Ca(II), Sr(II) and Ba(II) ion interaction with the rheumatoid arthritis drug tenoxicam: Structural, thermal, and biological characterization

Article abstract of DOI:10.1002/aoc.4055

Recently, one of the most common conditions that manifests as joint and muscle inflammation is rheumatoid arthritis. One of the treatments for this arthritis includes non-steroidal anti-inflammatory drugs (NSAIDs) of the oxicam family, and the widest used drug in this family is tenoxicam (Tenox). In this study, the complexation properties of the drug Tenox with Ca(II), Sr(II) and Ba(II) ions in a (dichloromethane + water) binary solvent system are reported. The formed metal complexes were characterized structurally, thermally, and biologically. Tenox was found to act as a chelate monoanionic ligand towards all metal ions with complexation stoichiometry of 1:2 (Metal: Tenox) for Ca(II) and Sr(II) ions, and 1:1 for Ba(II) ions. The Tenox ligand behaves as a bidentate ligand when coordinated with Sr(II) or Ba(II) ions and as a tridentate ligand when coordinated with Ca(II) ions. The Sr(II) and Ba(II) complex of the Tenox ligand exhibited marked inhibitory effect on the cell growth of the C. albicans species.

Full text of DOI:10.1002/aoc.4055

Received: 5 July 2017
DOI: 10.1002/aoc.4055
Revised: 28 July 2017
Accepted: 30 July 2017
F U L L P A P E R
Ca(II), Sr(II) and Ba(II) ion interaction with the rheumatoid
arthritis drug tenoxicam: Structural, thermal, and biological
characterization
Abdel Majid A. Adam
Department of Chemistry, Faculty of
Recently, one of the most common conditions that manifests as joint and
muscle inflammation is rheumatoid arthritis. One of the treatments for this
arthritis includes non‐steroidal anti‐inflammatory drugs (NSAIDs) of the
oxicam family, and the widest used drug in this family is tenoxicam (Tenox).
In this study, the complexation properties of the drug Tenox with Ca(II), Sr(II)
and Ba(II) ions in a (dichloromethane + water) binary solvent system are
reported. The formed metal complexes were characterized structurally,
thermally, and biologically. Tenox was found to act as a chelate monoanionic
ligand towards all metal ions with complexation stoichiometry of 1:2 (Metal:
Tenox) for Ca(II) and Sr(II) ions, and 1:1 for Ba(II) ions. The Tenox ligand
behaves as a bidentate ligand when coordinated with Sr(II) or Ba(II) ions and
as a tridentate ligand when coordinated with Ca(II) ions. The Sr(II) and Ba(II)
complex of the Tenox ligand exhibited marked inhibitory effect on the cell
growth of the C. albicans species.
Science, Taif University, Taif, Al‐Haweiah,
P.O. Box 888, Zip Code 21974, Saudi
Arabia
Correspondence
Abdel Majid A. Adam, Department of
Chemistry, Faculty of Science, Taif
University, Taif, Al‐Haweiah, P.O. Box
888, Zip Code 21974, Saudi Arabia.
Email: majidadam@yahoo.com
KEYWORDS
antimicrobial test, metal complex, tenoxicam, thermal properties
1 | INTRODUCTION
strengthens the clinical activity of the drug, and its neutral
molecule exists in the keto–enol form (Figure 1). The
Painful disorders of the muscles and joints may be due
to rheumatoid arthritis. Currently, non‐steroidal anti‐
inflammatory drugs (NSAIDs) are used astherapeutic
treatment for this disease.[1] Oxicams are among the most
important members of the NSAID family.[2] The most stud-
ied species of the family is tenoxicam (Tenox), IUPA name:
4‐hydroxy‐2‐methyl‐N‐2‐pyridinyl‐2H‐thieno(2,3‐e)‐1,2‐
complexation data on oxicams with metals are important
in pharmaceutical and medical applications.
