Tetrahedron 133 (2023) 133276
lable at ScienceDirectContents lists avaiTetrahedron
journal homepage: www.elsevier .com/locate/ tetA new sulfonamide-based chemosensor for potential fluorescent
detection of Cu2þ and Zn2þ ions
Cephas Amoah a, Collins Obuah a, b, *, Michael Kojo Ainooson a, b, Louis Hamenu a,
Anita Oppong a, Alfred Muller b
a Department of Chemistry, University of Ghana, Legon, Accra Ghana
b Department of Chemical Sciences, University of Johannesburg, Auckland Park, 2006, Johannesburg, South Africaa r t i c l e i n f o
Article history:
Received 14 December 2022
Received in revised form
12 January 2023
Accepted 16 January 2023
Available online 21 January 2023
Keywords:
Fluorescent probes
Quantum yield
Electronic transition
Photophysical properties
Pyrazole derivatives* Corresponding author. Department of Chemistry
Accra, Ghana.
E-mail address: cobuah@ug.edu.gh (C. Obuah).
https://doi.org/10.1016/j.tet.2023.133276
0040-4020/© 2023 Elsevier Ltd. All rights reserved.a b s t r a c t
In recent times, there has been an increased demand in the search for probing materials for numerous
substances in the environment such as the detection of metals ions. In this study, a new class of
pyrazolyl-sulfonamide derivatives of para-nitroaniline were synthesized following a multistep approach.
The ligands and complexes were characterized using NMR spectroscopy, IR spectroscopy, and mass
spectrometry. All the compounds C1eC3 were synthesized in very good yields (85%e92%) and their
photo-physical properties measured. All the compounds show fluorescence behaviour with emissions
within the UV and far visible range with quantum yields between 7.7% and 25.7%. TD-DFT calculations
predictions for the electronic transitions present are in good agreement with experimental observations.
Fluorescent probing studies conducted on the compounds show that C1eC3were analytically sensitive
and possessed signi 2þficant selectivity towards Cu (for C3) and Zn2þ (for C1 and C2) ions with detection
limits between 0.011 and 0.103 mg/L for Cu2þ ions and 0.002e0.135 mg/L for Zn2þ ions. Overall, C1 was
found to be the most sensitive molecule for the metals studied, having good quantum yield and better
selectivity for Zn2þ ion compared to Cu2þ.
© 2023 Elsevier Ltd. All rights reserved.1. Introduction
In recent times, research has been geared towards the design of
molecules for fluorescent metal detection, recognition and reac-
tivity. This is because, fluorescent materials have found numerous
applications as probes, bio-imaging, lasers, and display screens
among others [1]. The target therefore has been towards the syn-
thesis of materials with high luminescence properties such as high
molar absorptivity, high quantum yield and large stoke shift [2].
The intended application also generally plays a key role in the
desired properties, such as deep blue light emitting molecules are
desirable for OLEDS with a characteristic shorter wavelength
whiles longer wavelength are desirable for molecules intended for
imaging purposes.
In this regard, different classes of compounds have been studied,
for example single organic fluorophore molecules [3e6] while ze-
olites [7,8], fluorescent polymers [9], quantum dots [10] and, University of Ghana, Legon,organometallic compounds [11e13] have also been researched for
their photophysical properties.
In the use of organic fluorophores, molecules such as fluorescein
[14], rhodamine [15,16], acridine [17,18], and oxazine derivatives
[19,20] are the most studied groups of compounds. On the other
hand, research on fluorescent sulfonamides, primarily focused on
the sulfonamide being used as a substituent on an already existing
or active fluorophore has also been reported.
Studies on fluorescent probes for metal detection have largely
been successful for probing metals such as Fe3þ, Fe2þ, Cu2þ, Zn2þ,
Hg2þ, Pb2þ, and Cd2þ [21e24]. Other ions like the uranyl ion have
also gained attention as a result of contamination from nuclear
reaction sites [25]. The capacity of a sensor molecule to detect an
ion has been ascribed to numerous reasons, chiefly being the
structure of the molecule that is the functional groups present on
the molecule, which determines its binding or level of interaction
with a metal ion.
