Quick and simple formation of different nanosized charge-transfer complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics

Article abstract of DOI:10.1016/j.crci.2015.05.019

A quick and simple procedure for the synthesis of nanosized complexes of the drug moxifloxacin (MOX) is described. MOX nanoparticles were synthesized via charge-transfer (CT) interactions with the organic acceptors picric acid (PA), chloranilic acid (CLA) and chloranil (CHL). The structure and morphology of these nanoparticles were fully characterized using physicochemical techniques, such as UV-visible, IR, ¹H NMR and ¹³C NMR spectroscopies, XRD, SEM, TEM, and elemental and thermal analyses. Notably, it has been found that the complexation of MOX with an organic acceptor leads to well-organized nanoparticles with a main diameter in the range of 10-20nm. Interestingly, the direct carbonization of the complex containing the PA acceptor leads to nanoporous carbon material with uniform morphology. This method is an efficient way to remove and utilize discarded MOX antibiotic in other products.

Full text of DOI:10.1016/j.crci.2015.05.019

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Contents lists available at ScienceDirect
Comptes Rendus Chimie
www.sciencedirect.com
´
Full paper/Memoire
Quick and simple formation of different nanosized
charge-transfer complexes of the antibiotic drug
moxifloxacin: An efficient way to remove and utilize
discarded antibiotics
Abdel Majid A. Adam a, , Moamen S. Refat a,b, Hosam A. Saad a,c
*
a Department of Chemistry, Faculty of Science, Taif University, Al-Haweiah, PO Box 888, 21974 Taif, Saudi Arabia
b Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
c 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:
A quick and simple procedure for the synthesis of nanosized complexes of the drug
moxifloxacin (MOX) is described. MOX nanoparticles were synthesized via charge-transfer
(CT) interactions with the organic acceptors picric acid (PA), chloranilic acid (CLA) and
chloranil (CHL). The structure and morphology of these nanoparticles were fully
characterized using physicochemical techniques, such as UV–visible, IR, 1H NMR and
13C NMR spectroscopies, XRD, SEM, TEM, and elemental and thermal analyses. Notably, it
has been found that the complexation of MOX with an organic acceptor leads to well-
organized nanoparticles with a main diameter in the range of 10–20 nm. Interestingly, the
direct carbonization of the complex containing the PA acceptor leads to nanoporous carbon
material with uniform morphology. This method is an efficient way to remove and utilize
discarded MOX antibiotic in other products.
Received 20 March 2015
Accepted after revision 28 May 2015
Available online xxx
Keywords:
Moxifloxacin
Nanostructured materials
SEM
TEM
Nanoporous carbon
´
ß 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
an important topic in pharmacology, chemistry, biology
and medicine. Such interactions play crucial roles in many
The study of nanostructured materials has become a
popular area of research because of their unique physical
and chemical properties. Furthermore, the charge-transfer
(CT) or proton-transfer (PT) interactions between drugs or
biological compounds and small molecular acceptors have
attracted considerable interest because of their unique
physical and chemical properties and wide range of
applications [1–9]. The chemistry of these interactions is
processes; therefore, understanding these interactions is
important for understanding drug-receptor binding and
the drug’s mechanism of action as well as obtaining
quantitative estimates of drugs [10–16]. To investigate
these roles more fully, the physical and chemical proper-
ties of drug-acceptor complexes can be enhanced if the
complexes are prepared on the nanoscale. For several
years, we have investigated the synthesis, characterization
and application of various CT and PT interactions [17–
32]. As part of our continuing interest in this field, in this
work, we sought to obtain nanoscale CT or PT complexes of
the drug moxifloxacin (MOX) with various organic
*
Corresponding author.
E-mail address: majidadam@yahoo.com (A.M.A. Adam).
http://dx.doi.org/10.1016/j.crci.2015.05.019
1631-0748/ß 2015 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Adam AMA, et al. Quick and simple formation of different nanosized charge-transfer
complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics. C. R. Chimie
(2015), http://dx.doi.org/10.1016/j.crci.2015.05.019

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A.M.A. Adam et al. / C. R. Chimie xxx (2015) xxx–xxx
H
(MOX; C21H24FN3O4ꢂHCl; 437.89) was supplied by Sig-
OH
ma–Aldrich Chemical Co. (USA). The organic acceptors
picric acid (PA; C6H3N3O7; 229.10), chloranilic acid (CLA;
C6H2Cl2O4; 208.98) and chloranil (CHL; C6Cl4O2; 245.88)
(Fig. 1) were purchased from Merck (Darmstadt, Germany)
and used without modification. HPLC-grade methanol was
also purchased from Merck (Darmstadt, Germany). Stan-
dard stock solutions of the drug MOX and acceptors at a
concentration of 5.0 ꢃ 10ꢁ3 M were freshly prepared prior
to each series of measurements by dissolving precisely
weighed quantities in a 100 mL volumetric flask. The stock
solutions were protected from light. Solutions for spectro-
scopic measurements were prepared by mixing appropri-
ate volumes of the MOX and acceptor stock solutions with
the solvent immediately before recording the spectra.
OCH3
O2N
NO2
N
HCl
OH
N
F
N
O
H
H
NO2
PA
O
MOX
O
O
Cl
OH
Cl
Cl
Cl
Cl
Cl
HO
O
O
CHL
CLA
2.2. Instruments
Fig. 1. (Color online.) The structure of drug moxifloxacin (MOX) and
organic acceptors.
