Abstract: The interaction of Glycyl-L-leudne with trivalent paramagnetic lanthanide cations, Yb³⁺ and Ho³⁺, was studied by ¹³C NMR The lanthanide-induced shifts are separated into contact and dipolar components. It was found that the carbon atom adjacent to the carboxyl group experiences significant contact interaction and therefore the ytterbium-induced shifts cannot be directly used for the analysis of the peptide conformation at least in this case. In aqueous solution (pH 3.31) the peptide is coordinated to the lanthanide ions via its carboxyl group. The peptidc linkage and the amino group are not involved in the coordination. The peptide conformation is analysed from the values of the geometric factor and the results indicate that in the complex the segments C1-C2-C5-C6, C2-C5-C6-C8 and C2-N-C3-C4 arc in trans form while C2-C5-C6-C7 and C1-C2-N-C3 in gauch form.

Key words: Lanthanide complex, Glycyl-L-leucine, Conformation, Lanthanide-induced shift