Preparation, structure and microbial evaluation of metal complexes of the second generation quinolone antibacterial drug lomefloxacin

Article abstract of DOI:10.1016/j.molstruc.2010.07.041

Lomefloxacinate of Y(III), Zr(IV) and U(VI) were isolated as solids with the general formula; [Y(LFX)₂Cl₂]Cl·12H ₂O, [ZrO(LFX)₂Cl]Cl·15H₂O and [UO ₂(LFX)₃](NO₃)₂·4H ₂O. The new synthesized complexes were characterized with physicochemical and diverse spectroscopic techniques (IR, UV-Vis. and ¹H NMR spectroscopies) as well as thermal analyses. In these complexes lomefloxacin act as bidentate ligand bound to the metal ions through the pyridone oxygen and one carboxylate oxygen. The kinetic parameters of thermogravimetric (TGA) and its differential (DTG), such as entropy of activation, activation energy, enthalpy of activation and Gibbs free energy evaluated by using Coats-Redfern and Horowitz-Metzger equations for free lomefloxacin and three complexes were carried out. The bond stretching force constant and length of the UO bond for the [UO₂(LFX) ₃](NO₃)₂·4H₂O complex were calculated. The antimicrobial activity of lomefloxacin and its metal complexes was tested against different bacterial species, such as Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) as Gram-positive and Gram-negative bacterial species and also against two species of antifungal, penicillium (P. rotatum) and trichoderma (T. sp.). The three complexes are of a good action against three bacterial species but the Y(III) complex exhibit excellent activity against Pseudomonas aeruginosa (P. aeruginosa), when compared to the free lomefloxacin.

Full text of DOI:10.1016/j.molstruc.2010.07.041

Journal of Molecular Structure 981 (2010) 130–138
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Preparation, structure and microbial evaluation of metal complexes of the
second generation quinolone antibacterial drug lomefloxacin
*
Sadeek A. Sadeek , Walaa H. El-Shwiniy
Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 May 2010
Received in revised form 21 July 2010
Accepted 26 July 2010
Available online 4 August 2010
Lomefloxacinate of Y(III), Zr(IV) and U(VI) were isolated as solids with the general formula;
[
Y(LFX)
2
Cl
2
]Clꢀ12H
2
O, [ZrO(LFX)
2
Cl]Clꢀ15H
2
O and [UO
2
(LFX)
3
](NO
3
)
2
ꢀ4H
2
O. The new synthesized com-
plexes were characterized with physicochemical and diverse spectroscopic techniques (IR, UV–Vis. and
1
H NMR spectroscopies) as well as thermal analyses. In these complexes lomefloxacin act as bidentate
ligand bound to the metal ions through the pyridone oxygen and one carboxylate oxygen. The kinetic
parameters of thermogravimetric (TGA) and its differential (DTG), such as entropy of activation, activa-
tion energy, enthalpy of activation and Gibbs free energy evaluated by using Coats–Redfern and Horo-
witz–Metzger equations for free lomefloxacin and three complexes were carried out. The bond
Keywords:
LFX
TGA
UV–Vis. spectra
Infrared
stretching force constant and length of the U@O bond for the [UO
2
(LFX)
3
](NO
3 2
) ꢀ4H
2
O complex were cal-
culated. The antimicrobial activity of lomefloxacin and its metal complexes was tested against different
bacterial species, such as Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas aeru-
ginosa (P. aeruginosa) as Gram-positive and Gram-negative bacterial species and also against two species
of antifungal, penicillium (P. rotatum) and trichoderma (T. sp.). The three complexes are of a good action
against three bacterial species but the Y(III) complex exhibit excellent activity against Pseudomonas aeru-
ginosa (P. aeruginosa), when compared to the free lomefloxacin.
Kinetic parameters
1
H NMR
Ó 2010 Elsevier B.V. All rights reserved.
1
. Introduction
Fluoroquinolones belong to a group of synthetic antimicrobial
or LFX to bovine serum albumin (BSA) in physiological solution
were investigated by multi-spectroscopy. Copper ion plays an
important role in organism’s growth, cell division, protein synthe-
sized, the activity of metal enzymes and induce the conformation
of nucleic acid changed [9].
Lomefloxacin hydrochloride (Formula 1) sold under the follow-
ing brand names in English speaking countries Maxaquin, Okacyn,
Uniquin is one of the second generation drug of the quinolone anti-
biotics, transcriptase inhibitor and stable under ordinary condi-
tions with color off – white to yellow crystals.
The crystal structures of several free quinolone molecules have
been determined [10–14]. It is interesting to note that in most
cases the carboxylic group is not deprotonated and the hydrogen
atom of this group is hydrogen bonded to an adjacent 4-oxo atom.
In a few examples [15–18], the carboxylic group is protonated and
the molecule thus exists in a zwitterionic form with protonated
terminal nitrogen of the piperazine ring in a solid state.
agents being clinically used over the past thirty years and derived
from basic structure of nalidixic acid and have substituents at N-1,
C-5, C-7; position 8 and a fluorine atom at position 6. Some fluoro-
quinolones have been used in the development of anticancer drugs,
and others have demonstrated anti-HIV activity [1–3].
