Naphthalene and pyrrole substituted guanidine in selective sensing of Cu2+, Hg2+, Pb2+ and CN− ions under different conditions

Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. Compound 1 efficiently distinguishes Cu²⁺, Hg²⁺ and Pb²⁺ ions by exhibiting different responses in fluorescence. While compound 1 exhibited turn-on emission selectively in the presence of Hg²⁺ and Pb²⁺ ions in CH₃CN and CH₃CN–H₂O (1:1, v/v), respectively, it showed decrease in emission upon interaction with Cu²⁺ ion in CH₃CN. Furthermore, the Cu-1 ensemble has been established as a potential probe for selective detection of CN^? ion over a series of other anions involving colour change (in ordinary light: colourless to light yellow and under UV light: colourless to sky blue). Theoretical insight has been invoked to understand the mode of metal–ligand interaction.     

A rhodamine hydrazide–4-nitroindole-3-carboxaldehyde based turn on Hg2+ chemosensor: cytoplasmic live cell imaging,logic gate and memory device applications and computational studies

A new, highly sensitive probe L² for the selective detection of Hg²⁺ in organo-aqueous (H₂O:CH₃CN, 1:1, v/v, HEPES buffer, pH 7.2) medium has been synthesized from rhodamine 6G-hydrazide and 4-nitroindole-3-carboxaldehyde. It was thoroughly characterized by physicochemical techniques including single crystal X-ray diffraction studies. The reaction of L² with Hg²⁺ gives a 1:1 stoichiometry resulting in a 146 fold fluorescence enhancement and a binding constant (K_f) of 3?×?10⁴ M^?1. The spirolactam form of the probe is non-fluorescent; however, it shows dual channel (absorbance and fluorescence) recognition of Hg²⁺ via CHEF effect through the opening of the spirolactam ring. The quantum yields of L² (0.00045) and L²-Hg²⁺ (0.29) show the higher stability of complex in the excited state over the free ligand. The 44.5?nM LOD value demonstrates the detection of Hg²⁺ at a very low concentration range. Cell imaging studies show the cytoplasmic recognition of Hg²⁺ by L². Experimental results are comparable with theoretical values obtained by DFT studies. The fluorescence emission of the complex was completely quenched by I^- and from the reversibility studies an advance level INHIBIT logic gate and memory device can be framed.     

Effect of the Counterion on Light Emission: A Displacement Strategy to Change the Emission Behaviour from Aggregation‐Caused Quenching to Aggregation‐Induced Emission and to Construct Sensitive Fluorescent Sensors for Hg2+ Detection

In this paper, a simple strategy to change the emission behaviour of luminogenic materials was developed. Tetraphenylethene (TPE)‐functionalised benzothiazolium salts with different counteranions (TPEBe?X; X=I^?, ClO₄^? and PF₆^?) were designed and synthesised. All the luminogens show weak red emission in the solution state that originates from intramolecular charge transfer from TPE to the benzothiazolium unit. Whereas aggregate formation enhances the light emission of TPEBe?ClO₄ and TPEBe?PF₆, that of TPEBe?I is quenched, thus demonstrating the phenomena of aggregation‐induced emission and aggregation‐caused quenching. TPEBe?I works as a light‐up fluorescent sensor for Hg²⁺ in aqueous solution with high sensitivity and specificity owing to the elimination of the emission quenching effect of the iodide ion by the formation of HgI₂ as well as the induction in aggregate formation by the complexation of Hg²⁺ with the S atom of the benzothiazolium unit of TPEBe?I. A solid film of TPEBe?I was prepared that can monitor the level of Hg²⁺ in aqueous solution with a detection limit of 1 μM .     

