Trace electrochemical detection of Ni2+ ions with bidentate N,N′-(ethane-1,2-diyl)bis(3,4-dimethoxybenzenesulfonamide) [EDBDMBS] as a chelating agent

Article abstract of DOI:10.1016/j.ica.2017.05.024

The heavy metals are naturally occurring elements and becoming the main source of pollution in our eco-environment due to their commercial applications. So, for the probe of heavy metal cations, bidentate chelating agents N,N′-(ethane-1,2-diyl)bis(4-metho

Full text of DOI:10.1016/j.ica.2017.05.024

Accepted Manuscript
Research paper
2
+
Trace electrochemical detection of Ni ions with bidentate N, N'-(ethane-1,2-
diyl)bis(3,4-dimethoxybenzenesulfonamide) [EDBDMBS] as a chelating agent
Tahir Ali Sheikh, Muhammad Nadeem Arshad, Mohammed M. Rahman,
Abdullah M. Asiri, Hadi M. Marwani, Rabiul Awual, Wafa A. Bawazir
PII:
S0020-1693(17)30375-4
http://dx.doi.org/10.1016/j.ica.2017.05.024
ICA 17593
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Accepted Date:
10 March 2017
10 May 2017
Please cite this article as: T.A. Sheikh, M.N. Arshad, M.M. Rahman, A.M. Asiri, H.M. Marwani, R. Awual, W.A.
2
+
Bawazir, Trace electrochemical detection of Ni
ions with bidentate N, N'-(ethane-1,2-diyl)bis(3,4-
dimethoxybenzenesulfonamide) [EDBDMBS] as a chelating agent, Inorganica Chimica Acta (2017), doi: http://
dx.doi.org/10.1016/j.ica.2017.05.024
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2+
Trace electrochemical detection of Ni ions with bidentate N, N'-
(ethane-1,2-diyl)bis(3,4-dimethoxybenzenesulfonamide)
[EDBDMBS] as a chelating agent
a,b
a,b
a,b,
Tahir Ali Sheikh , Muhammad Nadeem Arshad , Mohammed M. Rahman *,
a,b
a
c
a
Abdullah M. Asiri , Hadi M. Marwani , Md. Rabiul Awual , and Wafa A. Bawazir
a
Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi
Arabia
b
Center of Excellence for Advanced Materials Research (CEAMR), Faculty of Science, King
Abdulaziz University, Jeddah 21589, Saudi Arabia
c
RENESA, 3-3-22 Sakuraguchi, Kobe-shi, Hyogo 657-0036, Japan
*
Corresponding address:
Dr. Mohammed M. Rahman,
Center of Excellence for Advanced Materials Research &
Chemistry Department, Faculty of Science,
King Abdulaziz University, Jeddah 21589,
P.O. Box 80203, Saudi Arabia
Email: mmrahman@kau.edu.sa&mmrahmanh@gmail.com
Phone: +966-59-6421830; Fax: +966-026952292

Abstract:
The heavy metals are naturally occurring elements and becoming the main source of
pollution in our eco-environment due to their commercial applications. So, for the probe of
heavy metal cations, bidentate chelating agents N,N'-(ethane-1,2-diyl)bis(4-methoxybenzene
sulfonamide) [EDBMBS] and N,N'-(ethane-1,2-diyl)bis(3,4-dimethoxybenzenesulfonamide)
[
EDBDMBS] were synthesized in this study. These chelating agents were characterized by
UV/Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic
1
13
resonance ( H-NMR & C-NMR), in addition to single crystal x-ray diffraction and x-ray
photoelectron spectroscopy (XPS) analysis. After the characterization, I-V technique was
executed using electrometer to check the affinity of our synthesized chelating agents against the
+
3+
3+
2+
4+
2+
2+
2+
2+
3+
wide range of heavy metal cations (Ag , Al , Au , Ba , Ce , Co , Ni , Pb ,Sn & Y ). It
2
+
2+
was found that it has selective affinity with Nickel (Ni ) cations. Ni is one of the most toxic
heavy metal presents in the environmental contaminants. EDBMBS and EDBDMBS onto flat-
glassy carbon electrode were fabricated with conducting coating agents to fabricate a sensitive
2
+
and selective Ni ions sensor in short response time in phosphate buffer phase. The comparative
study of EDBMBS/Nafion/GCE and EDBDMBS/Nafion/GCE was performed and found that
fabricated EDBDMBS/Nafion/GCE cationic-sensor exhibited higher sensitivity, large-dynamic
concentration ranges, long-term stability, and improved electrochemical performances towards
2
2+
nickel ions. The calibration plot is linear (r = 0.9929) over the large Ni concentration ranges
-2
(
1.0 nM to 1.0 mM). The sensitivity and detection limit is ~2.3417 µA.µM.cm and ~0.78 nM
signal-to-noise ratio, at a SNR of 3) respectively. This novel effort initiated a well-organize way
(
of efficient cationic sensor development with nafion conducting binder deposited on GCE for
toxic pollutants in environmental and health-care fields in large scales. Therefore, the proposed
EDBDMBS/Nafion/GCE offers a cost-effective compound that can be considered as a viable
2+
alternative for effectively detecting and removing toxic Ni from water samples.
2
+
Key words: Chelating agents; EDBMBS; EDBDMBS; Ni
ions; I-V method;
Sensitivity, Environmental study

