Synthesis, spectroscopic characterization, DFT studies and antibacterial assays of a novel silver(I) complex with the anti-inflammatory nimesulide

Article abstract of DOI:10.1016/j.poly.2012.02.002

A novel silver(I) complex with nimesulide (NMS) of composition AgC ₁₃H₁₁N₂O₅S was synthesized and characterized by chemical and spectroscopic measurements, density functional theory (DFT) studies and biological

Full text of DOI:10.1016/j.poly.2012.02.002

Polyhedron 36 (2012) 112–119
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Polyhedron
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Synthesis, spectroscopic characterization, DFT studies and antibacterial assays
of a novel silver(I) complex with the anti-inflammatory nimesulide
Raphael E.F. de Paiva a, Camilla Abbehausen a, Alexandre F. Gomes b, Fábio C. Gozzo b, Wilton R. Lustri c,
André L.B. Formiga a, Pedro P. Corbi a,
⇑
a Inorganic Chemistry Department, Institute of Chemistry, University of Campinas – UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil
b Organic Chemistry Department, Institute of Chemistry, University of Campinas – UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil
c Biological and Health Sciences Department – UNIARA, 14801-320 Araraquara, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel silver(I) complex with nimesulide (NMS) of composition AgC13H11N2O5S was synthesized and
characterized by chemical and spectroscopic measurements, density functional theory (DFT) studies
and biological assays. Infrared (IR), ESI-QTOF-mass spectrometric (MS) analyses and 1H, 13C and
[1H–15N] nuclear magnetic resonance (NMR) studies indicate that NMS acts as a bidentate ligand, being
coordinated to Ag(I) through the nitrogen and one of the oxygen atoms of the sulphonamide group. The
proposed structure based on the experimental data was confirmed as a minimum of the potential energy
surface (PES) with the calculation of the hessians, showing no imaginary frequencies. Also, the theoretical
IR spectra of the free ligand and of the silver(I) complex (Ag–NMS) are in a good agreement with the
experimental data. Theoretical Time-Dependent DFT (TD-DFT) studies confirmed that the observed tran-
Received 16 December 2011
Accepted 3 February 2012
Available online 9 February 2012
Keywords:
Silver(I)
Nimesulide
Metal complex
Density functional theory
ESI-QTOF-MS
sitions in the UV–Vis spectra of the NMS and Ag–NMS are due to p–
p⁄ transitions. The antibacterial activ-
ity of Ag–NMS was evaluated by an antibiogram assay, using the disk diffusion method. The complex
showed an effective antibacterial activity against Staphylococcus aureus (Gram-positive), and Escherichia
coli and Pseudomonas aeruginosa (Gram-negative) pathogenic bacterial cells.
Ó 2012 Elsevier Ltd. All rights reserved.
Antibacterial activity
1. Introduction
drastically reducing the use of silver compounds [5,6]. Only in
the 1960s, when Moyer et al. [7] introduced the use of a 0.5% silver
Biological and pharmacological activities of silver(I)-based com-
pounds have been explored for a long time [1,2]. The first report
concerning the use of silver in wound treatment is dated to the
18th century, when silver nitrate was used in the treatment of ul-
cers [3]. In the 20th century, the biological activities of silver com-
pounds were shown to be associated primarily to presence of
silver(I) ions [4]. In the 1940s, however, with the advances in the
isolation of the fungus Penicillium notatum and purification of pen-
icillin, penicillin-derived antibiotics started to be used worldwide
as the main pharmaceutical agents against bacterial infections,
nitrate solution for the treatment of burns, did silver-based com-
pounds start to be considered again. Moyer proposed that at this
low concentration the silver nitrate does not interfere with epider-
mal proliferation and possess antibacterial properties against
Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia
coli [8]. In 1968, silver-sulfadiazine, a silver(I)–sulphonamide
complex, was introduced clinically for treatment of burns and skin
wounds. Due to its efficacy, silver-sulfadiazine has been used in
medicine since the 1970s as an antibacterial agent. At the present
time, most of the silver(I)-based compounds are commercially
available in the form of wound dressings, such as ActicoatÒ (Smith
and Nephew) and ActisorbÒ (Johnson and Johnson) [9], which have
some intrinsic benefits like stimulation of healing in indolent
wounds, prophylactic applications and treatment of critically
colonized wounds [10].
Abbreviations: NMS, nimesulide; Ag–NMS, silver(I) complex with nimesulide;
NMR, nuclear magnetic resonance; IR, infrared; ESI-QTOF-MS, electrospray ioniza-
tion quadrupole time-of-flight mass spectrometry; TMS, tetramethylsilane; DMSO,
dimethyl sulfoxide; LANL2DZ, Los Alamos National Laboratory-2nd version on
double zeta function; B3LYP, Becke3–Lee Young Parr functional; ATCC, American
type collection cell; MH, Mueller–Hinton agar; BHI, Brain–heart infusion medium;
CFU, colony forming unit; PCM, polarizable continuum model; PES, potential energy
surface.
