Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 4, pp. 575−580.
Pleiades Publishing, Ltd., 2013.
Original Russian Text © I.M. Lipatova, E.A. Mezina, Yu.V. Butina, 2013, published in Zhurnal Prikladnoi Khimii, 2013, Vol. 86, No. 4, pp. 616−623.
AND POLYMERIC MATERIALS
A Spectrophotometric Study of the Ionic Complexation
between Chitosan and Anionic Dyes
I. M. Lipatova, E. A. Mezina, and Yu. V. Butina
Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
Received December 4, 2012
Abstract—Formation conditions and composition of ionic complexes in dilute mixed solutions of chitosan and
anionic dyes containing two or more sulfo groups were studied. Immediately after mixing the components, only
one sulfo group of the dye interacts with chitosan to form a soluble complex of stoichiometric composition. With
time, the other sulfo groups of the dye also become involved in the interaction, which results in the formation of
an insoluble complex in which the dye behaves as cross-linking polyvalent anion.
Much attention is given in Russia and other countries
to studying intermolecular interactions of water-soluble
polyelectrolytes with low-molecular-weight organic com-
pounds containing groups that dissociate in water. The
molecular compounds and complexes formed in these sys-
tems often exhibit new unique properties differing from
those of the components taken separately. Noncovalent
interactions between the polyelectrolytes and oppositely
charged dyes were the subject of numerous studies [1–3].
In particular, it was found that the metachromasy observed
on adding a polyelectrolyte to solutions of dyes and
manifested as a change in the spectral characteristics of
dyes is due to the dye aggregation at the polymer chain
. It should be noted, however, that the majority of such
studies deal with systems based on synthetic polyelectro-
lytes. Nevertheless, studies of intermolecular interactions
between charged organic compounds and water-soluble
biopolymers are of considerable interest.
Chitosan occupies a particular place among bio-
polymers. When dissolved in weakly acidic media, it
behaves as a polycation. Chitosan is a natural linear
polysaccharide formed by chitin deacetylation in the
presence of base agents. Its chain is nonbranched
and consists of β-(1→4)-2-amino-2-deoxy-D-glucan
residues. The formation of soluble and insoluble ionic
complexes of chitosan with oppositely charged organic
compounds was studied in most detail for chitosan–
anionic surfactant systems [4, 5]. Only a few papers
consider the capability of chitosan to bind anionic dyes
and certain prospects for practical use of this property.
For example, Glazunov and Gorbach  suggest using
an anionic dye for determining the content of amino
groups in chitosans. Interesting studies were made on
the development of chitosan-containing coatings doped
with dyes as pH indicators and as substances for optical
sensors for the detection of toxic vapors [7, 8]. Chito-
san–anionic dye systems can be readily monitored by
spectrophotometric methods and can therefore be used
as model systems for predicting the ionic interaction
of chitosan with negatively charged biologically active
substances and drugs. From the theoretical viewpoint,
chitosan–anionic dye systems can be of interest insofar
as soluble dyes, as a rule, contain several anionic groups,
which should give rise to certain speciﬁ c features of the
ionic complexation as compared, e.g., to well studied
chitosan–anionic surfactant systems.
The goal of this study was the determination of the
formation conditions and composition of ionic complexes
of chitosan with organic dyes of various stereochemical
conﬁ gurations, containing several anionic groups.