Synthesis, enhanced spectroscopic characterization and electrochemical grafting of N-(4-aminophenyl)aza-18-crown-6: Application of DEPT, HETCOR, HMBC-NMR and X-ray photoelectron spectroscopy

Article abstract of DOI:10.1016/j.molstruc.2010.08.024

This work describes the synthesis, characterization and electrochemical grafting of N-(4-aminophenyl)aza-18-crown-6 (4APA18C6). The key step in the synthesis is the reaction of N-phenylaza-18-crown-6 (PA18C6) with sodium nitrite. The compound, N-(4-nitros

Full text of DOI:10.1016/j.molstruc.2010.08.024

Journal of Molecular Structure 982 (2010) 162–168
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, enhanced spectroscopic characterization and electrochemical grafting
of N-(4-aminophenyl)aza-18-crown-6: Application of DEPT, HETCOR,
HMBC-NMR and X-ray photoelectron spectroscopy
c
c
Pervin Deveci a, Bilge Taner a, Zafer Üstündag˘ b, Emine Özcan a, , Ali Osman Solak , Zeynel Kılıç
⇑
a Selcuk University, Faculty of Science, Department of Chemistry, Konya, Turkey
b Dumlupınar University, Faculty of Arts and Sciences, Department of Chemistry, Kütahya, Turkey
c Ankara University, Faculty of Science, Department of Chemistry, Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
This work describes the synthesis, characterization and electrochemical grafting of N-(4-aminophenyl)aza-
18-crown-6 (4APA18C6). The key step in the synthesis is the reaction of N-phenylaza-18-crown-6
(PA18C6) with sodium nitrite. The compound, N-(4-nitrosophenyl)aza-18-crown-6 (NOPA18C6) could not
be isolated purely from the reaction mixture, but a reduction of the residue with SnCl2 gave the desired aza-
crown ether, N-(4-aminophenyl)aza-18-crown-6 (4APA18C6). To confirm its proposed structure detailed
characterization techniques such as elemental analysis, FT-IR, 1H NMR, 13C NMR, DEPT, HETCOR, HMBC
and ESI mass-spectrometry were used. Due to the importance of azacrown compounds in the field of analyt-
ical chemistry, in the derivatization of dyes, chemical sensors and ionic extraction, as molecular receptors,
grafting of 4APA18C6 on the glassy carbon (GC) surface has been investigated by amine oxidation to gain
new insight into the modification area. The oxidation mechanism has been established, and the results are
in accordance with the attachment of amines to a glassy carbon surface by cyclic voltammetry. The modifica-
tion of 4APA18C6 molecules onto the glassy carbon surface was verified by cyclic voltammetry (CV), X-ray
photoelectron spectroscopy (XPS) reflection–absorption infrared spectroscopy (RAIRS) and ellipsometry.
The film on the GC surface was formed according to the layer-by-layer mechanism and the ellipsometric
thickness was obtained around 11.5 1.1 nm.
Received 12 March 2010
Received in revised form 22 July 2010
Accepted 13 August 2010
Available online 22 August 2010
Keywords:
N-phenylaza crown
N-(4-aminophenyl)aza-18-crown-6
Two dimensional spectroscopy
Glassy carbon
Surface characterization
X-ray photoelectron spectroscopy
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
properties of these compounds. Such changes produce agents with
different sensitivities and selectivities for metal ions, including
Crown ethers remain among the most important building
blocks in supramolecular chemistry since their discovery in 1967
by Pedersen [1]. Numerous crown ethers have been prepared and
several detailed reviews have been published giving an overview
of the syntheses and properties of these compounds [2,3]. Aza
crown ethers occupy a specific place among the macrocyclic crown
ether ligands because of both their fascinating structures and high
abilities of ligation with both alkali and alkaline earth as well as
heavy-metal guest cations [4]. Because of their remarkably com-
plex properties, the study of azacrown ethers has largely contrib-
uted to the development of host–guest interactions by improving
selective fluorescent sensors for cation detection [5,6]. Several
workers have reported azacrown ether derivatives with chromo-
genic groups [7,8] and it is known that varying the size of the aza-
crown ether ring or the chromophoric side arm can modify the
azacrown ether based dyes possessing a potential anionic site at-
tached to the chromophore [9]. In addition, azacrown ethers are
an important class of organic compounds that have found applica-
tion in such diverse areas as synthetic receptors in molecular rec-
ognition processes [10] and, in some cases, anion complexation
properties that are similar to those in certain biological systems
[11,12]. They have an enhanced ligating ability for alkyl (or aryl)
ammonium salts [13,14] and for transition metal cations [15,16]
over the conventional crown ethers. The study of the electrochem-
ical properties of organic compounds on GC widely attracts the
interest of electrochemists and surface scientists because this kind
of study can be essential for the development of new electronic
devices and electrosynthesis [17]. In modification areas, GC elec-
trodes are often used owing to their good electrochemical conduc-
tivity, and chemical and electrochemical inactivity [18]. Although
the application of macrocyclic crown ether ligands, especially aza-
crown ethers as low molecular weight receptors used in assessing
noncovalent bondings important in chemistry and biochemistry
attracts intense attention, electrochemical grafting of crown ether
⇑
Corresponding author. Tel.: +90 332 2233859; fax: +90 332 2412499.
