Protein binding affinity of biologically active thiourea based half-sandwich Ru(II) cymene complexes

Article abstract of DOI:10.1016/j.poly.2019.114175

Half-sandwich (η⁶-p-cymene) complexes bearing either neutral functionalized N,S-bidentate thiourea ligands or a mono-negative N,N-aminoquinoline ligand were screened for their antibacterial and antifungal activities as well as cell viability ag

Full text of DOI:10.1016/j.poly.2019.114175

Polyhedron 175 (2020) 114175
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journal homepage: www.elsevier.com/locate/poly
Protein binding affinity of biologically active thiourea based
half-sandwich Ru(II) cymene complexes
Ahmed M. Mansour a, , Krzysztof Radacki b
⇑
a
Department of Chemistry, Faculty of Science, Cairo University, Gamma Street, Giza, Cairo 12613, Egypt
Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
b
a r t i c l e i n f o
a b s t r a c t
Half-sandwich (g
6-p-cymene) complexes bearing either neutral functionalized N,S-bidentate thiourea
ligands or a mono-negative N,N-aminoquinoline ligand were screened for their antibacterial and antifun-
gal activities as well as cell viability against non-malignant HEK293 (human embryonic kidney cells). The
haemolysis parameters (HC10 and HC50) were determined to get some information about the compatibil-
Article history:
Received 20 September 2019
Accepted 8 October 2019
Available online 18 October 2019
ity of the toxic compounds with the blood components. The protein binding affinity of hen white egg
Keywords:
6
lysozyme (HEWL), a model protein, towards the synthesized (
g
-p-cymene) complexes was investigated
Half-sandwich Ru(II)
Antimicrobial activity
Protein interaction
TDDFT
by ESI-MS. Metalation of HEWL was achieved through both covalent and non-covalent modes of interac-
tion. To recognize if the metalation site of HEWL is the His15 side chain, the reactions between the com-
plexes and imidazole were theoretically and experimentally studied by quantum chemical calculations,
UV–Vis and NMR. Exchange of the nitrogen coordination site of the thiourea ligand from the pyridine to
the benzothiazole moiety induced higher potency against Staphylococcus aureus, Candida albicans and
Cryptococcus neoformans var. grubii.
Thiourea
Ó 2019 Elsevier Ltd. All rights reserved.
1
. Introduction
focused on using bidentate ancillary ligands instead of two mon-
6
odentate molecules [7–9]. [RuCl(
g
-p-Cym)(en)] (en = ethylenedi-
To date, significant attention has been awarded to half-sand-
amine) showed excellent cytotoxicity [7], which was improved
wich Ru(II) arene complexes with the formula [Ru(arene)(L-L)
by replacing ethylenediamine with acetylacetone or bipyridine-
thiol [8], and was diminished by introducing 2,2 -bipyridine [9].
0/n+
0
X]
zene,
thracene; X = leaving group) due to their noticeable air stability,
structural diversity and solubility in water [1]. The non-labile
(L-L = ancillary ligand(s); arene = p-cymene (p-Cym), ben-
9,10-dihydro-anthracene and 5,8,9,10-tetrahydroan-
The type of arene moiety played an important role in determining
the cytotoxic activity of a series of [RuCl(arene)(en)] [6c,7].
The chemistry of thiourea derivatives furnished with potential
coordination sites (pyridyl and quinolinyl) and their metal com-
plexes have received noteworthy interest due to their biological
[10] and industrial applications [11]. Urease, a nickel enzyme,
hydrolyses urea in microbes and the soil. This was the motivation
for investigation of Ni(II) thiourea complexes as biological models
[12]. Some thiourea derivatives showed promising inhibitory activ-
ity towards protein tyrosine kinases and NADH oxidase [13]. While
the thiourea motif is a central pharmacophore in drug discovery, it
p
-
bonded arene moiety stabilizes the Ru(II) ion in a ’’piano-stool’’
geometry by settling down on the top of the stool. Exchange of
the leaving group (X) with a water molecule enhances the interac-
tion with some biomolecules [2]. Replacement of the ancillary
ligand permits modifications of the physicochemical properties of
the arene complexes for a variety of applications, including biolog-
ical activity [3] and catalysis [4]. [Ru(arene)(L-L)X]0 complexes
/n+
exhibited high hydrophobicity values, which enabled membrane
6
permeation within a cell. [RuCl
2
(g
-p-Cym)(PTA)] (RAPTA-C) and
has not been extensively investigated as an ancillary ligand in the
6
6
[
2
RuCl (g
-benzene)(PTA)] (RAPTA-B) (PTA = 1,3,5-triaza-7-phos-
synthesis of Ru(
g
-p-Cym) complexes. Because of their vital role as
phatricyclo-[3.3.1.1]-decane) have been developed as leading can-
didates in preclinical surveys [6] due to their in vivo selective
activities in the inhibition of metastasis growth [5]. Sadler’s group
anion acceptors, bis(thiourea) ligands and their functionalized Ru
6
(
g -p-Cym) complexes were studied in the context of anion sens-
6
ing [14]. The antiproliferative activity of a series of Ru(
g -p-Cym)
complexes, bearing mono- and bidentate acylthioureas, against
MDA-MB-231 and A549 cell lines was assessed; complexes with
⇑
Corresponding author.
E-mail address: mansour@sci.cu.edu.eg (A.M. Mansour).
bidentate ligands showed better activity than the monodentate
6
ones [15a]. Similarly, Ru(
g
-p-Cym) complexes with bidentate
https://doi.org/10.1016/j.poly.2019.114175
277-5387/Ó 2019 Elsevier Ltd. All rights reserved.
0

2
A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
N-phenyl-N’-benzoyl thiourea-derived ligands were more potent
than those with monodentate coordination on screening against
ronment of the Ru(g
6-p-Cym) unit. While this contribution was
in progress, the crystal structure of 2 (Scheme 1) was published
by Kollipara [23]. The lysozyme affinity of 1–3 towards HEWL
was investigated by ESI-MS. Although, various HEWL binding
side-chains were expected to be involved in the metalation pro-
cess, the previously published X-ray crystallographic data of HEWL
adducts indicated that the His15 side chain was the powerful point
human cancer cell lines (HCT-116, NCL-H460, SiHa and SW480),
6
with IC50 values in the low
l
M [15b]. Mononuclear Ru(
g
-p-
Cym) based complexes of (3-picolyl)thiourea derivatives were
synthesized and analyzed by single-crystal X-ray diffraction [16].
