The structure and the conformational equilibria in aqueous and methanolic solutions of YbDOTMA (DOTMA = (1R,4R,7R,10R)-alpha,alpha',alpha",alpha""-tetramethyl-1,4,7,10-tetraaza- cyclododecane-1,4,7,10-tetraacetic acid) are investigated and the dynamics studied by means of NMR methods. The presence of two isomeric forms in slow exchange is confirmed and quantitatively characterized by EXSY. The exchange peaks are assigned to the inversion of the conformation of the macrocycle ring. No evidence is obtained of a reorientation of the methyl acetate substituents. The protons switch between positions with the same geometrical factors, i.e. positions that would have the same pseudocontact shifts were it not for the different magnetic susceptibility anisotropies of the two species; steady-state NOE spectra on the major form allow unequivocal assignment of the conformations of the two isomers.
Solution equilibria in YbDOTMA, a chiral analogue of one of the most successful contrast agents for MRI, GdDOTA
DI BARI, LORENZO;SALVADORI, PIERO
2000-01-01
Abstract
The structure and the conformational equilibria in aqueous and methanolic solutions of YbDOTMA (DOTMA = (1R,4R,7R,10R)-alpha,alpha',alpha",alpha""-tetramethyl-1,4,7,10-tetraaza- cyclododecane-1,4,7,10-tetraacetic acid) are investigated and the dynamics studied by means of NMR methods. The presence of two isomeric forms in slow exchange is confirmed and quantitatively characterized by EXSY. The exchange peaks are assigned to the inversion of the conformation of the macrocycle ring. No evidence is obtained of a reorientation of the methyl acetate substituents. The protons switch between positions with the same geometrical factors, i.e. positions that would have the same pseudocontact shifts were it not for the different magnetic susceptibility anisotropies of the two species; steady-state NOE spectra on the major form allow unequivocal assignment of the conformations of the two isomers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