The complexation of oxicams with several metal
ions improved their anti‐inflammatory effects.[7–10] Metal
complexes of Tenox with several transitional metal ions,
some post‐transitional metal ions, and one of the actinide
metal ions have been investigated and reported in the
literature. Examples of these metal ions are Cr(III),[11,12]
Mn(II),[12,13] Fe(II),[13] Fe(III),[11–16] Co(II),[12–15,17]
thiazine‐3‐carboxamide 1,1‐dioxide.Tenox is
a well‐
established non‐steroidal anti‐inflammatory drug, widely
used as treatment for various musculoskeletal and joint
disorders, rheumatoid arthritis, knee osteoarthritis, acute
gout, and symptomatic relief of pain, inflammation and
post‐surgical pain. It is characterized by its good efficacy
and reduced side effects in comparison to other
NSAIDs.[3–6] It has a five‐membered heteroatom ring that
Ni(II),[12–15]
Cu(II),[12–15,18,19]
Zn(II),[12,13,15,17]
Cd(II),[11,17] Al(III),[11] Sb(III),[11] Bi(III),[11] and UO2
(II).[15] To the best of our knowledge, metal complexes
of Tenox with alkali or alkaline earth metal ions have
not been reported in the literature up to now. Hence,
the present study provides new insights and throws more
Appl Organometal Chem. 2017;e4055.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4055

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O
O
O
O
The obtained pale yellow solid complexes were filtered
and washed several times with deionized water and
DCM to remove any traces of the unreacted starting
materials and to obtain a pure product. The products
were then collected and dried under vacuum over anhy-
drous CaCl2 for 48 h.
S
CH3
S
CH3
N
N
H
N
H
N
S
S
O
O
N
OH
O
N
FIGURE 1 The keto‐enol from of tenoxicam (Tenox)
light on the chelation behavior of Tenox towards some
alkaline earth metal ions, which may help in understand-
ing the chelating tendency of Tenox towards metals.
This work includes two parts of investigation:
2.3 | Physical and spectroscopic
measurements
(i) Chemistry:
The micro−analytical analyses of %C, %H and %N were
calculated using a Perkin Elmer CHN 2400. The metal
contents were determined gravimetrically. The IR spectra
with KBr discs were measured on a Bruker FT−IR
Spectrophotometer (4000–400 cm−1). The electronic
absorption spectra were recorded in a DMSO solvent
within 200−800 nm using a UV2−Unicam UV/Vis
Spectrophotometer with a 1.0 cm quartz cell.
This part aimed to synthesize the Tenox metal com-
plexes with Ca(II), Sr(II), and Ba(II) ions in a (dichloro-
methane + water) binary solvent system, to characterize
the obtained complexes by elemental and spectroscopic
data, and to obtain their thermal properties using
TG analysis along with their kinetic−thermodynamic
parameters.
(ii) Biology:
2.4 | Biological evaluation
This part aimed to examine the antimicrobial activity
of the synthesized complexes against two Gram‐positive
bacteria, two Gram‐negative bacteria and two fungi.
2.4.1 | In vitro antibacterial activity
The antibacterial activity of the prepared complexes and
the pure solvent was tested in vitro using the modified
Bauer–Kirby disc diffusion method.[20] The utilized
test organisms were Staphylococcus aureus (MSSA 22)
and Bacillus subtilis (ATCC 6051) as examples of
Gram‐positive bacteria and Escherichia coli (K 12) and
Pseudomonas aeruginosa (MTCC 2488) as examples of
Gram‐negative bacteria. The experiments were con-
ducted in the microanalysis facility at Cairo University,
Egypt. Briefly, 100 μL of the test bacteria was grown
in 10 ml fresh medium and left to reach a count of
108 cells/mL on average.[21] Then, a 100 μL suspension
of microbes was spread onto agar plates. The nutrient
agar medium consisted of 1.5% agar‐agar, 0.5% NaCl,
0.2% yeast extract, 0.1% beef extract, and 0.5% pep-
tone.[22] Isolated colonies of each organism that may
play a pathogenic role were selected from the primary
agar plates and tested for susceptibility by incubation
for 48 h at 37°C. The diameter of the zone of inhibition
in mm (including the disc) were measured using slip-
ping calipers from the National Committee for Clinical
Laboratory Standards (NCCLS, 1993).[23] The screening
was performed using 100 μg/mL of the complex. An
antibiotic disc containing Tetracycline (Antibacterial
agent, 30 μg/disc, Hi‐Media) was employed as the posi-
tive control. A filter disk impregnated with 10 μL of sol-
vent (distilled water, chloroform, DMSO) was employed
as the negative control.
