Sodium dodecyl sulfate-polyethyleneimine-water system. Self-organization and catalytic activity

Article abstract of DOI:10.1007/s11172-005-0299-y

Concentration boundaries within which polymer-colloid structures exist in a sodium dodecyl sulfate-polyethyleneimine-water system were determined. The catalytic effect of this composition was found for the hydrolysis of phosphonic acid esters. The found acceleration of hydrolysis up to 25-fold is caused by reagent concentrating in a catalytic complex.

Full text of DOI:10.1007/s11172-005-0299-y

Russian Chemical Bulletin, International Edition, Vol. 54, No. 3, pp. 641—649, March, 2005
641
Sodium dodecyl sulfate—polyethyleneimine—water system.
Selfꢀorganization and catalytic activity
L. Ya. Zakharova,aꢀ F. G. Valeeva, D. B. Kudryavtsev, A. V. Bilalov, A. Ya. Tret´yakova,
a
a
b
b
a
a
b
L. A. Kudryavtseva, A. I. Konovalov, and V. P. Barabanov
aA. E. Arbuzov Institute of Organic and Physical Chemistry,
Kazan Research Center, Russian Academy of Sciences,
8
ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 73 2253. Eꢀmail: lucia@iopc.kcn.ru
b
Kazan State Technological University,
6
8 ul. K. Marksa, 420015 Kazan, Russian Federation
Concentration boundaries within which polymer—colloid structures exist in a sodium
dodecyl sulfate—polyethyleneimine—water system were determined. The catalytic effect of
this composition was found for the hydrolysis of phosphonic acid esters. The found acceleraꢀ
tion of hydrolysis up to 25ꢀfold is caused by reagent concentrating in a catalytic complex.
Key words: phosphorus acid esters, hydrolysis, kinetics, surfactant—polymer complex,
sodium dodecyl sulfate, polyethyleneimine, pseudoꢀphase model.
Mixed systems surfactant—polymer are objects of a
promising interdisciplinary scientific area that attract great
researchers´ interest.1 The development of this avenue
of investigation is stimulated by a wide scope of practiꢀ
cally useful properties of mixed solutions and a possibility
of their purposeful control by the variation of the compoꢀ
nent ratio in the system. In addition, the study of regulariꢀ
ties of the formation of polymolecular ensembles extends
potentialities of selfꢀassembly modelling in biological sysꢀ
tems. The main goal of fundamental studies of aqueous
surfactant—polymer solutions is to prove the combined
aggregation, find concentration boundaries for the existꢀ
ence of mixed structures, estimate their stability, and charꢀ
acterize the nature of intermolecular interactions. The
reactivity of compounds in mixed polymer—colloid sysꢀ
tems is poorly studied and, therefore, is one of the main
tasks of the present work.
combined aggregates are formed in these systems mainly
due to hydrophobic interactions. To gain more compreꢀ
hensive information on the contribution from differꢀ
ent types of intermolecular interactions in the surfacꢀ
tant—polymer systems, we continued to study the cataꢀ
lytic properties of PEIꢀbased compositions, using an unꢀ
likely charged surfactant, sodium dodecyl sulfate (SDS).
The hydrolysis of phosphonates 1—3 was studied as a
model process (Scheme 1).
—6
Scheme 1
7
,8
We have previously studied the physical and cataꢀ
lytic properties of polymer—colloid systems based on the
cationic surfactant cetyltrimethylammonium bromide
(
CTAB) and polyethyleneimine (PEI). Different points
of view about the possible cooperative binding of cationic
surfactants with nonionic and likely charged polymers
can be found in the literature. The published results
1
2
3
X
R
NO2
Et
NO2
nꢀС Н
Br
Et
9
7,8
6
13
favor the hypothesis on the selfꢀorganization and formaꢀ
tion of supramolecular structures in the CTAB—PEI sysꢀ
tem. These structures efficiently catalyze the hydrolysis of
phosphorus esters. Taking into account that the electroꢀ
static interaction contributes unfavorably to the free enꢀ
ergy of formation of complexes of the likely charged surꢀ
factant and polymeric species, it should be assumed that
Experimental
Compounds 1—3 were synthesized by a known procedure.10
Sodium dodecyl sulfate (Sigma) and branched PEI (Aldrich,
molecular weight 30000) containing the primary, secondary,
and tertiary nitrogen atoms in a ratio of 1 : 2 : 1 were used. Molar
concentrations of PEI presented in the work are based on the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 630—638, March, 2005.
066ꢀ5285/05/5403ꢀ0641 © 2005 Springer Science+Business Media, Inc.
1

642
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Zakharova et al.
monomeric unit. The hydrolysis kinetics was studied by spectroꢀ
photometry on a Specord Мꢀ400 instrument in the pseudoꢀfirst
regime from a change in the absorbance of the leaving group
anion. The apparent rate constants (kapp) were determined from
The first term in the right part (F ) of Eq. (2) characterizes
a change in the microenvironment of reagents when the reaction
is transferred from the aqueous to micellar phase, and the secꢀ
m
ond term (F ) determines the effect of reagent concentrating in
c
the plot ln(А – А) = –kappt + const, where А and А∞ are the
aggregates.
