Synthesis of a tweezer-like bis(arylthiaalkoxy)calix[4]arene as a cation sensor for ion-selective electrodes: An investigation of the influence of neighboring halogen atoms on cation selectivity

Article abstract of DOI:10.1039/b211381c

Two novel tweezer-like 25,27-dihydroxy-26,28-bis(phenylthiaethoxy)calix[4]arenes 6 and 7 were synthesized by the reaction of 25,27-dihydroxy-26,28-bis(bromoethoxy)calix[4]arenes 3 and 4 for the evaluation of their ion-selectivity in ion-selective electrodes (ISEs). X-ray structural analysis indicated that calix[4]arene 7 is in an interesting infinite linear aggregate via self-inclusion. For investigation of the influences of substitutes on the behavior of the ISEs, the halogen substituted aryl analogues of 25,27-dihydroxy-26,28-bis(arylthiaethoxy)calix[4]arenes 8-12 were also synthesized and their ISE performances were evaluated under the same conditions. ISEs based on 6-12 as neutral ionophores were prepared, and their selectivity coefficients for Ag⁺ (log K_Ag.M^pot) were investigated against other alkali metal, alkaline-earth metal, lead, ammonium ions and some transition metal ions using the fixed interference method (FIM). These ISEs showed excellent Ag⁺ selectivity over most of the interfering cations examined, except for Hg^2- having relative smaller interference (log K_Ag.Hg^pot ≤ 2.1). The ¹⁹F NMR spectra of 9 and 9·AgClO₄ were recorded for investigation the fluorine environments in the complex. The ¹⁹F NMR spectra strongly suggested that the fluorine atoms on ionophore 9 participated in ligation with silver cation.

Full text of DOI:10.1039/b211381c

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Synthesis of a tweezer-like bis(arylthiaalkoxy)calix[4]arene as a
cation sensor for ion-selective electrodes: an investigation of the
influence of neighboring halogen atoms on cation selectivity†‡
Xianshun Zeng,*a Hao Sun,a,c Langxing Chen,b Xuebing Leng,a Fengbo Xu,a Qinshan Li,a
Xiwen He,b Wenqin Zhang*c and Zheng-Zhi Zhang*a
a State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin, 300071,
P. R. China
b Department of Chemistry, Nankai University, Tianjin, 300071, P. R. China
c Department of Chemistry, Tianjin University, Tianjin, 300072, P. R. China
Received 21st November 2002, Accepted 29th January 2003
First published as an Advance Article on the web 25th February 2003
Two novel tweezer-like 25,27-dihydroxy-26,28-bis(phenylthiaethoxy)calix[4]arenes 6 and 7 were synthesized by the
reaction of 25,27-dihydroxy-26,28-bis(bromoethoxy)calix[4]arenes 3 and 4 for the evaluation of their ion-selectivity
in ion-selective electrodes (ISEs). X-ray structural analysis indicated that calix[4]arene 7 is in an interesting infinite
linear aggregate via self-inclusion. For investigation of the influences of substitutes on the behavior of the ISEs, the
halogen substituted aryl analogues of 25,27-dihydroxy-26,28-bis(arylthiaethoxy)calix[4]arenes 8–12 were also
synthesized and their ISE performances were evaluated under the same conditions. ISEs based on 6–12 as neutral
pot
ionophores were prepared, and their selectivity coefficients for Agϩ (logKAg,M) were investigated against other alkali
metal, alkaline-earth metal, lead, ammonium ions and some transition metal ions using the fixed interference method
(FIM). These ISEs showed excellent Agϩ selectivity over most of the interfering cations examined, except for Hg2ϩ
pot
having relative smaller interference (logKAg,Hg ≤ 2.1). The 19F NMR spectra of 9 and 9ؒAgClO4 were recorded for
investigation the fluorine environments in the complex. The 19F NMR spectra strongly suggested that the fluorine
atoms on ionophore 9 participated in ligation with silver cation.
ition metal ions. The interferences of Hg2ϩ towards these
Introduction
electrodes are almost eliminated. However, when hard donor
Recently, research in the area of sensor development for metal
groups are close to these soft donors, such as hydroxy and ester
ion detection in chemical and biological applications has
groups, the lower discrimination of Hg2ϩ becomes a major
received much attention. A large number of ionophores based
problem in these ionophore-based ISEs. At the same time, some
on artificial host–guest theory and some natural hosts have
recent work has demonstrated that a π-system could provide
been employed in ion-selective electrodes (ISEs) as neutral
binding sites for many cations via a cation–π interaction21 and
carriers.1 In particular, the application of host–guest chemistry
it was also employed in ionophore-based ISEs.22 These results
to sensor development has proved to be a very valuable detec-
prompted us to design some new ionophores to investigate on
the influence factors for the same type of ionophores with some
tion method.2 Up to date, receptors including crown ethers,
cryptands and calixarenes have been synthesized as molecular
different neighboring groups for understanding the implication
agents for the binding of all kinds of cationic and anionic
of ion binding mechanism in ionophore-based ISEs. In this
species in ISEs.1,3 As a large family of host molecules, calix-
paper, ionophoric models using sulfur atoms as soft binding site
arenes have received much consideration in the past years. Since
and the halogens close to the soft sulfur donors as assistant
the first application of calix[4]arene tetraester as a Naϩ-select-
donors participating in ligation with the silver ion are
ive ionophore in ISEs,4 a large number of calix[4]arene deriv-
demonstrated.
