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

Carbamates weaken the luminol-H2O2 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-H2O2 CL are investigated using fluorescence quenching and quantum chemistry simulations for the first time in this work. Carbamate-SCC interactions studied using fluorescence spectroscopy show that with the increasing concentration of the SCC, the fluorescence of carbamate is quenched regularly, and the quenching mechanism is a static quenching process. Binding constants (K-B) of the three carbamates with SCC are CBL (4.39 x 10(5)) >CBF (1.46 x 10(4)) >MTC (2.16 x 10(3) L/mol), which is completely harmonious with the capacity to inhibit CL of the carbamates. Furthermore, the carbamate-SCC interaction energies from 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 of carbamate-SCC complexes reduces the SCC catalytic activity and the CL intensity decreases. In addition, a novel flow injection chemiluminescence method for the determination of carbamate was established based on carbamate inhibiting CL of the SCC-luminol-H2O2 CL system under alkaline conditions. This work may contribute to the study of the mechanism of CL inhibition using fluorescence quenching and quantum chemistry calculation methods.