the dye should be introduced. It was found that 5×10
-6
mol L
-1
concentration of dye
was sufficient for the formation of IA. The molar absorptivity for IA with Astra
Phloxine was 56000 mol
-1
L cm
-1
, while with rhodamine 6G – 47000 mol
-1
L cm
-1
.
The high selectivity of the described approach is mainly determined by the fact
that formation of poorly soluble ionic associates of iodide complexes with basic dyes
is possible only for a few number of metal ions. In addition, the degree of formation of
specific ionic associates depends on the concentration of iodide, the stability of the IA,
and the acidity of the solution.
Investigation of the factors influencing on the interaction of organic dyes with
polyelectrolytes. The binding of dye molecules to cationic, anionic and neutral
polyelectrolytes has been extensively studied by spectral techniques. The existing data
provide insight into small molecule – macromolecule interactions, which are of major
importance in biochemistry. Particularly the interactions between anionic dyes with
cationic proteins has been the subject of numerous studies. Changes in the absorption
or fluorescence spectrum of the dye upon binding have been attributed mainly to
electrostatic interactions.
Marked changes also occur in the spectra of organic anions when synthetic
polymers are added. Charged as well as nonionic polymers have been shown to interact
with various organic dyes. Not only polymers are able to induce spectral changes but
also surfactants have been shown to aggregate with dye molecules in aqueous solution.
The origin of the spectral shifts is still a matter of debate in the literature. Dye
aggregation was held responsible for the occurrence of the new band in the case of
Methyl Orange (MO) in aqueous solutions of cationic polymers [33].
It was shown in many examples that formation of ion pairs do not results in the
change of spectra. The spectrum of crystal violet in the solvents of low dielectric
constant (toluene, hexane, carbon tetrachloride) where it exists almost exclusively in
molecular form in fact is the same as in polar solvents (water, ethanol, acetone,
pyridine) where cation of this dye is completely solvated by solvent molecules [34].
Interaction of sulfonphtaleine dyes with polyelectrolytes. Solutions of dyes
and polyelectrolytes (PE) can be considered as very interesting and promising systems
for the study of interactions between dye and organized medium. Microenvironment
of polyelectrolytes is similar to that created by surfactants at concentrations higher than
their critical micelle concentration.
Copolymers of acrylamide and trimethylammonium ethyl acrylate chloride
(CPAT) are widely used as flocculants in the water treatment and purification. They
are produced with different charge density, which is varied in the range from 5 to 95%.
Charge density is related with fraction of positively charged trimethylammonium ethyl
acrylate groups.
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