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A quinoline-based simple receptor (bis(2-quinolinylmethyl)benzylamine = 1) as a Zn(2+) selective fluorescent chemosensor showed a large fluorescent enhancement with a blue shift in the presence of Zn(2+) which is attributed to a chelation enhanced fluorescence (CHEF) effect with inhibition of a photoinduced electron transfer (PET) process of 1. In particular, this receptor could clearly distinguish Zn(2+) from Cd(2+). The binding mode of 1 and Zn(2+) was found to be a 1:1 and confirmed by Job plot, (1)H NMR titration and ESI-mass spectrometry analysis., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A new metal ion sensor that contains quinoline and pyridylaminophenol has been synthesized. In acetonitrile and in the presence of Zn(2+), the sensor fluoresces. In contrast, in aqueous solutions the sensor fluoresces in the presence of Cd(2+). The fluorescence of the molecule is selective for Zn(2+) or Cd(2+) and shows no fluorescence with other metal ions. The crystal structure of the Cd(2+) complex shows coordination through the amide and phenol oxygens, as well as the amine nitrogen of the sensor. The sensor also acts as a colorimetric sensor for Co(2+) by changing color from colorless to yellow. The color change is selective for Co(2+) and is not observed with other metal ions. The unique combination of pyridine and phenol groups with quinoline results in the properties of this sensor.

Zinc sensors based on 2,3-dipicolylamine (DPA) and quinoline have been synthesized. They fluoresced in the presence of Zn(2+) and remained fluorescent when other metal ions were present. Fluorescence enhancement of the sensors was not seen for most other metal ions. In vitro studies with fibroblasts showed fluorescence when sensor and Zn(2+) were present. As seen by single crystal X-ray analysis, four nitrogens from the sensor bind to Zn(2+). These new sensors have lower binding constants than the pentadentate sensors based on 2,2-DPA.