A novel turn-on fluorescent probe for Hg2+ detection based on rhodamine B spirolactam derivative

ABSTRACT

In this work, a new turn-on fluorescent probe 1 for Hg²⁺ ions detection based on rhodamine B spirolactam was reported. Among tested metal ions, probe 1 shows high selectivity towards Hg²⁺ in the the mixture solution of methanol and 0.02 M HEPES buffer (V/V = 9:1, pH = 7.2). No absorption and emission band of probe 1 was observed in the range from 450 to 700 nm. While only addition of Hg²⁺ to probe 1 could lead to appearance of a new absorption band centered at 553 nm and a fluorescence emission band around 577 nm upon excitation at 520 nm. Moreover, it exhibits excellent linear relationship (R² = 0.9993) between fluorescence intensity at 577 nm and the concentration of Hg²⁺ from 1.6 to 32 μM. The sensing mechanism was proven to be spirolactam ring open induced by Hg²⁺ through ¹H NMR, MS, absorption and fluorescence spectra. In addition, probe 1 could detect Hg²⁺ in real water samples and on filter paper, which demonstrates its application in environment science.     

A ratiometric fluorescent probe for zinc ions based on the quinoline fluorophore

A ratiometric fluorescent zinc probe 1 of carboxamidoquinoline with a carboxylic acid group was designed and synthesised. Probe 1 exhibits high selectivity for sensing Zn²⁺; about a 13-fold increase in fluorescence emission intensity and an 82?nm red-shift of fluorescence emission are observed upon binding Zn²⁺ in EtOH/H₂O (1?:?1, V/V) solution. The ratiometric fluorescence response is attributed to the 1?:?1 complex formation between probe 1 and Zn²⁺ which has been utilised as the basis for the selective detection of Zn²⁺. The analytical performance characteristics of the proposed Zn²⁺-sensitive probe were investigated. The linear response range covers a concentration range of Zn²⁺ from 2.0?×?10^?6 to 5.0?×?10^?5?mol?L^?1 and the detection limit is 2.7?×?10^?7?mol?L^?1. The determination of Zn²⁺ in both tap and river water samples shows satisfactory results.     

A new quinoline-based chemosensor in ratiometric sensing of Hg2+ ions

A new quinoline-based chemosensor 1 has been designed and synthesised. Its metal ion-binding properties have been documented in organic and aqueous organic solvents. While chemosensor 1 recognises Hg²⁺ ions (K _a = 2.15 × 10⁴ M^? 1) by exhibiting ratiometric change in emission in CHCl₃/CH₃OH (1:1, v/v), under similar condition both Zn²⁺ and Cd²⁺ ions are sensed by significant non-ratiometric increase in emission with measurable red shift. In DMSO/H₂O (5:95, v/v), the sensor 1 exhibits a greater selectivity towards Hg²⁺ ions (K _a = 9.20 × 10³ M^? 1) over the other metal ions examined.     

Multiple-color aggregation-induced emission-based Schiff base sensors for ultrafast dual recognition of Hg2+ and pH integrating Boolean logic operations

Seven Schiff base fluorescent sensors (L¹?L⁷) with multiple-color aggregation-induced emission (AIE) properties for detection of Hg²⁺ ions and pH integrating Boolean logic operations were reported. With appropriate ligand-to-metal coordination (L?HgCl₂) and AIE characteristic, L?HgCl₂ can aggregate into nanoparticles, followed by activation of strong emission, therefore, the “turn-on” assay for detection of Hg²⁺ can be established. Sensing mechanism was calculated through single-crystal X-ray diffraction, Job’s Plot, Benesi?Hildebrand equation, dynamic light scattering, scanning electron microscopy, and elemental mapping analysis. Density functional theory calculations revealed that L?HgCl₂ can avoid one-electron transfer and retain bright luminescence compared with that of L. Different (highest unoccupied orbit) HOMO and (Lowest empty orbit) LUMO energy gaps enable the different electron transitions, resulting in the multiple-color fluorescence properties. Especially, L¹?L⁷ exhibit pH-dependent fluorescent characteristics: different electron-donating ability of the substituent groups for L¹?L⁷ show different titration jump of pH. Advanced level molecular logic gates have been constructed integrating the sensing of Hg²⁺ and pH. More importantly, the L-coated test paper applied in Hg²⁺ sensing makes tracing possible, which is convenient for confidential purposes.     