atives for potentiometric measurements has subsequently been
We report herein the synthesis of two novel tweezer-like
reported. The success of these calix[4]arene derivatives results
receptor molecules 25,27-dihydroxy-26,28-bis(phenylthiaeth-
from the three-dimensional structure of the parent calix[4]-
arenes, which provide a scaffold on which various functional
oxy)calix[4]arenes 6–7 and their analogues 25,27-dihydroxy-
26,28-bis(arylthiaalkoxy)calix[4]arenes 8–12 together with their
groups can be attached to the phenolic oxygens. In fact, many
Agϩ selectivity behavior monitored by electromotive force
calixarenes have been successfully used as ionophores in main
measurements of polymer membrane electrodes based on these
group metal ion-selective electrodes,4–12 but only a few examples
novel Agϩ-selective ionophores. Comparison of the ISE per-
have shown selectivity for transition metal ions in calixarene-
formances of ionophores 6 and 7 with its halogen-substituted
analogues on the chain-substituted phenyls of ionophores
8–12, together with the influence of the tether length of the
same type receptors towards the ISE behavior of 6–12 will serve
based ISEs.13–16 In our previous work, calix[4]arene-based
receptors which are sensitive to the Agϩ ion by incorporating
nitrogen, sulfur, selenium or phosphorus atoms on the lower-
rim of the calix[4]arene scaffold have been developed.17–20 We
to promote further understanding of the structure–selectivity
found that using calix[4]arene derivatives containing sulfur,
relationships and the influence of halogen atoms on the
nitrogen, selenium atoms as ionophores in ISEs exhibited a
Agϩ-ISEs.
good Agϩ-selectivity against most of interfering ions such as
alkali metal ions, alkaline earth metal ions, lead ion and trans-
Results and discussion
† CCDC reference number 198110. See http://www.rsc.org/suppdata/
ob/b2/b211381c/ for crystallographic data in .cif format.
‡ Dedicated to Prof. Zhi-Tang Huang on the occasion of his 75th
birthday.
Syntheses
25,27-dihydroxy-26,28-bis(arylthiaalkoxy)calix[4]arenes 8–12
were obtained in good yields by the reaction of 25,27-
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 0 7 3 – 1 0 7 9
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Scheme 1 Reagents and conditions: (i) BrCH2(CH2)nBr, acetonitrile, potassium carbonate, refluxed for 24 h; (ii) thiophenol, potassium carbonate,
THF, refluxed for 6 h.
dihydroxy-26,28-bis(bromoalkoxy)calix[4]arenes 3–5 with
thiophenol in the presence of potassium carbonate as a base
(Scheme 1). The products were purified by column chromato-
graphy and then recrystallized from CH2Cl2 and MeOH. The
yields of 6–12 are between 59% and 74%. The 1H NMR spectra
of compounds 6–12 indicated that they kept the cone conform-
ation in solution, which can be easily judged from the two
doublets of the protons within the methylene bridge as well as
the separation of the protons of the aromatic units of the calix
skeleton. The protons within the chain-substituted phenyl of
compounds 6 and 7 gave multiplet peaks between 7.44 ppm and
7.09 ppm. The protons within the chain-substituted phenyl
groups in compounds 8–12 are usually separated into several
groups of multiplet peaks. As can be seen from Fig. 1b, the
2Ј-fluorophenyls in compound 9 give four groups of multiplet
peaks at 7.45 (td), 7.15 (ddd), 7.11 (dd) and 6.96 ppm (ddd),
respectively. The 2Ј,5Ј-dichlorophenyls in compounds 10–12
usually give three groups of multiplet peaks.
The silver complex of 25,27-dihydroxy-26,28-bis(3Ј-(2Љ-
fluorophenylthia)propoxy)-5,11,17,23-tetra-tert-butylcalix[4]-
arene (9ؒAgClO4) was synthesized by stirring the mixture of
calix[4]arene 9 and silver perchlorate (AgClO4) in methylene
chloride at ambient temperature for 4 h. The resulting solution
was filtered and condensed to dryness under reduced pressure.
After titration with ethyl ether and filtration, 9ؒAgClO4 was
obtained as a white powder in 95% yield. As can be seen from
Fig. 1a, the protons within the 2Ј-fluorophenyls also give four
groups of multiplet peaks. But they have downfield shift of
all the eight hydrogens compared with free ligand 9. The 5Ј-
hydrogens give multiplets at 7.75 ppm with a downfield shift of
0.3 ppm. The 3Ј, 4Ј and 6Ј hydrogens are downfield shifted by
0.14 ppm, 0.04 ppm and 0.01 ppm, respectively. As can be seen
from Fig. 1, the cone conformation of the calix skeleton also
distorted with the introduction of silver cation. All of the
hydrogens within the calix skeleton have shifts more or less after
coordination with silver cation. To investigate the environments
of the fluorine atoms in the complex, the 19F NMR spectra of
9 and 9ؒAgClO4 were measured in CDCl3 (Fig. 2). The free
ionophore 9 gives strong multiplet peaks at Ϫ(34.46–34.54)
ppm and weak multiplet peaks at Ϫ(34.61–34.71) ppm. These
multiplets can be rationalized by the chain-substituted fluoro-
phenyls being in conformational equilibrium with some
intramolecular weak C–H ؒ ؒ ؒ F hydrogen bonds in liquid
Fig. 1 1H NMR spectra of 9 (b) and 9ؒAgClO4 (a).
medium (as illustrated in Chart 1a). The proton NMR spectra
also supported this hypothesis. As can be seen from Fig. 1b,
the weak multiplets at 7.85 ppm and 7.35 ppm indicated that
9 had several conformers in solution. The 19F NMR spectra
of 9ؒAgClO4 not only supported this conformational equi-
librium (Fig. 2b and Chart 1b), but also suggested that the
fluorine atoms participated in ligation with the silver cation.