Fluoroquinolones inhibit the bacterial DNA gyrase or the topo-
isomerase IV enzyme, resulting the inhibition of DNA replication
and transcription [4–7]. Fluorine atom at position 6 enhances gyr-
ase inhibition and cell penetration. Piperazinyl substituents pro-
vide activity against Gram-negative bacteria and pyrrolidinyl
moity is active against Gram-positive cocci. The function substi-
tuted at position 8 is to control anaerobe activity [7].
The complexation of lomefloxacin with five metal ions (Al3+,
Ca2+, Mg , Bi , and Fe ) commonly found in antacid or vitamin
preparations has been studied. The pharmaceutical and biophar-
maceutical implications of the effects of metal ion complexation
on the aqueous solubility of lomefloxacin are discussed [8]. The
binding reactions of lomefloxacin–copper(II) complex (LFX–Cu)
2+
3+
3+
Crystal structures of quinolone complexes indicate that neutral
quinolones in the zwitterionic state are capable of forming simple
complexes [19–25]. The mechanism of the interaction between
quinolone and metal cations was chelation between the metal
and the 4-oxo and adjacent carbonyl groups. Since these functional
groups are required for antibacterial activity. Also the crystal struc-
*
Corresponding author.
1
ture of free lomefloxacin was used together with H NMR data on
E-mail address: Sadeek59@yahoo.com (S.A. Sadeek).
0
022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.07.041

S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
131
O
O
by using atomic absorption method. A spectrometer model PYE-
UNICAM SP 1900 fitted with the corresponding lamp was used
for this purposed. Electronic spectra of lomefloxacin and the iso-
lated solid complexes were obtained in the region of 800–
F
OH
2
00 nm using UV-3101PC Shimadzu. Thermogravimetric (TGA)
and differential (DTG) thermogravimetric analyses were carried
out under N -atmosphere using detectors model TGA-50H Shima-
2
dzu. The rate of heating of the sample was kept at 10 °C/min. Molar
N
N
ꢂ4
conductivities in DMSO at 7.0 ꢁ 10 M were measured on CON-
SORT K410.
+
H N
2
F
Cl-
2.1. Synthesis of lomefloxacin metal complexes
An ethanolic solution (20 ml) of lomefloxacin hydrochloride
(
1 mmol, 0.3878 g) and NaOH (1 mmol, 0.04 g) was added to an
Formula 1. 4-(3-Carboxy-1-ethyl-6,8-difluoro-4-oxo-1,4-dihydroquinolin-7-yl)-2-
methylpiperazin-1-iumchloride.
ethanolic solution of YCl (0.5 mmol, 0.0977 g) and the reaction
mixture was stirred for 3 days at 30 °C in water bath. The solution
3
was left for slow evaporation, after that a yellowish white
the aluminum complexes in molecular modeling of the lomefloxa-
cin-Al (3:1) complex [14]. The authors suggested that three
lomefloxacin molecules are coordinated to aluminum through car-
boxylic oxygen and 4-keto oxygen. The synthesis and characteriza-
tion of new metal complexes with fluoroquinolones antibacterial
agents are of great importance for understanding the drug-metal
ion interaction and taking into account their potential pharmaco-
logical use.
To continue our investigation in this area [26–30], we report in
the present article, the isolation and characterization of new metal
complexes formed from the interaction of lomefloxacin with Y(III),
Zr(IV) and U(VI) in the solvent. The prepared solid complexes are
characterized using spectroscopic and thermal analysis techniques.
The thermal behavior of these complexes was also studied. The
antibacterial activity of the investigated complexes was tested
against two Gram-negative bacteria such as Escherichia coli
[
Y(LFX)
was filtered under vacuum, washed with ethanol and dried. In a
similar way, the Faint yellowish and Light green [ZrO(LFX) Cl]
Clꢀ15H O and [UO (LFX) ](NO ꢀ4H O complexes were prepared
by using methanol and acetone as a solvent instead of ethanol
and using ZrOCl O and UO (NO O in 1:2 and 1:3 M ra-
2
Cl
2
]Clꢀ12H
2
O product was deposited.The solid obtained
2
2
2
3
3
)
2
2
2
ꢀ8H
2
2
3
)
2
ꢀ6H
2
tios. Unfortunately we were not able to obtained appropriate
monocrystals to perform X-ray diffraction analysis. Qualitative
black ring test for ionic nitrate using freshly prepared FeSO
tion and concentrated sulfuric acid, a black ring of FeSO
4
solu-
ꢀNO is
4
formed led to the presence of nitrate as counter ions in the ura-
nyl/LFX complex and for the other complexes the qualitative reac-
tions revealed the presence of chloride as counter ions. The three
complexes were characterized by their elemental analysis, infra-
1
red, electronic, H NMR and thermal analyses.
(E. coli) and Pseudomonas aeruginosa (P. aeruginosa) and one
Gram-positive species Staphylococcus aureus (S. aureus) and anti-
fungal activity was also investigated against two species, penicil-
lium (P. rotatum) and trichoderma (T. sp.).
2.2. Antimicrobial activity
Antibacterial activity of the ligand and its metal complexes was
investigated by a previously reported modified method of Beecher
and Wong [31], against different bacterial species, such as S. aureus,
E. coli and P. aeruginosa and antifungal screening was studied
against two species, P. rotatum and T. sp. The tested microorgan-
isms isolates were isolated from Egyptian soil and identified
according to the standard mycological and bacteriological keys
for identification of fungi and bacteria as stock cultures in the
microbiology laboratory, Faculty of Science, Zagazig University.
