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Cation exchange macrocyclic ligands

With the cylindrical cryptands, each macrocycle may bind one cation so that both mono- and dinuclear cryptates may be formed. Although the 12-membered (N202) macrocycles of ligand 5 are too small to bind two cations within each of the macrocycles, variable temperature 13C-NMR measurements have revealed intramolecular cation exchange between identical sites at the top and bottom of this cryptand, for Ca2+, Sr2+, and Ba2+. Cation jump between the two sites is fast with respect to intermolecular cation exchange, modeling the elementary jump processes of cations between binding sites in membrane channels (91). [Pg.18]

Preliminary kinetic results on cation exchange in cryptates [ligand (21)] show some correlation with thermodynamic parameters, but only go a small way towards the complete elucidation of the mechanism. Metal replacement in complexes of macrocyclic ligands is also illustrated by studies of several metalloporphyrins. ... [Pg.194]

FIGURE 7 Proposed interlayer arrangements of exchangeable cations and associated macrocyclic ligands in complexes with montmorillonite and vermiculite. = radius of the macrocyclic cavity r, = radius of cations Mi = interlayer distance. [Pg.115]

In solvent of low permittivity, where the cation will be very weakly solvated, there is an effective competition between a macrocyclic ligand, C, and the counter anion, A , for the metal, M. From ultrasonics and IR spectra on the Na /18-crown-6 system in propylene carbonate, which show a dependence on the nature as well as the concentration of the anion present, it has been proposed that such a competition process between the anion and the macrocycle is also relevant in solvents with a much higher permittivity it is suggested that this could account for the bimolecular mechanism proposed as a path for metal exchange and complex dissociation, given by Eq. (1). [Pg.187]

Aime, S., Barge, A., Bruce, J.I., et al. (1999) NMR, relaxometric, and structural smdies of the hydration and exchange dynamics of cationic lanthanide complexes of macrocyclic tetraamide ligands. Journal of the American Chemical Society, 121, 5762-5771. [Pg.427]


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See also in sourсe #XX -- [ Pg.391 ]




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Cation exchange

Cation exchangers

Cationic exchangers

Cations cation exchange

Exchangeable cations

Ligand exchange

Ligands cationic

Ligands ligand exchange

Macrocycles Macrocyclic ligands

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