The fluorine atoms that participated in ligation with the
silver cation gave a strong peak at 2.56 ppm and the free
fluorine atoms gave a weak peak at 31.77 ppm. Compared with
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 0 7 3 – 1 0 7 9
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Fig. 3 X-ray structure of compound 7. All hydrogen atoms have been
omitted for clarity.
other two phenyls that linked the side arms form an interplanar
angle of 45.2Њ. The torsion angles of the two tethers that link
the phenyls and the calix skeleton are 81.4Њ [O(1)–C(45)–C(46)–
S(1)] and 178.0Њ [O(3)–C(53)–C(54)–S(2)], respectively. The
O ؒ ؒ ؒ O separations of the adjacent four oxygen atoms on the
lower rim of the calix[4]arene are between 2.74 and 2.90 Å,
which indicates that there are strong hydrogen bonds and
strong O ؒ ؒ ؒ O interactions between the four oxygen atoms. It
is interesting to note that compound 7 forms an infinite linear
aggregate via self-inclusion (Fig. 4). As shown in Fig. 4, the
phenyl attached to S(2) was imbedded within the hydrophobic
cavity of four aromatic groups and their four tert-butyl substi-
tutions as guest via weak interactions. Many weak interactions
exist in this inclusion situation. The strongest weak interactions
among all the weak contacts are the CH–π interactions. The
carbons [C(8A) and C(30A)] within the tert-butyl groups par-
ticipate in CH–π interactions from the two faces of the included
phenyl. The distances of C(8A) and C(30A) to the centroid
of the included phenyl are 3.99 Å and 3.85 Å, respectively.
The centroid ؒ ؒ ؒ H separations are 3.04 and 2.93 Å, with
centroid ؒ ؒ ؒ H–C(35) angles of 139.3Њ and 159.7Њ. Another
type of CH–π interaction in this inclusion complex is the con-
tacts of the aromatic C–H within the included phenyl with the
π-systems of the calix unit. The hydrogen H(58a) on the C(58)
forms a strong aromatic CH–π interaction with the phenyls
labelled C(35A), C(36A), C(37A), C(42A), C(43A) and C(44A)
of the calix framework. The C(58) ؒ ؒ ؒ centroid distance is 3.67
Å, with a H(58A) ؒ ؒ ؒ centroid distance of 2.80 Å and with a
C(58)-H(58A) ؒ ؒ ؒ centroid angle of 151.9Њ. However, the
distance of hydrogen H(56A) to the centroid of the aromatic
ring labelled C(13A), C(14A), C(15A), C(20A), C(21A) and
C(22A) is relatively longer than the H(58A) ؒ ؒ ؒ centroid
distance (3.18 Å, and with a C(56) ؒ ؒ ؒ centroid distance of
3.99 Å).
Fig. 2 19F NMR spectra of 9 (a) and 9ؒAgClO4 (b).
Chart 1 Conformational equilibria of 9 (A) and 9ؒAgClO4 (B).
the free ionophore 9, the ligation fluorine atoms have a 32 ppm
downfield shift and the free fluorine atoms have a 2.7 ppm
downfield shift.
Ion selectivity
X-ray crystallography of 7
The Agϩ selectivity of phenylthiaethoxy functionalized calix[4]-
The X-ray structure of calix[4]arene 7,23 grown by slow evap-
oration from the CH2Cl2–MeOH solution was elucidated for
determination of its structure (Fig. 3). As shown in Fig. 3, 7 is in
a ‘pinched’ cone conformation in the solid state. The sulfur
atoms (S(1) and S(2)) are disordered (only one position is
shown in Fig. 3 for clarity). The adjacent four phenyls within
the calix framework form interplanar angles between 71.9Њ and
106.3Њ. The two phenyls bearing hydroxy groups were tilted
away from the cavity with an interplanar angle of 83.3Њ. The
arenes 6 and 7 were evaluated by the potentiometric selectivity
coefficients (logKAg,M). For comparison, arylthiaalkoxy
pot
functionalized calix[4]arene 8–12 were examined under the
same conditions. The polymer membrane was composed of
PVC as the matrix, dibutyl phthalate (DBP) as the membrane
solvent, and a arylthiaalkoxy functionalized calix[4]arene as
the ionophore. The membranes also contained 75 mol% of
potassium tetrakis(4-chlorophenyl)borate (KTpClPB) relative
to the ionophore for the purpose of reducing membrane resist-
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 0 7 3 – 1 0 7 9
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Fig. 4 Infinite linear aggregate of compound 7 via self-inclusion in solid state.
