Determination of L‐Cystine by a New Sensitive Cucurbit[7]uril/palmatine Probe

In the presence of cucurbit7]uril (CB7]), the CB7] could react with palmatine, which served as a sensitive fluorescence probe, to form host‐guest stable complexes and the fluorescence intensity of the complexes was greatly enhanced. The fluorescence intensity decreased linearly with an increasing number of L‐cystine in the inclusion system. The experimental results show that there exists a competition between L‐cystine and palmatine for the CB7] hydrophobic cavity and L‐cystine occupies the space of CB7] cavity, leading palmatine molecules to be forced to reside in the aqueous environment. Based on the fluorescence quenching of the CB7]/palmatine complexes resulting from complex formation between CB7] and L‐cystine, a spectrofluorimetric method for the determination of L‐cystine in aqueous solution in the presence of CB7] was developed. The linear relationship between the corresponding values of the fluorescence quenching ΔF and L‐cystine concentration was obtained in the range of 6.0 to 1.5×10³ ng·mL^?1, with a correlation coefficient (r) of 0.9996. The detection limit was 2.0 ng·mL^?1. The application of the present method to the determination of L‐cystine in tablets gave satisfactory results. This paper also discussed the mechanism of the fluorescence indicator probe.