1
. Introduction
Organic compounds with electron donating functional groups have impressive
significance for the scientists for further studies and inventions in chemistry owing to
considerable number of applications such as medicinal, biological [1], catalysis [2] and
organometallic [3] chemistry. Due to the presence of electron donating functional group
such types of molecules have also gained much attention in environmental chemistry [4]
and used as an environmental remediation by detection, extraction and estimation of toxic
metal ions [5-8]. Sulfonamides or sulfa drugs have been discovered as early as 1939 [9]
and well known pharmaceutical agent because of low cost, less toxicity and effective
against the bacterial disease [10]. In addition to antibacterial activity this drug also exhibit
antifungal [11], anticancer, antiviral [12], anti-inflammatory [13], anticonvulsants [14],
diuretic [15], HIV protease inhibitor [16] and carbonic anhydrase activities [17].
Generally, sulfonamides are synthesized by simple reactions of sulfonyl chlorides with
primary amine or secondary amine [18]. This reaction is also known as Hinsberg’s test for the
detection of primary and secondary amine. –SO NH- functional group in their structure make
2
them impressive in environmental chemistry and have applications for the detection of toxic
metal ions by the capability of donating the unshared pare of electrons from N-H group to metal
elements. Recently, for this reason, sulfonamides and its analogue such as N,N'-(ethane-1,2-
diyl)bis(2,5-dimethoxybenzenesulfonamide) (EBDMBS) and (E)-4-methyl-N0-(1-(pyridin-2-
yl)ethylidene)benzenesulfonohydrazide (MPEBSH) have been used for the detection of Co(II)
and Cd(II) in aqueous solution, respectively. [19, 20]. Likewise, N′-[1-(Pyridin-2-
yl)ethylidene]benzenesulfonohydrazide
(PEBSH)
and
(E)-N′-
Nitrobenzylidene-
Benzenesulfonohydrazide (NBBSH) have been reported for Hg(II) [21, 22]. As well as, N, N’-

ethylenebis (ethane sulfonamide) has been employed for the removal of Ni(II), Fe(VI) and Cr(II)
in aqueous solution by ICP-OES [23]. Heterocyclic sulfonamides such as sulfadiazine,
sulfamerazine, sulfapyridine, sulfisoxazole and many others have been used to make complex
with Cu(II) [24]. Acetazolamide and its analog have been used for the probe of Cu(II) and form
the dimer complexes [25]. Acetazolamide has also been employed for the determination of
Zn(II), Cu(II), Ni(II) and Co(II) by potentiometry both in water system [26]. So, keeping in view
the environmental applications of sulfonamides, the plan of the study was to develop the ion
selective electrode for the probe of toxic metal ions based on bis-sulfonamide as a bidentate
chelating agent. 1,2-diaminoethane & its derivatives act as bidentate ligands and has been used in
the formation of many metal complexes [23, 27, 28]. Bis-sulfonamides were synthesized by the
reaction of 1,2-diaminoethane with aryl sulfonyl chlorides at 1:2 mole ratio respectively in water,
Scheme 1. 4-methoxy benzenesulphonyl chloride is selected to synthesize the bis-sulfonamide
and has been reported as an antimicrobial agent [29]. In this work, comparative study of bis-
sulfonamide of 4-methoxy benzenesulfonyl chloride with its analogue was done in terms of
sensing the toxic metal ions quantitatively & qualitatively. Both molecules are new in term of
crystal structures.
Nickel, one of the most well-known heavy transition metal that existed extensively in
different food stuffs of both animal and vegetable origins, is essential for carrying out a
number of necessary functions in industrial and healthcare applications [30, 31]. It also
constitutes significant constituent to uphold selective and specific activity of numerous
enzymes involved in carbohydrate, amino acid as well as lipid metabolism of both
bacterium and higher organisms [32]. Nickel ions at low concentrations offer essential
trace nutrients, but would exhibit toxic effects under overloading conditions. Nickel,

mostly at higher doses, would result in geno-toxic and mutagenic activity, and its geno-
toxicity may be aggravated through the generation of DNA-damaging reactive oxygen
species (ROS) and the inhibition of DNA repair [33]. Accumulating confirmations
2
+
recommend that Ni is a toxic and carcinogenic element closely linked to several
diseases including cancer of nasal lungs, dermatitis, asthma, and disorders of the
respiratory and central nervous systems [34, 35]. Therefore, the International Agency for
Research on Cancer (IARC) classified nickel compounds as group 1 carcinogenic to
humans in 1990 [36], and the American Environmental Protection Agency (EPA) set the
2
+
maximum contaminant level goal (MCLG) for Ni in drinking water to be 0.07 mg/L
while the safe-exposure standard for drinking water was set as 20.0 ng/mL by the World
Health Organization (WHO) [37].
The identification and measurement of nickel at low concentrations thus became
2
+
increasingly important [38]. Recently, determination of Ni ions can be realized by a number of
conventional methods including gravimetry with dimethylglyoxime, voltametric, capillary
electrophoresis, and spectrophotometric techniques like flame and graphite furnace atomic
absorption spectrophotometry, flow injection spectrophotometry, ICP-AES and flame
photometry [39]. However, requirement for complicated sample pretreatment and infrastructure
backup greatly limited their application for routine analysis of myriad environmental samples
[
40]. In view of those problems, the sensory techniques offered an important alternative to meet
the drawbacks confronting the large-equipment-dependent detecting methods, and have been
extensively applied for reliable and expedient measurement of heavy metal ions [41, 42]. The
colorimetric methods, in particular, stand out extremely attractive since they can be easily read
out with low-cost and economical portable instruments and even naked eyes. As for nickel