pot
Table 1 Selectivity coefficient (logKAg,M) of the electrodes based on
ionophores 6–12
with other interfering cations being examined. It is interesting
to note that, despite four tert-butyls residing on the upper-rim
of ionophore 7, ISEs based on 6 and 7 exhibited characteristic
ion selectivity tendencies, which resemble each other. In other
words, the tert-butyl on the upper-rim of 7 results in a distinct
difference in ISEs. Although different halogen atoms are intro-
duced to the chain-substituted phenyls of the calix[4]arenes
8–12. 8–12-based ISEs also gave the same ion selectivity ten-
dencies as those of 6- and 7-based ISEs. For the same ion, the
selectivity coefficients are fairly close to each other (the
pot
logKAg,M
Ion
6
7
8
9
10
11
12
Agϩ
Naϩ
Kϩ
0
0
0
0
0
0
0
Ϫ4.0
Ϫ3.8
Ϫ3.7
Ϫ4.0
Ϫ4.2
Ϫ4.3
Ϫ3.7
Ϫ3.9
Ϫ4.2
Ϫ3.8
Ϫ2.2
Ϫ3.8
Ϫ3.7
Ϫ3.8
Ϫ4.3
Ϫ4.3
Ϫ4.2
Ϫ3.6
Ϫ3.8
Ϫ3.8
Ϫ3.7
Ϫ2.3
Ϫ3.9
Ϫ3.9
Ϫ3.9
Ϫ4.0
Ϫ4.4
Ϫ4.1
Ϫ4.3
Ϫ4.4
Ϫ4.0
Ϫ3.0
Ϫ2.1
Ϫ3.7
Ϫ3.8
Ϫ3.9
Ϫ3.8
Ϫ4.3
Ϫ4.0
Ϫ4.2
Ϫ4.3
Ϫ3.8
Ϫ3.0
Ϫ2.1
Ϫ4.1
Ϫ3.9
Ϫ4.1
Ϫ4.0
Ϫ4.3
Ϫ4.2
Ϫ4.2
Ϫ4.4
Ϫ4.0
Ϫ3.0
Ϫ2.2
Ϫ4.0
Ϫ3.8
Ϫ4.0
Ϫ3.9
Ϫ4.3
Ϫ4.2
Ϫ4.2
Ϫ4.4
Ϫ4.0
Ϫ3.0
Ϫ2.1
Ϫ4.0
Ϫ3.8
Ϫ4.0
Ϫ3.9
Ϫ4.4
Ϫ4.1
Ϫ4.3
Ϫ4.5
Ϫ3.9
Ϫ3.0
Ϫ2.5
ϩ
NH4
Ca2ϩ
Mg2ϩ
Ni2ϩ
Cu2ϩ
Zn2ϩ
Cd2ϩ
Pb2ϩ
Hg2ϩ
pot
logKAg,M values fluctuate by no more than 0.4 orders of mag-
nitude for the same ion), except for the Zn2ϩ, Cu2ϩand Pb2ϩ
,
which fluctuate by close to 0.5 orders of magnitude. As can be
seen from Table 1, with the introduction of halogen atoms to
the chain-substituted phenyls of 8–12, the discrimination of
Zn2ϩ and Cu2ϩ is larger than 0.5 orders of magnitude and the
discrimination of Pb2ϩ is lower than 0.7 orders of magnitude
compared with those of 6- and 7-based ISEs. In spite of the
weak fluctuations of Zn2ϩ, Cu2ϩ and Pb2ϩ, the performance of
6–12-based ISEs is superior to that displayed by a traditional
Ag2S-based electrode and is satisfactory as an Agϩ-ISE. The
ance and suppressing permeation of counteranions in the
aqueous phase into the membrane phase. The potentiometric
selectivity coefficients for Agϩ, determined by the fixed inter-
ference method, are illustrated in Table 1. The selectivity
fact that polymer membranes containing ionophores 6–12 gave
pot
pot
excellent logK values (≤Ϫ3.0) against Naϩ, Kϩ, NH ϩ, Ca2ϩ
,
coefficient (logKAg,M) represents the preference of the ISE (or
I,M
4
Mg2ϩ, Ni2ϩ, Cu2ϩ, Zn2ϩ, Cd2ϩ and Pb2ϩ means that 6–12-based
ISEs possess high Agϩ selectivity and only weakly respond to
the above interfering ions. The strong Hg2ϩ interfering in some
ionophore-based ISEs24–26 and traditional Ag2S-based ISE27 is
PVC membrane) containing the arylthiaalkoxy functionalized
calix[4]arene for Agϩ over the other cations. Therefore, the
pot
I,M
coefficients logK
represents the ability of an ISE (or
membrane) to recognize different ions under the same con-
pot
I,M
pot
ditions. The smaller the logK value, the greater the electrode
largely eliminated in the present ISEs (logKAg,Hg ≤ Ϫ2.1 for the
preference for the primary ion (Iϩ) over the interfering ion
present ISEs). The possible explanation is that those ions with
(Mϩ).
high hydration energies, such as Naϩ, Kϩ, NH4ϩ, Ca2ϩ, Mg2ϩ
,
pot
Pb2ϩ and most divalent transition metal ions, can not strongly
interact with sulfur donors in the ionophores, while less heavily
hydrated soft Agϩ coordinates to soft sulfur donors selectively.
The fact that polymer membrane containing 8–12 gave lower
The potentiometric selectivity coefficient, KAg,M determined
here is defined by the Nicolsky–Eisenman equation [eqn. (1)].
(1)
pot
pot
I,M
logK values of Zn2ϩ and Cu2ϩ and larger logK values of
I,M
Pb2ϩ against most interfering ions than any one of 6- and 7-
based ISEs means that 8–12-based ISEs possess larger Agϩ
selectivity than any one of 6- and 7-based ISEs of Zn2ϩ and
Cu2ϩ and lower Agϩ selectivity than any one of 6- and 7-based
ISEs of Pb2ϩ. This can be tentatively rationalized that the two
halogen atoms closing to the soft sulfur atoms in the iono-
phores 8–12 are participation in the ligation with the cations to
some extent. To prove this hypothesis, a silver perchlorate com-
plex of 9 was prepared and characterized. Because the fluorine
atom is a good 19F NMR probe in the complex, the 19F NMR
where E represents the experimentally observed potential, R
the gas constant, T the thermodynamic temperature in K, F the
Faraday constant, aAg the Agϩ activity, aM the activity of the
interfering cation, and ZM the charge of the interfering cation.
