A thiazolo[4,5-b]pyridine-based fluorescent probe for detection of zinc ions and application for in vitro and in vivo bioimaging

A GFP Inspired 8-Methoxyquinoline-Derived Fluorescent Molecular Sensor for the Detection of Zn2+ by Two-Photon Microscopy

An effective, GFP-inspired fluorescent Zn2+ sensor is developed for two-photon microscopy and related biological application that features an 8-methoxyquinoline moiety. Excellent photophysical characteristics including a 37-fold fluorescence enhancement with excitation and emission maxima at 440 nm and 505 nm, respectively, as well as a high two-photon cross-section of 73 GM at 880 nm are reported. Based on the experimental data, the relationship between the structure and properties was elucidated and explained backed up by DFT calculations, particularly the observed PeT phenomenon for the turn-on process. Biological validation and detailed experimental and theoretical characterization of the free and the zinc-bound compounds are presented.

Recent Advances in N-Heterocyclic Small Molecules for Synthesis and Application in Direct Fluorescence Cell Imaging

Nitrogen-containing heterocycles are ubiquitous in natural products and drugs. Various organic small molecules with nitrogen-containing heterocycles, such as nitrogen-containing boron compounds, cyanine, pyridine derivatives, indole derivatives, quinoline derivatives, maleimide derivatives, etc., have unique biological features, which could be applied in various biological fields, including biological imaging. Fluorescence cell imaging is a significant and effective imaging modality in biological imaging. This review focuses on the synthesis and applications in direct fluorescence cell imaging of N-heterocyclic organic small molecules in the last five years, to provide useful information and enlightenment for researchers in this field.

A Schiff-based AIE fluorescent probe for Zn2+ detection and its application as "fluorescence paper-based indicator"

A Schiff-based aggregation induced emission (AIE) fluorescent probe with excited intramolecular proton transfer (ESIPT) mechanism was synthesized by grafting 2-hydrazinobenzothiazole onto 2,6-diformyl-4-methylphenol. The probe recognizes Zn²⁺ selectively and sensitively, accompanied by a significant fluorescence emission increasement change from light yellow-green to strong green. Additionally, a stabilization time of at least 30 min was kept in the recognition process. Besides, a linear relationship was observed between the concentration of Zn²⁺ and the fluorescence intensity at 525 nm (0.05-10 µM). And thus, the probe can detect Zn²⁺ quantitatively in aqueous solution with a low detection limit of 1.9 × 10^-8 M. Based on the AIE property and the selective recognition of Zn²⁺, SCH was strategically loaded on the filter paper to develop a novel paper-based indicator for on-site and high-efficiency detection of Zn²⁺. The results showed that the paper-based indicator could be conveniently applied to the visual inspection of Zn²⁺ as expected and SCH in the paper-based indicators fortunately exhibited a better stability. Furthermore, our comprehensive application evaluations have confirmed that SCH was capable of detecting Zn²⁺ in real water samples and imaging Zn²⁺ in living cells roundly.

Site-Selective Cross-Coupling of Polyhalogenated Arenes and Heteroarenes with Identical Halogen Groups

Methods to functionalize arenes and heteroarenes in a site-selective manner are highly sought after for rapidly constructing value-added molecules of medicinal, agrochemical, and materials interest. One effective approach is the site-selective cross-coupling of polyhalogenated arenes bearing multiple, but identical, halogen groups. Such cross-coupling reactions have proven to be incredibly effective for site-selective functionalization. However, they also present formidable challenges due to the inherent similarities in the reactivities of the halogen substituents. In this Review, we discuss strategies for site-selective cross-couplings of polyhalogenated arenes and heteroarenes bearing identical halogens, beginning first with an overview of the reaction types that are more traditional in nature, such as electronically, sterically, and directing-group-controlled processes. Following these examples is a description of emerging strategies, which includes ligand- and additive/solvent-controlled reactions as well as photochemically initiated processes.

Simple Synthesis of Fused Thiazolo[4,5-b]pyridines through Successive SNAr Processes

A convenient process is described for the synthesis of novel thiazolo[4,5-b]pyridines fused with triazole or pyrimidine rings. The base-promoted reactions of 2-chloro-3-nitropyridines with 1,3-(S,N)-binucleophiles (triazole-5-thiols, 4-oxopyrimidine-2-thiones) resulted in nucleophilic substitution of the chlorine atom and subsequent S–N-type Smiles rearrangement followed by nucleophilic substitution of the nitro group. Reactions with pyrimidine-2-thiones were carried out as one-pot processes while, in the case of triazole-5-thiols, isolation of intermediate substitution products was found to be preferable.

A novel bimacrocyclic polyamine-based fluorescent probe for sensitive detection of Hg2+ and glutathione in human serum

Detection of glutathione in human serum is of great importance for clinical diagnosis of various diseases, such as AIDS, diabetes mellitus, Alzheimer disease and cancer. In this work, a new water-soluble bismacrocyclic polyamine-derived compound, namely L, which contains two molecules of 4-nitro-1,2,3-benzoxa-diazole as the fluorophores, was designed and prepared. The experiments of selectivity of L toward metal ions showed it could rapidly and sensitively detect Hg²⁺ with a detection limit of 27 nM. Furthermore, the cell imaging and co-staining experiments in HeLa cells demonstrated that the L-Hg²⁺ probe had selectivity for the Golgi apparatus to a certain degree. Moreover, it had excellent selectivity for biothiols, especially for glutathione. Finally, the probe was successfully applied to sensitively detect glutathione (GSH) in human serum and fetal bovine serum.

Zn homeostasis in genetic models of Parkinson's disease in Caenorhabditis elegans

While the underlying mechanisms of Parkinson's disease (PD) are still insufficiently studied, a complex interaction between genetic and environmental factors is emphasized. Nevertheless, the role of the essential trace element zinc (Zn) in this regard remains controversial. In this study we altered Zn balance within PD models of the versatile model organism Caenorhabditis elegans (C. elegans) in order to examine whether a genetic predisposition in selected genes with relevance for PD affects Zn homeostasis. Protein-bound and labile Zn species act in various areas, such as enzymatic catalysis, protein stabilization pathways and cell signaling. Therefore, total Zn and labile Zn were quantitatively determined in living nematodes as individual biomarkers of Zn uptake and bioavailability with inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) or a multi-well method using the fluorescent probe ZinPyr-1. Young and middle-aged deletion mutants of catp-6 and pdr-1, which are orthologues of mammalian ATP13A2 (PARK9) and parkin (PARK2), showed altered Zn homeostasis following Zn exposure compared to wildtype worms. Furthermore, age-specific differences in Zn uptake were observed in wildtype worms for total as well as labile Zn species. These data emphasize the importance of differentiation between Zn species as meaningful biomarkers of Zn uptake as well as the need for further studies investigating the role of dysregulated Zn homeostasis in the etiology of PD.