Novel pyrazoline and pyrazole "turn on" fluorescent sensors selective for Zn2+/Cd2+ at λem 480 nm and Fe3+/Fe2+ at λem 465 nm in MeCN

A small series of simple pyrazoline and pyrazole based sensors, all derived from the same chalcone precursors, were synthesised, characterised and screened for their fluorescence "turn on" properties in the presence of multiple metals. Pyrazole 8 displayed an excellent fluorescence profile with approx. 20× fold increase in λem 480 nm with Zn2+ compared to a 2.5× fold increase with Cd2+. Pyrazole 9 displayed a 30× fold increase at λem 465 nm for Fe3+ compared to Fe2+ with a Fe3+ limit of detection of 0.025 μM. The corresponding pyrazolines displayed contrasting properties with important implications for future pyrazoline and pyrazole sensor design.

Selective Sensing of Iron by Pyrrolo[2,3-c]Quinolines

This paper reports development of an iron sensor, 2-(3H-pyrrolo[2,3-c]quinolin-4-yl)aniline (APQ). The fluorophore facilitates micromolar detection of Fe³⁺/Fe²⁺ in the presence of various cations, including well-known interfering cations Co²⁺and Cu²⁺ by the process of fluorescence quenching. Graphical Abstract.

Ultra-fast zinc ion detection in living cells and zebrafish by a light-up fluorescent probe

As the second most abundant transition metal after iron in biological systems, Zn²⁺ takes part in various fundamental life processes such as cellular metabolism and apoptosis, neurotransmission. Thus, the development of analytical methods for fast detection of Zn²⁺ in biology and medicine has been attracting much attention but still remains a huge challenge. In this report, we develop a novel Zn²⁺-specific light-up fluorescent probe based on intramolecular charge transfer combined with chelation enhanced fluorescence induced by structural transformation. Addition of Zn²⁺ in vitro can induce a remarkable color change from colorless to green and a strong fluorescence enhancement with a red shift of 43 nm. Moreover, the probe shows an extremely low detection limit of 13 nM and ultra-fast response time of less than 1 s. The Zn²⁺ sensing mechanism was fully supported by TDDFT calculations as well as HRMS and ¹H NMR titrations. The recognition of Zn²⁺ in living Hela cells as well as the MTT assay demonstrate that the probe can rapidly light-up detect Zn²⁺ in vivo with low cytotoxicity and good cell-permeability. Furthermore, the probe can also be successfully applied to bioimaging Zn²⁺ in living zebrafish.

A highly sensitive fluorescent probe for bioimaging zinc ion in living cells and zebrafish models

A simple OFF–ON fluorescent probe was prepared and successfully applied for bioimaging Zn²⁺ in living systems.

Zinc(II) Ion Sensing in Aqueous Micellar Solution Using Modified Bipyridine-Based "Turn-On" Fluorescent Probes and its Application in Bioimaging

The bipyridine-based constructs 4-(pyridine-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ) and [6-(3H-pyrrolo[2,3-c]quinolin-4-yl)pyridin-2-yl]methanol (PPQ-OH) and their assemblies with surfactants are evaluated as turn-on fluorescent sensors for Zn²⁺ ions in aqueous solution. This study strives to overcome the problem of low water solubility of the hydrophobic PPQ and PPQ-OH by using micelles. Whereas the ligands show selective sensing behavior for Zn²⁺ over important biological cations including Na⁺ , K⁺ , Ca²⁺ , Mg²⁺ in anionic sodium dodecyl sulfate and non-ionic Tween 80 micelles, no Zn²⁺ sensing is observed in cationic cetyltrimethylammonium bromide micelles. Unlike in DMF, Cd²⁺ interference is observed in aqueous conditions, which can be avoided either by performing the study at pH≥9 or by carrying out a time-resolved fluorescence study. Analysis of the Job plot data, the fluorescence lifetimes, and experiments on varying micellar shape and pH, confirms that the coordination volume of the resulting octahedral metal complex and formation of a five-membered chelate ring are critical factors for Cd²⁺ interference. The described sensing systems are capable of detecting Zn²⁺ ions at the micromolar level. Additionally, it is shown that PPQ and PPQ-OH can be used to detect Zn²⁺ in HeLa cells under physiological conditions in bioimaging studies.

Synthesis and anti-cancer activity of 1,4-disubstituted imidazo[4,5-c]quinolines

Synthesis of 4-substituted imidazo[4,5-c]quinolines using a Yb(OTf)₃ catalyzed modified Pictet–Spengler reaction as the key final step.

Indolizines and pyrrolo[1,2-c]pyrimidines decorated with a pyrimidine and a pyridine unit respectively

The three possible structural isomers of 4-(pyridyl)pyrimidine were employed for the synthesis of new pyrrolo[1,2-c]pyrimidines and new indolizines, by 1,3-dipolar cycloaddition reaction of their corresponding N-ylides generated in situ from their corresponding cycloimmonium bromides. In the case of 4-(3-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine the quaternization reactions occur as expected at the pyridine nitrogen atom leading to pyridinium bromides and consequently to new indolizines via the corresponding pyridinium N-ylides. However, in the case of 4-(2-pyridyl)pyrimidine the steric hindrance directs the reaction to the pyrimidinium N-ylides and, subsequently, to the formation of the pyrrolo[1,2-c]pyrimidines. The new pyrrolo[1,2-c]pyrimidines and the new indolizines were structurally characterized through NMR spectroscopy. The X-ray structures of two of the starting materials, 4-(2-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine, are also reported.

Synthesis of 4-substituted oxazolo[4,5-c]quinolines by direct reaction at the C-4 position of oxazoles

Cu(TFA)₂ catalysed synthesis of 4-arylsubstituted oxazolo[4,5-c]quinolines/[1,8] naphthyridines has been described via a modified Pictet–Spengler method, without prefunctionalization of the unreactive 4^th position of oxazoles.

Highly selective fluorescence imaging of zinc distribution in HeLa cells and Arabidopsis using a naphthalene-based fluorescent probe

2-(N,N-Dimethylamino)naphthalene-based probe 1 was found to exhibit a dramatic enhancement in fluorescence upon addition of Zn²⁺, but not with any other metal ions.