E-mail address: emineozcann@gmail.com (E. Özcan).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.08.024

P. Deveci et al. / Journal of Molecular Structure 982 (2010) 162–168
163
derivatives and their binding properties on the glassy carbon
surfaces have not been throughly investigated [19–21]. For that
reason, we think that immobilization of azacrown ethers on glassy
carbon surfaces can generate new materials with interesting prop-
erties due to their above mentioned specific complexation abilities
with different alkaline, alkaline earths, and alkyl (or aryl) ammo-
nium cations.
radiation (1486.6 eV) as an X-ray anode. Ellipsometric thickness
measurement of 4APA18C6 film was made with an ELX-02C/01R
Model (Germany) high precision discrete wavelength ellipsometer.
The wavelength was 532 nm for all experiments. The thickness val-
ues of the films at the GC-20 (Tokai, Japan) surface were deter-
mined from the average of the measurements using an incidence
angle of 70°.
The goal of this research is to characterize of the structure of
4APA18C6 in detail for the first time by using elemental analysis,
FT-IR, 1H NMR, 13C NMR, DEPT, HETCOR, HMBC and ESI mass-spec-
trometry, and to perform a modified GC surface using this unique
compound to gain new insight into the modification area by the
amine oxidation. In addition, this study also reports the character-
ization of the modified surface by using CV, XPS and RAIRS. Ellips-
ometry was used as a means of determining the thicknesses of the
4APA18C6 nanofilm at GC.
2.3. Synthesis of the azacrown ethers
2.3.1. N-(Phenylaza-18-crown-6) sodium perchlorate monohydrate,
[NaPA18C6] ClO4ÁH2O
This compound was prepared using a modification of the proce-
dure reported in the literature [23,24].
A two-necked flask
equipped with a dropping funnel was evacuated and refilled with
argon, and then 300 mL dry THF and NaH (60% suspension in
paraffin oil) (6.40 g, 16.1 Â 10À2 mol) were added and refluxed.
N-phenyldiethanolamine (14.5 g, 8.11 Â 10À2 mol) and tetraethyl-
eneglycol ditosylate (40.2 g, 8.11 Â 10À2 mol) were dissolved in
300 mL dry THF and then slowly added dropwise to the reaction
mixture. The addition was completed in 3 h, and refluxing was
continued for another 5 h. After cooling, the solid was filtered
and washed with THF, and the filtrate was concentrated under re-
duced pressure. The residue dissolved in 10 mL methanol. To this
solution, a solution of sodium perchlorate monohydrate (11.3 g,
8.11 Â 10À2 mol) in 15 mL methanol was added. The mixture was
refluxed for 10 min after which the mixture was concentrated to
a small volume followed by the addition of ethylacetate. The mix-
ture was evaporated and the residue was recrystallized from ethyl-
acetate, to give 19.2 g (50%) of the sodium perchlorate complex,
mp.: 148 °C.
