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Thermochimica Acta 560 (2013) 104– 111

Contents lists available at SciVerse ScienceDirect

Thermochimica Acta

jo ur nal home p age: www.elsev ier .com/ locate / tca

hermal and spectral characterization of a binary mixture (acyclovir anduocinolone acetonide): Eutectic reaction and inclusion complexes with-cyclodextrin

aniela-Crina Marinescu, Elena Pincu, Ioana Stanculescu, Viorica Meltzer ∗

niversity of Bucharest, Faculty of Chemistry, Department of Physical Chemistry, Bd. Regina Elisabeta 4-12, Bucharest, 030018, Romania

r t i c l e i n f o

rticle history:eceived 10 October 2012eceived in revised form 7 March 2013ccepted 12 March 2013vailable online 20 March 2013

eywords:

a b s t r a c t

The thermal and structural properties of acyclovir (ACV) and fluocinolone acetonide (FA) have beenstudied alone and in the corresponding binary mixture, using differential scanning calorimetry (DSC),hot stage microscopy (HSM) and Fourier Transform Infrared spectroscopy (FT-IR).

The temperatures and enthalpies of solid–solid transitions and melting for the pure compounds wereobtained from the DSC data. The predominant crystalline or amorphous character of pure compoundswas noticed by HSM experiments and the characteristics absorption bands were obtained using FT-IR

cyclovirluocinolone acetonideutectic-Cyclodextrin

nclusion complexes

spectroscopy.For the binary mixtures, a eutectic reaction was observed in all DSC curves at 526 K, followed by decom-

position, a phenomenon that was confirmed by FT-IR measurements. The phase diagram and Tamman’splot suggest a eutectic composition at xACV = 0.80. From the DSC curves and FT-IR spectra obtained forthe mixtures of active principle ingredients (APIs) with �-CD we concluded that the inclusion complexesformation takes place for 1:1 mole ratio.

© 2013 Elsevier B.V. All rights reserved.

. Introduction

The use of eutectic mixtures for pharmaceutical applicationsas first described by Sekiguchi and Obi. In the eutectic com-osition, both components are in reduced particle size and wellispersed. When eutectic reaction occurs, the temperature duringrug processing must be kept lower than the eutectic tempera-ure. Eutectic reaction may form from mixtures of active principlengredients (APIs), mixtures of APIs and excipients and mixtures ofxcipients [1].

Pharmaceutical materials with a higher bioavailability that con-ain and efficiently release two drugs represent a modern andhallenging preoccupation in the pharmacological industry of ourays. A particular importance is granted to binary mixtures con-isting of APIs with different chemical properties and structure, butith pharmacological action for the same condition [2].

The substances used in this study are acyclovir (ACV), fluoci-olone acetonide (FA) and �-cyclodextrin (�-CD).

Fluocinolone acetonide (FA), chemically known as (6�,�-difluoro-11�,16�,17,21-tetrahydroxypregna-1,4-diene-3,20-ione cyclic 16,17-acetal with acetone), is a corticosteroid topically

∗ Corresponding author. Tel.: +400213159249; fax: +400213159249.E-mail address: viomel@gw-chimie.math.unibuc.ro (V. Meltzer).

040-6031/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.tca.2013.03.013

used in the treatment of various skin disorders and of inflamma-tory eye, ear and nose diseases. It exhibits high anti-inflammatoryactivity and is usually employed in formulation as a cream, gel,lotion or ointment [3,4].

Acyclovir (ACV), chemically known as [9-(2-hydroxy-ethoxylmethyl) guanine], is a synthetic purine nucleoside analogderived from guanine. ACV is known for the inhibitory activityagainst herpes simplex virus (HSV), mainly HSV-1, HSV-2, andvaricella-zoster virus (VZV), by stopping replication of viral DNAdue to its affinity for the enzyme thymidine kinase encoded byHSV and VZV [5].

