Preparation of the ferrocene-substituted 1,3-distal p-tert-butylcalix[4]arene based QCM sensors array and utilization of its gas-sensing affinities

Article abstract of DOI:10.1016/j.jorganchem.2014.06.004

The article describes the synthesis of the new ferrocene-substituted calix[4]arene derivative 4 as sensitive layer, and suggests that the immobilization of it is on a quartz crystal microbalance gold electrode via the drop-casting method in order to produce the calix[4]arene-based QCM sensor. In addition, sensor response of the calix[4]arene-based QCM sensor was investigated towards carbon dioxide (CO₂) and carbon monoxide (CO). The sensing and selectivity studies show that the ferrocene-substituted calix[4]arene-based QCM sensor is an effective gas sensor toward both carbon dioxide and carbon monoxide.

Full text of DOI:10.1016/j.jorganchem.2014.06.004

Journal of Organometallic Chemistry xxx (2014) 1e5
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Preparation of the ferrocene-substituted 1,3-distal p-tert-butylcalix[4]
arene based QCM sensors array and utilization of its gas-sensing
affinities
,
,
Serkan Sayin a *, Cebrail Ozbek b, Salih Okur b c, Mustafa Yilmaz a
a Selcuk University, Department of Chemistry, Konya, Turkey
b Izmir Institute of Technology, Faculty of Science, Department of Physics, Urla, Izmir, Turkey
c Department of Material Science and Engineering, Faculty of Engineering and Architecture, Izmir Katip Celebi University, 35620 Izmir, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The article describes the synthesis of the new ferrocene-substituted calix[4]arene derivative 4 as sen-
sitive layer, and suggests that the immobilization of it is on a quartz crystal microbalance gold electrode
via the drop-casting method in order to produce the calix[4]arene-based QCM sensor. In addition, sensor
response of the calix[4]arene-based QCM sensor was investigated towards carbon dioxide (CO2) and
carbon monoxide (CO). The sensing and selectivity studies show that the ferrocene-substituted calix[4]
arene-based QCM sensor is an effective gas sensor toward both carbon dioxide and carbon monoxide.
© 2014 Elsevier B.V. All rights reserved.
Received 19 March 2014
Received in revised form
3 June 2014
Accepted 4 June 2014
Available online xxx
Keywords:
Calixarene
Ferrocene
QCM electrode
Carbon dioxide sensing
Carbon monoxide sensing
Introduction
Calixarenes, produced by a condensation reaction of phenol and
formaldehyde represent very useful building blocks in supramo-
Carbon dioxide and carbon monoxide are known serious hazard
gases for living systems in the atmosphere [1e8]. An increasing
concentration of carbon dioxide along with the other greenhouse
gases in the atmosphere, is causing the global temperature to in-
crease, and results in its toxic and harmful effects which reaches
both people and fauna alike [1e3]. Carbon dioxide is released into
the environment by anthropologic movements, fossil fuel com-
bustion, cement production, sewers, grain silos, ship holds, space-
crafts, and submarines [4,5]. Carbon monoxide is also known to be
toxic and dangerous for living systems in multiple environments. A
dangerous effect is seen in humans, especially, as the bloodstream
carries carbon monoxide through the lungs, and causes carbon
monoxide to interact with hemoglobin (Hb), which carries the
body's oxygen. This interaction creates carboxyhemoglobin (COHb),
thereby reducing the oxygen-delivering capacity of the blood
leading to the organs and tissues [7,8]. In high concentrations,
carbon monoxide causes fatal intoxication in humans [9].
lecular chemistry [10e13]. Indeed, their easy preparation, unlimited
functionalization, and differently-sized cavities of calixarenes make
them unique macrocyclic compounds [14e16]. These advantages
help calixarenes acquire the promising organic materials for
enzyme-mimics, ion carriers, solid-phase support materials, ion
selective electrodes, drug-deliveryagents, and catalysis applications
[17e20]. Chemical modification of them with various functional
groups also provides selectivity associating with their complexation
properties depending on host-guest, electrostatic, hydrogen
bonding, ion-dipole, and dipoleedipole interactions [19e23].
