Interaction of V IV O, V V O 2 and Cu II with a Peptide Analogue SalGly‐ L ‐Ala

The formation of complexes of a tripeptide analogue, salicylglycyl‐ L ‐alanine [HOC 6 H 4 C(O)NHCH 2 C(O)NHCH(CH 3 )COOH, H 2 SalGly‐ L ‐Ala], was studied with Cu II , V IV O and V V O 2 in aqueous solution using pH‐potentiometric and spectroscopic (UV/Vis, CD, EPR and 51 V NMR) techniques. The results demonstrated the ambidentate character of the ligand. The metal ion‐induced deprotonation and subsequent coordination of the two neighbouring amide groups was shown to occur in a cooperative way in the pH range 5−6. At pH ≈ 6.5 a complex with an (O − , 2 × CON − , COO − ) binding set becomes predominant for both Cu II and V IV O. The affinity of the phenolate‐O − for V IV O is high and the ligand is bound to this metal ion even at pH values greater than 10. Conversely, the affinity for V V O 2 is significantly lower and no interaction between this metal oxo‐ion and the ligand could be detected in the pH range 2−12. In contrast, with the dipeptide analogue H 2 SalGly, chelation involving the deprotonated amide‐N − could be unambiguously detected. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)