Alkylated 1,4-diazabicyclo[2.2.2]octanes: Self-association, catalytic properties, and biological activity

Article abstract of DOI:10.1007/s11172-012-0016-7

Aggregation of 1-hexadecyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide in the presence of diethyl 4-nitrophenyl phosphate was studied using 1H NMR spectroscopy. The quantitative characteristics of the aggregation were determined. The data obtained were use

Full text of DOI:10.1007/s11172-012-0016-7

Russian Chemical Bulletin, International Edition, Vol. 61, No. 1, pp. 113—120, January, 2012
113
Alkylated 1,4ꢀdiazabicyclo[2.2.2]octanes:
selfꢀassociation, catalytic properties, and biological activity*
E. P. Zhiltsova,a T. N. Pashirova,a R. R. Kashapov,a N. K. Gaisin,b O. I. Gnezdilov,c S. S. Lukashenko,a
A. D. Voloshina,a N. V. Kulik,a V. V. Zobov,a L. Ya. Zakharova,a and A. I. Konovalova
aA. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center of the Russian Academy of Sciences,
8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843 2) 273 2253. Eꢀmail: lucia@iopc.ru
bKazan State Technological University,
68 ul. K. Marksa, 420015 Kazan, Russian Federation
cE. K. Zavoisky Kazan Institute of Physical Engineering, Kazan Research Center of the Russian Academy of Sciences,
10/7 ul. Sibirskii trakt, 420029 Kazan, Russian Federation
Aggregation of 1ꢀhexadecylꢀ4ꢀazaꢀ1ꢀazoniabicyclo[2.2.2]octane bromide in the presence
of diethyl 4ꢀnitrophenyl phosphate was studied using 1H NMR spectroscopy. The quantitative
characteristics of the aggregation were determined. The data obtained were used to explain the
catalytic effect of micelles on the hydrolysis of the phosphate. It was found that the aggregation
properties and biological activity of alkylated monoꢀ and dicationic 1,4ꢀdiazabicycloꢀ
[2.2.2]octanes are correlated.
Key words: alkylated 1,4ꢀdiazabicyclo[2.2.2]octanes, association, critical micelle concenꢀ
tration, aggregation number, hydrolysis, biological activity.
Solutions of surfactants are widely used in modern
technology, including such areas as the synthesis of nanoꢀ
particles and mesoporous materials, dispersion of carbon
nanotubes, oil extraction, catalysis, biodiagnostics, etc.1—5
Cationic surfactants are of particular research interest for
a number of reasons. Having a hydrophobic fragment and
positively charged groups, cationic surfactants can insert
themselves into lipid bilayers and efficiently interact with
intracellular membranes, the phosphate groups of nucleic
acids, and other negatively charged biosubstances. This
makes cationic surfactants very attractive for design of
nonviral vectors, carriers for drugs and diagnostic agents,
and antimicrobial medicines. Cationic surfactants are traꢀ
ditionally employed in micellar catalysis for decomposiꢀ
tion of organophosphorus ecotoxicants via basic hydrolyꢀ
sis.6 At the same time, the head groups of cationic surfacꢀ
tants substantially vary in chemical structure, including
the charged atom (N, P, or S) and its substituents; the
presence of cyclic head groups is also possible. This allows
systematic investigations of homologous series to find
structure—property correlations. The use of surfactants
containing aryl7 and various functional substituents in the
head group,8 as well as passing from hexadecyl(trimethyl)ꢀ
ammonium bromide to hexadecylpyridinium bromide,9
enhances the catalytic activity of micellar systems in the
hydrolysis of phosphorus acid esters. Only few cationic
surfactants with a bicyclic head group have been docuꢀ
mented as micelleꢀforming catalytic agents.10,11 At the
same time, such surfactants are better ligands to metal
ions and thus can enhance the catalytic activity of systems
by forming metallomicelles10 rather than ordinary miꢀ
celles; in addition, such surfactants can be functionalized
and transformed from the monoꢀ to dicationic type.11
In the present work, we studied the catalytic and bioꢀ
logical activities of some cationic surfactants (1—6) conꢀ
taining a bicyclic fragment in the head group and analyzed
the results obtained with consideration of their micelleꢀ
forming and solubilizing properties.
n = 12 (1), 14 (2), 16 (3), 18 (4)
R = H (5), OH (6)
For our catalytic activity studies, we carried out basic
hydrolysis of diethyl 4ꢀnitrophenyl phosphate (7) in a miꢀ
cellar solution of monocationic 1,4ꢀdiazabicyclo[2.2.2]ꢀ
octane (3) (Scheme 1). Prior to this experiment, we exꢀ
amined the aggregation of cationic surfactant 3 in the
presence of phosphate 7 by FTꢀNMR spectroscopy with
a pulsed magnetic field gradient (PFG FTꢀNMR) to estiꢀ
* Dedicated to Academician of the Russian Academy of Sciences
V. N. Charushin on the occasion of his 60th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 110—118, January, 2012.
1066ꢀ5285/12/6101ꢀ113 © 2012 Springer Science+Business Media, Inc.

