Competitive supramolecular interaction of carbachol and berberine with cucurbit[7]uril and its analytical application

Carbachol (CCH) is non-fluorescent in aqueous solution. This property makes its determination through direct fluorescent method impossible. Berberine (BER) exhibits very weak fluorescence emissions in aqueous solution. However, In acidic medium and room temperature, BER can react with CB[7] to form stable complex and the fluorescence intensity of the complex was greatly enhanced. The dramatic quenching of the fluorescence intensity of CB[7]-BER complex was observed with the addition of CCH. The competitive supramolecular interaction between CCH and BER for occupancy of the cucurbit[7]uril (CB[7]) cavity was studied by spectrofluorometry, 1H NMR, and molecular modeling calculation. Based on the significant quenching of the supramolecular complex fluorescence intensity, a simple, rapid, and sensitive fluorescence probe method for the determination of CCH in pharmaceutical dosage forms and in biological fluids was developed. The linear range of the method was from 0.01 μg mL− 1 to 1.5 μg mL− 1. The limit of detection was 0.003 μg mL− 1. This shows that the proposed method has promising potential for quality control, forensic identification, drug abuse or therapeutic monitoring, pharmacokinetics, and clinical application.