ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2006, Vol. 32, No. 7, pp. 469–473. © Pleiades Publishing, Inc., 2006.
Original Russian Text © V.G. Alekseev, E.A. Milashs, S.V. Larin, O.Yu. Shigina, 2006, published in Koordinatsionnaya Khimiya, 2006, Vol. 32, No. 7, pp. 492–496.
one of the most frequently used antibiotics [1, 2]. Its
molecule contains electron-donor functional groups
, C(O)NH) and thus is potentially capa-
ble of forming coordination compounds with metal cat-
ions. The introduction of Zn and Cd salts into aqueous
and methanol solution of ampicillin was found to pro-
mote its solvolysis [3–5].
The authors of [3–5] believe that the reason for the
observed phenomenon lies in the formation of complex
compounds. At the same time, the chemical properties
of ampicillin as a ligand are poorly studied, and only
several publications [6–9] are devoted to this subject.
The aim of this work was to study the inﬂuence of the
ionic strength of solutions on the composition and sta-
bility of Zn(II) and Cd(II) complexes with ampicillin
and to determine their thermodynamic formation con-
). In previous investigations of acid–base
equilibria in HAmp solutions [10, 11] it was shown that
HAmp behaves as amino acid and occurs as
on pH of a medium.
The sodium salt of ampicillin NaAmp (Ferein, Mos-
cow) was used. The analysis revealed that the content
of active compound in preparation was no less than
99%. The NaOH solution (
= 0.0460 mol/l) was pre-
pared from a sample of metallic sodium; the concentra-
tion was determined by pH-metric titration. The
solutions were prepared from
samples of reagent grade salts; the concentrations
0.0190 and 0.0196 mol/l, respectively, were determined
from complexometric titration; 0.05 M
pared from ﬁxanal.
The titration solutions were prepared just before the
experiment. A specimen of NaAmp (0.5 g) was placed
in a 500-ml measuring ﬂask and a 2M solution of
was added in volume that provided the required value
of the ionic strength (
). After NaAmp dissolution,
54 ml of a 0.05 M
solution (2 g-equiv) was
added in order to convert ampicillin from
cation and then water was added to bring
the volume of a solution to the mark. The obtained solu-
tion (100 ml) was placed in a temperature-controlled
), 5 ml of the metal salt solution was added,
and the reaction solution was titrated with a NaOH
solution. All reagent solutions were prepared using
twice-distilled water, which was previously reﬂuxed to
The pH values were measured to
Microtechna M120 pH meter (Czech) with a glass elec-
trode and a saturated calomel reference electrode cali-
brated against buffer solutions of Na
(pH 9.20 at
) and KH
(pH 1.68 at
). All calcula-
tions, plotting of curves, statistical processing, and
extrapolations were performed with Origin 7.5 pro-
gram (OriginLab Corporation ).
Complexation of Ampicillin with Zn and Cd Cations
in Potassium Nitrate Solutions
V. G. Alekseev, E. A. Milashs, S. V. Larin, and O. Yu. Shigina
Tver State University, Tver, Russia
Received March 9, 2005
—Constants of formation of monoligand Zn(II) and Cd(II) complexes with ampicillin anion at
background electrolyte (0.1, 0.4, 0.7, and 1.0 mol/l) were determined by potentiometric titration.
Concentration constants were extrapolated to zero ionic strength according to the Hückel equation and thermo-
dynamic formation constants
(3.43 and 3.80, respectively) were
obtained. The possible structures of complexes were discussed.