114
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Zhiltsova et al.
with a pulsed gradient G of the polarizing magnetic field. The
spectrometer was equipped with a Pulsed Field Gradient attachment
producing gradient strengths up to 0.53 T m–1. The D values were
determined from the decline of the integral intensity of the stimꢀ
ulated spin echo signals for the protons of different groups in the alkyl
and cyclic fragments of the surfactant; the decline was caused by
a field gradient change in a sequence of three 90ꢀpulses:
mate the influence of the solubilizate on the aggregation
properties of the surfactant and quantitatively describe the
binding of phosphate 7 by micelles 3. The hydrolysis kiꢀ
1
netics of phosphate 7 was studied by H and 31P NMR
spectroscopy and UV spectrophotometry. In addition, we
tested the biological activity of monoꢀ and dicationic
1,4ꢀdiazabicyclo[2.2.2]octane derivatives 1—6 and studied
its relationship with the aggregation properties of the
surfactants under consideration.
,
(1)
where  is the gyromagnetic ratio of the nucleus (proton),  is the
gradient pulse length, and  is the pulse spacing. Depending on
the magnitude of the selfꢀdiffusion coefficients measured, the
constant times  and  were varied from 5 to 10 ms and from
50 to 70 ms, respectively. These times are much longer than the
time of molecular exchange between the free and micellar comꢀ
ponents of the solution. The coefficients D were determined by
averaging the values obtained from the 1H NMR signals for
different fragments of the surfactants and for the phenyl protons
of solubilizate 7. The errors of D determination were ~2 and
~5% at high and low concentrations of the surfactant, respecꢀ
tively. The temperature of samples was maintained with a therꢀ
mostatic system of the spectrometer.
Scheme 1
1H and 31P NMR spectra were recorded on a Bruker AVANCE
400 instrument (162 MHz); 31P chemical shifts were referenced
to H3PO4 as the external standard.
Experimental
The kinetics of the reactions was studied by measuring the
increasing optical density of the absorption band of the 4ꢀnitroꢀ
phenolate anion at 400 nm on a Specord UVꢀVis spectrophotoꢀ
meter in temperatureꢀcontrolled cells. The apparent reaction
rate constants kapp (s–1) were determined from a firstꢀorder equation.
Compounds 1—4 were prepared from 1,4ꢀdiazabicycloꢀ
[2.2.2]octane (DABCO) and appropriate alkyl bromides as deꢀ
scribed earlier.12
1ꢀEthylꢀ4ꢀhexadecylꢀ1,4ꢀdiazoniabicyclo[2.2.2]octane dibroꢀ
mide (5). A solution of cationic surfactant 3 (3 g, 7.2 mmol) and
ethyl bromide (7.8 g, tenfold excess) in acetonitrile (30 mL) was
refluxed for 10 h. After the reaction was completed, the solvent
and unreacted ethyl bromide were removed. The precipitate of
the salt that formed was dissolved in a small amount of ethanol,
reprecipitated from the hot solution with acetone, and dried
The initial concentration of compound 7 was 5•10–5 mol L–1
.
Results and Discussion
The plots of the coefficients D of surfactant 3 and the
solubilizate (phosphate 7) in D2O vs. the total concentraꢀ
tion of the surfactant Ct are shown in Fig. 1. Below the
critical micelle concentration (CMC), the D values for the
surfactant and the solubilizate are constant (4.2•10–10 and
6.2•10–10 m2 s–1, respectively) (see Fig. 1, inset). Thereꢀ
fore, the molecules of surfactant 3 and phosphate 7 at subꢀ
CMC concentrations diffuse in solution like free monoꢀ
meric species. In addition, the vicinity of the inflectional
areas (see Fig. 1, inset) suggests that the selfꢀdiffusion of
solubilizate molecules is related to the selfꢀdiffusion of
surfactant molecules forming micelles.
According to the published data,13 CMC can be deterꢀ
mined most precisely from a plot of Dobs vs. 1/Ct (Fig. 2).
The breakpoints on plots 1 and 2 correspond to the surfacꢀ
tant concentrations of 9•10–4 and 1.6•10–3 mol L–1, reꢀ
spectively. The higher CMC determined from plot 2 can
be attributed to the fact that the decreasing selfꢀdiffusion
coefficient of the surfactant reflects not only micellization
but also the formation of premicellar aggregates that canꢀ
not solubilize organic substrates because of their low agꢀ
gregation numbers. A similar discrepancy in CMC values
is characteristic for probeꢀinvolving experiments.14 Earliꢀ
in vacuo. Yield 2.95 g (78%), m.p. 216—218 C. IR (KBr), /cm–1
:
2960, 2920, 2850, 1464, 1397, 1113, 1058, 855, 806, 724.
1H NMR (D2O), : 0.85 (t, 3 H, N+CH2CH2(CH2)13CH3,
J = 6.6 Hz); 1.28—1.40 (m, 26 H, N+CH2CH2(CH2)13CH3));
1.44 (t, 3 H, N+CH2CH3, J = 7.3 Hz); 1.88 (br.s, 2 H,
N+CH2CH2(CH2)13CH3); 3.70—3.71 (m, 4 H, N+CH2CH2ꢀ
(CH2)13CH3 + N+CH2CH3); 4.05—4.15 (m, 12 H, 2 N+(CH2)3).
