Synthesis and characterization of novel calix[4]arene piperazine derivative for the extraction of transition metals and dichromateions

Article abstract of DOI:10.1007/s10847-009-9709-4

This article displays the synthesis of N-(2-tosylato)ethylpiperazine (ii) and 5,11,17,23-tetra-tert-butyl-25,27-bis-(2-piprazinoethyl)-26,28-dihydroxycalix[4]arene (3). Compounds (ii) and 3 were characterized through elemental analysis, FT-IR, ¹

Full text of DOI:10.1007/s10847-009-9709-4

J Incl Phenom Macrocycl Chem (2010) 67:295–302
DOI 10.1007/s10847-009-9709-4
ORIGINAL ARTICLE
Synthesis and characterization of novel calix[4]arene piperazine
derivative for the extraction of transition metals and dichromate
ions
•
Fozia Tabassum Minhas Shahabuddin Memon
•
M. I. Bhanger
Received: 6 June 2009 / Accepted: 13 November 2009 / Published online: 22 November 2009
Ó Springer Science+Business Media B.V. 2009
Abstract This article displays the synthesis of N-(2-tosy-
lato)ethylpiperazine (ii) and 5,11,17,23-tetra-tert-butyl-
25,27-bis-(2-piprazinoethyl)-26,28-dihydroxycalix[4]arene
(3). Compounds (ii) and 3 were characterized through ele-
mental analysis, FT-IR, 1H NMR and/or 13C NMR studies.
The transition metal cations (Hg2?, Co2?, Ni2?, Cu2?, and
Cd2?) and dichromate anion were studied by liquid–liquid
extraction experiment. The results showed that compound 3
has moderate but selective extraction ability for Hg2? and
dichromate anion. Comparison between extraction proper-
ties of compound 3 with previously reported 5,11,17,23-
tetra-tert-butyl-25,27-bis(isoniazidylcarbonylmethoxy)-
26,28-dihydroxy-calix[4]arene (4) and protonated pyridini-
um form of 4 (5) is also described.
and/or neutral species [1–4]. They are widely applied in
enzyme mimetics [5], ion sensitive electrodes [6], sensors
[7], selective membranes [8, 9], separation [10, 11], and
catalysis [12].
Transition metals such as (Hg2?, Co2?, Ni2?, Cu2?, and
Cd2?) are known as toxic due to their accumulative nature
and continual existence in the environment. The presence
of these toxicants in water and soil cause health hazard at
concentrations above than permissible limits. Therefore,
main goal of modern research is the synthesis of versatile,
environmental friendly and reusable extractants for reme-
diation of these trace metals. Generally, calix[4]arene
derivatives are employed because of their stable confor-
mational isomers and remarkable extraction properties for
selective removal of toxic metal ions. They have been
extensively used as selective ligands for a wide range of
metal ions, such as, sodium [13–15], lithium [16], calcium
[17, 18], silver [19], mercury [20, 21], cesium [22], or to a
lesser extent anions [23–27] in extraction, transport and ion
selective electrodes. Obviously, soft donor atoms such as
nitrogen [28, 29], sulphur [30] or phosphorus [31] have
been introduced in calix[4]arene molecule to increase its
affinity toward soft metal ions.
Keywords Calixarene ꢀ Liquid–liquid extraction ꢀ
Complexation ꢀ Chromium ꢀ Metals
Introduction
Much attention is being paid now-a-days for design and
synthesis of supramolecular receptors that can selectively
separate the toxic ions from aqueous environment at tem-
perate conditions. Over the last two decades, calixarenes, a
fascinating class of macrocyclic oligophenols, have
received considerable attention due to their distinctive
three dimensional molecular structures and ease of one-pot
synthesis. These versatile macrocyclic compounds have an
ability to bind or complex selectively with cations, anions
Chromium (VI) is a carcinogen in humans and animals,
as chromates and dichromates being both mutagenic and
genotoxic. Thus, presence of chromate and dichromate
anions in soil and water causes high toxicity [32, 33].