detection, a majority of the sensors depend on electrochemical measurement using dye-
encapsulated membranes [43, 44], screen-printed electrodes [45], and adsorptive stripping
voltammetry [46]. To date, only limited number of chemosensors have been published to detect
nickel ions through indirect or direct colorimetric analysis [47, 48]. Most of those studies
involved time-consuming procedures to synthesize and purify specific ionophores, which
unavoidably complicates the fabrication and increases cost. And even so, only limited
performance has been realized in view of selectivity, sensitivity and stability. Here, we describe
a facile, reliable and low-cost electrochemical sensor for trace nickel detection based on the
methoxy
bi-functional
N,N'-(ethane-1,2-diyl)bis(3,4-dimethoxybenzenesulfonamide)
[
EDBDMBS]. It is an excellent cationic sensing application to confirm the electrical sensing
properties with lab-made bidentate EDBMBS or EDBDMBS compounds. EDBDMBS permits
very sensitive transduction of the liquid/surface interactions into modify in the chemical
properties. The significant prospect is to appearance a variety of active functional group offers
different vision of modification of the toxic nickel ions sensing possessions. EDBDMBS has
2
+
been used to fabricate a simple and efficient Ni sensor and assessed the chemical sensing
performance selectively considering nickel ions at room conditions. To the best of our
2
+
knowledge, this is the first report for detection of Ni with EDBDMBS using simple,
convenient, and reliable I-V technique in short response time.
O
R
Cl
S
O
S
O
NH S
O
O
2
H CO
NH
OCH3
NH2
3
+
H N
2
H CO
3
O
R
R
1
2a, R = H
b, R = OCH3
3
a, R = H
2
3b, R = OCH3

Scheme 1: Synthesis of chelating agents (EDBDMBS/EDBMBS)
2
. Experimental Section
.1. Materials and Methods
,4-Dimethoxy benzenesulphonyl
2
3
chloride
(DMBSC)
and
4-methoxy
benzenesulphonyl chloride (MBSC) were obtained from Aldrich, USA. 1,2-diaminothane
acquired from BDH, Poole, England. Analytical grade solvents (Acetone and Ethanol)
were also taken BDH, Poole, England. 5 % Nafion, disodium phosphate, monosodium
phosphate, silver nitrate, aluminum chloride, gold chloride, barium sulphate, cerium
chloride, cobalt nitrate, nickel nitrate, lead chloride, stannous chloride and yttrium nitrate
were purchased from sigma-Aldrich. All these chemicals were used without any further
purification. A Stuart Scientific SMP3, version 5.0 melting point apparatus (Bibby
Scientific Limited, Staffordshire, UK) was used to record the melting points, and the
1
reported melting points are uncorrected. H-NMR spectra were recorded on an
AVANCE-III 600 MHz & 800 MHz instrument (Bruker, Fallanden, Switzerland) at 300
K, and chemical shifts are reported in ppm with reference to the residual solvent signal.
FT-IR spectra were recorded as neat on a Thermo Scientific NICOLET iS50 FT-IR
spectrometer (Thermo Scientific, Madison, WI, USA). UV-vis. studies were performed
by using Evolution 300UV/VIS spectrophotometer (Thermo Scientific). XPS experiment
was conducted for the determination of binding energies (eV) of each elements existed in
EDBDMBS especially N, O, C element by a K-α1 spectrometer Thermo scientific -α1
1
with an e citation ra i ation so r ce
1 α1 e am spot si e
.
m pass
-8
energ
. e
press re
10 torr). I-V technique was executed by using

Electrometer (Kethley, 6517A, Electrometer, USA) for measuring the current responses
2
+
in two electrode systems for target Ni cations based on EDBDMBS in buffer phase at
room conditions, where GCE and Pd-wire was used as working and counter electrode
respectively.
2
.2.
General method for the synthesis of 3a & 3b
N,N'-(ethane-1,2-diyl)bis(4-methoxybenzenesulfonamide) [EDBMBS] (3a) and N,N'-(ethane-
,2-diyl)bis(3,4-dimethoxybenzenesulfonamide)[EDBDMBS] (3b) were synthesized following
1
literature method [49]. A mixture of 1, 2-diaminoethane and aryl sulfonyl chlorides: {4-methoxy
benzene sulfonyl chloride (2a) and 3, 4-dimethoxy benzene sulfonyl chloride (2b)} (at 1:2 mole
ratio) in 15 mL of water stirred at room temperature in reaction flask. The progress of reaction
mixture was monitored by examining the pH of medium, with equal intervals of times, which
kept constant at 8-9 with occasional addition of 1 N sodium carbonate. The products (3a) & (3b)
were precipitate out on completion of the reaction which was confirmed by TLC. The
precipitates were filtered, washed with plenty of distilled water and dry at room temperature.
2
.3. N, N'-(ethane-1,2-diyl)bis(4-methoxybenzenesulfonamide)(3a)
1
Molecular weight: 400.47 g, Yield 83.79 %; m.p. 153 °C; H-NMR: (850 MHz)(CDCl )
3
δ:7.758 (4H, d, 2 x Ar-H, J = 8.5), 6.968 (4H, d, 2 x Ar-H, J = 9.35) 4.940 (2H, s, 2 x -NH-),
1
3
3
1
1
.870 (6H, s, 2 x –OCH ), 3.046 (4H, s, 2 x –CH -); C-NMR: (850MHz) (CDCl ) δ: 163.12,
3 2 3
30.89, 129.27, 114.43, 55.67, 42.93; IR (neat) vmax: 3290, 3110, 2979, 2945, 2905, 2844, 1600,
-1
593, 1497, 1461, 1336, 1262, 1155, 1022, 831, 671 cm ; λmax: 248 nm
2
.4. N, N'-(ethane-1,2-diyl)bis(3,4-dimethoxybenzenesulfonamide) (3b)
1
Molecular weight: 460.52176 g, Yield 89.57 %; m.p. 187-189 °C; H-NMR: (600
MHz)(CDCl3) 7.434 (2H, dd, 2 x Ar- , J = 2.4, 8.4), 7.296 (2H, d, 2 x Ar- , J = 1.8),
δ
:
H
H