4ꢀHexadecylꢀ1ꢀhydroxyethylꢀ1,4ꢀdiazoniabicyclo[2.2.2]ꢀ
octane dibromide (6). A solution of cationic surfactant 3 (1 g,
2.4 mmol) and 2ꢀbromoethanol (0.359 g, 1.2ꢀfold excess) in
acetonitrile (20 mL) was refluxed for 20 h. The precipitate of
the salt that formed was filtered off, recrystallized from ethanol,
and dried in vacuo. Yield 0.82 g (63%), m.p. 190—192 C.
IR (KBr), /cm–1: 3346, 2958, 2920, 2851, 1468, 1398, 1378,
1
1123, 1087, 1056, 865, 722. H NMR (D2O), : 0.86 (t, 3 H,
N+CH2CH2(CH2)13CH3, J = 8.6 Hz); 1.27—1.39 (m, 26 H,
N+CH2CH2(CH2)13CH3); 1.86 (br.s, 2 H, N+CH2CH2ꢀ
(CH2)13CH3); 3.79 (s, 2 H, CH2CH2OH); 4.11—4.18 (m, 14 H,
2 N+(CH2)3 + N+CH2CH2OH).
Diethyl 4ꢀnitrophenyl phosphate (7) (Sigma) was used as
purchased.
The dependence of the selfꢀdiffusion coefficient D of the
surfactant molecules and solubilizate (phosphate 7) molecules
was measured on a Bruker AVANCE 400 FTꢀNMR spectrometer

Alkylated 1,4ꢀdiazabicyclo[2.2.2]octanes
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 1, January, 2012
115
Dobs•1010/m2 s–1
pf = Cf/Ct, pm = Cm/Ct, pf = 1 – pm.
(3)
Dobs•1010/m2 s–1
6
4
2
Using Eqs (2) and (3), one can derive an equation for
the concentrations of the free (Cf) and micellar compoꢀ
nents (Cm) of the surfactant and the solubilizate:
2
1
6
2
Cf = Ct – Cm = Ct(Dobs – Dm)/(Df – Dm).
(4)
5
Ct•103/mol L–1
It is thought that the selfꢀdiffusion coefficient of surꢀ
factant molecules is virtually insensitive to micellization
and that its value at concentrations above CMC differs
only slightly from that at CMC (Df,CMC); for superꢀCMC
values, an insignificant correction is applied to allow for
the hindrances presented by micelles:
0
1
2
3
4
3
1
2
1
3
Df = Df,CMC(1 + /2)–1
,
0
10
20
30
Ct•103/mol L–1
where  is the volume fraction of the micellar surfactant;
 = M(Ct – CMC)/, where M and  are the molar mass
and density of the surfactant, respectively. Its molar mass
(0.393 kg mol–1) was determined with allowance for Br–
counterions bound, the binding degree taken to be 0.7.18
Fig. 1. Plots of the observed selfꢀdiffusion coefficient of cationic
surfactant 3 (1) and phosphate 7 (2) vs. the surfactant concentraꢀ
tion at 30 C (C7 = 10–3 mol L–1); the tangent to curve 1 at high
surfactant concentrations (3). The inset: curves 1 and 2 at low
surfactant concentrations.
The molar mass of the solubilizate is 0.275 kg mol–1
.
The coefficients D for micelles (Dm) were determined
from a tangent 3 (see Fig. 1) at high concentrations of
surfactant 3. This approach is based on data15 obtained with
hexamethyldisiloxane as a hydrophobic probe. We found
that the concentration dependence of D for the solubiliꢀ
zate (Dm) coincides with that for the surfactant 3 (Dobs) at
C3 > 10–2 mol L–1. At C3 = 2•10–3—1•10–2 mol L–1, the
concentration dependence of Dm coincides with the tangent
er,15 we have found that the CMC of cationic surfactant 3
in D2O containing no substrate is 8.5•10–4 mol L–1; i.e.,
the presence of phosphate virtually does not change the
micelleꢀforming properties of the surfactant.
When analyzing the experimental results, we used the
pseudophase model of micellization, or the twoꢀstate modꢀ
el.13,16,17 Within this approach, the observed D value of
the surfactant and the solubilizate (provided that the free
and micellar components of a solution undergo rapid exꢀ
change) can be represented as the contributions of moleꢀ
cules in the free (Df) and micellar states (Dm):
to the curve Dobs of the surfactant for C3 > ~10–2 mol L–1 15
.
With known Dobs, Df, and Dm values, one can calculate by
formula (4) the concentrations of the surfactant and the
solubilizate in the free and micellar states.