Silver(I)-based antiseptics have been shown to possess lower
propensity to induce antimicrobial resistance than other antibiotics
[11], and simultaneously have a remarkably low human toxicity
when compared to other heavy metal ions [12], which are desirable
properties forantimicrobialagents. Accordingto theliterature, there
are three possible mechanisms for inhibition of bacteria growth by
⇑
Corresponding author. Tel.: +55 19 35213130; fax: +55 19 35213023.
E-mail address: ppcorbi@iqm.unicamp.br (P.P. Corbi).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.02.002

R.E.F. de Paiva et al. / Polyhedron 36 (2012) 112–119
113
silver(I) ions: (a) interference in the electron transport system, (b)
2. Experimental
DNA-binding and (c) interaction with the cell membrane [13].
One approach to obtain new silver(I)-based compounds is to
combine some specific classes of biologically active molecules with
silver ions [14]. In some cases, silver complexes with antibiotics
have been shown to be more effective than the free antibiotics
[15]. Following this approach, new metal–organic complexes with
antibacterial activities have been synthesized and described in the
literature. Kazachenko et al. [16] investigated the synthesis and
antimicrobial activities of silver complexes with the amino acids
histidine and tryptophan. Both compounds showed a good antibac-
terial activity against Gram-negative and Gram-positive bacterial
strains, with low toxicity. Ruan et al. [17] synthesized silver(I)
complexes with carbazole carboxylate ligands exhibiting an anti-
bacterial activity superior to penicillin against strains of Bacillus
subtilis. Isab and Wazeer [18] reported the synthesis and character-
ization of a monodentate silver(I) complex with captopril, which
exhibits a high antimicrobial activity against P. aeruginosa when
compared to the free ligand. Poyraz et al. [19] reported the synthe-
sis of silver(I) complexes with triphenylphosphine and aspirin or
with salicylic acid. The complexes exhibited higher cytotoxic activ-
ity than cisplatin against leiomyosarcoma cells and human breast
adenocarcinoma cells. Furthermore, a recently published silver(I)
complex with acesulfame was also shown to possess inhibitory
activity against Mycobacterium tuberculosis with a minimal inhibi-
2.1. Materials and equipment
Nimesulide (>99%) and analytical grade silver(I) nitrate (AgNO3)
were purchased from Sigma–Aldrich laboratories. Potassium
hydroxide (>85%) was purchased from Fluka. Elemental analyses
for carbon, hydrogen and nitrogen were performed using a Perkin
Elmer 2400 CHNS/O Analyzer. Infrared (IR) spectra were measured
in KBr pellets using a Bomem MB-Series Model B100 FT-IR spectro-
photometer in the range 4000–400 cm–1 with resolution of 4 cm–1
.
Solution-state 1H, 13C and the [1H–15N] correlation nuclear magnetic
resonance spectra were recorded on a BrukerAvance III 400 MHz
(9.395T). The 1H NMR spectra were obtained at 400.1 MHz while
the 13C–{1H} spectra were obtained at 125.7 MHz. Samples were
analyzed in deuterated dimethylsulfoxide-d6 solutions and
the chemical shifts were given relative to tetramethylsilane (TMS).
The UV–Vis spectra were recorded in 1.67 ꢁ 10–6 molLꢀ1 water
solutions using 10.00 mm quartz cuvettes in a Hewlett–Packard
8453A diode array spectrophotometer. Electrospray ionization
quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS) mea-
surements were carried out in a Waters Synapt HDMS instrument
(Manchester, UK). The complex was dissolved in methanol and the
resulting solution was directly infused into the instrument’s ESI
source at a flow rate of 15 l
Lminꢀ1. Typical acquisition conditions
tory concentration (MIC) value of 11.6 l
molLꢀ1, and also against
were capillary voltage 3 kV, sampling cone voltage 20 V, source tem-
perature 100 °C, desolvation temperature 200 °C, cone gas flow
30 Lhꢀ1, desolvation gas flow 900 Lhꢀ1, Trap and Transfer collision
energies at 6 and 4 eV, respectively. The ESI(+) mass spectra (full
scans) and fragment ion spectra for quadrupole-isolated ions
(QTOF-MS/MS) were acquired in reflectron V-mode at a scan rate
of 1 Hz. For fragment ion experiments, the desired ion was isolated
in the mass-resolving quadrupole, and the collision energy of the
Trap cell was increased until the sufficient fragmentation was ob-
served. Prior to the analyses, the instrument was calibrated with
phosphoric acid oligomers (H3PO4 0.05% in H2O/MeCN 50:50).
E. coli, P. aeruginosa and Enterococcus faecalis [20].
The sulphonamides represent an attractive class of ligands with
antibiotic properties. Such compounds are characterized by the
presence of a sulphonamide group (O2SNH). Nimesulide and sulfa-
diazine are two well known examples of sulphonamides.
