Tuned Cd2+ Selectivity: Showcase of Electronic and Regio-Effect of π-Extended Di-2-Picolylamine-Substituted Quinoline-Based Tolans

π-Extended di-2-picolylamine (DPA)-substituted 8-hydroxyquinoline (8-HQ) tolans (2) were synthesized for testing electronic and regio-effects. The electron-poor CN-tolan (2b) showed clear selectivity for Cd2+ (>>Zn2+) over other metal ions via turn-on fluorescence, while the electron-rich MeO-tolan (2a) displayed no clear metal selectivity. Furthermore, considering that there was no significant energy difference between the Cd2+ complexes of 1 and 2b, the intended regio-effect (7- vs. 5-substituted effect) did not induce steric hindrance. Thus, the regio-effect is mainly electronic. Considering the above, 2a and 2b constitute a complete showcase in which electronic and regio-effects modulate the metal selectivity. The fluorescence titration of 2b (10 mM) with Cd2+ showed that the limit of detection (LOD) of the Cd2+-selective 2b was 158 nM in PBS (phosphate-buffered saline) (10 mM, pH 7.2) containing 50% MeOH.

A 4-(1H-Benzo[d]oxazole-2-yl)-2-methoxyphenol as Dual Selective Sensor for Cyanide Ion Detection

A dual sensor based on benzoxazole containing moiety S3 was successfully synthesized and applied for detection of CN− ion. The S3 molecule changed its colour for dark brown to dark green on addition of the CN− ion only in DMSO solvent. The limit of detection (LOD) and association constant (Kass) values was 0.4 × 10−6 M and 1.0 × 107 M−1; and 0.46 × 10−4 M and 1.0 × 105 M−1 determined by UV-visible spectroscopic titration and fluorescence titration, respectively.

Fluorescence chemosensor containing 4-methyl-7-coumarinyloxy, acetylhydrazono and N-phenylaza-15-crown-5 moieties for K+ and Ba2+ ions

A new aza-15-crown-5 derivative 1 bearing coumarin and hydrazone moieties was synthesized and characterized. The fluorescent sensing behavior and selectivity of 1 toward different metal ions in ethanol were investigated. There are 4-fold and 2-fold fluorescence enhancements of 1 at λem=406 nm upon addition of five equivalents of K+ and Ba2+, respectively. The fluorescence titration revealed the stoichiometry of 1:1 for 1-K+1-Ba2+ complexes and the binding constants (lgKs) of 4.11 for 1-K+ and 3.61 for 1-Ba2+. Compound 1 can be used as a fluorescent chemosensor for K+ and Ba2+ through discriminable photoresponse signals. The calculated detection limits for K+ and Ba2+ are 2.28 μm and 5.21 μm, respectively.

Tri- and hexanuclear heterometallic Ni(ii)–M(ii) (M = Ca, Sr and Ba) bis(salamo)-type complexes: synthesis, structure and fluorescence properties

Tri- and hexanuclear Ni(ii)–M(ii) (M = Ca, Sr and Ba) complexes have been synthesized and characterized structurally. Fluorescence titration experiments show that the coordinating capabilities in the central O6 site are in the order of Ca(ii) > Sr(ii) > Ba(ii).

Mechanism, kinetics, and antimicrobial activities of 2-hydroxy-1-naphthaldehyde semicarbazone as a new Jack bean urease inhibitor

A new inhibitor of jack bean urease, 2-hydroxy-1-naphthaldehyde semicarbazone, was synthesized and employed to investigate the inhibitory mechanism of HNDSC on jack bean urease by kinetic and fluorescence titration assay, and its antibacterial activities were also investigated.

Metal-induced dynamic conformational and fluorescence switch of quinone-appended Zn-porphyrin

In this report, we have designed and synthesized a novel switching molecule whose fluorescence can be switched via dynamic conformational change between expanded and shrunk states induced by metal complexation and decomplexation. The switching molecule is composed of three kinds of components, namely, a Zn 2+-porphyrin fluorophore, two quinone quenchers, and their linkers containing a 4,4′-bipyridine moiety. UV-vis and fluorescence titration studies revealed that metal complexation of the bipyridine units with Zn 2+ ions induced the dynamic structural change of the molecular shape and simultaneous enhancement of fluorescence of the Zn 2+-porphyrin fluorophore.