Regarding these properties, calixarenes have also been employed as
gas sensors for NO2, CO2, and CO, as well as humidity gases [24e26].
In the present study, an amino derivative of calixarene was
reacted with ferrocene carboxaldehyde, which exhibits anion
recognition effects based on a strong electrostatic interaction, to
produce a new ferrocene-conjugated calixarene derivative as an
effective sensor for toxic gases. The ferrocene-conjugated calixar-
ene derivative was immobilized for the first time onto a quartz
crystal microbalence gold electrode via the drop-casting method in
order to investigate its sensor capacity towards carbon monoxide
and carbon dioxide gases by using quartz crystal microbalence
* Corresponding author. Fax: þ90 332 2410106.
E-mail address: saynserkan@gmail.com (S. Sayin).
http://dx.doi.org/10.1016/j.jorganchem.2014.06.004
0022-328X/© 2014 Elsevier B.V. All rights reserved.
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S. Sayin et al. / Journal of Organometallic Chemistry xxx (2014) 1e5
(QCM) techniques, the preferred technique for determining the
sorption properties of hosts with respect to the specific gas as a
guest.
Preparation of QCM electrodes
In order to prepare QCM electrodes, 4.7 mg of the ferrocene-
substituted calixarene 4 or 2.6 mg of p-tert-butylcalix[4]arene 1,
which was used as a reference molecule, was dissolved in 4 mL of
chloroform, respectively. The prepared solutions, each of which
were 1 mM, were ultrasonicated for an hour to dissolve the com-
pound thoroughly. Finally, the prepared solutions were kept at
room temperature for 48 h. The step after preparation of the so-
lutions was to clean the surface of gold coated QCM electrodes as
follows: the QCM electrodes were cleaned in an ultrasonic bath in
acetone, ethanol, propanol and distilled water for 15 min, respec-
tively and then dried with high purity nitrogen. After cleaning QCM
Experimental
General remarks
TLC analyses were carried out on DC Alufolien Kieselgel 60 F254
(Merck). All reactions, unless otherwise noted, were conducted
under a nitrogen atmosphere. All starting materials and reagents
used were of standard analytical grade from Merck or Aldrich and
used without further purification. 1H NMR was recorded on a
Varian 400 MHz spectrometer. FTIR spectra were obtained on a
PerkineElmer 1605 FTIR spectrometer using KBr pellets and 100/
ATR Sampling Accessory. The cyclic voltammetric (CV) studies were
carried out according to the literature procedure [27]. Elemental
analyses were performed using a Leco CHNS-932 analyzer. Melting
points were determined on a Gallenkamp apparatus in a sealed
capillary glass tube and are uncorrected. A Shimadzu 160 A UVevis
apparatus was used to analyze absorbance of the ferrocene-
conjugated p-tert-butylcalix[4]arene (4) in CH2Cl2 solutions.
electrodes, 5 mL of each solution was dropped onto them and they
were kept at room temperature to dry. The structures of the
calixarene-modified QCM electrodes were determined by FTIR
spectrum (see Fig. 1).
Adsorption and desorption of the ferrocene-substituted calix[4]
arene 4 and p-tert-butylcalix[4]arene 1 were investigated under
exposure of CO and CO2 gas. Gas sensing properties of each deriv-
ative was investigated by using the Quartz Crystal Microbalance
(QCM) technique. A 2-channel gas-flow system controlled via PC
was set. Gas sensor responses of each calixarene film were
measured by the frequency shift response with a flow gas system
according to the Sauerbrey relation. The schematic of the mea-
surement system is depicted in Fig. 2. A time-resolved electro-
chemical QCM (EQCM) with the model of CHI400A Series from CH
Instruments (Austin, USA) was used to measure the change in the
resonance frequency of quartz crystals between gold electrodes
during adsorption and desorption. The range of oscillation fre-
quencies of QCM is between 7.995 MHz and 7.950 MHz. AT- cut
quartz crystals with a fundamental frequency of 7.995 MHz were
obtained from International Crystal Manufacturing Co. (ICM). The
Syntheses
The syntheses of compounds 1e3 were carried out according to
the literature procedures [28e30]. The ferrocene-substituted calix
[4]arene (4) is herein reported for the first time.