The results obtained can be used to estimate the numꢀ
ber of surfactant and solubilizate (phosphate) molecules
in micelles. The volume of a micelle (Vm) is a sum of the
volumes occupied by surfactant (VSurf) and solubilizate
Dobs = pfDf + pmDm,
(2)
where pf and pm are the relative contents of the free and
micellar components in solution, respectively,
molecules (VPh
)
Dobs•1010/m2 s–1
Vm = VSurfnSurf + VPhnPh
,
(5)
where VSurf = MSurf/(SurfNA) is the volume occupied by
a surfactant molecule, VPh = MPh/(PhNA) is the volume
occupied by a solubilizate molecule in the micelle, MSurf
and MPh are the molecular masses of the surfactant and
the solubilizate, Surf and Ph are the densities of the surꢀ
factant and the solubilizate, nSurf and nPh are the numbers
of surfactant and solubilizate molecules in the micelle,
and NA is Avogadro´s number. With consideration to the
aggregation number of the micelle N = nSurf + nPh, Eq. (5)
can be rewritten as follows:
2
6
5
1
4
3
2
1
0
1
2
3
1/Ct•10–3/L mol–1
.
(6)
Fig. 2. Plots of the observed selfꢀdiffusion coefficient of cationic
surfactant 3 (1) and phosphate 7 (2) vs. the reciprocal concenꢀ
tration of the surfactant at 30 C.
If formula (6) is supplemented with a solubilization
factor defined as  = nPh/nSurf = Cm,Ph/Cm,Surf, where

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 1, January, 2012
Zhiltsova et al.
Cm,Ph/(CPh – Cm,Ph
)
Cm,Ph and Cm,Surf are the concentrations of solubilizate
and surfactant molecules in micelles, then the expression
for the micelle aggregation number takes the form
5
4
3
2
1
0
N = VmNA(1 + )/[MSurf/Surf + (MPh/Ph)].
(7)
Under the assumption that micelles are spherical speꢀ
cies, the micelle volume can be calculated by the formula
Vm = (4/3)R3, where R is the radius of "dry" (i.e., deꢀ
prived of the hydration shell) micelles. With allowance for
only one layer of hydrated water present in the hydration
shell of micelles, the radius of dry micelles can be defined
as a difference between the hydrodynamic radius of miꢀ
celles Rh calculated by the Stokes—Einstein equation
Rh = kT/(6Dm),
and the diameter of water molecules d; so R = Rh – d. The
viscosity coefficient of a micellar solution can be calculatꢀ
ed by the Einstein—Simha formula19
0
0.01
0.02
0.03
Cm,Surf/mol L–1
 =  (1 + 2.5),
0
Fig. 3. Plot of the ratio of the molar concentrations of phosꢀ
phate 7 in the micellar and aqueous phases vs. the concentration
of cationic surfactant 3 in the micelles.
where 0 = 0.969 cP is the viscosity of the pure solvent
(D2O at 30 C).20 The densities of the surfactant and the
solubilizate were taken to be 103 kg m–3. The number of
solubilizate molecules in micelles was calculated by the
formula
phate on the initial segment of the plot is a linearly inꢀ
creasing function of the surfactant concentration with
a tendency toward saturation. The partition coefficient
calculated from the slope of the linear segment is 211,
which agrees well with previous data.18
Solubilization by surfactant micelles changes not only
the quantitative characteristics of the micellar system but
also the reactivity of the solubilizate, which is evident from
the basic hydrolysis of phosphate 7 (see Scheme 1).
The hydrolysis of phosphate 7 gives products 8 and 9,
regardless of the presence of the surfactant in the system
(1H and 31P NMR data). The chemical shifts of their
signals are given in Table 2.
The hydrolysis kinetics of phosphate 7 was studied by
1H NMR spectroscopy; the data obtained are shown in
Fig. 4. Both in the absence (see Fig. 4, a) and in the
presence of surfactant 3 (see Fig. 4, b), we observed the
decreasing intensity of the signal for phosphate 7 (the H
and H protons) and the increasing intensities of the sigꢀ
nals for products 8 (the OCH2 protons) and 9 (the H and
H protons) during the hydrolysis reaction (see Scheme
1). The apparent rate constants of the hydrolysis are
2.5•10–4 and 9.1•10–4 s–1 in the absence and in the presꢀ
ence of a 0.02 M solution of the surfactant, respectively;
i.e., a micellar solution of cationic surfactant 3 catalyzes
the reaction by a factor of 3.6.
nPh = N/(1 + 1/).
The experimental and calculated parameters are sumꢀ
marized in Table 1. It can be seen that an increasing conꢀ
centration of surfactant 3 in solution increases the relative
fraction of surfactant molecules in micelles, the total conꢀ
centration of micelleꢀbound phosphate molecules, and the
radius and aggregation number of micelles but decreases
the number of solubilizate molecules in micelles.
Using the data obtained, one can calculate the coeffiꢀ
cient of partition of the solubilizate between the micellar
and aqueous phases from the ratio of the corresponding
molar concentrations: CPh/(1 – Cm,Ph), where CPh is the
total concentration of phosphate 7 in solution.18 It can be
seen in Fig. 3 that the fraction of the micelleꢀbound phosꢀ
Table 1. Parameters of the system cationic surfactant 3—phosꢀ
phate 7—D2O at 30 C*
Сt•103 Сm,Surf•103 Сm,Ph•104 Dm•1011
R

N nPh
/m2 s–1 /Å
mol L–1
3
5
10
20
48
2.2
4.3
9.5
19.5
47.0
2.9
4.5
6.3
8.0
8.5
7.6
7.0
6.6
6.2
5.2
28.3 0.134 151 18
30.3 0.095 183 16
32.5 0.066 224 14
34.3 0.040 261 10
The catalytic effect of micelles 3 on the hydrolysis of
phosphate 7 was confirmed by spectrophotometric meaꢀ
surements. The plot of the apparent rate constant of the
hydrolysis of phosphate 7 vs. the surfactant concentration
is shown in Fig. 5; the curve shows a distinct peak. Such a
37.5 0.018 338
6
* C7 = 10–3 mol L–1
.

