Interaction of beryllium(II) ion with glutathione in aqueous solution

Beryllium is found naturally into various forms like gemstones, beryl and chrysoberyl. It is also used in the electronics industry as high thermal conductivity material and in nuclear industry for its high neutron moderating ability [1]. Chronic beryllium disease (CBD) is an occupational lung disorder, in exposed industry workers. Recent studies have identified a strong association between CBD and some human leukocyte antigen that contain glutamic acid [2]. The complexation between Be2+ ion and glutathione (H3L) has been studied at 25° C in 0.1 mol dm3 NaClO4 as ionic media, by potentiometric measurements of the hydrogen ion concentration. The determination of the equilibrium constants has been carried out by evaluating the quantity ZH, which represents the average number of protons released per glutathione molecule, as a function of the pH. Experimental data for Be2+glutathione system, processed by Hyperquad program [3], are interpreted by the following equilibria: Be2+ + H3L = BeH2(H3L) + 2 H+ log (const.) = 3.19 ± 0.04 Be2+ + H3L = BeH4(H3L) + 4 H+ log (const.) = 11.71 ± 0.06 Furthermore, the interaction between Be2+ and glutamic acid (H2A), conducted in the same experimental conditions, has been also considered to understand the role of glutamic acid residues toward the complexation. Measurements are consistent with equilibrium: Be2+ + H2A = BeH2(H2A) + 2 H+ log (const.) = 6.30 ± 0.08 To establish which sites of the ligand are involved in the coordination with the berillyum ion, 1HNMR spectra are obtained in absence and in presence of metal ion as a function of pH