To ascertain the constituents, purity and compositions of
the synthesized complexes, the carbon, hydrogen, and
nitrogen contents were analyzed using a PerkinElmer
2400 series CHN microanalyzer (USA). The UV–Vis spectra
were recorded in methanol over a wavelength range of 200–
800 nm using a PerkinElmer Lambda 25 UV–Vis double-
beam spectrophotometer with quartz cells. The path length
of the cells was 1.0 cm. The infrared (IR) spectra of the solid
products (as KBr discs) were acquired at room temperature
using a Shimadzu FT–IR spectrophotometer (Japan) over the
acceptors and to explore the benefits of CT interactions in
removing and utilizing discarded amounts of this drug.
MOX, or 1-cyclopropyl-7-(2,8-diazobicyclo[4.3.0]nonane)-
6-fluoro-8-methoxy-1,4-dihydro-4-oxo-3-quinoline car-
boxylic acid), is
a fourth-generation fluoroquinolone
antibiotic. Its structure is shown in Fig. 1. Currently, this
drug is being extensively used in the treatment of
respiratory system disease for its broad spectrum of
antimicrobial activity against respiratory tract pathogens,
including Gram-positive and Gram-negative organisms,
anaerobic bacteria and atypical respiratory tract pathogens
[33]. This work focused on the following objectives:
range of 4000–400 cmꢁ1 1H and 13C NMR spectra were
.
collected on a Bruker DRX-250 spectrometer operating at
600 MHz. The measurements were performed at ambient
temperature using DMSO-d6 (dimethylsulfoxide, d6) as the
solvent and TMS (tetramethylsilane) as the internal refer-
ence. Thermogravimetric(TG)analysiswasperformedusing
ꢀ
ꢀ
ꢀ
synthesizing CT or PT nanoparticles of MOX with
different organic acceptors (i.e. PA, CLA and CHL);
verifying the complexation stoichiometry using CHN
elemental analysis and spectrophotometric titrations;
calculating the formation constant (K), molar extinction
a
Shimadzu TGA–50H thermal analyzer (Japan) with
standard platinum TG pans. The measurements were
conducted at a constant heating rate of 10 8C/min over
the temperature range of 25–600 8C in a nitrogen atmo-
sphere using alumina powder as the reference material. The
X-ray diffraction (XRD) profiles were obtained using a
PANalytical X’Pert PRO X-ray powder diffractometer equip-
ped with a Ge(III) secondary monochromator. Cu Ka1 was
employed as the radiation source, with a wavelength of
coefficient (e) and other spectroscopic data using the
Benesi–Hildebrand equations;
ꢀ
characterizing the nanoparticles by elemental and
spectroscopic data (UV–Vis, IR, 1H and 13C NMR);
obtaining the thermal properties using TG analysis;
determining the kinetic ꢁ thermodynamic parameters
ꢀ
ꢀ
0.154056 nm. The samples were scanned with 2u between
(i.e., E*, A,
D
S*,
D
H*, and
D
G*) using the Coats–Redfern and
58 and 908. The microstructure and morphology were
analyzed by a scanning electron microscope (SEM, Quanta
FEG 250 instrument). The instrument was operated at an
accelerating voltage of 20 kV. The particle size was analyzed
by transmission electron microscope (TEM, JEOL JEM-1200
EX II, Japan). The instrument was operated atan accelerating
voltage of 60–70 kV.
Horowitz–Metzger methods;
ꢀ
observing and differentiating the microstructures of
these nanoparticles using X-ray diffraction (XRD) and
scanning electron microscopy (SEM) techniques;
proving the nanometry using transmission electron
microscopy (TEM);
ꢀ
ꢀ
carbonizing the complexes to obtain a method for the
removal of this antibiotic as porous carbon material.
2.3. Preparation of materials
2.3.1. Nanoparticle syntheses
2. Experiment and calculations
A simple synthetic protocol was used for the prepara-
tion of nanostructured complexes of MOX. A typical
procedure for the preparation is briefly described as
follows. First, 2 mmol of MOX in a methanol solvent
(20 mL) was added to 20 mL of a solution containing
2 mmol of the acceptor (either PA, CLA or CHL) in the same
2.1. Chemicals and solutions
All the chemicals used were of analytical grade and
were used as purchased. Moxifloxacin hydrochloride
Please cite this article in press as: Adam AMA, et al. Quick and simple formation of different nanosized charge-transfer
complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics. C. R. Chimie
(2015), http://dx.doi.org/10.1016/j.crci.2015.05.019

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3
solvent. The resulting mixture was stirred at room
temperature for approximately half an hour. A change in
color occurred, and the solution was allowed to evaporate
slowly at room temperature, resulting in the precipitation
of the solid complexes. The precipitates were isolated,
filtered and further purified using the same system and a
recrystallization process to obtain the pure product. The
products were then collected and dried in vacuo for 48 h.
The excellent agreement between the experimental and
calculated values of C, H and N indicated that the
synthesized nanoparticles were free of impurities. The
stoichiometry of the interaction between the drug MOX
and the acceptors was found to have a 1:1 ratio.
C–F, C5O). Anal. calcd. for C27H28FClN6O11 (666.99), C,
48.58; H, 4.20; N, 12.59; Found, C, 48.38; H, 4.29; N, 12.31.