Chromium (VI) is more toxic than chromium (III) due to its
greater solubility and mobility. Chromium (VI) requires
intracellular reduction for activation and this in vivo
reduction can produce several reactive intermediates such
as chromium (V) and chromium (IV) that can damage
DNA [33]. The considerable quantities of Chromium (VI)
are found near areas of industrial activities such as
leather tanning, textile dyeing, wood preserving, plating
F. T. Minhas ꢀ S. Memon (&) ꢀ M. I. Bhanger
National Center of Excellence in Analytical Chemistry,
University of Sindh, Jamshoro 76080, Pakistan
e-mail: shahabuddinmemon@yahoo.com
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J Incl Phenom Macrocycl Chem (2010) 67:295–302
operations, oil drilling, or locations where large tanks have
been cleaned with chromium (VI) solutions. The manu-
facture of inks, pigments, glass, ceramics and glues can
also be affected sites [34]. One way of the chromium (VI)
removal is its reduction to chromium (III), which forms
insoluble oxides and hydroxides that require extra filtration
for their separation. Therefore, in order to directly remove
chromium (VI) from aqueous solution, the liquid–liquid
extraction method with anion host is useful [35].
Calix[4]arene-based anion hosts are preferable because
their aromatic core structure is stable to oxidation and they
are suitable extractants due to exclusive characteristics of
hydrogen bonding, p–p interactions, electrostatic interac-
tions, and dipole–dipole moments [36, 37]. An early use of
a calixarene for the extraction of chromium (VI) employed
amine substituents on the narrow rim of the calix[4]arene
which can form hydrogen bond with the oxoanions [38].
Subsequently, the longer alkyl chain homologs have also
been found to extract Cr(VI) as the protonated diaminoc-
alix[4]arene derivative [39]. The pyridine substituted
calix[4]arene derivatives have also been used to synthesize
pH reversible chromium(VI) extractants [40, 41]. Calixa-
renes with amide substituents have been used for hydro-
gen bonding with the oxoanions [42, 43]. Recently,
calix[4]arenes with nitrile substituents act as phase transfer
extractants for chromium(VI) [44]. Crown ether moiety
incorporated into the structure of the calix[4]arene has also
been proven to be a complementary binding site for oxo-
anion salts [23, 24].
on a Perkin Elmer Lambda 35 UV/Vis spectrophotometer
using standard 1.00 cm quartz cells. For pH measurement
781-pH/ion meter (Metrohm Switzerland) was used.
Mechanical shaker (Gallenkamp) with temperature con-
troller was used for shaking. Elemental analyses were
performed using a CHNS instrument model Flash EA 1112
elemental analyzer. All the reagents used were purchased
from Merck (Darmstadt, Germany) and were used as sup-
plied. Thin layer chromatography (TLC) was performed on
precoated silica gel plates (SiO2, PF254, Merck). All
aqueous solutions were prepared with deionized water that
had been passed through a Millipore Milli-Q Plus water
purification system.
Synthesis
p-tert-Butylcalix[4]arene (2) was synthesized by the
method described by Gutsche [45]. The compounds 4 and 5
were reported previously [41]; while the other compounds
(ii and 3) were synthesized as follows:
N-(2-tosylato)ethylpiperazine (ii)
N-(2-hydroxy)ethylpiperazine (3.9 g, 3.7 mL, 30 mmol)
and 10 mL solution of 0.1 M NaOH were dissolved in THF
(50 mL). To the stirred mixture maintained at 0 °C,
p-toluenesulfonyl chloride (12 g, 63 mmol) in THF
(15 mL) was added drop wise over 2 h. Stirring was con-
tinued for an additional 2 h at the same temperature, i.e.
0 °C. The mixture was then poured into 10% aqueous
hydrochloric acid at 0 °C. Addition of 30 mL saturated
solution of NaHCO3 causes precipitate formation of di-
tosylate, which were filtered, washed with water and then
dried in vacuum. Yield 7.94 g, 93%, Mp: 118–120 °C.