In a study conducted by Supuran and coworkers, fluorescein
based sulfonamides are used as candidates for the development of
imaging and therapeutic strategies in the management of hypoxic
tumors which suppress carbonic anhydrase inhibitors [26]. One key
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276finding was that the sulfonamide moiety aside its fluorescence
enhancement was essential in contributing to the solubility of the
fluorophores in water. Another study done by Yin and colleagues,
reported the synthesis of naphthalimide-sulfonamide fused dansyl
sulfonamide fluorescent probes with dual emission [27]. These
molecules were selective in the probing of glutathione of lysosome
and capable of tracking them. Also, in a study by Rashatasakhon
et al., new sulfonamide-spirobifluorene derivatives were synthe-
sized and found to be good chemosensors with selectivity towards
Au(III) ions [28]. It was shown that the sulfonamide portionwas key
in the complexation of the Au(III) ions which resulted in a
quenching of the fluorescent intensity. The range of sulfonamide
derivatives as fluorescence materials span from enhance solubility
to good probing properties, thus making this class of compounds
the potential to be the next generation of fluorescent molecules for
imaging or probing materials. Despite all these advances, the
application of sulfonamides as central motif as a fluorescence ma-
terial has not been explored to the best of our knowledge.
Herein, we report on the synthesis of a new family of sulfon-
amide ligands bearing the pyrazolyl and nitroaniline groups. Their
fluorescent properties identify them as blue light emitters and are
good selective probes for the detection of Zn2þ and Cu2þ ions in
solution.
2. Results and discussion
2.1. Synthesis of compounds
Compounds C1, C2 and C3 were prepared from the addition
reaction involving para-nitroaniline and their respective sulfonyl
chloride adducts (Schemes 1) [29]. The formation of the products
was guided by stoichiometry addition of the para-nitroaniline to a
number of sulfonyl chloride moieties with the pyrazole backbone.
The compounds were obtained as yellowish brown to brown solids
with good yields between 85 and 92%. The compounds were pu-
rified by column chromatography, using a solvent system of a
mixture of ethyl acetate-methanol in a 7:3 ratio. They were further
characterized by IR and NMR spectroscopies, and mass
spectrometry.
FT-IR spectroscopy on the compounds showed prominent NeH
vibrational peaks showing at around 3431 cm1 and NeO peaks at
around 1526 and 1347 cm1 (Fig. S1). The absence of a twin peak
usually expected around 3300 cm1 for primary amine and the
presence of an NeH corresponding to a secondary amine suggest
the formation of the products. 1H NMR spectrum of C1 showed the
presence of an NeH proton peak at 6.61 ppm and aromatic protons
integrating for five protons between 8.10 ppm and 8.35 ppm for the
phenyl attached to the pyrazole, while the aniline protons were
observed as two doublets between 7.00 ppm and 7.80 ppm (Fig. S2).
13C{1H}-NMR also confirmed the formation of C1 with peaks at
10.65 ppm and 11.14 ppm for the pyrazolyl methyl protons and
peaks between 124.47 ppm and 148.22 ppm for the aromatic car-
bons (Fig. S3).
The 1H NMR spectrum of C2 show similar patterns as C1 with
additional protons from the aniline group giving total integration of
eight protons, indicating addition of the para-nitroaniline to the
double sulfonated intermediate (Fig. S4 and Scheme 1). 13C{1H}-
NMR spectra also showed carbon peaks at 11.1 ppm and 11.9 ppm
for the pyrazolyl methyl protons as well as 124.2 ppme148.2 ppm
for the aromatic carbons (Fig. S5). Compound C3, on other hand
showed the absence of the pyrazolyl proton usually around
6.00 ppm in the 1H NMR spectrum, confirming a double sulfonation
on the di-tert-butyl pyrazole. Also, the NeH peak was observed at
5.45 ppm with an integration of 2 protons while the anilinic pro-
tons showed two doublets at 7.13 ppm and 8.17 ppm each with an2
integration of four protons (Fig. S6). 13C{1H}-NMR spectra also
showed carbon peaks at 28.4 ppm and 33.5 ppm for the pyrazolyl
tert-butyls as well as 126.4 ppme156.5 ppm for the aromatic car-
bons (Fig. S7). In all C1 was synthesized as having a single sulfon-
amide group whiles C2 and C3 both possessed double sulfonamide
groups.