2. Experimental
2.1. Chemicals
Tetraethylene glycol (Merck), sodium hydroxide (Merck), p-tolu-
enesulphonyl chloride (Merck), calcium chloride (Merck), sodium
hydride (60% suspension in paraffin oil) (Merck), N-phenyldietha-
nolamine (Merck), sodium perchlorate monohydrate (Merck),
sodium nitrite (Merck), sodium carbonate (Merck), anhydrous mag-
nesium sulfate (Merck), tin(II) chloride (Fluka), silver nitrate (Fluka),
activated carbon (Sigma–Aldrich), tetrabutylamonium-tetrafluoro-
borate (TBATFB) (Fluka), potassium ferricyanide (Sigma–Aldrich),
potassium ferrocyanide (Merck), potassium chloride (Merck), ferro-
cene (Sigma), acetonitrile (MeCN) (Sigma), isopropyl alcohol (IPA)
(Sigma), tetrahydrofuran (THF) (Merck), dichloromethane (Merck),
methanol (Merck), ethylacetate (Sigma–Aldrich), hydrochloric acid
(Merck), ethanol (Merck) were reagent grade quality and used as re-
ceived from the supplier. All of the processes were performed in
aqueous media, and the preparation of the aqueous solutions was
carried out using an ultra pure quality of water with a resistance
IR (cmÀ1): 3339, 3062, 3038, 2962, 2915, 2878, 1649, 1626,
1597, 1494, 1251, 1110, 882, 735, 623 cmÀ1 1H NMR (CDCl3,
.
400 MHz, 25 °C): d = 1.56 (s, 2H, H2O), 3.59–3.78 (m, 24H, NCH2,
OCH2), 6.80–6.85 (m, 3H, ArH), 7.21–7.27 (m, 2H, ArH), 13C NMR:
d = 51.35, 69.08, 69.12, 69.32, 69.62, 71.13, 116.37, 119.39,
129.55, 149.58, C18H31NO10NaCI: calcd. C 45.05, H 6.51, N 2.92;
found C 45.15, H 6.48, N 2.90.
of ꢀ18.3 M
X
cm (Human Power 1+ Scholar purification system). Be-
fore electrochemical experiments, solutions were purged with pure
argon gas (99.999%) for at least ten minutes and an argon atmo-
sphere was maintained over the solution during experiments. Tetra-
ethyleneglycol ditosylate was prepared according to the published
method [22]. NaPA18C6 and PA18C6 were prepared according to
the modified methods reported in the literature [23,24]. The new
compounds NOPA18C6 and 4APA18C6 were synthesized according
to the modification of the reported procedure [24].
2.3.2. N-Phenylaza-18-crown-6, [PA18C6]
This compound was prepared using a modification of the proce-
dure reported in the literature [23]. N-phenylaza-18-crown-6 so-
dium perchlorate monohydrate (19.2 g) was decomposed by
treatment with a mixture of CH2Cl2:H2O (1:1); the organic layer
was separated, dried and evaporated to give N-phenylaza-
18-crown-6, 10.1 g of (50%), mp.:35 °C.
IR (cmÀ1): 3059, 3024,2950, 2900, 2869, 2800, 1599, 1573,
1465, 1250, 1115, 839, 749. 1H NMR (CDCl3, 400 MHz, 25 °C):
d = 3.60–3.77 (m, 24H, NCH2, OCH2), 6.64–6.69(m, 3H, ArH),
7.17–7.21(m, 2H, ArH).13C NMR: d = 51.52, 68.94, 70.90, 70.98,
71.03, 71.06, 111.85, 116.10, 129.51, 147.99, C18H29NO5: calcd. C
63.69, H 8.61, N 4.13; found C 63.50, H 8.63, N 4.11.
2.2. Apparatus
Elemental analyses (C, H, N) were determined using a LECO-932
CHNSO model analyzer. The 1H and 13C NMR spectra were re-
corded on a Varian 400 MHz spectrometer in CDCl3 with trimeth-
ylsilane as an internal standard. Infrared spectra were recorded
directly as KBr pellets and directly from the film deposited on GC
electrode in a FTIR spectrometer Bruker-Tensor 27 (Bruker Optics
Inc., Ettlingen, Germany). Melting points were determined using
an electrothermal apparatus and were uncorrected. All the electro-
chemical experiments were performed using a Gamry Reference
300 workstation (Gamry, USA). The working electrode was a bare
or modified glassy carbon (GC) disk (BAS) with a geometric area
of 0.027 cm2. The reference electrode was either an Ag/AgCl/
KCl(sat.) used in aqueous media or an Ag/Ag+ (0.01 M) used in
MeCN. The auxiliary electrode was a Pt wire. The surface of the
sample was analyzed using a SPECS X-ray photoelectron spectrom-
2.3.3. N-(4-Nitrosophenyl)aza-18-crown-6, [NOPA18C6]
This compound was prepared by modifying the procedure re-
ported in the literature [24]. N-Phenylaza-18-crown-6 (3.39 g,
10.1 mmol) was dissolved in 5 mL warmed hydrochloric acid
(37%). Ice was then added and the mixture was stirred at a temper-
ature below 5 °C. An aqueous solution of NaNO2 (0.71 g,
10.1 mmol) in 2 mL H2O was slowly added. After this addition,
the mixture was stirred for 20 min. The mixture separated into
two layers upon the addition of ice water (30 mL) and dichloro-
methane (20 mL). The mixture was adjusted to basic conditions
upon vigorous stirring using saturated Na2CO3. The aqueous layer
was extracted with dichloromethane several times. The dichloro-
methane extracts that were green in color were combined, and
eter (Berlin, Germany) system with unmonochromatized Al K
a

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P. Deveci et al. / Journal of Molecular Structure 982 (2010) 162–168
dried over anhydrous magnesium sulfate. After filtration, the sol-
vent was evaporated to dryness, leaving behind a green residue.
