Addition of nucleophiles to the 9-cyano-10-methylacridinium cation: utilization in their chemiluminescent assay Original Research Article

The addition products obtained when the 9-cyano-10-methylacridinium cation reacts with nucleophiles exhibit absorption spectra that differ from the parent molecule. The equilibrium constants of this process were determined on the basis of these spectra and then compared with the theoretically predicted values at the PM3, PM3(COSMO), DFT and DFT(PCM) levels of theory. Additionally, experimental acidity constants of nucleophiles were compared with the theoretically derived values in order to discover which of their forms most probably undergoes addition to the cation. The paper also outlines the analytical procedure facilitating the assay of nucleophiles which utilizes their ability to be added to the 9-cyano-10-methylacridinum cation. This involves the conversion, at a suitable pH, of the non-bonded cation to 10-methylacridin-9(10H)-one and the substitution of addition products with OOH− according to the SN2 mechanism; this latter process is accompanied by chemiluminescence. Determination of the intensity of chemiluminescence—proportional to the concentration of nucleophiles—can be applied, after calibration, to their quantitative assay. The optimal conditions for the analytical applications of this procedure and the detection limits are reported. This combined approach provides a framework for extending the method to other nucleophiles.