2.2. UVevis and fluorescent studies
The electronic absorption properties of the sensor molecules
C1eC3 were studied at room temperature in methanol.
All the measurement were conducted in methanol between
270 nm and 800 nm with the spectra bands observed in the near
ultraviolet region using a concentration of 0.25e0.45mM. From the
spectra, the prominent band was observed at around 370.0 nm for
all the molecules synthesized (Fig. 1a) which corresponds to either
a p - p* transition or an n-p* transition or both which is charac-
teristic of bands resulting from a nitro aniline derivative. Also, it can
be deduced that the stoichiometric difference in the molecules had
less effect on the overall change in the absorption maxima in the
molecules. That is the presence of a double sulfonamide did not
result in much change in the wavelength of maximum absorption
compared to the single sulfonamide molecule. However, a slight
hypsochromic shift was observed that is from 371 nm in C1 to
370.5 nm and 370 nm in C2 and C3 respectively, this could be due to
the overall complexity and bulkiness of their structures.
For fluorescent studies of themolecules C1e C3, it was observed
that all themolecules exhibitedmultiple emission bandswithin the
UV region, the lower visible region, and the upper visible region.
Maximum emissions were observed for the molecules when they
were excited between 260 nm and 280 nm. As expected, the
emission bands of the compounds were weaker in energies
compared to their absorption bands which infers that the energy
absorbed by the photonwas expended in exciting it, hence emitting
a lower energy when returning to the ground state. Emissions
within the UV region were the most intense and were between
302 nm and 313 nm while an emission wavelength of
605 nme623 nm were observed closer to the NIR region (Fig. 1b)
and were more desirable especially for bio-imaging studies.
Also, emissions within the UV and Visible range suggest that the
molecules where blue light to orange light emitters, a featurewhich
is desirable for their use as OLEDs. One peculiar observation was
that the presence of a double sulfonamide in C2 and C3 resulted in a
red shift of the emission wavelength. For example, in C1 emission
observed at 302 nmwas found similarly at 313 nm and 305 nm for
C2 and C3 likewise those found at 605 nm for C1were also found at
620 nm and 623 nm for C2 and C3 respectively.
The quantum yield of the compounds C1eC3 were also exam-
ined using a 1.00 mM concentration of fluorescein in 0.1 M KOH
solution as the reference. A concentration range of 0.25e0.45 nM
was prepared for the compounds and quantum yield measured at
room temperature. The quantum yields of the compounds were
observed to be between 7.7% and 25.5%. C1 and C2 both exhibiting
an appreciable quantumyield of 25.7% and 15.2% respectively while
the di-tert-butylpyrazole derivative, C3 had the least quantumyield
(Table 1). This can be ascribed to the higher degree of steric present
in C3 and as a result of the stronger electron donating effect of the
tert-butyl substituent on the pyrazole compared to that from the
methyl groups, thus affecting the extent of conjugation in the
molecule.
From the quantum yield values of C1 and C2, it can be deduced
that they possess a higher propensity of being used to fluoresce
incoming light compared to C3 as the quantum yield represent the
probability of a compound to emit fluorescent radiation when
returning from a relatively higher excited state. This observation
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276
Scheme 1. Synthesis of substituted pyrazolyl sulfonamides, C1eC3.
Fig. 1a. UVeVis absorption Spectra of C1, C2 and C3. Fig. 1b. Fluorescent spectra of C1, C2 and C3.