一种近红外发射荧光探针的合成及其荧光增强识别Hg2+

汞离子(Hg~(2+))由于高毒性以及容易对环境和人体造成损害,其检测越来越受到人们的重视。本文基于4-(二乙氨基)水杨醛设计合成了一种近红外发射荧光探针L,该探针可在MeCN/HEPES(体积比2/8,pH=7.4)缓冲溶液中高选择性地荧光增强识别Hg~(2+),其具有合成简便、抗干扰能力强、适用pH范围宽等特点。进一步研究表明,探针L可用于真实水样中Hg~(2+)的检测。     

A violet emission from optically excited mercury vapour. Kinetics of the formation and decay of excited dimers and trimers

A new electronic systems has been observed from excited Hg vapour, which is assigned to collisionally induced emission from the Hg₂ O^±_g first excited states of the dimer: Hg₂O^±_g + M → 2Hg(6 ¹S₀) + M + hv(γ_max 3950 A). For M = N₂, the rate coefficient is 5.3(±0.7) × 10^?19 cm³ molecule^?1 at 298 K. From time resolved measurements of the luminescence in the afterglow following pulsed excitation, the decay rate of the green emission, in an excess of N₂, is shown to be a linear function of [Hg][N₂]. It is concluded that the reaction which controls the decay of the excitation is formation of an excited trimer in a termolecular reaction; the trimer is the carrier of the green emission: Hg₂ O^±_g + Hg(6 ¹S₀ + Hg(6¹S₀ + N₂ → Hg₃³Π_u + N₂. The rate coefficient is 1.10(±0.07) × 10^?30 cm⁶ molecule^?2 s^?1 at 298 K.     

A highly selective nanogold-aptamer catalytic resonance scattering spectral assay for trace Hg using HAuCl4-ascorbic acid as indicator reaction

Single strand DNA (ssDNA) was used to modify nanogold to obtain a nanogold-aptamer resonance scattering (RS) probe (NGssDNA) for Hg²⁺, based on the formation of stable thymine-Hg²⁺-thymine (T-Hg²⁺-T) mismatches and aggregation of the released nanogold particles. After removing the aggregated particles by filtrate membrane, the excess NGssDNA in the filtration solution exhibit catalytic effect on the gold particle reaction between HAuCl₄ and ascorbic acid (AA) that appear as RS peak at 596 nm. When Hg²⁺ concentration increased, the RS intensity at 596 nm decreased. The decreased intensity is linear to Hg²⁺ concentration in the range of 0.00008-0.888 ng/mL Hg²⁺, with detection limit of 0.000034 ng/mL. The nanogold-aptamer catalytic RS assay was applied to determination of Hg²⁺ in water with satisfactory results.     

Solvent-Assisted Naked Eye Sensing of Hg2+ by a Chemoreceptor Derived from Diazocoupling of Sulfathiazole with Diethyl Malonate

Abstract

2-{[4-(Thiazol-2-ylsulfamoyl)-phenyl]-hydrazono}-malonic acid diethyl ester (R1) and 2-{[4-(5-methyl-isoxazol-3-ylsulfamoyl)-phenyl]-hydrazono}-malonic acid diethyl ester (R2) were synthesized through diazocoupling of sulfathiazole and sulfamethoxazole, respectively, with diethyl malonate. They were characterized through various spectroscopic and mass spectral studies. R2 was also characterized through a single crystal X-ray diffraction (XRD) study. Only R1 selectively recognized Hg²⁺ from a wide range of metal ions through naked-eye change. A color change from orange to olive green was observed upon addition of 1.0 equivalent of Hg²⁺ as its chloride salt to the 1 × 10^?3 M DMSO solution of R1. The role of DMSO in the sensing process appears to be the crucial one, because the solvent-assisted band of R1 at 482 nm observed in its UV-Vis spectrum in DMSO did not appear in its spectra recorded in nujol or in a polar aprotic solvent. The UV-Vis and ¹H NMR titrations revealed that the formation of six-membered 1:1 chelate between R1 and Hg²⁺ triggering the desolvation of R1

as the key step towards its sensing activity. The determination of binding stoichiometry between R1 and Hg²⁺ along with binding constant has also been discussed.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT      