As shown in Table 1, polymer membranes incorporating
pot
calix[4]arene 6–12 as ionophores gave excellent logKAg,M values
(≤Ϫ3.0) against most of the interfering cations examined (i.e.,
Naϩ, Kϩ, NH4ϩ, Ca2ϩ, Mg2ϩ, Ni2ϩ, Zn2ϩ, Cu2ϩ, Cd2ϩ and Pb2ϩ),
except for Hg2ϩ gave a relatively lower discrimination compared
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 0 7 3 – 1 0 7 9
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Table 2 The response characteristics of silver ISEs based on 6–12
Ionophore
6
7
8
9
10
11
12
Slope/mV decadeϪ1
Linear range/M
Response time/s
R
56.6 1.2
55.5 1.3
52.9 0.85
50.5 0.84
50.7 1.3
10Ϫ5.0–10Ϫ1.3
<10
0.9980
45.9 0.95
10Ϫ5.0–10Ϫ1.3
<12
0.9987
49.3 1.2
10Ϫ5.3–10Ϫ1.3
<10
10Ϫ5.3–10Ϫ2.0
10Ϫ5.3–10Ϫ2.0
10Ϫ5.3–10Ϫ1.0
10Ϫ5.3–10Ϫ1.3
<10
0.9983
<10
0.9981
<10
0.9990
<10
0.9980
0.9981
spectra were recorded for the free ligand 9 and 9ؒAgClO4 under
the same conditions. As shown in Fig 2, the 19F NMR strongly
suggested that the fluorine atoms within the ionophore 9
participate in ligation with silver ion.
Experimental section
General remarks
Melting points were determined with a Boetius Block appar-
atus. 1H NMR spectra were recorded on a JEOL JNM-AL 300
spectrometer at 300 MHz in CDCl3 solution, using tetramethyl-
silane as an internal standard. Elemental analyses were
performed by Perkin-Elmer 2400C instrument. FAB-MS
spectra were obtained on a VG ZAB-HS spectrometer. X-ray
crystallographic data were obtained on a Bruker Smart 1000
instrument. Poly(vinyl chloride) (PVC), potassium tetrakis(4-
chlorophenylborate) (KTClPB) were purchased from Fluka
(Buchs, Switzerland). Dibutyl phthalate (DBP) was obtained
from Shanghai Chemical Reagent Corporation (Shanghai,
China). The silver nitrate (guaranteed reagent) and analytical
reagent grade nitrates of sodium, potassium, ammonium,
calcium, magnesium, cadmium, copper, nickel, zinc, lead and
mercury were supplied by Tianjin Chemical Reagent Factory.
All solutions were prepared with distilled deionized water.
Solvents were dried and purified according to literature
methods.28 Compounds 3–5 were prepared according to the
literature procedures.25,29
Comparing the potentiometric selectivity coefficients
pot
(logKAg,M) for most of main group metal ions and most of
transition metal ions of compounds 6–12 based ISEs with
our previous reported alkylthiaalkoxy functionalized calix-
[4]arenes,15,16 we found that the discrimination of Naϩ and Kϩ
of the present described ISEs is much larger than those of
alkylthiaalkoxy functionalized calix[4]arene derivatives-based
ISEs.15,16 There are two possibilities to explain these selective
tendencies. The first one is that the π-systems of the phenyls of
compounds 6 and 7 close to the soft sulfur donors participate in
the coordinating of silver ion as assistant donors via cation–π
interactions. In fact, many reports reveal that cation–π inter-
actions exist widely in solid state or in solution phase.21 The
second one is that the ionophores exhibit the signs of ditopic
receptors, namely, the four oxygen atoms on the lower-rim of
calix[4]arene act as a hard donor center and the two arylthia
groups act as a soft coordinate center. The hard donor center
has an affinity for high hydrate ions, and the soft donor center
has a selective affinity for the silver ion. Because the two centers
are close to each other, they cooperate in the binding of cation
species. Compared with the alkyl group, the bulk phenyls in
ionophores 6 and 7 controlled the soft centers as the main
binding site while they ligated to guest cations.
General procedures for the preparation of 25,27-dihydroxy-
26,28-bis(arylthiaalkoxy)calix[4]arenes 6–12
In a 100 mL round-bottomed flask, was added anhydrous
potassium carbonate (170 mg, 1.23 mmol), thiophenol or
substituted thiophenol (4 mmol), THF (50 ml) and calix-
[4]arene dibromide (0.5 mmol). The system was degassed, and
then the suspension was refluxed under nitrogen for 6 h. The
solvent was removed under reduced pressure. The residue was
dissolved with water (200 mL) and dichloromethane (30 mL).
The organic layer was separated and washed with water (20 mL
× 2). The final separated organic layer was dried with
anhydrous magnesium sulfate. After filtration, the filtrate was
condensed to dryness. The solid residue was purified by column
chromatography (petroleum ether/CH2Cl2, 3 : 1). The obtained
product was further purified by recrystallization from ethanol.
Besides the differences in the ion-selectivities, there are some
differences in the values of the properties of 6–12-based ISEs.
