Turn-On Solid-State Fluorescent Determination of Zinc Ion by Quinoline-Based Covalent Organic Framework

A new quinoline-based COF (covalent organic framework), obtained by Povarov reaction, containing 2,6-diisopropylphenyl moieties as substituents over the heterocyclic ring is described for detecting Zn2+ in aqueous solution. The introduction of the mentioned bulky phenyl rings into the network favors an increase of the distance between the reticular sheets and their arrangement, obtaining a new material with an alternating AB type stacking. The new material exhibits good selectivity to detect Zn2+ by fluorescence emission in aqueous solutions up to a concentration of 1.2 × 10-4 m of the metal ion. In order to have a deeper insight into the interaction between the COF and the zinc cation, a thorough spectroscopical, microscopical, and theoretical study is also presented and discussed in this communication.

Tri-armed Schiff base fluorescent sensor for the rapid recognition of Zn(II): application in live cell imaging, test strips and TLC

Various metal ions exist in nature and human beings and play limitless vital roles in both the atmosphere and biology. A fundamental and useful aspect is the qualitative and quantitative assessment of Zn(II) at concentration levels as low as parts per billion (ppb). Thus, the design and development of novel fluorescent turn-on receptors have gained significant interest because of their potential for use in live cell imaging to detect biologically relevant metal ions with high selectivity and sensitivity. The present research illustrates the design and synthesis of a novel fluorescent sensor [(1,3,5-triazine-2,4,6-triyl)tris(hydrazine-2-yl-1-ylidene)tris(methaneylylidene)]tris(2,4-di-tert-butylphenol) (THDBP) for the selective and sensitive probing of Zn(II). The sensor exhibited a fluorescence turn-on mechanism upon treatment with Zn(II) ions at λemi. 503 nm in aq. acetonitrile. The formation of a 1 : 3 complex between THDBP and Zn(II) is confirmed from the Job plot and ESI-MS spectrum. The evaluated limit of detection (LOD) and association constant (Ka) of the sensor THDBP for Zn(II) were found to be 1.03 × 10-10 M and 2.33 × 108 M-1, respectively. Further research demonstrates the practical application of the sensor for the detection of Zn(II) ions in live cells. The sensing ability of the sensor THDBP was also explored through inexpensive test strips and TLC sheets.

Recent developments in the synthesis and applications of terpyridine-based metal complexes: a systematic review

Terpyridine-based metal complexes have emerged as versatile and indispensable building blocks in the realm of modern chemistry, offering a plethora of applications spanning from materials science to catalysis and beyond. This comprehensive review article delves into the multifaceted world of terpyridine complexes, presenting an overview of their synthesis, structural diversity, and coordination chemistry principles. Focusing on their diverse functionalities, we explore their pivotal roles in catalysis, supramolecular chemistry, luminescent materials, and nanoscience. Furthermore, we highlight the burgeoning applications of terpyridine complexes in sustainable energy technologies, biomimetic systems, and medicinal chemistry, underscoring their remarkable adaptability to address pressing challenges in these fields. By elucidating the pivotal role of terpyridine complexes as versatile building blocks, this review provides valuable insights into their current state-of-the-art applications and future potential, thus inspiring continued innovation and exploration in this exciting area of research.

Recent Advances in Fluorescent Probes for Zinc Ions Based on Various Response Mechanisms

Zinc is a vital metal element with extensive applications in various fields such as industry, metallurgy, agriculture, food, and healthcare. For living organisms, zinc ions are indispensable, and their deficiency can lead to physiological and metabolic abnormalities that cause multiple diseases. Hence, there is a significant need for selective recognition and effective detection of free zinc ions. As a probe method with high sensitivity, high selectivity, real-time monitoring, safety, harmlessness and ease of operation, fluorescent probes have been widely used in metal ion identification studies, and many convenient, low-cost and easy-to-operate fluorescent probes for Zn²⁺ detection have been developed. This article reviews the latest research advances in fluorescent chemosensors for Zn²⁺ detection from 2019 to 2023. In particular, sensors working through photo-induced electron transfer (PET), excited state intramolecular proton transfer (ESIPT), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), chelation-enhanced fluorescence (CHEF), and aggregation-induced emission (AIE) mechanisms are described. We discuss the use of various recognition mechanisms in detecting zinc ions through specific cases, some of which have been validated through theoretical calculations.