FTIR (KBr) v: 3064 (CH), 3414 (NH), 1595 (aromatic
In the present paper, the need of a versatile receptor
molecule capable of anchoring cationic as well as anionic
guest species especially chromium (VI) has been explored.
Herein, we report synthesis and characterization of a new
piperazine derivative of calix[4]arene (3) as well as
investigation of its extraction properties toward the toxic
metals and dichromate ions. A comparison between the
extraction properties of 3 with previously reported [41]
pyridine substituted calix[4]arene derivative (4) and its
protonated pyridinium form (5) is also demonstrated.
1
C=C), 1167 (S–O); H NMR d: 2.43 (s, 3H, CH3); 2.48
(t, 4H, J = 3 Hz, NCH2); 2.56 (t, 4H, J = 3 Hz, HNCH2);
2.99 (t, 2H, J = 3 Hz, NCH2); 3.58 (t, 2H, J = 4 Hz,
OCH2); 7.40 (d, 2H, J = 8 Hz, ArH); 7.63 (d, 2H,
J = 8 Hz, ArH); Anal. Calcd for C13H20N2O3S: C, 54.90;
H, 7.08; N, 9.85; S, 11.28. Found: C, 55.03; H, 6.96; N,
9.75; S, 11.76.
Experimental section
Materials and instrumentation
5,11,17,23-Tetra-tert-butyl-25,27-bis-(2-piprazinoethyl)-
26-dihydroxycalix[4]arene (3)
Melting points were determined on a Gallenkamp appara-
tus (UK) in a sealed glass capillary tube and are uncor-
A mixture of p-tert-butylcalix[4]arene (10.0 g, 15.43 mmol)
and K2CO3 (2.13 g, 15.43 mmol) in acetonitrile (200 mL)
was stirred for 30 min; then N-(2-tosylato)ethyl piperazine
(8.75 g, 30.82 mmol) was added and the reaction mixture
was refluxed for 76 h. The mixture was concentrated to one-
third of its volume under vacuum and added it drop wise in
ice cold 0.1 N HCl solution with continuous stirring. The
1
rected. H NMR and 13C NMR spectra were recorded on a
Bruker 400 MHz spectrometer in CDCl3 using TMS (tet-
ramethyl silane) as internal standard at room temperature.
IR spectra were recorded on a Thermo Nicollet AVATAR
5700 FTIR spectrometer using KBr pellets in spectral
range 4,000–400 cm-1. UV/visible spectra were recorded
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J Incl Phenom Macrocycl Chem (2010) 67:295–302
297
precipitates formed were washed with deionized water. Yield
8.2 g, 61%, Mp. [160 °C (decom.); FTIR(KBr)/cm-1
3177(b) (vOH), 3399(b) (vNH); H NMR d: 1.19 (s, 36 H,
½MðPicÞnðLÞxꢂ
Kex
¼
ð2Þ
n
x
½Mnþꢂ½Picꢂ ðLÞꢂ
If we introduce the distribution coefficient D, as given in
:
1
C(CH3)3); 1.54 (s, 8H, NCH2); 2.42 (s, 1H, NH); 3.01 (s, 2H,
NCH2O); 3.48 (d, 4H, J = 13 Hz, ArCH2Ar); 3.56 (s, 2H,
NCH2O); 4.22 (d, 4H, J = 13 Hz, ArCH2Ar); 7.03 (s, 8H,
ArH); 7.24 (s, 2H, ArOH); 13C NMR d: 146.68, 144.37,
129.70, 127.87, 127.70, 126.31, 125.94, 125.57, 77.3, 77.2,
77.01, 76.69, 34, 32.62, 31.40, 31.22, ppm; Anal. Calcd for
C56H80N4O4: C, 77.02; H, 9.23; N, 6.42. Found: C, 76.97; H,
9.08; N, 6.35.
Eq. 3, and taking log of both sides, we obtain Eq. 4;
½MðPicꢁÞnðLÞxꢂ
D ¼
ð3Þ
ð4Þ
½ðMnþÞꢂ
n
log D ¼ logðKex½Picꢁꢂ Þ þ x log½Lꢂ
Consequently, a plot of log D versus log [L] leads to a
straight line with a slope that should be equal to the number
of ligand molecules per ion in the extraction species.