苯乙烯三嗪衍生物的合成及在重金属离子识别中的应用

合成了2,4-二(2-噻吩乙烯基)-6-(4'-N,N-二甲氨基苯乙烯基)-1,3,5-均三嗪(2)并鉴定了其结构。在乙腈-水混合介质中,化合物2在355和416nm处呈现双吸收峰,加入Cu²⁺,Hg²⁺ 和Fe³⁺ 后,均在520nm附近形成新的吸收峰。化合物2与Cu²⁺、Hg²⁺ 和Fe³⁺ 均形成1:1型配合物,其结合常数分别为1.9×10⁵L·mol^-1,6.6×10³L·mol^-1,2.7×10³L·mol^-1。对照化合物4与金属离子的光谱响应与化合物2相似,仅吸收峰的位置不同。因此,可认为化合物2和4中三嗪环中的N和噻吩环中的S与Cu²⁺、Hg²⁺ 和Fe³⁺ 共同配位形成了稳定的金属配合物。     

Rhodamine-labelled new architecture for dual sensing of Co and Hg ions

A new rhodamine-based chemosensor 1 has been designed and synthesized. The receptor selectively recognizes Co²⁺ and Hg²⁺ ions in CH₃CN/water (4:1, v/v; 10 μM tris HCl buffer, pH 6.8) by showing different extents of change in emission. The disappearance of colour of mercury-ensemble of 1 followed by appearance of distinct bluish colour under UV illumination upon addition of l-cysteine distinguishes Hg²⁺ from Co²⁺ ions. The receptor shows in vitro detection of both the ions in human cervical cancer (HeLa) cells.     

Unexpected highly selective fluorescence ‘turn-on’ and ratiometric detection of Hg based on fluorescein platform

Methylated fluorescein 1 was explored for fluorescence ‘turn-on’ and ratiometric detection of Hg²⁺ in THF and CH₂Cl₂/MeOH (v/v=9:1), respectively, with unexpected high selectivity. In the presence of Hg²⁺, characteristic structured absorption band of 1 diminished and a new sharp band appeared at 445 nm. Meanwhile a blue shifted and enhanced emission was observed. The ratio of the fluorescence intensity at 559 and 478 nm increased linearly with [Hg²⁺], and solution color changing from yellow to cyan under irradiation at 365 nm in CH₂Cl₂/MeOH. Job plot indicated a 1:1 stoichiometry for 1-Hg²⁺ complex in solution. ¹H NMR titration and IR spectra suggested the coordination of carbonyl group in xanthene moiety to Hg²⁺, affording its spectral behavior. Compound 2 bearing two triazolyl amino esters in place of methyl group showed quite similar behavior to Hg²⁺, which indicated that substituents did not interfere with the specific binding behavior of fluorescein platform. Our work presents a new way to explore xanthene dyes as new chemosensors by modulating electron density on the xanthene ring through non-covalent interactions with carbonyl group.     

Dimedone‐decorated conjugated polymer: Tandem knoevenagel‐michael post‐modification synthesis and its application as optical probe for Hg2+ and ClO− in high‐water‐fraction mediums

High‐efficiency, mild‐conditioned tandem Knoevenagel–Michael reaction was utilized to post‐modify aldehyde‐containing, triphenylamine‐based precursor conjugated polymer ( CP1 ) to afford dimedone‐decorated aimed polymer ( CP2) . The chemical structure of CP2 was verified by FTIR and ¹H NMR analyses. With the introduction of aqueous Hg²⁺, fluorescence of CP2 in THF‐water mixture (V _THF/V _water = 1/100) (buffered with 5 mM sodium dihydrogen phosphate‐disodium hydrogen phosphate (PB), pH = 7.4) altered significantly, with the emission changed from blue to orange. Besides this, CP2 also displayed specific optical response to ClO^? in another probing medium (V _THF/V _water = 1/100, buffered with 50 mM PBS (with NaCl in PB, pH = 7.4). The detailed probing process and the plausible detection mechanism of CP2 to Hg²⁺ and ClO^? were systematically investigated here. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1067–1076     