3
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276
Table 1 Table 2
Quantum yield values of C1, C2 and C3. Energies of C1eC3 from geometry optimized calculation using B3LYP/6-311G(d,p).
Compound Molar Absorptivity (L/mol cm)  103 Quantum Yield (%) Compound Energy (Hatrees) Energy (Kcal/mol) Energy (KJ/mol)
Fluorescein 3.01 93.0 C1 1575.687984 984017.146 4136968.802
C1 2.15 25.7 C2 2615.349382 1633285.689 6866599.802
C2 3.17 15.2 C3 2851.260355 1780612.092 7485984.062
C3 3.35 7.7suggests that the compounds can be further explored for use in
fluorescent applications including probing purposes.
2.3. Theoretical calculation analysis
DFT calculations were used to determine the energies of the
stable minima of the three molecules C1e C3 as well as the UV/Vis
spectrum using the B3LYP/6-311G(d,p) level of theory. According to
the calculations the molecules were nonlinear at the stable minima
(Fig. 2) with the energies presented in Table 2 below; The energies
of the tert-butyl substituted pyrazole molecule, C3, was higher
which is expected due to the overall complexity/bulkiness pre-
sented by the tert-butyl groups.
UVeVis calculations were computed using the time dependent
density DFT theory and the traditional B3LYP functional. The
calculated spectra of the molecules corresponded to the experi-
mental in that they both showed single strong absorptionwith very
slight difference in their maximum wavelength from C1 to C3 that
is 299 nm for C1, 305 nm for C2 and 300 nm for C3 (Fig. 3) as well as
with similar absorption intensities to the experimental spectra
(Fig. 1a).
However, the calculated spectra were at lower wavelength with
a lmax difference of about 70 nm towhich could be attributed to the
solvation difference present in the spectra from the experimental
measurement. The absorption for C1 at 299 nm corresponded to an
excitation from the ground state to the second excited state
(S0eS2) whiles absorptions at 305 nm and 300 nm correspond to
S0eS3 and S0eS4 for C2 and C3 respectively.
To understand the electronic distribution during the excitation
of electrons, the frontier orbitals were also determined from theFig. 2. Geometry optimized structures o
4
absorption calculations shown in Fig. 4.
The molecular orbitals of C1 to C3 show very similar transitions
from the HOMO to the LUMO orbitals and for the HOMO-1 to the
LUMOþ1 orbitals which are characterized by p ep* transitions
from the phenyl groups and n- p* from the heteroatoms present. In
C1, electronic transitions occur from the HOMO/LUMO orbitals
around the nitrophenylsulfonamide, while the HOMO-1/LUMO
orbitals are the high contributors to the electronic transition in
both C2 and C3 with electronic transition occurring around the
phenyl substitution on the pyrazolyl and the nitro-
phenylsulfonamide attached.
2.4. Ultra trace analysis
Ultra-trace analysis of Cu2þ and Zn2þ ions were performed on
compounds C1eC3 as they showed good quantum yields. The
analysis was conducted using fluorescence spectroscopy and
UVeVis absorbance measurement as a comparable analytical
technique. Titration measurements were conducted using a fixed
concentration of approximately 20 mM of the sensor molecules and
0e5.00 mg/L of the Zn2þ and Cu2þ ions.
For sensor molecule C1, it was observed that the addition of the
Cu2þ ions resulted in a decrease in the absorbance which showed
that a specie had been attached (Fig. 5a). Similar observation was
made when fluorescence measurement was done except that the
reduction in the intensity was much significant compared to that
from the UV measurement. A further increase in the Cu2þ ion
concentration resulted in a switch off of the fluorescence of the
molecule, C1 (Fig. 5c).
Hence, it could be deduced that the addition of the Cu2þ ion
resulted in a quenching of the fluorescence of the molecule C1, af C1eC3 using B3LYP/6-311G(d,p).