Synthesis of p-tert-butylcalix[4]arene-diester (2)
Yield: 14 g (63.4%); mp: 202e207 ꢀC. FTIR (KBr): 1750 cmꢁ1 (C]
O). 1H NMR (CDCl3):
d
0.97 (s, 18H, But), 1.24 (s, 18H, But), 3.35 (d,
4H, J ¼ 12.6 Hz, AreCH2eAr), 3.85(s, 6H, eOCH3), 4.45 (d, 4H,
J ¼ 12.6, AreCH2eAr), 4.78 (s, 4H, eOCH2CO), 6.85 (s, 4H, ArH), 7.05
(s, 4H, ArH), 7.10 (s, 2H, OH).
density (r m)
) of the crystal is 2.684 g/cm3, and the shear modulus (
of quartz is 2.947 ꢂ 1011 g/cm s2. Around oscillation frequency of
7.995 MHz, a net change of 1 Hz corresponds to 1.34 ng of gas
molecules adsorbed or desorbed onto the crystal surface of an area
of 0.196 cm2. Gas flow into test cell were supplied by two mass flow
meters (MKS,179A Mass-Flo®) and RS232 controlled gas flow con-
trol unit (MKS).
Synthesis of 5,11,17,23-tetra-tert-butyl-25,27-
dihydrazinamidecarbonylmethoxy-26,28-dihydroxy-calix[4]arene
(3)
Yield: 1.6 g (53.3%); mp: 330e333 ꢀC. FTIR (KBr): 1687 cmꢁ1
(NeC]O). 1H NMR (400 MHz, CDCl3):
d
1.02 (s, 18H, But), 1.26 (s,
18H, But), 2.15 (d, 4H, J ¼ 1.6 Hz, NH2), 3.42 (d, 4H, J ¼ 13.3 Hz,
AreCH2eAr), 4.11 (d, 4H, J ¼ 13.2 Hz, AreCH2eAr), 4.63 (s, 4H,
eOCH2), 6.92 (s, 4H, ArH), 7.10 (s, 4H, ArH), 7.70 (s, 2H, eOH), 9.61
(brs, 2H, NH).
Synthesis of ferrocene-conjugated p-tert-butylcalix[4]arene (4)
To a solution of 3 (0.6 g, 0.756 mmol) in 30 mL THF, a solution of
ferrocene carboxyaldehyde (0.3 g, 1.542 mmol) in 150 mL THF was
added. The reaction mixture was refluxed for 2 days. The volatile
component was evaporated to dryness, and the residue was dis-
solved in CHCl3 and washed with water to adjust pH 7.0. The
organic layer was then dried over MgSO4, filtered off and evapo-
rated to dryness. The crude was purified by column chromatog-
raphy (SiO2, EtOAc/MeOH, 20/1). Yield: 85%, m.p.; 184e186 ꢀC. FTIR
(ATR) cmꢁ1: 1641 (CH]N) and 1674 (C]O). 1H NMR (400 MHz,
CDCl3):
d 8.20 (s, 2H, HC]N), 7.52 (s, 2H, eNH), 7.13 (s, 4H, ArH),
7.09 (s, 2H, eOH), 6.91 (s, 4H, ArH), 4.75 (s, 4H, OCH2), 4.66 (brs, 4H,
C5H4), 4.37 (brs, 4H, C5H4), 4.14e4.21 (m, 14H, AreCH2eAr and
C5H5), 3.51 (d, 4H, J ¼ 13.5 Hz, AreCH2eAr), 1.27 (brs, 18H, But), 1.0
(brs, 18H, But). 13C NMR (100 MHz, CDCl3):
d 169.26 (CO), 153.60,
153.03, 150.43, 139.53, 139,48, 129.46, 129.21, 126.02, 125.25, 76.21,
73.94, 73.80, 68.57, 67.92, 38.98, 37.24, 31.54. Anal. Calcd. for
C
70H80Fe2N4O6: C, 70.94; H, 6.80; N, 4.73. Found (%): C, 70.74; H,
6.91; N, 4.68.