2.3.1.3. MOX–CLA complex. Reddish-brown powder; IR
(KBr, cmꢁ1): nmax 3400
n
(O–H)carboxylic
(C5O)carboxylic, 1629 (C5O)ketonic, 1326
as(C–N). 1H NMR (DMSO-d6, 600 MHz):
= 0.99–1.19 (m,
, 2839–2717
n
(NH2+), 1711
n
n
n
d
4H, 2 CH2, 200 and 300 protons), 1.81 (m, 4H, 2 CH2, 30 and 40
protons), 2.65 (t, 2H, CH2, 20 protons), 2.94 (m, 1H, CH, 40a
proton), 3.62 (s, 3H, OCH), 3.65 (d, 2H, CH2, 50 protons),
3.74 (d, 2H, CH2, 70 protons), 3.85 (m, 1H, NCH, 70a proton),
4.19 (m, 1H, NCH, 100 proton), 5.78 (s, 2H, chloranilic acid
OH), 7.66 (d, 1H, C5 proton), 8.63 (s, 1H, C2 proton), 9.05 (s,
0
2H, H2N+1 proton), 10.10 (s, 1H, COOH proton). 13C NMR
2.3.1.1. MOX free drug. Pale yellow powder; IR (KBr, cmꢁ1):
(DMSO-d6, 600 MHz): d = 7.72, 9.24, 17.15, 20.21 (4 CH2),
ymax 3394
(C5O)carboxylic, 1621
NMR (DMSO-d6, 600 MHz):
n
(O–H)carboxylic
(C5O)ketonic, 1323
= 0.97–1.17 (m, 4H, 2 CH2, 200
,
2817–2705
n
(NH2+), 1708
as(C–N). 1H
24.18 (CH), 42.90, 53.88 (2 NCH2), 54.90, 54.94 (1 NCH,
1 NCH2), 62.61 (OCH3), 107.6, 107.8, 115.8, 117.8, 135.2,
137.0, 140.5, 152.2, 155.3, 162.8, 164.4, 165.1, 167.2 (Ar–C,
C–Cl, C–F, C5O). Anal. calcd. for C27H27Cl3FN3O8 (646.87),
C, 50.09; H, 4.17; N, 6.49; Found, C, 50.15; H, 4.30; N, 6.92.
n
n
n
d
and 300 protons), 1.79 (m, 4H, 2 CH2, 30 and 40 protons), 2.65
(t, 2H, CH2, 20 protons), 2.92 (m, 1H, CH, 40a proton), 3.59 (s,
3H, OCH), 3.62 (d, 2H, CH2, 50 protons), 3.73 (d, 2H, CH2, 70
protons), 3.84 (m, 1H, NCH, 70a proton), 4.17 (m, 1H, NCH,
2.3.1.4. MOX–CHL complex. Pale brown powder; IR (KBr,
100 proton), 7.65 (d, 1H, C5 proton), 8.63 (s, 1H, C2 proton),
cmꢁ1): ymax 3390
n
n
(O–H)carboxylic, 2851
(C5O)carboxylic, 1623 (C5O)ketonic, 1325
NMR (DMSO-d6, 600 MHz):
= 0.99–1.20 (m, 4H, 2 CH2, 200
n
(NH2+), 1670
as(C–N); 1H
0
8.92 (s, 2H, H2N+1 proton), 10.19 (s, 1H, COOH proton). 13
C
n
n
NMR (DMSO-d6, 600 MHz):
d
= 7.70, 9.22, 17.15, 20.23
d
(4 CH2), 24.20 (CH), 42.92, 53.87 (2 NCH2), 54.95, 54.98
(1 NCH, 1 NCH2), 62.62 (OCH3), 107.5, 107.6, 117.4, 135.0,
137.2, 140.1, 152.2 (6 Ar–C), 155.0 (C–F), 167.4, 177.2
(2 C5O). Anal. calcd. for C21H24FN3O4ꢂHCl (437.89), C,
57.55; H, 5.71; N, 9.59; Found, C, 57.52; H, 5.76; N,
9.63. The structure of the drug MOX with its corresponding
atom numbering scheme is shown in Fig. 2.
and 300 protons), 1.80 (m, 4H, 2 CH2, 30 and 40 protons), 2.60
(t, 2H, CH2, 20 protons), 2.90 (m, 1H, CH, 40a proton), 3.61 (s,
3H, OCH), 3.64 (d, 2H, CH2, 50 protons), 3.71 (d, 2H, CH2, 70
protons), 3.81 (m, 1H, NCH, 70a proton), 4.20 (m, 1H, NCH,
100 proton), 7.60 (d, 1H, C5 proton), 8.62 (s, 1H, C2 proton),
0
8.04 (s, 2H, H2N+1 proton), 10.08 (s, 1H, COOH proton). 13
C
NMR (DMSO-d6, 600 MHz):
d = 7.65, 9.18, 17.20, 20.25
(4 CH2), 24.24 (CH), 42.88, 53.85 (2 NCH2), 54.91, 54.90
(1 NCH, 1 NCH2), 62.58 (OCH3), 108.5, 109.1, 117.0, 135.8,
137.6, 139.8, 140.5, 152.8, 155.5, 166.9, 169.7, 175.4 (Ar–C,
C-Cl, C–F, C5O). Anal. calcd. for C27H25Cl5FN3O6 (683.77),
C, 47.38; H, 3.66; N, 6.14; Found, C, 47.15; H, 3.71; N, 6.50.
