Pharmacology & Pharmacy, 2011, 2, 212-225
doi:10.4236/pp.2011.23030 Published Online July 2011 (http://www.scirp.org/journal/pp)
Binary and Ternary Complexes of Arteether
β-CD—Characterization, Molecular Modeling and
in Vivo Studies
Renu Chadha1*, Sushma Gupta1, Natasha Pathak1, Geeta Shukla2, Dharamvir Singh Jain3,
Raghuvir R. S. Pissurlenkar4, Evans C. Coutinho4
1University Institute of Pharmaceutical Sciences, Panjab University, Chandigarh, India; 2Department of Microbiology, Panjab Uni-
versity, Chandigarh, India; 3Department of Chemistry, Panjab University, Chandigarh, India; 4Department of Pharmaceutical Chem-
istry, Bombay College of Pharmacy, Mumbai, India.
Received April 10th, 2010; revised May 30th, 2011; accepted June 22nd, 2010.
ABSTRACT
The purpose of the present work is to improve the antimalarial activity of arteether through enhancing its solubility
subsequently bioavailability by incorporating the drug into the cyclodextrins cavity. The effect of hydrophilic polyvinyl
propylene (PVP) polymer on the complexation and solubilizing efficiencies of cyclodextrins (CDs ) is also elucidated.
Inclusion of arteether molecule in solid state was evidenced by Differential scanning calorimeter (DSC), Powder X-ray
diffractometery (PXRD), and in solution state by NMR and solution calorimetry. A 1:1 stoichiometry was proposed by
the phase solubility studies both in presence and absence of PVP. The most plausibe mode of inclusion of arteether into
the CD cavity is revealed by molecular modeling studies utalizing Fast Rigid Exhaustive Docking acronym. Solution
calorimetry was used further to confirm 1:1 stiochiometry in presence or absence of PVP by determining the enthalpy
of interaction between the drug and cyclodextrins. The inclusion of drug was found to be exothermic process accompa-
nied by small positive value of entropy (ΔS˚). The methylated-β-CD showed the best ability to solublize arteether which
is approximately at par with β-CD in the presence of PVP. Better complexation efficiency of β-CD in presence of PVP
is also reflected by the higher numerical values of stability constant (K). Compelete eradication of the parasite from the
blood and highest anti-malarial pharmacological activity was observed in the complexes of arteether with M-
 -CD
while 83.7% was observed for ternary complexes of
 -CD in presence of PVP.
Significance of Work: The encapsulation of the arteether by CDs has resulted in improvement of solubility, dissolu-
tion and consequently the bioavailability leading to enhanced antimalarial activity of this poorly soluble antimalarial
drug
Keywords: Arteether, Cyclodextrins, Ternary Complexes, Complexation Efficiency, In Vivo Studies
1. Introduction
Arteether, a semi synthetic derivative of artemisinine, is
active constituent of the plant, Artemisia annua [1]. It is
a blood scihozonticide and active against all stages of
Plasmodium falciparum. The drug is also used for the
treatment of cerebral malaria as well as for the chloro-
quine resistant cases [2-5]. Unfortunately, it is water-
insoluble (17 µg/ml at room temperature) [6] and the
formulation causes difficulties to the biopharmaceutical
scientist. Moreover, the therapeutic efficacy is greatly
hampered due to its poor bioavailability as ~ 40% of the
drug degrades in the stomach [7-8]. Unless a drug is de-
livered to its target area at a rate and concentration that
minimize side effects and maximize therapeutic effects,
the drug is not beneficial to the patient and, though po-
tentially useful, may be discarded. Moreover, from an
economic point of view, low oral bioavailability results
in wasting of a large portion of an oral dose and adds to
the cost of drug therapy, especially when the drug is an
expensive one [9,10]. Cyclodextrins (CDs), especially β-
CD and its derivatives (Methyl-β-CD, and Hydroxypro-
pyl- β-CD) have been established as potential candidates
to alter physical, chemical and biological properties of
these molecules through the formation of inclusion com-
plexes [11-16]. However, due to several factors including

Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies 213
toxicity, cost and bulk, and the amount of CD in the
dosage form has to be reduced as far as possible. One of
the approaches to achieve this is by enhancing the com-
plexation efficiency of CDs by incorporating with wa-
ter-soluble polymers [17-20].
Thus, the rationale of this study is to improve the
solubility as well as therapeutic efficacy of arteether by
encaging the drug in the hydrophobic cavity of cyclo-
dextrin. The stability constant along with other thermo-
dynamic parameters which are pre-requisite for formula-
tion development are determined by solution calorimetry.
These parameters are further used to find the relationship
between noncovalent structure and free energy of bind-
ing to include the roles of enthalpy and entropy of asso-
ciation. The emphasis of the current study is laid to
evaluate the efficacy of these complexes and on the in-
vivo model to monitor their suitability in enhancing the
bioavailability.
Literature survey has revealed that not much data is
avialable on the inclusion complexes of this poorly solu-
ble drug. However, few reports are present on the NMR
studies and molecular modeling studies of the prepared
complexes. Thermodynamic parameters accompaning
the inclusion as well as animal studies are also lacking
[21-23].