∞
absorbance of the solution at the time moment t and at the end
of the reaction, respectively. The weighed leastꢀsquares method
was used, and average arithmetical values of three measureꢀ
ments differed by at most 5% were taken into account. The
conductivity was measured on a CDMꢀ2ꢀd conductometer (Denꢀ
mark). The surface tension was determined by the Wilhelmy
ring method.11 The degree of protonation of the polymer was
estimated by the potentiometric titration of a PEI solution on a
pHꢀ340 instrument, using a 0.1 М aqueous solution of HCl as
titrant.
The equilibrium surfactant concentration was measured by
the potentiometric method using an EMꢀVgꢀ01 modified indusꢀ
trial heterogeneous membrane electrode selective to a dodecyl
sulfate ion. The calomel electrode (Crytur, type 102) was used as
the reference electrode. All measurements were carried out at
Results and Discussion
To estimate the selfꢀorganization in the
SDS—PEI—water system, we studied the conductometꢀ
ric properties of solution as a function of the surfactant
concentration at different unchanged concentrations of
the polyelectrolyte. The concentration plots of the conꢀ
ductivity (χ) for several PEI concentrations are presented
in Fig. 1 as an example. In these plots, three linear regions
are observed with breaks in the points С and С . In this
1
2
case, the plot of conductivity vs. surfactant concentraꢀ
tion is assumed to be linear with breaks in the points
corresponding to the formation of aggregates.
11
2
98 K in a temperatureꢀcontrolled cell, whose design allowed
13—15
Table 1
potentiometric and viscosimetric measurements to be carried
out simultaneously. The electrode function was fulfilled in the
whole interval of surfactant concentrations under study. The
slope ratio of the electromotive force plot vs. surfactant concenꢀ
tration E = f(–logсsurf) in the region below the critical miꢀ
celle concentration (CMC) of sodium dodecyl sulfate was
contains the critical concentrations and characteristics of
the linear regions calculated by the equation y = ax + b,
where а is the slope of the plot, and b is the section cut in
the ordinate. As can be seen from the analysis, the emꢀ
phasized sections are linear with a good correlation coefꢀ
ficient (R ≥ 0.99). This confirms that three regions were
substantially isolated in the plots for mixed surfacꢀ
tant—polymer systems, unlike individual micellar soluꢀ
tions of surfactants. Perhaps, this choice is somewhat arꢀ
bitrary at a PEI concentration of 0.01 mol L for which a
and b are close in the B and C sections (see Table 1). In
this case, probably, we cannot exclude that at such a low
concentration of the polymer its influence on the selfꢀ
organization process is insignificant and the micellization
process does not involve macromolecules and is characꢀ
(58±4)/рсsurf mV for SDS. All potentiometric measurements were
carried out on an Mꢀ120 potentiometer (Мicrotechna) with an
accuracy of ±1 mV at 25 °С. For experimental details, see Ref. 5.
The hydrodynamic behavior of macromolecules in solution
was concluded from viscosimetric data. The viscosities of PEI
solutions and their mixtures with surfactants were measured on
a VPZhꢀ1 Ubbelohdeꢀtype viscosimeter with a capillary diamꢀ
eter of 0.54 mm. The error for measurements of viscosity was at
most 1%.
–
1
Kinetic data were analyzed in the framework of the pseudoꢀ
phase model using the equation12
terized by only one break in the С point (CMC). The
1
corresponding linearization of the data of the conductoꢀ
metric dependence with the isolation of two linear reꢀ
,
(1)
where k´app (L mol–1 s–1) is the secondꢀorder rate constant obꢀ
tained by the division of kapp into the overall nucleophile conꢀ
χ•10–3/µSm cm–1
centration; k2,w and k2,m (L mol–1
s ) are the secondꢀorder rate
–1
constants in the aqueous and micellar phases, respectively; K
S
1
–
1
and КNu (L mol ) are the binding constants of the substrate and
nucleophile, respectively; V is the molar volume of the surfacꢀ
tant; and C is the surfactant concentration minus the critical
association concentration.
3
2
The use of the modified form of Eq. (1) to express the cataꢀ
lytic effect, which is equal to the ratio of the apparent rate
constant and the firstꢀorder reaction rate constant in an aqueous
solution of PEI in the absence of SDS, makes it possible to
estimate quantitatively the contribution of different factors to
the micellar effect
2
3
1
4
0
0
.02
0.04
0.06 CSDS/mol L–1
(
kapp/k )
= Fm•Fc,
(2)
w max
Fig. 1. Conductivity (χ) of aqueous SDS—PEI solutions vs. SDS
.
concentration at different PEI concentrations (25 °С): 0.2 (1),
0
.1 (2), 0.02 (3), and 0 mol L– (4).