2.3.1.2. MOX–PA complex. Yellow powder; IR (KBr, cmꢁ1):
ymax 3390
n
(O–H)carboxylic, 2894–2798
(+N–H. . .Oꢁ), 1708
(C5O)carboxylic
1347
as(C–N). 1H NMR (DMSO-d6,
d
= 0.97–1.18 (m, 4H, 2 CH2, 200 and 300 protons),
n
(NH2+), 2675,
1623
2599, 2518
y
n
,
n
(C5O)ketonic
,
n
600 MHz):
1.81 (m, 4H, 2 CH2, 30 and 40 protons), 2.67 (t, 2H, CH2, 2’
protons), 2.93 (m, 1H, CH, 40a proton), 3.59 (s, 3H, OCH),
3.63 (d, 2H, CH2, 50 protons), 3.75 (d, 2H, CH2, 70 protons),
3.85 (m, 1H, NCH, 70a proton), 4.18 (m, 1H, NCH, 100 proton),
7.65 (d, 1H, C5 proton), 8.49 (s, 1H, HN+1 protons), 8.63 (s,
2.3.2. Preparation of carbon materials
The porous carbons were simply prepared by the direct
carbonization of the complex containing the PA acceptor in
a furnace at 400 8C for 1 h under N2 atmosphere. The as-
prepared non-activated carbon product was ground into
powder with a particle size of 2–3 mm and characterized
by XRD, SEM and TEM techniques.
1H, C2 proton), 8.79 (s, 2H, picric acid protons), 9.84 (s, 2H,
0
H2N+1 protons), 10.22 (s, 1H, COOH proton). 13C NMR
(DMSO-d6, 600 MHz):
d = 8.37, 9.57, 17.56, 20.49 (4 CH2),
34.11, 34.15, 48.59, 54.45, 54.50, (CH, NCH, NCH2), 61.74
(OCH3), 106.3, 118.9, 125.2, 134.4, 136.4, 140.41, 140.48,
141.7, 150.3, 152.2, 160.8, 165.8, 175.92, 175.95 (Ar–C,
2.4. Calculations
The spectroscopic data were used to calculate the
formation constant (K), the molar extinction coefficient (
[34], the energy of the interaction (ECT) [35], the oscillator
strength (f) [36], the transition dipole moment ( ) [37],
and the standard free energy ( G8) [38] for the synthesized
complexes in solution, using the equations described
elsewhere in the literature. Two different methods were
employed to evaluate the kinetic–thermodynamic para-
meters: the Coats–Redfern method and the Horowitz–
Metzger method. The kinetic–thermodynamic data were
used to calculate the activation energy (E*), the frequency
factor (A), the enthalpy of activation (H*), the entropy of
activation (S*) and the Gibbs free energy of activation (G*)
e)
m
4`
3`
N
3``
2``
1``
D
H
2`
1`
5`
OCH3
8
1
7
N
N
2
3
H
H
7`
OH
6
F
4
O
5
O
Fig. 2. (Color online.) The structure of drug MOX with atom numbering.
Please cite this article in press as: Adam AMA, et al. Quick and simple formation of different nanosized charge-transfer
complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics. C. R. Chimie
(2015), http://dx.doi.org/10.1016/j.crci.2015.05.019

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in the solid state using the Coats–Redfern [39] and
Horowitz–Metzger methods [40]. Finally, the particle size
of the complexes was estimated from their XRD patterns
based on the highest-intensity line, using the well-known
Debye–Scherrer formula [41].
interaction at 344 nm for MOX–PA, 325 nm for MOX–CLA,
and 335 nm for MOX–CHL. The stoichiometry of the MOX–
acceptor interactions in solution was obtained from the
spectrophotometric titrations by determining the conven-
tional molar ratio according to previously published
protocols [42]. The electronic spectra of the MOX–acceptor
systems were recorded at varying acceptor concentrations
and a constant MOX concentration. The composition of the
complexes was determined graphically by plotting the
absorbance on the ordinate against the volume of the
acceptor (in mL) on the abscissa. Representative spectro-
photometric titration plots based on the characterized
absorption bands are shown in Fig. 4. The results show that
the greatest interaction between MOX and each acceptor
occurred at a donor:acceptor ratio of 1:1, indicating that
1:1 complexes were formed. These stoichiometric values
are consistent with the data obtained by the elemental
analysis of the solid state complexes.
3. Results and discussion
3.1. Structural characterization
3.1.1. UV–visible measurements
MOX (5.0 ꢃ 10ꢁ4 M) was mixed with each acceptor
solution (5.0 ꢃ 10ꢁ4 M) in a methanol solvent, and the
reaction was allowed to proceed at room temperature. The
UV–visible spectrum of each reaction mixture was then
recorded against a reagent blank solution. A change in the
color was observed as the MOX and acceptor solutions
were mixed. These changes provided strong evidence of
interactions between the MOX and the acceptors. Fig. 3
displays the UV–visible absorption spectra of the MOX and
acceptors, along with the spectra of the prepared
complexes. It is clear from the spectra that each complex
exhibits an absorption band presumably caused by CT
3.1.2. The spectroscopic data
The 1:1 Benesi–Hildebrand equation [34] was used to
determine the spectroscopic parameters of the synthe-
sized complexes. Fig. 5 shows a representative 1:1 Benesi–
4
MOX
MOX
CLA
PA
Complex
Complex
3
2
1
0
344 nm
3
325 nm
2
1
0
300
400
500
300
400
500
λ (nm)
λ (nm)
MOX
CHL
Complex
3
2
1
0
335 nm
300
350
400
450
500
λ
(nm)
Fig. 3. (Color online.) Electronic absorption spectra of the MOX complexes with PA, CLA and CHL acceptors.
