Supramolecular systems based on aminomethylated calix[4]resorcinarene and a cationic surfactant: Catalysts of the hydrolysis of esters of phosphorus acids

Article abstract of DOI:10.1134/S003602441201013X

Kinetics of alkaline hydrolysis of 4-nitrophenyl esters of tetracoordinated phosphorus acids in micellar solutions of aminomethylated calix[4]resorcinarene containing sulfonatoethylene groups on the lower rim of the macrocycle, 4-aza-1-hexadecyl-azoniabicyclo[2.2.2]octane bromide and their mixtures was investigated spectrophotometrically. It is established that the catalytic effect of aggregates depends on the concentration of calixarene and surfactants, pH, presence of lanthanum salt and reaches more than two orders of magnitude. The parameters of the catalyzed reactions and their dependence on the composition are determined.

Full text of DOI:10.1134/S003602441201013X

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2012, Vol. 86, No. 2, pp. 200–204. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © R.R. Kashapov, T.N. Pashirova, E.P. Zhiltsova, S.S. Lukashenko, A.Yu. Ziganshina, L.Ya. Zakharova, 2012, published in Zhurnal Fizicheskoi Khimii,
2012, Vol. 86, No. 2, pp. 256–261.
CHEMICAL KINETICS
AND CATALYSIS
Supramolecular Systems Based on Aminomethylated
Calix[4]resorcinarene and a Cationic Surfactant:
Catalysts of the Hydrolysis of Esters of Phosphorus Acids
R. R. Kashapov, T. N. Pashirova, E. P. Zhiltsova, S. S. Lukashenko, A. Yu. Ziganshina,
and L. Ya. Zakharova
Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences,
Kazan, 420088 Russia
eꢀmail: Zhiltsova@iopc.ru
Received February 18, 2011
Abstract—Kinetics of alkaline hydrolysis of 4ꢀnitrophenyl esters of tetracoordinated phosphorus acids in
micellar solutions of aminomethylated calix[4]resorcinarene containing sulfonatoethylene groups on the
lower rim of the macrocycle, 4ꢀazaꢀ1ꢀhexadecylꢀazoniabicyclo[2.2.2]octane bromide and their mixtures was
investigated spectrophotometrically. It is established that the catalytic effect of aggregates depends on the
concentration of calixarene and surfactants, pH, presence of lanthanum salt and reaches more than two
orders of magnitude. The parameters of the catalyzed reactions and their dependence on the composition are
determined.
Keywords: calix[4]resorcinarene, alkylated 1,4ꢀdiazabicyclo[2.2.2]octane, hydrolysis, catalysis, esters of
phosphorus acids.
DOI: 10.1134/S003602441201013X
INTRODUCTION
tants is thus undoubtedly of interest and could be useꢀ
ful in the development of catalysis.
In recent years, considerable attention has been
given to the development of new catalytic systems
based on the principles of supramolecular chemistry. A
key role is assigned to designing catalytic compositions
based on calixarenes, which have high selectivity for
many organic reactions, particularly the hydrolysis of
esters of phosphorus acids [1–4]. This reaction is a
convenient model for studying the patterns of the most
important biochemical reactions. Moreover, the
cleavage of phosphoester bonds is one way of detoxifiꢀ
cation for organophosphorus neurotoxins and toxiꢀ
cants [5, 6]. A wide range of studies of this process with
traditional surfactants (anionic, cationic, nonionic)
acting as catalysts have already been published [2, 7, 8].
In this work, the influence of supramolecular
systems based on the new calix[4]resorcinarene,
which contains aminomethylated fragments on the
upper rim and sulfonate groups on the lower rim of
the macrocycle (CR) and a cationic surfactant
4ꢀazaꢀ1ꢀhexadecylꢀazoniabicyclo[2.2.2]octane
broꢀ
mide (HAOB), on the reaction of hydrolytic
decomposition of 4ꢀnitrophenyl esters of tetracoorꢀ
dinated phosphorus acids—4ꢀnitrophenylꢀOꢀbutylꢀ
chloromethylphosphonate (NBCP) and bis(4ꢀnitroꢀ
phenyl)methylphosphonate (BNMP) (Scheme 1)—
was investigated.