As an alternative, the published 8-aminoquinoline coordinated
6
Ru(
g
-p-Cym) complex, closely related to compound 3 (Scheme 1),
of interaction [19–21]. To recognize the possibility of binding
6
was evaluated as a catalyst for the conversion of bioderived furans
4a].
The interactions of biologically active compounds with some
His15 to Ru(
g
-p-Cym) complexes 1–3, the reactions between
[
the complexes and HEWL were studied. The observed electronic
transitions were assigned with the aid of time-dependent density
functional theory calculations (TD DFT). Compounds 1–3 were
evaluated for their potential antibacterial and antifungal activity,
as well as cell viability against non-malignant cells (human embry-
onic kidney cells (HEK293)). Finally, the compatibility of 1–3 with
blood components was assessed.
model proteins have recently attracted new interest because of
the lack of knowledge on how these molecules communicate with
the cell components. Such interactions are vital to get an insight
about the toxicity and resistance of drugs, biodistribution and
pharmacokinetics [17]. Some model proteins, such as hen egg
white lysozyme (HEWL), were used as biocompatible carriers to
deliver some biologically active molecules into living cells [18].
2
. Results and Discussion
6
The reactivity of some Ru(
g
-p-Cym) based compounds towards
HEWL was investigated by X-ray crystallography and spectromet-
2
.1. Synthesis and characterization
ric methods [19,20]. The surface-accessible histidyl side-chain
6
(
His15) of HEWL reacted with a carbene coordinated Ru(
g
-p-
The pure thiourea ligands were synthesized in good yields by
Cym) compound via the cleavage of the cymene unit and oxidation
the reaction of phenyl isothiocyanate and the corresponding pri-
mary amines in either ethanol or pyridine by following the pub-
lished methods [24]. The reaction of [RuCl(
with the thiourea ligands (L and L
6
of the metal centre [19]. A 1.6 Å X-ray refined model of [RuCl
2
(g -
p-Cym)(HEWL)] showed that metalation occurred at the His15
6
l
-Cl)(
g
-p-Cym)]
2
6
side-chain [20]. The structure of [RuCl(
l-Cl)(g
2
-p-Cym)] , with
H
Benzo
) in methanol yielded
an apo-Ferritin nanocage, refined at 1.73 Å, revealed the existence
of three Ru bound sites per Ferritin monomer [21]. Destabilization
6
H
Benzo
[
RuCl(
g
-p-Cym)(L)]Cl (L = L (1) and L
(2)). Interestingly,
Q
the phenyl isothiocyanate part of L (Fig. S1) was eliminated from
the reaction of L and [RuCl(l-Cl)(g -p-Cym)] (Scheme 1). Differ-
2
ent spectroscopic and analytical tools were used to elucidate the
structures of 1–3 (Figs. S2–5). However, the explicit proof of the
N,S-bidentate mode of L
finally obtained from single crystal X-ray analysis (Fig. S6) [23].
The downfield shift of pyridine-H6 (L ) and benzothiazole-H7
of the adducts was detected upon soaking HEWL with [RuCl(
l
-Cl)
Q
6
6
(g
2
-p-Cym)] [22].
In the present contribution, we report the preparation of Ru(
g
6-
p-Cym) complexes bearing either N,S-bidentate thiourea ligands (1
and 2) (Scheme 1) or the mono-negative 8-amino quinoline ligand
Benzo
towards the Ru(II) cymene unit was
(3). The novelty of the N,S-bidentate ligand system is based on
H
modulation of the RuACl bond strength by variations in the envi-
Benzo
(
L
) from d = 8.19 and 7.84 ppm [24] to d = 8.82 and 8.54 ppm,
Scheme 1. Synthesis of Ru(g
6-p-Cym) based complexes 1–3.

A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
3
considering the solvent effect, may be ascribed to the coordination
assignments are tabulated (Table S4). The calculated electronic
spectra of the Ru(g -p-Cym) complexes 1–3 are shown in Fig. S8.
6
of the heterocyclic ring to the Ru(II) ion. In comparison with 1 and
2
, the disappearance of 13C@S and phenyl-NH signals from the
In the 200–600 nm range, the theoretical spectrum of 1 displayed
four main bands centred at 537, 410, 262 and 232 nm. In addition,
weak electronic transitions, assigned to HOMO–1 ? LUMO + 1,
HOMO ? LUMO + 1 and HOMO–1 ? LUMO/LUMO + 2 are shown
at 592, 582 and 515 nm, respectively. Based on the descriptions
of the frontier molecular orbitals (Fig. 1), the transitions at 592,
NMR spectra of 3 is a sign for the elimination of phenyl isothio-
1
cyanate. While two NH signals are seen in the H NMR spectrum
Q
of L at d = 10.75 and 10.62 ppm (Fig. S4), only one NH signal is
observed at d = 11.47 ppm in the spectrum of 3. For 1 and 2, the
H
Benzo
NH signals at d = 9.66 (L ) and 10.72 ppm (L
) [24] move down-
field to d = 12.06 and 11.64 ppm due to a change in the electron
density of C@S upon complex formation and/or participation of
the NH groups in H-bonds with the ionic chloride ligands
582 and 515 nm are d-d in nature. Generally, the ground-state of
6
low-spin Ru(II) complexes (t2g
e
g
) in piano-stool and octahedral
1
geometries is
A1g [28]. In increasing order of energy, the excited-
5
1
3
3
1
(Fig. S6). The electrospray ionization mass spectrum of 1, in the
positive mode, showed two typical fragments at m/z = 500.0487
parison between the calculated and the previously published transi-
tions [29] revealed that the absorption at 515 nm is assigned to the
singlet–singlet transitions, while those at 582 and 592 nm are
+
+
{
3 3
1–Cl–CH } , and 464.0725 {1–Cl–H–CH } . For 2, the peaks
observed at m/z = 535.9802 and 520.0443 are assigned to {2–
2
+
+
1
1g ? T2g and 1
3
3
2
Cl} and {2–2Cl–CH
3
} , in that order. The ESI-MS(+) of 3 showed
assigned to the forbidden transitions;
respectively.
A
A
1g ? T1g
,
+
two unique peaks at m/z = 382.0862 {3–Cl–H–CH
3–Cl–CH
3
} and 338.3414
+
{
3
3
–(CH )
2
CH]} .
The calculated spectrum of 2 showed four main bands at 533,
3
97, 302 and 252 nm, as well as a shoulder at 223 nm. Three weak
2
.2. DFT/TD DFT
electronic transitions assigned to d-d transitions (Fig. 1) are allo-
cated at 563, 533 and 481 nm. The observed electronic spectrum
of 2 (in chloroform) exhibited a band at 311 nm as well as two
shoulders at 405 and 259 nm. The transition at 405 nm may be
assigned to a MLCT band [28].
