Speciation in the oxovanadium(IV)/glutathione system

Amperometric Sensing Based on Glutathione Protected Au25 Nanoparticles and Their pH Dependent Electrocatalytic Activity

“…The pH dependent electrocatalytic activity of the Au 25 ME can be understood by considering the pK a s of the polyprotic acids involved in this experiment. The glutathione ligand is a tripeptide that possesses three pK a s of 2.1, 3.5 and 9.4 [34], where pK 1 and pK 2 correspond to the deprotonation of the carboxyl groups and pK 3 correspond to that of the ÀNH 3 + group. The acidity of glutathione ligand may significantly drop when the ligands are bound to gold particles due to the electrostatic effect of the neighboring ligands, which could cause the pK a values to be as much as 2 units higher compared to the free ligand [35].…”

Model studies related to vanadium biochemistry: recent advances and perspectives

“…20 More detailed speciation studies of this system have shown an even higher complexity. 21,22 In the most recent and complete study, combining pH-potentiometry with EPR spectroscopy, visible absorption and circular dichroism measurements, it was shown that in the pH range between 5 and 7.5 and at any ligand-to-metal ratio between 10 and 140, the predominant complex, is a 2:1 species in which each GSH molecule coordinates through one Oatom of the deprotonated carboxylate group and the amino N-atom of the glutamyl residue. 22 Four other species were identified in other pH-ranges.…”

Speciation in the chromium(III)-glutathione system

“…The ionization constants of the glutathione, GSH, H 3 L (Scheme 1) (Armas et al, 2001), indicate the deprotonation of the carboxylic group (H 3 L, species), the SH group of the cys residue ( H 2 L -species) and the NH 3 + group of the γ-glu residue (HL 2-species), respectively. These three deprotonations occur when the GSH solutions are titrated with NaOH or KOH.…”

“…From β pqr (Table 2) and β pr constants of the glutathione (Armas et al, 2001), the formation constants of the complex species formed can readily be calculated according to the equilibria shown in Table 3.…”

“…Previously we obtained the stability constants corresponding to the equilibria (1) (this work) and (7) (Armas et al, 2001) in the same conditions of temperature and ionic medium. We also analyze the experimental potentiometric data using the level L 3-for the ligand, according to the equilibrium (8)…”