Specifically, nimesulide (C13H12N2O5S, Fig. 1, NMS) is a non-
steroidal anti-inflammatory drug (NSAID), used in the treatment
of acute or chronic inflammatory processes of the respiratory tract
and the oral cavity, tendinitis and rheumatoid arthritis [21]. The
activity of NMS is associated with its antioxidant capability, since
NMS can block the formation of the radical anion superoxide
Å ꢀ
(O2 ) and other reactive oxygen species (ROS), which are related
2.2. Synthesis of the complex
to the inflammatory process and pain. In addition, NMS selectively
inhibits action of cyclooxygenase-2 (COX-2) and the inflammatory
process. Due to the presence of the sulphonamide group, nimesu-
lide can be considered a suitable ligand to coordinate both hard
and soft acids. The present work describes the synthesis, spectro-
scopic characterization and antibacterial assays of a novel silver(I)
complex with nimesulide.
The silver(I) complex with nimesulide (Ag–NMS) was synthe-
sized by the reaction of 10.0 mL of an aqueous solution containing
8.0 ꢁ 10ꢀ4 mol (0.2466 g) NMS and 8.8 ꢁ 10ꢀ4 mol (0.0494 g) KOH
with 2.0 mL of an aqueous solution containing 8.8 ꢁ 10ꢀ4 mol
(0195 g) AgNO3. The synthesis was carried out with stirring and
at room temperature. After 1 h of constant stirring, the yellowish
solid obtained was vacuum filtered, washed with cold water, and
dried in a desiccator over P4O10. Anal. Calc. for AgC13H11N2O5S: C,
37.6; H, 2.7; N, 6.7. Found: C, 37.8; H, 2.4; N, 6.7%. The yield of
the synthesis was 89%. The Ag–NMS complex is slightly soluble
in water, and it is soluble in methanol, ethanol, acetonitrile and
dimethylsulfoxide. No single crystals were obtained to provide an
X-ray crystallographic study.
2.3. Molecular modeling
Geometric optimizations were carried out using GAMESS software
[22] with a convergence criterion of 10–4 a.u. in a conjugate gradi-
ent algorithm. The LANL2DZ [23] effective core potential was used
for silver and the atomic 6-31G (d, p) basis set [24–27] for all other
atoms. Density functional theory (DFT) calculations were per-
formed by using the B3LYP [28,29] gradient-corrected hybrid to
solve the Kohn–Sham equations with a 10–5 a.u. convergence crite-
rion for the density change. The final geometries were confirmed as
minima of the potential energy surface (PES) with calculation of
the hessian.
Fig. 1. Schematic structure of NMS with carbon atom numbering.

114
R.E.F. de Paiva et al. / Polyhedron 36 (2012) 112–119
The harmonic vibrational frequencies and intensities were cal-
culated at the same level of theory with the analytical evaluation
of second derivatives of energy as a function of atomic coordinates,
and the calculated intensities were used to generate the theoretical
spectra. Frequencies were scaled by a factor of 0.9614, as recom-
mended by Scott and Radom [30]. Simulated vibrational spectra
were obtained from the sum of Lorentzian functions with
20 cmꢀ1 half-bandwidths using the software MOLDEN 4.7 [31].
TD-DFT was employed to calculate theoretical UV–Vis spectra
and, in these calculations, the Polarizable Continuum Model
(PCM) [32] was used to simulate the effect of water in the elec-
tronic transitions.
2.4. Biological assays
Three referenced bacteria (E. coli – ATCC 25922, P. aeruginosa –
ATCC 27853, and S. aureus – ATCC 25923) were used in this study.
The antibiogram assay was performed by the disc diffusion method
[33,34]. The Ag–NMS complex was tested in Mueller–Hinton (MH)
agar plates. The microorganisms (E. coli, P. aeruginosa and S. aureus)
were transferred to separate test tubes containing 5.0 mL of sterile
brain heart infusion (BHI) medium and incubated for 18 h at 35–
37 °C. Sufficient inocula were added in new tubes until the turbid-
ity equaled 0.5 McFarland (ꢂ1.5 ꢁ 108 CFU mLꢀ1). The bacterial
inocula diluted with BHI (McFarland standard) were uniformly
spread using sterile cotton swabs on sterile Petri dishes of MH agar.
Sterile filter paper discs of 10 mm in diameter were aseptically
impregnated with 800
procedure: 20 mg of Ag–NMS complex were diluted in 1.0 mL of
absolute ethanol and homogenized. Then, 40 L of the solution
were taken with a micropipette and transferred to the paper discs.
Sterile discs impregnated with 800 g of pure NMS, used as a neg-
ative control, were prepared as follows: 20 mg of NMS were dis-
solved in 1.0 mL of water and 40 L of the homogenized solution
lg of Ag–NMS according to the following
l
Fig. 2. Heteronuclear [1H–15N] multiple bond coherence spectra of (a) NMS and (b)
Ag–NMS.
l
l
group appears at 369.7 ppm in the NMS spectrum, while for the
complex, it appears at 371.0 ppm. The minor chemical shift of
1.3 ppm, when compared to the 15N shift of the nitrogen of the sul-
phonamide group, suggests that NMS is not coordinated to Ag(I)
through the NO2 group.
were transferred to the paper discs. Three positive controls were
used: ceftriaxone, gentamicine and AgNO3.
