A new Hg2+ fluorescent sensors based on 1,3-alternate thiacalix[4]arene (L) and the complex of [L+Hg2+] as turn-on sensor for cysteine

A new thiacalix[4]arene derivative in a 1,3-alternate conformation bearing four naphthalene groups through crown-3 chains has been synthesized, which exhibits high selectivity toward Hg2+ by forming a 1:2 complex, among other metal ions ( Na+, K+, Mg2+, Ba2+, Ca2+, Sr2+, Cs+, Mn2+, Fe2+, Cd2+, Co2+, Ni2+, Cu2+, Li+, and Zn2+) with a low detection limit (3.30×10−7 M). The metal ion-binding properties were studied by fluorescence, AFM, and 1H NMR spectroscopy. The in situ prepared [Hg2++L] complex shows well recognition ability for cysteine with a low detection limit (2.23×10−7 M) through fluorescence turning on. The mechanism of fluorescence turning on is the host L releasing from [L+Hg2+] for [Cys+Hg2+] complex formed. Thus the paper reports secondary-sensor design: Hg2+ as a first sensor for [L+Hg2+] form, cysteine as a second sensor for Hg2+ releasing from the [L+Hg2+] complex after cysteine adding in.