The advantage of applying macrocyclic receptors is
that the cavity size and conformation of the molecule
can be varied by its directed functionalization [1, 9].
The presence of additional binding sites in the moleꢀ
cules of calixarene and the possibility of implementing
inclusive interactions that enhance the effect of the
concentration of reagents and are conducive to the
catalytic effect of systems suggest the promising appliꢀ
cation of calixarenes in catalytic systems. It should be
noted that calixarene–surfactant systems are relatively
new and have a multitude of features, as compared to
conventional catalysts. The study of selfꢀorganizing
mixed compositions based on calixarenes and surfacꢀ
Table 1. 31P NMR chemical shifts of the reaction products
of hydrolysis NECP and NBCP in the absence and presꢀ
ence of HAOB and CR at 25
°
C
System
NECP
δ
31P, ppm
System
δ
31P, ppm
14.4
14.0
14.2
NBCP–CR
NECP
13.9
NECP–HAOB
NECP–CR
(17.7)
(18.5)
NBCP
Note: C
= 0.02 mol/l, C
= 0.01 mol/l (the chemical shift of NECP and NBCP in
= 0.02 mol/l, C
= 0.05 mol/l,
NECP
NBCP
HAOB
C
CR
water, respectively).
200

SUPRAMOLECULAR SYSTEMS BASED
N
201
HO
OH
+
N
N C16H33
Br–
4
(CR)
(HAOB)
SO3Na
O
O
R1
R2
R1
R2
surf., CR
C H NO ꢀ4 + 2OH–(H O)
+ –OC6H4NO2ꢀ4 + H2O,
PO−
PO
6
4
2
2
R1 = ClCH2, R2 = OC4H9 (NBCP); R1 = CH3, R2 = OC6H4NO2ꢀ4 (BNMP).
R1 = ClCH2, R2 = OC2H5 (NECP).
Scheme 1.
The alkaline hydrolysis of 4ꢀnitrophenylꢀOꢀethylꢀ
RESULTS AND DISCUSSION
chloromethylphosphonate (NECP) was also examꢀ
ined as evidence for the mechanism of the process.
The hydrolysis of esters of phosphorus acids was
selected as a model of the process. The test process
begins with the release of 4ꢀnitrophenol anion fixed by
the spectrophotometric method for the absorption
band at 400 nm and the corresponding acid, whose
EXPERIMENTAL
31
formation was confirmed by P NMR spectroscopy
Our CR macrocycle was prepared by reacting
calix[4]resorcinarene with the sulfonatoethylene
fragment on the lower rim with bis(dimethylꢀ
amino)methane. The CR structure was confirmed by
1H NMR spectroscopy and elemental analysis.
HAOB was prepared by reacting 1,4ꢀdiazabicyꢀ
clo[2.2.2]octane with cetylbromide according to the
procedure in [10]. The NBCP, BNMP, and NECP
substrates were synthesized as in [11, 12].
31P NMR spectra of NBCP, NECP, and their
hydrolysis products were recorded on a Bruker
MSLꢀ400 instrument (162 MHz) relative to an exterꢀ
nal standard (H3PO4).
(Table 1). As in the absence and presence of CR and
surfactant, the formed acids are characterized by sigꢀ
nals in the 13.9–14.4 ppm range. Initial phosphonates
(NECP and NBCP) are characterized by signals of
7.17 ppm and 18.5 ppm, respectively (Table 1).