Analytical procedure
Picrate and/or dichromate extraction experiments were
performed using Pederson’s experimental procedure [46].
10 mL of a 2.5 9 10-5 M aqueous picrate solution or
1 9 10-4 M aqueous dichromate solution (pH of dichro-
mate solution has been maintained by 0.01 M KOH/HCl
solution) and 10 mL of 1 9 10-3 M solution of calixarene
in CHCl3 were vigorously agitated in a stoppered glass
tube with a mechanical shaker for 2 min; then magnetically
stirred in a thermostated water bath at 25 °C for 1 h.
Finally left standing for an additional 30 min so that the
two phases separate distinctively. The concentration of
picrate/dichromate ion remaining in the aqueous phase was
then determined spectrophotometrically. Blank experi-
ments showed that no picrate/dichromate extraction
occurred in the absence of calixarene. The percent
extraction (E %) has been calculated as:
Results and discussion
Synthesis and characterizations
Several aspects of the ionophoric properties of calixarenes
and their derivatives toward metal cations and anions were
explored experimentally. Here in this study, the objective
of calixarene derivatization is to build molecular assembly
that is efficient for both metal cations and dichromate
anions. The factors which determine the selectivity of an
ionophore toward metal cations are the nature, usefulness
of donor sites and size of the calix macro ring. Hence,
synthetic scheme has been developed for the derivatization
of p-tert-butylcalix[4]arene; such synthetic route is shown
in Scheme 1. The synthetic procedures of compounds 1, 4
and 5 were published previously [41, 45]. While reaction
steps leading from (i) to (ii) and 2 to 3 (Scheme 1) are
reported first time.
E ð%Þ ¼ ½ðCo ꢁ CÞ=Coꢂ ꢃ 100
where Co and C are the initial and final concentrations of
picrate and/or dichromate ions before and after the
extraction, respectively. The experiments have been
repeated even then the experimental error may be 2%.
Transition metal picrates were prepared by stepwise
addition of a 1 9 10-2 M metal nitrate solution to a
2.5 9 10-5 M aqueous picric acid solution and stirred at
25 °C for 1 h.
Initially, N-(2-tosylato)ethylpiperazine (ii) has been
synthesized by treating N-(2-hydroxy)ethylpiperazine with
p-toluenesulfonyl chloride in basic media and 5,11,17,23-
tetra-tert-butylcalix[4]arene (2) was prepared through the
base catalyzed condensation reaction as reported by Gut-
sche [45]. Afterwards, treatment of compound 2 with N-(2-
tosylato)ethylpiperazine (ii) in acetonitrile and in the
presence of K2CO3 produced 3 in 61% yield. The com-
pounds (ii) and 3 were characterized through elemental
analysis, FT-IR, 1H NMR and/or 13C NMR. The formation
of (ii) was confirmed by the appearance of the character-
istic (S–O) band at 1,167 cm-1 and the disappearance of
Log–log plot analysis
In order to characterize the extraction ability, the depen-
dence of the distribution coefficient D of the cation was
examined between the two phases upon the calixarene
(O–H) band at 3,356 cm-1 in its FT-IR spectrum. The H
1
concentration.
NMR data of compound (ii) explained the splitting pattern
of disubstituted aromatic nucleus at 7.40 and 7.63 ppm.
The FT-IR spectrum indicates the synthesis of compound 3
by the presence of amine band at 3,399 cm-1. The con-
formational characteristics of calix(n)arenes were easily
anticipated by the splitting pattern of the ArCH2Ar meth-
nþ
M
.