The nutrient agar medium for antibacterial was (0.5% Peptone,
0.1% Beef extract, 0.2% Yeast extract, 0.5% NaCl and 1.5% Agar–
2
. Materials and methods
Metal salts and solvents were purchased from Merck Germany.
lomefloxacin was obtained from Sigma, these materials used with-
out further purification.
The infrared spectra of the three solid complexes, lomefloxacin
and the final products of the thermogravimetric analysis were re-
corded from KBr discs using FTIR 460 plus, 1H NMR spectra were
recorded on Varian Mercury VX-300 NMR Spectrometer using
Agar) and for antifungal (3% Sucrose, 0.3% NaNO
3 2 4
, 0.1% K HPO ,
DMSO-d
6
as solvent. C, H, N and halogen elemental analysis were
0.05% KCl, 0.001% FeSO , 2% Agar–Agar) was prepared and then
4
carried out on a Perkin Elmer CHN 2400. The percentage of Y(III),
Zr(IV) and U(VI) metal ions were determined gravimetrically by
transforming the solid products into oxide, and also determined
cooled to 47 °C and seeded with tested microorganisms. After
solidification 5 mm diameter holes were punched by a sterile
cork-borer. The investigated compounds, i.e., ligand and their com-
Table 1
Elemental analysis and physico-analytical data of lomefloxacin (LFX) and its metal complexes.
Compounds MWt. (MF.)
Yield%
Mp (°C)
Color
Content (calculated) found
%
C
%H
%N
%M
–
%Cl
LFX
–
110
170
190
180
White
(52.60)
52.59
(36.65)
36.63
(35.47)
35.47
(40.29)
40.27
(5.16)
5.16
(5.59)
5.59
(5.91)
5.89
(4.28)
4.28
(10.83)
10.82
(7.55)
7.51
(7.30)
7.30
(9.14)
9.14
(9.57)
9.54
(6.17)
6.15
–
3
87.801 (C17
Y(LFX) Cl
]Clꢀ2H
113.4 (C34
Cl]Clꢀ15H
150.22 (C34
(LFX) ](NO
519 (C51
H
20
N
3
O
O
3
F
2
Cl)
Cl Y)
Cl Zr)
[
1
2
2
2
79.80
90.20
69.20
Yellowish white
Faint yellowish
Light green
(7.99)
H
62
N
6
O
18
F
4
3
7.99
(7.93)
7.91
(15.67)
15.66
[
ZrO(LFX)
2
2
O
1
H
68
N
6
O
22
F
4
2
[
UO
2
3
3
)
2
ꢀ4H
2
O
(10.14)
10.12
1
H
65
N
11
O
21
F
6
U)

1
32
S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
plexes, were introduced in Petri-dishes (only 0.1 ml) after dissolv-
Table 2
Infrared frequenciesa (cm
ꢂ1
)
and tentative assignmentsb for: (A) lomefloxacin
ꢂ4
ing in DMSO at 7.0 ꢁ 10 M. These culture plates were then incu-
(
[
LFX) as
UO (LFX)
a
ligand; (B) [Y(LFX)
2
Cl
2 2
]Clꢀ12H O, (C) [ZrO(LFX)
2
Cl]Clꢀ5H
2
O, and (D)
bated at 37 °C for 20 h for bacteria and for 7 days at 30 °C for fungi.
The activity was determined by measuring the diameter of the
inhibition zone (in mm). Growth inhibition was calculated with
reference to the positive control, i.e., lomefloxacin.
2
3
](NO O.
3
)
2
ꢀH
2
A
B
C
D
Assignments
3438m,br 3430m,br
3414m,br 3438m,br
m
m
m
2
(O–H); H O; COOH
(C–H); aromatic
(C–H); aliphatic
3056m
2966vw
2933m
2890w
2845m
2757m
3055m
2928ms
2891w
2846m
2759w
2703ms
3055m
2927m
2849w
2756w
2700m
3059m
2987w
2926w
2847m
3
. Results and discussion
Lomefloxacinates of Y(III), Zr(IV) and U(VI) were prepared as
solids of a color characteristic of the metal ions. The prepared com-
plexes are hydrates with various degrees of hydration and with a
metal to ligand ratio a mounting to 1:2 for Y(III), Zr(IV) and 1:3
for U(VI). The structures of the complexes suggested from the ele-
mental analysis agree well with their proposed formula (Table 1).
The found values of elemental analysis agree well with the calcu-
lated percentage of C, H, N and halogen data are in a well agree-
ment with each other and prove the molecular formulas of the
prepared complexes. The physical characteristic of these com-
plexes are given in Table 1. The molar conductance values of the
lomefloxacin and their Y(III), Zr(IV) and U(VI) complexes were
2701ms
2661w
þ
2663w
2588vw
2458s
–
1617s
1527w
2660vw
2444s
2461m
m
(—NH
)
2
2
2
1
–
635vw
455s
725vs
–
–
m
m
m
(C@O); COOH
ꢂ
1620vs
1529vs
1627s
1582w
as(COO )
1618vs
(C@O)phenyl breathing
modes
1
1
1
1
526ms
497s
471w
456vw
1496s
1470vs
–
1524s
1451vw
1473vs
–CH: deformations of CH
2
1413w
–
ꢂ
2
ꢂ1
1385w
1335m
1286vw
1250m
1200ms
1170w
1093ms,sh 1090m
1042ms,sh 1049m
1014vw
1395vw
1330ms
1281vw
1254ms
1210m
1388vs
1328ms
ms(COO )
found at 56.18, 281.27, 253.66 and 293.18 S cm mol at 25 °C,
respectively.