1

Surfactant—polyethyleneimine—water system
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
643
Table 1. Conductivity in the SDS—PEI—water system vs. surfactant concentration: the critical concentrations С and С , slope (a) of
1
2
the linear sections A, B, and C, and the section cut in the ordinate (b) by the A, B, and C sections (see Fig. 1; А corresponds to the
lower concentration С ; B, in the concentration interval С —С ; С, higher than the С concentration)
1
1
2
2
CPEI
С1
С2
А
B
C
mol L–1
b
a
R (n)*
b
a
R (n)
b
a
R (n)
0
**
0.0085
—
1.656
19.03
0.997 (5)
578.1 18055
0.997 (6)
(
CMC)
0
0
0
0
0
0
.01
0.0048
0.01
—
0.014
0.0155 49.58
0.02
31.70
31.70
51.0
125206
125206
124607
124043
124333
115046
0.999 (4)
0.999 (4)
0.994 (5)
0.995 (6)
0.994 (4)
0.997 (9)
623
681
29796
24735
0.97 (3)
687
24665
0.997 (6)
.01** 0.0048
0.998 (9)
0.991 (4)
0.994 (4)
0.9999 (3) 1230
0.995 (5) 2406
.02
.05
.1
0.0051
0.0074
0.008
466.1 49530
335.6 86430
566.6 60569
765.3 27550
1136
0.991 (6)
0.991 (8)
0.99999 (4)
0.995 (4)
31662
29875
17133
72.14
133.8
.2
0.016
0.035
1205
50619
*
*
R is the correlation coefficient, and n is the number of points in the section.
* Section B above the С concentration.
1
gions indicates a small increase in the correlation coeffiꢀ
cient (see Table 1).
the critical association concentration, corresponds to the
onset of combined aggregation of surfactant and polymer
molecules at which small friable surfactant aggregates are
formed in solution. They are peripherally bound to the
macromolecules. In the case of rather long flexible polyꢀ
mers, polymeric chains undergo globulization with incluꢀ
sion of surfactant aggregates (see Fig. 2). The formation
of combined structures continues up to the surfactant
This type of conductometric plots (see Fig. 1) is charꢀ
acteristic of a wide scope of polymer—colloid systems,
including compositions based on anionic surfactants conꢀ
1
3—15
taining uncharged polymers and polyelectrolytes.
According to the current concepts, depending on the polyꢀ
mer and surfactant types, complex nanostructures can
form in solution, and their composition and structure are
determined by all intermolecular interactions between a
macromolecule and surfactant. Typical structures are
concentration equal to С , which is named the polymer
2
saturation concentration, after which usual micelles unꢀ
bound to the polymer are formed in solution along with
2
,9
shown in Fig. 2. The С concentration, which is named
the polymer—colloid complexes.
1
a
b
c
Fig. 2. Nanostructures of the intrapolymeric (a, b) and interpolymeric (c) types.

644
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Zakharova et al.
ηsp (CPEI)–1/dL g–1
The interaction of polyelectrolytes with unlikely
charged surfactants,1
6—22
including selfꢀorganization in
a
7
the PEIꢀbased systems,1
8—22
has a complex character.
The structure of supramolecular systems is determined by
the mutual influence of components in the surfacꢀ
tant/polyelectrolyte pair, molecular weight, flexibility,
branching, and concentration regime of a polyelectrolyte
solution. According to the commonly accepted point of
view, the cooperative interaction with formation of
nanostructures also can occur in the surfactant—polyꢀ
electrolyte system (see Fig. 2). The polymer—colloid comꢀ
plexes that formed can be intrapolymeric (involving one
polymeric chain) or interpolymeric (involving several
macromolecules). However, in some works researchers
prove the nonꢀcooperative interaction of the polyion with
an oppositely charged surfactant. According to the known
data,22 the first step is nonꢀcooperative binding to form
stoichiometric surfactant—polymer complexes. The next,
cooperative step is accompanied by the formation of
intrapolymeric micelles with low aggregation numbers at
a surfactant concentration much lower than the CMC. As
6
1
1
2
3
0
1
0–3
CSDS/mol L–1
ηsp (CPEI)–1/dL g–1
3
3
2
2
1
.5
.0
.5
.0
.5
b
a result, the formation of the polymer—colloid complexes
can be accompanied1
7,22
by a change in the macromolꢀ
ecule conformation and morphology of surfactant aggreꢀ
gates. Taking into account that PEI is a weak polyelectroꢀ
lyte, we decided to use the polymer—colloid complexes
presented in Fig. 2 as model structures for data interpreꢀ
tation.
1.0
0
.5
When PEI additives were introduced into a surfactant
solution, the conductivity increased (see Fig. 1) and conꢀ
tinued to increase with an increase in the polymer conꢀ
centration. This is caused by the fact that in an aqueous
solution without a buffer (pH 9—10) PEI is a weak elecꢀ
trolyte and introduces the intrinsic contribution to the
conductivity of the system. The С and С values increase
0
.1
0.2
0.3
0.4
0.5
CPEI/g dL–1
Fig. 3. a. Isotherms of the reduced viscosity of PEI solutions
with different concentrations: 0.0073 (1), 0.0365 (2), and
.073 mol L– in the presence of SDS (25 °С). b. Reduced
1
0
viscosity of PEI solutions vs. polyelectrolyte concentration.