It should be noted that the amphiphilic additives
(surfactant and calixarene) used in our study of
hydrolysis are able to selfꢀorganize. The presence of
associates in both individual and mixed aqueous soluꢀ
tions of surfactant and calixarene was shown earlier by
tensiometry, conductivity, potentiometry and dynamic
light scattering. It was established that aggregates form
in aqueous solutions of HAOB at concentrations
above 0.001 mol/l corresponding to the critical
micelle concentration (CMC1), and the structure is
altered at a concentration of 0.011 mol/l (CMC2)
[13]. In CR solution, the formation of aggregates
The reaction kinetics was studied spectrophotoꢀ
metrically by an increase in optical density of the
absorption band of 4ꢀnitrophenol anion at 400 nm on
a Specord UVꢀVis spectrophotometer in thermostatꢀ
ted cuvettes. The rate constants observed were deterꢀ
mined from an equation of the first order. The subꢀ
strate (NBCP, BNMP) concentration at the beginning
occurs at CMC1 = 9.3
tion of mixed associates in a binary HAOB–CR sysꢀ
tem ( CR = 0.001 mol/l) and alteration of the structure
×
10–3 mol/l [14]. The formaꢀ
c
of the reaction was 5 × ×
10–5–1 10–4 mol/l. The conꢀ
occurs in the concentration of 3–10 times lower than
in the individual solutions of surfactant and the macꢀ
rocycle [14]. In addition, a lower degree of counterion
centration of free bromide ion was determined by an
Iꢀ160MI ion meter with an ELISꢀ131Br bromine–
selective electrode. A 10101 ESrꢀelectrode was used as
a reference electrode.
binding (
β
) equal to 0.74–0.79 (Table 2) is characterꢀ
istic of mixed systems, whereas, according to [14]
β
value is equal to 0.81–0.89 for individual surfactant
solutions. The degree of binding for counterions
determines the surface potential of micelles and hence
the effect of the concentration of reactants and cataꢀ
lyst efficiency.
Table 2. Degree of binding of a bromide ion with HAOB–
CR (0.001 M) aggregates in water, 25°C
cHAOB, mol/l
β
cHAOB, mol/l
β
The change in the colloidal state of individual and
mixed systems based on HAOB and CR is manifested
in the kinetics of hydrolysis of esters of phosphorus
0.01
0.02
0.79
0.74
0.06
0.08
0.77
0.77
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202
KASHAPOV et al.
cHAOB
1
×
103, mol/l
0
2
3
1
20
16
12
8
12
8
2
3
4
4
0
0
4
cHAOB
8
12
×
104, mol/l
Fig. 1. Dependences of the
k hydrolysis reaction of NBCP on the concentration of GAOB in the absence (1) and presence of
o
CR (
2,
3
),
c
= 0.001 mol/l,
с
= 0.001 mol/l (1, 2), pH 11 (1), pH 10 (2), pH 9 (3), 25°С.
CR
NaOH
acids. The observed rise in the rate constants (
of the hydrolysis of NBCP with a subsequent tendency tude of the catalytic effect of the system (km
k
o, s–1) (more than three orders of magnitude) and the magniꢀ
k0), 46.
/
to leave the dependence at a plateau occurs upon an
increase in surfactant concentration (Fig. 1). Such a
dependence is typical for micellarꢀcatalyzed reacꢀ
tions, and according to the pseudoꢀphase model of
micellar catalysis is explained by the concentration of
the reactants in a colloidal phase, i.e., the transitionꢀ
ing of reagents (hydroxide ions and the phosphoric
substrate) from the bulk of the solution into aggregates
and the complete binding of the phosphonate by
aggregates in the area of high concentrations of surfacꢀ
tant [15, 16]. Table 3 shows the parameters of the catꢀ
alyzed reaction, calculated using the equation [15]
The presence of calixarene in HAOB solution leads to
a reduction in CMC1, an increase in КS, and to a lower
pH via the acid–base interactions of amino groups
with water. As can be seen from Table 3, the catalytic
effect of binary HAOB–CR systems is lower than the
individual solutions of cationic surfactant, but the
heightened catalytic effect of mixed aggregates is
observed at lower pH.