Discs impregnated with Ag–NMS, pure NMS and the positive
controls were dried and sterilized in a vertical laminar flow under
UV radiation for 45 min before the experiment. All impregnated
discs were placed on the surface of the solid agar. The plates were
incubated for 18 h at 35–37 °C and examined thereafter. Clear
zones of inhibition formed around the discs were measured and
the complex sensitivity was assayed from the diameter of the clear
inhibition zones (in millimeters). All experiments were performed
in duplicate.
Solution state 1H NMR spectroscopy was applied to obtain fur-
ther details about the coordination sites of NMS to Ag(I). The ob-
tained spectra for NMS and Ag–NMS are presented in Fig. 3,
while the corresponding assignments and chemical shifts are pre-
sented in the Table 1.
First, the hydrogen which appears as a singlet at 10.2 ppm in
the NMS 1H NMR spectrum is no longer observed in the spectrum
of the Ag–NMS complex. This signal is attributed to the hydrogen
atom bonded to the nitrogen of the sulphonamide group of NMS.
This data leads us to consider the loss of the hydrogen atom of
the (O2SNH) group of NMS and nitrogen coordination to the metal
center. This evidence, in addition to the expressive 15N chemical
shift of the (N–H) group when the ligand and the complex data
are compared, confirms nitrogen coordination of the sulphonamide
3. Results and discussion
3.1. Nuclear magnetic resonance spectroscopy
Solution state 1H, 13C and [1H–15N] heteronuclear multiple bond
coherence (HMBC) NMR spectra were obtained in order to identify
the coordination sites of NMS to Ag(I). The spectra of the Ag–NMS
complex were analyzed by comparison to the NMR spectra of free
NMS. The structure of NMS with carbon assignments is shown in
Fig. 1.
Nitrogen coordination of the sulphonamide group of NMS to
Ag(I) was primarily evaluated by [1H–15N] multiple bond coher-
ence NMR spectroscopy [35,36]. The 15N spectra are provided in
Fig. 2. In the NMS spectrum, the 15N chemical shift of the nitrogen
atom of the sulphonamide group is observed at 115.1 ppm, while
in the Ag–NMS spectrum, this signal is observed at 144.3 ppm.
group to Ag(I). Observing the
Dd values presented in the Table 2, it
is also possible to note that all hydrogens are shifted upfield upon
coordination. The most pronounced shift (ꢀ0.42 ppm) occurs for
the hydrogen atoms of the methyl group, which is bonded to the
sulfur atom of the sulphonamide group.
Solution state 13C NMR spectroscopy was employed to evaluate
the electronic density changes in the NMS molecule upon coordi-
nation. Table 2 summarizes the carbon chemical shifts for NMS
and the Ag–NMS complex.
The Table 2 shows that changes in the electronic density of the
carbon atoms do not strictly follow the same standard as the
changes of the hydrogen atoms upon coordination. It is also evi-
The observed
D
d (d complex ꢀ d ligand) of 29.2 ppm indicates
coordination of NMS to Ag(I) through the nitrogen atom of the sul-
phonamide group. On the other hand, the nitrogen atom of the NO2
dent that the methyl carbon presents a pronounced upfield
Dd

R.E.F. de Paiva et al. / Polyhedron 36 (2012) 112–119
115
Fig. 3. 1H NMR spectra of (a) NMS and (b) Ag–NMS.
Fig. 4. Infrared vibrational spectra of (a) NMS and (b) Ag–NMS.
Table 1
The 1H NMR assignments, chemical shifts and multiplicity for NMS and Ag–NMS –
D
d
represents the difference between the chemical shifts of the complex and the free
ligand.
and wagging deformation modes in the ranges 568–520 and 529–
487 cmꢀ1, respectively. Lastly, the
(C–S) vibration band is ex-
pected in the range 773–754 cmꢀ1
m
Assignment
NMS d (ppm)
Ag–NMS d (ppm)
D
d (ppm)
Multiplicity
.
CH3
20,60
40
3.20
2.78
ꢀ0.42
ꢀ0.23
ꢀ0.18
ꢀ0.20
ꢀ0.12
ꢀ0.15
ꢀ0.11
–
s
d
t
The IR spectra of NMS and the Ag–NMS complex are shown in
Fig. 4. The IR spectrum of NMS exhibits all the characteristic sulph-
onamide bands. The (N–H) stretching appears as a sharp and in-
tense signal at 3284 cmꢀ1. The four signals of the sulphonyl
7.16–7.18
7.25–7.29
7.47–7.51
7.53–7.54
7.73–7.75
8.01–8.04
10.2
6.93–6.95
7.07–7.11
7.27–7.31
7.41–7.42
7.58–7.60
7.90–7.93
–
30,50
3
t
d
d
dd
s
group also appear: the m , ms(O@S@O) at
as(O@S@O) at 1342 cmꢀ1
6
5
NH
1153 cmꢀ1, the scissoring deformation at 553 cmꢀ1 and the wagging
deformation at 516 cmꢀ1. The (C–S) stretching at 754 cmꢀ1and the
s = singlet, d = doublet, dd = double doublet and t = triplet.