The response characteristics of silver ISEs such as response
slope, linear range and response time are summarized in
Table 2. As can be seen from Table 2, the Nernstian slopes of 6-
and 7-based ISEs are 56.6 1.2 and 55.5 1.3 mV decadeϪ1 to
the activity of Agϩ within the activity range 10Ϫ5.3–10Ϫ2.0
M
AgNO3. The relevant values of 8–12-based ISEs are between
52.9 0.85 and 45.9 0.95 mV decadeϪ1 to the activity of Agϩ
within the activity range 10Ϫ5.3–10Ϫ1.0 M AgNO3. The Nernstian
slope of 6- and 7-based ISEs is remarkably higher than that of
8–12-based ISEs. One possible explanation is that the halogen
atoms participated in the ligation with silver cation when it is
close to the sulfur donors. The extra binding with halogens
causes a relatively strong binding of the silver ion compared
with that of 6- and 7-based ISEs. The stronger binding of the
silver ion might interfere in the rapid ion exchange at the
membrane electrodes’ interface. The response time of 6–12-
based ISEs is within 12 s.
25,27-Dihydroxy-26,28-bis(2Ј-phenylthiaethoxy)calix[4]arene
(6).
Calix[4]arene 6 was obtained as a white powder in 72% yield
(250 mg) by the reaction of 3 (319 mg, 0.5 mmol) with thio-
phenol according to the general procedure, mp169–170 ЊC. H
1
NMR(200 MHz, CDCl3): 7.85(s, 2H, OH), 7.44–7.22(m, 10H,
Ph–H), 7.04(d, J = 7.4 Hz, 4H, m-Ar–H), 6.90(d, J = 7.3 Hz,
4H, m-Ar–H), 6.69(t, J = 7.3 Hz, 2H, p-Ar–H), 6.65(t, J = 7.3
Hz, 2H, p-Ar–H), 4.30(d, J = 13.1 Hz, 4H, ArCH2Ar),
4.16(t, J = 7.1 Hz, 4H, OCH2), 3.47(t, J = 7.1 Hz, 4H, SCH2),
3.34(d, J = 13.1 Hz, 4H, ArCH2Ar). FAB/MS m/z 696.2 ([M ϩ
1]ϩ, Calc. 696.4). Calc. for C44H40O4S2: C, 75.83; H, 5.79.
Found: C, 76.03; H, 6.00.
Conclusions
Tweezer-like receptor molecules 25,27-dihydroxy-26,28-bis-
(phenylthiaethoxy) calix[4]arenes 6 and 7 have been synthesized
as sensors for Agϩ-selective electrodes. 25,27-dihydroxy-26,28-
bis(arylthiaalkoxy) calix[4]arenes 8–12 were also prepared for
the comparison of the performance of 6- and 7-based ISEs. The
polymer membranes containing 6–12 gave good selectivity for
25,27-Dihydroxy-26,28-bis(2Ј-phenylthiaethoxy)-5,11,17,23-
tetra-tert-butylcalix[4]arene (7)
pot
Agϩ (logKAg,M ≤Ϫ3.0) against most of the interfering cations
examined (i.e., Naϩ, Kϩ, NH4ϩ, Mg2ϩ, Ca2ϩ, Ni2ϩ, Cu2ϩ, Zn2ϩ
,
Cd2ϩ and Pb2ϩ). These ionophores also gave good discrimin-
The above procedure was repeated starting with 25,27-di-
hydroxy-26,28-bis(2Ј-bromoethoxy)-5,11,17,23-tetra-tert-butyl-
calix[4]arene (4) (431 mg, 0.5 mmol) to get a white powder of
7 in 61% yield (282 mg), mp 159–160 ЊC. 1H NMR: 7.65(s, 2H,
OH), 7.36–7.09(m, 10H, Ph–H), 6.97(s, 4H, Ar–H), 6.71(s, 4H,
pot
ation of Hg2ϩ(logKAg,M ≤ Ϫ2.1). The performance of the
present ISEs is superior to that displayed by a traditional Ag2S-
based electrode. The halogen atoms participated in the ligation
with silver cation being proved by 19F NMR spectra.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 0 7 3 – 1 0 7 9
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Ar–H), 4.21(d, J = 12.9 Hz, 4H, ArCH2Ar), 4.05(t, J = 5.3 Hz,
4H, OCH2), 3.45(t, J = 5.3 Hz, 4H, SCH2), 3.21(d, J = 12.9 Hz,
4H, ArCH2Ar), 1.21(s, 18H, t-Bu–H), 0.88(s, 18H, t-Bu–H).
FAB/MS m/z 921.4 ([M ϩ 1]ϩ, Calc., 920.5). Calc. for
C60H72O4S2: C, 78.22; H, 7.88. Found: C, 78.51; H, 7.90.
25,27-Dihydroxy-26,28-bis(3Ј-(2Љ,5Љ-dichlorophenylthia)-
propoxy)-5,11,17,23-tetra-tert-butylcalix[4]arene (12).
The above procedure was repeated starting with 5 (445 mg, 0.5
mmol) to get a white powder of 12 in 73% yield (395 mg), mp
84–85 ЊC. 1H NMR(300 MHz, CDCl3): 7.63 (s, 2H, OH),
7.34(d, 2H, J = 1.8 Hz, Ph–H), 7.21(d, 2H, J = 7.9 Hz, Ph–H),
7.02(s, 4H, Ar–H), 6.99(dd, 2H, J = 7.9 Hz, J = 1.8 Hz, Ph–H),
6.84(s, 4H, Ar–H), 4.25(d, 4H, J = 12.9 Hz, ArCH2Ar), 4.10(t,
4H, J = 5.6 Hz, OCH2), 3.50(t, 4H, J = 6.7 Hz, SCH2), 3.32(d,
4H, J = 12.9 Hz, ArCH2Ar), 2.23(m, 4H, CH2CH2S), 1.26(s,
18H, t-Bu–H), 0.98(s, 18H, t-Bu–H). FAB/MS m/z 1086.4 ([M
ϩ 1]ϩ, Calc., 1086.2). Calc. for C62H72Cl4O4S2ؒ0.5CH2Cl2: C,
66.45; H, 6.51. Found: C, 66.26; H, 6.58.