2 | MATERIALS AND METHODS
2.1 | Materials
Tenox (C13H11N3O4S2; 337.37 g/mol), calcium chloride
(CaCl2; 110.98 g/mol), strontium chloride hexahydrate
(SrCl2·6H2O; 266.62 g/mol), and barium chloride
dihydrate (BaCl2·2H2O; 244.26 g/mol) were procured
from the Sigma−Aldrich Chemical Company (St. Louis,
MI, USA) and used as received. Sodium hydroxide and
solvents were obtained from Merck (Darmstadt, Ger-
many) and used without special treatment. The water
used in this study was highly pure deionized water
obtained from a Milli‐Q water purification unit (Berlin,
Germany).
2.2 | Synthesis of Tenox complexes
A solution of the respective metal chloride salt (Cu(II),
Sr(II), or Ba(II)) dissolved in deionized water (1 mmol,
20 ml)) was added gradually to a stirred dichloromethane
(DCM) solution of the Tenox ligand (2 mmol, 20 ml).
The pH of the solution was adjusted to ~ 7–8 using
0.1 M sodium hydroxide. The resulting mixtures were
refluxed at 60°C and further stirred for 1 h for comple-
tion of the precipitation of the synthesized complexes.

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2.4.2 | In vitro antifungal activity
3.1.2 | Infrared spectra
The prepared complexes were also screened for their
antifungal properties using the modified Bauer–Kirby
disc diffusion method. The utilized test organisms were
Aspergillus flavus (laboratory isolate) and Candida
albicans.[20] The complexes were dissolved in DMSO.
The medium consisted of 2% agar‐agar, 0.001% FeSO4,
0.05% KCl, 0.1% K2HPO4, 0.3% NaNO3, and 3%
sucrose.[21] The disk diffusion method for filamentous
fungi followed the approved standard method (M38‐A)
developed by the NCCLS.[24] The disk diffusion method
for yeast, which was developed with the standard
method (M44‐P) by the NCCLS, was employed.[25] The
plates that were inoculated with filamentous fungi or
yeast were incubated for 48 h at 25°C or 30°C, respec-
tively. The antifungal activity of the complexes was
determined by measuring the diameters of the sterile
zone (mm) and was compared with that of
Amphotericin B (30 μg/disc, Hi‐Media), which was used
as the standard antifungal agent (positive control). A
filter disk impregnated with 10 μL of solvent (distilled
water, chloroform, DMSO) was employed as the negative
control.
(a) Tenox vibrational modes
Table 2 lists and compares the characteristic IR vibra-
tions for the free Tenox and the synthesized metal com-
plexes. Free Tenox shows the following characteristic
vibrations on the IR spectrum: (i) O–H vibrations: the
strong broad band observed at 3386 cm−1was assigned to
O–H stretching vibrations. The O–H in‐plane bending
vibration appeared as a strong band at 1202 cm−1
,
whereas the O–H out‐of‐plane deformation vibration
was observed at 632 cm−1. The broadness of the ν(O–H)
band is indicative of hydrogen bonding and in the absence
of hydration in the free ligand. This result suggested that
the most likely cause was intramolecular bonding involv-
ing the oxygen or nitrogen atoms of the secondary amide
group.[14,26] (ii) N–H vibrations: band centered at 3130 cm
−1
as a medium intensity band assigned to the ν(N–H)
vibrations. (iii) CONH vibrations: the very strong band
observed at 1636 cm−1 was assigned to the carbonyl
stretch of the secondary amide group (−CO–NH–). (iv)
C = N vibrations:mthe band located at 1598 cm−1 was
assigned to the C = N stretching mode of pyridyl nitrogen.
(v) SO2 vibrations: the bands observed at 1330 and
1041 cm−1 were assigned to νas(SO2) and νa(SO2) vibra-
tions, respectively. The bands observed at 582 and
528 cm−1 were assigned to SO2 scissoring and wagging
modes, respectively.
3 | RESULTS AND DISCUSSION
3.1 | Chemistry
3.1.1 | CHN results
(b) Complexes vibrational modes
Table 1 lists the elemental analysis data of the synthesized
Tenox complexes. The elemental analyses of the com-
plexes indicated a 1:2 metal‐to‐ligand stoichiometry for
Ca(II) and Sr(II) ions, and a 1:1 metal‐to‐ligand stoichi-
ometry for Ba(II) ions. All the complexes are obtained as
hydrates with the Tenox ligand present as a mono‐anionic
ligand. The results comply with the suggested formulas
of [Ca(Tenox)2]·6H2O, [Sr(Tenox)2(H2O)2]·6H2O and
[Ba(Tenox)Cl(H2O)3]·2H2O. The synthesized complexes
had pale yellow colored precipitates, with percentage
yields of 75, 81 and 78% for Ba(II), Sr(II), and Ca(II)
complexes, respectively, with melting points > 250°C.