two characteristic bands of the nitro (NO2) group
mas(NO2) at
1522 cmꢀ1 and s(NO2) at 1317 cmꢀ1 are also observed.
m
The Ag–NMS IR spectrum supplies remarkable evidence about
coordination of NMS to Ag(I). The first, and most pronounced evi-
Table 2
13C NMR assignments and chemical shifts for NMS and the Ag–NMS complex.
dence, is the disappearance of the
m(N–H) band, due to the loss of
the hydrogen atom of the sulphonamide group upon coordination.
Assignment
NMS d (ppm)
Ag–NMS d (ppm)
Dd (ppm)
Furthermore, the mas(O@S@O) and ms(O@S@O) vibration bands are
shifted by 48 cmꢀ1 to lower energy values. This suggests the partic-
ipation of the sulphonyl group in the coordination of the NMS to
CH3
3
6
40.89
112.4
119.3
119.5
121.1
124.9
130.3
135.6
143.1
147.5
155.0
38.52
113.4
117.9
118.4
120.4
123.7
129.9
137.2
145.6
140.0
156.2
ꢀ2.37
1.0
ꢀ1.4
ꢀ1.1
ꢀ0.7
ꢀ1.2
ꢀ0.4
1.6
2.5
0.5
1.2
Ag(I). It is interesting to note that the shift of the
mas(O@S@O)
5
20,60
40
and s(O@S@O) bands to lower energies in the IR spectrum of
m
Ag–NMS is related to the weakening of the S@O bond. Nakamoto
[39] has shown that this effect is observed when the coordination
occurs through the oxygen atom of the sulphonyl group. Based on
the observed data, coordination of NMS to Ag(I) seems to occur in a
bidentate form through the nitrogen atom and one of the oxygen
atoms of the sulphonamide group.
30,50
1
10
2
4
upon coordination, just like the hydrogen atoms of this group. This
evidence leads us to consider that the sulphonyl group (O@S@O) is
also participating in the ligand coordination to Ag(I) since the
methyl group exhibits remarkable chemical shifts on 1H and 13C
NMR spectra when the ligand and the complex are compared.
3.3. Electronic absorption spectroscopy
The UV–Vis electronic absorption spectra of NMS and the Ag–
NMS complex are shown in Fig. 5. The NMS spectrum is dominated
by p–
p⁄ transitions and exhibits an absorption band in the visible
region at 389 nm. This transition is centered in the nitro-aryl ring
and it is low-lying due to the electron-withdrawing properties of
the NO2 substituent. There are at least three less intense absorp-
tion bands in the UV region at 195, 225, and 270 nm. Coordination
to Ag(I) does not change the spectrum profile but the bands be-
come stronger, especially the one in the visible at 389–391 nm,
which is responsible for the Ag–NMS complex intense yellow col-
our, is enhanced by a factor of 22. Molar extinction coefficient var-
ies from 570 molꢀ1 cmꢀ1 in NMS to 12655 molꢀ1 cmꢀ1 in Ag–NMS.
3.2. Infrared vibrational spectroscopy
The infrared (IR) vibrational spectra of different sulphonamides
have been studied and reported in the literature [37,38]. For
S-methyl sulphonamides, the
in the range 3320–3250 cmꢀ1. Moreover, four characteristic bands
of the sulphonyl group are observed: the as(O@S@O) around
1350 cmꢀ1, the s(O@S@O) around 1160 cmꢀ1, and the scissoring
m(N–H) vibration band is observed
m
m

116
R.E.F. de Paiva et al. / Polyhedron 36 (2012) 112–119
Fig. 5. Experimental (solid) and theoretical (vertical dash lines) UV–Vis electronic absorption transitions of (a) Ag–NMS and (b) NMS. Top and right axis correspond to the
parameters of the theoretical spectra.
Fig. 6. Fragment mass spectrum for the Ag–NMS monoprotonated ion, [AgNMS+H]+, of m/z 414.95.
This is strong evidence that one of the coordination sites is the
nitrogen atom of the sulphonamide group, which is bonded to
the nitro-aryl ring.
3.4. Mass spectrometric measurements
The ESI-QTOF-MS analyses of Ag–NMS demonstrate the presence
of the proposed monomeric form of the complex in solution (Supple-
mentary data #1) as single charged monoprotonated ions
([AgNMS+H]+, m/z 414.95), as well as minor sodium and potassium
adducts, [AgNMS+Na]+ and [AgNMS+K]+ at m/z 436.93 and 444.24,
respectively. There were also observed, even in low abundance,
the dimeric complex ([Ag2NMS2+H]+, m/z 828.91), as well as the
respective sodium and potassium adducts. Trimeric ions were only
observed as sodium and potassium adducts ([Ag3NMS3+Na]+ and
[Ag3NMS3+K]+) at m/z 1264.82 and 1280.80, respectively. The free
NMS ligand was also observed, mainly as sodium and potassium
adducts of m/z 331.04 and 347.01, respectively. The presence of
Fig. 7. Optimized structure for the Ag–NMS complex.