25,27-Dihydroxy-26,28-bis(2Ј-(2Љ-florophenylthia)ethoxy)-
calix[4]arene (8).
Reaction of 3 (319 mg, 0.5 mmol) with 2-fluorothiophenol
according to the general procedure gave 8 as a white powder in
59% yield (216 mg), mp 176–178 ЊC. 1H NMR(300 MHz,
CDCl3): 7.68(s, 2H, OH), 7.42(td, 2H, J = 7.5 Hz, J = 1.5 Hz,
Ph–H), 7.13(ddd, 2H, J = 7.8 Hz, J = 1.5 Hz, J = 1.8 Hz, Ph–H),
7.00(d, 2H, J = 7.8 Hz, Ph–H), 6.98(d, 4H, J = 7.5 Hz, m-Ar–
H), 6.96(m, 2H, Ph–H), 6.78(d, 4H, J = 7.8 Hz, m-Ar–H),
6.62(t, 2H, J = 7.8 Hz, p-Ar–H), 6.59(t, 2H, J = 7.5 Hz, p-Ar–
H), 4.22(d, 4H, J = 12.9 Hz, ArCH2Ar), 4.08(t, 4H, J = 7.0 Hz,
OCH2), 3.48(t, 4H, J = 7.0 Hz, SCH2), 3.28(d, 4H, J = 12.9 Hz,
ArCH2Ar). FAB/MS m/z 732.1 (Mϩ, Calc., 732.2). Calc. for
C44H38F2O4S2ؒ1/3CH2Cl2: C, 69.95; H, 5.12. Found: C, 69.76;
H, 5.41.
Silver complex of 25,27-dihydroxy-26,28-bis(3Ј-(2Љ-florophenyl-
thia)propoxy)-5,11,17,23- tetra-tert-butylcalix[4]arene
(9ؒAgClO4)
To a 50 mL reactor, was added calix[4]arene 9 (50 mg,
0.05 mmol), silver perchlorate (AgClO4) (10.3 mg, 0.05 mmol)
and methylene chloride (30 mL). The mixture was stirred for 4 h
at ambient temperature. The resulting solution was filtered. The
filtrate was condensed to dryness under reduced pressure. Ethyl
ether (10 mL) was added to the colorless residue and stirred for
1 h. The white precipitates were filtered off and washed with
ether (5 mL). 9ؒAgClO4 was obtained in 95% yield (57.5 mg).
1H NMR(300 MHz, CDCl3): 7.75(dd, 2H, J = 7.5 Hz, J = 1.5
Hz, Ph–H), 7.29(m, 4H, Ph–H, OH), 7.15(t, 2H, J = 7.5 Hz,
Ph–H), 7.06(s, 4H, Ar–H), 7.04(t, 2H, J = 7.8 Hz, Ph–H),
6.79(s, 4H, Ar–H), 4.18(d, 4H, J = 12.9 Hz, ArCH2Ar), 4.02(t,
4H, J = 4.8 Hz, OCH2), 3.68(t, 4H, J = 3.6 Hz, SCH2), 3.32(d,
4H, J = 12.9 Hz, ArCH2Ar), 2.21(m, 4H, OCH2CH2), 1.29(s,
18H, t-Bu–H), 0.95(s, 18H, t-Bu–H); 19F NMR(282 MHz,
CDCl3): Ϫ2.56(s); FAB/MS m/z 1091.3 ([M-ClO4]ϩ, Calc.,
1091.5). Calc. for C62H74F2O4S2ؒAgClO4: C, 62.44; H, 6.25.
Found: C, 62.25; H, 6.19%.
25,27-Dihydroxy-26,28-bis(3Ј-(2Љ-florophenylthia)propoxy)-
5,11,17,23-tetra-tert-butylcalix [4]arene (9).
The above procedure was repeated starting with 25,27-di-
hydroxy-26,28-bis(3Ј-bromo-propoxy)-5,11,17,23-tetra-tert-
butylcalix[4]arene 5 (445 mg, 0.5 mmol) to get a white powder
of 9 in 74% yield (362 mg), mp 81–82 ЊC. 1H NMR(300 MHz,
CDCl3): 7.73(s, 2H, OH), 7.45(td, 2H, J = 7.7 Hz, J = 1.8 Hz,
Ph–H), 7.15(ddd, 2H, J = 6.3 Hz, J = 1.8 Hz, J = 2.7 Hz, Ph–H),
7.11(dd, 2H, J = 7.5 Hz, J = 1.5 Hz, Ph–H), 7.04(s, 4H, Ar–H),
7.03(ddd, 2H, J = 7.8 Hz, J = 1.8 Hz, J = 1.5 Hz, Ph–H), 6.86(s,
4H, Ar–H), 4.26(d, 4H, J = 12.9 Hz, ArCH2Ar), 4.09(t, 4H, J =
5.7 Hz, OCH2), 3.43(t, 4H, J = 6.9 Hz, SCH2), 3.33(d, 4H, J =
12.9 Hz, ArCH2Ar), 2.21(m, 4H, OCH2CH2), 1.27(s, 18H,
t-Bu–H), 1.00(s, 18H, t-Bu–H); 19F NMR(282 MHz, CDCl3):
