EQUILIBRIUM STUDIES OF SELENITE AND SELENATE IONS WITH THE RECEPTOR COMPLEX FORMED BY CU2+ AND 1,4,7,13,16,19-HEXAAZA-10,22-DIOXACYCLOTETRACOSANE (OBISDIEN)

摘要

The complexation of selenite (SeO32-) and selenate (SeO32-) ions in the cavity of the macrocyclic ligand OBISDIEN was studied in the absence and presence of Cu2+ ions and in the presence of bromide ions. Potentiometric equilibrium determinations allowed us to determine the species formed in the absence and presence of Cu(II) ions for the systems studied in the p[H] range 2-12. In the absence of metal ions the strength of binding of SeO42- increases from the monoprotonated to hexaprotonated species of OBISDIEN. The reverse effect occurs for the HSeO3- ion, with the strength of binding decreasing from the monoprotonated to the most protonated species. In the OBISDIEN:Cu2+:Br- system, the bromide ions contribute to the stabilisation of binuclear complexes. A similar role is played by selenite anions in the OBISDIEN:Cu2+:Br- :SeO32- systems. All SeO42- ions are complexed in the OBISDIEN:Cu2+:SeO32-:SeO42-:Br(-)1:2:1:1:6 system; in the p[H] range 2-12, selenite and bromide ions are mostly free. At p[H] 8.1 which is the p[H] of sea water, in the absence of other complexing agents, all the selenite and bromide ions are free while the selenate ions are complexed, (mu-hydroxo) (mu-selenate) dicopper(II)-OBISDIEN being the major species present. [References: 33]