Chromogenic and fluorogenic sensing of Cu2+ based on coumarin

A water-soluble colorimetric chemosensor for sequential probing of Cu2+ and S2- and its practical applications to test strips, reversible test, and water samples

A water-soluble colorimetric chemosensor NHOP ((E)-1-(2-(2-(2-hydroxy-5-nitrobenzylidene)hydrazineyl)-2-oxoethyl)pyridin-1-ium) chloride) was developed for the sequential probing of Cu2+ and S2-. NHOP underwent a color change from pale yellow to colorless in the presence of Cu2+ in pure water. The binding ratio between NHOP and Cu2+ was confirmed to be 1:1 by the Job plot and ESI-MS (electrospray ionization mass spectrometry). The detection limit of NHOP for Cu2+ was calculated as 0.15 μM, which was far below the EPA (Environmental Protection Agency) standard (20 μM). The NHOP-coated test strip was able to easily monitor Cu2+ in real-time. Meanwhile, the NHOP-Cu2+ complex reverted from colorless to pale yellow in the presence of S2- through the demetallation. The stoichiometric ratio between NHOP-Cu2+ and S2- was determined to be 1:1 by analyzing the Job plot and ESI-MS. The detection limit of NHOP-Cu2+ for S2- was calculated as 0.29 μM, which was very below the WHO (World Health Organization) guideline (14.7 μM). NHOP successfully achieved the quantification for Cu2+ and S2- in water samples. NHOP could work as a sequential probe for Cu2+ and S2- at the biological pH range (7.0-8.4). Moreover, NHOP could successively probe Cu2+ and S2- at least three cycles because of its reversible property. The detection mechanisms of NHOP for Cu2+ and NHOP-Cu2+ for S2- were demonstrated with Job plot, ESI-MS, and DFT (density functional theory) calculations. Therefore, NHOP could work as an efficient sequential probe for Cu2+ and S2- in environmental systems.

Shedding Novel Photophysical Insights Toward Discriminative Detection of Three Toxic Heavy Metal Ions and a hazard class 1 nitro-explosive By Using a Simple AIEE Active Luminogen

In this work, we introduced a simple aggregation-induced emission enhancement (AIEE) sensor (PHCS) which can selectively detect and discriminate three environmentally and biologically imperative heavy metal ions (Cu2+, Co2+ and Hg2+) and a hazard class 1 categorized nitro-explosive picric acid (PA) in differential media. By virtue of its weak fluorescence attributes in pure organic medium owing to the synergistic operation of multiple photophysical quenching mechanisms, the molecular probe showcased highly selective 'TURN ON' fluorogenic response towards hazardous Hg2+ with a limit of detection (LOD) as low as 97 nM. Comprehensive investigation of binding mechanism throws light on the cumulative effect of probe-metal complexation induced chelation enhanced fluorescence (CHEF) effect and subsequent AIEE activation within the formed probe-metal adducts. Noteworthily, the probe (PHCS) can be readily used in real water samples for the quantitative determination of Hg2+ in a wide concentration range. In addition, the probe displayed modest colorimetric recognition performances to selectively detect and discriminate two essential heavy metal ions (Cu2+ and Co2+) with a LOD of 96 nM and 65 nM for Cu2+ and Co2+ respectively, in semi-aqueous medium. Intriguingly, based on high photoluminescence efficiency, the AIEE active nano-aggregated PHCS displayed a remarkable propensity to be used as a selective and ultra-sensitive 'TURN-OFF' fluorogenic chemosensor towards PA with LOD of 34.4 ppb in aqueous medium. Finally, we specifically shed light on the interaction of PHCS hydrosol towards PA using some unprecedented techniques, which helped uncover new photophysical insights of probe-explosive molecule interaction.

A sensitive fluorescence sensor based on a glutathione modified quantum dot for visual detection of copper ions in real samples

Copper (Cu²⁺), as a heavy metal, accumulates in the human body to a certain extent, which can induce various diseases and endanger human health. Rapid and sensitive detection of Cu²⁺ is highly desired. In present work, a glutathione modified quantum dot (GSH-CdTe QDs) was synthesized and applied in a "turn-off" fluorescence probe to detect Cu²⁺. The fluorescence of GSH-CdTe QDs could be rapidly quenched in the presence of Cu²⁺ through aggregation-caused quenching (ACQ), resulting from the interaction between the surface functional groups of GSH-CdTe QDs and Cu²⁺ and the electrostatic attraction. In the range of 20-1100 nM, the Cu²⁺ concentration showed a good linear relationship with the fluorescence decline of the sensor, and the LOD is 10.12 nM, which was lower than the U.S. Environmental Protection Agency (EPA) defined limit (20 μM). Moreover, aiming to attain visual analysis, colorimetric method was also used for rapidly detecting Cu²⁺ by capturing the change in fluorescence color. Interestingly, the proposed approach has successfully been applied for the detection of Cu²⁺ in real samples (i.e., environment water, food and traditional Chinese medicine) with satisfactory results, which provides a promising strategy for the detection of Cu²⁺ in practical application with the merits of being rapid, simple and sensitive.

