Lanthanide bicarbonate

Dickins, R. S. Gunnlaugsson, T. Parker, D. Peacock, R. D. Reversible anion binding in aqueous solution at a cationic heptacoordinate lanthanide centre selective bicarbonate sensing by time-delayed luminescence. Chem. Commun. 1998, 16, 1643-1644. 

The lanthanides show ability to form complexes with hydroxide and carbonate ions. Although the lanthanide hydroxides and carbonates are very insoluble, some soluble complexes like Eu(OH) and Eu(C03)2 may be formed. Although HCOJ is the predominant species in the pH range studied, bicarbonate complexes are not formed [147, 148],... 

A study has been made of the emission of some related Tb and Eu macrocylic complexes, immobilized in a sol-gel glass, which is made pH-dependent either by perturbing the energy of the aryl singlet or triplet state, or by modulating the degree of quenching of the lanthanide excited state. The effect of bicarbonate chelation on the polarized luminescence from chiral... 

Lanthanide (especially Eu and Tb ) CPL has undergone somewhat of a renaissance recently. For example, the CPL of Eu with chiral septadentate ligands related to 1,4,7,10-tetraazo-cyclododecane tetra-acetic acid (DOTA) has been used to monitor bicarbonate binding under physiological conditions (Figure 4). ... 

UV-difference spectroscopy, and other studies in vitro with plutonium (IV), tho-rium(IV) and a number of trivalent lanthanides, have demonstrated that, like iron, two lanthanide or actinide metal atoms are bound per transferrin molecule (Duffield and Taylor 1986, Taylor et al. 1991, Zak and Aisen 1988). Saturation of the lanthanide- or actinide-containing transferrin with excess iron results in a liberation of the f element, thus suggesting that these metals are binding to the two iron-binding sites on the transferrin molecule (Taylor et al. 1991). These studies have also shown that bicarbonate is necessary, as a synergistic anion, for the binding of actinides and lanthanides to transferrin. 

Use of table 3a in calculations of lanthanide seawater complexation requires that the total inorganic carbon concentration of seawater (Cr) be partitioned into dissolved aqueous carbon dioxide (C02aq), bicarbonate (HCOj) and carbonate (COj ). Since only a small fraction ( 14%) of COf in seawater is in the form of free ions, with the remainder being ion-paired as NaCOj, CaCO and MgCO, use of table 3a constants requires an assessment of carbonate and bicarbonate ion-pairing equilibria. Table 3b shows a more convenient stability constant formulation wherein lanthanide carbonate stability constants are expressed in terms of total (free plus ion-paired) carbonate ion concentrations in seawater ([C03"]t)- These results can be compared with direct observations of europium carbonate complexation in synthetic seawater (Lee and Byrne 1994). The GdCOj and Gd(C03)2 formation constant results of Lee and Byrne (1994), expressed in terms of... 

---