ (ppy: 2-phenylpyridine; bPCPC: 2-([2,2'-bipyridine]-4-carbonyl)-N-phenylhydrazinecarbothioamide) containing a thiosemicarbazide unit was designed and synthesized. The thiosemicarbazide unit was a sensitive functional group to Hg²⁺, when it reacted with Hg²⁺, it was desulphurized and thus led to the formation of 1,3,4-oxadiazole, [(ppy)₂Ir(bPCPC)]PF₆ resultantly was used as a "turn-on" chemodosimeter for luminescent detection of Hg²⁺ in DMF/PBS buffer solution at pH = 7-11. Except for Ag⁺, recognition capability of [(ppy)₂Ir(bPCPC)]PF₆ to Hg²⁺ was not interfered by other common metal ions (Co²⁺, Li⁺, Zn²⁺, Pb²⁺, K⁺, Al³⁺, Na⁺, Mn²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Cr³⁺, Ba²⁺, Mg²⁺, Ni²⁺ and Ca²⁺). The detection limit was 1.83 × 10^-9 mol∙L^-1 (0.37 ppb), which indicated the complex was a highly sensitive chemiluminescent detection reagent of Hg²⁺.

Coumarin Thiourea-Based Fluorescent Turn-on Hg2+ Probe That Can Be Utilized in a Broad pH Range 1-11

A novel coumarin-thiourea conjugate was synthesized facilely. It served as a fluorescent turn-on chemosensor for selective detection of Hg²⁺ ion over other common competitive metal ions including Li⁺, Na⁺, K⁺, Ag⁺, Cu²⁺, Fe²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺, Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺ and Fe³⁺ ions based on the Hg²⁺-promoted desulfurization and cyclization reactions. Addition of Hg²⁺ ion to the sensor solution in 2:8 EtOH/H₂O induced a hypsochromic shift of the UV-Vis absorption band from 360 nm to 340 nm accompanying distinct enhancement in the absorption intensity while addition of other metal ions failed to bring about substantial change in the absorption spectra. Addition of Hg²⁺ to the sensor solution also caused marked increase in the fluorescence emission intensity and most common competitive metal ions did not interfere with the selective sensing of Hg²⁺ ion by the sensor. The detection limit of Hg²⁺ ion by the probe was calculated to be 1.46 × 10^-7 M and the probe could be utilized for selective detection of Hg²⁺ ion by fluorescence turn-on mode over a broad pH range of 1-11.

Rhodamine spirolactam sensors operated by sulfur-cooperated metal complexation

New rhodamine Schiff base sensors were developed to improve selective sensing by introducing sulfide, ester, and dithiocarbonate groups, as well as using ketones coupled to rhodamine-hydrazine. Metal sensing proceeded through the 1:1 complexation of the metal ion for most sensors in the presence of Cu²⁺ and Hg²⁺. A sensor carrying a dithiocarbonate group responded selectively to Hg²⁺ showing a strong colorimetric change and intense fluorescence. The association constants of the sensors were determined from a linear plot performed at micro-molar concentrations to afford values in the range of 10⁴. Sensing was interrupted at the initial time of Hg²⁺ exposure due to the isomerization of imine and preferential metal bonding of two dithiocarbonate groups regardless of the main structure of rhodamine. The sensors exhibited the reversible and reproducible performance for Hg²⁺ sensing.

A New Reactive 1,8-Naphthalimide Derivative for Highly Selective and Sensitive Detection of Hg2

A 1,8-naphthalimide derivative with a reactive aliphatic hydroxyl was designed and synthesized as a fluorescent probe. Its structure was characterized by IR, ¹H NMR, ¹³C NMR, LC-MS and HPLC. The probe showed high selectivity and sensitivity to Hg²⁺ over other metal ions such as Pb²⁺, Na⁺, K⁺, Cd²⁺, Cr³⁺, Zn²⁺, Cu²⁺, Ni²⁺, Ca²⁺, Fe³⁺, Fe²⁺, Co²⁺, Mn²⁺ and Mg²⁺ in MeCN/H₂O (15/85, v/v). The increase in fluorescence intensity was linearly proportional to the concentration of Hg²⁺ in the range of 18-40 μM with a detection limit of 1.38 × 10^-7 mol/L. The probe could work in a pH span of 4.3-9.0 and respond to Hg²⁺ quickly with strong anti-interference ability. Job's plot suggested a 1:2 complex of the probe and Hg²⁺.

Fluorescent conjugated polymers based on thiocarbonyl quinacridone for sensing mercury ion and bioimaging

Highly sensitive FRET-based thiocarbonyl quinacridone fluorescent conjugated polymers for the sensing and bioimaging of mercury ion have been developed.