Please cite this article in press as: Adam AMA, et al. Quick and simple formation of different nanosized charge-transfer
complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics. C. R. Chimie
(2015), http://dx.doi.org/10.1016/j.crci.2015.05.019

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5
1:1
1.7
1.6
1.5
1.4
1:1
2.55
2.50
2.45
2.40
CLA complex
PA complex
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
mL added of acceptor
mL added of acceptor
2.0
1.8
1.6
1.4
1:1
CHL complex
1.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
mL added of acceptor
Fig. 4. (Color online.) Spectrophotometric titration curves for the MOX complexes with PA, CLA and CHL acceptors.
Hildebrand plot of the MOX complexes. The values of both
observed between the standard free energy change (
DG8)
K and
with the other spectroscopic parameters (e.g., f,
G8), are provided in Table 1. Fig. 5 reveals that the
e
have been determined from these data and, along
and the formation constant (K). The values of G8 become
more negative as the formation constant for the molecular
complex increases.
D
m
, ECT and
D
correlation coefficient (r) of the straight lines is > 0.99. The
complex containing the CHL acceptor shows a higher K
value than the other complexes. This high value of K
reflectsthe relatively highelectronacceptanceabilityof CHL
and suggests that the MOX–CHL complex is strongly bound
andhighlystable. Thestabilityofthecomplexesdecreasesin
the following order: MOX–CHL > MOX–CLA > MOX–PA. All
3.1.3. IR measurements
The IR absorption spectra of the solid complexes were
recorded in the wave number range 4000–400 cmꢁ1 using
KBr discs. The IR spectra of the solid products were
recorded and are depicted in Fig. 7. The IR spectrum of the
free MOX was characterized by principal absorption peaks
the
tion between MOX and the acceptors is exothermic and
spontaneous. The G8 values of the complexes for the
DG8 values are negative, indicating that the complexa-
at 3394 cmꢁ1 for
2950 cmꢁ1 for C–H symmetric and asymmetric stretching,
1708 and 1621 cmꢁ1 for (C5O), 1515 and 1457 cmꢁ1 for
(C5C), 1323 cmꢁ1 for (C–N), 1186 cmꢁ1 for monofluo-
n(O ꢁ H), 2817–2705 for
n
(NH2+),
D
n
n
different acceptors are ordered as follows: CHL > CLA > PA.
We note that this ordering is consistent with the stability of
the MOX complexes. Linear correlations were observed
between several pairs of spectroscopic parameters (Fig. 6).
For example, a very strong linear correlation (r = 0.9960)
exists between the oscillator strength (f) and the dipole
n
robenzene stretching, and 834 cmꢁ1 for C–H bending of
substituted benzene. The IR spectrum of the MOX–PA
complex is characterized by a group of medium bands at
2675, 2599 and 2518 cmꢁ1. These new broadened bands
are attributed to n
(+N–H) and confirm the migration of the
moment (
m
) in solution. This finding indicates that the
PA proton towards the nitrogen of the MOX quinoline ring
to form an intermolecular H-bonded ion pair (+N–H. . .Oꢁ).
Additionally, the characteristic band observed at
1323 cmꢁ1 that results from the
n(C–N) vibration of the
oscillator strength values of the complexes in solution
increased as their dipole moment values increased. In
addition, a very strong linear relationship (r = 0.9955) is also
Please cite this article in press as: Adam AMA, et al. Quick and simple formation of different nanosized charge-transfer
complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics. C. R. Chimie
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PA complex
CLA complex
1.6
1.2
0.8
0.4
0.0
2.5
2.0
1.5
1.0
0.5
0.0
100 150 200 250 300 350 400 450 500 550
100 150 200 250 300 350 400 450 500 550
(Cd+Ca)x10-6
(Cd+Ca)x10-6
CHL complex
2.0
1.5
1.0
0.5
0.0
100 150 200 250 300 350 400 450 500 550
(Cd+Ca)x10-6
Fig. 5. (Color online.) The 1:1 Benesi–Hildebrand plots of the MOX complexes with PA, CLA and CHL acceptors.
free MOX shifts to ꢄ 1347 cmꢁ1 in MOX–PA. The observed
pyrrolidine ring, and all of them are sp3 hybridized
nitrogens. They differ from each other in basicity, mainly
due to resonance, which decreases the basicity and the
steric hindrance. The most basic one is the nitrogen of the
piperidine ring, with its lone pair of electrons occupied by
the formation of the hydrochloride sat. The least basic one
is the nitrogen of the quinoline ring, with its lone pair of
electrons dispersed to the ring through the resonance with
shift in the n(C–N) band upon complexation suggests that
this group participated directly in the complexation. All
these observations indicate the presence of hydrogen
bonding in this complex [43–57].
The MOX molecule contains three nitrogen atoms in
(C–N) groups: the nitrogen of the piperidine ring, the
nitrogen of the quinoline ring, and the nitrogen of the
the
a, b unsaturated ketones. The middle one is the
nitrogen of the pyrrolidine ring, with its lone pair of
electron dispersed to the ring through the plus mesomeric
(+M) effect of the benzene ring along with the indicated
(–I) effect of the ortho fluorine atom. The last is the
nitrogen atom most expected to be able to accept the acidic
proton of PA. In the CLA and CHL complexes, the vibrational
Table 1
Spectral properties of the MOX complexes.