To get an insight into the observed electronic transitions of 1–3,
TD DFT calculations of the ground-state optimized structures
Fig. S7) of 1–3 were carried out with the PCM(CHCl )/CAM-
(
3
B3LYP [25]/LANL2DZ [26] method. Initially, geometry optimization
was performed at the B3LYP [27]/LANL2DZ level of theory, starting
from the crystallographic coordinates (CCDC 1940322) without
any symmetry restriction. The atomic coordinates of the optimized
ground-state structures and energy values are given in Tables S1–
Seven bands are recognised in the calculated spectrum of 3 at
611, 448, 328, 302, 269, 240 and 220 nm. In the visible-range, a
group of d–d transitions arising from HOMO ? LUMO + 1,
HOMO-1 ? LUMO + 1, HOMO ? LUMO, HOMO ? LUMO + 2, and
HOMO–3 ? LUMO + 1 is designated at 610, 502, 447, 436 and
396 nm, respectively (Fig. S9). Experimentally, the absorption elec-
tronic spectrum of 3 showed two shoulders at 441 and 278 nm.
3. The 30 lowest-energy electronic excitation states were calcu-
lated. The energies of the selected electronic transitions and their
Fig. 1. Descriptions of the frontier molecular orbitals involved in the lowest energy calculated transitions of 1 (left) and 2 (right) obtained at the TD/CAM-B3LYP/LANL2DZ
level of theory.

4
A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
The calculated data of 3 compare well with the experimental find-
nature of binding to get an insight into their mechanism of action.
After administration of anticancer drugs, there is a highly probabil-
ity for binding covalently or non-covalently [31] with some pro-
teins containing a surface accessible histidyl side chain. Such
interactions may influence the toxicity and the resistance of the
drugs, biodistribution and pharmacokinetics. Some model proteins
were investigated as biocompatible carriers to deliver some cyto-
toxic molecules into cells. These arguments have inspired us to
1
1
1
1
ings; the shoulder observed at 441 nm ( A1g ? T2g/ A1g ? T1g
)
compares well with the calculated value at 448 nm.
2.3. Interaction with protein
Ru(g
6-p-Cym) complexes have been shown to exhibit anti-
cancer activity [6b,7,30] and thus it is essential to explore the
Fig. 2. Deconvoluted ESI-MS spectra of HEWL treated with complexes (a) 1, (b) 2 and (c) 3 in a 1:1 reaction ratio at room temperature.

A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
5
investigate the reactions of 1–3 with HEWL by electrospray ioniza-
tion mass spectrometry. HEWL is a small (14303.8500 Da) positive
charged enzyme composing of one single protein-chain (129
amino acid residues and 4 cystine disulfide bonds). The lysozyme
affinity of 1–3 was studied by reacting one equivalent of HEWL
with either one or fifteen equivalents of each complex. Particularly,
the ESI(+) MS of 1, recorded for 1:15 (HEWL: complex) ratio, man-
ifested a peak at 14811.8742 Da (Fig. 2a), which compares well
with the mass of a non-covalent formed HEWL adduct [31] con-
immediately red on mixing with imidazole; addition of imidazole
to the complexes (1 and 2) induced a red shift (Fig. S10) to the tran-
sitions at 286 and 336 nm to 332 and 367 nm in the electronic
absorption spectra of 1 and 2. The latter transitions at 332 and
367 nm are seen at 321 and 360 nm in the spectrum of adduct 3
(Fig. 3). These noticeable spectral changes may be ascribed to the
partial exchange of the coordinated chloride ligand or change of
the coordination mode of the thiourea ligand from N,S-bidentate
to the S-monodentate mode.
6
H
+
6
taining the cationic part of 1, {[RuCl(
g
-p-Cym)L ]} . An adduct
The reaction between the synthesized Ru(
g
-p-Cym) com-
6
H
2+
1
peak assigned to {HEWL + [Ru(
g
-p-Cym)L ]} (m/z 14775.8769)
plexes and imidazole was investigated by solution NMR ( H and
1
1
3
was observed in the mass spectrum of adduct 1 (Fig. 2a); such a
fragment indicates the presence of covalent mode of interaction
through the elimination of a coordinated chloride ion. Therefore,
both covalent and non-covalent modes of interaction were
observed when HEWL reacted with compound 1. For 2, the
obtained data from 1:1 and 1:15 (HEWL: complex) reaction mix-
tures, measured directly or after incubation for 24 h, revealed that
C). The reactions were followed at different time intervals. The
H NMR spectrum of adduct 1 shows a set of unique signals with
respect to the signals of the free complex 1 (Fig. 4). The reaction
was completed within 3 h. The signals of the coordinated imida-
zole ring appear at d = 8.92, 8.20, 7.07 and 7.00 ppm. The upfield
shift of pyridine-H6 from d = 8.82 to 7.97 ppm may be attributed
to detachment of the pyridine N atom from the coordination
sphere of the Ru(II) ion and the presence of pyridine-H6 in the con-
ical areas of the imidazole ring [32] . The anisotropic effects of the
n+
only {HEWL+Ru} adduct species was formed, which was detected
at 14423.7582 Da. Eventually, a decomposed ruthenium contain-
ing species, in which most of the original ligands had been elimi-
nated, was observed attached to the protein in the mass
spectrum of adduct 2 (Fig. 2b) [31].
H
imidazole and phenyl moieties of L induced a significant change
to the cymene ring; the pattern of the aromatic protons is changed,
and the signals of the aliphatic groups are upfield shifted. Similar
spectral changes were observed when imidazole was added to 2
The ESI(+) MS of 1:1 (HEWL: complex 3), either recorded imme-
diately or after 24 h, showed a peak at 1617.8564 Da (Fig. 2c) allo-
1
(Fig. S11). The H NMR spectrum of adduct 2 is characterized by
Q +
cated to {HEWL + RuL } . Therefore, complex 3 reacted covalently
three imidazole signals at d = 7.81, 7.00 and 6.78 ppm Because of
the simplicity of structure 3 and the possibility of formation of dif-
ferent imidazole adduct species, it was difficult to recognize the
type of interactions by NMR spectroscopy.
with HEWL via the loss of p-cymene and chloride ligands. Addi-
n+
n+
tionally, two peaks assigned to {HEWL+Ru } and {HEWL+2Ru
}
were observed at 14410.8108 and 14506.7841 Da, respectively.