We studied the effect of the associates formed by
individual CR molecules on the hydrolytic cleavage of
esters of phosphorus acids using the example of the
alkaline hydrolysis of BNMP. Raising the CR concenꢀ
tration increases the observed rate constants (Fig. 2).
At the same time, the dependence (as in the individual
HAOB solutions) tends to a plateau at high concentraꢀ
tions, indicating the complete binding of the substrate
(phosphonate) by macrocycle aggregates. Table 4 lists
the parameters of catalyzed hydrolysis of BNMP calꢀ
culated according to Eq. (1). It can be seen that at
pH 9.0, the system under investigation is characterꢀ
ized by a low CMC value (as stated above, at the neuꢀ
kmKS(csurf − CMC) + k0
,
(1)
kн =
1 + KS(csurf − CMC)
where ko is observed rate constant of first order, s–1;
k0 and km are reaction rate constant in bulk solvent and
micellar phase, s–1
; KS is binding constant of the subꢀ
strate with the aggregates, l/mol; csurf is concentration
of surfactant, mol/l.
In the individual HAOB solutions at pH 11, the
studied process is characterized by a relatively high tral pH the CMC of macrocycle is 9.3
×
10–3 mol/l)
binding constant of the substrate with the aggregates and a catalytic effect of 5.
Table 3. Parameters of NECP hydrolysis catalyzed by HAOB and HAOB–CR aggregates at 25 C
°
System
HAOBa
HAOB–CRa,b
pH
k
m, s–1
K
S, l/mol
CMC1
×
103, mol/l
km
46
5.0c
14c
/
k0c
11
10
9.0
0.16
4900
14000
6900
0.89
0.35
0.18
0.0019
HAOB–CRb
0.00051
c
a
b
Note:
C
= 0.001 mol/l; C = 0.001 mol/l; The effect of aggregates is relative to the k alkaline hydrolysis of NECP in the absence
NaOH
CR
o
of CR and HAOB.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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SUPRAMOLECULAR SYSTEMS BASED
203
1
It was of interest to assess the role of new agents,
salts of La(III), that exert a catalytic effect on the
hydrolysis of esters of phosphorus acids by electroꢀ
philic mechanism [17] and thereby increase the resultꢀ
ant action of system on the process. It was established
that the presence of La(NO3)2 leads to a reduction in
pH from 9.0 to 7.1 (as a result of the hydrolysis of lanꢀ
thanum salts [18]) and an increase in the catalytic
effect of up to 650 (i.e., by a factor of 130) (Table 4). In
addition to the contribution of homogeneous (electroꢀ
philic) catalyst, this phenomenon could be due to an
increase in substrate binding by CR aggregates (the
binding constant KS of the substrate by CR aggregates
in the presence of salts increases fourfold, Table 4),
and to an increase in the proportion of the cationic
form of the CR with protonation of nitrogen atoms of
calixarene in a more acidic environment [19]. An
increase in the proportion of cationic centers favors
the binding of the nucleophilic reagent (hydroxide
ion).
ko
×
104, s−
2
1
20
15
10
5
6
8
10
12
14
103, mol/l
cCR
×
Fig. 2. Dependences of the observed rate constant for
BNMP hydrolysis on CR concentration in the absence (
and presence ( ) of La(NO ) . ( = 0.0056 mol/l.
) pH 9.0; ( ) pH 7.1; 25°С
1)
2
2)
c
La(NO3)2
3 2
(1
2
.
(a)
300
200
100
0
2.0
1.6
1.2
0.8
2
1
7.5
8.0
8.5
9.0
pH
9.5
10.0
(b)
60
40
20
0
20
10
0
4
3
8
9
10
11
pH
Fig. 3. Dependences of the observed reaction rate constant of alkaline hydrolysis of NBCP (
1, 2) and BNMP (3, 4) in the presence
of 0.014 mol/l CR ( ) and the catalytic effect of CR ( ) on pH at 25°С
1
,
3
2
,
4
.