2. Experimental
2.1. Preparation of Binary Complexes
Arteether (Ae) with β-CD, M-β-CD or HP-β-CD was
mixed in 1:1 molar ratio by different methods as given
below
2.1.1. Physical Mixing (PM)
Physical mixtures were prepared by simple mixing of
drug with the selected CD in mortar and to ensure uni-
form mixing. The vials filled with the mixtures were
subjected to vortex mixing for 5 min.
2.1.2. Kneading (KN)
Drug and CD was blended together in mortar with water;
a paste was obtained and this was kneaded for 90 min.
The product was then dried under vacuum at 40˚C for 48
h and passed through a 150 µm mesh and stored in a
glass vial in vaccum dessicator.
2.1.3. Freeze-Drying Method (LY)
The required 1:1 stoichiometric quantity of drug was
added to aqueous solution of the selected CD and was
agitated on a magnetic stirrer for 24 hrs. The resulting
solutions was frozen at (–80˚C) in deep freezer for over-
night. This was then lyophilized under 17.2 m Torr for
48 hrs. The samples were transferred immediately into a
vacuum desiccator and dried over silica gel under vac-
uum for at least 24 hrs.
2.2. Preparation of Ternary Cyclodextrin
Complexes
2.2.1. Physical Mixing (PM).
Physical mixtures were prepared by simple mixing of
drug, β-CD and 0.20% PVP in mortar to ensure uniform
mixing. The vials filled with this were subjected to vor-
tex mixing for 5 min.
2.2.2. Kneading (KN).
Drug and β-CD were blended together in mortar with
0.20% of PVP for 90 min and a paste was obtained. The
product was then dried under vacuum at 40˚C for 48 hrs
and passed through a 150 µm mesh and stored in a glass
vial in vacuum dessicator.
2.2.3. Lyophilized Suspension Method (LY Susp).
Ternary complexes were prepared by dissolving the
equimolar amounts of arteether and β-CD with 0.20%
PVP in water. The resulting solution was stirred at room
temperature for 48 hr. The solid residue was then sepa-
rated by centrifugation at 15000 rpm for 15 minutes and
upper liquid layer was filtered over a 0.45 Millipore filter
paper. The filtrate was then lyophilized under 17.2 mTorr
for 48 hrs and placed in vacuum desiccators.
2.2.4. Co evaporated (CoE) Solid System Method
Equimolar amounts of arteether and β-CD systems with
0.20% PVP dissolved in water. The resulting solution
was evaporated on a rota vapour at 60˚C to get a solid
residue. The prepared system was dried in vacuum des-
iccators.
3. Characterization
Binary and ternary inclusion complexes of arteether were
characterized in solid phase by DSC, PXRD, FT-IR,
mass spectrometry and in solution phase by solution
calorimetry and NMR
3.1. Phase Solubility Studies of Arteether with or
without 0.2% PVP
Phase solubility diagrams of arteether for both binary
and ternary systems with various CDs in phosphate
buffer (pH 6.8) were obtained according to Higuchi and
Connors [24]. An excess amount of are was added to 100
ml buffer or CD buffered solutions with a concentra- tion
of v/v (2 to150 mM) in 20 ml glass vials with or without
a polymer (0.20% PVP). The suspensions were sealed
and shaken in water-bath shaker MSW-275 (Macroscien-
tific works, Delhi) at 37 ± 0.5˚C for 24 hrs to ensure
equilibrium. After equilibration, aliquots of the super-
natant were withdrawn, filtered through 0.45 µm milli-
pore filter paper, and the arteether content was de- ter-
mined spectrophotometerically at λ 230 nm (UV/VIS.
Spectrophotometer (Perkin Elmer Lamda 15, USA). The

214 Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies
presence of CDs did not interfere with the spectropho-
tometric assay of the drug.
3.2. Mass Spectrometry
ESI-MS studies were performed using a Q-ToF quadru-
ple time of flight mass spectrometer (Waters) equipped
with an electrospray source. The sample was introduced
via a syringe pump at a flow rate of 5 µL/min. High flow
rate nitrogen gas was employed as the nebulizing gas as
well as the drying gas to aid desolvation. The sheath gas
flow rate was 0.5 µL·min–1. After optimization of the MS
parameters, the spray voltage was set to 2.5 kV in the
positive mode, and the heated metal capillary tempera-
ture was set at 80˚C. The mass scale was calibrated by
using the standard calibration procedure and compounds
provided by manufacturer.
3.3. Differential Scanning Calorimetry (DSC)
DSC thermograms were obtained on DSC, (Q20, TA
Instruments-Waters LLC, USA). The calorimeter was
calibrated for temperature and heat flow accuracy using
the melting of pure indium (mp 156.6˚C and ∆H of 25.45
J·g–1). The temperature range was from 50˚C - 350˚C
with a heating rate of 10˚C per minute.
3.4. X-Ray Powder Diffraction
Powder diffraction patterns were recorded on an X-ray
diffractometer (XPERT-PRO, PANalytical, Netherlands,
Holand) with Cu as tube anode the diffractograms were
recorded under following conditions: voltage 40 kV, 35
mA, angular range 5 and fixed divergence slit.
3.5. Fourier Transform Infrared Spectrometry
(FT-IR)
The FT-IR spectra were obtained on FT-IR spectrometer,
Mode spectrum RXI, Perkin Elmer, England over the
range 400 - 4000 cm–1. Dry KBr (50 mg) was finely
ground in an agate mortar and samples of drug and their
complexes (1 - 2 mg) were subsequently added and
mixed gently. A manual press was used to form the pel-
lets.