Alkylated 1,4ꢀdiazabicyclo[2.2.2]octanes
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 1, January, 2012
117
Table 2. Chemical shifts  of the 1H and 31P NMR signals
for compounds 7—9 in solutions of cationic surfactant 3
(0.02 mol L–1) at 35 C
kapp•104/s–1
a
2.0
Comꢀ
pound


Н
P
Н
Н
OCH2
CH3
1.5
1.0
0.5
7
8
9
–1.59 7.41; 7.42b 8.31; 8.31b 4.29; 4.30b 1.33b
–2.29
—
—
—
3.88; 3.89b 1.22b
6.40; 6.49b 7.95; 8.04b
—
—
a For the designations of the protons, see Scheme 1.
b The chemical shifts in the absence of the surfactant.
0.01
0.02
Ct•103/mol L–1
profile is typical of micelleꢀcatalyzed processes,18 suggestꢀ
ing the formation of a micelle—substrate complex via bindꢀ
ing of phosphate molecules by surfactant aggregates. The
kinetic data (see Fig. 5) were analyzed in terms of the
pseudophase model of micellar catalysis:18
Fig. 5. Plot of the apparent rate constant of the hydrolysis of
phosphate 7 vs. the concentration of cationic surfactant 3 at
25 C (CNaOH = 10–3 mol L–1).
where k2,app (L mol–1 s–1) is the apparent secondꢀorder
rate constant obtained by dividing kapp by the concentraꢀ
tion of the nucleophile, k2,0 and k2,m (L mol–1 s–1) are the
secondꢀorder rate constants in the solvent bulk and the
micellar pseudophase, respectively, V (L mol–1) is the
molar volume of the surfactant, and KPh and KNu (L mol–1)
are the micelleꢀbinding constants of the phosphate and
the nucleophile, respectively.
The parameters of the micelleꢀcatalyzed hydrolysis of
phosphate 7 in the presence of surfactant 3 at 25 C for
CNaOH = 10–3 mol L–1 and C7 = 5•10–5 mol L–1 were
calculated by Eq. (8) and are given below
,
(8)
a
I (arb. units)
100
2
80
60
40
20
0
–1
a
k2,m
KPh
L mol–1
3800 70
KNu (kapp•k0
)
Fm Fc
max
/L mol–1 s–1
1
0.0012
23
0.125 180
0
50
100 150 200
250 300
t/min
a k0 is the apparent rate constant of the hydrolysis of phosphate 7
in the absence of any surfactant.
I (arb. units)
100
Note the high micelleꢀbinding constant of phosphate 7
(KPh) and a 23ꢀfold increase in its hydrolysis rate in the
presence of surfactant 3. In the context of the pseudophase
model, the maximum acceleration of the reaction is deꢀ
scribed by the equation
b
2´
3´
80
60
40
20
0
,
(9)
~
where the first cofactor on the rightꢀhand side reflects the
change in the microenvironment of the reagents upon their
passage from the solvent into the micellar phase (Fm) and
the second cofactor reflects the concentration of the reꢀ
agents in the micellar phase (Fc).
Clearly, the concentration factor (Fc = 180) makes
a major contribution to the reaction acceleration, while
the microenvironment factor (Fm < 1) lowers the reaction
rate. Some discrepancy in the quantitative parameters
1´
0
20
40
60
80
100
t/min
Fig. 4. Integral intensity profiles of the 1H NMR signals for
substrate 7 (1, 1´) and reaction products 8 (2, 2´) and 9 (3)
during the hydrolysis of phosphate 7 in the absence (a) and in the
presence of cationic surfactant 3 (b) at 35 C (C7 = 10–3 mol L–1
C3 = 0.02 mol L–1, CNaOH = 0.02 mol L–1).
,

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Russ.Chem.Bull., Int.Ed., Vol. 61, No. 1, January, 2012
Zhiltsova et al.
obtained by NMR spectroscopy and spectrophotometry is
quite explainable. The specificity of either technique reꢀ
quires a special algorithm and individual experimental conꢀ
ditions, including the concentrations of the reagents and
the reaction times. The slightly higher rate constants deꢀ
termined from NMR data are due to the higher pH value
of the solution. The binding constant calculated for phosꢀ
phate 7 from spectrophotometric data (see above) is higher
than that found from NMR data; this may be attributed to
the presence of NaOH, which causes salting the organic
substrate out of the aqueous phase into the micellar one.
At the same time, the revealed trends agree well with, and
complement, each other. For instance, the calculated high
binding and partition constants of the phosphate provide
clear explanation to the catalytic effect of micelles as
a result of concentration of the reagents and to the deꢀ
creasing reaction rate constant with an increase in the
surfactant concentration (see Fig. 5) as a result of dilution
of the reagents in the micellar phase (see Table 1, the
decreasing number of phosphate molecules per micelle).
