Jean-Claude Bunzli - Thermodynamic and structural study of inclusion complexes between trivalent lanthanide ions and native cyclodextrins

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  Fatin-Rouge,N., Bunzli,J.C.G. Inorganica Chimica Acta  1999 293 (1) 53-60

  Abstract: The interaction of trivalent   lanthanide ions (Ln(3+)) with native cyclodextrins (CDs) is   investigated in acidic and basic aqueous media. At low pH, the   association constants for 1:1 complexes are in the range log K =   2-4 (mu = 0.1 M, NaCl or TMACl), as determined by   pH-potentiometric study of the hydrolysis of the Ln ions in   absence and in presence of CDs. The thermodynamic parameters of   the inclusion reaction show that the complexation of Ln(3+) ions   inside the CD cavity is entropically driven and does not depend   upon the host. H-1 and C-13 NMR spectra point to inclusion of   La3+ cations in the cavity of alpha-CD occurring in the narrowest   part of the host molecule, close to the C-5 carbon atoms.   alpha-CD acts like a crown ether, its anomeric oxygen atoms being   the donor atoms. Complexation of Tb3+ by partially deprotonated   a-CD was investigated at pH 12.33: C-13 NMR measurements show   that complexation occurs at the OH-3 secondary hydroxyl groups of   alpha-CD while UV-Vis spectrophotometric titration leads to an   apparent constant log K-app approximate to 4.2 (1:1 complex).   Lifetime measurements of the Eu(D-5(0)) and Tb(D-5(4)) levels   confirm these findings. (C) 1999 Elsevier Science S.A. All rights   reserved

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