Exploring inhibition of chemiluminescence mechanisms with fluorescence quenching studies and interaction energy calculations

Abstract

Carbamates weaken the luminol-H2 O2 chemiluminescence (CL) catalyzed by sodium copper chlorophyll(SCC). The capacity to inhibit the CL of three carbamates is in the order of carbaryl (CBL) >carbofuran (CBF)>metolcarb (MTC). Mechanisms of carbamates inhibiting SCC-luminol-H2 O2 CL are investigated using fluorescencequenching and quantum chemistry simulations for the first time in this work. Carbamate-SCC interactions studiedusing fluorescence spectroscopy show that with the increasing concentration of the SCC, the fluorescence of carbamateis quenched regularly, and the quenching mechanism is a static quenching process. Binding constants (KB) of the threecarbamates with SCC are CBL (4.39 × 10 5) >CBF (1.46 × 10 4) >MTC (2.16 × 10 3 L/mol), which is completelyharmonious with the capacity to inhibit CL of the carbamates. Furthermore, the carbamate-SCC interaction energiesfrom quantum chemistry simulations are CBL-porphyrin copper (PPCu) (–30.1), CBF-PPCu (–21.0), and MTC-PPCu(–19.9 kJ/mol), which is also identical to their inhibiting capacity. This provides further evidence that the formation ofcarbamate-SCC complexes reduces the SCC catalytic activity and the CL intensity decreases. In addition, a novel flowinjection chemiluminescence method for the determination of carbamate was established based on carbamate inhibitingCL of the SCC-luminol-H2 O2 CL system under alkaline conditions. This work may contribute to the study of themechanism of CL inhibition using fluorescence quenching and quantum chemistry calculation methods.