Analysis in solution state
3.6. 2D COESY, Proton Nuclear Magnetic
Resonance (1H-NMR) and 13C NMR
Spectroscopy
1H-NMR, 13C NMR and 2D COESY spectra in d6 DMSO
of arteether and inclusion complexes were recorded with
a Brucker AC 300˚C NMR spectrometer apparatus oper-
ating at 300 MHz using tetramethylsilane as an internal
standard. For 2D COESY experiments, samples were
equilibrated for at least 24 hrs.
3.7. Molecular Modeling Studies
3.7.1. Computational Details
The computational studies were carried out on a Linux
Cluster (ROCKS 5.4). The structure preparation, simula-
tions analysis were carried out with Maestro version 9.1,
(Schrödinger LLC, New York, NY, 2010), while docking
studies were carried out with Fast Rigid Exhaustive
Docking acronym (FRED version 2.2.5, OpenEye Scien-
tific Software, Santa Fe, USA [25,26]. The Molecular
Dynamics simulations were performed using Desmond
(version 2.4, DE Shaw Research, NY, USA).
3.7.2. Structure Preparation
The 3D structures of β-cyclodextrin (β-CD) and arteether
were retrieved from the Protein Data Bank [27] and
PubChem (CID 72416). The geometries of the structures
were optimized after the assignment of atom types and
charges based on the OPLS 2005 force field in Schrö-
dinger Suite.
3.7.3. Docking Studies
The β-CD molecule was subsequently imported into the
program FRED-RECEPTOR (version 2.2.5) for docking.
First the active site box where the ligand or guest is ex-
pected to bind is defined and the shape of the active site
is described by two shape potential contours, referred to
as the inner and outer contour. It is essential that the
docked host guest poses fit within the shape of the outer
contour and ensures that the center of at least one heavy
atom of any docked pose touches the inner contour.
Docking succeeds the grid generation protocol in the
second step. The docking is a rigid body process involv-
ing only rotational and transitional motions of the guest
molecule inside the host cavity. The arteether: β-CD
configurations of the guest molecule inside the host are
rated by the intrinsic scoring function Chemgauss 3. The
predominant configurations are stored for further analy-
sis.
3.7.4. MD Simulations
Before simulation the complex of Ae-β-CD was solvated
with TIP3P waters [28] to form a water shell 10 Å thick
around the Ae-β-CD complex. The solvated host guest
system was simulated for a period of 5 ns with the ‘NPT
relaxprotoco l’ in Desmond. The protocol involves an
initial minimization of the solvent with the solute re-
strained. The minimization is followed by short MD
simulations of 12 - 24 ps in sequential NVT and NPT
ensembles with the Langevin thermostat and barostat
[29]. The temperature was maintained by coupling to an
external 300 K bath based on the Langevin algorithm
[29]. The pressure was isotropically restrained to 1 bar
with the Langevin barostat. High-frequency vibrations
were removed by applying the SHAKE algorithm [30]
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Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies 215
by constraining all bonds to their equilibrium values.
Initial velocities were generated randomly from a Max-
well distribution at 300 K in accordance with the masses
assigned to the atoms. The trajectories and corresponding
energies were sampled every 5 ps. No constraints were
applied on the β-CD-arteether system during the simula-
tions, so as to avoid introduction of any artifacts in the
ligand conformation in the binding site.
3.8. Microcalorimetric Study
Isoperibol solution calorimetry (ISC) (Calorimetry Sci-
ence Corporation, UTAH, USA) model 4300 was used
for thermal measurements. The calorimeter consists of a
constant temperature bath held at 37˚C (± 0.005˚C) and
heater assembly. The drug was filled into batch adaptor
of volume 0.9 ml, sealed on both sides with ‘O’ rings and
cover glass. The batch adaptor holding the drug was in-
serted into the Dewar flask containing buffer (25 ml).
The combined unit was then lowered in the calorimeter
bath. The glass stirrer was rotated at 100 revolutions/min.
and was allowed to equilibrate for 90 min. The ampoule
was shattered automatically by means of plunger and
temperature change noted. The performance of the sys-
tem was checked using KCl, which has known enthalpy
of solution and a good agreement (± 0.03 kJ/mol), was
found with published value
3.9. Dissolution Study:
The dissolution studies of the arteether and its binary and
ternary complexes were performed in 900 ml of phos-
phate buffer (pH 6.8 using) USP (12) apparatus at pre-
equilibrated temperature 37 ± 0.5˚C and at a stirring rate
of 50 rpm. Drug and its inclusion complexes each con-
taining 100 mg of drug were filled in hard gelatin cap-
sules. Samples was withdrawn at different intervals for a
period of 6 hr and analyzed spectrophotometrically at λ
230 nm.
3.10. In Vivo Studies: Evaluation of
Pharmacological Antimalarial Activity of
Arteether, Its Binary and Ternary
Complexes in Mice
Four to five weeks old BALB/c mice (25 - 30 g) were
procured and maintained in the Central Animal House.
They were provided with standard pellet diet and water
ad libtum. Experiments were performed as per guidelines
of Control and Supervision on Experiments on Animals
(CPC-SEA) committee. The experimental protocol was
approved by Institutional Animal Ethics Committee (A. I.