þ nPicꢁðaqÞ þ x½LꢂðorgÞ $ ½MðPicÞnðLÞxꢂðorgÞ
ð1Þ
ðaqÞ
If the general extraction equilibrium is assumed to be
Eq. 1 the overall extraction equilibrium constant Kex is
given by Eq. 2;
1
1
ylene protons in the H NMR spectroscopy. Thus, the H
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J Incl Phenom Macrocycl Chem (2010) 67:295–302
Scheme 1 Synthetic pathways
for (ii) and 3 as well as
structures of 4 and 5
HO
TsO
N
N
Tosyl Chloride
-
OH/H2O/THF
N
H
N
H
(ii)
(i)
OH
OH
O
O
-
(ii) / C H3CN
N
N
OH/HCHO
K2CO3
OH
OH
HO
OH
N
H
N
H
OH
1
2
3
OH
OH
OH
OH
O
O
HN
O
O
O
O
O
O
O
NH
NH
HN
NH
NH
HN
NH
O
O
O
-
N
N
+
N
I
N
+
-
CH3
I
H3C
4
5
NMR data showed that the compound 3 has cone confor-
mation that is clearly shown by a pair of doublets at 3.48
and 4.22 ppm.
Table 1 Extraction of metal picrates with ligands
Picrate salt extracted (%)a
Ligand
Cd2?
Co2?
Cu2?
Hg2?
Ni2?
2b
3
4b
9.4
7.9
9.9
15.5
52.3
96.9
6.3
Two-phase solvent extraction
7.8
10.8
63.5
3.9
7.1
Metal cations
64.7
90.0
71.9
Aqueous phase, [metal nitrate] = 1 9 10-2 M; [picric acid] =
2.5 9 10-5 M; organic phase, chloroform, [ligand] = 1 9 10-3 M;
at 25 °C, for 1 h
This work is focused on identifying the premeditated
necessities for the two-phase extraction and possibly the
binding ability of the ionophore 3 toward selected metal
ions such as (Hg2?, Co2?, Ni2?, Cu2? and Cd2?). Solvent
extraction was carried by using chloroform solution of
compound 3 to extract metal picrates from the aqueous
phase. The equilibrium concentration of picrates in the
aqueous phase was determined spectrophotometrically.
The data obtained from compounds 2, 4, 5 were incorpo-
rated for comparison purposes [41]. The experiments have
been repeated and pH (i.e. 3.5 pH) of the picrate solution
before and after the extraction has been noted. It has been
observed that no significant change in pH takes place. It
means that the cation extraction is taking place. From the
data given in Table 1, it is observed that extraction ability
of compound 2 is negligible. However, the change in its
extraction ability was observed with the introduction of
two piperazine groups onto the 1,3-positions of the lower
rim of 2 to produce 3; which shows a selective nature
toward Hg2? among transition metal cations. It may be
a
Experimental error may be as 2%
b
Reference [41]
explained on the fact that the nature of each metal ion
differs from the other including their softness, ionic radii
and coordination properties etc. Thus, the smaller or higher
extraction is an indication of the interaction between the
ligand and the metal ion, therefore; on the basis of these
observations the order may be written as Cu(II) \ Ni(II)
\ Cd(II) \ Co(II) \ Hg(II).
Figure 1 shows the extraction into chloroform at dif-
ferent concentrations of the ligand 3 for Hg2?. A linear
relationship between log D versus log [L] is observed with
the slope of line for Hg2? by the ligand 3 which is equal to
0.9, suggesting that the ligand 3 forms a 1:1 complex with
Hg2?. From observations we deduce that the size of a
macrocycle ring alone does not play a major role in the
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J Incl Phenom Macrocycl Chem (2010) 67:295–302
299
complexation phenomenon, but the nature and ionic
diameters of the metal ions as well as the conformation of
the calixarene cavity, the effectiveness and cooperative
aggregation of functional groups are also important in
complexation. Moreover, this phenomenon may reflect the
‘hard and soft acids and bases’ concept introduced by
Pearson [47]. As this environment exists (Scheme 2) due to
the presence soft element i.e. N containing functionalities,
where soft interactions favor the complexation with the
more polarizable transition metal ion especially Hg2?
which is known as soft metal cation. It is also due to the
cone conformation of calixarene moiety that provides
exactly such cavities. By contrast, the substitution of iso-
niazid groups in 2 with pyridine moieties has enhanced the
complexation ability of 4 toward transition metal cations.