The green residue was used in the synthesis of N-(4-aminophe-
nyl)aza-18-crown-6 directly without purification.
2.4.2. Preparation of 4APA18C6 nanofilm on GC
A modification of GC electrodes was performed in a solution of
1 mM 4APA18C6 in 0.1 M TBATFB in acetonitrile vs. Ag+/Ag
(0.01 M) reference electrode using CV with
a scan rate of
100 mV sÀ1 for 10 cycles between 0 V and 2.6 V. The 4APA18C6
solution was deaerated with argon for at least 10 min prior to
grafting. A fresh sample of 4APA18C6 was used for each modifica-
tion process. Following the modification, electrodes were rinsed
with acetonitrile and kept in a dust free argon atmosphere until
use.
2.3.4. N-(4-aminophenyl)aza-18-crown-6. [4APA18C6]
This was prepared by a modification of a literature procedure
[24]. The crude N-(4-nitrosophenyl)aza-18-crown-6 was dissolved
in 3 mL hydrochloric acid (37%) and 1.6 mL water. SnCl2 (1.85 g,
10.1 mmol) was then added in portions while stirring at 40 °C.
Water (20 mL) was added to dilute the solution after 20 min and
the mixture was allowed to continue stirring for another 30 min.
After the addition of NaOH (40%), the crude product appeared as
a brown oil. The mixture was extracted with dichloromethane sev-
eral times and the combined dichloromethane extracts were dried
over anhydrous magnesium sulfate. After filtration, the solvent
was evaporated to dryness leaving brown oils. Subsequent recrys-
tallization from acetonitrile gave the product as brown crystals at
quantitative yield, mp.: 37 °C.
3. Results and discussion
The synthetic strategy for the formation of the aza crown ethers
involves a reaction between tetraethyleneglycol ditosylate and N-
phenylenediethanolamine with excess NaH refluxing in THF
(Scheme 1).
Azacrown derivatives were unambiguously characterized by
elemental analyses, FT-IR, 1H and 13C NMR spectroscopies as well
as 4APA18C6 compound was characterized by DEPT and 2D-NMR
spectroscopies (HETCOR and HMBC) and ESI high resolution mass
spectrometry. Azacrown derivatives (NaPA18C6 and PA18C6) were
obtained in good yields, while the amino compound 4APA18C6
was obtained in quantitative yield.
IR (cmÀ1): 3438, 3370, 3057, 3024, 2904, 2890, 2700, 1631,
1597, 1507, 1472, 1279, 1194, 1101, 836, 751.1H NMR (CDCl3,
400 MHz, 25 °C): 3.51 (s, 2H, NH2), 3.60–3.73 (m, 24H, CH2O and
CH2N) 6.68 (dd, 2H, ArH), 7.20 (dd, 2H, ArH).13C NMR: d = 51.50,
68.95, 70.93, 71.01, 71.06, 71.09, 111.77, 116.03, 129.51, 148.02.
EI MS: m/z 355.2517 [MH]+. C18H30N2O5: calcd. C 61.00, H 8.53, N
7.90; found C 60.98, H 8.57, N 7.98.
3.1. Spectroscopic characterizations of azacrown ethers
In the FTIR spectra of NaPA18C6, 4APA18C6 and PA18C6 com-
pounds, characteristic asymmetric and symmetric medium inten-
sity stretching vibrations of mAr–H are observed at 3070–
2.4. Electrochemical studies
3057 cmÀ1 and 3038–3024 cmÀ1
. Asymmetric and symmetric
2.4.1. Cleaning and preparing the GC electrode for modification
Glassy carbon electrodes were prepared by first polishing them
with fine wet emery papers with grain size of 4000 (Buehler, Lake
CAOAC stretching vibration bands are observed at 1110 and
882 cmÀ1 for NaPA18C6; at 1101 and 836 cmÀ1 for 4APA18C6
and at 1115 and 839 cmÀ1 for PA18C6 compounds, respectively.