E. C.). Plasmodium berghei (NK 65) strain was used for
evaluation of antimalarial activity in vivo studies and was
maintained in the mice. All the mice belonging to control
group were challenged with 106 P. berghei infected RBCs
intraperitonial (i/p). After challenge mean percent para-
sitaemia, percent activities of various complexes of ar-
teether along with animal survivality were monitored.
Mean percent parasitaemia was calculated for each group
on every alternate day upto 30 days by tail blood smear,
fixed in methanol and stained in Giemsa stain by count-
ing at least 500 cells.
Mean percent parasiteamia = infected RBCs × 100/Total
No. of RBCs
Animals were divided into 6 groups and each group
comprised of 6 animals (n = 6). These were treated with
single dose therapy (6 mg/kg of arteether) two times a
day on 1 day of PI for 7 days to monitor the efficacy and
potency of prepared lyophilized binary and ternary com-
plexes. Each animal were treated with arteether equal to
100 µl.
1) Control group—treated with 0.5% carboxymethyl
cellulose (CMC) suspension;
2) Standard group—administered arteether in 0.5%
CMC suspension;
3) Test group 1—treated with binary Ae-β-CD com-
plex in 0.5% CMC suspension;
4) Test group 2—treated with binary Ae-M-β-CD
complex in 0.5% CMC suspension;
5) Test group 3—treated with binary Ae-HP-β-CD
complex in 0.5% CMC suspension;
6) Test group 4—treated with ternary Ae-β-CD-PVP
complex in 0.5% CMC suspension;
3.11. Statistical Analysis
Data was expressed as mean ± S. D. and parasitaemia as
well as in vitro drug release of the arteether and its bi-
nary and ternary inclusion complexes were statistically
assessed by one-way ANOVA followed by Turkey’s test
using Jandel sigma stat 2.0 version. Differences were
considered significant at P < 0.05.
4. Results and Discussion
Equilibrium Phase Solubility Studies:
The equilibrium phase solubility of the arteether in-
creased in a linear fashion as a function of
 -CD, M-  -
CD and HP-
 -CD concentration and followed an AL-type
system. The linear host-guest correlation with slope less
than one suggested the formation of first order soluble
complexes (Figure 1).
The increment in the solubility of drug depends upon
inclusion ability of cyclodextrin molecules with the solu-
bilization strength increasing in the order: β-CD <
HP-β-CD < M-β-CD.
Selection of Third Component: To select the most ap-
propriate third component for enhancing the solublizing
efficiency of CDs several water-soluble polymers viz.
PVP, hydroxylpropyl methyl cellulose (HPMC), poly-

216 Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies
Figure 1. Phase solubility diagram of arteether with β-CD,
M-β-CD and HP-β-CD as well as with β-CD in the presence
of 0.20% PVP at 37˚C (Ae-β-CD-PVP).
Figure 2. Comparison of phase solubility of arteether in the
presence of various solubilizing agents.
ethylene glycol (PEG) and poloxamer were tried (Figure
2). This experiment is very important as several poly-
mers have opposite effect [19,31]. The addition of PVP
was found to be best and resulted in 20 times increase in
solubility as compared to the 13.4 fold increase in its
absence at the same concentration of binary complex
(Figure 2). Only β-CD is used for further studies be-
cause of its low cost and less parental toxicity as to
M-β- CD and HP-β-CD. Interestingly, the enhancement
in solubility of drug in presence β-CD and PVP is ap-
proxi- mately equal to that in presence of M-β-CD alone.
The addition of water-soluble polymers to the CD solu-
tion did not change the type of phase-solubility dia-
grams (1:1 stoichiometry) obtained for binary systems
(Figure 2).
4.1. Analysis in Solid State
4.1.1. Electronspray Ionization Mass Spectrometry
(EI-MS)
ES-MS spectroscopy allows us to provide the evidence
of complexation and stoichiometry of the molecular
complexes on the basis of their molecular weights in the
Figure 3. Mass spectra of arteether with (a) β-CD, (b) M-β-
CD, (c) HP-β-CD.
vaporized form. Peaks observed in mass spectra at m/z
1157, 1448, 1623, and 1693 correspond to the charged
[
 -CD+ Na]+, [Ae +  -CD + H]+, [Ae + M-  -CD + H]+,
and [Ae + HP-
 -CD + H]+ respectively revealing the
formation of 1: 1 inclusion complexes (Figure 3).
4.1.2. Differential Scanning Calorimetry (DSC)
Analysis
The presence of drug peaks with reduced intensity as
well as broadening of drug fusion peak in the binary
physical mixtures and kneaded mixtures of drug with β-
CD, M-β-CD and HP-β-CD indicates weak interaction
between them. The disappearance of an endothermic
peak in lyophilized complexes may be attributed to an
amorphous state and proper fit of the drug inside the cav-
ity illustrating true inclusion (Figure 4).
Similarly, in the ternary systems of arteether, the
characteristic endothermic peak of arteether is present
with reduced intensity in the physical mixtures, coevapo-
rated systems and kneaded complexes but complete ab-
sence of melting endotherm in case of lyophilized com-
plexes is observed (Figure 5). The interesting feature of
the ternary complexes is the absence of the decomposi-
tion peak in lyophilized suspension system as well as in
co evaporated ternary system supporting the fact that
the inclusion of the drug has enhanced its physical sta-
bility.
