The Catalytic Impact of Ethionine on the Multi-Step
Electroreduction of Bi(III) Ions in Chlorates(VII) Solutions
Published online: 21 July 2017
The Author(s) 2017. This article is an open access publication
Abstract It was concluded that the presence and the proton-
ation of the ethionine (Et) have effects on the rate of the multi-
step process of Bi(III) electroreduction in the 2 mol dm
chlorates(VII). The catalytic activity of ethionine increases
with increasing amounts of NaClO
in the basic electrolyte
solution. Increased amounts of HClO
in chlorate(VII) solu-
tions causes a decreased rate of the Bi(III) ion electroreduction
process in the presence of ethionine. This confirms the as-
sumption on the variety of active complexes mediating the
passage of electrons.
Standard rate constants
Ethionine is an ethyl analogue of methionine and has a very
destructive influence on the livers of living organisms and
disrupts the activity of many enzymes. Ethionine interferes
with the methionine metabolism, leading to depletion of the
primary methyl donor, S-adenosylmethionine . It is a
strongly carcinogenic metabolite contributing to the develop-
ment of most types of human cancer .
Therefore, it is necessary to monitor the level of ethionine
and to demonstrate new methods for determination of this
amino acid in various environments.
The cap-pair effect opens the door to determination of ions
of many depolarisers in weak complexing solutions [3, 4]and,
indirectly, of catalysing substances.
Studies on the kinetics of various depolarisers in the pres-
ence of electrode substances are comprehensively discussed in
the literature [5–11]. It was demonstrated that the structures of
the inter-phase area caused by adsorption of organic com-
pounds on the surface of mercury play a significant role in
the mechanism of the cap-pair effect. A significant role in the
catalytic electroreduction of the depolariser is also played by
water activity [12, 13].
The reversibility of Bi(III) electroreduction in
chlorates(VII) increases with decreasing water activity .
It has also been shown that the process of Bi(III) ion
electroreduction is catalysed by methionine , cysteine
and cystine [16, 17]. Values of the standard rate constant k
 indicate that the catalytic effect of amino acids grows—in
the order of cystine < methionine < cysteine—for
chlorates(VII) with high water activity (from 1 to 4 mol dm
For higher concentrations of chlorates(VII) (from 5 to
), the comparable effect of amino acids on the rate
of electroreduction of Bi(III) ions is observed . Also, the
significant changes in the kinetics of the Bi(III) ions
electroreduction process and in the presence of homocysteine
or homocystine apropos and the change of HClO
ratio in the solutions of chlorates(VII) were found [18, 19].
With an increase in the amount of NaClO
in the basic
electrolyte solution, the catalytic activity of both homo-
cysteine and homocystine increases. However, an increase
in the amount of HClO
in chlorate(VII) solutions does
not cause significant changes in the kinetics of the Bi(III)
ions electroreduction in the presence of these amino acids.
* Agnieszka Nosal-Wiercińska
Department of Analytical Chemistry and Instrumental Analysis,
Faculty of Chemistry, M. Curie-Skłodowska University, M.
Curie-Skłodowska Sq. 3, 20-031 Lublin, Poland
Electrocatalysis (2017) 8:492–497