Spectral Discrimination of Chiral Macrocyclic Paramagnetic Metal Complexes by NMR Techniques≠

✍ Scribed by Silvio Aime; Mauro Botta; Simonetta Geninatti Crich; Enzo Terreno; Pier Lucio Anelli; Fulvio Uggeri

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 127 KB
• Volume: 5
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/(sici)1521-3765(19990401)5:4<1261::aid-chem1261>3.0.co;2-s

✦ Synopsis

The anionic lanthanide(iii) complexes of the macrocyclic ligand 1,4,7,10-tetraazacyclododecane-N,N',N'',-N'''-tetramethylenephosphonate (DOTP) are present in aqueous solution as a racemic mixture of two enantiomeric forms interconverting slowly on the NMR time scale. The metal chelates form diasteroisomeric complexes with the organic base N-methyl-d(À)-glucamine which, in the case of the Eu III derivative, have distinguishable 1 H, 13 C and 31 P NMR spectra. The bonding interaction responsible for the spectral resolution has been studied as a function of pH, temperature and complex/substrate molar ratio. Qualitative analysis of the Dy(TOTP)-induced shift and line broadening of the 13 C resonance of Nmethyl-d(À)-glucamine has suggested that the ion-pairing interaction involves bridging by the organic base between two uncoordinated oxygen atoms of two adjacent phosphonate groups of the metal complex. This bonding scheme combines electrostatic and hydrogenbonding interactions and results in a marked stereoselectivity. The association equilibria were obtained by analysis of NMR titration data and by considering a 1:2 bonding model for the complex/ substrate adduct.