1
1
1
1
1
1
331s
d
b
2
(–CH )
298vw
257ms
208s
166s
116m
1266s
m
m
m
(C–O),
(C–N),
(C–C)
1203w
1168vw
1133w
1090m
1051ms
1024vw
904vw
846w
3.1. Infrared absorption studies
1175vw
r 2
d (–CH )
The infrared spectra of lomefloxacin and their [Y(LFX)
2
Cl
2
]
1093ms
1043s
Clꢀ12H
2
O, [ZrO(LFX)
2
Cl]Clꢀ15H
2
O
and [UO
2
(LFX)
3
](NO
3
)
2
ꢀ4H
2
O
1014m
complexes are usually similar, Fig. 1. The presence of the broad
ꢂ1
978w
980vw
928s
890m
849w
807ms
–
929ms
889m
–CH-bend; phenyl
water bands in the 3414–3438 cm zone confirms the presence
9
8
30s
89s
of water molecules in all complexes Table 2, however, the absence
ꢂ1
of the very strong absorption band at 1725 cm , arising from the
850m
8
–
–
–
7
6
06ms
carboxylic group (COOH) for under investigation complexes, states
–
–
927vs
810ms
–
737ms
660m
m
m
m
as(U@O)
(U@O)
(Zr@O)
–
–
s
808ms
740m
653m
ꢂ
39ms
50m
735ms
655m
d
b
(COO )
m
(M–O) + ring
deformation
5
5
4
50w
14m
80w
545w
509m
482vw
566w
546m
454vw
550vw
520w
441m
w = Weak, sh = shoulder, v = very, br = broad, and d = bending.
a
s = Strong.
b
m
= Stretching.
that the hydrogen ions in the lomefloxacin molecules are substi-
tuted by the metal ions and the lomefloxacinate is the coordination
ligand [14,25,32,33]. The stretching asymmetric (
m
as) of carboxyl-
ꢂ1
ate group between 1617, 1620 and 1627 cm and of the symmet-
ꢂ1
ric vibrations
(m )
s
from 1385 to 1395 cm
confirm these
ꢂ1
hypotheses. The band observed at 1618 cm in the spectrum of
the free lomefloxacin has been assigned before to the stretching
vibration of the carbonyl group
m
(C@O) [3,25,34–37]. The shift of
ꢂ1
the carbonyl group to a lower value, Table 2, from 1618 cm to
ꢂ1
ꢂ1
ꢂ1
1
527 cm
for Y(III), 1529 cm
for Zr(IV) and 1582 cm
for
U(VI) indicates coordination of lomefloxacin through oxygen atom
of the carbonyl group. The coordination of the metal ions via oxy-
gen carboxylate is confirmed by the
m
(M–O) bands at 655, 545 and
ꢂ1
ꢂ1
5
09 cm for Y(III), 653, 566, 546 and 454 cm for Zr(IV) and at
ꢂ1
6
60, 520 and 441 cm for U(VI). According to the above discussion
the lomefloxacinate is coordinated with the metal ions as biden-
tate through oxygen atom of carbonyl and one oxygen atoms of
carboxylic group.
The stretching vibration
free lomefloxacin and its complexes at almost the same region,
Fig. 1. Infrared spectra of: (A) lomefloxacin (LFX) as
Y(LFX) Cl O, (C) [ZrO(LFX) Cl]Clꢀ15H O, and (D) [UO (LFX)
]Clꢀ12H
complexes.
a
ligand; (B)
](NO
ꢀ4H
þ
m
(NH ) observed in the spectra of
[
2
2
2
2
2
2
3
3
)
2
2
O
2

S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
133
ꢂ1
2
663–2444 cm . The infrared spectra of the prepared complexes
all are infrared active. The four vibrations of the UO
2
unit in the com-
0
00
0
0
display changes in the aromatic ring vibrations in comparison to
the corresponding absorption bands for free ligand (Table 2).
plex are of the type 3A and A , these are
m
s
(U@O), A ;
mas(U@O), A ;
0
00
d(UO ), A and d(UO ), A . The data given in Table 2 show that the
2 2
For [UO
2
(LFX)
3
](NO
3
)
2
ꢀ4H
2
O complex, the most probable struc-
m
as(U@O) absorption band of this complex occurs as a very strong
ꢂ1
ture is shown in Formula 2, where the six oxygen atoms of their
LFX ligands occupy equatorial positions around the central metal
atom U(VI), forming a plane containing the six-membered rings
and the two oxygen atoms of the uranyl group occupy axial posi-
tions. The complex possesses one plane of symmetry and no axes
singlet at 927 cm
810 cm as a medium strong. These assignments for the stretching
s
and the m (U@O) absorption band occur at
ꢂ1
vibrations of the uranyl group, UO
known for many dioxouranium(VI) complexes [28,29,38,39]. The
(U@O) value was used to calculate both the bond length and force
constant, F(U@O), for the UO bond in our complex according to the
2
, agree quite well with those
m
s
of symmetry therefore may have C
s
symmetry and are expected to
2
display 459 vibrational fundamentals which are all monodegener-
ate. These are distributed between motions of the type A and A ;
known method [39,40]. The calculated bond length and force con-
0
00
ꢂ1
stant values are 1.732 Å and 641.01 N m
.