Although ACV is one of most used antiviral drugs, in the litera-ture are reported some problems related to its physical properties.One of the problems is the low bioavailability in solid pharmaceu-tical drugs, reported to be around 15–30% [6], and it is poorly watersoluble. The transdermal absorption of ACV administrated topicallywas also reported to be low, and most researchers developed sometechniques to increase this property [5].

�-Cyclodextrin (�-CD) is a cyclic water soluble oligosaccharidecontaining seven glucopyranose units bonded together by �-(1,4)linkages, obtained from enzymatic conversion of starch. �-CD was

chosen for this study considering the APIs molecular structure andthe economical and commercial availability. Complex formation orinclusion complexation occurs when the CD molecule partially orfully entraps a guest compound in its hydrophobic cavity [7,8].

D.-C. Marinescu et al. / Thermochimica Acta 560 (2013) 104– 111 105

Table 1Physico-chemical properties of pure compounds: FA and ACV.

Denomination Chemical formula Molecularmass/g mol−1

Melting point/K �fusH/kJ mol−1 �fusS/J mol−1 K−1

Literature Experimental DSC(Exp.) DSC(Exp.)

2]

11]

abcpdt[

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2

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10m(em

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FA C24H30F2O6 452.488 539.15–547.15 [

ACV C8H11N5O3 225.20 528.15–529.15 [

In the specialty literature are reported different trials regarding strategy of combined treatment [9], with a possible incrementalenefit of antiviral agents in addition to corticosteroids. Corti-osteroids, with their powerful anti-inflammatory effect, have aotential role to play in the reduction or minimization of nerveamage when administered together with antiviral therapy, andherefore may improve the outcome for patients Bell Palsy disorder10].

One aim of this study was to determine the behavior of theinary mixture of ACV and FA, through the construction of the phaseiagram and Tamman’s plot, based on the results of DSC experi-ents, as well to investigate the structure of prepared mixtures

sing FT-IR spectroscopy and HSM.The second aim of this study was to prepare and characterize

he APIs–�-CD inclusion complexes, thus binary mixtures FA- �-D, ACV-�-CD and ternary mixtures (binary mixture of APIs with-CD) with 1: 1 and 1:2 mole ratios, reported to mole of binaryixture.

. Experimental

ACV (Merck, purity ≥98%), FA (Aldrich, purity ≥98%) and �-CDFluka, purity ≥99%) were commercially available and used withouturther purification.

Binary mixtures of APIs of known concentration were preparedn order to cover the entire region of phase diagram, with varying

ole fraction within the range 0.00 – 1.00 by weighing, grindingnd homogenizing in normal lab conditions. Thirteen samples ofCV and FA binary mixtures with the following mole fractions ofCV (xACV): 0.20, 0.30, 0.40, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80,.85, 0.90 and 0.95 were prepared.

Binary mixtures of each API and �-CD were prepared in a 1:1 and:2 mole ratio and ternary mixtures of APIs (with xACV = 0.40, 0.60,.80) and �-CD were prepared considering the medium molecularass of the binary mixture of APIs and using 1:1 and 1:2 mole ratio

one mole of binary mixture), by weighing, grinding and homog-nizing in normal lab conditions and also by solvent evaporationethod.The melting temperature and enthalpy of fusion of pure com-

ounds and mixtures were determined by DSC using a Perkin

lmer Diamond DSC equipment, under a heating/cooling rate of 10egree/min over a temperature range of (291.15–571.15) K for purePI, (291.15–551.15) K for binary mixtures of APIs and (291.15–21.15) K for �-CD and its mixtures, in inert atmosphere (helium,

Fig. 1. Structural formula fo

DSC:550.51 ± 0.65 HSM: 546.15 Melting anddecomposition

–

DSC:534.51 ± 0.30 HSM: 535.15 18.27 ± 0.07 34.18 ± 0.13

30 ml/min flow). At least three replicates of each measurement(pure compounds and mixtures) have been performed.

