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 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.
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