Synthesis, crystal structures and studies on Hg2+ sensing by the diazo derivatives of sulfathiazole and sulfamethoxazole

Article abstract of DOI:10.1080/17415993.2012.716844

Diazocoupling of sulfathiazole and sulfamethoxazole with 2,4-pentanedione led to the syntheses of compounds R1 and R2. These were fully characterized by single crystal X-ray diffraction studies in conjunction with UV-visible, IR, ¹H NMR, and ma

Full text of DOI:10.1080/17415993.2012.716844

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Synthesis, crystal structures and studies
on Hg2+ sensing by the diazo derivatives
of sulfathiazole and sulfamethoxazole
K. K. Upadhyay a , Shalini Upadhyay a , Ajit Kumar a & Kamlesh
Thapliyal b
a Department of Chemistry, Faculty of Science , Banaras Hindu
University , Varanasi , 221005 , Uttar Pradesh , India
b Department of Chemistry , Indian Institute of Technology ,
Kanpur , 208016 , Uttar Pradesh , India
Published online: 18 Sep 2012.
To cite this article: K. K. Upadhyay , Shalini Upadhyay , Ajit Kumar & Kamlesh Thapliyal (2012)
Synthesis, crystal structures and studies on Hg2+ sensing by the diazo derivatives of sulfathiazole and
sulfamethoxazole, Journal of Sulfur Chemistry, 33:5, 573-582, DOI: 10.1080/17415993.2012.716844
To link to this article: http://dx.doi.org/10.1080/17415993.2012.716844
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Journal of Sulfur Chemistry
Vol. 33, No. 5, October 2012, 573–582
Synthesis, crystal structures and studies on Hg2+ sensing by
the diazo derivatives of sulfathiazole and sulfamethoxazole
K.K. Upadhyaya,*, Shalini Upadhyaya, Ajit Kumara and Kamlesh Thapliyalb
aDepartment of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005,
Uttar Pradesh, India; bDepartment of Chemistry, Indian Institute of Technology, Kanpur 208016,
Uttar Pradesh, India
(Received 2 May 2012; final version received 26 July 2012)
Diazocoupling of sulfathiazole and sulfamethoxazole with 2,4-pentanedione led to the syntheses of com-
pounds R1 and R2. These were fully characterized by single crystal X-ray diffraction studies in conjunction
with UV–visible, IR, 1H NMR, and mass spectral studies. Both the compounds were further screened for
their possible use in metal ion recognition. Interestingly, compound R1 showed a selective naked-eye
response for Hg2+, while R2 did not give a color change for any metal ions. These results can be under-
stood in terms of a solvent-assisted low-energy absorption band in R1 that disappeared upon interaction
with Hg2+. This absorption band was not observed in the case of compound R2 that consequently failed
to show any naked-eye color change in the presence of metal ions.
Keywords: sulfa drug; 2, 4-pentanedione; diazo derivatives; crystal structure; Hg2+ sensing
1. Introduction
Cations are ubiquitous and play crucial roles in our ecosystem as well as in living systems (1).
A variety of metal ions play pivotal roles in various metallo-enzymes. For example, Mn2+, Cu2+
,
and Zn2+ in superoxide dismutase (2), Zn2+ in carboxypeptidase, and carbonic anhydrase (3, 4)
*Corresponding author. Email: drkaushalbhu@yahoo.co.in
ISSN 1741-5993 print/ISSN 1741-6000 online
© 2012 Taylor & Francis
http://dx.doi.org/10.1080/17415993.2012.716844
http://www.tandfonline.com

