Solution behaviour of myo-inositol hexakisphosphate in the presence of multivalent cations. Prediction of a neutral pentamagnesium species under cytosolic/nuclear conditions.

myo-Inositol hexakisphosphate (InsP6) is an ubiquitous and abundant molecule in the cytosol and nucleus of eukaryotic cells whose biological functions are incompletely known. A major hurdle for studying the biology of InsP6 has been a deficiency of a full understanding of the chemistry of its interaction with divalent and trivalent cations. This deficiency has limited our appreciation of how it remains in solution within cells, and the likely degree to which it might interact in vivo with physiologically important cations such as Ca2+ and Fe3+. We report here the initial part of the description of the InsP6-multivalent cation chemistry, including its solution equilibria studied by high resolution potentiometry and (for the Fe(III)/Fe(II) couple) cyclic voltammetry. InsP6 forms anionic complexes of high affinities and 1:1 stoichiometry with Mg(II), Ca(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II). Of particular importance is the observation that, in the exceptional case of Mg(II), InsP6 forms the species [Mg5(H2L)] (L representing fully deprotonated InsP6); this soluble neutral species is predicted to be the predominant form of InsP6 under nuclear or cytosolic conditions in animal cells. Contrary to previous suggestions, InsP6 is predicted not to interact with cytosolic calcium even when calcium is increased during signalling events. In vitro, InsP6 also forms high affinity 1:1 complexes with Fe(III) and Al(III). However, our data predict that in the biological context of excess free Mg(II), neither Fe(III) nor Fe(II) are complexed by InsP6.

Redox behavior of Re(V)-amino acid containing complexes.

Three cationic complexes containing the [Re((V))O](3+) core (general formula [ReO(dien-H)(aa)](+), dien=diethylenetriamine, aa=glycine, alanine, valine) were studied on polycrystalline Au electrodes employing cyclic voltammetry techniques. The electrochemical behavior of the amino acids (aa) was also evaluated. Experiments were performed at pH 7.0 aqueous solutions at room temperature. The voltammogram of the complex showed current contributions related to the [Re((VI))O](4+)/[Re((V))O](3+) redox couple, the counterion, and the amino acid ligand.

Voltammetric Characterization of trans-Dioxo Ethylenediamine Complexes of Re(V) in Aqueous Solutions.

The electrochemical behavior of trans-[Re((V))O(2)(en)(2)]I and trans-[Re((V))O(2) (en)(2)]ClO(4) (en=ethylenediamine) complexes was studied by cyclic voltammetry on Au electrodes. Experiments were performed in aqueous solutions at pH 7.0 and at room temperature. The complex voltammogram was characterized by Re-containing species, assigned to the [Re((V))O(2)(en)(2)](+)/[Re((IV))O(2)(en)(2)] couple, and I-containing species. To overcome I interference, the electrochemical response of Re complexes was segregated by performing a reductive desorption of adsorbed I from Au. Copyright 2001 Academic Press.