In the 1H NMR spectra characteristics of NaPA18C6 and
4APA18C6, both aza crown ether functionalities and the benzene
ring are easily identified. The signals in all the 1H NMR spectra of
the azacrown ether-functionalized compounds can be grouped into
two regions. The first region includes signals with chemical shifts
between 7.17–7.27 ppm and 6.64–6.85 ppm, which are assigned
Bluff, IL, USA) followed by 0.1 lm and 0.05 lm alumina slurry on a
polishing pad (Buehler, Lake Bluff, IL, USA) to gain a mirror-like
appearance. The electrodes were sonicated for 15 min in water
and in 50:50 (v/v) isopropyl alcohol and acetonitrile (IPA + MeCN)
solution purified over activated carbon. Before derivatization, the
electrodes were dried with an argon gas stream.
Scheme 1. Synthetic scheme for 4APA18C6.

P. Deveci et al. / Journal of Molecular Structure 982 (2010) 162–168
165
to the aromatic protons. The second region shows the peaks with
chemical shifts at 3.59–3.78 ppm as multiplets for the protons of
ethylenic chains.
The 13C NMR spectra of the compounds NaPA18C6 and PA18C6
confirmed the proposed structures (Scheme 1). In the 13C NMR
spectra of both compounds, ten expected different carbon atoms
are observed that are consistent with the structures of the com-
pounds on the basis of molecular symmetry (Scheme 2).
The structure of the new compound, 4APA18C6, is characterized
in detail using elemental analysis, FT-IR, 1H-, 13C NMR, DEPT, HET-
COR, HMBC and ESI mass-spectrometry. In the 1H NMR spectrum
of this compound, aromatic protons are observed at 7.20 ppm for
H9 and 6.68 ppm for H8 as two doublets of doublets (3JHH = 7.2 Hz
and 4JHH = 1.7) (Fig. 1).The protons of the ethylenic chains moieties
shows peaks with chemical shifts at 3.59–3.78 ppm as multiplets.
In the 13C NMR spectrum of 4APA18C6 (Fig. 2), ten different car-
bon atoms are observed which are consistent with the proposed
structure of the compound on the basis of molecular symmetry
(Scheme 2). Distortionless enhancement of NMR signals by polari-
zation transfer (DEPT) is used to better discriminate the different
types of carbons present in 4APA18C6 (Fig. 2).
Fig. 2. The 13C NMR and DEPT spectra of 4APA18C6.
The DEPT spectrum of 4APA18C6 gives the CH2 peaks at 51.50,
68.95, 70.93, 71.01, 71.06, and 71.09 ppm, and CH peaks at 111.77
and 129.51 ppm. It can be seen that there is no CH3 peak in the
DEPT spectrum. The other peaks of 13C NMR except for the peaks
in DEPT spectrum are non-protonated carbons. The chemical shifts
of different carbons and the assignments of the protons are made
using the correlation experiments and written on the spectra in
Figs. 3 and 4.
Assignments of the protons and carbons are also made by two
dimensional heteronuclear-correlated experiments, HETCOR,
(Fig. 3) using delay values that correspond to 1J(CH), and HMBC
(Fig. 4) using delay values that correspond to 2J(CH) or 3J(CH)
and even 4J(CH) between the carbons and protons.
Fig. 3. HETCOR spectrum of 4APA18C6.
Scheme 2. The numbering of azacrown ethers for 1H- and 13C NMR.
Fig. 4. HMBC spectrum of 4APA18C6.
The mass spectrum and the elemental analysis of 4APA18C6
support the reduction reaction of NOPA18C6 with SnCl2. The mass
spectrum of 4APA18C6 (Fig. 5) contains peak at m/z = 355.2517
which corresponds to [MH]+.
In addition, further characterization of 4APA18C6 was also per-
formed at the solid surface by the covalent grafting of this mole-
cule onto the GC substrate using CV, XPS, RAIRS and ellipsometry
as described in the following sections.
