Sequential recognition of zinc ion and hydrogen sulfide by a new quinoline derivative with logic gate behavior

Abstract

A Schiff base-type fluorescent chemosensor L has been synthesized and characterized to relay recognition of Zn²⁺ and H₂S. Among various metal ions, only Zn²⁺ induces the fluorescence enhancement of the sensor L and results in an “Off–On” type sensing with excellent selectivity and high sensitivity in aqueous solution. The lowest detection limit for Zn²⁺ is 1 × 10⁻⁷ M. Density functional theory calculation for L and the resultant zinc complex is also performed in this study. The chemosensor also exhibits fluorescence quenching with Cu²⁺ in aqueous solution. Fluorescent changes of L upon the addition of Zn²⁺ and Cu²⁺ is utilized as an INHIBIT logic gate at the molecular level, using Zn²⁺ and Cu²⁺ as chemical inputs and the fluorescence intensity signal as the output. On the other hand, the consequent product of L and Zn²⁺, L–2Zn, is an excellent indicator for H₂S for displacement of Zn²⁺ from the complex L–2Zn. Its H₂S sensing behavior is not interfered with by reduced glutathione (GSH), L-cysteine (L-Cys), and even bovine serum albumin (BSA) indicates that L–2Zn is able to detect H₂S without any distinct interference from these biological thiols. The addition of H₂S leads to the fluorescence quenching of L–2Zn, forming an “On–Off” type sensing system. Therefore, the sensing process for Zn²⁺ and sequential detection of H₂S is a reversible one, and also constitutes an “Off–On–Off” type fluorescence monitoring system. This Zn²⁺ and H₂S sequential recognition via fluorescence relay enhancement and quenching give probe L the potential utility for Zn²⁺ and H₂S detection in aqueous media and biological samples.