The Tenox ligand reacted as the enolate anion, and as
such, no O–H vibration was expected in the complexes.
Analysis of the complexes showed them to be hydrated,
and it is therefore suggested that hydrogen‐bonded water
molecules could be responsible for the intensity and
broadness of the broad absorption centered in the
3500–3330 cm−1 region. The N–H stretch observed in the
free Tenox as a medium intensity band at 3130 cm−1was
seen in the complexes as a weak absorption centered at
the same position but partially obscured by the
board bands due to hydrogen bonding. The band of the
TABLE 1 Analysis of the synthesized Tenox complexes
Formula
Elemental analyses; % Found (% Calcd.)
weight
(g/mol)
Yield
(%)
Complexes
C
H
N
Metal
[Ca(Tenox)2]·6H2O
820.80
904.36
599.14
78
81
75
38.07 (38.01)
3.83 (3.90)
10.19 (10.23)
4.93 (4.88)
[Sr(Tenox)2(H2O)2]·6H2O
[Ba(Tenox)Cl(H2O)3]·2H2O
34.46 (34.50)
25.97 (26.04)
3.93 (3.98)
3.39 (3.34)
9.25 (9.29)
7.08 (7.01)
9.75 (9.69)
22.86 (22.92)

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TABLE 2 Characteristic IR wavenumber (cm−1) and tentative assignments for free Tenox, and the synthesized complexes
Complexes
Free
Tenox
Ca(II)
Sr(II)
Ba(II)
Assignmentsa
3386
3399
3382
3455, 3333
ν(O–H); H2O
3130
3119
3092
1636
1598
1530
1436
1388
1330
1202
1151
1041
632
3131
3121
3095
1621
1521
1479
1420
1385
1329
1226
1147
1038
641
3130
3120
3099
1636
1522
1483
1424
1391
1330
1198
1147
1039
640
3129
3117
3097
1635
1528
1477
1430
1387
1328
1238
1145
1039
634
ν(N–H)
ν(C‐H); aromatic
νs(C‐H) + νas(C‐H)
ν(CONH)
ν(C = N)
ν(C = C); aromatic ring
δ(C‐H) deformation
CH3 deformation
νas(SO2)
δ(O–H) in‐plane bending
ν(C–O)
νs(SO2)
δ(O–H) out‐of‐plane bending
582
585
584
583
δ
sciss.(SO2)
wag(SO2)
528
527
529
528
δ
aν, stretching; νs, symmetrical stretching; νas, asymmetrical stretching; δ, bending.
(−CO–NH–) group was lowered by 15 cm−1 in the Ca(II)
complex and observed at 1621 cm−1, indicating the
involvement of the C = O of the amide moiety in chelate
formation with Ca(II) ions. This band was unshifted in
the case of Sr(II) and Ba(II) complexes. The band of the
C = N stretching mode located at 1598 cm−1 in the free
Tenox and shifted to lower wavenumbers in all chelates.
It was observed at 1521 in the Ca(II) complex, at
1522 cm−1 in the Sr(II) complex, and at 1528 cm−1 in
the Ba(II) complex. These shifts confirmed the participa-
tion of pyridyl nitrogen of the Tenox ligand in coordina-
tion with metal ions. The four vibrations of the SO2
modes, νas(SO2), νa(SO2), δsciss.(SO2), and δwag(SO2), were
found at the same position as in free Tenox, suggesting
that the SO2 group of the Tenox ligand did not participate
in the complexation with metal ions.
