Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The structure and the conformational equilibria in aqueous and methanolic solutions of YbDOTMA (DOTMA = (1R,4R,7R,10R)-α,α′,α′′,α′′′′-tetramethyl-1,4,7,10-tetraazacyclododecane-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.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99141_s.pdf or from the author.
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