1
2
with an increase in the polyelectrolyte concentration (see
Table 1). Different tendencies for changing these critical
PEI solutions, being the plot of the reduced viscosity
η /С
vs. polymer concentration, is presented in Fig. 3.
sp PEI
1
4,15
surfactant concentrations were observed.
In our case,
An increase in η /С
with the dilution of a polymer
sp PEI
as in the works,1
4,15
there is a tendency for extending the
solution is a characteristic manifestation of the effect of
polyelectrolyte swelling caused by the enhancement of
the Coulomb repulsion of likely charged polymeric segꢀ
ments with a decrease in the ionic strength of the solution
during dilution. The results of viscosimetric analysis of
PEI solutions with different concentrations in the presꢀ
ence of SDS are presented in Fig. 3. It is known that the
addition of a surfactant to a polyelectrolyte solution gives
different types of plots of the specific viscosity vs. surfacꢀ
tant concentration. As a rule, for the oppositely charged
surfactant, the effect is high compared to an uncharged or
likely charged surfactant. Based on an insignificant change
in the viscosity of the studied PEI samples, one should
expect a weak interaction between SDS and PEI upon
surfactant addition. A potentiometric study carried out
using the electrodes selective toward a dodecyl sulfate ion
showed that this is not true. The isotherms of dodecyl
area where combined structures exist (designated by the
С and С concentrations) with an increase in the polymer
1
2
concentration. It should be noted that the interpretation
of the conductometric results is not final: different explaꢀ
nations of the anomalous change in the conductivity in
2
1,22
SDS—PEI solutions can be found in the literature.
Therefore, this problem requires an additional study.
Although the catalytic effect of mixed surfacꢀ
tant—polymer solutions is mainly manifested at surfacꢀ
tant concentrations higher than the CMC and is caused
by reaction transfer from an aqueous solution to mixed
aggregates, we studied the physical properties of the soluꢀ
tion in a wide interval of surfactant concentrations lower
and higher than the CMC to reveal the motive forces of
catalysis and characterize intermolecular interactions that
occur in the catalytic complex. The viscosity isotherm of

Surfactant—polyethyleneimine—water system
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
645
B
γ/mN m–1
1
0
.00
.96
1
46
4
4
4
3
4
2
0
8
2
3
1
1
0–3
CSDS/mol L–1
2
Fig. 4. Degree of binding of dodecyl sulfate ions in PEI solutions
with different concentrations vs. logarithm of the SDS concenꢀ
tration in the SDS—PEI—water system: 0.0073 (1), 0.073 (2),
36
3
3
4
–
1
and 0.0365 mol L (3).
–
4
–3
–2
logCSDS
sulfate ion binding in PEI solutions with different conꢀ
centrations are shown in Fig. 4. They represent the plots
of degree of binding B vs. surfactant concentration, where
В is determined as a ratio of the molar concentration of
the bound surfactant to its analytical concentration in
solution. The В values never become lower than 0.95,
even at low SDS concentrations, i.e., the surfactant molꢀ
ecules introduced into a PEI solution are bound almost
completely. For the likely charged polyelectrolyte and
Fig. 5. Surface tension isotherms of the SDS—PEI—water sysꢀ
tem at different PEI concentrations (25 °С): 0 (1), 0.1 (2), and
0.2 mol L– (3).
1
shaped copolymers. The addition of a surfactant enhances
this effect, so that the γ values become lower than those
for an SDS solution without PEI. Note that, when the
CMC of the surfactant is achieved, the surface tension of
SDS—PEI—water mixtures increases but remains lower
than that for a micellar surfactant solution. The latter is
probably due to the desorption of some surfactant ions
that are unbound to PEI from the liquid—air interface to
the solution bulk during micellization. The researchers
examined the adsorption properties of polymer—colloid
solutions and proposed theoretical models of the surface
behavior for different surfactant—polymer pairs. The type
of the plots (see Fig. 5) is characteristic
charged polyelectrolytes at their fairly high concentration
in solution.
Before kinetic studies, we estimated the change in the
pH of the system under experimental conditions. As
known, PEI in an aqueous solution is involved in the acidꢀ
base equilibrium due to a lone electron pair (Scheme 2, а),
5
surfactant, В do not usually exceed 0.6—0.7. High deꢀ
grees of binding at a weak change in the hydrodynamic
properties assume a considerable contribution of hydroꢀ
phobic interactions to selfꢀorganization. This assertion is
favored by the fact that PEI in an aqueous solution withꢀ
out buffer and salt additives is a weak polycation. The
highest degree of binding (>0.99) was observed for a soluꢀ
2,16
–
1
tion with the lowest PEI content (0.0073 mol L ). At
this concentration, a PEI macromolecule takes the most
unfolded conformation due to the effect of polyelectroꢀ
lyte swelling, which is indicated by the viscous flow data
2,16
of weakly
(
see Fig. 3). Therefore, the PEI concentration of this
order provides the best accessibility of surfactant bindꢀ
ing sites for polymeric chains. It cannot be excluded
that a certain contribution to the enhancement of the
SDS—PEI interaction is made by a change in the fraction
of PEI—PEI crossꢀlinking interactions with dilution of
the polyelectrolyte solution.