This indicates the presence of two Ru bound sites per HEWL. No
significant change was observed by increasing the reaction ratio
between HEWL and 3. In the absence of X-ray crystallographic data
of the HEWL adducts formed from 1–3, it is difficult to allocate pre-
cisely the position of the covalent and non-covalent modes of
interaction.
The imidazole adducts of 1 (Fig. S12) and 2 (Fig. S13) were anal-
1
3
ysed by solution C NMR to explore the coordination environment
around the Ru(II) ion and the probability of the detachment of the
pyridine coordination centre. The spectra of the imidazole adducts
3
(in CHCl ) were compared with those of the parent compounds. As
shown in Fig. 5, the coordination of imidazole to 2 causes cleavage
of the Ru(II)–N bond, where the signal of pyridine-C6 moves down-
field from d = 154 to 161 ppm. In comparison with the parent com-
According to previously published crystallographic studies
[
2,20,24], lysozyme has numerous binding sites where metalation
1
3
can occur. This includes mainly the surface accessible His15 side-
chain and the closeness of adjacent Arg14 and Asp87. The interac-
tions between 1–3 and imidazole, a model of the histidine residue,
were studied by UV–Vis and NMR spectroscopies in chloroform.
Because of the poor solubility of histidine in chloroform, imidazole
was chosen for this study. The yellow solutions of 1–3 turned
plex, the C NMR signals of the coordinated imidazole ring are
shown at d = 138.8, 123.8 and 120.9 ppm. Therefore, coordination
of imidazole to 1 and 2 occurs via the detachment of the hetero-
cyclic coordination arm.
To recognize whether the coordination mode of the thiourea
derivative in compounds 1 and 2 is preserved during the interac-
Fig. 3. UV–Vis spectral changes of complex 3 (in chloroform) upon addition of imidazole (Im) at t = 0 and after incubation for 16 h.

6
A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
Fig. 4. 1H NMR spectral changes of complex 1 (in CDCl
) upon addition of imidazole (Im) (a) free complex 1, (b) 30 min, (c) 3 h, (d) 12 h and (e) 24 h.
3
tion with HEWL or not, the sums of the electronic and zero-point
energies of the proposed adduct structures (Fig. 6) were compared.
Two imidazole adduct structures were assumed; adduct a is
assigned to the structure in which the coordinated chloride ligand
is replaced by imidazole, with the preservation of the bidentate
mode of the ancillary ligand, while the adduct b is allocated to
the structure in which the coordination mode of the thiourea
ligand is changed from the bidentate mode into a monodentate
mode, leaving an empty position in the piano-stool configuration
for the incoming imidazole. The structure of adduct b was observed
for other closely related published thiourea arene complexes [17].
It is worth mentioning that adduct b (ꢀ1362.513115 Hartree) is
more stable than a (ꢀ1347.257667 Hartree). Based on the NMR
and theoretical data, the imidazole ligand occupies a position in
6
the coordination sphere of Ru(
g
-p-Cym) complexes, when the
thiourea changes its bidentate mode of chelation into monodentate
via the detachment of the coordinated nitrogen atom.
2.4. Antimicrobial and cytotoxic activity
The in vitro antibacterial activities of [RuCl(
l
-Cl)(
g
6-p-Cym)]2
6
and the Ru(
g -p-Cym) based complexes 1–3 were assessed against
some Gram-negative bacteria; Klebsiella pneumoniae ATCC 700603,
Acinetobacter baumannii ATCC 19606, Pseudomonas aeruginosa
Fig. 5. 13C NMR spectral changes of complex 2 (in CDCl
) upon addition of imidazole (Im).
3

A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
7
Fig. 6. Local minimum proposed imidazole adducts of complex 1, (a) adduct a and (b) adduct b obtained at the B3LYP/LANL2DZ level of theory.
Table 1
Minimum inhibitory concentrations (
l
g/mL) determined for the Ru(
g
6-p-Cym) thiourea complexes.#
E. coli
K. pneumoniae
A. baumannii
P. aeruginosa
S*
1
2
>32
>32
>32
>32
>32
>32
>32
>32
>32
>32
>32
>32
>32
>32
>32
>32
3
S. aureus
C. albicans
C. neoformans
S*
1
2
>32
16
4
32
>32
4
>32
>32
8
3
8
4
2
#
Full names: Staphylococcus aureus ATCC 43300, Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 700603, Acinetobacter baumannii ATCC 19606, Pseudomonas
6
2
aeruginosa ATCC, Candida albicans ATCC 90028 and Cryptococcus neoformans var. grubii H99; ATCC 208821; S*: [RuCl(l-Cl)(g -p-Cym)] .
ATCC 700603 and Escherichia coli ATCC 25922, as well as a Gram-
positive bacterium (Staphylococcus aureus ATCC 43300). The toxic-
ity (MIC) is measured by a dose–response assay [33]. While com-
pounds 1–3 were inactive against the Gram-negative bacteria
inhibitory concentrations (lg/mL) (Table 1) were determined as
the lowest concentration at which the growth was completely
reserved, well-defined by an inhibition of 80% and 70% for Candida
albicans ATCC 90028 and Cryptococcus neoformans var. grubii H99,
respectively. Complexes 2 and 3 exhibited exciting antifungal
(Table 1), they were strongly potent against Staphylococcus aureus
in the following order: 2 (6.77 nM) > 3 (19.3 nM) > 1 (29.9 nM). It
seems that the inhibitory activity is influenced by the cell wall
structure of the bacteria, which is vital for the survival of bacteria.
The mode of action of some antibiotics involves the inhibition of
the synthesis of peptide-glycan. While Gram-positive bacteria have
a thick cell wall of many layers of peptidoglycan and teichoic acids,
Gram-negative bacteria possess a comparatively thin cell wall
comprising of a few layers of peptidoglycan walled by a second
lipid layer of lipopolysaccharides and lipoproteins that form a
hydrophilic permeability barrier and affords extra protection
against hydrophobic drugs. In comparison, exchange of the pyri-
dine ring with the benzothiazole moiety led to a significant
improvement in the toxicity against Staphylococcus aureus. Com-
pounds 1–3 exhibited superior potency to Staphylococcus aureus
activity against Candida albicans with MIC values of 6.77 and
6
9.65 nM, respectively. While compound 1 and [RuCl(
l-Cl)(g
-p-
Cym)]
2
were inactive to Cryptococcus neoformans, compound 3
(4.83 nM) was more potent than 2 (13.5 nM) against the same
fungus.