Thus, the micellization of monocationic 1,4ꢀdiazabicycloꢀ
[2.2.2]octane derivative 3 substantially affects the apparꢀ
ent rate constants of the basic hydrolysis of micelleꢀbound
phosphate 7.
Another area of our research is design of polyfunctionꢀ
al nanosystems21 combining a number of practically useꢀ
ful properties such as solubilizing and catalytic (or inhibiꢀ
tive) activity and anticorrosive and antimicrobial effects.
Such systems can be used, e.g., under the operating condiꢀ
tions of oilꢀfield equipment.22 In this case, the high values
of some of a system´s parameters should not serve as
a system performance criterion; instead, it is advisable to
design systems with a set of properties comparable with
those of known analogs. In the context of this approach,
we tested alkylated DABCO derivatives for biological acꢀ
tivity and tried to find a correlation between their antiꢀ
microbial activity and aggregation characteristics.
electrostatic and hydrophobic interactions with cell memꢀ
branes.23 The antimicrobial activity of a surfactant largely
depends on the length of its alkyl radical; in homologous
series, this activity becomes stronger as the number of
carbon atoms (n) increases to 12—16.24 However, the corꢀ
relation between antimicrobial and aggregation properties
still remains a controversial problem. Here we estimated
the bacteriostatic, fungistatic, bactericidal, and fungicidal
effects of quaternized DABCO derivatives on the indicaꢀ
tor test strains of microorganisms Staphylococcus aureusꢀ
209 P (St. aureus), Escherichia coli F50 (E. coli), Bacillus
cereus 8035 (B. cereus), Pseudomonas aeruginosa 9027 (Ps.
aeruginosa), Trichophyton gipseum (Tr. gipseum), Aspergilꢀ
lus niger (Asp. niger), and Candida albicans (C. alb.) and
studied a relationship between the antimicrobial and miꢀ
celleꢀforming properties for the above homologous series.
Antibacterial (ciprofloxacin (10)) and antifungal drugs
(amphotericin B (11)), as well as hexadecyl(trimethyl)ꢀ
ammonium bromide (12), which is structurally similar to
the cationic surfactants under study, served as reference
compounds. The results obtained are summarized in
Tables 3 and 4.
We found that the acute toxicity of compounds 1, 2,
and 3 injected intraperitoneally into laboratory mice is
LD50 = 61.1, 50.9, and 61.1 mg kg–1, respectively. Acꢀ
cording to the toxicity classification,25 these compounds
can be rated as moderately toxic (toxicity class III); they
are less toxic by a factor of ~2.5 than surfactant 12
(LD50 = 24.0).
It turned out that surfactants 1—6 exhibit high antiꢀ
microbial activity often against both bacterial and fungal
strains and are comparable in efficiency with the reference
drugs. When the effects of the homologous compounds
studied are differential, their antimicrobial properties
largely depend on the length of the hydrocarbon radical
and are best for n = 18. This trend holds for almost all the
test strains and is especially pronounced for static activity.
Some of the compounds studied are superior to surfacꢀ
tant 12 in antimicrobial activity. The influence of the head
group can clearly be seen with St. aureus: replacement of
Surfaceꢀactive quaternary ammonium salts are known
to exhibit antimicrobial activity due to the presence of the
positively charged site and an alkyl radical, which ensure
Table 3. Bacteriostatic and fungistatic effects of monoꢀ and dicationic 1,4ꢀdiazabicyclo[2.2.2]octane derivatives
Surfactant
Bacteriostatic and fungistatic effects/g mL–1
St. aureus
E. coli
B. cereus Ps. aeruginosa
Tr. gipseum
Asp. niger
C. alb.
1
2
3
4
5
6
10
11
12
12.5
3.1
0.3
0.3
0.5
0.5
0.25
—
250
62.5
6.3
6.3
7.8
6.3
0.5
—
31.3
7.8
1.9
1.9
1.9
1.9
0.25
—
3.1
>500
>500
500
500
500
500
0.5
—
250
>500
500
62.5
15.6
250
62.5
—
>500
>500
500
125
>500
500
–
125
62.5
3.1
0.78
31.3
3.1
–
–
31.3
20
62.5
–
3.1
0.5
6.3

Alkylated 1,4ꢀdiazabicyclo[2.2.2]octanes
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 1, January, 2012
119
Table 4. Bactericidal and fungicidal effects of monoꢀ and dicationic 1,4ꢀdiazabicyclo[2.2.2]octane derivatives
Surfactant
Bactericidal and fungicidal effects/g mL–1
St. aureus
E. coli
B. cereus
Ps. aeruginosa
Tr. gipseum
Asp. niger
C. alb.
1
2
3
4
5
6
10
11
12
>500
500
5
5
50
50
0.25
—
>500
>500
>500
>500
>500
>500
0.5
>500
>500
500
500
500
500
0.25
—
>500
>500
>500
>500
>500
>500
0.5
>500
>500
500
31.3
>500
500
—
31.3
500
>500
>500
>500
500
>500
>500
–
>500
500
50
5
125
50
—
0.39
50
—
>500
—
>500
20
>500
50
500
the head group in structure 12 by a bicyclic fragment (catꢀ
ionic surfactant 3) enhances the bactericidal effect by an
order of magnitude (see Table 4). It should also be noted
that the antifungal effect of compound 4 on Tr. gipseum
and C. alb. is much higher than those of compounds 12
and 3. The fungistatic effects of the octadecyl homolog on
these strains are higher by factors of 2—4 and 4, respecꢀ
tively, (see Table 3) and its fungicidal effects, by factors of
16 and 10 (see Table 4).
