title: Ligand-substitution mode capillary electrophoretic reactor: extending capillary electrophoretic reactor toward measurement of slow dissociation kinetics with a half-life of hours.
abstract: A method employing capillary electrophoresis (CE) was developed to determine the rate constant of the very slow spontaneous dissociation of a complex species. The method uses a CE reactor (CER) to electrophoretically separate components from a complex zone and, thus, spontaneously dissociate a complex. The dissociation is accelerated by ligand substitution (LS) involving a competing ligand added to the electrophoretic buffer. The LS-CER method is validated using the dissociation of a Ti(IV)-catechin complex and EDTA as a competing ligand. There is good agreement between the spontaneous dissociation rate constant (k(d) = (1.64 +/- 0.63) x 10(-4) s(-1)) and the rate constant obtained by a conventional batchwise LS reaction (k(d) = (1.43 +/- 0.04) x 10(-4) s(-1)). Furthermore, the usefulness of the method is demonstrated using a Ti(IV)-tiron complex, for which k(d) = (0.51 +/- 0.43) x 10(-4) s(-1), corresponding to a half-life (t(1/2)) of 3.8 h. Notably, a single run of LS-CER for the Ti(IV) complex is completed within 40 min, implying that LS-CER requires a considerably shorter measurement time (roughly equal to t(1/2)) than conventional CER. LS-CER can be widely applied to determine the spontaneous dissociation rates of inorganic diagnostic and therapeutic reagents as well as of biomolecular complexes.
authors.affiliation: Laboratory of Environmental Analytical Chemistry, Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aramaki-Aoba, Aoba-ku, Sendai 980-8579, Japan. iki@orgsynth.che.tohoku.ac.jp
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Iki
authors.forename: Mariko
authors.initials: M
authors.lastname: Takahashi
authors.forename: Toru
authors.initials: T
authors.lastname: Takahashi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Hoshino
mesh_terms: D004492:Edetic Acid / Q000737:chemistry; D019075:Electrophoresis, Capillary / Q000379:methods*; D006207:Half-Life; D007700:Kinetics; D008024:Ligands; D014025:Titanium / Q000032:analysis* / Q000737:chemistry
chemical_list: D008024:Ligands; D004492:Edetic Acid; D014025:Titanium