A novel macrocycle acridine-based fluorescent chemosensor for selective detection of Cd2+ in Brazilian sugarcane spirit and tobacco cigarette smoke extract

Cd2+-Specific Fluorescence Response of Methoxy-Substituted N,N-Bis(2-quinolylmethyl)-2-methoxyaniline Derivatives

The N3O1 tetradentate ligand, TriMeOBQMOA (N,N-bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methoxyaniline), was developed as a Cd2+-specific fluorescent sensor. The structure of TriMeOBQMOA is half of TriMeOBAPTQ (N,N,N',N'-tetrakis(5,6,7-trimethoxy-2-quinolylmethyl)-1,2-bis(2-aminophenoxy)ethane), which is a tetrakisquinoline derivative of the well-known calcium chelator BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid). The fluorescent Cd2+ selectivity of TriMeOBAPTQ (IZn/ICd = 5.3% in the presence of 3 equiv of metal ions in MeOH-HEPES buffer (9:1)) comes from the formation of fluorescent dinuclear cadmium (M2L) and nonfluorescent OH-bridged dizinc ((μ-OH)M2L) complexes. TriMeOBQMOA also exhibits excellent Cd2+ specificity in fluorescence enhancement (IZn/ICd = 2.3% in the presence of 5 equiv of metal ions in DMF-HEPES buffer (1:1, HEPES 50 mM, KCl 0.1 M, pH = 7.5)) via substantial formation of a highly fluorescent bis(μ-chloro)dinuclear cadmium complex ([Cd2(μ-Cl)2L2]2+), which is in equilibrium with the mononuclear Cd2+ complex ([CdLCl]+), and extremely poor stability of the TriMeOBQMOA-Zn2+ complex. The all-nitrogen derivatives of BQMOA and BAPTQ, namely, N,N-BQDMPHEN (N,N-bis(2-quinolylmethyl)-N',N'-dimethyl-1,2-phenylenediamine) and BPDTQ (N,N,N',N'-tetrakis(2-quinolylmethyl)-2,2'-(N,N'-dimethylethylenediamino)dianiline), respectively, and their methoxy-substituted derivatives were also prepared, and the fluorescent metal ion sensing properties are discussed.

Recent Advancements in Fluorometric and Colorimetric Detection of Cd2+ Using Organic Chemosensors: A Review (2019-2024)

In recent decades, heavy metal ions have emerged as a significant global environmental concern, posing threats to the delicate balance of ecosystems worldwide. Their introduction into ecosystems occurs through various activities and poses a serious risk to human health. Among heavy metal ions, Cd2+ is recognized as a highly toxic pollutant. Its widespread use contributes to its accumulation in the environment. Chronic exposure to Cd2+ ions present serious risks to both the environment and human health. Therefore, the detection of these metal ions are very important. Organic fluorometric and colorimetric detection have emerged as promising tools for this purpose, offering advantages such as high sensitivity, selectivity, and sometimes reversibility. This review offers a comprehensive overview of the recent advancements in the fluorometric and colorimetric detection of Cd2+ using organic chemosensors from 2019 to 2024. We delve into key aspects of these studies, including the design strategies employed to design novel chemosensors and the underlying sensing mechanisms. Furthermore, we explore the diverse applications of these organic chemosensors, ranging from environmental monitoring to biomedical diagnostics. By analyzing the latest research findings, this review aims to offer insights into the current state-of-the-art in the field of Cd2+ detection using organic chemosensors. Additionally, it highlights the potential opportunities and challenges that lie ahead, paving the way for future advancements in this important area of research.

A thiophene-linked terpyridine based phenanthridine chemoreceptor for Cd2+ and Cr3+ selective ratiometric fluorescence detection in environmental water and rice samples

BACKGROUND

The studied materials, Cadmium (Cd2+) and Chromium (Cr3+) are highly toxic, and it focuses on investigating various environmental sources, such as industrial processes and waste water. When quantities of Cr3+ and Cd2+ exceed the allowable limit, biological toxicity and hazardous environmental pollution are unavoidable. In order to address this problem, we introduce 5-(5-(4-([2,2':6',2″-terpyridin]-4'-yl) phenyl) thiophen-2-yl)-7,8,13,14-tetrahydrodibenzo [a,i] phenanthridine (TPTP), a dual-emission response chemosensor that employs a colorimetric and fluorescence turn-on approach for the rapid, sensitive, and discriminate detection of Cr3+ and Cd2+ ions.

RESULTS

We created a newly designed luminous TPTP sensor based on intramolecular charge transfer (ICT). TPTP sensor probe specifically determined Cr3+ and Cd2+ ions with an immediate colour shift from cyan to green and orange in CH3CN: H2O (6:4) solvent solution. The permissible level set by the Environmental Protection Agency (EPA) of the United States for the presence of Cr3+ and Cd2+ ions in drinking water was higher than the detection level of 3.5 and 9.7 nM, by this sensor respectively. NMR titrations, HRMS, and theoretical calculation methods were employed to examine the accurate sensing processes of TPTP and complexes.