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204
KASHAPOV et al.
Table 4. Parameters of BNMP hydrolysis catalyzed by CR aggregates at 25
°
C
System
pH
km
×
103, s–1
K
S, l/mol
ККМ1
×
103, mol/l k0
×
105,b s–1
26
km/
k0d
CR
CR–La(NO3)2a
9.0
7.1
1.3
2.2
440
5.2
7.5
5.0
650 (11e)
1800
0.34 (20c)
a
Notes:
= 0.0056 mol/l.
C
La(NO3)2
b
c
d
e
k alkaline hydrolysis of BNMP in the absence of CR [12].
o
k alkaline hydrolysis of BNMP in La(NO ) solution in the absence of CR.
o
3 2
The effect of aggregates is relative to the k alkaline hydrolysis of BNMP in the absence of CR and CR–La(NO ) mixes, respectively.
o
3 2
The effect of aggregates is relative to the k alkaline hydrolysis of BNMP in La(NO ) solution.
o
3 2
2. L. Zakharova, A. Mirgorodskaya, E. Zhiltsova, et al.,
Molecular Encapsulation: Organic Reactions in Conꢀ
strained Systems (Wiley, UK, 2010), pp. 397–420.
The different distribution of charge on a molecule
of calix[4]resorcinarene upon a change in the pH of
the medium thus demonstrates that the action of CR
on the reaction kinetics of alkaline hydrolysis is
pHꢀdependent. This is also evidenced by a reduction
of the catalytic effect of the CR in the reaction of alkaꢀ
line hydrolysis of the investigated substrates with
increasing pH. Raising pH from 7.8 to 10.2 (in the case
NBCP) and up to 11.3 (in the case BNMP) leads to a
reduction of the catalytic effect of the macrocycle,
respectively, from 320 to 4 (i.e., eightyfold) (Fig. 3a)
and from 22 to 1.3 (i.e., by a factor of 17) (Fig. 3b).
3. I. S. Ryzhkina, Ya. A. Babkina, S. S. Lukashenko, et al.,
Izv. Akad. Nauk, Ser. Khim., No. 12, 2026 (2002)
[Russ. Chem. Bull. 51, 2183 (2002)].
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Moscow, 1973), Vol. 1 [in Russian].
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et al., Izv. Akad. Nauk, Ser. Khim., No. 7, 1331 (2004).
CONCLUSIONS
8. Micellization, Solubilization and Microemulsions, Ed. by
K. M. Mittel (Plenum, New York, 1977; Mir, Moscow,
1980).
Our investigations have shown that a system based
on aminomethylated calix[4]resorcinarene containing
sulfonatoethylene groups on the lower rim of the macꢀ
rocycle, cationic surfactant 4ꢀazaꢀ1ꢀhexadecylꢀazoniꢀ
abicyclo[2.2.2]octane bromide and their mixtures
have a catalytic effect on the hydrolysis of 4ꢀnitropheꢀ
nyl esters of tetracoordinated phosphorus acids. The
favorable effect of amphiphilic additives is due to their
ability to form in aqueous solutions individual and
mixed aggregates, the transition of reagent from the
mass of solution into these aggregates, and the course
of the chemical process in the new phase. The presꢀ
ence of La(III) ions enhances the catalytic effect of
calixarene aggregates due to complex manifestations
of micellar and homogeneous (electrophilic) catalyst,
and to favorable changes in the characteristics (the
degree of binding of counterions and surface charge)
of the macrocycle aggregates.
9. Y. Aoyama, Y. Tanaka, and S. Sugahara, J. Am. Chem.
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ACKNOWLEDGMENTS
8, 271 (1970).
This work was financially supported by the Russian
Foundation for Basic Research, project nos. 09ꢀ03ꢀ
00572ꢀa and 10ꢀ03ꢀ90416ꢀUkr_a.
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