The apparatus was calibrated for temperature and enthalpy bymelting high purity indium. Sample of 4 to 10 mg were transferredinto aluminum crucibles that were sealed and weighed with thePartner XA balance with a precision of 10 �g.

The FT-IR spectra of pure API, binary mixtures of APIs and binaryand ternary mixtures of APIs with �-CD were obtained using aVertex 70-Bruker spectrophotometer with the following param-eters: resolution 4 cm−1; spectral range: (4000–400) cm−1; beamsplitter: KBr. Each sample has been dispersed in about 300 mg ofanhydrous KBr and the resulting powder was grounded in an agatemortar. Spectra were processed and analysed with the OPUS soft-ware. Atmospheric compensation, vector normalization of wholespectra and baseline correction using straight lines and one itera-tion additional concave rubberband correction were applied to thespectra.

The microstructure of pure APIs and binary mixtures of APIs wasrecorded using a hot stage polarizing microscope (HSM – Nikon 50iPol microscope with a Linkam THMS 600 hot stage and a TMS 94temperature controller) a heating-cooling rate of 10◦/min over atemperature range of (291.15–551.15) K in normal lab conditions atatmospheric pressure, and interesting regions were photographed.

3. Results and discussion

3.1. Analysis of pure compounds

Before building the phase diagram of ACV–FA binary mixture,the pure compounds were studied from physico-chemical pointof view. In Table 1 are presented the physico-chemical properties,determined by DSC and HSM for each pure compound.

The structural formulas for the studied compounds are shownin Fig. 1.

The DSC study of the pure compounds (Fig. 2) showed that themelting process is followed rapidly by the decomposition. For FA(Fig. 2) the DSC curve presented a broad small endothermic peak inthe temperature range (446–466) K, attributed to solid–solid tran-sition to Form A into the Form B, forms related enantiotropically,as already reported in the literature [5]. The second endothermic

peak was attributed to the melting process of Form B and occurs attemperature 550.51 K and is followed by many exothermic eventscharacteristic to the thermal decomposition. By HSM was revealedthe mainly amorphous character of FA, melting process and the

r FA (a) and ACV (b).

106 D.-C. Marinescu et al. / Thermochimica Acta 560 (2013) 104– 111

ftw

tHdc

b

a�dA

t�ıa

wvbga

[14–16]. The next endothermic events in the DSC curves, at higher

Fig. 2. DSC curves for pure compounds.

eature of a polymorphic transition in liquid, closely followed byhermal decomposition (Fig. 3a). The polymorphic character of FAas also noted in the literature [4].

For ACV, the DSC curve (Fig. 2) showed the melting processaking place at 534.51 K, temperature similar to that obtained bySM, 535.15 K (Fig. 3b). The enthalpy of fusion was 81.13 J g−1. Theecomposition process was indicated by exothermic peak in DSCurve at 539.39 K.

The chemical structures of FA, ACV and �-CD were establishedy FT-IR spectroscopy (Fig. 4).

From the FT-IR spectrum of FA (Fig. 4a) the following char-cteristic bands are obtained: �OH = 3403 cm−1, �C=O = 1708 cm−1,C=C = 1669 cm−1, �C=C = 1611 cm−1, in good agreement with theata already reported in the literature and corresponding to Form

[6].For ACV, the characteristic bands obtained from the FT-IR spec-

ra (fig. 4b) are also similar to those found in the literature [12]:OH = 3439 cm−1, �CH = 2928, �C=O = 1694 cm−1, �R-NH = 1575 cm−1,CH2 = 1484 cm−1, ıCH = 1347 cm−1, �NH2,NH = (3312–3175) cm−1

nd �amide,primary alcohol = (1575–1106) cm−1.In the IR spectrum of �-CD (Fig. 4c) a wide band is registered

ith the absorption maximum at 3368 cm−1, caused by the valenceibrations of the O–H bonds in the primary C–OH group connected

y the intermolecular hydrogen bonds or in the secondary hydroxylroups connected by the intramolecular hydrogen bonds. Also,n absorption band with a maximum at 2927 cm−1 is observed,