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276
Fig. 3. Calculated Spectra of C1eC3 obtained using the TD-DFT B3LYP/6-311G(d,p) level of theory.property which is significant of the molecule being used for prob-
ing. Zn2þ ions on the other hand resulted in a much appreciable
increase in the absorbance of C1 as well as the fluorescence in-
tensity (Fig. 5b and d). Also, the spectra from the addition of both
the Cu2þ and Zn2þ ions revealed that they all exhibited different
interactive effect with the sensor molecule C1 which showed how
selective it is towards the two ions.
UVeVis absorbance measurement for sensor molecule C2, also
showed similar trend to C1, likewise the fluorescencemeasurement
except that the increase in concentration of the metal ions did not
result in a switch off of the fluorescent of the molecules (Fig. 6aed).
For sensor molecule C3, addition of both Cu2þ and Zn2þ ions
resulted in an increase of the absorbance (Fig. 7a and b). However,
the addition of Cu2þ resulted in the formation of new absorbance
peak at around 280 nm which was absent in the spectra of the
molecule C3 alone (Fig. 7a). Also, fluorescence measurement
revealed a slight increase in the intensity when Zn2þ ions were
added. However, an increase in the concentration of Cu2þ ions
resulted in a decrease in the fluorescent intensity, then finally a
switch off of the fluorescent of the molecule C3 (Fig. 7c and d).
These observations revealed that C3 was a better sensor mole-
cule for probing of Cu2þ ions and was also selective. Overall, all the
molecules were selective and produced different response espe-
cially towards the probing of Cu2þ ions.
The mechanism of the sensor molecules as they interact with
the Zn2þ ions is predicted to occur by a breaking of the Excited State
Intramolecular Proton Transfer, ESIPT as the Zn2þ ions bind with the
sensor molecules leading to an enhanced fluorescence. Whiles the
Cu2þ ions on the other hand, follows a gradual quenching of the
fluorescence emission as the concentration increases, predicted to
follow a metal-induced fluorescence quenching approach.5
The detection limits of the sensor molecules were estimated
from a plot of (F-Fₒ)/Fₒ (where F represent the fluorescent intensity
at a particular concentration and Fₒ represent the fluorescence in-
tensity of the pure molecule) against the concentration of the Cu2þ
and Zn2þ ion concentration at emission wavelength of 302 nm,
305 nm and 313 nm for C1, C2 and C3 respectively and a linear
relation with R2 between 0.9802 and 1.00 (Figs. S8eS10). The
detection limits from both the fluorometric and UVeVis titrations
are tabulated in Table 3.0. From all the sensor molecules, it was
observed that the detection limits from the fluorometric titrations
were lower than that of the UVeVis. Hence presented a more
analytically sensitive probing tool for the metal ions.
Also, the detection limits for the metal ions were within ranges
that are comparable to those reported in literature [30e32]. Over-
all, the sensors C1 and C2 were analytically sensitive toward the
determination of Zn2þ ions whiles C3 was more analytically sen-
sitive towards the detection of Cu2þ ions.3. Conclusion
Three pyrazolyl-based sulphonamides sensor molecules were
successfully synthesized and characterized following a single pot
reaction. Photo-physical studies revealed that the molecules were
fluorescent, showing emission bands at the UV and far visible re-
gions. Also, they exhibited good quantum yields, a property which
led to a probing study of the compounds on Cu2þ and Zn2þ metal
ions. Probing studies revealed that all the sensors exhibited a rapid
response toward increasing concentrations of themetal ions, which
was essential for a further development toward their usage as po-
tential probing molecules.
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276
Fig. 4. Frontier Orbitals of C1eC3 from TD-DFT B3LYP/6-311G (d,p) level of theory.
Fig. 5a. UV absorption spectra of C1 and 0e5.00 mg/L of Cu2þ ions. Fig. 5b. UV absorption spectra of C1 and 0e5.00 mg/L of Zn2þ ions.4. Experimental section
4.1. Materials and methods
Unless otherwise stated, all manipulations were carried out
under nitrogen atmosphere using standard Schlenck techniques.