4.1.3. Powder X-Ray Diffraction (PXRD) Analysis
Comparison of these diffraction patterns of physical
mixtures and kneaded binary complexes of all three CDs
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Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies 217
Figure 4. DSC thermograms of (a) Arteether (b) Ae-  -CD-
PM (c) Ae-  -CD-KN (d) Ae-  -CD LY (e) Ae-M-  -CD-PM (f)
Ae-M-
 -CD-KN (g) Ae-M-  -CD-LY (h) Ae-HP-  -CD-PM (i)
Ae-HP-
 -CD-KN (j) Ae-HP-  -CD-LY.
Figure 5. DSC thermograms of arteether with (a) Ae-β-CD–
PVP-PM (b) Ae-β-CD-PVP-CoE (c) Ae-β-CD-PVP-KN (d)
Ae-β-CD-PVP-LY.
with those of pure components shows a reduced number
of signals, with remarkably lowered intensity indicating
incomplete inclusion phenomenon (Figure 6). The evi-
dence of complete disappearance of drug peaks in the
PXRD diffraction pattern of lyophilized complexes indi-
cates the entrapment of drug inside the CD cavity with
the formation of true inclusion complex with amorphous
nature except β-CD which shows diffused diffraction
pattern.
The ternary systems showed complete amorphous halo
Figure 6. XRPD pattren of a) Arteether (b) Ae-  -CD-PM (c)
Ae-
 -CD-KN (d) Ae-  -CD LY (e) Ae-M-  -CD-PM (f) Ae-
M-
 -CD-KN (g) Ae-M-  -CD-LY (h) Ae-HP-  -CD-PM (i)
Ae-HP-
 -CD-KN (j) Ae-HP-  -CD-LY.
Figure 7. XRPD pattren of arteether with (a) Ar-β-CD–
PVP-PM (b) Ar-β-CD-PVP-CoE (c) Ar-β-CD-PVP-KN (d)
Ar-β-CD-PVP-LY.
and is attributed to a complete interaction between all the
three components. Some diffraction peaks with lower
intensity are still detectable in the ternary complex
withβ-CD which may be attributed to a crystalline nature
f β-CD (Figure 7). o

Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies 218
Figure 8. FTIR spectra of (a) Arteether (b) Ae-  -CD-PM (c) Ae--CD-KN (d) Ae-  -CD LY (e) Ae-M-  -CD-PM (f) Ae-M-  -
CD-KN (g) Ae-M-  -CD-LY (h) Ae-HP-  -CD-PM (i) Ae-HP-  -CD-KN (j) Ae-HP-  -CD-LY.
4.1.4. Fourier Transform Infrared Spectroscopy
(FT-IR)
FT-IR could not give much useful information as the
spectra of complexes of β-CD, M-β-CD and HP-β-CD
were found quite similar to their pure CDs because of the
coincidently absorption of the both the host and guest
molecule in most of the special regions coincidently ab-
sorption in most of spectral region. Bands of the included
part of the guest molecule are masked by the bands of the
spectrum of CDs. However, the small shifts in characte-
ristic bands of drug at 1450 cm–1, 1376 cm–1, and 1036
cm–1 undoubtedly confirm the presence of drug in all the
complexes (Figure 8-9).
4.2. Analysis of Binary and Ternary Systems in
Solution Phase
4.2.1. Proton NMR Spectroscopy
Proton magnetic resonance spectroscopy plays a vital
role in predicting the exact geometry of complex and
also to characterize the binding mode. A downfield shift
is observed in the cycloheptane protons H-d, H-g, H-h,
H-m and H-n of drug molecule (Table 1) indicating the
insertion of the whole drug molecule inside the cavity Figure 9. FTIR spectra of (a) Ar-β-CD-PVP-PM (b) Ar-β- CD-PVP-CoE (c) Ar-β-CD-PVP-KN (d) Ar-β-CD-PVP-LY.

Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies 219
Table 1. Variation of 1H chemical shifts before and after inclusion ∆δ = δ (complex) – δ (Free).
Arteether δdrug δae-b-cd, ae-M-b-cd, ae-HP- b-cd complexes (ppm) Δδae-b-cd, ae-M-b-cd, ae-HP- b-cd complexes (ppm)
H-a 4.7545 4.6279, 4.685, 4.6383 –0.1266, –0.0695, –0.01162
H-b 5.5163 5.7255, 5.3974, 5.4213 0.2092, –0.1189, –0.095
H-c 3.5223 3.3756, 3.3918, 3.3835 –0.1467, –0.1305, –0.1388
H-d 2.1766 2.1853, 2.1681, 2.0437 0.0087, 0.02787, 0.01297
H-e 1.244 1.1519, 1.147, 1.1574 0.0921, –0.097, –0.00866
H-f, j 1.355 1.347, 1.34832, 1.3538 –0.00802, –0.0068, –0.01336
H-g 2.428 2.4014, 2.4051, 2.4023 0.00266, 0.0229, 0.0257
H-h 1.781 1.799, 1.796, 1.697 0.018, 0.015, –0.084
H-i 1.5938 1.5525, 1.6039, 1.5575 –0.04132, 0.0101, –0.03627
H-k 2.5073 2.5066, 2.5072, 2.5072 –0.0007, –0.0001, –0.0001
H-l 0.8958 0.8905, 0.8928, 0.8445 –0.00525, –0.003, –0.00545
H-m 0.8390 0.8400, 0.8423, 0.8949 0.00105, 0.0033, 0.009
H-n 1.2865 1.2933, 1.2944, 1.2946 0.0068, 0.0079, 0.0099
H-o 3.0218 3.056, 3.0328, 3.085 –0.0342, –0.011, –0.0632
Figure 10. (a) The chemical structure of arteether (b) Inclu-
sion mode of drug into cyclodextrin cavity.
except ether linkage which is protruding outside the
cavity. Insertion was favored towards the cycloheptane
ring of the artemisinin derivatives due to its narrower
dimension (2.89 A˚) as compared to the opposite end of
the drug molecule, consisting of two cyclohexane rings
(6.9 A˚) (Figure 10).
