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Titolo:
CONFORMATIONAL AND COORDINATION EQUILIBRIA ON DOTA COMPLEXES OF LANTHANIDE METAL-IONS IN AQUEOUS-SOLUTION STUDIED BY H-1-NMR SPECTROSCOPY
Autore:
AIME S; BOTTA M; FASANO M; MARQUES MPM; GERALDES CFGC; PUBANZ D; MERBACH AE;
Indirizzi:
UNIV TURIN,DIPARTIMENTO CHIM INORGAN CHIM FIS & CHIM MAT,VIA P GIURIA7 I-10127 TURIN ITALY UNIV LAUSANNE,INST CHIM MINERALE & ANALYT,BCH CH-1015 LAUSANNE SWITZERLAND UNIV COIMBRA,FAC CIENCIAS BIOL,DEPT BIOQUIM P-3000 COIMBRA PORTUGAL
Titolo Testata:
Inorganic chemistry
fascicolo: 10, volume: 36, anno: 1997,
pagine: 2059 - 2068
SICI:
0020-1669(1997)36:10<2059:CACEOD>2.0.ZU;2-L
Fonte:
ISI
Lingua:
ENG
Soggetto:
NUCLEAR MAGNETIC-RESONANCE; WATER-EXCHANGE; MACROCYCLIC LIGAND; CRYSTAL-STRUCTURE; DYNAMICS; LANTHANUM(III); EUROPIUM(III); TETRAAZA; BEHAVIOR; CHELATE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
39
Recensione:
Indirizzi per estratti:
Citazione:
S. Aime et al., "CONFORMATIONAL AND COORDINATION EQUILIBRIA ON DOTA COMPLEXES OF LANTHANIDE METAL-IONS IN AQUEOUS-SOLUTION STUDIED BY H-1-NMR SPECTROSCOPY", Inorganic chemistry, 36(10), 1997, pp. 2059-2068

Abstract

A variable-temperature, -pressure, and -ionic strength H-1 NMR study of the DOTA complexes of different trivalent cations (Sc, Y, La, Ce --> Lu) (DOTA = aza-1,4,7,10-tetrakis(carboxymethyl)cyclododecane) yielded data that are in contradiction with the hitherto used model of onlytwo enantiomeric pairs of diastereoisomers that differ in the ligand conformations. A two-isomer equilibrium cannot explain the newly observed apparent reversal of the isomer ratio at the end of the series. Asboth conformers may lose their inner sphere water molecule, a coordination equilibrium may be superimposed on this conformational equilibrium, as shown by large positive reaction volumes for the isomerization of [Ln(DOTA)(H2O)(x)](-) (Ln = Yb, Lu; x = 1, 0). The isomerization of[Nd(DOTA)(H2O)](-) and [Eu(DOTA)(H2O)](-) is purely conformational, as shown by near-zero reaction volumes. The measured isomerization enthalpies and entropies agree with this model. The shift of the isomerization equilibria by a variety of non-coordinative salts depends on the ligand conformation rather than the presence or absence of the inner sphere water molecule. This results from weak ion binding and water solvent stabilization of one ligand conformation, rather than the decrease of the activity of the bulk water in the solution, as shown by UV-vis measurements of the coordination number sensitive transition F-5(0) --> D-7(0) of Eu(III) as a function of ionic strength. Fluoride ions replace a water molecule in the inner coordination sphere, preferentially for one of the conformational isomers, as proven by F-19-NMR shiftsand the appearance of a third set of resonances corresponding to [Eu(DOTA)F](2-) in the H-1-NMR spectrum of [Eu(DOTA)(H2O)](-).

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Documento generato il 12/07/20 alle ore 02:02:03