By comparing the IR spectra of the Tenox ligand with
the spectral data of the synthesized metal complexes, it
was clear that in all cases Tenox acted as a chelate
mono‐anionic ligand. In the case of Sr(II) and Ba(II) com-
plexes, the Tenox ligand behaved as a bidentate ligand
coordinated with the Sr(II) or Ba(II) ions through the
enolate oxygen atom and pyridyl nitrogen atom. The car-
bonyl oxygen atom of the amide group did not participate
in the complexation with these two meat ions. However,
the Tenox ligand behaved as a tridentate ligand towards
Ca(II) ions bonded through the enolate oxygen atom,
the carbonyl oxygen atom of the amide group, and the
pyridyl nitrogen atom. This coordination towards Ca(II)
ions could be attributed to its smaller ionic radius
compared with Sr(II) and Ba(II). The ionic radii of
Ca(II), Sr(II), and Ba(II) were 114, 132, and 149 pm,
respectively. The synthesized complexes suggested an
octahedral stereochemistry with two Tenox chelatesin
the case of Ca(II) and Sr(II) complexes, and one Tenox
chelate in the case of the Ba(II) complex as presented in
Figure 2.
O
O
O
O
S
CH3
S
CH3
N
N
H
H
N
N
S
S
O
O
N
O
O
N
H2O
Ca
Sr
.6 H2O
.6 H2O
OH2
S
O
N
O
O
N
O
S
N
H
N
H
N
N
H3C
S
H3C
S
O
O
O
O
O
O
N
S
CH3
H
N
S
O
O
N
H2O
Ba
.2 H2O
OH2
H2O
Cl
FIGURE 2 The speculated structure of the synthesized Tenox
complexes

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representative thermograms are illustrated in Figure 4.
The possible thermal degradation patterns for these com-
plexes are shown in Table 3. The study of the thermo-
grams of the complexes provided several observations.
The observed weight losses were in agreement with the
theoretical losses. The complexes underwent several
decomposition steps resulting in a metal carbonate
(CaCO3, SrCO3, or BaCO3) as the final decomposition
product. Only the decomposition of the Sr(II) complex
showed almost complete decomposition of the ligand
molecules without any carbon residue. Complexes of
Ca(II) and Sr(II) ions were thermally decomposed in three
decomposition steps, whereas the Ba(II) complex exhib-
ited a two‐stage degradation. The degradation data
strongly supported the proposed formation of the synthe-
sized complexes and their structures.
3.1.3 | UV–Vis. Spectra
Figure 3 shows the UV–Vis. spectra of the synthesized
complexes in DMSO solvent in the region of 20−800
nm. Free Tenox ligands exhibit three maximum absorp-
tion bands at 205, 265, and 360 nm.[27] These absorption
bands existed within the ultraviolet region of 200−400
nm. Upon chelation with metal ions, there was an inter-
esting change in the electronic properties of the system.
New bands in the visible region due to the charge transfer
interaction from ligand to metal (L → M) or metal to
ligand (M → L) can be observed, which may help us
obtain more information about the geometrical structure
of the complexes.[28] In the synthesized complexes, the
π → π* electronic transition peaks were observed at 275
and 315 nm for the Ca(II) complex, 244 and 282 nm for
the Sr(II) complex, and 258 nm for the Ba(II) complex.[29]
These peaks can be assigned to the π → π* transitions in
the aromaticity of pyridine and thiophene rings. The
peaks belonging to n → π* transitions were exhibited at
wavelengths of 381, 369, and 357 nm, for Ba(II), Sr(II)
and Ca(II) complexes, respectively. These peaks are most
likely due to the n → π* transitions of –NH, −OH, and
the carbonyl of the amide group beside the nitrogen atom
of the pyridine ring. The Ca(II) complex exhibited a band
in the visible region located at 396 nm, which can be
attributed to the ligand‐to‐metal charge transfer bands of
LMCT from the electronic lone pairs of carbonyl oxygen
to the metal ions.[30]
Ca(II) complex
The Ca(II) complex was thermally decomposed in three
decomposition steps within the 40–740°C temperature
range. The first decomposition step was in the temperature
range of 25–233 °C, and had weight loss of approximately
13.65% attributed to the loss of all of the coordinated and
uncoordinated water molecules (6H2O). The release and
pyrolysis of the first tenoxicam anion (Tenox−) occurred
in the second decomposition step in the temperature range
of 233–385°C with an observed weight loss of 40.46%.
The pyrolysis of the second Tenox− occurred in the
temperature range of 385–740 °C with an observed weight
loss of 26.05% (cal. = 26.32%). The final decomposition
product was CaCO3(calcite form) with some residual
carbon.
3.1.4 | Thermogram analyses
To emphasize the structures and compositions of the
synthesized Tenox complexes, thermal analysis (TG) was
carried out for the Ca(II), Sr(II), and Ba(II) complexes.