Ϫ34.46∼ Ϫ 34.54(m), Ϫ 34.61∼ Ϫ 34.71(m); FAB/MS m/z 984.2
(Mϩ, Calc., 984.5). Calc. for C62H74F2O4S2ؒCH2Cl2: C, 70.83; H,
7.17. Found: C, 71.13; H, 7.22.
Silver selectivity evaluated by potentiometric selectivity
coefficient and membrane electrode
The typical procedure for membrane preparation is as follows:
Poly(vinylchloride) (PVC) (120 mg, 32–33%), dibutyl phthalate
(DBP) (240 mg, 64–65%), phenylthiapropoxy functionalized
calix[4]arene (4 mg, 1%), potassium tetrakis(p-chlorophenyl)-
borate (KTClPB) (0.75%) were dissolved in 5 mL of THF. This
solution was then poured into a flat-bottomed petri dish of 16
mm inner diameter and 50 mm height. Gradual evaporation of
the solvent at room temperature gave a transparent, flexible
membrane of about 0.3 mm in thickness. A disk of 7 mm in
diameter was cut from the PVC membrane and incorporated
into a PVC tube tip with THF. After injection of 0.001 M
aqueous solution of AgNO3 as the internal solution, the
electrode was conditioned by soaking in 0.001 M aqueous
solution of AgNO3 for 24 h. The external reference electrode
is a double junction type Ag/AgCl glass electrode. The com-
position of the electrochemical cell is given as Ag|AgCl|0.001 M
AgNO3¦ PVC membrane¦sample solution|1 M KNO3|4 M
KCl|Hg2Cl2|Hg.
25,27-Dihydroxy-26,28-bis(2Ј-(2Љ,5Љ-dichlorophenylthia)ethoxy)-
calix[4]arene (10).
Reaction of 3 (319 mg, 0.5 mmol) with 2,5-dichlorothiophenol
according to the general procedure gave 10 as a white powder in
62% yield (257 mg), mp 203–204 ЊC. 1H NMR (300 MHz,
CDCl3): 7.61(s, 2H, OH), 7.27(d, 2H, J = 2.4 Hz, Ph–H), 7.17(d,
2H, J = 8.4 Hz, Ph–H), 7.02(d, 4H, J = 6.9 Hz, m-Ar–H),
6.99(dd, 2H, J = 8.4 Hz, J = 2.4 Hz, Ph–H), 6.82(d, 4H, J = 7.5
Hz, m-Ar–H), 6.66(t, J = 6.9 Hz, 2H, p-Ar–H), 6.61(t, J = 7.5
Hz, 2H, p-Ar–H), 4.25(d, 4H, J = 13.2 Hz, ArCH2Ar), 4.15(t,
4H, J = 6.9 Hz, OCH2), 3.53(t, 4H, J = 6.9 Hz, SCH2), 3.34(d,
4H, J = 13.2 Hz, ArCH2Ar). FAB/MS m/z 834.3 (Mϩ, Calc.,
834.1). Calc. for C44H36Cl4O4S2: C, 63.31; H, 4.35. Found: C,
63.12; H, 4.38.
25,27-Dihydroxy-26,28-bis(2Ј-(2Љ,5Љ-dichlorophenylthia)ethoxy)-
5,11,17,23-tetra-tert-butyl-calix[4]arene (11).
The above procedure was repeated starting with 4 (431 mg, 0.5
mmol) to get a white powder of 11 in 65% yield (342 mg), mp
135Ϫ136 ЊC. H NMR(300 MHz, CDCl3): 7.23(d, 2H, J = 2.4
EMF measurements
1
Hz, Ph–H), 7.19(d, 2H, J = 8.4 Hz, Ph–H), 7.08(s, 2H, OH),
7.01(dd, 2H, J = 8.4 Hz, J = 2.4 Hz, Ph–H), 6.99(s, 4H, Ar–H),
6.75(s, 4H, Ar–H), 4.23(d, 4H, J = 13.2 Hz, ArCH2Ar), 4.13(t,
4H, J = 6.6 Hz, OCH2), 3.48(t, 4H, J = 6.6 Hz, SCH2), 3.28(d,
4H, J = 13.2 Hz, ArCH2Ar), 1.23(s, 18H, t-Bu–H), 0.90(s, 18H,
t-Bu–H). FAB/MS m/z 1059.2 ([M ϩ 1]ϩ, Calc., 1058.3). Calc.
for C60H68Cl4O4S2ؒ0.5CH2Cl2: C, 65.96; H, 6.31. Found: C,
65.85; H, 6.33.
All EMF (electromotive force) measurements were made at
25
1 ЊC, using a pH/mV meter. The sample solution was
magnetically stirred and kept in a thermostated water bath. The
performance of the electrodes was investigated by measuring
their potential in 10Ϫ7∼10Ϫ1 M solution of AgNO3. The EMF
values were corrected by subtracting the liquid-junction
potential between the external reference electrode and the
sample solution in the high Agϩ concentration.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 0 7 3 – 1 0 7 9
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15 (a) M. T. Lai and J. S. Shih, Analyst, 1986, 111, 891; (b)
Acknowledgements
S. K. Srivastava, V. K. Gupta and S. Jain, Anal. Chem., 1996, 68,
1272.
The National Natural Science Foundation of China (No.
20102003) and the Foundation of Nankai University supported
this work.
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S. Maeda, Talanta, 1999, 48, 705.
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O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 0 7 3 – 1 0 7 9
1079