NH2+
NH2+
F
N
N
F
N
N
F
F
O
O
O
Cl
O
O
O
O
O
O
O
O
Zr
Cl
Y
N
N
N
N
Cl
O
O
F
F
F
F
+H2N
+H2N
+
H N
NH2+
2
F
N
F
N
F
F
O
O
N
N
O
U
O
O
H
O
H
O
O
O
O
F
O
H
N
N
+
H N
F
2
Formula 2. The coordination mode of Y(III), Zr(IV) and U(VI) with lomefloxacin.

1
34
S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
3.2. UV–Vis. spectra
The formation of the metal complexes was also confirmed by
UV–Vis. spectra. Fig. 2 shows the electronic solid reflection spectra
of free lomefloxacin and its metal complexes and Table 3 reports
the reflection spectra from 800 to 200 nm. The reflection spectrum
of free lomefloxacin shows bands at 214, 298 and 304 nm which is
ꢃ
ꢃ
assigned to p–p and n–p transitions. For the three complexes the
absent of the reflection band at 298 nm and the shift of the other
reflectance bands kmax to higher and to lower values attributed to
Fig. 2. Electronic reflection spectra of: (A) lomefloxacin (LFX) as a ligand; (B)
2
Y(LFX) Cl O, (C) [ZrO(LFX) O, and (D) [UO (LFX) ](NO O
[
2
2
]Clꢀ12H
2
2
Cl]Clꢀ15H
2
2
3
3
2
) ꢀ4H
complexes.
Table 3
UV–Vis. spectra of lomefloxacin and its metal complexes (200–800 nm).
Assignments (nm)
LFX
LFX complex with
Y(III)
Zr(IV)
U(VI)
ꢃ
p–
p
transitions
214
225, 238
248
–
252
–
259
–
2
98
ꢃ
n–p
transitions
304
–
303, 321
311, 355
566
307, 342
379
3
55
Fig. 3. TGA and DTG diagrams of: (A) lomefloxacin (LFX) as
Y(LFX) Cl O, (C) [ZrO(LFX) Cl]Clꢀ15H O, and (D) [UO (LFX)
]Clꢀ12H
complexes.
a
ligand; (B)
[
2
2
2
2
2
2
3
](NO
)
3 2
ꢀ4H
2
O
Ligand–metal charge-transfer
567
567

S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
135
Table 4
The maximum temperature Tmax (°C) and weight loss values of the decomposition stages for Y(III), Zr(IV), and U(VI) lomefloxacins.
Compounds (MF.)
Decomposition
Tmax (°C)
Weight loss (%)
Calc.
Found
LFX (C17
H
20
3
N O
3
F
2
Cl)
First step
319, 553
100
99.99
Total loss, residue
100, 0.0
100, 0.0
[
Y(LFX)
2
Cl
2
]Clꢀ12H
2
O (C34
H
62
N
6
O
18
F
4
Cl
3
Y)
Zr)
First step
Total loss, residue
310, 509, 604
89.86
89.86, 10.14
89.98
89.98, 10.02
[
ZrO(LFX)
2
Cl]Clꢀ15H
2
O (C34
H
68
N
6
O
22
F
4
Cl
2
First step
Second step
Total loss, residue
46
302, 583
7.83
71.03
78.86, 21.14
7.82
71.19
79.01, 20.99
[
UO
2
(LFX)
3
](NO
3
)
2
ꢀ4H
2
O (C51H
65
N
11
O
21
F
6
U)
First step
Second step
Total loss, residue
158
335, 482, 551
4.74
69.59
74.33, 25.67
4.73
69.57
74.30, 25.70
complexation behavior of lomefloxacin towards metal ions. The
complexes of Y(III), Zr(IV) and U(VI) show new band around
this associated with the loss of the three lomefloxacin ligand and
nitrate counter ion forming uranium oxide as a final product.
To supporting our conclusion of the absence of all ligand and
counter ions and forming metal oxides, we made infrared spectra
for the residue of ignition, which clearly shows the bands associ-
ated to the metal oxides and disappeared the ban22ds characteris-
tic for the lomefloxacin and counter ions.
According to these conculsions, the decomposition mechansims
proposed for LFX and thier complexes are summarized as
follows:
5
66 nm, which may be assigned to the ligand to metal charge-
transfer [3,27–29,34].
3.3. Thermogravimetric analyses
Thermogravimetric (TGA) and differential thermogravimetric
(
DTG) were carried out for the free lomefloxacin and isolated solid
complexes [Y(LFX) Cl O, [ZrO(LFX) Cl]Clꢀ15H and
]Clꢀ12H
UO (LFX) ](NO O under N flow. Fig. 3 represents the TGA
ꢀ4H
The proposed structure formula on the basis of the results dis-
cussed in this paper located as shown in Formula 2.
2
2
2
2
2
O
[
2
3
3
)
2
2
2
and DTG curves and Table 4 gives the maximum temperature val-
ues for decomposition along with the corresponding weight loss
values for each step of the decomposition reaction. These data sup-
port the proposed complexes structures.
3.4. The kinetic studies
There has been increasing interest in determining rate-depen-
dent parameters of solid-state non-isothermal decomposition
reactions by analysis of TGA curves. Several equations have been
proposed to analyze a TGA curves and obtain values for kinetic
parameters [41–47].