The measurements were carried out under a nitrogen
atmosphere in the temperature range of 25–800 °C. Their
Sr(II) complex
The thermogram of the Sr(II) complex indicated that it
decomposed in three degradation steps at temperature
ranges of 25–205, 205–290, and 290–750°C. The first
decomposition step had a weight loss of approximately
16.12% attributed to the loss of the 8H2O molecules. The
release and pyrolysis of the two Tenox− began and was
completed in the next two steps. The first one occurred
within a temperature range 205–290°C with a weight loss
of 37.27%. The second step occurred within the range of
290–750°C with a weight loss of 30.06%, leaving SrCO3
free of any residual carbons.
Ca (II) complex
Sr (II) complex
Ba (II) complex
1.0
0.5
0.0
Ba(II) complex
The thermogram of the Ba(II) complex exhibited two
steps, and its thermal decomposition began at 170°C.
The first degradation step occurred within a temperature
range of 25–225°C, corresponding to weight loss of
14.95% and assigned to the loss of the 5H2O molecules.
The second step occurred within the 225–600°C
200
400
600
800
)
)
nm
FIGURE 3 The UV–Vis. Spectra of the synthesized Tenox
complexes

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(a)
Sr(II) complex
Ca(II) complex
Temperature[oC]
(c)
Ba(II) complex
Temperature[oC]
FIGURE 4 The TGA curves of the synthesized Tenox complexes
TABLE 3 Thermal decomposition data for the synthesized Tenox complexes
TG
TG% mass loss
range
(°C)
Complex
Stages
Found
Calculated
Lost species
Ca(II)
I
II
25–233
233–385
385–740
‐
13.65
40.46
26.05
19.60
13.16
40.98
26.32
19.50
6H2O
Tenox−
III
Residue
C7H10N3OS2
CaCO3 (calcite form) +5C
Sr(II)
Ba(II)
I
II
25–205
205–290
290–750
‐
16.12
37.27
30.06
16.35
15.92
37.19
30.52
16.32
8H2O
Tenox−
C12H10N3OS2
SrCO3
III
Residue
I
II
25–225
225–600
‐
14.95
37.90
46.87
15.02
37.96
46.95
5H2O
C5H10N3OClS2
BaCO3 + 7C
Residue
temperature range (obs. = 37.90, cal. = 37.96%) and was
assigned to the loss of the C5H10N3OClS2 moiety. The
final decomposition product was barium carbonate
(BaCO3) with some residual carbon as the final products.
parameters (i.e. the activation energy (E*), the enthalpy
of activation (H*), the frequency factor (A), the Gibbs
free energy of activation (G*), and the entropy of
activation (S*)): the Coats–Redfern method[31] and the
Horowitz–Metzger[32] method. The kinetic−thermody-
ynamic parameters (E*, A, ΔS*, ΔH* and ΔG*) associated
with the synthesized complexes were evaluated graphi-
cally (Figures 5 and 6) by employing the two methods,
and the evaluated data are tabulated in Table 4. The ther-
modynamic data obtained from the two methods were
3.1.5 | Kinetic−thermodynamic
properties
Based on the thermogravimetric curves, two methods
were used to evaluate the kinetic−thermodynamic

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(a)
(b)
Sr(II) complex
Ca(II) complex
1000/T(K)
(c)
Ba(II) complex
1000/T(K)
FIGURE 5 Kinetic‐thermodynamic curves of the synthesized Tenox complexes using coats−Redfern (CR) method
(a)
(b)
Sr(II) complex
Ca(II) complex
(c)
Ba(II) complex
FIGURE 6 Kinetic‐thermodynamic curves of the synthesized Tenox complexes using Horowitz−Metzger (HM) method

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TABLE 4 Kinetic‐thermodynamic parameters of the synthesized Tenox complexes using the coats–Redfern (CR) and Horowitz–Metzger
(HM) methods
Parameter
Complex
Stage
1st
Method
E (kJ mol−1
6.75×105
6.76×105
)
A (s−1
2.17×1061
6.91×1061
)
ΔS (J mol−1 K−1
9.24×102
9.34×102
)
ΔH (kJ mol−1
6.71×105
6.71×105
)
ΔG (kJ mol−1)
1.53×105
1.48×105
r
Ca(II)
CR
HM
0.98142
0.97905
Sr(II)
Ba(II)
1st
1st
CR
HM
5.01×104
5.21×104
4.32×102
1.31×103
−1.99×102
−1.90×102
4.59×104
4.79×104
1.47×105
1.45×105
0.96091
0.96143
CR
HM
3.23×104
3.60×104
3.69
16.1
−2.39×102
−2.26×102
2.80×104
3.17×104
1.52×105
1.50×105
0.96034
0.99900
comparable and could be considered in agreement with
each other. The E* values for complexes were high, reveal-
ing the high stability of the complexes due to their cova-
lent bond characteristics. By comparing the E* values for
the main decomposition stage of the complexes, I
observed the following trend: Ca(II) > Sr(II) > Ba(II).