6
3
1
2
.923 (2H, d, 2 x Ar-
.064 (4H, s, 2 x -CH2-); C-NMR: (600MHz) (CDCl3)
21.11, 110.63, 109.55, 56.31, 56.23, 43.00; IR (neat) vmax
H, J = 9), 3.939 (6H, s, 2 x –OCH3), 3.928 (6H, s, 2 x –OCH3),
1
3
δ
:
152.85, 149.37, 130.92,
3245, 3085, 2967, 2938,
:
-1
875, 2845, 1592, 1510, 1469, 1442, 1329, 1262, 1237, 1159, 1021, 720 cm ; λmax: 248
nm, 283 nm
2
+
2
.5. Fabrication of Ni sensor with EDBDMBS/GCE
Phosphate buffer solution (PBS, 0.1 M, pH 7.0) is prepared by mixing 0.2 M Na HPO4
2
and 0.2 M NaH PO solution in 100.0 mL de-ionize water. GCE is made by EDBDMBS
2
4
with 5 % ethanolic nafion solution as a conducting agent. Subsequently it is moved into
the air at room condition for 12 hours until the film is completely uniform, stable, and
dry. A chemical cell is mounted with EDBDMBS coated GCE as a working electrode and
Pd wire is used as a counter electrode. Nickel solution (0.1 M) is diluted at different
concentrations in DI water and used as a target chemical. Amount of 0.1 M PBS (pH 7.0)
is kept constant in the small-beaker as 5.0 mL throughout the chemical analysis. Analyte
solution is prepared with different concentrations of cadmium from 1.0 nM to 0.1 M. The
sensitivity is calculated from the slope of current versus concentration from the
calibration plot by considering the active surface area of nickel cationic sensors. Keithley
electrometer is used as a voltage sources for I-V method in two electrodes system.
2
.6.
Crystallography
The two new sulfonamide molecules were crystallized. The Molecule 3a was crystalized in
ethyl-acetate under slow evaporation and crystal seeding techniques while molecule 3b was
crystalized in acetone-ethanol (20: 80) under slow evaporation process. Both of the samples were
checked under microscope and screened out to collect data for structural characterization. The

selected samples were glued over glass needle fixed on a copper rod with magnetic base. The
whole sample assembly was mounted on Agilent SuperNova (Dual source) Agilent Technologies
Diffractometer, equipped with microfoc s C / Mo α ra iation for a ta collection. Mo α
radiations were used for these samples. The data collection was accomplished using CrysAlisPro
software [50] at 9
n e r the C α ra iati on. The str c t re sol t ion was performe sing
2
SHELXS–97 method [51] and refined by full–matrix least–squares methods on F using
SHELXL–97 method [51], in-built with WinGX [52]. All non–hydrogen atoms were refined
anisotropically by full–matrix least squares methods [51]. The Figures were generated through
PLATON [53] and ORTEP [54] in built with WinGX [52].
All the aromatic C-H hydrogen atoms were positioned geometrically and treated as riding
atoms with C–H = 0.93 Å and Uiso(H) = 1.2 Ueq(C) carbon atoms. Similarly, the methyl and
methylene hydrogen atoms were also positioned geometrically with Cmethyl-H = 0.96 Å Uiso(H) =
1
.5 Ueq(C) and Cmethylene-H = 0.97 Å Uiso(H) = 1.5 Ueq(C). The N-H hydrogen atoms were
located through fourier map and refined with N-H = 0.85(1) Å in molecule 3b and with N-H =
.84(1)-0.85(1) Å in molecule 3a. Uiso (H) was set to 1.2Ueq for N atoms in both molecules.
0
The Crystal data were deposited at the Cambridge Crystallographic Data Centre and following
deposition numbers have been assigned 1520938 and 1520939 which are known as CCDC
number for molecules I and II respectively. Crystal data can be received free of charge on
application to CCDC 12 Union Road, Cambridge CB21 EZ, UK. (Fax: (+44) 1223 336-033; e-
mail: data_request@ccdc.cam. ac.uk).
3
. Results and Discussion

1
13
3
.1. Nuclear Magnetic Resonance ( H-NMR & C-NMR) chracterization of
ethane-1,2-diyl)bis(4-methoxybenzenesulfonamide) or 3a:
The desired amino ligand 3a for the sensing of heavy metal was synthesized by simple
N,N'-
(
reaction of 1, 2-diaminoethane (0.081 ml, 0.00122 mol) with 4-methoxy benzene sulfonyl
chloride (0.5042 g, 0.00244 mole) in water. HCl was produced during the progress of the
reaction as a byproduct, which shifts the pH of the reaction from basic to acidic. The HCl
was neutralized by the addition of 1 N sodium carbonate and solution pH was maintained
about 8 to 9. Precipitates of the product were obtained at the end of the reaction which
was confirmed by TLC. It was filtered and recrystallized from ethylacetate by seeding
method.
In addition to different spectroscopic techniques, single crystal X-ray diffraction
studies were also carried out in order to assure and elucidate the structure of our target
1
13
ligand. The spectra of H-NMR and C-NMR are shown in Figs. S1 & S2. The six
protons of two methoxy (-OCH ) groups attached to two aromatic rings at para position
3
gave one singlets at δ 3.870 ppm. One singlet belongs to four protons of two methylene (-
CH -) group was observed at δ 3.046 ppm. The two aromatic rings accompanied total
2
eight aromatic protons at -ortho and -meta position. These eight aromatic protons gave
the two doublets at δ 7.758 and 6.968 ppm with coupling constant J = 8.5 & 9.35
respectively, four each, it reveals that two aromatic protons in each ring are of same
nature. The two protons of two –NH- groups adjacent to methylene/sulfonyl group were
appeared as singlet at δ 4.94 ppm. All this discussion explains the center of symmetry of
molecules, Fig. 1a, but x-ray diffraction is against it, Fig. 2.

