Interactions between cyclodextrins and Tm-III chelates of polyazamacrocycles as studied by NMR in aqueous solution

The interactions between a-, b-, and g-CD and the Tm-III chelates of the ma crocyclic polyaminopolycarboxylates DOTA and NOTA were studied with the use of H-1- and C-13-NMR shift and relaxation rate measurements. Interactions were only observed between Tm(DOTA)(-) and g-CD. The structure and the stab ility of the concerning supramolecular structures was elucidated by fitting of the NMR titration curves to a theoretical model. It appears that an inc lusion compound is formed, where the hydrophobic macrocyclic part of the ch elate sits in the g-CD cavity. This inclusion compound binds a second Tm(DO TA)(-) molecule at the outside lower rim of the CD cone. The binding occurs probably via hydrogen bonds between non-chelated carboxylate oxygen atoms of the concerning Tm(DOTA)(-) and CH2OH groups of the g-CD molecule, which are in a favorable position due to opening of the g-CD cone angle as a resu lt of the inclusion of the first g-CD.