Host–guest complexes of cucurbituril with 4-amino-4′-nitroazobenzene and 4,4′-diaminoazobenzene in acidic aqueous solutions

(Note: The full text of this document is currently only available in the PDF Version )

Roland Neugebauer and Wilhelm Knoche


Abstract

The thermodynamics and kinetics of the reaction of cucurbituril (Cuc) with 4-amino-4′-nitroazobenzene (DO3) and 4,4′-diaminoazobenzene (Diam) have been studied in aqueous HCl, and it is shown that DO3 is well suited as an indicator for uncomplexed Cuc (actual concentration of Cuc) and Diam is well suited as an indicator for the total concentration of Cuc (sequestering agent) in aqueous solutions. The formation of 1∶1 guest–host complexes is observed. For proton concentrations up to 1 mol dm–3, DO3 reacts according to eqn. (a), with the values for the dissociation constant of DO3H+ log(Ka/dm3 mol–1) = –2.42, DO3H22+ log(Kb/dm3 mol–1) = 0.53, for the stability constant of CucDO3H+ log (Kc/mol dm3) = 8.05 and for the rate constant of complex formation log (kf[hair space][hair space]/dm3 mol–1 s–1) = 5.25. Reaction enthalpies and activation energies have also been determined. The complexation of Cuc with Diam has been studied in 0.1–1 mol dm–3 HCl where a very strong complexation has been observed.


References

  1. L. Mock, ‘Cucurbituril’Top. Curr. Chem., Springer-Verlag, Berlin, Heidelberg, 1995, vol. 175 Search PubMed.
  2. R. Hoffmann, W. Knoche, C. Fenn and H.-J. Buschmann, J. Chem. Soc., Faraday Trans., 1994, 90, 1507 RSC.
  3. P. Cintas, J. Incl. Phen. Mol. Recog. Chem., 1994, 17, 205 Search PubMed.
  4. CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, 59th edn., 1978–79 Search PubMed.
  5. A. Robinson and R. H. Stokes, Electrolyte Solutions, Butterworth, London, 2nd edn., 1970 Search PubMed.
  6. W. Davies, Ion Association, Butterworth, London, 1962 Search PubMed.
  7. W. Bunting and S. Dimitrios, J. Am. Chem. Soc., 1990, 112, 779 CrossRef CAS.
Click here to see how this site uses Cookies. View our privacy policy here.