1
3
Similarly, for further confirmation of target ligand C-NMR spectrum was also
collected to observe the number of carbon atoms. The two peaks were appeared at δ 42.93
&
55.67 ppm which belong to two carbon atoms of methylene group attached to amine
group & two methoxy carbon atoms attached to aromatic ring respectively. The aromatic
C-atoms were appeared in aromatic region with the range values from δ 114.43 to 163.12
ppm.
1
13
3
.2.
H-NMR & C-NMR characterization of N,N'-(ethane-1,2-diyl)bis(3,4-
dimethoxybenzenesulfonamide) or 3b:
Same method was adopted, as stipulated above in the discussion of 3a, to synthesize
the second 3b molecule using 1, 2-diaminoethane (0.071 ml, 0.001056 mol) with 3,4-
dimethoxy benzene sulfonyl chloride (0.500 g, 0.002112 mol) in water. The product was
recrystallized from acetone-ethanol (20:80) to carry out single crystal X-ray diffraction
1
13
studies. The H-NMR and C-NMR spectra are also shown in Figs. S3 & S4.
The twelve protons of two methoxy groups at –meta & -para position gave two
singlets at δ 3.939 and 3.928 ppm respectively, six each. The one more singlet belong to
four protons of two methylene group was also observed at δ 3.064 ppm, which elucidate
its center of symmetry (both halves are identical), Fig. 1b. The single crystal X-Ray
diffraction also favors the center of symmetry in this molecule, Fig. 3. The six protons in
two aromatic rings were of different nature because of substitution of methoxy at -meta
position. The four protons out of six, two each from two aromatic rings, at position 2 and
5
appeared as doublet at δ 7.296 and 6.923 ppm with coupling constant J = 1.8 & 9
respectively. The remaining two protons at position 6 emerged as doublet of doublet at δ
.434 ppm with coupling constant J = 2.4 & 8.4, it reveals that these protons have -ortho
7

and -meta effect. The protons of –NH- group disappeared in the spectrum but we
observed both protons in single crystal determination.
1
3
C-NMR spectrum also satisfied the no. of carbon atoms in target ligand 3b. The four
methoxy carbon atoms were appeared at δ 56.31 and 56.23 ppm. The two carbon atoms of
methylene group attached to amine observed at δ 43.00 ppm. The aromatic C-atoms peaks
were came into view in aromatic region with the range values from δ 109.55 to 152.85
ppm.

1
13
1
13
Fig. 1. (a) H-NMR & C-NMR of EDBMBS (b) H-NMR & C-NMR of EDBDMBS

3
.3. Comparative Optical absorption characteristic (FTIR, UV/VIS) of 3a & 3b:
Optical absorption spectroscopy provides the simple information about the functional
group (in FTIR spectroscopy) and conjugation (in UV/VIS spectroscopy) whether it is
present or not in organic compounds.
So, FTIR analyses were also performed in order to confirm the functional group for
both molecules 3a
& 3b and spectra are shown in Figs. S5 & S6.
-
1
1
The N-H stretching peaks of 3a and 3b were appeared at 3290 and 3245 cm
respectively. The N-H bending and wagging in 3a were appeared at 1593 & 671 cm
-
-1
respectively and in 3b these were observed at 1592 & 720 cm . The C-N stretching
-1
vibrations were appeared at 1262 and 1022-1021 cm in both molecules. A C-C-N
-1
bending in 3b was also come out at 1237 cm . Asymmetric & symmetric stretching
-1
-1
vibrations of S=O in 3a were appeared at 1336 cm and 1155 cm respectively while in
-1
-1
3
b
it seemed at 1329 cm and 1159 cm with strong intensity. Asymmetric and
symmetric stretching peaks for aliphatic C-H for both molecules come into view in the
-1
range of 2844-2979 cm . The C-H asymmetric bending of –OCH in 3a and 3b was also
3
-1
emerged in the range of 1461-1469 cm . Medium and small peaks in 3a at 3110 and in
-1
3b at 3085 cm were belonged to aromatic C-H stretching. Aromatic C=C stretching
-1
were also observed for both molecules in the range of 1442-1600 cm . In 3a C-H bending
-1
of para substituent benzene appeared at 831 cm .
For quantitative UV/VIS spectroscopy, the solutions of 6.24 x 10 mol/L & 1.08 x 10
-5
-4
mol/L concentration were prepared for both molecules in chloroform and spectra were
recorded on UV/VIS spectrophotometer at room temperature in the range of 200-600 nm.
The λmax is 248 nm, for molecule 3a and Fig. S7. For 3b, the λmax observed are 248 nm