574 K.K. Upadhyay et al.
and Ni2+ in urease (5). On the other hand, metal ions such as Cd2+, Hg2+, and Pb2+ are well
documented in the literature to be harmful to our ecosystem (6–10). In this context, the itai–itai (9)
and minamata (10) diseases caused by Cd2+ and Hg2+, respectively, are well documented in the
literature. Hence, accurate qualitative and quantitative sensing of ions has topped the agendas of
chemists for the last couple of decades. In this regard, colorimetric sensors are especially attractive
because they would allow ‘naked-eye’detection of ions without resort to any costly spectroscopic
instrumentation.
This study is part of our current research interest directed toward synthesis, characterization, and
evaluation of colorimetric receptors for ions of biological and environmental relevance (11–15).
The selection of sulfa drugs as the starting material for this study was based on their ready avail-
ability, low price, and the presence of ligating groups. Sulfonamide and its substituted derivatives
are extensively used in medicine for their antibacterial properties (16–19). In the field of ion sens-
ing, very few sulfa drug derivatives have been used as a constituent of molecular chemosensors
for cations. In contrast, several sulfa drug-based receptors have been reported in the literature for
anions (20–23).
We report herein the synthesis and characterization of two diazo derivatives of sulfathiazole
(R1) and sulfamethoxazole (R2). Both the compounds (R1 and R2) were further screened for
their possible use in metal ion recognition. Compound R1 showed solvatochromism and solvent-
assisted naked-eye sensing for Hg2+, while R2, which is an oxygen analog of R1, was unable to
show any sensing behavior toward Hg2+
.
2. Results and discussion
2.1. Crystal structure of compounds R1 and R2
The relevant crystal structure data along with structure determination details of compounds R1
and R2 are given in Table 1.
A perusal of Table 1 clearly showed that both R1 and R2 adopted a triclinic pattern with
−
P−1 symmetry. The N3 N4 bond lengths in R1 and R2 were found to be 1.30 and 1.31Å,
−
respectively, which matched well with N N bond lengths reported in the literature (11).
Thus, it was concluded that both R1 and R2 existed in their hydrazo rather than azo forms
(Figure 1).
2.2. Sensing studies
2.2.1. UV–visible studies
The UV–visible spectra of R1 and R2 showed broad absorption bands in nujol at 409, and 358 nm
and at 390 and 353 nm, respectively. R1 was absorbed at 493 and 411 nm at 1 × 10−3 M in DMSO
solution, while R2 did not show any variation in λmax in DMSO in comparison to nujol. Hence,
only R1 was studied in a series of solvents having different polarities with the results summarized
in Table 2. The corresponding UV–visible absorption spectra and color changes are given in
Figure 2.
As it can be seen from Table 2 and Figure 2, R1 showed an additional broad peak at 480–493 nm
in polar solvents such as DMSO, DMF, and acetone, due to the formation of an intermolecular
hydrogen bond as shown in Scheme 1.
The solvent-sensitive peak at 493 nm is responsible for the orange color of R1 in these solvents,
=
=
while in other solvents, without an X O group (where X S, C, or N), neither this broad solvent-
assisted peak nor the orange red color was observed. The non-occurrence of solvatochromic

Journal of Sulfur Chemistry 575
Table 1. Crystal data and structure refinements for compounds R1 and R2.
Identification code
Compound R1
Compound R2
CCDC number
Empirical formula
Formula weight
Crystal system
Space group
T (K)
706686
C17H21N4O5S2
425.50
746351
C15H16N4O5S
364.38
Triclinic
Triclinic
P−1
P−1
100 (2)
100 (2)
λ, MoKα
a (Å)
0.71069
7.977(5)
0.71069
5.455(5)
b (Å)
8.980(5)
10.835(5)
14.479(5)
93.850(5)
100.553(5)
90.814(5)
839.1(9)
2, 1.442
0.228
380
c (Å)
14.569(5)
87.238(5)
74.525(5)
78.945(5)
987.1(9)
2, 1.432
0.307
444
α (◦)
β (◦)
γ (◦)
V (Å3)
Z, ρcalc (Mg m−3
)
μ (mm−1
F (0 0 0)
)
Crystal size (mm3)
θ range for data collection
Index ranges
0.20 × 0.16 × 0.14
0.15 × 0.09 × 0.05
2.3–27.9
2.3–28.8
−10 <= h <= 10,
−11 <= k <= 8,
−18 <= l <= 19
6475
−7 <= h <= 7,
−11 <= k <= 14,
−18 <= l <= 19
6834
Reflections collected
Reflections/restraints/parameters
4660/0/253
1.101
0.0715/0.2006
0.0991/0.2610
0.623/−0.467
3753/0/234
1.104
0.0407/0.1226
0.0480/0.1256
0.401/−0.327
Goodness-of-fit on F2
R1a, wR2b (I > 2σ(I))
R1a, wR2b (all data)
Largest difference peak/hole, e Å−3
Notes: aR = ꢀFo| − |Fcꢀ/ |Fo|.
bwR2 = { [w[(Fo − Fc2)2]/ [w(Fo2)2]}
.
2
1/2
behavior in R2 may be a consequence of the presence of the oxygen-containing oxazole ring
in place of the sulfur-containing thiazole ring in R1. This observation is a consequence of a
substituent effect, which is in accordance with a literature report (24).
Due to the presence of the solvent-assisted peak and orange color of compound R1, we further
screened this compound for its possible use in the field of metal ion sensing. The 1.0 × 10−3 M
DMSO solution of compound R1 was treated with one equivalent of d10 metal ions as their chloride
salts.Among the d10 metal ions, only Hg2+ showed a naked-eye color change from orange to olive
green with the 493 nm band nearly vanishing for compound R1 (Figure 3 and Table 3) for this ion.
The rest of the d10 metal ions (Zn2+ and Cd2+) were not able to produce any significant spectral
or naked-eye color changes.
In order to further understand the binding characteristics of R1 toward Hg2+, UV–visible
titration studies were also performed. On concomitant additions of Hg2+ (as its chloride salt) to
the 1.0 × 10−3 M DMSO solution of R1, the solvent-assisted band at 493 nm started vanishing,
and it was almost vanished on the addition of two equivalents of Hg2+.At this stage, the color of the
R1 solution turned olive green from orange, which is easily observable to the naked-eye. Further
addition of Hg2+ up to 3.0 equivalents did not produce any UV–visible spectral or naked-eye color
change (Figure 4).
The non-linear fitting of UV–visible titration data for compound R1 was done with the 1:2
([G]/[H]) binding equation (25), yielding an association constant of (1.48 0.05) × 103 M−2
withasatisfactorycorrelationcoefficientvalue r2 = 0.9985(Figure 5).The1:2bindingstoichiom-
etry between Hg2+ and R1 was also confirmed by mass spectrometric studies for R1+HgCl2 that
yielded an (M+H) peak at 932.4 (see ESI; Figure S5) as expected for its mass.