Upfield shift in H-e, H-b, H-f protons of the molecule
is due to the variation in the local polarity. In two-di-
mensional (2D) COESY spectra, the appearance of cross
peaks (Figure 11) between H-5 protons of CD and H-b
and H-n protons support our proposed inclusion mode
involving insertion of cycloheptane ring with endoper-
oxide bridge deep into the cavity. Besides this, cross
peaks are also present between H-3 protons of CD and
H-a proton of oxygen containing cycloheaxane ring of
drug.
4.2.2. Molecular Modeling Studies
Arteether was docked into the cavity of β-CD using
FRED which places the guest into the active cavity using
a rotational and translational motion resulting into rigid
conformations. The best configurations are identified
using the intrinsic scoring function Chemgauss 3. During
docking, it was observed that the arteether molecules
oriented itself inside the β-CD cavity in two different
ways. In case-1, the ethoxy fragment protrudes into the
Figure 11. 1H COESY of arteether with (a) β-CD, (b) M-β-
CD and (c) HP-β-CD.

220 Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies
Figure 12. RMSD mapped over a 5 ns MD trajectory for
the two orientations studied for the Ae:β-CD inclusion com-
plex using initial configuration obtained from docking as
the reference.
β-CD pocket with the artemisinin core interacting at the
surface interaction with β-CD while in case-2 the ar-
temisinin core is buried in the β-CD cavity (Figure 12).
These two cases were further simulated using MD pro-
tocol in Desmond.
A post simulation, the binding energy was analyzed
for two cases of the arteether: β-CD inclusion complex in
terms of Coulombic, Van der Waals. Also intermolecular
H-bonds between arteether and β-CD were mapped along
the 5 ns MD trajectory. Singular H-Bond interacttion is
seen to be present between the hydroxyl group at posi-
tion 3rd of the glucose subunit in β-CD with the oxygen
atom of the ether bridge in the arteether core ring in the
both the case studies. The stability of the inclusion com-
plex was evaluated on the basis of the root-mean- square
deviation (RMSD) for heavy atoms computed using the
initial structure (docking pose) as the reference state.
From the RMSDs calculated for the structural snapshots
collected every 4.8 ps over the entire 5 ns simulation it is
relevant that there is a fluctuation in the interactions and
structural configuration of inclusion complex of type
case-1 while a degree of steadiness is observed for the
case-2 which is evident from the Table 2/Figure 13 for
the inclusion complex. The case-2 inclusion complex
attains stability after 500 ps of simulation; seen from the
RMSDs standard deviation values of 0.18 against 0.39
for case-2 and case-1. Here, it can be evident that the
arteether: β-CD complex can be more stable when the
arteether core is embedded in the β-CD cavity. The
binding energies (presented in Table 2) were computed
for the complexes over the entire simulation trajectory
using the below given formula:


B
indingcomplexHost guest
GG GG
The mean binding energy computed for arteether: β-
CD complex is –5.6 kcal/mol (23 kJ/mol and –4.8 kcal/mol
(20.08 kJ/mol) for the case-1 and case-2 studies. The
arteether core interacts with β-CD at the secondary face
in case-1 while it is partially buried in the β-CD cavity
for case-2 (Figure 14) These results are in accordance
with the NMR data suggesting that case-2 represents the
Figure 13. 3D-model to depict the interaction of artether
(guest) with β-cyclodextrin (host) in the two cases for Ae: β-
CD inclusion complex.
Table 2. Interaction energies (Coulombic, vander Waal), H
bond counts and RMSD (w.r.t. frame zero in simulation)
computed over the MD trajectory of the Ae: β-CD inclusion
complex.
Sr. No.Case study
Binding
Energy
(Kcal/mol)
RMSD
(for 5 ns)
RMSD (af-
ter 500 ps)
1. Case-1 (ethoxy of ar-
teether buried into β-CD –5.6 0.41 0.34
2.
Case-1 (artemisinin
coreof arteether buried
into β-CD
–4.8 0.39 0.18
most favorable mode of inclusion between arteether and
 -CD.
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Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies 221
4.2.3. Micro Calorimetric Studies of Inclusion
Complexes in Presence or Absence of PVP



int exp
sol sol CD
H
H
Hvl


 (1)
Stability constant and other thermodynamic parameters
were calculated by determining the enthalpy of solution
of the drug in absence and presence of CDs as well as
PVP. The molar enthalpy of solution of drug (ΔsolH(M))
was found to be exothermic in phosphate buffer (pH 6.8).
Enhanced exothermic behavior was exhibited by the drug
in presence of CDs and further enhancement was ob-
served when both CDs and 0.20% PVP were present.