Complex
Property
MOX–PA
MOX–CLA
MOX–CHL
frequencies of
n(O–H) and n(C–N) of MOX do not shift,
lmax (nm)
Formation constant; K
(L/mol)
344
325
335
which indicates that these groups do not participate in the
complexation. The carbonyl and chloro groups in the CLA
or CHL acceptor are electron-withdrawing, removing
electron density from the aromatic ring and thereby
causing it to become an electron-accepting moiety. Thus,
because of the electron-withdrawing effect of the CLA or
CHL acceptor and the good electron-donating ability of the
MOX, the interaction between MOX and the acceptor can
103 ꢃ 104
106 ꢃ 104
135 ꢃ 104
Extinction coefficient;
emax (L/mol/cm)
Energy value; ECT (eV)
Oscillator strength; f
26 ꢃ 105
17 ꢃ 105
21 ꢃ 105
3.62
3.83
3.71
1.59
1.86
3.00
Dipole moment;
Standard free energy
change; G8 (kJ/mol)
m
3.40
–3.43 ꢃ 104
3.58
–3.44 ꢃ 104
4.62
–3.50 ꢃ 104
D
occur through
p
!
p* charge migration [58,59].
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Fig. 6. (Color online.) Linear correlations of some spectroscopic parameters.
3.1.4. 1H and 13C NMR measurements
the –COOH proton appeared as a singlet at 10.19 nm. The
signal due to the phenolic proton (–OH) of the PA acceptor,
The 600 MHz 1H and 13C NMR spectra of the synthe-
sized complexes were measured in DMSO-d6 at room
temperature and are shown in Figs. 8 and 9, respectively.
According to the 1H NMR spectrum of free MOX, the
protons of the piperidine ring were observed as a singlet
signal at 8.92 ppm corresponding to (2H, NH2+), and
which is observed at
d
ꢄ 11.94 ppm [60] in the spectrum of
the free PA acceptor, is no longer observed. Instead, a new
signal is observed at approximately ꢄ 8.49 ppm. This
singlet signal is assigned to the proton of the +NꢁH
species formed by proton-transfer from the OH group of PA
Fig. 7. (Color online.) A. IR spectrum of the free MOX. B. IR spectrum of the MOX–PA complex. C. IR spectrum of the MOX ꢁ CLA complex. D. IR spectrum of
the MOX–CHL complex.
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Fig. 8. (Color online.) A. 1H NMR spectrum of the MOX–PA complex. B. 1H NMR spectrum of the MOX–CLA complex. C. 1H NMR spectrum of the MOX–CHL
complex.
to the nitrogen atom of the MOX quinoline ring [61]. The
singlet peak observed at 9.05 and 8.04 ppm in the MOX–
CLA and MOX–CHL complexes, respectively, has been
assigned to the +NH2 protons of MOX. We note that these
peaks represent very small shifts relative to the analogous
peak in the spectrum of free MOX (8.92 ppm). The 13C
NMR spectrum of free MOX showed 20 resolved carbon
signals. The carbon signals of the seven CH2 groups were
complexes, common changes in the values of the 13C
chemical shifts in MOX can be observed as a result of its
complexation with the organic acceptors. The structures
of the synthesized complexes have been confirmed by IR,
1H and 13C NMR spectral data. The data obtained by these
techniques are consistent with each other and support the
predicted structures. The complexation of the drug MOX
with the PA acceptor leads to hydrogen bonding, whereas
observed at
54.98 ppm and the two CH carbons at
54.95. The aromatic carbons showed six signals at
d
7.70, 9.22, 17.15, 20.23, 42.92, 53.87, and
a direct
p
!
p* transition is observed between MOX and
d
24.20 and
the CLA or CHL acceptor. Fig. 10 illustrates the proposed
structures of the MOX complexes.
d
(107.5, 107.6), 117.4, 135.0, 137.2, 140.1, and 152.2 ppm.
The carbon signals of the two carbonyl groups were
3.2. Thermal characterization
observed at d 167.4 and 177.2 ppm, d 155.0 (C–F), and the
OCH3 carbon at 62.62 ppm. In the 13C NMR spectra of the
products, the appearance of 24, 23 and 22 distinct
resonant carbon signals in the spectra of the PA, CLA
and CHL complexes, respectively, is consistent with the
proposed molecular structure of these complexes. For all
3.2.1. Thermogram properties
The thermal decomposition and stability of the
synthesized complexes were investigated by TG
analysis. The possible thermal degradation patterns for
these complexes are collected in Table 2, and their
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9
O2N
NO2
O
N
O
F
H
N
O2N
OH
O
H
N
H
H
Cl
OCH3
H
H
N
Cl
Cl
MOX - PA
H
H
H
N
H
H
H
O
O
N
F
H
O
O
Cl
N
N
F
HO
Cl
H3CO
H3CO
Cl
O
N
Cl
O
OH
O
HO
O
HO
MOX - CHL
MOX - CLA
Fig. 10. (Color online.) Proposed structural formula for the proton-
transfer complex; MOX–PA and charge-transfer complexes; MOX–CLA
and MOX–CHL.
representative TG thermograms are depicted in
Fig. 11. The analysis of these thermograms provided the
following observations:
ꢀ
ꢀ
ꢀ
the observed weight loss is in excellent agreement with
the theoretical predictions;
the MOX–CHL complex exhibited good thermal stability
up to 200 8C;
the complexes are stable up to ꢄ 130, 150 and 200 8C for
MOX–PA, MOX–CLA and MOX–CHL, respectively. Thus,
these complexes are stable in the solid state at room
temperature and can be stored for several months
without degradation;
ꢀ
the CLA and CHL complexes exhibit a one-stage
degradation process, while the PA complex was ther-
mally decomposed in approximately two decomposition
steps;
ꢀ
ꢀ
the decomposition of the complexes is almost complete
without any carbon residue;
the degradation data stronglysupporttheformation ofthe
synthesized complexes and their proposed structures.