576 K.K. Upadhyay et al.
Figure 1. X-ray crystal structure of compounds R1 and R2 (ORTEP diagram).
Table 2. UV–visible absorption bands of R1 in solid
and solution states.
S.no.
Medium
UV–visible bands (nm)
1
2
3
4
5
6
Nujol
DMSO
DMF
Acetonitrile
Acetone
Chloroform
409, 358
493, 411
480, 409
404, 306
490, 404, 354
409
Similar additions of Zn2+ and Cd2+ as their chloride salts to 1.0 × 10−3 M DMSO solutions of
R1 did not produce any significant visible spectral changes (Figure 3). The change of the counter
anion of Hg2+ did not affect its interaction with R1 either in terms of naked-eye or spectral
changes. Hg2+ sensitive papers (prepared by soaking the strips of Wattman filter paper No. 42 in
a saturated solution of the R1 in DMSO) produced similar types of naked-eye changes when they

Journal of Sulfur Chemistry 577
Figure 2. Absorption spectra of 1 × 10−3 M DMSO solution of R1 in different solvents and respective color changes.
Scheme 1. Weak interaction of polar solvents with compound R1.
Figure 3. Absorption spectral pattern of 1 × 10−3 M DMSO solution of R1 on addition of 1.0 equivalents of Zn2+
,
Cd2+, and Hg2+
.

578 K.K. Upadhyay et al.
Table 3. UV–visible spectral bands and color changes of
1.0 × 10−3 M DMSO solution of R1 on separate addition of 1.0
equivalents each of Zn2+, Cd2+, and Hg2+ as their chloride salts.
Species
Color
Wavelength (nm)
R1
Orange
493, 411
491, 406
490, 416
493, 412
R1:Zn2+
R1:Cd2+
R1:Hg2+
Dark orange
Dark orange
Olive green
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
460
480
500
520
540
560
580
Wavelength (nm)
Figure 4. Absorption spectra of 1 × 10−3 M DMSO solution of R1 on concomitant addition of 0.0–3.0 equivalents of
Hg2+
.
were dipped into solutions of Hg2+ in DMSO, while they did not produce any color change by
dipping into the respective solutions of Zn2+ and Cd2+ (Figure 6).
2.2.2. 1H NMR titration studies
To further look into the nature of host–guest interactions, 1H NMR titration experiments (see ESI;
ESI; Figure S6 and S7) were performed by adding varying equivalents of Hg2+ (0–3 equivalents)
as its chloride salt to a 5 × 10−3 M DMSO-d6 solution of R1. The chemical shifts in δ ppm
for –NH protons are given in Table 4. When comparing the two NHs of compound R1, the proton
at N-3 absorbed downfield (13.63 δ ppm) in comparison to N-2 (12.71 δ ppm). The downfield
shifting of the NH at N-3 position in DMSO-d6 may be a consequence of intramolecular hydrogen
bonding with COCH3 (one of acetyl group of R1), which was further supported by the dilution
experiment with CDCl3 (see ESI; Figure S8).
The most important change upon concomitant additions of Hg2+ to R1 was the gradual van-
ishing of the N-2H proton signal. The complete vanishing of this proton was achieved upon the
addition of 2.0 equivalents of Hg2+, indicating the loss of N-2H as the result of its complexation
with HgCl2.