SIGNIFICANCE

This is an effective method of detecting Cr3+ and Cd2+ ions in an environmental system using a ratiometric methodology. In addition, TPTP was used to determine the concentration of Cr3+ and Cd2+ ions in natural water and food samples. Fluorescent bio-imaging studies revealed that the present sensor TPTP could identify Cr3+ and Cd2+ ions inside living HeLa cells. A paper kit analysis has been done on TPTP, which has a time-to-result of less than 1 s and offers a cost-effective assay. As a result, the platform offers portability.

Cd2+-Selective Fluorescence Enhancement of Bisquinoline Derivatives with 2-Aminoethanol Skeleton

The development of fluorescent Cd2+ sensors requires strict selectivity over Zn2+ because of the high availability of Zn2+ in the natural environment. In this paper, bisquinoline-based fluorescent sensors with a 2-aminoethanol backbone were investigated. The weak coordination ability of quinoline compared to well-studied pyridine is suitable for Cd2+ selectivity rather than Zn2+. In the presence of 3 equiv. of metal ions, TriMeO-N,O-BQMAE (N,O-bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methylaminoethanol (3)), as well as its N,N-isomer TriMeO-N,N-BQMAE (N,N-bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methoxyethylamine (6)), exhibits Cd2+-selective fluorescence enhancement over Zn2+ in DMF-HEPES buffer (1:1, 50 mM HEPES, 0.1 M KCl, pH = 7.5) (IZn/ICd = 26-34%), which has similar selectivity in comparison to the corresponding ethylenediamine derivative TriMeOBQDMEN (N,N'-bis(5,6,7-trimethoxy-2-quinolylmethyl)-N,N'-dimethylethylenediamine) under the same experimental condition (IZn/ICd = 24%). The fluorescence mechanisms of N,O- and N,N-isomers of BQMAE are quite different, judging from the fluorescence lifetimes of their metal complexes. The Cd2+ complex with TriMeO-N,O-BQMAE (3) exhibits a long fluorescence lifetime similar to that of TriMeOBQDMEN via intramolecular excimer emission, whereas the Cd2+ complex with TriMeO-N,N-BQMAE (6) exhibits a short lifetime from monomer emission.

A novel phenanthridine and terpyridine based D-π-A fluorescent probe for the ratiometric detection of Cd2+ in environmental water samples and living cells

A "turn-on" Donor-π-Acceptor (D-π-A) containing phenanthridine-functionalized extended π-conjugate terpyridine, 5-(4'-([2,2':6',2''-terpyridin]-4'-yl)-[1,1'-biphenyl]4-yl)7,8,13,14-tetrahydrodibenzo [a, i] phenanthridine (TBTP) was synthesised. It shows strong selectivity for the detection of toxic Cd²⁺ without interference from other metal ions. In the presence of Cd²⁺, the absorption of the TBTP changes dramatically along with the fluorescent emission with the large Stokes shift of 6300 cm^-1. When the compound TBTP is exposed to UV light, its colour changes from blue to orange over the addition of Cd²⁺. Adding other transition metal ions has no effect. This is based on the mechanism of intramolecular charge transfer. The detection limit for Cd²⁺ was found to be around 1.181 × 10^-8 M. An investigation of the sensing mechanism includes job plot, NMR titration, DFT calculation, and HRMS analyses. Excitingly, the recognition of Cd²⁺ in CH₃CN: H₂O (8:2, v/v) medium is quantitative without interference from Zn^2+, which is a common interferent for Cd²⁺. Furthermore, the probe was used for detecting Cd²⁺ in real water samples and cell imaging in living cells was also performed.

Zinc ion detection using a benzothiazole-based highly selective fluorescence "turn-on" chemosensor and its real-time application

A new photochromic fluorescence chemosensor was devised and effectively synthesized using benzothiazole and imidazopyridine derivatives. A "turn-on" fluorescence sensor BIPP for Zn²⁺ detection was developed and has a quick response, excellent sensitivity, and remarkable selectivity over other metal ions. When Zn²⁺ was added to the BIPP solution, a new strong fluorescence emission peak at 542 nm formed with a considerable increase in intensity. The fluorescence color of the BIPP solution changed from blue to bright green. The binding ratio 8 : 2 was found between BIPP and Zn²⁺ by the results of Job's plot, HRMS and ¹H-NMR. The detection limit (LOD) of BIPP towards Zn²⁺ was determined to be 2.36 × 10^-8, which is remarkably low. The ability to detect Zn²⁺ in real water samples demonstrates that BIPP may also be used in environmental systems. Additionally, BIPP can be used to measure Zn²⁺ levels in living cells.