The ΔG* values were positive for the complexes, revealing
that the thermal decomposition was a non‐spontaneous
process, i.e., the complexes were thermally stable.[33]
The ΔS* values were found to be negative except for the
Ca(II) complex. The negative values of the ΔS* indicated
that the activated complexes had a more ordered structure
than the reactants or that the reaction was slower than
normal [34]. The ΔS* values of the complexes occurred in
a decreasing order as follows: Ca(II) > Sr(II) > Ba(II).
The positive values of ΔH* meant that the decomposition
process was endothermic.
against two Gram‐negative bacterial strains (Pseudomonas
aeruginosa [P. aeruginosa] and Escherichia coli [E. coli])
and two Gram‐positive bacterial strains (Bacillus subtilis
[B. subtilis] and Staphylococcus aureus [S. aureus]).
Tetracycline was employed as the standard drug (positive
control) for comparison with the bacterial results. The
results from the agar disk diffusion tests are presented in
Table 5 and are statistically illustrated in Figure 7. The
inhibition zone diameters of Tetracycline (in mm) against
S. aureus, B. subtilis, E. coli, and P. aeruginosa were found
to be 30, 34, 32, and 34 mm, respectively. Under identical
conditions, the corresponding values for the free Tenox
were 14, 14, 11 and 10 mm. Therefore, free Tenox had
moderate inhibitory activity against all bacterial strains.
The highest growth inhibition was induced by the Sr(II)
complex. The inhibition zone diameters of the Sr(II)
complex were found to be 23, 23, 19, and 19 mm against
S. aureus, B. subtilis, E. coli, and P. aeruginosa, respectively.
Under identical conditions, the corresponding values for
the Ba(II) complex were 21, 20, 20, and 17 mm and were
19, 14, 15, and 12 mm for the Ca(II) complex.
3.2 | Biology
3.2.1 | Antimicrobial test
The synthesized complexes were also examined for
their antifungal properties against two fungal species,
Candida albicans (C. albicans) and Aspergillus flavus
(A. flavus). The biological profiles of the antifungal results
were compared with Amphotericin B, which is a standard
The bioefficacy of the synthesized Tenox complexes was
screened against the growth of various bacterial and
fungal strains in vitro to evaluate their antimicrobial
potential. The antibacterial activity was screened in vitro
TABLE 5 Antibacterial and antifungal activities of free Tenox and the synthesized metal complexes
Inhibition zone diameter in mm at 100 μg/ml
Bacteria strains
Gram–positive strains
Gram–negative strains
Fungi strains
Sample
S. aureus
B. subtilis
E. coli
P. aeruginosa
A. flavus C. albicans
DMSO (control)
0.0
0.0
0.0
0.0
0.0
0.0
Standards
Tetracycline (Antibacterial agent)
Amphotericin B (Antifungal agent)
30.0
‐
34.0
‐
32.0
‐
34.0
‐
‐
‐
18.0
19.0
Free Tenox
14.0
14.0
11.0
10.0
0.0
0.0
Complexes Ca(II)
19.0
23.0
21.0
14.0
23.0
20.0
15.0
19.0
20.0
12.0
19.0
17.0
0.0
0.0
15.0
10.0
22.0
20.0
Sr(II)
Ba(II)

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diameters of the Sr(II) and Ba(II) complexes were found
to be 22 and 20 mm against C. albicans, respectively.
These values were equipotent to the standard drug
Amphotericin B. Therefore, the Sr(II) and Ba(II) complex
of the Tenox ligand displayed excellent toxicity towards
the C. albicans strains.
