Dissociation kinetics and complexation equilibrium studies of a Zn II complex with l,5-bis(2-hydroxy-5-sulfophenyl)-3-cyanoformazan during capillary electrophoretic separation process

Toru Takahashi, Yuka Takehara, Hitoshi Hoshino

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5 Citations (Scopus)

Abstract

The dissociation kinetics and the complexation equilibrium of a Zn II complex with 1,5-bis(2-hydroxy-5-sulfophen-yl)-3-cyanoformazan (hscf: H5L) during capillary electrophoretic (CE) separation process were studied. The solvolytic dissociation reaction rate constants of the Zn II-hscf complex ([ZnL]3-) (kd) in the pH range of 6.4 to 8.0 were determined with a CE-based dissociation kinetic analysis method. Small kd values on the order of 10-5s-1 showed the remarkable kinetic inertness of [ZnL]3-, which was detectable in the CE system. The stability constant of [ZnL]3- (KZnL) at 293 K and I = 0.10 was estimated to be [ZnL 3-]/{[Zn2+][L5-]} = 1o 24.2±0.3 through the spectrophotornetric titration. The thermodynamic stability of [ZnL]3- in the pre-capillary complexation stage was thus demonstrated. In contrast, it was shown that the CE separation environment is thermodynamically unsuitable for the metal complexes based on the conditional stability constant of [ZnL]3-, which was determined under CE separation conditions, and the concentration of free HSCF in the complex band in the capillary. Thus, the "stability" of metal complex in the CE system strongly depends on kinetic inertness rather than thermodynamic stability, though their thermodynamic stability is necessary for the pre-capillary derivatization step.

Original languageEnglish
Pages (from-to)910-915
Number of pages6
JournalBulletin of the Chemical Society of Japan
Volume80
Issue number5
DOIs
Publication statusPublished - 2007 Dec 1

ASJC Scopus subject areas

  • Chemistry(all)

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