Fig. 3. HSM pictures obtain

Fig. 4. The FT-IR spectra obtained for FA (a), ACV (b) and (c) �-CD.

representing the valence vibrations of the C–H bonds in the CHand CH2 groups. In the region 1400–1200 cm−1, the absorptionbands of the deformation vibrations of the C–H bonds in the pri-mary and secondary hydroxyl groups of �-CD (1412, 1366, 1335,1302, 1239 cm−1), and in the region 1200–1030 cm−1 the absorp-tion bands of the valence vibrations of the C–O bonds in the etherand hydroxyl groups (1079 and 1027 cm−1) are registered, in goodagreement with the literature data [13].

3.2. Analysis of binary mixtures of ACV–FA

The DSC curves obtained ACV- FA system, for different compo-sitions, shown in fig. 5 and were registered using the temperaturerange (293.15–551.15) K in order to avoid decomposition ofbinary mixtures. The figure presents only the temperature range(440–555) K, were the thermal events occurs.

The DSC data obtained for the binary mixtures ACV–FA arepresented in Table 2. The DSC curves exhibit the melting process fol-lowed by decomposition as already seen for the pure compounds.However, a simple eutectic point represented by the first endother-mic peak, located in good approximation at 526 K can be seen for allstudied mixtures. The eutectic temperature was taken as the onsettemperature at the solid transition, as applied by most researchers

temperature, were attributed to the melting and decompositionof the excess component. Due to the decomposition phenomena,the values of these peaks are approximated and can be seen that

ed for FA (a) ACV (b).

D.-C. Marinescu et al. / Thermochimica Acta 560 (2013) 104– 111 107

tf

tatv

l

wTppa

tstes

tts

TM

Fig. 6. Phase diagram of binary mixture ACV–FA: (a) ©—ideal temperatures

Fig. 5. DSC curves for binary mixtures of ACV and FA.

his process occurs closely to the eutectic temperature as the moleraction of ACV increases.

The mixing process is regarded as the ideal solution model andhe transition temperature of mixture is always lower than that ofny of the pure compounds. Thus, the eutectic transition tempera-ure, for the binary mixture, can be calculated according to Schroderan Laar equation [17]:

n xi = −(�fusHoi /R)(1/T − 1/Tfus,i)

here xi is the mole fraction of the components at the temperature, R the gas constant, �fusHi

◦ the molar enthalpy of fusion of com-onent i (i = ACV, FA) and Tfus,i is the melting temperature of theure component (Table 1). In Fig. 6 are shown the phase diagramnd Tamman’s plot for the binary mixture.

The experimental phase diagram (Fig. 6a) shows deviation fromhe ideal behavior in the entire composition range. Presences ofolid–solid transition characteristic to the FA (Form A) in the mix-ures with high molar fraction of FA influence the position of theutectic peak comparatively with the eutectic peak position corre-ponding to high molar fraction of ACV.

In order to determine the eutectic composition of binary mix-ure ACV–FA, the enthalpy of the eutectic peak is plotted againsthe mole fraction of ACV (Fig. 6b). In the case of a simple eutecticystem, the Tamman plot show a triangle shape. For this system

able 2elting temperature and enthalpy of the binary system ACV–FA.

xACV 1st DSC peak 2nd DSC peak

TEutectic/K �HEutectic/J g−1 T/K

0.00 – – 553.420.10 522.15 8.10 552.450.20 523.41 18.05 549.970.30 522.68 31.09 546.620.40 523.44 39.52 544.520.45 526.10 44.43 526.100.50 525.82 50.81 525.820.55 526.10 53.16 531.220.60 526.70 68.17 532.260.65 526.50 72.23 531.430.70 526.88 82.45 531.670.75 526.51 90.98 530.640.80 526.10 102.81 526.100.85 526.65 96.36 531.390.90 525.63 87.55 530.310.95 527.03 82.03 531.601.00 – – 534.39

curve, �—liquidus temperatures curve, (b) +—solidus temperatures curve; (c) �-—Tamman’s plot.

