ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2006, Vol. 32, No. 1, pp. 39–44. © Pleiades Publishing, Inc., 2006.
Original Russian Text © L.M. Ramenskaya, V.V. Zhandarev, M.E. Goshin, 2006, published in Koordinatsionnaya Khimiya, 2006, Vol. 32, No. 1, pp. 42–48.
8-Hydroxyquinoline (HOx) and its complexes with
biometals exhibit pronounced bactericidal and fungi-
cidal properties and, hence, are potential medicines [1–
3]. 1,2,3,4-Tetrahydro-8-hydroxyquinoline (HTOx) is
not toxic and is also of interest as a pharmaceutically
bioactive substance with antibacterial effect . It can
be used as the starting component or model compound
for the creation of medicines from composite hydro-
substituted 8-hydroxyquinolines and prediction of their
biological and therapeutic effect, as well as ecologi-
cally safe reagent for the precipitation of heavy metal
cations during water detoxication . Data on the phys-
icochemical properties of HTOx are lacking and, there-
fore, the study of its behavior in an aqueous solution
and in the presence of biometal cations seems urgent.
Unlike HOx, the naphthalene ring of HTOx contains
an additional hydrogen atom in each position 1, 2, 3,
and 4 , for which reason the acid–base and complex-
ating properties of this ligand can be changed.
The purpose of this work is to study the acid–base
equilibrium and possible complexation of 1,2,3,4-tet-
rahydro-8-hydroxyquinoline with Cu
, and Cd
ions in an aqueous solution.
HTOx was synthesized at the Chair of General and
Bioorganic Chemistry of the Yaroslavl State University
 and identiﬁed from
H NMR spectra. A solu-
tion of HTOx (
mol/l) was prepared by disso-
lution of an HTOx sample with an exact weight in a
solution with an equimolar amount of HCl. Working
solutions of HTOx–HCl (pH 4.26), HTOx–0.5HCl
(pH 5.64), and HTOx–1.5NaOH (pH 10.02) were pre-
pared by dilution of the starting solution and addition of
a required amount of alkali. Copper(II), zinc, and cad-
mium nitrates (reagent or analytical grade) were recrys-
tallized from aqueous solutions of these salts. The con-
centration of metal ions in solutions was determined
trilonometrically . Solutions of HCl and NaOH were
prepared from the corresponding reagents (reagent
grade), and the concentration was reﬁned by standard
procedures. Solutions of HTOx were stored in the dark.
The electronic absorption spectra of the HTOx
working solutions in the presence and absence of the
metal cations were recorded on an SF-46 spectropho-
tometer at 293 K. The spectra were measured against
water in a cell with
= 1 cm in a region of 340–700 nm.
The concentrations of the metal and ligand were
mol/l. The pH values of the solutions were mea-
sured on a METER OP-211/1 pH-meter with a glass
measuring electrode and an Ag/AgCl reference elec-
trode. The instrument was calibrated using standard
buffer solutions. the absorption spectra and pH of solu-
tions were measured at certain time intervals after prep-
aration. The obtained pH values are given in the table.
Dissociation and Coordinating Ability
in Aqueous Solution
L. M. Ramenskaya*, V. V. Zhandarev**, and M. E. Goshin**
* Institute of Solution Chemistry, Russian Academy of Sciences,
Akademicheskaya 1, Ivanovo, 153045 Russia
** Yaroslavl State University, ul. Sovetskaya 14, Yaroslavl, 150000 Russia
Received February 16, 2005
—The state of 1,2,3,4-tetrahydro-8-hydroxyquinoline is studied spectrophotometrically in the near-
UV and visible regions at different pH in an aqueous solution in the presence and absence of Cu
cations. The dissociation constant (
(293 K)) is estimated from the pH-metric data. The stability
of the complexes formed decreases in the series Cu
. The inﬂuence of tetrahydro atoms on the
dissociation, complexation, and change in the state of 1,2,3,4-tetrahydro-8-hydroxyquinoline in an aqueous
solution is discussed.