Irreversible coumarin based fluorescent probe for selective detection of Cu2+ in living cells

Copper ion (Cu²⁺) is an essential part of the living organisms. Cu²⁺ ions play a vital role in many biotic processes. An abnormal amount of Cu²⁺ ions may result in serious diseases. Herein, a novel "fluorescent ON" probe NC-Cu to trace minute levels of Cu²⁺ ions in presence of various biological active species has been developed. Lysosomal cells targeting group (Morpholine) was added to the probe. The spectral properties of probe NC-Cu were recorded in HEPES buffer (0.01 M, pH = 7.4, comprising 50% CH₃CN, λ_ex = 430 nm, slit: 5 nm). The synthesized probe NC-Cu work based on copper promoted catalytic hydrolysis of hydrazone and shows remarkable fluorescence enhancement. The reaction of the probe with Cu²⁺ ions was completed within 20 min. An excellent linear relationship (R² = 0.9952) was found and the limit of detection (LOD, according to the 3σ/slope) for Cu²⁺ ions was calculated to be 5.8 µM. Furthermore, NC-Cu was effectively functional in the living cells (KYSE30 cells) to trace Cu²⁺ ions.

Differential Detection of Strong-Acids in Weak-Acids: A combination of Benzimidazole-carbazole backbone with AIE luminophores as highly sensitive and selective turn-on fluorescent probes

o-BzcDPE and p-BzcDPE have been synthesized and used as probes for strong acid detection. The probes contain an aggregation-induced emission luminogens (AIEgens) that is incorporated with benzimidazole-carbazole backbone. Both probes...

3-(Bromoacetyl)coumarins: unraveling their synthesis, chemistry, and applications

This review emphasizes recent developments in synthetic routes of 3-(bromoacetyl)coumarin derivatives. Also, chemical reactions of 3-(bromoacetyl)coumarins as versatile building blocks in the preparation of critical polyfunctionalized heterocyclic systems and other industrially significant scaffolds are described. Recent advances of 3-(bromoacetyl)coumarins as attractive starting points towards a wide scale of five and six-membered heterocyclic systems such as thiophenes, imidazoles, pyrazoles, thiazoles, triazoles, pyrans, pyridines, thiadiazins as well as fused heterocyclic systems have been reported. Additionally, this review covers a wide range of analytical chemistry, fluorescent sensors, and biological applications of these moieties, covering the literature till May 2021.

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 3.3 μM. 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.

Pathway for biodegrading coumarin by a newly isolated Pseudomonas sp. USTB-Z

Coumarin is widely used in personal care products and pharmaceutical industry, which leads to the release of this compound into environment as an emerging contaminant. Here, a promising strain USTB-Z for biodegrading coumarin was successfully isolated from botanical soil and characterized as a potential novel Pseudomonas sp. based on 16S rDNA sequence analysis and orthologous average nucleotide identity tool. Initial coumarin up to 800 mg/L could be completely removed by USTB-Z within 48 h at the optimal culture conditions of pH 7.3 and 30 °C, which indicates that USTB-Z has a strong capacity in coumarin biodegradation. The biodegradation products of coumarin were further investigated using HPLC and Q-TOF LC/MS, and melilotic acid and 2,3-dihydroxyphenylpropionic acid were identified. The draft genome of strain USTB-Z was sequenced by Illumina NovaSeq, and 21 CDSs for NAD (P)-dependent oxidoreductase, 43 CDSs for hydrolase, 1 CDS for FAD-depend monooxygenase, 1 CDS for 3-hydroxycinnamic acid hydroxylase, 21 CDSs for dioxygenase, and 5 CDSs for fumarylacetoacetate (FAA) hydrolase were annotated and correlated to coumarin biodegradation. The present study provides a theoretical basis and microbial resource for further research on the coumarin biodegradation.