the enthalpy of the eutectic presents a different linear behavior.In the composition range xACV < 0.80, Tamman plot present twostraight lines with different slope. The first linear dependence isaffected by the solid–solid transition of FA present in excess whilefor xACV > 0.50 the triangle shape of Tamman diagram is retrieved.As expected, the enthalpies values of the eutectic reaction formole fractions below the eutectic composition increased linearlyuntil the exact composition of the eutectic point. For compositionsgreater than the eutectic composition, the enthalpies also decreaselinearly until crossing the composition axis at its extremities for aphase diagram with no solid solution formation or at the concen-tration where the solid solution appears [18,19]. This diagram alsoindicate a eutectic composition of the ACV–FA system at xACV = 0.80,were registered the higher enthalpy value.

In case of binary mixtures, the FT-IR spectra were recordedbefore and after the dynamic temperature regime (Fig. 7). The FT-IRspectra recorded before the dynamic temperature regime indicatethat the binary mixtures spectra represent a sum of individualcompounds spectra with certain variations of band intensity andposition based on molar fractions of each compound, as seen inTable 3. Thus, the most spectacular band shifts are observed forthe OH group, at 3439 cm−1 for ACV and 3403 cm−1 for FA, respec-tively. With the decrease of the mole fraction of ACV, the band at

3439 cm−1 is shifted at 3436 cm-1 showing the involvement of theOH group in a stronger H bond and the band at 3403 cm−1 is shiftedto higher frequency at 3406 cm−1 probing the participation of OH

108 D.-C. Marinescu et al. / Thermochimica Acta 560 (2013) 104– 111

Table 3Characteristic adsorption bands for the binary mixture of APIs.

�/cm−1 ACV FA xACV

0.30 0.40 0.55 0.60 0.70 0.80

�OH 3439 3403 3436 3437 3437 3438ob ob m m m m3404 3404 3404 3404 3405 3406sh sh sh - - -

�NH2,NH 3312–3175 – sh sh sh 3327 3317 33153177 3178 3177 3177 3176 3176

�CH 2928 2941 2940 2940 2940 2939 2939 2938m m m m m mob ob ob ob ob ob

�C=O ob 1709 1709 1708 1708 1708 ob ob– 1669 – 1694 1694 1695 1694 16941694 – 1670 1670 1670 1670 1671

�c=c 1608 1611 1611 1611 1610 1610 1610 1609ıCH2 1484 – 1482 1483 1484 1484 1483 1484ıCH 1347 sh 1345 1346 1346 1346 1346 1347ıR-NH 1575 – 1575 1576 1576 1576 1575 1575

m m m m

s

ifibFiIOfTCa

p

dde�w

FA

�primary,alcohol (1106) ob 1102

, strong; m, medium; w, weak; sh, shoulder; ob, overlapped bands.

n a weaker H bond. The increase of the N–H stretching frequencyrom 3313 cm−1 of ACV to 3322 in the binary mixture (xACV = 0.6)mplies that the primary amine group is participating in a weak Hond. The characteristic adsorption bands for CH, at 2941 cm−1 inA spectrum, move to lower wavenumbers in the binary mixtures,ndicating the establishment of strong vander Waals interactions.n agreement with statements of Masuda [6], the shift of H bondedH and NH bands to higher wavenumbers implies that the bond

orce constant increase due to the participation in weaker H bonds.his reasoning is valid for classical O-H···O, N–H···N bonds, but also–H···O, C–H···N and non-specific van der Waals/electrostatic inter-ction.

The C O valence and CH deformation bands presents small dis-lacements for the binary mixtures as can be seen form Table 3.