Journal of Sulfur Chemistry 579
0.30
0.25
0.20
0.15
0.10
0.05
1:2 binding (1.48+/–0.05)x10^3 M-2, r2 = 0.9985)
0.0000
0.0005
0.0010
[Hg2+]
0.0015
0.0020
Figure 5. Binding curve for 1:2 binding between R1 and Hg2+ as its chloride salt in DMSO.
Figure 6. Compound R1 strips showing color changes on dipping into the DMSO solution of d10 metal ions.
Table 4. 1H NMR spectral titration data of 1 × 10−3 M DMSO-d6
solution of R1 on the concomitant addition of Hg2+ (0–3 equivalents)
as its chloride salt (12.4–13.9 δ ppm).
Equivalents
of Hg2+
Chemical shifts in (δ ppm)
N–H(N-3)
N–H(N-2)
12.71
12.73
12.73
12.75
12.71
12.73
12.71
12.66
–
0.00
13.63
13.64
13.64
13.64
13.64
13.64
13.65
13.65
13.65
13.65
13.66
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.50
3.00
–
–

580 K.K. Upadhyay et al.
Thus, on the basis of UV–visible and 1H NMR titrations, additional support from mass spectral
data, (R1+HgCl2) that forms in DMSO in an equilibrium process (Scheme 2), may be proposed
as being responsible for the naked-eye sensing of Hg2+ by R1. However, in this study, the sensing
pathway involves a 1:2 ([G]/[H]) stoichiometry, compared to 1:1 in our previous report (12).
Scheme 2. Chemical structure image of binding of compound R1 with Hg2+
.
3. Experimental
3.1. Apparatus
The IR Spectra were recorded as KBr pellets on a Varian 3100 FT–IR spectrophotometer, while
UV–visible spectral studies were performed on a UV-1700 pharmaspec UV–VIS spectrophotome-
ter. The NMR spectral studies were performed on a JEOL AL 300 FT NMR spectrometer and the
chemical shifts are reported in δ ppm using tetramethylsilane as the internal standard.
3.2. Reagents and chemicals
The sulfathiazole and sulfamethoxazole were purchased from Sigma (USA) and used without
further purification, while sodium nitrite and sodium acetate were purchased from Qualigens
Fine Chemicals, Mumbai. Acetyl acetone and diethyl ether were purchased from Spectrochem
Pvt. Ltd., Mumbai. The remaining chemicals and solvents including spectroscopic grade DMSO
were purchased from Central Drug House (P) Ltd., Delhi.
3.3. X-ray diffraction studies
Crystals of R1 and R2 of suitable sizes were grown by the slow evaporation of their supersatu-
rated solutions in acetone and diethyl ether, respectively. The X-ray diffraction data for R1 and
R2 were collected at 100 K on a Bruker SMART APEX CCD diffractometer using graphite-
monochromated MoKα radiation (λ = 0.71069Å). The linear absorption coefficients, scattering
factors for the atoms, and the anomalous dispersion corrections were taken from international
tables for X-ray crystallography. The data integration and reduction were processed with SAINT
(26) software. An empirical absorption correction was applied to the collected reflections with
SADABS (27) using XPREP (28). The crystal structures were solved by the direct method using
SHELXTL (29) and refinements were done on F2 by a full-matrix least-squares technique using

Journal of Sulfur Chemistry 581
the SHELXL-97 (30) program package. For all the cases, non-hydrogen atoms were refined
anisotropically, while the hydrogen atoms were fixed geometrically and treated as riding atoms
using SHELXL default parameters.
3.4. Synthesis of compounds R1 and R2
Compounds R1 and R2 (Scheme 3) were synthesized according to a general literature procedure
(31–33). These were fully characterized by single crystal X-ray diffraction studies in conjunction
with IR, 1H NMR, and mass spectral studies (see ESI; Figure S1–S4).
Scheme 3. Synthetic procedure for compounds R1 and R2.
Conclusion
Thus, two diazo derivatives of sulfa drugs (R1 and R2) derived from the diazotization of sulfathi-
azole and sulfamethoxazole and their subsequent couplings over 2,4-pentanediaone are being
reported. These compounds were fully characterized by single crystal X-ray diffraction studies.
We were successful in establishing the use of R1 for the naked-eye recognition of a notorious
toxic metal ion like Hg2+ at a milimolar level.
Acknowledgements
SU is thankful to CSIR New Delhi for providing financial assistance in the form of a fellowship.
Supplementary material
Crystallographic data for the structures reported in this article have been deposited with the Cambridge Crystallographic
Data Centre (The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK; email: deposit@ccdc.cam.ac.uk; www:
http://www.ccdc.cam.ac.uk; fax: 44 1223 336033) and are available free of charge on request, quoting the Deposition No.
CCDC 706686 for compound R1 and 746351 for compound R2.

582 K.K. Upadhyay et al.
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