This is attributed to synergetic interaction between drug
and the cyclodextrin in the presence of PVP. The en-
thalpy of interaction was calculated by the following
equation:
where ∆Hint,(exp) is enthalpy of interaction between drug
and cyclodextrin per liter of solution, ∆solH and ∆solH(CD)
is enthalpy of solution of drug in buffer and in buffered
aqueous solution of cyclodextrin respectively, v (l) =
volume of sample cell in liters (0.025 L).
Enthalpy of interaction per mole of drug and β-CD
(∆Hint(M)) were calculated from Equation (2)

 
int exp
int
21
1
sol sol
MCD M
M
HH
Hab xx
H


 

(2)
where a and b are initial molar concentration of drug and
cyclodextrin, x1 and x2 are apparent mole fractions of the
Table 3. Interaction enthalpy of inclusion complexes ar- teether with M-β-CD.
Xcd M
Ae Mb-CD ∆Hint (L) ∆Hint(M)
0.900423 0.194872 1.762115 –0.04914 –1.0044
0.848566 0.166667 0.933921 –0.04495 –1.63382
0.790695 0.219231 0.828194 –0.04576 –1.74752
0.706543 0.371795 0.895154 –0.05853 –1.84778
0.645967 0.29359 0.535683 –0.03999 –1.92882
0.572393 0.294872 0.394714 –0.03445 –1.9983
0.518143 0.435897 0.468722 –0.04628 –2.04638
0.452116 0.328846 0.271366 –0.02991 –1.99351
0.40326 0.307692 0.20793 –0.0245 –1.90077
0.348924 0.305128 0.163524 –0.02153 –1.83722
0.299527 0.346154 0.148018 –0.02095 –1.69551
0.231709 0.580769 0.175154 –0.02886 –1.52697
0.176352 0.510256 0.109251 –0.02218 –1.43231
0.130904 0.635256 0.095683 –0.02079 –1.13747
0.073342 0.912821 0.072247 –0.01954 –0.79335
System K (M–1) ∆H˚ (kJ·mol–1) ∆G˚ (kJ·mol–1) ∆S˚ (J·mol–1·K–1)
Ae + β-CD 1123 ± 0.005 –8.58 ± 0.005 –18.10 ± 0.001 30.72 ± 0.005
Ae + HP-β-CD 1490 ± 0.008 –10.40 ± 0.006 –18.83 ± 0.001 27.20 ± 0.006
Ae + M-β-CD 2023 ± 0.010 –11.20 ± 0.006 –19.62 ± 0.001 27.15 ± 0.006
Ae + β-CD + PVP 1587 ± 0.016 –10.60 ± 0.013 –18.99 ± 0.001 27.72 ± 0.013

222 Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies
Figure 14. Dissolution study of arteether (a) binary systems
and (b) ternary systems.
drug and cyclodextrin ignoring the concentration of buff-
ers.
The detailed calorimetric data for arteether and M-β-CD
are given in Table 3.
The stoichiometry of the complex was ascertained util-
izing continuous variation method (Job’s plot) [32] by
plotting (∆Hint(M)) versus (x2) (Figure 15). It can be seen
that the minimum occurs at x2 = 0.5. This indicates that
complex has 1:1 stoichiometry and supports its determi-
nation by other techniques.
Similarly the enthalpy of interaction for ternary system
was calculated by subtracting the enthalpy of solution of
drug in presence of cyclodextrin and 0.20% PVP from
that in pure buffer (ΔsolH(M)). The binding parameters
were then calculated using Equations (1) and (2).
Now the thermodynamic constants are calculated as-
suming the following equilibria.
CD + arteether ↔ CD: arteethe (3)
The experimentally calculated enthalpy of interaction
(ΔHint(exp)) is proportional to the product of molar con-
centration of CD: arteether complex (c) in the solution at
equilibrium and enthalpy of binding per mole of drug
(ΔH˚)
ΔHint(exp) = ΔH˚ × c (4)
The binding constant K and enthalpy of binding (Hº)
for both binary and ternary systems were computed from
the experimentally determined enthalpy of interaction
(∆Hint(exp)). The calculations were done by our computer
program utilizing an iterative non-linear least square re-
gression method to minimize the value of Σ(∆Hint(exp) –
∆Hint(calc))2 and are given in Table 4.
The values of free energy of inclusion (G˚) and en-
tropy of inclusion (S˚) were calculated from the fol-
lowing equations and given in Table 4.
G˚ = – RTlnK (5)
S˚ = (H˚ – G˚)/T (6)
The experimentallly determined ∆G˚ (–18.10 kJ/mol)
is closer to the theoretically calculated binding energy
for case-2 (20.08 kJ/mol). These results clearly indicate
that in case-2 where the arteether core is embedded in the
β-CD cavity is more stable as to case-1 where arteether
core interacts on the surface of the CD cavity. Our NMR
data is also supporting this mode of inclusion.
The magnitude of K reflects optimum value for the in-
clusion of guest molecule inside the cavity of the cyclo-
dextrin molecule for both binary and ternary systems
(Table 4). The absolute value of K increases in the order
β-CD < HP-β-CD < M-β-CD. This shows that substi-
tutent groups for assisting in binding by lengthening the
cavity and thus increasing the hydrophobicity. Methyla-
tion also makes the environment more hydrophobic and
allows for increased adaptability of CD towards the guest
through enhanced flexibility. Enthalpy of binding (H˚)
is negative in all the cases reflecting an exothermic in-
teraction. The entrapment of drug molecule into the CD
cavity results in Van der Waal’s interaction between the
hydrophobic part of drug and walls of the CD cavity,
leading to enthalphic gain, but also induces the rear-
rangement of water molecules or loss of solvation of the
guest, affording an entropic gain.