and 283 nm, Fig. S8. The concentrations, intensities and observed λmax describe that there
are π-π* transition in both of molec l es.
3
.4.
Crystal Structure Description:
Both of these molecules were crystalized in monoclinic crystal system with P21/n and
P21/a space groups for 3a and 3b respectively, Figs. 2 & 3, Tables 1, S1 & S2. Molecule 3b has
center of symmetry in it. The geometry around the S atoms in both molecules is distorted
tetrahedral with <O1-S1-O2 = 119.41(8)° in molecule 3b while <O1-S1-O2 = 119.60(9)° and
<O4-S1-O5 = 119.75(9)°in molecule 3a and this is typical behavior of sulfonamide family [55-
5
8] The molecule 3b has center of symmetry so the planes generated through the fitted atoms of
aromatic rings are parallel to each other while the dihedral angle between the two aromatic rings
in molecule 3a is 14.39(2)°. Symmetry related N-H…O h rogen bon ing connects the
molecules to form an infinite chain along b axes in compound 3b. The similar interaction in
compound 3a connects the molecule along a axes to form an infinite long chain in its crystal
structure. This interaction in both compounds generates eight membered ring motifs, which can
2
be represented mathematically as R (8) [59]. In molecule 3b, the C-H…O t pe week interaction
2
connects the long chains to produce another infinite chain which goes diagonally along ac plane.
In molecule 3a the C-H…O interaction connects the molecule to form two-dimensional
framework Table 2 Figs. S9-S11. Overall these interactions give rise to formation of
supramolecular systems of these ligands.

Fig. 2: ORTEP diagram of molecule 3a with appropriate labels. Thermal ellipsoids were drawn
at 50% probability level.
Fig. 3: ORTEP diagram of molecule 3b with appropriate labels. Thermal ellipsoids were drawn
at 50% probability level.

Table 1. Crystal data and structure refinement for 3a and 3b
Identification code
3a
3b
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C H N O S
C H N O S
16
20
2
6
2
18 24
460.51
296(2)
2
8
2
400.46
296(2)
Monoclinic
monoclinic
P21/a
P2 /n
1
a/Å
b/Å
c/Å
α/°
β/°
8.0846(4)
11.0075(4)
20.2421(7)
90
10.1861(5)
7.6337(3)
14.2058(6)
90
100.825(4)
90
104.403(4)
90
γ/°
3
Volume/Å
1769.31(13)
4
1069.89(8)
2
Z
3
ρcalcmg/mm
1.503
0.338
840.0
1.429
0.296
484.0
-1
µ/mm
F(000)
3
Crystal size/mm
0.33 × 0.26 × 0.06
0.32 × 0.16 × 0.07
5.922 to 59.08°
θ ra nge for a ta collection 5.872 to 58.812°
Index ranges
-9 ≤ h ≤ 11 -8 ≤ k ≤ 14 - ≤
-1 ≤ h ≤ 1 -1 ≤ k ≤ 9 -19 ≤
l ≤ 7
l ≤ 15
Reflections collected
10717
6027
Independent reflections
Data/restraints/parameters
4271[R(int) = 0.0233]
4271/2/243
2608[R(int) = 0.0202]
2608/0/142
2
Goodness-of-fit on F
1.034
1.058
Final R in e es [I> σ I ]
Final R indexes [all data]
R = 0.0409, wR = 0.0940
R1 = 0.0386, wR2 = 0.0906
R1 = 0.0502, wR2 = 0.0988
0.30/-0.33
1
2
R = 0.0545, wR = 0.1029
1
2
-3
Largest diff. peak/hole / e Å 0.33/-0.39

Table 2
Hydrogen Bonds for Molecule 3a and 3b
Molecule 3a
D
H
A
d(D-H)/Å
d(H-A)/Å
d(D-A)/Å
D-H-A/°
1
2
3
C5 H5A O4
N1 H1N O4
0.93
2.58
2.137(13)
2.211(13)
3.450(2)
2.957(2)
3.026(2)
156.0
163(3)
160(3)
0.847(10)
N2 H2N O1
0.853(10)
1
2
3
3
/2-X,-1/2+Y,1/2-Z; -1+X,+Y,+Z; 1+X,+Y,+Z
Molecule 3b
D
H
A
d(D-H)/Å
d(H-A)/Å
d(D-A)/Å
D-H-A/°
1
2
C9 H9B O3
0.96
2.51
3.464(3)
2.992(2)
176.0
N1 H1
O1
0.83(2)
2.20(2)
158(2)
1
2
2
-X,-Y,2-Z; 1-X,-Y,1-Z
2
+
4
. Application: Detection of Ni ions with EDBDMBS/GCE:
The significant application of EDBDMBS assembled onto GCE as cationic sensors
2
+
(
especially Ni ions analyte in buffer system) has been executed for measuring and
detecting target chemical in aqueous solution. Enhancement of the EDBDMBS/GCE as
cationic sensors is in the initial stage and no other reports are available. The
EDBDMBS/GCE sensors have advantages such as stability in air, non-toxicity, chemical
inertness, electro-chemical activity, simplicity to assemble, ease in fabrication, and
2
+
chemo-safe characteristics. As in the case of Ni cations sensors, the incident of rationale