X-ray structure of two Schiff bases: TURN-ON sensing of Fe3+ and Al3+ in the HepG2 cell line

The efficiency of the fluorescence sensitivity of a sensor may be tuned by the modulation of the steric and electronic parameters in the structure. In this study, the thiophenyl Schiff base (E)-N¹-(phenyl(pyridin-2-yl)methyl)-N²-(thiophen-2-ylmethylene)benzene-1,2-diamine (HL') exhibited very high selectivity and a sensitive fluorescence enhancement towards Fe³⁺ with violet emission (λ_em, 385 nm; LOD, 3.8 nM). On the other hand, the naphthyl Schiff base (E)-1-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)imino)methyl)naphthalen-2-ol (H₂L'') exhibited fluorescence sensitivity towards Al³⁺, showing blue emission (λ_em, 502 nm; LOD, 3.3 nM) in H₂O (HEPES buffer, pH 7.4) medium. The emission enhancement of HL' upon binding to Fe³⁺ may be considered to be due to the restriction of intramolecular rotation, while the selectivity of H₂L'' towards Al³⁺ may be due to the turn on emission through the restriction of excited state intramolecular proton transfer (ESIPT) and the introduction of chelation enhanced fluorescence (CHEF). Furthermore, DFT computation supported the sensing strategy and the probes were applied for intracellular detection of Fe³⁺ and Al³⁺ in HepG2 cell lines.

Developing a new chemosensor targeting zinc ion based on two types of quinoline platform

A chemosensor DQ (2-(2-(quinolin-2-yl)hydrazinyl)-N-(quinolin-8-yl)acetamide), based on two quinoline moieties, has been synthesized. DQ could detect zinc ion through fluorescence turn-on in aqueous media. Limit of detection was calculated as 0.07 μM, far lower than the standard of WHO for zinc ion. The practicality of DQ was demonstrated via the successful results of reusability with EDTA, easy detection on the test strip, and precise quantification in real water samples. Additionally, sensor DQ could be applied to bioimaging of zinc ion in zebrafish. Sensing process of zinc ion by DQ was studied through fluorescence and UV-Vis spectroscopy, ¹H NMR titration, and ESI-mass spectrometry.

A Novel Donor-Acceptor Fluorescent Sensor for Zn2+ with High Selectivity and its Application in Test Paper

A novel donor-acceptor fluorescent sensor was designed and synthesized. The sensor exhibited high selectivity and sensitivity to Zn²⁺ in acetonitrile solution. When 3.0 equiv. of Zn²⁺ was added gradually, the emission intensity at 500 nm increased 54-fold, accompanied by the fluorescent color of the solution changed from dark to green. Job's plot and ESI-MS were carried out to verify a 1:1 stoichiometric complex was formed between the sensor and Zn²⁺. The limit of detection (LOD) to Zn²⁺ was measured to be 2.81 × 10^-9 mol L^-1. Moreover, the sensor not only could be used to detect Zn²⁺ in practical water samples with high accuracy, but also could be made into test paper for the qualitative detection for Zn²⁺.

Chromogenic and fluorogenic “off–on–off” chemosensor for selective and sensitive detection of aluminum (Al3+) and bifluoride (HF2−) ions in solution and in living Hep G2 cells: synthesis, experimental and theoretical studies

A simple pyridine-dicarbohydrazide based colorimetric and fluorometric chemosensor L was designed and synthesized for Al³⁺ ion sensing in organo aqueous solution.

A selective “turn-on” sensor for recognizing In3+ and Zn2+ in respective systems based on imidazo[2,1-b]thiazole

An imidazo[2,1-b]thiazole-based compound (X) was designed and synthesized as an “off–on–off” sensor for the multiple recognition of In³⁺ and Zn²⁺ in different systems.

Chemosensing properties and logic gate behaviors of graphene quantum dot-appended terpyridine

Graphene quantum dot-covalently appended terpyridine, GQDs-tpy, was synthesized and characterized by X-ray photoelectron spectroscopy, FTIR spectroscopy and transmission electron microscopy. GQDs-tpy was found to act as multifunctional chemosensors: a highly selective colorimetric chemosensor for Fe²⁺ as evidenced by an obvious color change from colorless to pink, and a typical fluorescence enhanced probe for Zn²⁺ over 13 metal cations even in practical water samples. Moreover, two-input XOR, INHIBIT and IMPICATION logic gates as well as four-input OR and NOR logic gates were constructed according to the characteristic responses of GQDs-tpy to a sequence of cations.

An ESIPT based chromogenic and fluorescent ratiometric probe for Zn2+ with imaging in live cells and tissues

A benzothiazole based fluorescent probe for selective and efficient detection of Zn²⁺ showing potential application in human breast cancer cells.

A colorimetric and “off–on” fluorescent Pd2+ chemosensor based on a rhodamine-ampyrone conjugate: synthesis, experimental and theoretical studies along with in vitro applications

We successfully designed and developed a rhodamine based “turn-on” chemosensor L for the detection of Pd²⁺ ions down to 1.19 × 10⁻⁵ M (11.9 μM).

A dual functional fluorescent sensor for the detection of Al3+ and Zn2+ in different solvents

A new fluorescent sensor, X, was designed and synthesized based on imidazo[2,1-b]thiazole and 2-hydroxy-1-naphthaldehyde, which could be used to detect Al³⁺ in methanol buffer solution and detect Zn²⁺ in ethanol buffer solution, respectively.