R.E.F. de Paiva et al. / Polyhedron 36 (2012) 112–119
117
Fig. 8. Kohn–Sham orbitals for (a) NMS and (b) Ag–NMS complex. Silver (gray), carbon (dark gray), nitrogen (blue), oxygen (red) and hydrogen (white).
Table 3
Antibiotic sensitive profile of bacterial strains against NMS, Ag–NMS, AgNO3, gentamicine and ceftriaxone.
Compounds
Results
P. aeruginosa
S. aureus
E. coli
Inhibition zone diameter (mm)
Inhibition zone diameter (mm)
Inhibition zone diameter (mm)
NMS
0.0
0.0
0.0
AgNO3
20.0 ( 0.1)
12.0 ( 0.1)
34.0 ( 0.1)
24.0 ( 0.1)
25.0 ( 0.1)
18.0 ( 0.1)
>42.0 ( 0.1)
24.0 ( 0.1)
12.0 ( 0.1)
18.0 ( 0.1)
30.0 ( 0.1)
20.0 ( 0.1)
Ag–NMS
Ceftriaxone
Gentamicine
sodium and potassium ions is most probably due to the use of potas-
sium hydroxide during the synthesis of the complex. An isotope pat-
tern comparison for the monoprotonated [AgNMS+H]+ ion (see
Supplementary data #1) shows a good agreement with the theoret-
ical predictions. The mass error was ꢀ0.5 ppm for the monoproto-
nated ion C13H11N2O5SAg+ (Calc. m/z 414.9518, exp. m/z 414.9516).
To further confirm the proposed composition of the [AgNMS+H]+
species, fragment ion spectrawere acquiredfor the monoprotonated
ion(Fig. 6). Thefragmentionspectrumof[AgNMS+H]+showstheloss
ofCH3SO2 (79 Da), whichcorresponds to themethyl-sulphone group
of theNMS ligand, followedby the loss of Ag (107 Da), as well a direct
loss of the NMS ligand (308 Da) from the precursor. The obtained
data confirmed the previously proposed composition.
3.5. Molecular modeling
Geometries of NMS and Ag–NMS were analyzed by theoretical
calculations using density functional theory (DFT) studies. The
equilibrium geometries were confirmed by the vibrational analy-
sis, showing no imaginary frequencies. The calculated geometry
for NMS is in a good agreement with the previously reported crys-
tallographic data [40].
According to the IR and NMR spectroscopic data, NMS is coordi-
nated to the silver atom through the nitrogen of the sulphonamide
group, and the oxygen of sulphonyl group could also be participat-
ing in ligand coordination. So, in order to confirm if coordination of
NMS to Ag(I) occurs in a monodentate form through the N atom or

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R.E.F. de Paiva et al. / Polyhedron 36 (2012) 112–119
in a bidentate form through the N and O atoms of the (O2SNH)
group, calculations were performed for the mono and bidentate
coordinations. Attempts to obtain coordination of NMS to the me-
tal solely through nitrogen atom were unsuccessful since the struc-
ture converged to coordination through the nitrogen atom of
sulphonamide and also through the oxygen of the sulphonyl group.
Calculations confirmed that the bidentate structure is a minimum
in the potential energy surface (PES), with the silver atom coordi-
nating through both the nitrogen and the oxygen atoms of sulph-
onamide group. The optimized structure for the Ag–NMS
complex is presented in the Fig. 7. The calculated Ag–N1 and Ag–
O1 bond distances are 1.952 and 2.572 Å. The calculated angles
N1–Ag–O1 and Ag–N1–S are 66.2° and 83.2°. The detailed bond
distances and angles are reported in Supplementary data #2.
The simulated IR spectra of NMS and Ag–NMS are in good
agreement with the experimental spectra, confirming all the
assignments. The simulated N–H stretching in the NMS spectrum
appears at 3421 cmꢀ1 and the experimental data shows it at
3284 cmꢀ1. Experimental absorptions in the IR spectrum of NMS
at 1342 and 1153 cmꢀ1 were confirmed by the simulated spectra
as the (O@S@O) asymmetrical and symmetrical stretching modes,
respectively. In this case, the calculated frequencies were1378 and
1134 cmꢀ1, respectively. The experimental spectrum of Ag–NMS
shows a shift to low energies of both O@S@O stretching modes
of 48 cmꢀ1 after coordination of the ligand to Ag(I). The simulated
spectra show that the asymmetrical stretching mode is expected to
be shifted to lower energies by 86 cmꢀ1, which corroborates to the
proposition of the participation of one of the oxygen atoms of the
sulphonyl group in the coordination of NMS to Ag(I).
binding capacity to tissue proteins and capacity to lead to struc-
tural changes in the bacterial cell wall. Silver also binds to bacterial
DNA and RNA, leading to inhibition of bacterial replication [41,42].