The presence of a second charged site is unfavorable
for antifungal activity: compound 5 is less efficient than
compound 3 against Tr. gipseum and C. alb. by factors of 4
and 10, respectively. However, the antimicrobial effect on
B. cereus, E. coli, and St. aureus remains virtually unꢀ
changed.
Therefore, introduction of a bicyclic fragment into
a cationic surfactant is of interest for the design of antiꢀ
microbial (notably, antifungal) drugs with low toxicity
for mammals; the best effect can be achieved by increasing
the alkyl chain length in surfactants of this type to
optimize the ratio of their lipophilic and hydrophilic
properties.
There are different ways of suppressing the bacterial
and fungal activity by synthetic surfactants; these ways are
contributed by several components. Obviously, the presꢀ
ence of a positively charged head group ensures, as a first
step, electrostatic interactions with both cell membranes
and a peptidoglycan layer containing negatively charged
carboxy groups. The content of the peptidoglycan compoꢀ
nent in the cell wall of Gramꢀpositive bacteria is higher by
nearly an order of magnitude (90%) than that in Gramꢀ
negative bacteria (~10%), which can be responsible for
the different levels of activity of the cationic surfactants
against bacteria of this type (see Table 3). The impact of
a surfactant on the membrane structure integrity of any
cell depends on its ability to insert itself into lipid bilayers
and thus the lipophilic nature of the surfactant is crucial
here. It is not improbable that the specific features of the
antimicrobial activity of this homologous series are subꢀ
stantially determined by the bicyclic fragment. When a surꢀ
factant is inserted into a lipid cell membrane, the rigid
bicyclic structure can irreversibly change the packing of
bioamphiphiles. In addition, the activity of a bicyclic surꢀ
factant depends on the charge density at its head groups,
which can appreciably differ from typical values of cationꢀ
ic surfactants.
The fact that the cationic surfactants exhibit antimiꢀ
crobial properties in concentrations considerably below
CMC suggests the participation of their individual moleꢀ
cules. However, the presence of organic substrates, as well
as an increase in the ionic strength of solution, can subꢀ
stantially decrease CMC.26 Therefore, it is not improbable
that the antimicrobial activity is contributed by aggregatꢀ
ed surfactant molecules. In addition, interactions of surꢀ
factants with bioamphiphiles always implies the formaꢀ
tion of local mixed structures and should correlate with
the aggregation activity of individual components. In the
context of the present work, we studied a relationship beꢀ
tween antimicrobial and micelleꢀforming properties of
homologous surfactants and derived the corresponding
equations. For this purpose, a regression analysis of
our experimental data was performed. Earlier,12 we have
determined the CMC of surfactants 1, 2, 3, and 4 in waꢀ
ter at 25 C by tensiometry (0.011, 0.004, 0.001, and
0.00012 mol L–1, respectively). We found parabolic correꢀ
lations between bacteriostatic activity (Cbac/mol L–1) and
logCMC for compounds 1—4:
St. aureus: log(Cbac–1) =
= –2.88 + 5.10(–logCMC) – 0.711(–logCMC)2 (R = 0.989),
E. coli: log(Cbac–1) =
= –4.07 + 5.02(–logCMC) – 0.700(–logCMC)2 (R = 0.989),
B. cereus: log(Cbac–1) =
= –1.81 + 4.14(–logCMC) – 0.589(–logCMC)2 (R = 0.999),
where R is the correlation coefficient.

120
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 1, January, 2012
Zhiltsova et al.
8. A. F. Popov, Pure Appl. Chem., 2008, 80, 1381.
A linear correlation model gave lower R values: 0.900
9. A. V. Zakharov, M. A. Voronin, F. G. Valeeva, E. F. Gubanꢀ
ov, in Struktura i dinamika molekulyarnykh sistem [Structures
and Dynamics of Molecular Systems], 2003, 10, Part 2, p. 89.
10. C. A. Bunton, A. A. Kamego, M. J. Minch, J. L. Wright,
J. Org. Chem., 1975, 40, 1321.
(St. aureus), 0.900 (E. coli), and 0.888 (B. cereus).
Correlations between fungistatic activity (Cfun/mol L–1)
and logCMC are described by parabolic and linear models
with very close correlation coefficients:
11. F. M. Menger, R. A. Persichetti, J. Org. Chem., 1987,
52, 3451.