The FT-IR spectra of binary mixtures, recorded after theynamic temperature regime indicate certain structural changes

ue to partial decomposition observed also in the DSC curves,specially on frequencies �C C = 1611 cm−1, �NH = 1575 cm−1,amide,primary alcohol = (1575–1106) cm−1 and �C O = 1708 cm−1,hose decrease in intensity is more obvious as the value of xACV

ig. 7. Representative FT-IR spectra obtained for different binary mixtures ofCV–FA, (- - -) before and (· · ·) after the DSC experiments.

1103 1105 1106 1106 1106

increases. The bands changes consist basically in the decrease ofthe intensity, disappearance of bands or bands shifts as seen inFig. 7 for different molar fraction of ACV.

The HSM pictures obtained for the binary mixtures with differ-ent molar fractions of ACV–FA system are presented in Fig. 8 andare confirming the processes already observed in the DSC curvesand the FT-IR spectra, but also some polymorphic transitions notdetected by the techniques already used.

Therefore, it can be observed some polymorphic transition forxACV = 0.55 and xACV = 0.7 around 523 K temperature. Also using thistechnique can be observed that at the same temperature, 533 K,decomposition is more pronounced as the molar fraction of ACV ishigher, as already seen in the FT-IR spectra and DSC curves.

3.3. ˇ-CD-APIs inclusion complexes

In order to improve the solubility in aqueous medium and over-come the decomposition process, the next step of this study was toencapsulate the pure APIs in �-CD and to characterize the interac-tions established between the binary mixtures of APIs of differentmole fractions and �-CD.

The existence of interactions between the components can beobtained by thermal analysis, DSC. When guest molecules areincluded in the CD cavity, their melting, boiling, and sublima-tion points usually shift to a different temperature or disappearwithin the temperature range at which the CD is decomposed[20,21].

The inclusion complexes of the FA, ACV and their binary mix-ture with �-CD were prepared and then characterized in the solidstate. The DSC thermograms of �-CD, FA and �-CD, ACV and �-CD, ACV–FA binary mixture with xACV = 0.40, 0.60, 0.80 and �-CDphysical mixtures with a molar ratio 1:1 and 1:2 are shown inFig. 9.

The DSC curve of �-CD (Fig. 9) showed a very broad endothermicpeak in the range of (351–361) K due to the elimination of crystal-lization water and melting with decomposition around (564–586) Ktemperature range, which was in concordance with the literaturedata [11]. The DSC thermogram of FA (Fig. 2) exhibited a sharpendothermic peak at 553.02 K, corresponding to its melting point,

followed by decomposition. The DSC curve of FA- �-CD 1:1 binarymixture obtained by mechanical activation (Fig. 9) and solventevaporation (distilled water) (Fig. 10) shows no thermal events,except the decomposition phenomena at higher temperature,

D.-C. Marinescu et al. / Thermochimica Acta 560 (2013) 104– 111 109

binary

i(soia�Itsra

sgtmcwxdc

Fig. 8. The HSM pictures obtained for the

ndicating the inclusion complex formation. The ACV thermal studyFig. 2) exhibited a sharp endothermic peak at 534.17 K, corre-ponding to its melting point, followed by decomposition. Scansf ACV- �-CD 1:1 binary mixture (Figs. 9 and 10) indicate also thenclusion complex formation, as already mentioned in the liter-ture [21]. The experiments performed using excess quantity of-CD (data not shown) did not provide any additional information.

n the case of the ternary mixtures formed by the APIs binary mix-ures and �-CD obtained by physical mixture method (Fig. 9) can beeen some differences between the DSC curves obtained for molaratio 1:1 and 1:2 respectively, between the binary mixture of APIsnd �-CD (mole ratio is reported at mole of binary mixture of APIs).

