The formation of highly stable inclusion complexes in aqueous solution between the organometallic cobaltocenium cation (Cob +) and the hosts cucurbituril (CB7) and cucurbituril (CB8) was used to develop a simple method, based on UV-vis titrations, to assay the purity of samples of these two hosts. The equilibrium association constant (K) of the Cob +@CB7 complex had been previously reported by our group as 5.7 × 10 9 M -1 at 25 °C in 50 mM sodium acetate medium. In this work, we determine a K value of 1.9 × 10 8 M -1 at 25 °C in the same medium for the Cob +@ CB8 complex. The high stability of these complexes and their decreased molar absorptivity coefficients (at 261 nm), compared to that for free Cob +, lead to straightforward titration plots when graphing absorbance versus concentration of added CB7 (or CB8) host, at constant Cob + concentration (Figure presented).
ASJC Scopus subject areas
- Organic Chemistry