Département de chimie moléculaire

A new cyclodecapeptide incorporating two prolylglycine sequences as $\beta$-turn inducers and bearing four side chains with acidic carboxyl groups for cation complexation was prepd. Structural anal. in water by 1H NMR spectroscopy and CD shows that this template adopts a conformation suitable for the complexation of lanthanide ions Ln3+, with its carboxyl groups oriented on the same face of the peptide scaffold. Luminescence titrns. show that mononuclear Ln-PA complexes are formed with apparent stability consts. of log $\beta$110≈6.5 (pH 7). The high-field water relaxivity values arising from the Gd-PA complex at 200-500 MHz were interpreted with mol. parameters detd. independently. The exptl. detd. water relaxivities are undoubtedly 30{%} higher than the expected values for this complex with two inner-sphere (IS) water mols. and a medium-range rotational correlation time ($\tau$R = 386 ps (±10 {%})). The existence of a large second-sphere (2S) contribution to the relaxivity caused by the interaction of water mols. with the hydrophilic peptide ligand by hydrogen-bonding is proposed. [on SciFinder(R)]