3.2. Characterization of 4APA18C6 modified glassy carbon surface
Although the synthesis and fascinating behavior of azacrown
derivatives have been exploited in a wide range of applications,
Fig. 1. 1H NMR spectrum of 4APA18C6.

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P. Deveci et al. / Journal of Molecular Structure 982 (2010) 162–168
which is assigned to amine oxidation, and when the potential is
repeatedly scanned over the same range, the peak rapidly dimin-
ishes in size. These observations are indicative of a formation of
a film on the electrode surface which blocks further oxidation of
the amine group of 4APA18C6. Scheme 3 shows the proposed over-
all reaction which results in formation of a surface CAN covalent
bond. Mechanistic studies have demonstrated that the initially-
formed radical cation deprotonates giving a C-centered radical, fol-
lowed by isomerisation to an amino radical which covalently cou-
ples to the surface [33–37] and is consistent with the results
described here.
Fig. 5. Mass spectrum of 4APA18C6.
The characteristics of the electrode coating with 4APA18C6
could be conveniently monitored by examining the various redox
probes response such as potassium ferricyanide and ferrocene by
CV technique. Fig. 7 shows cyclic voltammograms of approxi-
mately 1 mM K3[Fe(CN)6] (in 0.1 M KCl) and 1 mM ferrocene (in
0.1 M TBATFB in MeCN) recorded at a polished GC electrode and
a GC electrode modified with 4APA18C6. In comparison to the cyc-
lic voltammograms obtained at the bare and modified GC elec-
trode, the reversible wave for the ferricyanide and ferrocene at
the bare GC was almost completely precluded at the modified
surfaces.
including organic synthesis, catalysts [25], fluoroionophores
[26,27], receptors [28], and membrane sensors [29], there is no re-
ported literature including grafting of this compound to carbon
surfaces by amine oxidation. These molecules can serve as sensi-
tive and selective sensors of cations by binding them through the
azacrown ether moiety at solid surfaces [30–32]. Therefore immo-
bilization of these compounds onto the GC surface can be advanta-
geous in the field of cation sensor applications. For these reasons
we electrochemically immobilized the 4APA18C6 (Scheme 3) onto
the GC surface.
The grafting of primary amines to carbon surfaces by electrooxi-
dation in anhydrous conditions has been widely investigated [33–
35]. Fig. 6 shows cyclic voltammograms of 1 mM 4APA18C6
solution in acetonitrile containing 0.1 M TBATFB recorded at GC
electrode. The voltammograms are consistent with the grafting of
a blocking film to the GC electrode. The first cycle displays a quasi-
reversible (in appearance) and irreversible oxidation peaks. The
first one is observed at approximately 0.5 V and the second one
at 1.9 V. The less positive peak can be attributed to the oxidation
of redox active N atom in the azacrown ring and given the reso-
nance stabilized radical cation. This behavior is also observed for
N-phenylaza-15 crown-5 compound on a Pt surface, which is
structurally similar to 4APA18C6 but without amine substituent
[19–21]. There is an irreversible redox process at Epa = 1.9 V,
To further characterize 4APA18C6 grafted to the GC surface,
modified samples were then analyzed using XPS, which is a strong
tool to examine the elemental distribution on the solid electrode
Scheme 3. Possible grafting mechanism for 4APA18C6 on GC surface.
Fig. 7. Cyclic voltammograms of (a) 1 mM potassiumferricyanide (in 0.1 M KCl) vs.
Ag/AgCl/KCl sat reference electrode (b) 1 mM ferrocene (in 0.1 M TBATFB in MeCN)
vs. Ag/Ag+ reference electrode on bare GC (-) and on GC-4APA18C6 (-d-) electrodes.
Fig. 6. CV voltammogram for electrografting of 4APA18C6 on GC vs. Ag/Ag+
(0.01 M) in 0.1 M TBATFB in acetonitrile. Scan rate is 100 mV sÀ1
.
Scan rate is 100 mV sÀ1
.

P. Deveci et al. / Journal of Molecular Structure 982 (2010) 162–168
167
Fig. 8. XPS survey spectra for the (a) unmodified GC and (b) 4APA18C6 modified GC
surface.
surfaces. Fig. 8 shows the XPS survey spectra for unmodified GC
and 4APA18C6 modified GC surfaces. In Fig. 8, the C, N, O and F
peaks are observed, providing evidence that 4APA18C6 has been
immobilized onto the surface. The main difference between these
two spectra is the appearance of N1s and increase of O1s signals
after the modification of the carbon surface.