All organic solvents were dried and purified by distillation over6
standard reagents under nitrogen prior to use. Compounds chlor-
osulfonic acid, phenyl hydrazine, pentane-2,4-dione and 2,2,6,6-
tetramethyl-3,5-heptadione, were purchased from Sigma-Aldrich.
All chemicals were used as received. Similar methods as reported
by us were used for synthesizing the precursors of the sensor
molecules [24]. Infrared (IR) spectra of ligands were recorded on a
PerkinElmer Spectrum Two equipped with a diamond ATR.
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276
þ Fig. 6b. UV absorption spectra of C2 and 0e5.00 mg/L of Zn2þ ions.Fig. 5c. Fluorescence spectra of C1 and 0e5.00 mg/L of Cu2 ions.
Fig. 5d. Fluorescence spectra of C1 and 0e5.00 mg/L of Zn2þ ions. Fig. 6c. Fluorescence spectra of C2 and 0e5.00 mg/L of Cu2þ ions.
Fig. 6a. UV absorption spectra of C2 and 0e5.00 mg/L of Cu2þ ions.
Fig. 6d. Fluorescence spectra of C2 and 0e5.00 mg/L of Zn2þ ions.Elemental analyses were performed on a Vario Elementar III
microcube CHNS. GC-MS analysis of the samples was performed
using a PerkinElmer GC Clarus 580 Gas Chromatograph interfaced
to a Mass Spectrometer PerkinElmer (Clarus SQ 8 S) equipped with
ZB-5HT MS (5% diphenyl/95% dimethyl poly siloxane) fused a
capillary column (30  0.25 mm ID  0.25 mm DF). NMR spectra
were recorded on a Bruker 500 MHz instrument (1H at 500 MHz
and 13C{1H} at 125 MHz) at the Department of Chemistry, Univer-
sity of Ghana. The chemical shifts are reported in d (ppm) and
referenced to the residual proton and carbon signals 3.31 ppm and
49.0 ppm respectively of CD3OD NMR solvent. Absorption calcu-
lations have been performed using the Gaussian 09 program [33]
from the CHPC cluster, University of Johannesburg. The ground
state geometries were fully optimized using the hybrid B3LYP7
functional method with the 6-311G(d,p) as basis set. For all opti-
mized structures a frequency analysis at the same level of theory
was used to verify that it corresponds to the minimum potential
energy surface. For all the minima the number of imaginary fre-
quencies was zero. The absorption and emission properties were
calculated using time dependent density functional theory (TD-
DFT) in combination with B3LYP hybrid functional with 6-
311G(d,p) as basis set.4.2. Synthesis of compounds
Compounds 3,5-dimethyl-1-phenyl-1H-pyrazole-4-sulfonyl
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276
Fig. 7a. UV absorption spectra of C3 and 0e5.00 mg/L of Cu2þ ions. Fig. 7d. Fluorescence spectra of C3 and 0e5.00 mg/L of Zn2þ ions.
Fig. 7b. UV absorption spectra of C3 and 0e5.00 mg/L of Zn2þ ions.
Fig. 7c. Fluorescence spectra of C3 and 0e5.00 mg/L of Cu2þ ions.chloride, 3,5-di-tert-butyl-1-(4-(chlorosulfonyl)phenyl)-1H-pyr-
azole-4-sulfonyl chloride and 1-(4-(chlorosulfonyl)phenyl)-3,5-
dimethyl-1-phenyl-1H-pyrazole-4-sulfonyl chloride were pre-
pared following a multistep procedure as reported previously [29].