increasing the pH to 9—10. At this pH some amino groups
5%) exist in the protonated form. As can be seen
23
(
To reveal a reason for the high affinity of PEI to
SDS and the efficiency of the catalytic effect of
SDS—PEI—water compositions, we measured the surꢀ
face tension of the solutions at the air interface. The surꢀ
face tension isotherms of the studied mixtures and SDS
solution obtained by the Wilhelmy plate method are given
in Fig. 5. We found that the polymer—colloid complexes
that formed exhibit surfactant properties, so that already
at low surfactant concentrations the surface tension at the
liquid—air interface decreases sharply. This behavior is
characteristic of the dense interphase packing of combꢀ
Scheme 2
(
—CH CH NH—) + H O
2 2 n 2
+
–
(
—CH CH NH—) —H + OH ,
(a)
2
2
n
(—CH2CH2NH—)n + H2O + C12H25OSO3Na
+
–
(
—CH CH NH—) —H /C12H25OSO + NaOH,
2
2
n
3
(—CH CH NH—) —H+/OH– + C12H25OSO Na
2
2
n
3
+
–
(—CH CH NH—) —H /C12H25OSO3 + NaOH. (b)
2
2
n

646
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Zakharova et al.
pH
2.2
However, one should take into account a possibility of the
рК shift in the polymer—colloid complexes. The data
а
1
1
1
1
1
1
1
1
1
obtained agree well with the results of viscosimetric and
conductometric studies in which PEI demonstrates the
behavior of an uncharged polymer rather than polyelecꢀ
trolyte. Analysis of a possible effect of the concentration
of hydroxide ions formed by Scheme 2 on the results of
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
1
3
conductometric experiments showed that the absolute
values of specific conductivity corrected by the pH change
exceed insignificantly the experimental data and the С1
and С critical concentrations are independent of the pH
2
of solution.
In kinetic experiments, we studied the reactivity
of phosphonates 1—3 (see Scheme 1) in the
SDS—PEI—water system. We have earlier found the genꢀ
eral base catalysis of hydrolysis of phosphorus esters in the
1
2
3
2
4
presence of PEI. The reaction is catalyzed by uncharged
amino groups involved in the activation of a water molꢀ
ecule. Due to the electrostatic interaction with hydroxide
ions, the protonated amino groups can enhance the conꢀ
tribution of alkaline hydrolysis of substrates to the apparꢀ
ent rate constant.
CSDS/mol L–1
0
.05
0.10
Fig. 6. Plot of the pH of aqueous SDS—PEI solutions vs. SDS
concentration at different PEI concentrations: 0.2 (1), 0.05 (2),
7,8
We have shown that, unlike shortꢀchain polyamines
–
1
0
.1 mol L (3).
2
5
(
analogs of PEI), the plot of apparent rate constant vs.
PEI concentration is nonlinear and Sꢀshaped, which is
characteristic of enzymatic and micellar catalysis. The
apparent rate constant in PEI solutions for substrate 1 is
higher than those for substrates 2 and 3, which correꢀ
sponds to the behavior of these substrates in aqueous alꢀ
kaline solutions. However, according to our data, the
reactivity increased with an increase in the substrate hydroꢀ
phobicity in micellar solutions of cationic surfactants.
In the SDS—PEI—water system, hydrolysis is accelꢀ
erated compared to an aqueous solution of PEI (Fig. 7),
and the reactivity of the substrates decreases in the series
(
Fig. 6), in the presence of SDS, the pH of the solution
increases with an increase in the surfactant concentraꢀ
tion. Although we did not carry out special exact studies,
a comparison of the data in Figs 1 and 6 shows that the
region of a sharp pH change coincides with the interval of
SDS concentrations in which combined structures are
formed, according to the conductometric data. These
changes in the pH of the solution confirm convincingly
that the surfactant and polymer molecules interact, probꢀ
ably, via Scheme 2, b.1
26
27
3
We estimated the fraction of protonated PEI groups (α)
by variation of pH of the solution and polymer concenꢀ
tration using potentiometric titration (Table 2). The data
presented show that already at pH 8.5 the fraction of
protonated groups is close to 0.10, while in the kinetic
experiment (at pH 9—10) without a buffer the α value is
rather insignificant, which agrees with the published data
presented above (5%).2 In an SDS solution, with an
increase in the pH, the degree of protonation is still lower.
1
> 2 > 3, i.e., the same tendency is fulfilled as in water
and an aqueous PEI solution. Under the experimental
conditions, the catalytic effect for these substrates, which
is equal to the ratio of the apparent reaction rate constant
in the surfactant—PEI system to the rate constant in an
aqueous solution at the same pH, is 21, 13, and 8 times,
respectively. It is important that the shape of the kinetic
plots and quantitative data characterizing the reactivity of
the substrates in the SDS—PEI—water system differ subꢀ
stantially from the earlier obtained values for individual
SDS—water and PEI—water systems,
that the reaction occurs in the polymer—colloid comꢀ
plexes.