12. T. N. Pashirova, E. P. Zhiltsova, R. R. Kashapov, S. S.
Lukashenko, A. I. Litvinov, M. K. Kadirov, L. Ya. Zakharoꢀ
va, A. I. Konovalov, Izv. Akad. Nauk, Ser. Khim., 2010, 1699
[Russ. Chem. Bull., Int. Ed., 2010, 59, 1745].
C. alb.: log(Cfun–1) =
= –1.44 + 3.02(–logCMC) – 0.300(–logCMC)2 (R = 0.980),
log(Cfun–1) = 1.03 + 1.24(–logCMC) (R = 0.971).
13. M. Jansson, P. Stilbs, J. Phys. Chem., 1985, 89, 4868.
14. L. Ya. Zakharova, Yu. R. Kudryashova, N. M. Selivanova,
M. A. Voronin, A. I. Ibragimova, S. E. Solovieva, A. T.
Gubaidullin, A. I. Litvinov, I. R. Nizameev, M. K. Kadirov,
Yu. G. Galyametdinov, I. S. Antipin, A. I. Konovalov,
J. Membrane Sci., 2010, 364, 90.
15. N. K. Gaisin, O. I. Gnezdilov, T. N. Pashirova, E. P. Zhiltsꢀ
ova, S. S. Lukashenko, L. Ya. Zakharova, V. V. Osipova,
V. I. Dzhabarov, Yu. G. Galyametdinov, Kolloidn. Zh., 2010,
72, 755 [Colloid J. (Engl. Transl.), 2010, 72].
16. M. Jansson, P. Stilbs, J. Phys. Chem., 1987, 91, 113.
17. A. I. Rusanov, Mitselloobrazovanie v rastvorakh poverkhnosꢀ
tnoꢀaktivnykh veshchestv [Micellization in Solutions of Surfacꢀ
tants], Khimiya, St. Petersburg, 1992, 280 pp. (in Russian).
18. I. V. Berezin, C. Martinec, A. K. Yatsimirskii, Usp. Khim.,
1973, 42, 1729 [Russ. Chem. Rev. (Engl. Transl.), 1973,
42, 787].
19. C. Chachaty, T. Ahlnas, B. Lindstrom, H. Nery, A. M.
Tistchenko, J. Colloid Interface Sci., 1988, 122, 406.
20. Spravochnik khimika [A Chemist´s Handbook], Goskhimizꢀ
dat, Leningrad—Moscow, 1963, Vol. 1, p. 987 (in Russian).
21. L. Zakharova, A. Mirgorodskaya, E. Zhiltsova, L. Kudryavtꢀ
seva, A. Konovalov, in Molecular Encapsulation: Organic Reꢀ
actions in Constrained Systems, Eds U. H. Brinker, J. L.
Mieusset, John Wiley and Sons, Chichester, 2010, p. 397.
22. D. B. Kudryavtsev, A. R. Panteleeva, A. V. Yurina, S. S.
Lukashenko, Yu. P. Khodyrev, R. M. Galiakberov, D. N.
Khaziakhmetov, L. A. Kudryavtseva, Neftekhimiya, 2009,
49, 211 [Petrol. Chem. (Engl. Transl.), 2009, 49, 193].
23. V. M. Bakhir, B. I. Leonov, S. A. Panicheva, V. I. Prilutskii,
N. Yu. Shomovskaya, I. I. Strel´nikov, Yu. G. Suchkov, Dezꢀ
infektsionnoe delo [Disinfection Science], 2004, 44 (in Russian).
24. E. P. Tishkova, S. B. Fedorov, L. A. Kudryavtseva, Zh. V.
Molodykh, N. L. Kucherova, Sh. M. Yakubov, S. M. Gorꢀ
bunov, A. M. Zotova, L. V. Teplyakova, A. A. Abramzon,
Khim.ꢀFarm. Zh., 1989, 592 [Pharm. Chem. J. (Engl. Transl.),
1989, 418].
Correlations between bacteriostatic and fungistatic acꢀ
tivities and the number of carbon atoms in the surfactant
radical are described best by the parabolic model:
St. aureus: log(Cbac–1) = –7.57 + 1.45n – 0.0382n2 (R = 0.976),
E. coli: log(Cbac–1) = –8.67 + 1.43n – 0.0375n2 (R = 0.976),
B. cereus: log(Cbac–1) = –6.92 + 1.37n – 0.038n2 (R = 0.992),
C. alb.: log(Cfun–1) = 2.40 – 0.139n – 0.0183n2 (R = 0.979).
Thus, alkylated 1,4ꢀdiazabicyclo[2.2.2]octanes, which
are cationic surfactants with a bicyclic head group, form
micellar aggregates in water with a high solubilizing tenꢀ
dency toward diethyl 4ꢀnitrophenyl phosphate (an analog
of organophosphorus ecotoxicants), produce a considerꢀ
able catalytic effect on its basic hydrolysis, and are superiꢀ
or to analogs with acyclic head groups in some of the
characteristics of antimicrobial activity. We found a corꢀ
relation between the aggregation and antimicrobial propꢀ
erties. A number of useful properties combined in alkylꢀ
ated 1,4ꢀdiazabicyclo[2.2.2]octanes open up new scope
for the design of multipurpose nanostructured systems.
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Received January 18, 2011;
in revised form August 11, 2011