In the present investigation the general thermal behavior of the
lomefloxacin ligand and the three complexes in terms of stability
ranges, peak temperatures and values of kinetic parameters, are
shown in Table 5 (Supplementary data). The kinetic parameters
have been evaluated using the following methods and the results
obtained by these methods are compared with one another. The
following two methods are briefly discussed.
Lomefloxacin is thermally stable in the temperature range 25–
2
50 °C. Decomposition of the lomefloxacin started at 250 °C and fin-
ished at 600 °C with one stage at two maxima 319 and 553 °C and is
accompanied by a weight loss of 99.95%. The hydrated lomefloxaci-
nate of Y(III) is stable up to 245 °C and then decomposed in one step
at three maxima 310, 509 and 604 °C to yttrium oxide with interme-
diate formation of very unstable products which were not identified.
2 2
The thermal decomposition of [ZrO(LFX) Cl]Clꢀ15H O complex
proceeds with two main degradation steps. The first stage of
decomposition occurs at a temperature maximum of 46 °C. The
found weight loss associated with step is 7.82% and may be attrib-
uted to the loss of the five water molecules which is in good agree-
ment with the calculated values of 7.83%. The second stage of
decomposition occurs at two maxima 302 and 583 °C and the
weight loss found at this stage equals to 71.19% corresponds to loss
3.4.1. Coats–Redfern equation
The Coats–Redfern Eq. (1), which is a typical integral method,
can be represented as:
6
2
C H
4
2 2 4 2
+ 4C H + 2NH Cl + 4HF + 4NO + 4CO + 7H O.
Z
Z
ꢀ
ꢃꢁ
a
T2
d
ð1 ꢂ
a
a
A
u
ꢂE
For U(VI) complex the thermal decomposition exhibits two
¼
exp
dT
ð1Þ
n
main degradation steps. The first step of decomposition occurs
from 30 to 250 °C is accompanied by a weight loss of 4.73% in
agreement with the theoretical values 4.74% for the loss of the four
uncoordinated water molecules. The second step of decompostion
occurs at two maxima 302 and 583 °C with a weight loss of 69.59%
0
Þ
T1
RT
For convenience of integration, the lower limit T
1
is usually taken as
zero. This equation on integration gives:
ꢄ
3
2
19;553
C
ð1Þ C17
H
20
N
3
O
3
F
2
Cl
!
6C
2
H
2
þ 3CO þ C
2
H
C
4
þ 2HF þ 0:5H
2
þ 1:5N
þ 4HF þ 3HCl þ 10:5H
Þ2ClꢅCl ꢀ 10H O þ 5H
þ 2NH
Þ2 þ 4H
þ 6HF þ CO þ 11NO þ 3H
2
þ HCl
ꢂ
ꢃ
310;509;604
ꢄ
ð2Þ YðC17
H
19
N
3
O
3
F
Þ2Cl
2
Cl ꢀ 12H
Þ Cl Cl ꢀ 15H
2
O
!
YO1:5 þ 17C
2
H
2
2
O þ 6NO
ꢂ
ꢃ
ꢄ
4
6
C
ð3Þ ZrOðC17
H
H
19
19
N
N
3
O
O
3
3
F
2
2
O ! ½ZrOðC17
H
19
N
3
O
3
F
2
2
2
O
2
ꢂ
ꢃ
302;583
ꢄ
C
ð4Þ ZrOðC17
3
F
2
Þ Cl Cl ꢀ 10H
2
O
!
ZrO
2
þ 10C þ 6C
2
H
4
þ 4C
2
H
2
4
Cl þ 4HF þ 4NO þ 4CO þ 7H
2
O
2
ꢂ
ꢃ
ꢄ
ꢂ
ꢃ
1
58
C
ð5Þ UO
2
ðC17
H
19
19
N
3
O
3
F
2
Þ3 ðNO
3
Þ ꢀ 4H
2
O ! UO
2
ðC17
H
19
N
3
O
3
F
2
Þ3 ðNO
3
2
O
2
ꢂ
ꢃ
335;482;551
ꢄ
C
ð6Þ UO
2
ðC17
H
N
3
O
3
F
2
Þ3 ðNO
3
Þ2
!
UO
2
þ 10C þ 2C
2
H
4
þ 18C
2
H
2
2
O þ 0:5H
2

1
36
S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
Table 5
Thermal behavior and kinetic parameters determined using the Coats–Redfern (CR) and Horowitz–Metzger (HM) operated for Lomefloxacin and their complexes.