The C1s peak observed in the high resolution spectrum was
deconvoluted into two Gaussian peaks at 284.81 eV (CAC and
CAH), 286.60 eV (CAO and CAN) (Fig. 9a). Examination of the N1s
spectra (Fig. 9b) supports the analysis by C1s spectra and provides
the successful modification with 4APA18C6. By comparison of the
N1s photoemission peak with that of a reported spectrum of bare
GC, we conclude that the peak at 399.67 eV corresponds to aza-
crown ether (ANACA) nitrogen [38]. The residual high binding en-
ergy tail at 402.33 eV in the N1s spectra is assigned to the
quaternary nitrogen of Bu4N+ residue which is abundant in the
medium during the modification process [39]. The peak at
400.47 eV is assigned to the amine nitrogen of compound
4APA18C6 covalently bonded to the GC surface. In addition, the
high-resolution O1s peak at 532.87 eV (Fig. 9c) indicates that a
large amount of surface oxygen was present in the form of CAO
bonds most likely of azacrown ether oxygen atoms. The observa-
tion of the F1s peak at approximately 690 eV for 4APA18C6 modi-
fied GC surface is anticipated as some surface contamination by
the BFÀ4 ions of the supporting electrolyte during modification
[40]. A small O1s peak observed in the bare GC spectrum at about
530 eV is attributed to the surface oxides that form spontaneously
on most carbon surfaces due to the atmospheric attacks, as has
been reported in the literature [41,42].
Fig. 9. Deconvoluted narrow region XPS spectra of 4APA18C6 modified GC surface
In addition to the CV and XPS measurements, to confirm the
covalent attachment of 4APA18C6 to the GC surface, RAIRS mea-
surements were also performed. RAIRS spectra were acquired in
a range of 4000–600 cmÀ1 and shown in Fig. 10. Although, the peak
at 3400 cmÀ1 for NAH vibration [43] is not noticeable in the RAIRS
spectra, the weak NAH in plane vibration mode at 1676 cmÀ1 im-
plies the existence of NAH bonds for the immobilized 4APA18C6
[38]. A possible reason for the absence of NAH bands may be the
orientation of the molecules with respect to the surface. Since
RAIRS offers a means of probing vibrations at the surface which
have a dipole perpendicular to the surface [44], it is possible that
some of the NAH bonds are parallel to the surface. Therefore, ab-
sence of the main vibration of NAH does not necessarily imply
the lack of NAH bonds in the final structure. Saturated CAH
stretching vibration modes and aromatic ring modes (C@C stretch)
for the (a) C1s, (b) N1s, and (c) O1s
.
appeared between 2956–2906 cmÀ1 and 1513–1408 cmÀ1 range,
respectively. Additionally, observation of asymmetric and symmet-
ric CAOAC signals at approximately 1044 cmÀ1 and 932 cmÀ1
,
respectively, indicates that the proposed grafting has occurred.
Ellipsometric thickness of the 4APA18C6 film at the GC surface
was found as 11.5 1.1 nm by modeling the system using the soft-
ware of the instrument [45]. A four layer model was used as graph-
ite/glassy carbon substrate/4APA18C6 film/air to fit experimental
data. Refractive indices of 3.0841 for graphite, 1.9000 for GC,
1.0000 for organic layer, 1.0000 for air and extinction coefficients
of À1.7820 for graphite, À0.8100 for GC, 0.0000 for organic layer,
0.0000 for air are assigned, supposing thickness, refractive indices

168
P. Deveci et al. / Journal of Molecular Structure 982 (2010) 162–168
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In summary, a new aza crown derivative, 4APA18C6, was syn-
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mental analysis, FT-IR, 1H NMR, 13C NMR, DEPT, HETCOR, HMBC,
ESI mass-spectrometry. Due to the importance of azacrown com-
pounds in the field of analytical chemistry, chemical sensors and io-
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surface has been performed to obtain new insight into the modifi-
cation area and to generate new materials with interesting proper-
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of 4APA18C6 on the GC surface, was confirmed by various charac-
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the GC surface was formed according to the layer-by-layer mecha-
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This work was supported by TUBITAK (Scientific and Techno-
logical Research Council of Turkey) under the project numbers
108T655 and 106T622 and the Research Fund of Selcuk University
Project Number: 08101030. The authors thank Dr. Selda Keskin
from Middle East Technical University (Ankara) for acquiring XPS
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