is that the current response in I-V method of EDBDMBS/GCE considerably changes
2
+
when aqueous Ni analytes are adsorbed. The EDBDMBS/GCE was applied for
2
+
fabrication of cationic-sensor, where Ni ions were measured as target analyte. The
fabricated-surface of EDBDMBS sensor was prepared with conducting binders (5 %
Nafion) on the GCE surface. The fabricated GCE electrode was put into the oven at low
o
temperature (35.0 C) for 2.0 hour to make it dry, stable, and uniform the surface totally.
2
+
The EDBDMBS was employed for the detection of Ni ions in liquid phase. I-V
responses were measured with EDBDMBS coated thin-film (in two electrodes system). In
2
+
experimental section, it was already outlined the Ni ions sensing protocol using the
2
+
EDBDMBS/GCE modified electrode. The concentration of Ni ions was varied from 1.0
nM to 0.1 M by adding de-ionized water at different proportions.
Here, Fig. 4(a) is represented the I-V responses for uncoated-GCE (grey-dotted) and
EDBDMBS/GCE (red-dotted) electrodes. In PBS system, the EDBDMBS/GCE electrode
shows that the reaction is slightly increased owing to the presence of EDBDMBS on bare-
GCE surface. A considerable enhancement of current value with applied potential is
2
+
demonstrated with fabricated EDBDMBS/GCE in presence of target Ni ions analyte,
which is presented in Fig. 4(b). The blue-dotted and green-dotted curves were indicated
2
+
the response of the fabricated film before and after injecting 25.0 µL Ni solution in 5.0
mL PBS solution respectively. Significant increases of current are measured after
2
+
injection of target component in regular interval. I-V responses to varying Ni ions
concentration on thin EDBDMBS/GCE were investigated (time delaying, 1.0 sec;
response time, 10 sec) and presented in the Fig. 4(c). Analytical parameters (such as
sensitivity, detection limit, linearity, and linear dynamic range etc) were calculated from

the calibration curve (current vs. concentration), which was presented in Fig. 4(d). A wide
2
+
range of Ni ions concentration was selected to study the possible detection limit (from
calibration curve), which was examined in 1.0 nM to 0.1 M. The sensitivity was
-1
-2
calculated from the calibration curve, which was close to ~2.3417 µA.µM .cm . The
linear dynamic range (calculated from the Fig. 4(e) of the EDBDMBS/GCE sensor was
2
employed from 1.0 nM to 1.0 mM (linearly, r : 0.9929), where the detection limit was
3
N
calculated about 0.78 nM (ratio, / ). The EDBDMBS/GCE was exhibited higher current
S
2
+
response, where the electrical resistance decreases under the presence of target Ni ions
in PBS phase. The film resistance was decreased gradually (increasing the resultant
2
+
current) upon increasing the Ni ions concentration in bulk system.

Fig. 4: Control experiment and optimization of sensor. I-V responses of (a) GCE (without
2
+
EDBDMBS) and EDBDMBS/GCE (with EDBDMBS); (b) EDBDMBS/GCE (in absence of Ni
2
+
2+
ions) and Ni ions/ EDBDMBS/GCE (in presence of Ni ions); (c) concentration variations (1.0
2
+
nM to 0.1 M) of Ni ions, (d) calibration plot of EDBDMBS fabricated GCE (at +1.0 V).
2
+
Interference (for selectivity) was studied for Ni ions sensor in the presence of other
+
3+
3+
2+
4+
2+
2+
2+
3+
chemicals like Ag , Al , Au , Ba , Ce , Co , Pb , Sn , and Y using the EDBDMBS
embedded on flat GCE (Fig. 5a). The concentrations of all analytes were kept constant at 0.1 µM
level in PBS system. Here, it is clearly demonstrated that EDBDMBS/GCE sensor is the most
2
+
selective toward Ni ions compared with other cations. The excellent selectivity is ascribed to

2
+
the reasons are terminal functional groups have strong and stable interaction with Ni resulting
in the increase of current response in I-V system. To check the reproducibly and storage
stabilities, I-V response for EDBDMBS/GCE sensor was examined (Fig. 5b). After each
experiment, the fabricated EDBDMBS/GCE substrate was washed thoroughly with the
phosphate buffer solution and observed that the current response was not significantly decreased.
The sensitivity was retained almost same of initial sensitivity up to few days, after that the
response of the fabricated EDBDMBS/GCE electrode gradually decreased.
2
+
I-V characteristic of the EDBDMBS is activated as a function of Ni ions concentration at
room conditions, where improved current response is observed. As obtained, the current response
of the EDBDMBS/GCE-film is increased (-* interaction) with the increasing concentration of
2
+
Ni ions (Scheme 2a), however similar phenomena for toxic chemical detection have also been
2
+
reported earlier [60-63]. For a low concentration of Ni ions in liquid medium, there is a smaller
2
+
surface coverage of Ni ions molecules on EDBDMBS/GCE film and hence the surface reaction
2
+
proceeds steadily. By increasing the Ni ions concentration, the surface reaction is increased
significantly (gradually increased the response as well) owing to surface area (assembly of
2
+
2+
EDBDMBS/GCE; Scheme 2b) contacted with Ni ions molecules. Further increase of Ni ions
concentration on EDBDMBS/GCE surface, it is exhibited a more rapid increased the current
2
+
responses, due to larger area covered by Ni ions an the π-π* interaction of the f nc tional
2+
groups of EDBDMBS and Ni . The π-π* interaction co l be approaches as inter-molecular and
intra-molecular interactions of the functional compound [64, 65]. Usually, the surface coverage
2
+
of Ni ions on EDBDMBS/binders/GCE surface is reached to saturation, based on the regular
enhancement of current responses (Scheme 2c).