Fig. 1. FTIR spectra of the calixarene-modified QCM electrodes.
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S. Sayin et al. / Journal of Organometallic Chemistry xxx (2014) 1e5
3
binding properties toward carbon monoxide and carbon dioxide
gases as a new effective sensor. For this purpose, p-tert-butylcalix[4]
arene 1, and its diester derivative 2, were synthesized according to
the literature procedures [28,29]. The functionalization of the
diester derivative 2 at the lower rim was conducted with hydrazine
to produce 5,11,17,23-tetra-tert-butyl-25,27-dihydrazinamidecar
bonylmethoxy-26,28-dihydroxy-calix[4]arene (3) according to the
literature [30]. Next, 3 was treated with ferrocene carboxaldehyde to
produce a target calixarene-organoiron derivative 4 (Scheme 1). All
calixarene derivatives were characterized by using FTIR, 1H NMR
and elemental analysis techniques.
The FTIR spectra of the ferrocene-substituted calixarene 4 con-
firms its structure by appearing additional peak at 1641 cmꢁ1
wherein belongs the vibration stretch of CH]N bond. Moreover, 1H
NMR spectrum also confirms the formation of the ferrocene-
substituted calixarene 4 by the appearance of the characteristic
peak of imine protons (HC]N) at 8.20 ppm.
The UVevis spectra for 4 in CH2Cl2 solvent at 200e600 nm are
depicted in Fig. 3. The ferrocene-substituted calixarene 4 exhibits a
strong absorption at 290 nm, corresponding to the
p/p* transi-
tions, and a weak band at 460 nm due to the ded transition for the
iron of ferrocene [27].
Fig. 2. An experimental QCM setup of calixarene derivatives under different gases.
Results and discussion
The cyclic voltammetric (CV) study was used to investigate the
electrochemical properties of the ferrocene-substituted calixarene
4 (see Fig. 4). From the CV, it is clearly seen that the ferrocene-
substituted calixarene 4 exhibit one reversible oxidation wave
FceFcþ at E1/2 ¼ 0.53 V. The oxidation states given in Fig. indicate
that calixarene has an electronic communication with the ferrocene
units.
Selectively synthesis of calixarene containing organoiron derivative
as a sensor
The main goal of this work was the synthesis of a new calixarene,
containing organoiron derivative 4, and the exploration of its
OH
OHHO
OH
OH
i
ii
(1)
O
O
O
O
OH
O
OH
O
(2)
Fe
iii
Fe
H2N
O
NH2
O
NH
N
N
HN
H
O
O
O
NH
HN
O
O
OHOH
iv
Fe
+
OH
O
OH
O
(3)
(4)
Scheme 1. Synthesis of the ferrocene-substituted calix[4]arene 4. Reaction conditions: i) HCHO, NaOH; ii) methylbromoacetate, K2CO3, acetonitrile; iii) hydrazine, toluene/
methanol; iv) THF.
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4
S. Sayin et al. / Journal of Organometallic Chemistry xxx (2014) 1e5
Ref_Calix_CO
Ferrocene_Calix_CO
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
0
100
200
300
400
500
600
700
Time(sec)
Fig. 5. QCM frequency shifts of the QCM electrode modified with ferrocene-
substituted calix[4]arene 4 (Ferrocene_Calix_CO) and the QCM electrode coated with
p-tert-butylcalix[4]arene 1 (Ref_Calix_CO) for adsorption and desorption cycles under
carbon monoxide gase (CO).
