A novel small molecule fluorescent sensor for Zn2+ based on pyridine–pyridone scaffold

Synthesis and Chemosensory Properties of New Cyanosubstituted 2,2'-Bipyridine Derivatives

A series of novel 6-oxo-1,6-dihydro-[2,2'-bipyridine]-5-carbonitriles has been synthesized and characterized. Their photophysical properties in DMSO solution and aqueous medium as well as fluorescence response to the presence of metal ions have been investigated. The obtained 4-(4-methoxyphenyl)-6-oxo-1,6-dihydro-[2,2'-bipyridine]-5-carbonitrile has been shown as a selective fluorescent "turn-ON" probe for Cd²⁺ ions with LoD 0.359 µM, 1:1 metal-ligand ratio and binding constant of 5.2 × 10⁴ M^-1.

Coumarin-based colorimetric-fluorescent sensors for the sequential detection of Zn2+ ion and phosphate anions and applications in cell imaging

Two novel coumarin based fluorescent sensors CHP and CHS have been synthesized for the sequential detection of Zn²⁺ ion and phosphate anion (PA) in DMF/HEPES buffer medium (1/5 v/v, 10 mM, pH = 7.4). On the addition of Zn²⁺ ion to the solution of CHP or CHS resulted in a pronounced fluorescence enhancement, accompanying noticeable color change (under UV or daylight), while there was hardly obvious change with other competing metal ions co-existing. The detection limits (DL) of CHP and CHS toward Zn²⁺ were separately determined as 1.03 × 10^-7 (R² = 0.9886) and 1.87 × 10^-7 (R² = 0.9902). The PET binding processes were affirmed by spectroscopic techniques, HRMS experiments and theoretical calculations. Subsequently, the CHP-Zn²⁺ or CHS-Zn²⁺ complexes showed high selectivity fluorescence quenching toward PA by snatching Zn²⁺ ion from its complex and the binding processes were reversible. DLs were calculated as 2.07 × 10^-7 M (R² = 0.9928) and 2.63 × 10^-7 M (R² = 0.9954), respectively. Furthermore, the cell imaging experiments demonstrated that the sensors were capable of detecting of Zn²⁺ and PA in vitro cells.

Synthesis of a Novel Pyrazine⁻Pyridone Biheteroaryl-Based Fluorescence Sensor and Detection of Endogenous Labile Zinc Ions in Lung Cancer Cells

A small extent of endogenous labile zinc is involved in many vital physiological roles in living systems. However, its detailed functions have not been fully elucidated. In this study, we developed a novel biheteroaryl-based low molecular weight fluorescent sensor, 3-(phenylsulfonyl)-pyrazine–pyridone (5b), and applied it for the detection of endogenous labile zinc ions from lung cancer cells during apoptosis. The electron-withdrawing property of the sulfonyl group between the phenyl ring as an electron donor and the pyridone ring as a fluorophore inhibited the intramolecular charge transfer state, and the background fluorescence of the sensor was decreased in aqueous media. From the structure–fluorescence relationship analysis of the substituent effects with/without Zn²⁺, compound 5b acting as a sensor possessed favorable properties, including a longer emission wavelength, a large Stokes shift (over 100 nm), a large fluorescence enhancement in response to Zn²⁺ under physical conditions, and good cell membrane permeability in living cells. Fluorescence imaging studies of human lung adenocarcinoma cells (A549) undergoing apoptosis revealed that compound 5b could detect endogenous labile zinc ions. These experiments suggested that the low molecular weight compound 5b is a potential fluorescence sensor for Zn²⁺ toward understanding its functions in living systems.

Base-Promoted Selective Synthesis of 2H-Pyranones and Tetrahydronaphthalenes via Domino Reactions

A highly efficient domino protocol has been developed for the synthesis of 6-aryl-4-(methylthio/amine-1-yl)-2-oxo-2H-pyran-3-carbonitriles and 4-aryl-2-(amine-1-yl)-5,6,7,8-tetrahydronaphthalene-1-carbonitriles from simple and readily available α-aroylketene dithioacetals, malononitrile, secondary amines, and cyclohexanone. This elegant domino process involved consecutive addition-elimination, intramolecular cyclization, and ring opening and closing sequences. Notably, in situ generated 2-imino-4-(methylthio/amine-1-yl)-6-aryl-2H-pyran-3-carbonitrile plays multiple roles in the construction of various novel polyaromatic hydrocarbons.

[Development of Zn(2+) selective fluorescent probes for biological applications]

Zn(2+) is an essential element for life and is known to play important roles in biological processes including gene expression, apoptosis, enzyme regulation, immune system and neurotransmission. To investigate physiological roles of free or chelatable Zn(2+) in living cells, Zn(2+)-selective fluorescent probes are valuable tools. A variety of fluorescent probes based on quinoline, BF2 chelated dipyrromethene, fluorescein, etc. has been developed recently. In principle, such tools can provide useful information about zinc biology. However, most of the fluorescent probes presented so far possess a fluorescent core and a separate part for binding to Zn(2+) within the molecule, so that the molecular weight is usually large and the molecules are hydrophobic. As a result, the applications of such molecules in biological systems often face difficulties. Therefore, we need to develop a new class of fluorescent probes for Zn(2+) with improved molecular characteristics. If the initial core structure is small enough, the fluorescent probes may still be molecular weight below 500 with desirable physico-chemical properties, even after the modifications. In this review, we described novel low-molecular-weight fluorescent probes for Zn(2+) based on pyridine-pyridone. Small modification of pyridine-pyridone core structure brought about a marked improvement such as aqueous solubility, affinity toward Zn(2+), and fluorescence ON/OFF switching. Fluorescence images of Zn(2+) in cells showed that the pyridine-pyridone probe can be used in biological applications.

Spectrofluorimetric determination of phenylalanine based on fluorescence enhancement of europium ion immobilized with sol-gel method

The analysis of phenylalanine (Phe) in serum is widely performed for the screening of newborn phenylketonuria (PKU). In this work, a novel spectrofluorimetric method for the determination of Phe was developed based on the fluorescence enhancement of Ruhemann's purple, the reaction product between Phe and ninhydrin, upon coordination with Eu(3+). A filter paper disc containing immobilized reactants (ninhydrin and Eu(3+)) was fabricated by sol-gel method. The experimental parameters affecting the determination of Phe, such as the concentrations of immobilized reagents, the pH value, the reaction time and temperature were optimized. Under optimum conditions, the fluorescence intensity of Phe-ninhydrin-Eu(3+) system was linearly proportional to the concentration of Phe in the range from 5×10(-5) to 2×10(-3) mol L(-1), and the limit of detection was found to be 5.2×10(-6) mol L(-1). The relative standard deviation was 2.6% for ten replicate measurements of 1.5×10(-4) mol L(-1) of Phe. The method has merits of sensitivity, simplicity and low cost, and has been applied to the determination of Phe in artificial serum.