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In order to assess the molecular form of vanadium insulinmimetic complexes in cells, the interactions of V IV O-maltolate and V IV O-dipicolinate systems with adenosine 5Ј-triphosphate (ATP) and glutathione (GSH) in aqueous solution were studied by employing pH potentiometry, and EPR, CD and UV/Vis spectroscopy. The stoichiometries and stability constants of the complexes formed were determined at 25°C with an ionic strength of I = 0.2 mol dm -3 (KCl). The most probable binding mode of the complexes formed in solution was determined by means of various spectral methods. The

The formation of complexes of a tripeptide analogue, salicylglycyl‐L‐alanine [HOC6H4C(O)NHCH2C(O)NHCH(CH3)COOH, H2SalGly‐L‐Ala], was studied with CuII, VIVO and VVO2 in aqueous solution using pH‐potentiometric and spectroscopic (UV/Vis, CD, EPR and 51V 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 CuII and VIVO. The affinity of the phenolate‐O− for VIVO is high and the ligand is bound to this metal ion even at pH values greater than 10. Conversely, the affinity for VVO2 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 H2SalGly, chelation involving the deprotonated amide‐N− could be unambiguously detected. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The dipeptide and tripeptide analogues salicyl-L-aspartic acid (Sal-L-Asp) and salicylglycyl-L-aspartic acid (SalGly-L-Asp) were synthesized and their protonation and complex formation with V(IV)O2+ were studied in aqueous solution through the use of pH-potentiometry and spectroscopic (UV-Vis, CD and EPR) techniques. The phenolate terminus proved to be a good anchoring site to promote (i) the metal ion-induced deprotonation and subsequent coordination of the peptide amide group(s) in the pH range 4-5 for the dipeptide analogue, (ii) and in the pH range 5-6 in a very cooperative way for the tripeptide analogue. The results suggest that the presence of good anchoring donors on both sides of the amide groups is responsible for the cooperative deprotonation of the two amide-NH groups.

The reduced Schiff bases of salicylaldehyde and pyridoxal (and o-vaniline)

The reduced Schiff bases of salicylaldehyde [and o-vanillin (o-van)