Compounds
Decomposition range
K)
T
(K)
s
Method Parameter
Ra
SDb
(
ꢃ
ꢂ1
ꢃ
ꢃ
ꢃ
D
(kJ mol )
E
A (s
)
D
S
D
H
G
ꢂ1
ꢂ1 ꢂ1
ꢂ1
ꢂ1
(kJ mol
)
(J mol
K
)
(kJ mol
)
1
1
LFX
523–673
03–873
592
695
CR
HM
CR
137.71
137.97
114.12
102.66
1.242 ꢁ 10
ꢂ38.23
ꢂ30.03
ꢂ159.52
ꢂ121.82
132.79
133.04
108.34
96.88
155.42
150.82
219.21
181.55
0.8885 0.33
0.8781 0.16
0.9749 0.17
0.9886 0.05
1
4
6
1
3.33 ꢁ 10
6.73 ꢁ 10
6.27 ꢁ 10
7
HM
7
8
4
5
[
[
[
Y(LFX)
2
Cl
2
]Clꢀ12H
2
O
523–682
34–919
299–484
27–634
303–523
40–758
583
782
CR
HM
CR
97.87
110.77
107.07
82.38
3.02 ꢁ 10
3.92 ꢁ 10
2.71 ꢁ 10
1.27 ꢁ 10
16.19
83.96
ꢂ107.29
ꢂ85.91
90.30
105.92
100.06
85.88
155.60
156.01
232.01
207.30
0.8149 0.53
0.8629 0.22
0.9567 0.17
0.9833 0.05
7
ꢂ168.08
ꢂ155.21
HM
ZrO(LFX)
2
Cl]Clꢀ15H
2
O
319
575
CR
HM
CR
18.20
17.87
87.50
98.76
ꢂ222.32
ꢂ159.58
ꢂ118.35
ꢂ93.38
ꢂ214.88
ꢂ173.85
ꢂ215.25
ꢂ200.43
15.55
15.22
82.72
93.98
86.47
66.12
150.77
147.77
0.9464 0.16
0.9526 0.09
0.9714 0.16
0.9775 0.07
6
7
5
7.87 ꢁ 10
HM
15.87 ꢁ 10
UO
2
(LFX)
3
](NO
)
3 2
ꢀ4H
2
O
431
608
CR
HM
CR
24.03
39.55
40.16
44.24
53.52
74.43
72.25
20.45
35.94
35.10
39.18
113.06
110.87
166.00
161.04
0.9511 0.23
0.9863 0.06
0.9774 0.12
0.9721 0.07
5
HM
42.91 ꢁ 10
a
Correlation coefficients of the Arrhenius plots.
Standard deviation.
b
ꢄ
Þꢅ
ꢄ
ꢅ
ꢂ lnð1 ꢂ
a
ꢂE
AR
And
ln
¼
þ ln
ð2Þ
2
ꢃ
T
RT
uE
ꢃ
ꢃ
ꢃ
D
G ¼
D
H ꢂ T
D
S
ð8Þ
A plot of left-hand side (LHS) against 1/T was drawn using origin 6.0
program and the fit line is produced. E is the energy of activation in
kJ mol and calculated from the slope and A in (s ) from the inter-
cept. The entropy of activation
by using Eq. (3):
ꢃ
It is clear that the thermal decomposition process of the three com-
plexes indicate that the complexes are thermally stable. The posi-
tive
complexes. The greater negative values of
complexes are more ordered with thermodynamic stability. The
greater positive values of E indicate that the processes involving
in translational, rotational, vibrational states and a changes in
mechanical potential energy for complexes.
ꢂ1
ꢂ1
ꢂ1
ꢃ
ꢂ1
D
S in (J K mol ) was calculated
ꢃ
D
H
values postulate an endothermic nature of the formed
ꢃ
D
S reveal that the three
ꢀ
ꢁ
Ah
D
Sꢃ ¼ R ln
ð3Þ
ꢃ
K
B
T
s
B s
where K is the Boltzmann constant, h is the Plank’s constant and T
is the DTG peak temperature [48].
3
.4.2. Horowitz–Metzger equation
The Horowitz–Metzger equation is an illustrative of the approx-
imation methods. These authors derived the relation:
"
ꢂng#
1
ꢃ
f1 ꢂ ð1 ꢂ
a
Þ
E h
log
¼
for n–1
ð4Þ
2
ð1 ꢂ nÞ
2:303RTs
When n = 1, the LHS of Eq. (4) would be log[ꢂlog(1 ꢂ
a
)]. For a first-
order kinetic process the Horowitz–Metzger equation may be writ-
ten in the form:
ꢄ
ꢀ
ꢁꢅ
ꢃ
W
W
a
c
E h
log log
¼
ꢂ log 2:303
ð5Þ
2
2:303RTs
= w
where h = T ꢂ T
the reaction; w = mass loss up to time t. The plot of log[log(w
)] versus h was drawn and found to be linear from the slope of
s
, w
c
a
a
ꢂ w, w = mass loss at the completion of
a
/
w
c
ꢃ
which E was calculated. The pre-exponential factor, A, was calcu-
lated from the equation:
ꢃ
E h
2
A
¼
h
ꢆ
ꢇi
ð6Þ
ꢃ
E
RTs
u
exp ꢂ
RT
s
ꢃ
The entropy of activation,
thalpy of activation,
lated from;
D
S , was calculated from Eq. (3). The en-
ꢃ
ꢃ
D
H , and Gibbs free energy,
D
G , were calcu-
Fig. 4. 1H NMR spectra of: (A) [Y(LFX)
complexes in DMSO, dTMS..
Cl]Clꢀ15H
2
Cl
2 2
]Clꢀ12H O and (B) [ZrO(LFX)
2
2
O
ꢃ
ꢃ
D
H ¼ E ꢂ RT
ð7Þ

S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
137
Table 6
1
H NMR values (ppm) and tentative assignments for: (A) lomefloxacin (LFX) as a
ligand; (B) [Y(LFX)
2
Cl
2
]Clꢀ12H
2
O, and (C) [ZrO(LFX)
2
Cl]Clꢀ15H
Assignments
dH, –CH
2
O.