S. aureus
B. subtilis
E. coli
P. aeruginosa
The higher antimicrobial activity of the Tenox metal
complexes, compared with the free Tenox ligand, can
be explained according to Overtone's concept of cell
permeability.[35,36] Liposolubility is an important factor
that controls antimicrobial activity because cells are
surrounded by a lipid membrane, which favors the
passage of lipid‐soluble materials. When the metal ion
complexed with a ligand, the polarity of the metal ion is
reduced to a greater extent due to the overlap of the
ligand orbital and the partial sharing of the positive
charge of the metal ion with the donor groups in the
ligand. The complexation also increases the delocalization
of p‐electrons over the whole chelate ring, which
enhances the lipophilicity of the formed complex. The
increased lipophilicity enhances the penetration of the
metal complex into lipid membranes and blocking of
the metal binding sites on the enzymes of the microor-
ganism. Metal salts alone exhibit a higher activity than
their complexes with ligands, but they cannot be used as
antibacterial agents because of their toxicity and probabil-
ity of binding to the free ligands presented in the biologi-
cal systems, such as the nitrogen bases of nucleic acids
and proteins.
Tetracycline Free Tenox
Ca(II)
Sr(II)
Ba(II)
FIGURE 7 Statistical representation for antibacterial activity of
the standard drug, free Tenox, and the synthesized complexes
drug (positive control). The screening data are reported in
Table 5 and are statistically represented in Figure 8. The
inhibition zone diameters of Amphotericin B (in mm)
against A. flavus and C. albicans were found to be 18
and 19 mm, respectively. Under identical conditions, the
free Tenox had no inhibitory activity against the meta-
bolic growth of either fungal strain. The inhibition zone
C. albicans
A. flavus
3.2.2 | Activity index value
Antimicrobial activities of the synthesized complexes
were confirmed by calculating the activity index (%)
according to the following equation:
Inhibition zone diameter of Compound ðmmÞ
Activity index ð%Þ ¼
x100
Inhibition zone diameter of standard drug ðmmÞ
Amphotericin B
Tenox
Ca(II)
Sr(II)
Ba(II)
Table 6 lists the activity index values (%) for free
Tenox and its metal complexes. The complex containing
Sr(II) ions showed the highest activity indexes against all
FIGURE 8 Statistical representation for antifungal activity of the
standard drug, free Tenox, and the synthesized complexes
TABLE 6 Activity index (%) for the antimicrobial assay of free Tenox and the synthesized metal complexes
Activity Index (%)
Bacteria strains
Gram–positive strains
Gram–negative strains
Fungi strains
Sample
S. aureus
B. subtilis
E. coli
P. aeruginosa
A. flavus
C. albicans
Free Tenox
47
41
34
29
0
0
Complexes
Ca(II)
Sr(II)
Ba(II)
63
77
70
41
68
59
47
59
63
35
56
50
0
0
83
116
105
53

10 of 11
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microbes compared with other complexes. The activity
indexes of the complexes decreased in the following order:
Sr(II) > Ba(II) > Ca(II).
[10] E. Dubler, Biochemical and pharmaceutical aspects of metal
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Vol. 32, Marcel Dekker, New York 1996.
4 | CONCLUSION
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properties are reports for complexes of Ca(II), Sr(II)
and Ba(II) ions with the anti‐inflammatory drug
tenoxicam (Tenox).
ii) Complexation stoichiometry was found to be 1:2
(Metal: Tenox) for Ca(II) and Sr(II) ions and 1:1 for
Ba(II) ions.
[12] G. G. Mohamed, A. A. El‐Sherif, M. A. Saad, S. E. A. El‐Sawy, S.
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Sr(II) and Ba(II) ions involved the enolate oxygen
atom and pyridyl nitrogen atom, but it coordinated
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the carbonyl oxygen atom of the amide group, and
pyridyl nitrogen atom.
iv) The complexes underwent several decomposition
steps resulting in a metal carbonate (CaCO3, SrCO3,
and BaCO3) as the final decomposition product.
v) The Sr(II) and Ba(II) complexes exhibited marked
inhibitory effect on the cell growth of the C. albicans
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How to cite this article: Adam AMA. Ca(II),
Sr(II) and Ba(II) ion interaction with the
rheumatoid arthritis drug tenoxicam: Structural,
thermal, and biological characterization. Appl
Organometal Chem. 2017;e4055. https://doi.org/
10.1002/aoc.4055
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