Synthesis and properties of arsenic(III)-reactive coumarin-appended benzothiazolines: a new approach for inorganic arsenic detection

The EPA has established a maximum contaminant level (MCL) of 10 ppb for arsenic (As) in drinking water requiring sensitive and selective detection methodologies. To tackle this challenge, we have been active in constructing small molecules that react specifically with As(3+) to furnish a new fluorescent species (termed a chemodosimeter). We report in this contribution, the synthesis and spectroscopy of two small-molecule fluorescent probes that we term ArsenoFluors (or AFs) as As-specific chemodosimeters. The AFs (AF1 and AF2) incorporate a coumarin fluorescent reporter coupled with an As-reactive benzothiazoline functional group. AFs react with As(3+) to yield the highly fluorescent coumarin-6 dye (C6) resulting in a 20-25-fold fluorescence enhancement at λem ∼ 500 nm with detection limits of 0.14-0.23 ppb in tetrahydrofuran (THF) at 298 K. The AFs also react with common environmental As(3+) sources such as sodium arsenite in a THF/CHES (N-cyclohexyl-2-aminoethanesulfonic acid) (1:1, pH 9, 298 K) mixture resulting in a modest fluorescence turn-ON (1.5- to 3-fold) due to the quenched nature of coumarin-6 derivatives in high polarity solvents. Bulk analysis of the reaction of the AFs with As(3+) revealed that the C6 derivatives and the Schiff-base disulfide of the AFs (SB1 and SB2) are the ultimate end-products of this chemistry with the formation of C6 being the principle photoproduct responsible for the As(3+)-specific turn-ON. It appears that a likely species that is traversed in the reaction path is an As-hydride-ligand complex that is a putative intermediate in the proposed reaction path.

Metal coordination in photoluminescent sensing

Coordination chemistry plays an essential role in the design of photoluminescent probes for metal ions. Metal coordination to organic dyes induces distinct optical responses which signal the presence of metal species of interest. Luminescent lanthanide (Ln(3+)) and transition metal complexes of d(6), d(8) and d(10) configurations often exhibit unique luminescence properties different from organic dyes, such as high quantum yield, large Stokes shift, long emission wavelength and emission lifetimes, low sensitivity to microenvironments, and can be explored as lumophores to construct probes for metal ions, anions and neutral species. In this review, the design principles and coordination chemistry of metal probes based on mechanisms of PeT, PCT, ESIPT, FRET, and excimer formation will be discussed in detail. Particular attention will be given to rationales for the design of turn-on and ratiometric probes. Moreover, phosphorescent probe design based on Ln(3+) and d(6), d(8) and d(10)-metal complexes are also presented via discussing certain factors affecting the phosphorescence of these metal complexes. A survey of the latest progress in photoluminescent probes for identification of essential metal cations in the human body or toxic metal cations in the environment will be presented focusing on their design rationales and sensing behaviors. Metal complex-based photoluminescent probes for biorelated anions such as PPi, and neutral biomolecules ATP, NO, and H(2)S will be discussed also in the context of their metal coordination-related sensing behaviors and design approaches.

Preparation of 4,4'-bis-(carboxyl phenylazo)-dibenzo-18-crown-6 dye and its application on ratiometric colorimetric recognition to Hg2+

A multifunctional dye, 4,4'-bis-(carboxyl phenylazo)-dibenzo-18-crown-6 dye (BCADC) was designed and prepared via diazotization and coupling reaction of dibenzo-18-crown-6 with p-amino benzoic acid. The dye, combining crown ether ring, azo and carboxyl group, exhibits well-defined Hg(2+)-selective ratiometric colorimetric behavior, with the maximum absorbance peak changing from 354 nm to 408 nm exclusively. Under the optimum conditions, the recognition to Hg(2+) has a linear range of 2.5-58×10(-7) mol L(-1) with a 0.9978 correlation coefficient. The method was applied to analyse 3 environmental water samples with a detection limit of 2.9×10(-8) mol L(-1) and a relative standard deviation (R.S.D.) lower than 3.7% (n=5). The action mechanism between BCADC and metal ions was discussed by means of Job's plots and theoretical calculations.

7-Diethyl-amino-2-oxo-2H-chromene-3-carbohydrazide

The asymmetric unit of the title compound, C(14)H(17)N(3)O(3), contains two independent mol-ecules with different conformations of the ethyl groups. In the crystal, inter-molecular N-H⋯O hydrogen bonds link the mol-ecules into ribbons extending along the a axis.