It is plausible that many organometallic compounds have gen-
eral toxicity that is not related to microbes, but also affects
human cells. To address this issue, the toxicities of the title Ru
6
6
(
2
g -p-Cym) complexes and [RuCl(l-Cl)(g -p-Cym)] were evalu-
ated by measuring the cell viability against non-cancerous human
embryonic kidney cells (HEK293), as well as the blood compatibil-
ity with the cell components. Non-toxic complexes were defined
with CC50 > 32 lg/mL, HC10 > 32 lg/mL and HC50 > 32 lg/mL (the
concentration at 10% and 50% haemolysis). Unfortunately, com-
pounds 1–3 were potent to HEK293 in the following order: 2
(4.76 nM) > 1 (17.4 nM) > 3 (18.2 nM). However, the complexes
exhibited negligible haemolysis release, revealing the compatibil-
than silver sulfadiazine (MIC = lM) [34].
It is recognised that highly mortal fungal regular infections are
supported by C. albicans and C. neoformans. The antifungal activity
was evaluated against Candida albicans ATCC 90028 and Cryptococ-
cus neoformans var. grubii H99; ATCC 208821. The minimal
ity with the blood components, with HC10 > 32
HC50 > 32 g/mL.
lg/mL and
l

8
A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
Based on these preliminary biological data, the synthesized Ru
II) cymene complexes exhibited interesting antimicrobial activity
against Staphylococcus aureus, Candida albicans and Cryptococcus
neoformans var. grubii H99 as well as blood compatibility, and
therefore they show great potential for further studies.
4.2. Synthetic procedures
(
Q
4.2.1. Synthesis of 1-phenyl-3-(quinoline-8-yl) thiourea (L )
Q
The ligand (L ) was synthesized by a modified literature
method [36]. The reaction mixture of 8-amino quinoline (1 g,
6
.9 mmol) and phenyl isothiocyanate (2.8 g, 20.7 mmol) in pyri-
dine (25 mL) was stirred at room temperature for 48 h. Addition
of 2-propanol (300 mL) to the reaction mixture gave white crystals.
3
. Conclusion
’Piano-stool’’ Ru(g
6-p-Cym) complexes incorporating N,S-
The crystals were washed with 2-propanol, diethyl ether and dried
1
under vacuum. Yield: 33% (630 mg, 2.25 mmol). H NMR ([D
6
]
’
DMSO, 400.40 MHz) d, ppm: 10.75 (s, 1H, NH), 10.61 (s, 1H, NH),
bidentate thiourea ligands furnished with either a pyridyl or ben-
zothiazolyl group were synthesized and characterized using a vari-
ety of spectroscopic and analytical tools, including X-ray
diffraction analysis. Reaction between 1-phenyl-3-(quinoline-8-
yl) thiourea and [RuCl(
aminoquinolinyl Ru(
of the phenyl isothiocyanate group. With the aid of DFT and TDDFT
studies, the observed electronic transitions were assigned to
3
3
9
.24 (d,
JH,H = 8.3 Hz, 1H, Q-H2), 8.88 (m, 1H, Q-H4), 8.42 (d, J
H,
H
= 8.3 Hz, 1H, Q-H5), 7.68 (m, 1H, Q-H7), 7.60 (m, 4H, Ph-H2/
3
3
H6/Q-H3/H6), 7.50 (t,
JH,H = 7.5 Hz, 2H, Ph-H3/H5), 7.21 (t, J
H,
1
3
H
=
6
7.6 Hz, 1H, Ph-H4). C NMR ([D ] DMSO, 100.68 MHz) d,
6
l
-Cl)(g
-p-Cym)]
2
afforded
a
neutral
ppm: 177.8 (C@S), 148.7 (Q-C4), 138.9, 138.8, 136.7 (Q-C5),
6
g -p-Cym) complex through the elimination
1
1
35.1, 128.7, 127.8, 126.3, 125.0, 124.1, 122.1, 122.0 (Q-C7),
18.1 (Q-C2).
charge transfer and d–d transitions. The lysozyme binding affinity
4
.2.2. Synthesis of 1–3
6
of the title Ru(
mode ESI-MS. The pyridyl Ru(
g
-p-Cym) complexes was investigated by positive
The thiourea ligands (0.39 mmol, L , 90 mg; LBenz, 111 mg; LQ,
H
6
g -p-Cym) complex reacted with
6
1
08 mg) and [RuCl(
l
-Cl)(g
-p-Cym)]
2
(0.2 mmol, 126 mg) were
lysozyme through both covalent and non-covalent modes of bind-
ing. Eventually, a decomposed ruthenium containing species, in
which most of the original ligands were eliminated, was observed
dissolved in dried degassed methanol (25 mL) and stirred for one
day at 25 °C. The solvent was removed under vacuum and the
resulting solid was redissolved in acetonitrile (10 mL). Diethyl
ether (300 mL) was added to the solution, whereupon an orange
to be attached to the protein when lysozyme was soaked with the
6
Ru(g
-p-Cym)benzothiazolyl complex. To recognize the probabil-
(1, 2) or buff (3) precipitate was formed. Compound 2 was recently
ity of binding the surface accessible His15 side chain of lysozyme
to the complexes, the reactions between imidazole and the com-
plexes were experimentally investigated (UV–Vis and NMR) and
theoretically discussed. Detachment of the heterocyclic coordina-
tion centre and a change of the coordination mode from N,S-biden-
tate into S-monodentate occurred during the formation of the
imidazole adduct. The antimicrobial data showed that the title
complexes were only potent to Staphylococcus aureus; the benzoth-
prepared by a modified method to that recently published [23].
