Structural, Luminescence, and NMR Studies of the Reversible Binding of Acetate, Lactate, Citrate, and Selected Amino Acids to Chiral Diaqua Ytterbium, Gadolinium, and Europium Complexes
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- 作者：Rachel S. Dickins ; Silvio Aime ; Andrei S. Batsanov ; Andrew Beeby ; Mauro Botta ; James I. Bruce ; Judith A. K. Howard ; Christine S. Love ; David Parker ; Robert D. Peacock ; and Horst Puschmann
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：October 30, 2002
- 年：2002
- 卷：124
- 期：43
- 页码：12697 - 12705
- 全文大小：261K
- 年卷期：v.124,no.43(October 30, 2002)
- ISSN：1520-5126
文摘
The nature of the ternary complexes formed in aqueous media at ambient pH on reversiblebinding of acetate, lactate, citrate, and selected amino acids and peptides to chiral diaqua europium,gadolinium, or ytterbium cationic complexes has been examined. Crystal structures of the chelated ytterbiumacetate and lactate complexes have been defined in which the carboxylate oxygen occupies an "equatorial"site in the nine-coordinate adduct. The zwitterionic adduct of the citrate anion with [EuL1] was similar to thechelated lactate structure, with a 5-ring chelate involving the apical 3-hydroxy group and the 
-carboxylate.Analysis of Eu and Yb emission CD spectra and lifetimes (H2O and D2O) for each ternary complex, inconjunction with 1H NMR analyses of Eu/Yb systems and 17O NMR and relaxometric studies of the Gdanalogues, suggests that carbonate, oxalate, and malonate each form a chelated (q = 0) square-antiprismatic complex in which the dipolar NMR paramagnetic shift (Yb, Eu) and the emission circularpolarization (gem for Eu) are primarily determined by the polarizability of the axial ligand. The ternarycomplexes with hydrogen phosphate, with fluoride, and with Phe, His, and Ser at pH 6 are suggested tobe monoaqua systems with Eu/Gd with an apical bound water molecule. However, for the ternary complexesof simple amino acids with [YbL1]3+, the enhanced charge demand favors a chelate structure with theamine N in an apical position. Crystal structures of the Gly and Ser adducts confirm this. In peptides andproteins (e.g. albumin) containing Glu or Asp residues, the more basic side chain carboxylate may chelateto the Ln ion, displacing both waters.
-carboxylate.Analysis of Eu and Yb emission CD spectra and lifetimes (H2O and D2O) for each ternary complex, inconjunction with 1H NMR analyses of Eu/Yb systems and 17O NMR and relaxometric studies of the Gdanalogues, suggests that carbonate, oxalate, and malonate each form a chelated (q = 0) square-antiprismatic complex in which the dipolar NMR paramagnetic shift (Yb, Eu) and the emission circularpolarization (gem for Eu) are primarily determined by the polarizability of the axial ligand. The ternarycomplexes with hydrogen phosphate, with fluoride, and with Phe, His, and Ser at pH 6 are suggested tobe monoaqua systems with Eu/Gd with an apical bound water molecule. However, for the ternary complexesof simple amino acids with [YbL1]3+, the enhanced charge demand favors a chelate structure with theamine N in an apical position. Crystal structures of the Gly and Ser adducts confirm this. In peptides andproteins (e.g. albumin) containing Glu or Asp residues, the more basic side chain carboxylate may chelateto the Ln ion, displacing both waters.