Fig. 3. UVevis spectrum of the ferrocene-substituted calix[4]arene 4 (1.0 ꢂ 10ꢁ5 M in
CH2Cl2).
Sensing studies
Ref_Calix_CO2
Ferrocene_Calix_CO2
14
The removal of carbon monoxide (CO) and carbon dioxide gases
(CO2) from the atmosphere has gained high levels of attention
because of the toxic and serious hazardous effects of the gases on
the living systems. For this purpose, we were interested in syn-
thesizing a new p-tert-butylcalix[4]arene derivative at lower rim,
substituted with the ferrocene units as a host having well-binding
lobes for carbon monoxide and carbon dioxide gases. In order to
estimate sensing capacity of the ferrocene-substituted calixarene 4,
it was immobilized onto a quartz crystal microbalence gold elec-
trode via the drop-casting method [26]. Additionally, to determine
the impact of the organoiron units (ferrocene) of product 4 in the
sensing studies, p-tert-butylcalix[4]arene 1 was also immobilized
onto a quartz crystal microbalence gold electrode.
12
10
8
6
4
2
The sensing results indicated that the frequency responses of p-
tert-butylcalix[4]arene 1 immobilized QCM and the ferrocene-
substituted calixarene 4 immobilized QCM electrodes during the
sorption process under CO and CO2 gases (Figs. 5 and 6). Figs. 5 and
6 show that all calixarene-immobilized QCM electrodes have
different responses towards carbon monoxide and carbon dioxide.
The reason why the QCM electrode-immobilized with p-tert-
0
-2
0
100
200
300
Time(sec)
400
500
600
700
Fig. 6. QCM frequency shifts of the QCM electrode coated with ferrocene-substituted
calix[4]arene 4 (Ferrocene_Calix_CO2) and the QCM electrode coated with p-tert-
butylcalix[4]arene 1 (Ref_Calix_CO2) for adsorption and desorption cycles under car-
bon dioxide gase (CO2).
butylcalix[4]arene 1 has a sensing capacity for CO and CO2 gases
might be that calixarenes have a rigid structure and also have
strong complexation abilities such as host-guest, ion-dipole, dipo-
leedipole, and hydrogen bonding interactions. However, the fact
that the QCM electrode-immobilized with the ferrocene-
substituted calixarene 4 exhibited more sensing affinity than the
QCM electrode-immobilized with p-tert-butylcalix[4]arene 1 for
both gases would be assessed. This result was not surprising,
because the organoiron units (ferrocene) of calixarene 4 provide
additional complexation properties, such as cooperative affinities
and strong anion binding capabilities, to calixarene derivatives.
Conclusion
A new the ferrocene-substituted calix[4]arene 4 was synthe-
sized and then immobilized onto the surface of a quartz crystal
microbalence gold electrode by using the drop-casting method to
fabricate an organoiron-substituted calixarene-based QCM
Fig. 4. Cyclic voltammogram of the ferrocene-substituted calix[4]arene 4 (1.0 ꢂ 10ꢁ4
M
solution in CH2Cl2, and 0.1 M Bu4NPF6) estimated at a scan speed of 100 mV/s.
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5
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gases. p-tert-Butylcalix[4]arene was also immobilized onto the
QCM electrode, and its sensing capacity toward CO and CO2 gases
was investigated in order to compare and estimate the importance
of the calixarene contained within the ferrocene units. The results
indicated that both calixarene-immobilized QCM electrodes
depend on strong complexation properties of the calixarene
framework, such as host-guest, ion-dipole, dipoleedipole, and
hydrogen bonding interactions, which were effective receptors for
the adsorption of CO and CO2 gases. However, the QCM electrode
coated with ferrocene-substituted calix[4]arene 4 exhibited higher
sensing affinity than the QCM electrode coated with p-tert-butyl-
calix[4]arene because it acquired more complexation properties,
such as strongly anion binding and cooperative abilities, which
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