The synthesis and fluorescence properties of novel chromenone-crown ethers

o-Dihyroxy-3-phenylchromenone derivatives, namely, 6,7-dihydroxy-3-(3′,4′-dimethoxyphenyl)chromenone and 6,7-dimethoxy-3-(3′,4′-dihydroxyphenyl)chromenone, were obtained from 2,4,5-trihydroxybenzaldehyde/3,4-dimethoxyphenylacetic acid and 2-hydroxy-4,5-dimethoxybenzaldehyde/3,4-dihydroxyphenylacetic acid, respectively, in the presence of acetic anhydride and sodium acetate under an inert atmosphere, after treatment with MeOH/HCl(aq). The chromenone-crown ethers were prepared from cyclic condensation of o-dihydroxy-3-phenylchromenones with poly(ethylene glycol) ditosylates in the presence of CH₃CN/alkali metal carbonates. The chromatographically purified novel chromenone-crown ethers were identified by ¹H NMR, MALDI-TOF mass spectrometry and elemental analysis. The fluorescence and UV–vis spectroscopic properties of the obtained chromenone-crown ethers and their complexes with Li⁺, Na⁺ and K⁺ perchlorate salts were estimated in acetonitrile. The quantum yields of novel chromenone-crown ethers were determined by the comparative method.

     

A Schiff base fluorescence probe for highly selective turn-on recognition of Zn2+

A simple Schiff base CTS, synthesized between 2-hydroxy-1-naphthaldehyde and 2-benzylthio-ethanamine, was found to be a good turn-on fluorescence probe for the detection of Zn²⁺, due to the restriction of the rotation of the bond between CN and naphthalene ring and/or the blocking of the photo-induced electron transfer (PET) mechanism of the nitrogen atom to naphthalene ring. Excellent selectivity for Zn²⁺ was evidenced, over many other competing ions, including Fe³⁺, Cr³⁺, Ni²⁺, Co²⁺, Fe²⁺,Mn²⁺, Ca²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Mg²⁺, Ba²⁺, Cd²⁺, Ag⁺, Li⁺, K⁺, and Na⁺, in EtOH/HEPES buffer (95:5, v/v, pH = 7.4). It was noteworthy that Cd²⁺ had no interference with Zn²⁺. The stoichiometric complex of CTS-Zn²⁺ was determined to be 2:1 for CTS and Zn²⁺ in molar, based on the Job plot and single crystal X-ray diffraction data. The binding constant of the complex was 85.7 M^?2 with a detection limit of 5.03 × 10^?7 M. The fluorescence bio-imaging capability of CTS to detect Zn²⁺ in live cells was also studied. These results indicated that CTS could serve as a favorable probe for Zn²⁺.     

Simple imine linked colorimetric and fluorescent receptor for sensing Zn ions in aqueous medium based on inhibition of ESIPT mechanism

Herein, we report the highly selective binding of Zn²⁺ ion by the salicylaldimine based Schiff base chromogenic receptor 1 [(N,N′-bis (salicylidine)-o-phenylenediamine]. Receptor 1 senses Zn²⁺ ion in aqueous medium by colorimetric and fluorescent response in the presence of other metal ions like Pb²⁺, Hg²⁺, Sn²⁺, Cd²⁺. Receptor 1 on binding with Zn²⁺ ion exhibits fluorescence enhancement which is due to the inhibition of the (ESIPT) mechanism.     

Salicylaldehyde hydrazones as fluorescent probes for zinc ion in aqueous solution of physiological pH

Salicylaldehyde hydrazones of 1 and 2 were synthesized and their potential as fluorescent probes for zinc ion was investigated in this paper. Both of the probes were found to show fluorescence change upon binding with Zn²⁺ in aqueous solutions, with good selectivity to Zn²⁺ over other metal ions such as alkali/alkali earth metal ions and heavy metal ions of Pb²⁺, Cd²⁺ and Hg²⁺. They showed 1:2 metal-to-ligand ratio when their Zn²⁺ complex was formed. By introducing pyrene as fluorophore, 2 showed interesting ratiometric response to Zn²⁺. Under optimal condition, 2 exhibited a linear range of 0-5.0 μM and detection limit of 0.08 μM Zn²⁺ in aqueous buffer, respectively. The detection of Zn²⁺ in drinking water samples using 2 as fluorescent probe was successful.     

Synthesis of aza-crown ether-modified silver nanoparticles as colorimetric sensors for Ba2+

In this paper, we have demonstrated a facile strategy of preparing aza-crown ether (ACE)-modified silver nanoparticles (Ag NPs) by an efficient nano-conjugate technology named dithiocarbamate. This is the first report of using ACE to modify Ag NPs. ACE-modified Ag NPs have a good recognition of Ba²⁺, with the detection limit of 10^? 8 mol/l. It is reasonable to believe that Ba²⁺ induced the self-assembly of Ag NPs by the formation of the sandwich structure with ACE.

     

Thiazole sulfonamide based ratiometric fluorescent chemosensor with a large spectral shift for zinc sensing

A new thiazole sulfonamide (TTP, 1) based Zn²⁺ selective intrinsic chemosensor has been synthesized and investigated. The chemosensor shows a selective fluorescence enhancement (3.0 fold) with Zn²⁺ over biologically relevant cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) and biologically non-relevant cations (Cd²⁺) in an aqueous ethanol system. It produces an increase in the quantum yield and a longer emission wavelength shift (64 nm) on Zn²⁺ binding with the potential of a ratiometric assay.