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Paraquat substituent effect on complexation with a dibenzo-24-crown-8-based cryptand
Jinqiang Zhang1, Feihe Huang, Ning Li
1Department of Chemistry, Zhejiang University, Hangzhou, PR China.
Abstract:
Dibenzo-24-crown-8-based cryptand 4 forms 1:1 inclusion complexes with three paraquat derivatives, P1, P2, and P3, as demonstrated by proton NMR spectroscopy and X-ray analysis. However, it was found that methyl-substituted paraquat derivatives, P2 and P3, can bind cryptand 4 more strongly than non-methyl-substituted paraquat derivative P1. The association constants (Ka) were determined in acetone by using a UV-vis titration method to be 5.0 x 10(3) M(-1) for 4.P1, 1.0 x 10(5) M(-1) for 4.P2, and 1.2 x 10(5) M(-1) for 4.P3, respectively. In the solid state, 4.P2 and 4.P3 have similar T-type inclusion complexation conformations, which are very different from the pseudorotaxane-type complexation conformation of 4.P1. Theoretical calculations were done to explain these experimental results.
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