A
B
C
1
.31
1.28, 1.302
.42, 1.47
3.07, 3.14
.17, 3.37
1.17, 1.29, 1.37
1.47, 1.52
3.09, 3.13,
3.32, 3.36
3.56, 3.74
4.59
3
1
3
.51–3.61
.98
dH, –NH; piperazine
3
3
–
3.57, 3.59
4.58, 4.59
dH, –N–CH
dH, H
2
2
O
4
7.88
7.92, 8.94
–
.59, 4.61
+
7
7
1
.00
.57, 8.95
1.00
7.87
7.91, 8.93
–
dH, – NH
dH, –CH
dH, –COOH
2
2
aromatic
1
3
.5. The H NMR studies
To create harmony between the parts of the study, we embod-
Fig. 5. Statistical representation for biological activity of lomefloxacin and its
complexes.
1
ied the H NMR spectra of the lomefloxacin and its complexes with
Y(III) and Zr(IV) in Fig. 4. While their peaks assignments are given
1
in Table 6. The H NMR spectra of the compounds isolated from
be considered: (i) the chelate effect; (ii) the nature of the ligands;
systems containing quinolones and metal [26–30,49]; a minor
shifts were found. Small shifts could be due to the change in the
counter anion or to a different association of the quinolone
molecules.
(
iii) the total charge of the complex; (iv) the nature of the ion neu-
tralizing the ionic complex; and (v) the nuclearity of the metal cen-
ter in the complex. All of the five above mentioned factors are
present to our compounds except the second factor.
1
The H NMR data for the prepared solid complexes are in agree-
ment with coordination through the carboxylic group (disappeared
of the H(COOH) signal in our complexes) and small shifts for all
other peaks are shown, thus showing that the magnetic environ-
4
. Conclusion
ment of the aromatic rings has changed significantly with coordi-
1
nation. Also, according to the H NMR data for [Y(LFX)
2
Cl
2
]
Three new Y(III), Zr(IV) and U(VI) complexes with lomefloxacin
Clꢀ12H
2
O; dH, H
2
O: 4.57, 4.58, 4.59, 4.61 ppm and for [ZrO
(
LFX) in ethanol, methanol and acetone as a solvent have been syn-
(
LFX)
2
Cl]Clꢀ15H
2
2
O; dH, H O: 4.58 ppm which not found in the free
thesized. Elemental analysis, infrared, ultraviolet–visible, nuclear
magnetic resonance, conductance measurements and thermo-
gravimetric (TGA) and differential thermal analyses (DTG) have
been used to characterize the isolated solid complexes. The kinetic
parameters of thermogravimetric (TGA) and its differential (DTG),
such as entropy of activation, energy of activation, enthalpy of acti-
vation and Gibbs free energy evaluated by using the Coats–Redfern
and Horowitz–Metzeger equations. The bond stretching force con-
lomefloxacin, indicate the presence of water molecules.
3.6. Antibacterial and antifungal activities
The efficiencies of the lomefloxacin ligand and their metal com-
plexes have been investigated against two Gram-negative, E. coli
and P. aeruginosa and one Gram-positive, S. aureus, and antifungal
screening was studied against two species such as P. rotatum and T.
sp. microorganisms. The results presented in Table 7 and Fig. 5.
The results of the antibacterial study of the lomefloxacin and
the three complexes (Table 7) have inhibitory action against all
the three types of bacteria and no antifungal activity for ligand
and their metal complexes. All complexes show a good activity
against Gram-negative and Gram-positive microorganisms than
lomefloxacin and on the other hand, Y(III) complex exhibit excel-
lent activity against Gram-negative, P. aeruginosa. The nature of
the metal ion coordinated to a drug may have a significant role
to this diversity. In general for metal complexes showing antimi-
crobial activity, the following five principal factors [50–54] should
stant and length of the U@O bond for the [UO
2
3 3
(LFX) ](NO )
2 2
ꢀ4H O
complex were calculated. Antimicrobial studies were carried out
against several bacterial and fungal species. The results showed
significant increase in antibacterial activity of metal complexes
as compared with free ligand and no antifungal activity observed
for ligand and their complexes.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2010.07.041.
Table 7
The inhibitation diameter zone values (mm) for LFX and its compounds.
Compounds
Microbial species
Bacteria
Fungi
E. coli
P. aeruginosa
S. aureus
T. sp
P. rotatum
LFX
17 ± 0.1155
13 ± 0.2887
24 ± 0.2309
0
0
0
0
0
0
0
0
0
0
+
2
+3
+3
[Y(LFX)
[ZrO(LFX)
[UO (LFX)
2
Cl
2
]Clꢀ12H
Cl]Clꢀ15H
](NO
ꢀ4H
2
O
25.5 ± 0.2887
36 ± 0.3464
36 ± 0.1472
+
2
+2
+2
2
2
O
25.8 ± 0.1155
26 ± 0.4041
32 ± 0.7044
+
2
+2
+2
2
3
3
)
2
2
O
24 ± 0.4619
22 ± 0.201
30 ± 0.3464
Control (DMSO)
0
0
0
Statistical significance: (NS) not significant, P < 0.05; (+1) significant, P > 0.05; (+2) highly significant, P > 0.01; (+3) very highly significant, P > 0.001; student’s t-test.

1
38
S.A. Sadeek, W.H. El-Shwiniy / Journal of Molecular Structure 981 (2010) 130–138
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