2
Ni
+
2
+
Scheme 2. Schematic diagram. Mechanism of the probable interaction of Ni with
2
+
EDBDMBS/GCE. (a) Fabricated GCE electrode b π-π interaction between Ni ions and
EDBDMBS, and (c) resultant I-V response.
2
+
The Ni ions sensor based on EDBDMBS/GCE is also displayed good repeatability as well
as reproducibility with good stability for over week and no major changes in sensor responses
was found. After a week, the cationic sensor response with EDBDMBS/GCE was slowly
decreased, which may be due to the weak-interaction between fabricated EDBDMBS active
2
+
functional sides and Ni ions. The significant result was achieved by EDBDMBS/GCE, which
can be employed as efficient electron mediators for the development of efficient cationic sensors.
Actually, the response time was around 10.0 sec for the fabricated EDBDMBS/GCE to reach the
saturated steady-state level. The higher current and sensitivity of the fabricated EDBDMBS/GCE
compared to EDBMBS/GCE is attributed to the excellent absorption and adsorption ability with
bi-functional methoxy groups, which is presented in Fig. 5(c). Therefore, it was developed the
2
+
Ni sensor based on EDBDMBS/Nafion/GCE in total investigation. The estimated sensitivity of
the fabricated EDBDMBS/GCE sensor is relatively higher and detection limit is comparatively
2
+
lower than previously reported Ni sensors based on other nano-composite or materials

modified electrodes measured by I-V systems [66-69]. Due to EDBDMBS/binders/GCE, it
2
+
provides a favorable micro-environment for the Ni cations detection with good quantity. The
high sensitivity of EDBDMBS/GCE provides high electron communication features which
enhanced the direct electron transfer between the active sites of EDBDMBS and GCE. The
EDBDMBS/GCE system demonstrate a simple and reliable approach for the detection of toxic
chemicals. It also reveals the significant access to a large group of ligands/compounds for
detection of carcinogenic heavy metallic ions in wide-range of environmental applications.
2
+
Response time is measured as 13s for the detection of target N ions and presented in Fig. 5(d).

Fig. 5: Selectivity studied with various analytes using EDBDMBS/GCE. (a) I-V responses of
2
+
various analytes, (b) Current responses of analytes at +0.5V (Ni ions), (c) comparison of
current between EDBDMBS/GCE and EDBMBS/GCE, and (d) response time; Analyte
concentration was taken at 0.1 µM. Potential range: 0 to +1.5 V; Delay time: 1.0 Figure 2.
Selectivity studied with various analytes using EDBDMBS/GCE. (a) I-V responses of various
2
+
analytes, (b) Current responses of analytes at +0.5V (Ni ions), and (c) comparison of current
between EDBDMBS/GCE and EDBMBS/GCE; Analyte concentration was taken at 0.1 µM.
Potential range: 0 to +1.5 V; Delay time: 1.0 s.
5
.
Interference Effect:
Interference study is the impressive statistical approach in the field of analytical applied
+
3+
3+
2+
4+
2+
2+
2+
3+
science to study the effect of other cations (Ag , Al , Au , Ba , Ce , Co , Pb , Sn , Y ) in
2
+
2+
the presence of Ni on EDBDMBS/GCE for the development of selective electrochemical Ni
2
+
sensor [22]. The I-V response of EDBDMBS/GCE towards all cations in the presence of Ni (at
.
1
M an 5 .0 L in P S pH 7. were e amine an their interference effect in
2+
comparison with Ni were also investigated at the calibrated potential (+ 1.0 V). From the
interference study, it was found that designed EDBDMBS/GCE is very sensitive, selective and
2
+
reliable only for Ni detection and it does not reveals any significant change in current response
towards the other interfering toxic metal cations (Fig. 6 and Table S3).

Fig. 6. Interference study. Analytes concentration were taken at 0.1 µM. Potential: +1.0 V;
Delay time: 1.0 s.
2
+
The Ni interaction with EDBDMBS was also examined by the UV-Vis and FTIR
spectroscopy in addition to the X-ray photoelectron spectroscopy (XPS analysis). The results are
given the supporting information section. In UV-Vis spectrum, hyperchromic shift was observed
2
+
because intensity of absorbance increased in the presence of Ni , Fig. S12. As well as in FTIR
2
+
spectrum, intensities of the peaks in fingerprint regions decreased with the addition of Ni . The
-1
-1
-
two new peaks, one at 3512 cm and second at 3425 cm adjacent to N-H stretching at 3245 cm
1
were also appeared. In addition to these, little distortion of two N-H peaks as a shoulder like
-1
-1
appearance, one N-H stretching at 3245 cm and second N-H bending at 1592 cm , were also
2
+
observed which corroborate the interaction Ni with the newly synthesized EDBDMBS, Fig.
S13. From the XPS study, it is revealed that the shifting the N1s peak due to the interaction between
2
+
EDBDMBS and Ni . The total XPS study is presented in supporting information section (Figure S14).
6.
Conclusions
Two new chelating agents EDBDMBS and EDBMBS were synthesized with the aim to probe
the heavy metal ions and their comparison study with specific heavy metal cation. Classical

1
13
spectroscopic techniques like UV/Vis, FTIR, H-NMR & C-NMR were used for their structure
elucidation in addition to single crystal X-Ray diffraction analysis. The dihedral angles between
the different planes of molecules were measured. Inter and intra-molecular hydrogen bonding
interactions has been discussed on the basis of results obtained from single crystal data. This
extensive research is performed in terms of preparation and characterization of EDBDMBS and
2
+
EDBMBS and applied for the Ni ions sensor using I-V method. The analytical performance of
2
+
Ni ion sensor using EDBDMBS/GCE was higher and fascinated rather than EDBMBS/GCE by
reliable I-V method in terms of sensitivity, detection limit in short response time as well as
reproducibility. This novel idea imparts high selectivity and fast detection for nickel-ion to the
EDBDMBS fabricated GCE-probe. Potentially, the same concept might be applied to the
creation of new sensors for monitoring other cationic ions. Hence, this approach is introduced a
new route for efficient toxic cationic sensor development in environmental and healthcare fields.
Acknowledgments
The authors acknowledge the support of Chemistry department and center of Excellence for
Advanced Materials Research (CEAMR), King Abdulaziz University, Jeddah, Saudi Arabia.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://dx.doi.org/...................
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