4.2.1. Synthesis of 3,5-dimethyl-N-(4-nitrophenyl)-1-phenyl-1H-
pyrazole-4-sulfonamide (C1)
An ethanol solution (20mL) of 4-nitroaniline (0.26 g,1.85mmol)
was added to a stirring ethanol solution (30 mL) of 3,5-dimethyl-1-
phenyl-1H-pyrazole-4-sulfonyl chloride (0.50 g, 1.85 mmol). The
resultant mixture was refluxed at 45 C for 5 h to obtain a
yellowish-brown solution. This solution was evaporated to afford
yellowish brown solid after column purification using a solvent
system of a mixture of ethyl acetate-methanol in a 7:3 ratio.8
Yield ¼ 0.63 g (92%). 1H NMR (CD3OD): d 2.38 (s, 3H, CH3); 2.51 (s,
3H, CH3); 6.61 (s, 1H, NeH); 7.12 (d, 2H, 3JHH ¼ 7.5 Hz, Ph); 7.71 (m,
1H, Ph); 7.76 (t, 2H, 3JHH ¼ 8.0 Hz, Ph); 8.07 (d, 2H, 3JHH ¼ 8.0 Hz,
Ph); 8.17 (d, 2H, 3JHH ¼ 7.5 Hz, Ph). 13C{1H} NMR (CD3OD): d 10.65;
11.14; 109.28; 119.72; 124.47; 126.42; 128.59; 129.37; 131.16;
134.17; 135.47; 142.82; 147.97; 148.22. IR (Diamond ATR, cm1):
3431 y(NeH); 1528,1348 y(NeO). GCMS (EI) m/z [M]þ calcd.
372.090: Found: 372.263 (100%). Anal. Calcd for C17H16N4O4S: C,
54.83; H, 4.33; N,15.04; S, 8.61%. Found C, 54.95; H, 4.73; N,15.18; S,
8.41%.
Compound C2 and C3 was prepared in a similar manner as
described for C1, using appropriate reagents.4.2.2. Synthesis of 3,5-dimethyl-N-(4-nitrophenyl)-1-(4-(N-(4-
nitrophenyl)sulfamoyl)phenyl)-1H-pyrazole-4-sulfonamide (C2)
The compound 4-nitroaniline (0.374 g, 2.71 mmol) was reacted
with 1-(4-(chlorosulfonyl)phenyl)-3,5-dimethyl-1-phenyl-1H-pyr-
azole-4-sulfonyl chloride (0.5 g, 1.35 mmol) to give yellowish
brown solid. Yield ¼ 0.71 g (91%). 1H NMR (CD3OD): d 2.49 (s, 3H,
CH3); 2.51 (s, 3H, CH3); 7.21 (d, 4H, 3JHH ¼ 8.0 Hz, Ph); 7.58 (d, 1H,
3JHH ¼ 8.0 Hz, Ph); 7.70 (m, 1H, Ph); 8.00 (m, 1H, Ph); 8.07 (d, 1H,
3JHH ¼ 8.0 Hz, Ph); 8.20 (d, 4H, 3JHH ¼ 8.0 Hz, Ph). 13C{1H} NMR
(CD3OD): d 11.13; 11.19; 11.81; 11.90; 109.30; 109.38; 119.97; 124.23;
124.44; 126.66; 127.04; 127.97; 128.45; 128.47; 128.64; 129.34;
130.58; 131.18; 134.13; 137.03; 138.64; 143.89; 145.72; 147.84;
148.21. IR (Diamond ATR, cm1): 3431 y(NeH); 1526,1347 y(NeO).
GCMS (EI) m/z [MþH]þ calcd. 573.080: Found: 573.467 (100%).
Anal. Calcd for C23H20N6O8S2: C, 48.25; H, 3.52; N, 14.68; S, 11.20%.
Found C, 48.50; H, 3.64; N, 14.80; S, 11.11%.4.2.3. Synthesis of 3,5-di-tert-butyl-N-(4-nitrophenyl)-1-(4-(N-(4-
nitrophenyl) sulfamoyl)phenyl)-1H-pyrazole-4-sulfonamide (C3)
The compound 4-nitroaniline (0.305 g, 2.21 mmol) was reacted
with 3,5-di-tert-butyl-1-(4-(chlorosulfonyl)phenyl)-1H-pyrazole-
4-sulfonyl chloride (0.500 g, 1.10 mmol) to give dark brown solid.