The increased affinity of 4 than 3 may be due to the
presence of amide functionalities along with pyridine
binding sites, which provide an additional cooperativity in
extraction phenomenon.
0
y = 0.9909x
-0.2
-0.4
-0.6
-0.8
-1
-1.2
-1.4
-3.5
-3
-2.5
-2
-1.5
log [L]
Nevertheless, the superiority of 3 over 4 is that it has
found to be a selective ionophore for Hg2?; while 4 extracts
almost all the metal ions used in the experiments. Figure 2
shows FT-IR spectra of the compound 3 before and after
complexation with Hg2?. After complexation, shifting of
peaks has been observed, i.e. a peak shifts from 3,400 to
3,522 cm-1 and another from 3,177 to 3,167 cm-1, which
correspond to sec. amine (N–H stretching) and hydroxyl
(O–H stretching) functionalities, respectively. The shifting
of a peak from 1,483 to 1,379 cm-1 corresponding to C–N
stretching vibration also confirms the complex formation. A
proposed interaction of 3 with Hg2? is shown in Scheme 2.
Fig. 1 log D versus log [L] for the extraction of Hg2? by the ligand 3
from an aqueous phase into chloroform at room temperature
OH
OH
O
O
N
N
Hg2+
N
H
N
H
Dichromate anions
(a)
(b)
Anion identification and sensing is a more significant
research topic in supramolecular chemistry due to the
Scheme 2 Proposed interaction of Hg2? with ligand 3 a simple
structure b ball and stick model
Fig. 2 IR studies of a
compound 3 and b its complex
80
(a)
70
with Hg2?
60
50
40
1392
3400
30
20
1483
1361
3177
10
0
(b)
-10
-20
-30
3522
-40
3167
-50
-60
-70
1301
1356
1379
-80
3500
3000
2500
2000
1500
1000
Wavenumbers (cm-1)
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J Incl Phenom Macrocycl Chem (2010) 67:295–302
Table 2 Extraction of dichromate by ligand 3a at different pH
0
-0.5
-1
y= 0.7703x
Dichromate anion extracted (%)a
Ligand
pH
1.5
3.0
4.5
3b
4c
5c
a
57.5
60.8
\1.0
22.8
25.2
\1.0
2.70
\1
-1.5
-2
\ 1.0
Experimental error may be as 2%
Aqueous phase, [metal dichromate] = 1 9 10-4 M; organic phase,
-3.7
-3.2
-2.7
log [L]
-2.2
-1.7
b
chloroform, [ligand] = 1 9 10-3 M at 25 °C, for 1 h
c
Fig. 4 log D versus log [L] for the extraction of dichromate by the
ligand 3 from an aqueous phase into chloroform at room temperature
Reference [41]
anion An- by the anion receptor LHn? according to the
following equilibrium:
70
60
50
nþ
nꢁ
nðLH
Þ
þnAnnꢁ $ ½ðLHnþÞn; An
ꢂ
ð5Þ
ð6Þ
ð7Þ
org
org
The extraction constant Kex is described as under,
nꢁ
½ðLHnþÞn; An
ꢂ
org
40
30
20
10
0
org
n
Kex
¼
n
½Anꢁꢂaq½LH
ꢂ
nþ
Thus, Eq. 6 can be re-written as:
nþ
logDA ¼ logKex þ nlog½LH
ꢂ
3
org
4
Ligands
Where DA is defined as ratio of the analytical concentration
of the anion An- in both phases.
5
1
2
pH
3
DA ¼ ½Aꢂorg=½Aꢂaq
ð8Þ
Fig. 3 Plots of extraction (E %) versus pH following the two-phase
solvent extraction of dichromate with compounds 3, 4 and 5
Consequently a plot of log DA versus log [L] leads to a
straight line whose slope allows the stoichiometry of the
extracted species to be determined.
importance of a variety of anions in biological and environ-
mental locations. In order to investigate the extraction ability
of compound 3 toward anions; solvent extraction of K2Cr2O7
from aqueous into chloroform at different pH has been car-
ried out. The results are given in Table 2 (Fig. 3). Aqueous
solution of K2Cr2O7 shows no extraction into organic phase
in the absence of the extractant. The binding efficiencies of
reference compounds 4 and 5 (Scheme 1) are also given for
comparison and mechanism elucidation purpose.