The kinetic data were analyzed using Eq. (1) under
the assumption that the reaction is transferred from the
aqueous pseudoꢀphase to the polymer—colloid aggregates
3
7
,28
Table 2. Degree of protonation of PEI (α) at different pH and
concentrations of the polymer
which confirms
СPEI
α at pH
/
mol L–1
5
.5
6.0
6.5
7.0
7.5
8.0
8.5
0
0
0
0
.01
0.83 0.67 0.56 0.39 0.24 0.17 0.09
0.86 0.72 0.56 0.44 0.34 0.14 0.11
0.83 0.72 0.61 0.50 0.33 0.24 0.11
(
Table 3). There are published examples of the successful
.015
.02
.03
use of the Michaelis—Menten equation, which is norꢀ
mally applied to enzymatic catalysis, for the simulation of
kinetic data in polymeric colloidal solutions.
0.88 0.80
—
0.56 0.39 0.28 0.17
2
9,30
The preꢀ

Surfactant—polyethyleneimine—water system
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
647
3
–1
3
–1
kapp•10 /s
kapp•10 /s
4
3
2
1
0
0
0
0
6
5
4
3
2
1
0
0
0
0
0
0
3
4
1
2
2
1
3
4
0
0
0
.01
0.02
0.03
CSDS/mol L–1
0.01
0.02
0.03
CSDS/mol L–1
Fig. 8. Apparent hydrolysis rate constant of 1 in the
SDS—PEI—water system vs. SDS concentration at different
temperatures, СPEI = 0.1 mol L– : 55 (1), 45 (2), 35 (3),
and 25 °С (4).
Fig. 7. Apparent hydrolysis rate constant for substrates 1—3 in
the SDS—PEI—water system vs. SDS concentration in the abꢀ
sence of a buffer (1, 3; 2, 2; and 3, 1) and for substrate 1 in
1
the presence of the methylmorpholine buffer (4); С
=
PEI
–
1
0
.1 mol L , 45 °С.
Table 3). For the aqueous pseudoꢀphase, we obtained the
–
1
activation enthalpies ∆H = 56.6 kJ mol and activation
w
dominant contribution to the catalytic effect belongs to
the effect of reactant concentrating in the polymer—colꢀ
loid aggregates (see Table 3), whereas a change in the
microenvironment of reactant exerts an unfavorable inꢀ
fluence on the reactivity. The enhancement of the negaꢀ
tive influence of the microenvironment is a reason for a
decrease in the hydrolysis rate in the series of subꢀ
strates 1—3, despite the simultaneous increase in the conꢀ
centrating factor.
–
1
–1
entropies ∆Sw = –100.3 J mol
K . These data agree
with the expected values for the bimolecular reaction.
3
1
The activation parameters for reaction in the cataꢀ
lytic complex (see Table 3) differ insignificantly from
those presented above. We can conclude that the reacꢀ
tion mechanism remains unchanged when the reaction
transfers from the aqueous pseudoꢀphase to the polyꢀ
mer—colloid aggregates, i.e., general base catalysis of hyꢀ
drolysis of the substrate occurs. To exclude completely
the hypothesis on reaction acceleration with an increase
in the SDS concentration due to a significant contribuꢀ
tion of alkaline hydrolysis of substrates at an elevated pH,
we studied the hydrolysis kinetics of substrate 1 at conꢀ
stant pH 7.8 in a methylmorpholine buffer. As can be seen
from the data in Fig. 8, the catalytic effect, whose value is
equal to the effect of the system without a buffer, is also
observed in this case. It should also be taken into account
that the nucleophilic attack of hydroxide ions is impeded
because of their electrostatic repulsion from the negaꢀ
tively charged surface of the SDS aggregates.
For substrate 1, we studied the hydrolysis kinetics at
different temperatures (Fig. 8) and calculated the activaꢀ
tion parameters of reaction in different microphases (see
Table 3. Quantitative analysis of the kinetic data for the hydroꢀ
lysis of compounds 1—3 in the SDS—PEI—water system usꢀ
ing Eq. (1)
Comꢀ
poꢀ
und
T
/°С
KS
KNu
k2,m•104
/L (mol s)–1
Fm
Fc Fm•Fc
L mol–1
1
1
1
1
2
3
25
35
45
55
45
45
3627
73
56
83
82
183
117
5.2
14.2
23
47
5.5
2.6
0.13
0.13
0.13
0.125 111
0.051 257
0.049 168
187
134
163
25
17
21
14
13
8
On the contrary to the inhibition of hydrolysis in an
individual micellar solution of anionic surfactants at
high pH, the observed acceleration of the reaction in
the polymer—colloid system under study can be explained
when assuming that the general basic mechanism of caꢀ
talysis is retained and the contribution of alkaline hydroꢀ
lysis as an alternative or parallel reaction route is negꢀ
ligible.