6
H
[
RuCl(
ATR, diamond)
CC/CN), 1483, 1346, 1279, 764. H NMR (CDCl
ppm: 13.29 (br, 1H, NH), 12.06 (br, 1H, NH), 8.82 (dd,
g -p-Cym)(L )]Cl (1): Yield: 68% (143 mg, 0.27 mmol). IR
ꢀ1
(
m, cm : 2963 (w, CH), 1643 (w, CC/CN), 1615 (m,
1
3
, 400.40 MHz) d,
3
4
3
J
H,H = 5.8 Hz,
JH,H = 1.4 Hz, 1H, Py-H6), 7.75 (td,
JH,H = 7.4 Hz,
4JH,H = 1.6 Hz, 1H, Ph-H3 or H5), 7.61 (d,
3
J
H,H = 7.8 Hz, 1H, Py-
3
H3), 7.56 (m, 2H, Ph-H2/6), 7.39 (m,
H3 or H5), 7.30 (t,
JH,H = 7.6 Hz, 2H, Py-H4/Ph-
iazolyl complex is more potent than the pyridyl analogue. The
3
3
J
H,H = 7.6 Hz, 1H, Py-H5), 7.15 (t,
J
H,
6
aminoquinolinyl Ru(
g
-p-Cym) complex exhibited better toxicity
3
H
= 5.6 Hz, 1H, Ph-H4), 5.45 (d, 1H,
J
H,H = 6.0 Hz, p-Cym-H2 or
(
4.83 nM) against the fungal C. neoformans than the thiourea based
g -p-Cym) complexes. While the complexes induced severe
3
H6), 5.37 (d, 1H,
Cym-H3/5), 2.72 (sep,
CH
3
JH,H = 6.4 Hz, p-Cym -H6 or H2), 5.21 (m, 2H, p-
6
Ru(
3
J
H,H = 6.9 Hz, 1H, CH(CH
H,H = 2.2 Hz, 3H, CH(CH ), 1.15 (d,
, 100.68 MHz) d, ppm: 178.1
3 2
) ), 1.89 (s, 3H,
toxicity to non-malignant HEK293 cell lines, they exhibited excel-
lent compatibility with blood components. The synthesized Ru(II)
cymene complexes showed interesting antimicrobial activities
and therefore for further studies are highly encouraged.
3
3
3
), 1.17 (d,
J
3
)
2
JH,H = 2.1 Hz,
1
3
H, CH(CH )
3 2
).
C NMR (CDCl
3
(C@S), 154.5 (Py-C6), 153.1 (Py-C2), 140.3 (Ph-C3 or C5), 136.4
(Ph-C1), 129.1 (Py-C4/Ph-C3 or C5), 127.9 (Py-C5), 125.2
(Ph-C2/6), 121.3 (Ph-C4), 117.4 (Py-C3), 107.1 (p-Cym-C4), 100.1
(p-Cym-C1), 86.6 (p-Cym-C2 or C6), 85.4 (p-Cym-C6 or C2), 85.2
4
. Experimental
(p-Cym-C3 or C5), 84.3 (p-Cym-C5 or C3), 30.8 (CH(CH
CH(CH ), 22.2 (CH(CH ), 18.2 (CH ). ESI-MS (positive mode,
acetone) m/z: 500.0487 {1–Cl–CH
RuS, Calc.: C 49.34, H 4.71, N 7.85, S 5.99: Found: C
49.56, H 4.97, N 8.10, S 5.63%.
3 2
) ), 22.5
(
3
)
2
3
)
2
3
+
+
4.1. Materials and instruments
3 3
} , 464.0725 {1–Cl–H–CH } .
22 2 3
C H25Cl N
The thiourea ligands and their ruthenium(II) cymene complexes
6
Benzo
were synthesized using an argon atmosphere and dried degassed
solvents. The chemicals were purchased from the commercial
sources. The thiourea ligands (L and L
[RuCl(
0.28 mmol). IR (ATR, diamond)
CC/CN), 1605, 1593, 1519, 1385, 1254, 1075, 752. H NMR (CDCl
400.40 MHz) d, ppm: 14.61 (br, 1H, NH), 11.87 (br, 1H, NH), 8.54 (d,
g
-p-Cym)(L
)]Cl (2): [23] Yield: 72% (167 mg,
ꢀ1
m
, cm : 2911 (w, CH), 1643 (w,
H
Benzo
1
) [24] and [RuCl(
l
-Cl)
3
,
6
(g
-p-Cym)]
2
[35] were synthesized by following the published
3
3
procedures. UV–Vis spectra were recorded on an Agilent 8453
diode array spectrophotometer. IR spectra were recorded using a
Nicolet 380 FT-IR spectrometer fitted with a smart iTR ATR acces-
JH,H = 8.4 Hz, 1H, Benzo-H7), 7.70 (d, JH,H = 7.9 Hz, 1H, Benzo-H4),
3
3
4
7.60 (d,
JH,H = 7.9 Hz, 2H, Ph-H2/6), 7.53 (td, JH,H = 7.7 Hz, J
H,
H
= 1.1 Hz, 1H, Benzo-H5), 7.41 (m, 3H, Benzo-H6/Ph-H3/5), 7.33
1
13
3
sory. H and C NMR spectra were recorded with Bruker-Avance
(m, 1H, Ph-H4), 5.72 (d, JH,H = 6.3 Hz, 1H, p-Cym-H2 or H6), 5.36
1
13
1
3
4
00 ( H, 400.40 MHz; C{ H}, 100.70 MHz) spectrometers. Assign-
(m, 3H, p-Cym-H6 or H2/p-Cym-H3/5), 2.70 (sep,
J
H,H = 7.2 Hz,
H,H = 7.0 Hz, 3H, CH
). 13C NMR (CDCl
1
1
1
13
3
ments were done with the aid of { H, H} COS90 and { H, C}
HSQC. Electrospray mass spectra were run with a ThermoFisher
Exactive Plus instrument with an Orbitrap mass analyzer at a res-
olution of R = 70.000 and a solvent flow rate of 5 mL min . Elemen-
tal micro-analysis was performed with a Vario Micro Cube
analyzer of Elementar Analysen-systeme or an EA 3000 elemental
analyzer from HEKtech.
1H, CH(CH
3
)
2
), 1.83 (s, 3H, CH
3
), 1.18 (d,
J
3
(CH ), 1.10 (d,
3
)
2
J
H,H = 7.0 Hz, 3H, CH(CH
3
)
2
3
,
100.68 MHz) d, ppm: 175.6 (C@S), 160.4 (Benzo-C2), 150.0
(Benzo-C7a), 136.0 (Ph-C1), 130.0 (Benzo-C3a), 129.3 (Benzo-C6),
129.0 (Ph-C3 or C5), 128.1 (Ph-C4), 127.5 (Benzo-C5), 126.3 (Ph-
C3 or C5), 125.0 (Ph-C2/6), 124.8 (Benzo-C7), 122.0 (Benzo-C4),
105.3 (p-Cym-C4), 100.7 (p-Cym-C1), 88.0 (p-Cym-C2 or C6), 85.7
ꢀ1

A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
9
(p-Cym-C6 or C2), 84.2 (p-Cym-C3 or C5), 84.0 (p-Cym-C5 or C3),
Acknowledgments
3
3 2 3 2 3 2 3
0.7 (CH(CH ) ), 23.0 (CH(CH ) ), 21.7 (CH(CH ) ), 18.5 (CH ). ESI-
2+
MS (positive mode, acetone) m/z: 535.9802 {2–2Cl} , 520.0443
Antimicrobial screening was performed by CO-ADD (The Com-
munity for Antimicrobial Drug Discovery), funded by the Well-
come Trust (UK) and the University of Queensland (Australia)
+
{
2–2Cl–CH
3 2 3 2
} . C24H25Cl N RuS , Calc.: C 48.73, H 4.26, N 7.10, S
1
0.84; Found, C 48.70, H 4.38, N 7.11, S 10.74%. (For the character-
1
ization data of 2 given in Ref. [23], the assignments of the H NMR
signals were missing, only one NH signal was given and no
NMR data were reported. There was a typo mistake in the elemen-
tal analysis data of the published compound).