The results obtained show the potential application of the Ag–NMS
complex, for example, in topic formulations for the treatment of
wounds and burns.
4. Conclusions
The molar composition of the Ag–NMS complex was found to be
1:1 M/L. Infrared, ESI-QTOF-MS, UV–Vis and 1H, 13C and 15N NMR
spectroscopic data permitted proposing coordination of the ligand
to Ag(I) through the nitrogen and oxygen atoms of sulphonamide
group. Biological assays showed antibacterial activity of the com-
plex against Gram-positive and -negative bacterial strains.
Acknowledgments
This study was supported by grants from the Brazilian Agencies
FAPESP (São Paulo State Research Foundation, proc. 2006/55367-2
and2008/57805-2), and CNPq (Conselho Nacional de Desenvolvimento
Científico e Tecnológico, proc. 472468/2010-3 and 573672/2008-3).
Professor Corbi is also grateful to Professor Carol H. Collins for
English revision of the manuscript.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2012.02.002.
The Time Dependent (TD-DFT) calculations permitted us to ex-
plain the nature of the transitions observed in the UV–Vis spectra.
The predicted absorptions were showed with the experimental
electronic absorption spectra for both NMS and Ag–NMS in
References
[1] I. Tsyba, B.B.-K. Mui, R. Naguchi, K. Nomiya, Inorg. Chem. 42 (2003) 8028.
[2] K. Nomiya, S. Takahashi, R. Noguchi, J. Chem. Soc., Dalton Trans. (2000) 2091.
[3] H.J. Klasen, Burns 26 (2000) 117.
[4] R.H. Demling, L. DeSanti, Wounds 13 (Suppl A) (2001) 4.
[5] I. Chopra, J. Antimicrob. Chemother. 59 (2007) 587.
[6] R.H. Demling, M.D.L. DeSanti, Burns 28 (2002) 264.
[7] C.A. Moyer, L. Brentano, D.L. Gravens, H.W. Margraf, W.W. Monafo, Arch. Surg.
90 (1965) 812.
[8] C.G. Bellinger, H. Conway, Plast. Reconstr. Surg. 45 (1970) 582.
[9] S. Silver, L.T. Phung, G. Silver, J. Ind. Microbiol. Biotechnol. 33 (2006) 627.
[10] R.G. Sibbald, H. Orsted, G.S. Schultz, P. Coutts, D. Keast, Ost. Wound Man. 49
(2003) 23.
[11] S.A. Jones, P.G. Bowler, M. Walker, D. Parsons, Wound Repair Regen. 12 (2004)
288.
Fig. 5. All the observed bands are
p–
p⁄ transitions and the
HOMO–LUMO is the low-lying one. As observed in Fig. 8, these
Kohn–Sham orbitals are centered in the aryl groups and the LUMO
has a significant influence from the NO2 group, explaining why this
transition is low-lying. Essentially, all other transitions are of the
same kind since all of them have origin in
p orbitals. As seen in
Fig. 8, the frontier Kohn–Sham orbitals for the complex are very
similar to the NMS ones.
Apart from small shifts in the energies, calculations confirm
that coordination does not change the nature of the transitions.
Since the calculated oscillator strength is higher for Ag–NMS when
[12] Md.S.A.S. Shah, M. Nag, T. Kalagara, S. Singh, S.V. Manorama, Chem. Mater. 20
(2008) 2455.
compared to NMS, the p–
p⁄ transitions bands are more intense in
[13] K. Nomiya, H. Yokoyama, J. Chem. Soc., Dalton Trans. (2002) 2483.
[14] A. Kascatan-Nebioglu, A. Melaiye, K. Hindi, S. Durmus, M.J. Panzner, L.A. Hogue,
R.J. Mallett, C.E. Hovis, M. Coughenour, S.D. Crosby, A. Milsted, D.L. Ely, C.A.
Tessier, C.L. Cannon, W.J. Youngs, J. Med. Chem. 49 (2006) 6811.
[15] D.P. Rocha, G.F. Pinto, R. Ruggiero, C.A. de Oliveira, W. Guerra, A.P.S. Fontes, T.T.
Tavares, I.M. Marzano, E.C. Pereira-Maia, Quim. Nova 34 (2011) 111.
[16] A.S. Kazachenko, A.V. Legler, O.V. Per’yanova, Y.A. Vstavskaya, Pharm. Chem. J.
34 (2000) 257.
the complex (data available in Supplementary data #3).
3.6. Biological assays
The Ag–NMS complex was evaluated concerning its antibacte-
rial activities. Table 3 summarizes the results obtained for NMS
and the Ag–NMS complex against Gram-negative (E. coli and P.
aeruginosa) and Gram-positive (S. aureus) microorganisms. Silver
nitrate and the comercial antibiotics ceftriaxone and gentamicine
were used as positive controls.