1804
935
254
629
424
28
Note. ∆Hw = 56.6 kJ mol–1, ∆Sw = –100.3 J mol K–1, ∆Hm
=
–1
–
1
–1 –1
5
5.2 kJ mol , and ∆Sm = –121.7 J mol
K .

648
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
Zakharova et al.
3
–1
kapp•10 /s
resolubilization with the further increase in the SDS conꢀ
centration.
Unlike micellar sphere—cylinder transitions under the
action of organic and inorganic electrolytes, the break in
the plots (see Fig. 9) is not, probably, caused by changes
in the morphology of surfactant aggregates induced by the
electrolytic effect of PEI. At least two arguments in favor
of this assumption are known. First, the change in the rate
constant was observed in the region above the CMC and
also at low SDS concentrations. Second, we have previꢀ
3
0
a
2
1
0
0
0
0
.01
CPEI/mol L–1
7,8
ously observed the sharp change in the conductivity
3
–1
kapp•10 /s
and dielectric constant of a PEI solution at a concentraꢀ
–
1
tion of 0.01 mol L , which is rather close to the PEI
concentration in the break points (see Fig. 9). Therefore,
it seems reasonable to assume that the change in kapp is
caused by structural rearrangements of the intrinsic polyꢀ
electrolyte.
b
2
Thus, in this work we used different physicochemiꢀ
cal methods to study selfꢀorganization in the
SDS—PEI—water system and determined the concentraꢀ
tion boundaries within which polymer—colloid structures
exist. Hydrophobic interactions contribute substantially
to these structures. In parallel we studied the catalytic
effect of this composition in the hydrolysis of phosꢀ
phonates 1—3. Analysis of the kinetic data suggested that
the reaction mechanism is retained when the process is
transferred from the aqueous pseudoꢀphase to polyꢀ
mer—colloid complexes, which is confirmed by the close
activation parameters in the microphases.
0
0
.01
CPEI/mol L–1
3
–1
kapp•10 /s
c
8
4
0
0
.01
0.1
CPEI/mol L–1
Fig. 9. Apparent hydrolysis rate constant of 1 in the
SDS—PEI—water system vs. logarithm of the PEI concentraꢀ
tion at different SDS concentrations (45 °С): 0.01 (a), 0.0005 (b),
References
–
1
1. E. D. Goddard, Colloids Surf., 1986, 19, 255.
and 0.001 mol L (c).
2
3
. E. D. Goddard, J. Colloid Interface Sci., 2002, 256, 228.
. V. A. Kabanov, A. B. Zezin, A. A. Yaroslavov, and D. A.
Topchiev, Usp. Khim., 1991, 60, 595 [Russ. Chem. Rev., 1991,
60 (Engl. Transl.)].
. E. Sokolov, F. Yeh, A. Khokhlov, and V. Ya. Grinberg,
J. Phys. Chem., B, 1998, 102, 7091.
. A. V. Bilalov, I. R. Manyurov, A. Ya. Tret´yakova, and V. P.
Barabanov, Vysokomol. Soedin., Ser. A, 1996, 38, 94 [Polym.
Sci., Ser. A, 1996, 38 (Engl. Transl.)].
One of the priority tasks of our study of the reactivity
of phosphorus esters in organized media is the elucidation
of a relation between the structure of nanoaggregates and
4
5
3
2
their catalytic effect. We have studied the influence of
electrolyteꢀinduced micellar rearrangements on the hyꢀ
drolysis rate of phosphorus esters. Therefore, it was of
interest to carry out a similar study in the presence of a
polyelectrolyte. According to the previously developed
methodology,33 we analyzed the kinetic plots in the semiꢀ
logarithmic coordinates kapp—logCPEI at three fixed SDS
concentrations in the interval below and above the CMC.
The reactivity of substrate 1 changed dramatically at
6
. E. F. Panarin and V. V. Kopeikin, Vysokomol. Soedin., 2002,
4, 2340 [Polym. Sci., 2002, 44 (Engl. Transl.)].
4
7. D. B. Kudryavtsev, R. F. Bakeeva, L. A. Kudryavtseva, L. Ya.
Zakharova, and V. F. Sopin, Izv. Akad. Nauk, Ser. Khim.,
2000, 1510 [Russ. Chem. Bull., Int. Ed., 2000, 49, 1501].
. L. Ya. Zakharova, F. G. Valeeva, D. B. Kudryavtsev, A. R.
Ibragimova, L. A. Kudryavtseva, A. P. Timosheva, and V. E.
Kataev, Kinet. Katal., 2003, 44, 599 [Kinet. Catal., 2003, 44
Engl. Transl.)].
. J. C. Brackman and J. B. F. N. Engberts, Chem. Soc. Rev.,
993, 22, 85.