PAA Modified Upconversion Nanoparticles for Highly Selective and Sensitive Detection of Cu2+ Ions

Detection of the Cu²⁺ ions is crucial because of its environmental and biological implications. The fluorescent-based organic sensors are not suitable for Cu²⁺ detection due to their short penetration depth caused by the UV/visible excitation source. Therefore, we have demonstrated a highly sensitive and selective near-infrared (NIR) excitable poly(acrylic acid) (PAA) coated upconversion nanoparticles (UCNPs) based sensor for Cu²⁺ detection. We construct the PAA modified Na(Yb, Nd)F₄@Na(Yb, Gd)F₄:Tm@NaGdF₄ core-shell-shell structured UCNPs based sensor via a co-precipitation route. The upconversion emission intensity of the PAA-UCNPs decreases linearly with the increase in the Cu²⁺ concentration from 0.125 to 3.125 μM due to the copper carboxylate complex formation between Cu²⁺ and PAA-UCNPs. The calculated detection limit of the PAA-UCNPs based sensor is 0.1 μM. The PAA-UCNPs based sensor is very sensitive and selective toward detecting the Cu²⁺ ions, even when the Cu²⁺ co-exist with other metal ions. The EDTA addition has significantly reversed the upconversion emission quenching by forming the EDTA-Cu²⁺ complex based on their greater affinity toward the Cu²⁺. Therefore, the PAA-UCNPs based sensor can be a promising candidate for Cu²⁺ detection because of their higher sensitivity and selectivity under 980 nm NIR excitation.

Rational Design of π-Conjugated Tricoordinated Organoboron Derivatives With Thermally Activated Delayed Fluorescent Properties for Application in Organic Light-Emitting Diodes

A series of donor–acceptor (D–A) tricoordinated organoboron derivatives (1–10) have been systematically investigated for thermally activated delayed fluorescent (TADF)-based organic light-emitting diode (OLED) materials. The calculated results show that the designed molecules exhibit small singlet-triplet energy gap (ΔE_ST) values. Density functional theory (DFT) analysis indicated that the designed molecules display an efficient separation between donor and acceptor fragments because of a small overlap between donor and acceptor fragments on HOMOs and LUMOs. Furthermore, the delayed fluorescence emission color can be tuned effectively by introduction of different polycyclic aromatic fragments in parent molecule 1. The calculated results show that molecules 2, 3, and 4 possess more significant Stokes shifts and red emission with small ΔE_ST values. Nevertheless, other molecules exhibit green (1, 7, and 8), light green (6 and 10), and blue (5 and 9) emissions. Meanwhile, they are potential ambipolar charge transport materials except that 4 and 10 can serve as electron and hole transport materials only, respectively. Therefore, we proposed a rational way for the design of efficient TADF materials as well as charge transport materials for OLEDs simultaneously.

A FRET-based colorimetric and ratiometric fluorescent probe for the detection of Cu2+ with a new trimethylindolin fluorophore

The possible interaction mechanism between probe RhF and Cu²⁺ ions.

Chalcone scaffolds as photofunctional hybrid material of indolin-2-one-functionalized siloxy framework for optical sensing of Cu2+

The present article is about the synthesis of an indolin-2-one chalcone-based photofunctional hybrid for the selective and sensitive detection of Cu²⁺.

Colorimetric detection of iron and fluorescence detection of zinc and cadmium by a chemosensor containing a bio-friendly octopamine

A chemosensor containing a bio-friendly octopamine was developed for the colorimetric detection of iron and fluorescence detection of zinc and cadmium.

Fluorescence sensor for sequential detection of zinc and phosphate ions

A new, highly selective turn-on fluorescent chemosensor based on 2-(2'-tosylamidophenyl)thiazole (1) for the detection of zinc and phosphate ions in ethanol was synthesized and characterized. Sensor 1 showed a high selectivity for zinc compared to other cations and sequentially detected hydrogen pyrophosphate and hydrogen phosphate. The fluorescence mechanism can be explained by two different mechanisms: (i) the inhibition of excited-state intramolecular proton transfer (ESIPT) and (ii) chelation-induced enhanced fluorescence by binding with Zn(2+). The sequential detection of phosphate anions was achieved by the quenching and subsequent revival of ESIPT.

A highly selective fluorescent chemosensor based on naphthalimide and Schiff base units for Cu2+ detection in aqueous medium

A new Schiff base, 4-allylamine-N-(N-5-methylsalicylidene)-1,8-naphthalimide (1), has been designed and synthesized by combining a 1,8-naphthalimide moiety as a fluorophore and a Schiff base as a recognition group. Its photophysical properties were investigated by absorption and fluorescence spectroscopy, and this sensor exhibits a high fluorescence quantum yield of 0.75–0.91 inorganic solvents of different polarity. It also shows high selectivity for Cu2+ over other ions with fluorescence quenching in aqueous medium (pH=7.2). The reason for this phenomenon (fluorescence quenching) is attributed to the formation of a 1:1 complex between 1 and Cu2+ according to the Job plot and fluorescence titration. The sensor can be applied to the quantification of Cu2+ in a linear fashion from 0.5 to 5 μM with a detection limit of 0.23 μM. Additionally, the association constant (K a) between Cu2+ and 1 is 1.328×106 M− 1 in aqueous media.