1
3
C
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.poly.2019.114175.
6
Q
[
RuCl(
ATR, diamond)
CC/CN), 1589, 1568, 1466, 1379, 1220, 1154, 1085, 831, 775.
g -p-Cym)(L )] (3): Yield: 70% (113 mg, 0.27 mmol). IR
ꢀ
1
(
m, cm : 3393 (br, NH), 2964 (w, CH), 1624 (w,
1
H
References
3
3
NMR (CDCl , 400.40 MHz) d, ppm: 11.46 (br, 1H, NH), 9.26 (d, JH,
3
3
H
= 5.3 Hz, 1H, H2), 8.28 (d,
J
H,H = 8.2 Hz, 1H, H4), 8.14 (d,
J
H,
[1] N.P.E. Barry, P.J. Sadler, Chem. Commun. 49 (2013) 5106;
A.L. Noffke, A. Habtemariam, A.M. Pizarro, P.J. Sadler, Chem. Commun. 48
(2012) 5219;
3
H
= 7.3 Hz, 1H, H7), 7.68 (m, 1H, H6), 7.59 (d,
J
H,H = 7.6 Hz, 1H,
3
H5), 7.55 (m, 1H, H3), 6.29 (d,
H6), 5.92 (m, 2H, p-Cym-H2 or H6/p-Cym-H3 or H5), 5.72 (d,
JH,H = 5.8 Hz, 1H, p-Cym-H2 or
G. Gasser, N. Metzler-Nolte, Curr. Opin. Chem. Biol. 16 (2012) 84.
3
J
H,
[
2] A. Merlino, Coord. Chem. Rev. 326 (2016) 111.
3
H
= 5.9 Hz, 1H, p-Cym-H3 or H5), 2.64 (sep,
J
H,H = 7.2 Hz, 1H, CH
[3] V. Brabec, J. Kasparkova, Coord. Chem. Rev. 376 (2018) 75.
[4] K. Gupta, D. Tyagi, A.D. Dwivedi, S.M. Mobin, S.K. Singh, Green Chem. 17 (2015)
4618;
B. Therrien, Coord. Chem. Rev. 253 (2009) 493.
[5] P.J. Dyson, Chimia 61 (2007) 698.
3
(
CH
3
)
2
), 8.05 (s, 3H, CH
3
), 1.06 (d,
H,H = 6.9 Hz, 3H, CH(CH
J
H,H = 6.9 Hz, 3H, CH(CH ),
3 2
)
3
13
0
1
1
.91 (d,
J
)
3 2
) ppm.
3
C NMR (CDCl ,
00.68 MHz): d = 154.5 (C2), 146.2 (C8), 139.4 (C8a), 138.7 (C4),
30.1 (C7), 129.2 (C5), 128.8 (C4a), 126.4 (C6), 123.2 (C3), 103.9
[
6] C. Scolaro, A. Bergamo, L. Brescacin, R. Delfino, M. Cocchietto, G. Laurenczy, T.J.
Geldbach, G. Sava, P.J. Dyson, J. Med. Chem. 48 (2005) 4161;
R.E. Aird, J. Cummings, A.A. Ritchie, M. Muir, R.E. Morris, H. Chen, P.J. Sadler, D.
I. Jodrell, Br. J. Cancer 86 (2002) 1652.
(
p-Cym-C4), 99.5 (p-Cym-C1), 84.6 (p-Cym-C2 or C6), 84.3 (p-
Cym-C6 or C2), 83.3 (p-Cym-C3 or C5), 83.0 (Cym p-Cym-C5 or
C3), 30.9 (CH(CH ), 22.2 (CH(CH ), 18.5 (CH ). ESI-MS (positive
mode, acetone) m/z: 382.0862 {3–Cl–H–CH
3
)
2
3
)
2
3
[7] R.E. Morris, R.E. Aird, P.S. Murdoch, H. Chen, J. Cummings, N.D. Hughes, S.
Parsons, A. Parkin, G. Boyed, D.I. Jodrell, P.J. Sadler, J. Med. Chem. 44 (2001)
+
3
} , 338.3414 {3–Cl–
O, Calc.: C 49.72, H 5.71, N
.10; Found: C 49.64, H 5.09, N 6.17%.
3616.
+
CH
6
3
–(CH
3
)
2
CH]} . C19
H21ClN
2
Ru.2.5H
2
[8] T. Bugarcic, A. Habtemariam, J. Stepankova, P. Heringova, J. Kasparkova, R.J.
Deeth, R.D.L. Johnstone, A. Prescimone, A. Parkin, S. Persons, V. Brabec, P.J.
Sadler, Inorg. Chem. (2008) 47.
[
9] A. Habtemariam, M. Melchart, R. Fernandez, S. Perssons, I.D.H. Oswald, A.
Parkin, F.P.A. Fabbiani, J.E. Davidson, A. Dawson, R.E. Aird, D.I. Jodrell, P.J.
Sadler, J. Med. Chem. 49 (2006) 6858.
4.3. Density functional theory (DFT) calculations
[
10] N. Sunduru, K. Srivastava, S. Rajakumar, S.K. Puri, J.K. Saxena, P.M.S. Chauhan,
Bioorg. Chem. Lett. 19 (2009) 2570;
Ground-state geometry optimization and TDDFT calculations
were performed with Gaussian03 [37] using B3LYP [27], and the
basis set LANL2DZ (including LANL2DZ ECP) [27]. The starting
coordinates were obtained from the crystal structure (CCDC
D.E. Fuerst, E.N. Jacobsen, J. Am. Chem. Soc. 124 (2005) 12964;
A.M. Mansour, J. Therm. Anal. Calorim. 123 (2016) 571.
11] D.E. Fuerst, E.N. Jacobsen, J. Am. Chem. Soc. 124 (2005) 12964;
K.F. Khaled, Electrochim. Acta 54 (2009) 4345.