Yield ¼ 0.62 g (85%). 1H NMR (CD3OD): d 1.28 (s, 9H, CH3); 1.40 (s,
9H, CH3); 5.45 (s, 2H, NeH); 7.13 (d, 4H, 3JHH ¼ 7.0 Hz, Ph); 7.48 (d,
1H, 3JHH ¼ 8.0 Hz, Ph); 7.59 (t, 1H, 3JHH ¼ 7.5 Hz, Ph); 7.78 (s, 1H, Ph);
7.94 (d, 1H, 3JHH ¼ 7.0 Hz, Ph); 8.17 (d, 4H, 3JHH ¼ 7.0 Hz, Ph). 13C{1H}
NMR (CD3OD): d 28.41; 30.05; 33.48; 34.35; 119.175; 126.38;
126.88; 127.18; 127.67; 129.35; 129.61; 130.93; 143.240; 145.91;
149.42; 156.49. IR (Diamond ATR, cm1): 3431 y(NeH); 1529,1347
y(NeO). GCMS (EI)m/z [M]þ calcd. 656.170: Found: 656.315 (100%).
Anal. Calcd for C29H32N6O8S2: C, 53.04; H, 4.91; N, 12.80; S, 9.77%.
Found C, 53.05; H, 5.01; N, 12.89; S, 9.87%.
C. Amoah, C. Obuah, M.K. Ainooson et al. Tetrahedron 133 (2023) 133276
Table 3.0
Limit of Detection of the Cu and Zn ions from titration with C1eC3.
Compound Limit of detection for Cu2þ ions Limit of detection for Zn2þ ions
UV (mg/L) Fluorescence (mg/L) UV (mg/L) Fluorescence (mg/L)
C1 0.085 0.011 0.070 0.002
C2 0.210 0.079 0.085 0.031
C3 0.131 0.103 0.164 0.1354.3. UVevis and fluorimetric determination of Cu2þ and Zn2þ ions
All spectroscopic measurement were carried out at room tem-
perature. UVeVis Absorbance measurement were done on a UV-
1800 Shimadzu Spectrophotometer whiles fluorescent studies
were conducted on an RF-6000 Shimadzu Spectro-
fluorophotometer. The emission spectra were recorded after the
excitation wavelength up to 800 nm. The quantum yield was
calculated from the equation:

   !2
FX ¼FST 
GradX  hX 2 (Equation 1)GradST hST
Where, X and ST refer to the test and the standard samples
respectively. Grad refers to the integrated emission intensity, h
represents the refractive index of the solvents used for the samples
and 4 represents the quantum yield. Ultra-trace analysis for Cu2þ
and Zn2þ were conducted by in situ titration of a fixed concentra-
tion of the sensor molecules C1eC3 with varying concentration of
Cu2þ and Zn2þ (0.00, 0.25, 0.50, 0.75, 1.00, 2.00 and 5.00 mg/L).
Fluorescence and UVeVis measurement were carried on the
different analyte concentration in a 1 cm quartz cell respectively at
room temperature. All titrations were repeated in triplicates and
the limit of detection (LOD) of the ions were determined across the
various sensor molecules using a calibration plot of analyte con-
centration against (FeF0)/F0 for the fluorescent emission. Where F
represent the fluorescent emission intensity of the analyte and test
sample and F0 represent the fluorescent emission intensity of the
test sample alone. While the LOD from the UV measurement were
determined from a plot of analyte concentration versus the absor-
bance using the Beer Lambert equation. The LOD was calculated
from the equation:
  
LOD¼3:3 Sy S (Equation 2)
where Sy and S represent the standard deviation of calibration
curve and the slope respectively.Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Data availability
Data will be made available on request.Acknowledgments
We acknowledge the University of Ghana and the University of
Johannesburg for financial support for this project.9
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2023.133276.References
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