Table 2
Thermal decomposition data for the synthesized MOX complexes.
Compound Stages TG range TG% mass loss
Lost
(8C)
species
Fig. 9. (Color online.) A. 1H NMR spectrum of the MOX–PA complex. B. 1
H
Found Calculated
NMR spectrum of the MOX–CLA complex. C. 1H NMR spectrum of the
MOX–CHL complex.
MOX–PA
I
130–335 34.05
335–600 65.41
150–600 99.89
200–600 99.82
34.34
65.64
100.0
100.0
PA
II
I
MOX
MOX–LA
MOX + CLA
MOX + CHL
MOX–CHL
I
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PA complex
CLA complex
5
4
3
2
1
0
5
4
3
2
1
0
0
100
200
300
400
500
600
0
100
200
300
400
500
600
o
o
Tempreture [ C]
Tempreture [ C]
14
12
10
8
CHL complex
6
4
2
0
0
100
200
300
400
500
600
o
Tempreture [ C]
Fig. 11. (Color online.) TG thermogram plots of the MOX complexes with PA, CLA and CHL acceptors.
3.2.2. Kinetic properties
from the two methods are comparable and can be
considered to be in good agreement with each other. The
activation energy (E*) of the complexes is expected to
increase with the increasing thermal stability of the
complexes. Therefore, the E* value for the MOX–PA complex
is higher than for the other complexes, which indicates a
The kinetic–thermodynamic parameters (i.e., E*, A, H*, S*
and G*) associated with the MOX complexes were evaluated
graphically (Fig. 12) by employing the Coats–Redfern and
Horowitz–Metzger methods. The evaluated data are tabu-
lated in Table 3. The kinetic–thermodynamic data obtained
-0.2
CR method
HM method
-12.5
CLA
-0.4
CLA
-13.0
CHL
-0.6
CHL
PA
PA
-13.5
-0.8
-1.0
1.80
1.85
1.90
1.95
-10
-5
0
5
10
1000/T(K)
θ (Κ)
Fig. 12. (Color online.) Kinetic–thermodynamic plots for MOX complexes (CR; Coats–Redfern equation, HM; Horowitz–Metzger (HM) method).
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Table 3
Kinetic data of thermal decomposition determined using the Coats–Redfern (CR) and Horowitz–Metzger (HM) methods.
Compound
Method
Parameters
r
E*
A
(sꢁ1
D
S*
(J molꢁ1 Kꢁ1
D
H*
D
G*
(Jmolꢁ1
)
(J molꢁ1
)
)
)
(J molꢁ1
)
MOX–PA
MOX–CLA
MOX–CHL
CR
1.10 ꢃ 105
1.15 ꢃ 105
7.72 ꢃ 104
8.61 ꢃ 104
6.32 ꢃ 104
7.20 ꢃ 104
3.95 ꢃ 108
5.52 ꢃ 109
1.40 ꢃ 105
1.30 ꢃ 105
1.21 ꢃ 104
1.10 ꢃ 104
–8.32 ꢃ 101
–6.20 ꢃ 101
–1.48 ꢃ 102
–1.28 ꢃ 102
–1.65 ꢃ 102
–1.42 ꢃ 102
1.10 ꢃ 105
1.12 ꢃ 105
7.22 ꢃ 104
8.20 ꢃ 104
5.86 ꢃ 104
6.65 ꢃ 104
1.44 ꢃ 105
1.40 ꢃ 105
1.50 ꢃ 105
1.49 ꢃ 105
1.44 ꢃ 105
1.32 ꢃ 105
0.9984
0.9976
0.9975
0.9982
0.9994
0.9979
HM
CR
HM
CR
HM
higher thermal stability for this complex. Comparing the E*
values for the main decomposition step of the complexes,
we observed the following trend for the different acceptors:
materials and as a means to control the quality of the
synthesis. The surface morphology, nanometry, structural
features and characteristics of the synthesized complexes
were observed by XRD, SEM and TEM analysis. Fig. 13
shows the indexed XRD patterns of the synthesized
complexes, and Table 4 presents the XRD spectral data
for these complexes. The strongest diffraction peak was
PA > CLA > CHL. The negative values of D
S* indicate that the
activated complexeshave a more ordered structure than the
reactants. Moreover, these values suggest the formation of
donor–acceptor CT complexes [62]. The
D
S* values of the
complexes occur in decreasing order for the acceptors as
observed at diffraction angles 2u of 32.28, 13.128, and 6.948
follows: PA > CLA > CHL.
for the MOX–PA, MOX–CLA and MOX–CHL complexes,
respectively. The appearance of a strong and narrow sharp
diffraction peak indicated that the as-synthesized complex
was well crystallized and has a well-defined structure. The
particle size of these complexes was estimated from their
XRD patterns based on the highest-intensity value using
3.3. Structural characterization
The characterization of both the shape and size of CT or
PT complexes is important in the development of these
13.12o
MOX-CLA
3000
32.2o
MOX-PA
8000
6000
4000
2000
0
2000
1000
0
0
20
40
60
80
100
0
20
40
60
80
100
2θ (degrees)
2θ (degrees)
6.94o
MOX-CHL
3000
2000
1000
0
0
20
40
60
80
100
2θ (degrees)
Fig. 13. (Color online.) XRD spectra of the MOX complexes with the acceptors PA, CLA and CHL.