New Polymerizable Tetraaza Macrocycle Containing Two Acridine Units for Selective Fluorescence Sensing of Metal Ions

A new fluorescent bis(acridino)-macrocycle containing two allyl groups was synthesized and photophysically studied. Studies were carried out on metal ion recognition and selectivity-influencing effects including the determination of the relevant thermodynamic constants as logK and pK_a. The proposed sensor molecule is recommended for the development of Zn²⁺-selective optochemical analyzers based on covalently immobilized ionophores as it has a unique pH-independent metal ion recognition ability, which is not influenced by anions and other potentially occurring metal ions in biological samples.

A chalcone-based fluorescent chemosensor for detecting Mg2+ and Cd2

SBOD (sodium (E)-2-(3-[5-bromothiophen-2-yl]-3-oxoprop-1-en-1-yl)-4,6-dichlorophenolate) was designed and synthesized as a chalcone-based fluorescent turn-on chemosensor for Mg²⁺ and Cd²⁺ . SBOD selectively detected Mg²⁺ and Cd²⁺ through the increase in effective fluorescence. Detection limits of SBOD for Mg²⁺ and Cd²⁺ were calculated to be 3.8 μM and 2.9 μM, respectively. The binding modes of SBOD for Mg²⁺ and Cd²⁺ were determined to be 1:1 by ESI-MS and Job plot. Association mechanisms for SBOD to Mg²⁺ and Cd²⁺ were illustrated by ESI-MS, UV-vis, fluorescence spectroscopy, and calculations.

Mitochondria-targeted acridine-based dual-channel fluorescence chemosensor for detection of Sn4+ and Cr2O72- ions in water and its application in discriminative detection of cancer cells

The goal of the present work was to fabricate a new low-cost, easy-to-prepare, dual-channel fluorescence chemosensor comprised of acridine-diphenylacetyl moieties (NDA) to enable remarkable Sn⁴⁺ detection in water and biological medium. The resulting NDA-Sn⁴⁺ complex was utilized for the distinguished identification of Cr₂O₇^2- ions from other anions and biomolecules. These investigations involve the absorption, fluorescence, and electrochemical methods for the detection of Sn⁴⁺ and Cr₂O₇^2- ions in pure water. The mechanism for NDA-mediated Sn⁴⁺ detection was experimentally determined by FT-IR, NMR titrations, mass (ESI) analyses, and DFT calculations. The obtained results indicate that the NDA chemosensor possessed excellent performance characteristics including good water solubility and compatibility, quick response time (less than 10 s), high sensitivity (Sn⁴⁺ = 0.268 μM and Cr₂O₇^2- = 0.160 μM), and selectivity against coexisting metals, anions, amino acids, and peptides. The chemosensor NDA induced negligible toxicity in live cells and was successfully utilized as a biomarker for the tracking of Sn⁴⁺ in human normal and cancer cells. More importantly, NDA demonstrates distinguished recognition of Sn⁴⁺ in human cancer cells rather than in normal live cells. Additionally, NDA was shown to act as a mitochondria-targeted probe in FaDu cells.

Recent progress in cadmium fluorescent and colorimetric probes

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms. Therefore, its detection is of great significance in the fields of biology, environment and medicine. Fluorescent probe has been a powerful tool for cadmium detection because of its convenience, sensitivity, and bioimaging capability. In this paper, we reviewed 98 literatures on cadmium fluorescent sensors reported from 2017 to 2021, classified them according to different fluorophores, elaborated the probe design, application characteristics and recognition mode, summarized and prospected the development of cadmium fluorescent and colorimetric probes. We hope to provide some help for researchers to design cadmium fluorescent probes with higher selectivity, sensitivity and practicability.

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms.

Acridino-Diaza-20-Crown-6 Ethers: New Macrocyclic Hosts for Optochemical Metal Ion Sensing

Acridino-diaza-20-crown-6 ether derivatives as new turn-on type fluorescent chemosensors with an excellent functionality and photophysical properties have been designed and synthesized for metal ion-selective optochemical sensing applications. Spectroscopic studies revealed that in an acetonitrile-based semi-aqueous medium, the sensor molecules exhibited a remarkable fluorescence enhancement with high sensitivity only toward Zn2+, Al3+ and Bi3+, among 23 different metal ions. Studies on complexation showed a great coordinating ability of logK > 4.7 with a 1:1 complex stoichiometry in each case. The detection limits were found to be from 59 nM to micromoles. The new ionophores enabled an optical response without being affected either by the pH in the range of 5.5-7.5, or the presence of various anions or competing metal ions. Varying the N-substituents of the new host-backbone provides diverse opportunities in both immobilization and practical applications without influencing the molecular recognition abilities.