Figure 4 represents the extraction into chloroform at
different concentrations of 3 with dichromate. A linear
relationship between log DA versus log [L] is observed with
a slope of line for the dichromate anion by 3 that is equal to
0.7 at pH 1.5, suggesting that 3 forms a 1:1 complex with
-
dichromate anion. For this pH value, HCrO4 is the pri-
mary anionic form of Cr(VI) in aqueous solution. This is
attributed to the presence of following equilibrium:
2HCrOꢁ4 $ Cr2O27ꢁ þ H2O
ð9Þ
The % extraction data (Table 2; Fig. 3) demonstrated
that the extraction ratio decreases as the pH of the solution
increases, representing that the protonated form of 3 is a
successful host for the monoprotonated chromate anions. It
is in agreement with our previous studies, i.e. the com-
pound 4 has been observed to be a valuable extractant for
dichromate anions at low pH [41], which contain proton
switchable binding sites.
.
However, it is a well known fact that in acidic condi-
tions K2Cr2O7 is converted into H2Cr2O7 form and after the
-
ionization in aqueous solution it may exist as HCr2O7
/
Cr2O72- form. At lower pH HCr2O7- and Cr2O72- dimers
become the dominant Cr(VI) form, and pKa1 and pKa2
values of these equations are 0.74 and 6.49, respectively. It
allowed us to consider this simultaneous extraction of 1:1
complexes, according to the following equilibriae:
The extraction data for 3 has been analyzed by a clas-
sical slope analysis method. Assuming the extraction of an
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J Incl Phenom Macrocycl Chem (2010) 67:295–302
301
Scheme 3 Proposed interaction
between ligand 3 and anion at
low pH
OH
OH
OH
OH
OH
OH
O
O
O
O
+
An-
O
O
-
OH
+
N
N
N
N
N
N
N
N
N
H+
An-
+
An-
+
+
N
N
N
H
H
H
H
H
H
2
-
-
-
An- = HCrO / HCr2O7 / Cr2O7
4
Kex
ðLHþÞorg þ HCr2O7ꢁaq $ ðLHþ; HCr2Oꢁ7 Þorg
toward mercury among transition metal cations as com-
pared to pyridine derivative of calix[4]arene (4). It has also
been deduced that 3 is an efficient extractant for chromate/
dichromate anions at low pH. The variety of hydrogen
bonding motifs that occur in these calix[4]arene derivatives
may be of considerable importance for the future design of
novel calix[4]arene-based receptors/carriers.
ð10Þ
ð11Þ
Ke0x
2þ
2ꢁ
ðLH2
Þ
þ Cr2O27ꢁaq $ ðLH22þ; Cr2O7
Þ
org
org
According to these assumptions, the extraction constant has
been calculated from the experimental data with similar Kex
and Ke0 xvalues using Eq. 7 Calculations of these constant
values lead to log Kex ¼ log Ke0x ¼ 1:4913 ꢄ 0:2 for 3.
Moreover, less extractability of compound 3 as com-
pared to compound 4 is due to the fact that cavity formed
by piperazine moieties is less effective than the cavity
formed by isoniazid moieties; because it has four amide
groups and two pyridine binding sites. Thus, high
extractability of 4 as compared to 3 may be due to addi-
tional interaction of amide functionalities of isoniazid
group along with pyridinium binding sites, which are
suitable for binding the anions at low pH.
Acknowledgments We thank the Higher Education Commission
Islamabad (No. Ps4-086/HEC/Sch/2007) and National Centre of
Excellence in Analytical Chemistry, University of Sindh, Jamshoro,
Pakistan for the financial support of this work.
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