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Table 4
XRD spectral data for the synthesized complexes.
˚
Complex
2
u; (8)
u; (8)
d-spacing value; (A)
Height
b
; FWHM
Particle size (nm)
MOX–PA
MOX–CLA
MOX–CHL
32.2
13.12
6.94
16.1
2.7777
6.7426
8012.935
3014.896
3358.017
0.580
0.473
0.324
14.77
20.60
25.65
6.56
3.47
12.7268
the well-known Debye–Scherrer formula. The calculated
particle diameters of the MOX–PA, MOX–CLA and
MOX–CHL complexes were ꢄ 14.8, 20.6 and 25.7 nm,
respectively, which are in good agreement with the
results obtained by TEM. These values suggest that the
particle sizes of the complexes are within the nanoscale
range. Fig. 14A–C presents multiple SEM micrographs of
the outer surfaces of the synthesized complexes at
different levels of magnification (i.e., ꢃ1000, ꢃ2000,
ꢃ4000). The SEM micrographs of the particles revealed
that all of the complexes have a well-defined shape,
uniform matrix, distinct size and morphology with
homogeneously dispersed nanoparticles, indicating the
formation of homogeneous material. Visible morpholog-
ical change is observed between the MOX complexes.
From the high-quality and well-focused TEM micro-
Fig. 14. A. SEM and TEM images of the MOX–PA complex. B. SEM and TEM images of the MOX–CLA complex. C. SEM and TEM images of the MOX–CHL
complex.
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Fig. 15. XRD spectrum of the resultant porous carbon.
graphs (Fig. 14), it is inferred that all of the complexes
are spherical nanoparticles that are homogeneously
dispersed with no particle agglomeration. According to
these micrographs, most of the nanoparticles of the
MOX–PA, MOX–CLA and MOX–CHL complexes exhibit
diameters in the range of 6.5–14 nm, 6–31 nm and 8–
33 nm and main diameters of 10.3, 18.5 and 20.5 nm,
respectively. We note that these diameters are in good
agreement with the results calculated from the XRD
data.
100 nm. The XRD, SEM and TEM analyses confirm that the
direct carbonization of the complex leads to nanoporous
carbon material.
3.5. Why carbonize the complex containing the PA acceptor?
The experimental results presented here indicate that
the complexation of the drug MOX with the PA acceptor
instantly forms a yellow precipitate, while its complexa-
tion with the CLA or CHL acceptor forms a colored
precipitate after a short period of time. Furthermore, the
PA acceptor is soluble in both aqueous and organic media,
while CLA and CHL are not. Thus, the PA acceptor is more
suitable to remove MOX residues from either aquatic or
non-aquatic environments. In recent years, the occur-
rence and fate of pharmaceutically active compounds,
such as antibiotics in the environment, including water,
soil, and sediment, has drawn increasing public concern
worldwide and has been recognized as one of the
emerging issues in environmental chemistry. The pres-
ence of antibiotic residues in the environment increases
the risk of antibiotic-resistant pathogenic bacteria and
genes. Growing resistance means that what were once
effective and cheap antibiotics may become unsuitable for
treating infections [68–72]. The direct carbonization of
the complex containing the PA acceptor leads to a
nanoporous carbon material. So, this technique is an
efficient way to remove and utilize discarded MOX
antibiotic in other products based on complexation with
the PA acceptor.
3.4. Properties of carbon material
The as-prepared non-activated carbon product obtai-
ned from the direct carbonization of the MOX–PA complex
was ground into powder and characterized by XRD, SEM
and TEM techniques. Fig. 15 shows the XRD profile for the
resultant carbon. This profile displayed one broad peak
located at a 2u of approximately 258. It matches well with
the profile previously reported [63–66] for non-graphitic
carbon. The absence of a sharp diffraction pattern indicated
that the resulting porous carbon mainly possesses an
amorphous structure [67]. Furthermore, no impurity
diffraction was observed, confirming the absence of any
other X-ray traceable compounds in the carbon product.
The multiple SEM micrographs (Fig. 16) at different
degrees of enlargement (i.e., ꢃ1000, ꢃ5000, ꢃ10,000)
indicate the porosity behavior of the product. The highly
magnified (ꢃ120,000) TEM micrographs (Fig. 16) show
that the length of the carbon particles is approximately
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Fig. 16. SEM and TEM images of the resultant porous carbon.
4. Conclusions
acceptors (PA, CLA and CHL) were prepared, isolated and
characterized by a range of physicochemical methods. The
obtained nanoparticles possess interesting microstructu-
res and diameters of ꢄ 10–20 nm. Furthermore, this study
suggests that complexation with the PA acceptor may be
Nanostructured complexes derived from the reaction of
the drug MOX, a broad spectrum antibiotic against both
Gram-positive and Gram-negative bacteria, with organic
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potentially used to remove and utilize discarded MOX
antibiotic in other products as porous carbon materials
while shedding new light on the further development of
charge-transfer complexation for a wide range of environ-
mental applications.
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Please cite this article in press as: Adam AMA, et al. Quick and simple formation of different nanosized charge-transfer
complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics. C. R. Chimie
(2015), http://dx.doi.org/10.1016/j.crci.2015.05.019