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The effect of the head-group spacer length of 12-s-12 gemini surfactants in the host-guest association with beta-cyclodextrin

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Author

  • R. A. Carvalho
  • H. A. Correia
  • A. J. M. Valente
  • Olle Söderman
  • Markus Nilsson

Summary, in English

NMR spectroscopy has been used to study and characterize the interactions in solution between beta-CD and alkyl-alpha,omega-bis(dodecyldimethyl ammonium bromide) gemini surfactants with the following head-group spacer lengths: 2, 4, 6, 8, and 10. The application of the method of continuous variation gives as a result that 1:1 and 2:1 (beta-cyclodextrin-gemini) complexes are formed; the association stoichiometry is dependent on the spacer chain length, varying from 1.5 (for s = 2) to 1.8 (for s = 10). Assuming a two-step mechanism, the binding constants have been computed. In general, the overall binding constant slightly increases with an increase of the number of methylene groups in the spacer. The H-1 NMR spectra of the N-(CH3)(2) groups in beta-cyclodextrin/gemini mixed solutions are split into two peaks for 12-10-12, suggesting that the gemini spacer can thread the beta-cyclodextrin so that the latter is positioned between the gemini head-groups. Inspection of the ROESY spectra allowed the establishment of several spatial proximities between the protons from the beta-CD and the gemini and for a spacer length of 10, the data indeed indicate that complexes are formed with the CD molecule positioned between the two charged head groups with the spacer passing through the CD molecule. (C) 2010 Elsevier Inc. All rights reserved.

Department/s

Publishing year

2011

Language

English

Pages

725-732

Publication/Series

Journal of Colloid and Interface Science

Volume

354

Issue

2

Document type

Journal article

Publisher

Elsevier

Topic

  • Physical Chemistry

Keywords

  • Binding constants
  • structures
  • Supramolecular
  • H-1 NMR spectroscopy
  • Cyclodextrins
  • Gemini surfactants

Status

Published

ISBN/ISSN/Other

  • ISSN: 1095-7103