[
1
940322) without any symmetry restrictions. Vibrational modes
[12] M.A. Halcrow, G. Christou, Chem. Rev. 94 (1994) 2421.
[
[
13] S.R. Hubbard, J.H. Till, Rev. Biochem. 69 (2000) 373.
14] M. Laura Soriano, J.T. Lenthall, K.M. Anderson, S.J. Smith, J.W. Steed, Chem. Eur.
J. 16 (2010) 10818.
were calculated at the same level of theory. TD DFT calculations
were performed by the CAM-B3LYP [25]/LANL2DZ method using
the default continuum model (PCM) to introduce the solvent effect
[15] (a) L. Colina-Vegas, L. Luna-Dulcey, A.M. Plutín, E.E. Castellano, M.R.
Cominetti, A.A. Batista, Dalton Trans. 46 (2017) 12865;
for CHCl
.4. Biological activity testing
The antimicrobial activities and cell viabilities were assessed
3
.
(
b) S. Parveen, K.K.H. Tong, M.K. Rauf, M. Kubanik, M.A. Shaheen, T. Sohnel, S.
M.F. Jamieson, M. Hanif, C.G. Hartinger, Chem. Asian J. 14 (2019) 1262.
[
[
[
16] M. Kalidasan, R. Nagarajprakash, K. Mohan Rao, Transition Met. Chem. 40
4
(
2015) 531.
17] K.R. Barnes, S.J. Lippard, Met. Ions Biol. Syst. 42 (2004) 143;
J. Reedijk, Proc. Natl. Acad. Sci. USA 100 (2003) 3611.
18] M. Chaves-Ferreira, Inês S. Albuquerque, D. Matak-Vinkovic, A.C. Coelho, S.M.
Carvalho, L.M. Saraiva, C.C. Romão, G.J.L. Bernardes, Angew. Chem. 127 (2015)
according to standard broth microdilution assays [34] (Supporting
Information) recommended by NCCLS for bacteria and yeasts
1188;
(
M07-A8 and M27-A2) and the standards of the European Commit-
tee on Antimicrobial Susceptibility Testing (EDef7.1). [RuCl( -Cl)
, and compounds 1–3 were initially assessed at a
fixed concentration (usually 32 g/ml or 20 M), with a maximum
H. Tabe, K. Fujita, S. Abe, M. Tsujimoto, T. Kuchimaru, S. Kizaka-Kondoh, M.
Takano, S. Kitagawa, T. Ueno, Inorg. Chem. 54 (2015) 215;
F. Zobi, B. Spingler, Inorg. Chem. 51 (2012) 1210.
l
6
(g -p-Cym)]
2
[
[
[
19] M.P. Sullivan, M.K. Nieuwoudt, G.A. Bowmaker, N.Y.S. Lam, D. Truong, D.C.
l
l
Goldstone, C.G. Hartinger, Chem. Commun. 54 (2018) 6120.
20] I.W. McNae, K. Fishburne, A. Habtemariam, T.M. Hunter, M. Melchart, F. Wang,
M.D. Walkinshaw, P.J. Sadler, Chem. Commun. (2004) 1786.
21] Y. Takezawa, P. Bockmann, N. Sugi, Z. Wang, S. Abe, T. Murakami, T. Hikage, G.
Erker, Y. Watanabe, S. Kitagawa, T. Ueno, Dalton Trans. 40 (2011) 2190.
[22] M.P. Sullivan, M. Groessel, S.M. Meier, R.L. Kingstone, D.C. Goldstone, C.G.
Hartinger, Chem. Commun. 53 (2017) 4246.
23] L. Shadap, S. Diamai, V. Banothu, D.P.S. Negi, U. Adepally, W. Kaminsky, M.R.
Kollipara, J. Organomet. Chem. 884 (2019) 44.
[24] A.M. Mansour, A. Friedrich, Polyhedron 131 (2017) 13.
25] T. Yanai, D.P. Tew, N.C. Handy, Chem. Phys. Lett. 393 (2004) 51.
26] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270, J. Chem. Phys. 1985, 82, 284.
27] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
of 0.5% DMSO in the final assay concentration, against a series of
bacterial and fungal pathogens; Staphylococcus aureus ATCC
4
7
inosa ATCC 27853, Candida albicans ATCC 90028 and Cryptococcus
neoformans var. grubii H99; ATCC 208821. For a toxic compound,
a follow-up hit confirmation was triggered, where the toxicity
was measured by means of a dose–response assay against the
same strains
3300, Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC
00603, Acinetobacter baumannii ATCC 19606, Pseudomonas aerug-
[
[
[
[
[
[
28] A.M. Mansour, Polyhedron 78 (2014) 10.
29] C. Pretl, G. Tosi, P. Zannini, J. Inorg. Nucl. Chem. 41 (1979) 485;
A.M. Mansour, Appl. Organomet. Chem. 32 (2018).
Declaration of Competing Interest
[30] C.S. Allardyce, P.J. Dyson, D.J. Ellis, S.L. Heath, Chem. Commun. (2001) 1396.
[31] G. Ferraro, A.M. Mansour, A. Merlino, Dalton Trans. 47 (2018) 10130.
[32] A.M. Mansour, O.R. Shehab, Eur. J. Inorg. Chem. (2019) 2830.
[33] M.A. Blaskovich, J. Zuegg, A.G. Elliott, M.A. Cooper, ACS Infect. Dis. 1 (7) (2015)
285.
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.

1
0
A.M. Mansour, K. Radacki / Polyhedron 175 (2020) 114175
[
34] J. Jimenez, I. Chakraborty, M. Rojas-Andrade, P.K. Mascharak, J. Inorg. Biochem.
68 (2017) 13.
35] S.B. Jensen, S.J. Rodger, M.D. Spicer, J. Organomet. Chem. 556 (1998) 151.
36] M. Taha, N.H. Ismail, W. Jamil, K.M. Khan, U. Salar, S.M. Kashif, F. Rahim, Y.
Latif, Med. Chem. Res. 24 (2015) 1310;
D.M. Wiles, T. Suprunchuk, J. Chem. Eng. Data 14 (4) (1969) 506.
37] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
V.G. Zakrzewski, J.A. Montgomery, R.E. Stratmann, J.C. Burant, S. Dapprich, J.M.
Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M.
Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A.
Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K.
Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox,
T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C. Gonzalez, M.
Challacombe, P.M.W. Gill, B.G. Johnson, W. Chen, M.W. Wong, J.L. Andres, M.
Head-Gordon, E.S. Replogle, J.A. Pople, GAUSSIAN 03 (Revision A.9), Gaussian,
Inc., Pittsburgh, 2003.
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