It was observed that impregnated paper discs with Ag–NMS
exhibited inhibition zones for P. aeruginosa, S. aureus and E. coli,
of 12.0 0.1, 18.0 0.1 and 18.0 0.1 mm, respectively. These re-
sults confirm the sensitivity of the tested bacterial cells to the
Ag–NMS complex. The observed data for the complex are similar
to silver nitrate and gentamicine for the same tested strains, and
also to the Ag(I)–acesulfame complex early reported [20].
Nimesulide alone did not show inhibitory activity against the con-
sidered bacterial strains under the same experimental conditions.
As reported earlier, silver ions are considered responsible for the
antibiotic activity of silver complexes due to their high reactivity,
[17] B. Ruan, Y. Tian, H. Zhou, J. Wu, Z. Liu, C. Zhu, J. Yang, H. Zhu, J. Organomet.
Chem. 694 (2009) 2883.
[18] A.A. Isab, M.I.M. Wazeer, Spectrochim. Acta A 65 (2006) 191.
[19] M. Poyraz, C.N. Banti, N. Kourkoumelis, V. Dokorou, M.J. Manos, M. Simcic, S.
Golic-Grdadolnik, T. Mavromoustakos, A.D. Giannoulis, I.I. Verginadis, K.
Charalabopoulos, S.K. Hadjikakou, Inorg. Chim. Acta 375 (2011) 114.
[20] M. Cavicchioli, A.C. Massabni, T.A. Heinrich, C.M. Costa-Neto, E.P. Abrão, B.A.L.
Fonseca, E.E. Catellano, P.P. Corbi, W.R. Lustri, C.Q.F. Leite, J. Inorg. Biochem.
104 (2010) 533.
[21] B.J.R. Whittle, Fundam. Clin. Pharmacol. 17 (2003) 275.
[22] M.W. Schmidt, K.K. Baldridge, J.A. Boatz, S.T. Elbert, M.S. Gordon, J.H. Jensen,
S.K.N. Matsunaga, K. Nguyen, S. Su, T.L. Windus, M. Dupuis, J.A. Montgomery
Jr., J. Comput. Chem. 14 (1993) 1347.
[23] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299.
[24] R. Ditchfie, W.J. Hehre, J.A. Pople, J. Chem. Phys. 54 (1971) 724.
[25] W.J. Hehre, R. Ditchfie, J.A. Pople, J. Chem. Phys. 56 (1972) 2257.
[26] M.M. Francl, W.J. Pietro, W.J. Hehre, J.S. Binkley, M.S. Gordon, D.J. DeFrees, J.A.
Pople, J. Chem. Phys. 77 (1982) 3654.
[27] P.C. Harihara, J.A. Pople, Theor. Chim. Acta 28 (1973) 213.
[28] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.

R.E.F. de Paiva et al. / Polyhedron 36 (2012) 112–119
119
[29] C.T. Lee, W.T. Yang, R.G. Parr, Phys. Rev. B37 (1988) 785.
[30] A.P. Scott, L. Radom, J. Phys. Chem. 100 (1996) 16502.
[31] G. Schaftenaar, J.H. Noordik, J. Comput.-Aided Mol. Des. 14 (2000) 123.
[32] S. Miertus, E. Scrocco, J. Tomasi, Chem. Phys. 55 (1981) 117.
[33] A.W. Bauer, W.M. Kirby, J.C. Sheris, M. Turck, Am. J. Clin. Pathol. 45 (1996) 493.
[34] Clinical and Laboratory Standards Institute, Performance standards for
antimicrobial susceptibility testing, seventeenth informational supplement,
Wayne, PA, USA, 2007.
[36] C. Abbehausen, J.F. Castro, M.B.M. Spera, T.A. Heinrich, C.M. Costa-Neto, W.R.
Lustri, A.L.B. Formiga, P.P. Corbi, Polyhedron 30 (2011) 2354.
[37] J.N. Baxter, J. Cymerman-Craig, J.B. Willis, J. Chem. Soc. (1955) 669.
[38] M. Goldstein, M.A. Russell, H.A. Willis, Spectrochim. Acta A 25 (1969) 1275.
[39] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds – Part B, 5th ed., John Wiley & Sons, New York, USA, 1997. pp. 59–
104.
[40] L. Dupont, B. Pirotte, B. Masereel, J. Delarge, J. Geczy, Acta Crystallogr., Sect. 51
(1995) 507.
[41] M. Rai, A. Yadav, A. Gade, Biotechnol. Adv. 27 (2009) 76.
[42] J.J. Castellano, S.M. Shafii, F. Ko, G. Donate, T.E. Wright, R.J. Mannari, Int.
Wound J. 4 (2007) 114.
[35] (a) N. Juranic, S. Macura, Inorg. Chim. Acta 217 (1994) 213;
(b) P.P. Corbi, A.C. Massabni, T.A. Heinrich, C.M. Costa-Neto, J. Coord. Chem. 61
(2008) 2470;
(c) P.P. Corbi, A.C. Massabni, Spectrochim. Acta A 64 (2006) 418.