The enhancement of K upon addition of the PVP was
observed which indicates that the inclusion is facilitated
in presence of third component. This may be attributed to
the establishment of different interactions with CDs and
drug molecules such as hydrophobic bonds, Van der
Waals forces, or hydrogen bonds [18,33].
Polymers are known to interact with the outer sur-
faceof CDs and with drug-CD complexes, forming co-
complexes or aggregates that show higher stability con-
stants (Kc) values than those for the binary drug-CD
system [34]. They increase the complexation efficiency,
and therefore a smaller amount of CD can be used in the
preparation of the complex [17].
4.2.4. Dissolution Studies
Rapid dissolution is the characteristic behavior of inclu-
sion complexes but the comparative release of active
material was strongly affected by the method of formula-
tion. In binary systems, the lyophilized system exhibited
the best dissolution properties and was followed by
kneaded complex and physical mixtures (Figure 15).
Moreover, highest dissolution rate was found for M-β-
CD complex followed by that of HP-β-CD and β-CD.
The much-enhanced dissolution rate observed in ter-
nary system is due to (1) the enhancement of the com-
plexation and solubilization efficiencies of β-CD (2) the
stronger drug amorphization and better inclusion caused
y the combined action of β-CD and the hydrophilic b
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Binary and Ternary Complexes of Arteether β-CD—Characterization, Molecular Modeling and in Vivo Studies 223
Table 4. Thermodynamic parameters of inclusion complex of arteether with β-CD in presence of PVP.
S. No. Groups Treatment Mean % Parasitaemia* on day 8th PI % mortality (n = 6, t = 40 days)
1 Control group 0.5% CMC solution 49.23 ± 5.34 100
2 Standard group Arteether ~ (5 mg/kg) 38.48 ± 3.21 66.7
3 Test group 1 Ae-β-CD ~ (6mg/kg of arteether) 24.46 ± 3.03 50
4 Test group 2 Ae-M-β-CD ~ (6mg/kg of arteether)0.009 ± 0.0001 0
5 Test group 3 Ae-HP-β-CD ~ (6 mg/kg of arteether)8.95 ± 1.21 33.3
6 Test group 4 Ae-β-CD-PVP ~ (6 mg/kg of arteether)4.75± 0.034 16.7
Figure 15. Plot of ΔsolHint(M) versus mole fraction (x2) of
arteether with β-CD, M-β-CD, HP-β-CD and As-β-CD-PVP.
Figure 16. Antimalarial activity of β-CD lyophilized com-
plexes of arteether in P. berghei infected mice “(n = 6)” as
compared to drug.
polymers (Figure 13). Therefore, the lyophilized binary
and ternary complexes with the highest dissolution rate
are most suitable for the animal studies.
4.2.5. In Vivo Antimalarial Activity of Arteether and
Its Binary and Ternary Inclusion Complexes
Suspensions containing arteether, binary and ternary in-
clusion complexes were tested with respect to para-
sitemia progression and survival period. It was observed
that arteether alone (Standard Group) is insufficient to
prevent the mortality but significantly prolonged their
survival period (day 14 - 19) compared to control (day 9).
Test Group 1, Test Group 2 and Test Group 3 treated
mice died between 15 - 25 days, 20 - 26 and 27 - 35 days,
respectively (Table 5), whereas Test Group 4 (Ternary
lyophilized system) resulted in a 83.3% survival of in-
fected mice even after 30 days. The percent mortality
rate with arteether alone, β-CD complex, HP-β-CD com-
plex and ternary complexes of β-CD were 50%, 66.7%,
83.3% and respectively. However, M-β-CD (Test Group
3) complexes have resulted in complete clearance of the
parasite from peripheral blood. Significantly less (P <
0.001) mean percent parasitaemia is observed in the Test
Group 3 (0.009 ± 0.0001) compared to all test groups.
ANOVA have also shown significant (P < 0.05) antima-
larial activity of all binary and ternary complexes as to
arteether (Figure 16).
4.2.6. Conclusions
The present work proved the suitability of PVP as auxil-
iary substance in enhancing the complexation efficiency
of β-CD towards arteether. The free energy of binding
and inclusion mode of arteether is determined experi-
mentally as well as by theoretically mean binding energy
by molecular modeling studies. Higher numerical values
of K for M-β-CD complexes and ternary complexes of β-
CD in presence of PVP are accompained by increment
the in vitro dissolution rate and dissolution efficiency.
However, 100% survival rate and complete eradication
of parasite from was observed for only for Methylated β-
CD complexes.
5. Acknowledgements
The financial assistance provided by Indian Council of
Medical research (ICMR; BMS-45/29/2006), New Delhi,
India and Instrumentation assistance by Department of
Science Technology (DST), New Delhi is gratefully ac-
knowledged. The computational facilities supported by
the Department of Biotechnology (DBT; BT/TF-8/BRB/
2009) and Department of Science and Technology (DST;
SR/FST/LSI-163/2003), New Delhi are gratefully ac-
knowledged.
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