Selective sensing of Hg2+ via sol–gel transformation of a cholesterol-based compound

A cholesterol-based dithioacetal functionalised compound 1 has been designed, synthesised and successfully applied for the selective detection of Hg²⁺ ion. The specific Hg²⁺-induced deprotection of the thioacetal functionality of 1 resulted in sol-to-gel transition in DMF-H₂O (1:1, v/v) via the formation of precursor aldehyde 3. This Hg²⁺-prompted rapid sol to gel conversion is insensitive to the nature of Hg²⁺-salt. In the study, other metal ions did not show any change. To the best of our knowledge, this is a first time report of a chemodosimeter that functions as a selective ‘naked-eye’ Hg²⁺-detector by showing in situ sol-to-gel conversion.     

A highly selective fluorescent chemosensor for Fe (III) based on rhodamine 6G dyes derivative

A new fluorescent probe L based on the rhodamine 6G platforms for Fe³⁺ has been designed and synthesised. L showed excellent selectivity and high sensitivity for Fe³⁺ against other metal ions such as K⁺, Na⁺, Ag⁺, Cu²⁺, Co²⁺, Mg²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Fe²⁺, Hg²⁺, Ce³⁺ and Y³⁺ in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The distinct color change and the rapid emergence of fluorescence emission provided naked-eyes detection for Fe³⁺. The recognition mechanism of the probe toward Fe³⁺ was evaluated by Job’s plots, IR and ESI-MS. In order to further study their fluorescent properties, L + Fe³⁺ fluorescence lifetime was also measured. Moreover, the test strip results showed that these probes could act as a convenient and efficient Fe³⁺ test kit.     

A Fluorescent Probe for Hg2+ Based on Gold(I) Complex with An Aggregation‐Induced Emission Feature

A gold(I) complex that exhibited aggregation‐induced emission in acetonitrile‐water mixtures was designed. It showed high selectivity and sensitivity for Hg²⁺ in acetonitrile‐H₂O (1:1, V:V) solution. Dynamic light scattering measurements were conducted to verify that the addition of Hg²⁺ changed the particle size and induced fluorescence quenching.     

(Oligo)thienyl-imidazo-benzocrown ether derivatives: synthesis, photophysical studies and evaluation of their chemosensory properties

A series of novel (oligo)thienyl-imidazo-benzocrown ethers were synthesised through a simple method and evaluated as fluorimetric chemosensors for transition metal cations. Interaction with Ni²⁺, Pd²⁺, and Hg²⁺ in ACN/DMSO solution (99:1) was studied by absorption and emission spectroscopy. Chemoselectivity studies in the presence of Na⁺ were also carried out and a fluorescence enhancement upon chelation (CHEF) effect was observed following Hg²⁺ complexation. Considering that most systems using fluorescence spectroscopy for detecting Hg²⁺ are based on the complexation enhancement of the fluorescence quenching (CHEQ) effect, the present work represents one of the few examples for sensing of Hg²⁺ based on a CHEF effect.     

Chromenone-rhodamine conjugate for naked eye detection of Al3+ and Hg2+ ions in semi aqueous medium

Chromenone-rhodamine conjugate 1 has been synthesized and its metal ion binding properties have been studied in CH₃CN/water (3:1, v/v; 10 mM HEPES buffer; pH = 6.85). Compound 1 senses multiple metal ions such as Al³⁺ and Hg²⁺ by exhibiting turn on fluorescence and color change (colorless to pink). Al³⁺ and Hg²⁺ ions have been distinguished with the aid of tetrabutylammonium iodide (TBAI). While in the presence of I^? the pink color of the 1.Hg²⁺ complex was completely discharged; under identical conditions the pink color of 1.Al³⁺ complex was retained.