0. Pat. US 2922810, 1960; Chem. Abstr., 1960, 54, 9848.
8
–
1
0
.007—0.008 mol L PEI (Fig. 9). The absence of a
break in the plot obtained at an SDS concentration of
.001 mol L–1 can be related to the fact that at PEI conꢀ
(
0
9
–
1
centrations lower than 0.01 mol L homogeneity in this
system was violated, which impeded to study this concenꢀ
tration interval. Probably, at specific SDS to PEI ratios,
stoichiometric complexes are formed2 followed by their
1
1
11. V. I. Baranova, E. E. Bibik, N. M. Kozhevnikov, I. S. Lavrov,
,22
and V. A. Malov, Praktikum po kolloidnoi khimii [Laboratory

Surfactant—polyethyleneimine—water system
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 3, March, 2005
649
Works on Colloidal Chemistry], Vysshaya Shkola, Moscow,
25. R. F. Bakeeva, V. E. Bel´skii, L. A. Kudryavtseva, A. T.
Chetveryakova, and B. E. Ivanov, Izv. Akad. Nauk SSSR,
Ser. Khim., 1987, 756 [Bull. Acad. Sci. USSR, Div. Chem.
Sci., 1987, 36, 685 (Engl. Transl.)].
26. L. Ya. Zakharova, F. G. Valeeva, R. A. Shagidullina, and
L. A. Kudryavtseva, Izv. Akad. Nauk, Ser. Khim., 2000, 1366
[Russ. Chem. Bull., Int. Ed., 2000, 49, 1360].
27. L. Y. Zakharova, R. A. Shagidullina, and L. A. Kudryavtseva,
J. Mol. Liq., 2001, 91, 193.
28. L. Ya. Zakharova, S. B. Fedorov, L. A. Kudryavtseva, A. M.
Zotova, and V. E. Bel´skii, Izv. Akad. Nauk SSSR, Ser.
Khim., 1987, 2161 [Bull. Acad. Sci. USSR, Div. Chem. Sci.,
1987, 36, 2003 (Engl. Transl.)].
1
983, 215 pp. (in Russian).
1
2. K. Martinek, A. K. Yatsimirsky, A. V. Levashov, and I. V.
Beresin, Micellization, Solubilization, and Microemulsions,
Ed. K. L. Mittal, Plenum Press, New York—London,
1
977, 489.
3. S. M. Bystryak, M. A. Winnik, and J. Siddiqui, Langmuir,
999, 15, 3748.
4. F. M. Witte and J. B. F. N. Engberts, J. Org. Chem., 1987,
2, 4767.
5. Z. Hou, Z. Li, and H. Wang, Colloid Polym. Sci., 1999,
77, 1011.
1
1
1
1
1
1
5
2
6. Y. Touhami, D. Rana, G. N. Neale, and V. Hornof, Colloid
Polym. Sci., 2001, 279, 297.
7. E. A. Litmanovich, V. A. Kasaikin, A. B. Zezin, and V. A.
Kabanov, Dokl. Akad. Nauk, 2000, 373, 350 [Dokl. Chem.,
29. P. D. Miller, H. O. Spivey, S. L. Copeland, R. Sanders,
A. Woodruff, D. Gearhart, and W. T. Ford, Langmuir, 2000,
16, 108.
2
000 (Engl. Transl.)].
8. P. L. Dubin, M. E. Curran, and J. Hua, Langmuir,
990, 6, 707.
30. L. R. Lawin, W. K. Fife, and C. X. Tian, Langmuir, 2000,
16, 3583.
1
1
2
2
2
2
2
1
31. N. A. Loshadkin, in Toksichnye efiry kislot fosfora [Toxic
Phosphorus Esters], Mir, Moscow, 1964, 460 (in Russian).
32. D. B. Kudryavtsev, L. Ya. Zakharova, and L. A.
Kudryavtseva. Zh. Fiz. Khim., 2003, 77, 443 [Russ. J. Phys.
Chem., 2003, 77 (Engl. Transl.)].
9. T. K. Bronich, T. Cherry, S. V. Vinogradov, A. Eisenberg,
V. A. Kabanov, and A. V. Kabanov, Langmuir, 1998, 14, 6101.
0. Y. Li, S. M. Ghoreishi, J. Warr, D. M. Bloor, J. F. Holzwarth,
and E. WynꢀJones, Langmuir, 2000, 16, 3093.
1. M. A. Winnik, S. M. Bystryak, C. Chassenieux, V. Strashko,
P. M. Macdonald, and J. Siddiqui, Langmuir, 2000, 16, 4495.
2. R. Meszaros, L. Thompson, M. Bos, I. Varga, and T. Gilany,
Langmuir, 2003, 19, 609.
3. Y. Li, S. M. Ghoreishi, J. Warr, D. M. Bloor, J. F. Holzwarth,
and E. WynꢀJones, Langmuir, 2000, 16, 3098.
4. R. F. Bakeeva, L. A. Kudryavtseva, V. E. Bel´skii, and B. E.
Ivanov, Zh. Obshch. Khim., 1983, 53, 1058 [J. Gen. Chem.
USSR, 1983, 53 (Engl. Transl.)].
33. L. Y. Zakharova, D. B. Kudryavtsev, L. A. Kudryavtseva,
A. I. Konovalov, Y. F. Zuev, N. N. Vylegzhanina, N. L.
Zakhartchenko, and Z. S. Idiatullin, Mendeleev Commun.,
1999, 245.
Received December 10, 2003;
in revised form September 14, 2004