For the physical mixture method, in the case of 1:1 mole ratioome endothermic or exothermic events can be observed, sug-esting that this method does not give complete encapsulation;he phenomenon is obvious for the ternary system with 0.40

ole fraction of ACV. The complete disappearance of the two APIsharacteristic features was instead observed for systems prepared

ith xACV = 0.60 and 0.80, 1:1 molar ratio. For 1:2 molar ratio and

ACV = 0.40, 0.60 and 0.80, the characteristic peaks of APIs were notetected indicating that the drugs penetrated into the cyclodextrinavity (Fig. 9).

mixtures with different molar fractions.

For the solvent (distilled water) evaporation method, using1:1 and 1:2 molar ratio, the characteristic features of APIs werenot detected indicating the inclusion complex formation (Fig. 10).Because of its molecularly dispersed distribution and the protectionthat the complexation affords, the peaks were not detected due tothe displacement to the decomposition temperature of the �-CD.

Further, FT-IR spectroscopy was used to confirm the com-plexation of ACV–FA system with �-CD in solid state. Inclusioncomplex formation may be confirmed by IR spectroscopy becausebands resulting from the incorporated guest molecule are generallyshifted or their intensities are altered [11,22]. Changes in the repre-sentative adsorption bands of ACV and FA were found, confirmingthe complex formation between the pure APIs and �-CD.

The cyclodextrin bands are very intense in the CH and OH bandsarea and cover the FA and ACV peaks. Nevertheless, the ACV andFA bands are observed for example as shoulders at 2990 cm-1and 3179 cm-1. Following complexation, batochromic and hip-sochromic shifts and hipochrom and hyperchrom effects appear

indicating formation of strong hydrogen bonds and non-specificvan der Waals interactions. With the exception of the region from1760 to 1510 cm−1 where the cyclodextrin bands are absent or veryweak, the spectra of the inclusion complexes obtained by physical

110 D.-C. Marinescu et al. / Thermochimica Acta 560 (2013) 104– 111

Fm1

mai

fOip(dwa(ctit

Ft1

ig. 9. The DSC thermograms of �-CD, ACV and �-CD, FA and �-CD, ACV–FA binaryixture with xACV = 0.40, 0.60, 0.80 and �-CD, physical mixtures with a mole ratio

:1 and 1:2.

ixture or solvent evaporation method and pure cyclodextrin have similar shape taking into account the small frequency shifts andntensity modifications.

The ACV- �-CD inclusion complex spectrum, (Fig. 11) differsrom the FT-IR spectra registered for the pure components. TheH absorption band observed in the inclusion complex spectrum

s shifted to a lower frequency (3369 cm−1), comparing with theure ACV spectrum. The same phenomenon is observed for NH1575 cm−1) and C O (1693 cm−1) adsorption bands and for C–Heformation vibrations of �-CD (1412, 1335, 1302, 1239 cm−1)hich are shifted to higher wavenumbers. The characteristic

dsorption bands for primary and secondary amine form ACV3312–3175) cm−1are covered by the very intense OH band ofyclodextrinIn the case of FA and �-CD inclusion complex spec-

rum, comparing to the pure FA spectrum, the OH adsorption bands also shifted to lower frequencies. Meanwhile, the C O adsorp-ion band from pure FA is slightly shifted to higher wave number

ig. 10. The DSC thermograms of ACV and �-CD, FA and �-CD, ACV–FA binary mix-ure with xACV = 0.40, 0.60, 0.80 and �-CD, solvent method, with a mole ratio 1:1 and:2.

Fig. 11. FT-IR spectra of ACV and �-CD, FA and �-CD, ACV–FA binary mixture withxACV = 0.40 and 0.60 and �-CD, physical mixtures (p.m.) and solvent method (s.m.),with a molar ratio 1:1 and 1:2.

(from 1707 to 1709 cm−1) indicating participation to a weak hydro-gen bond and the C-H deformation vibrations of �-CD are shiftedto higher frequencies suggesting the existence of non specific vander Waals interactions. These results indicate that the vibrations ofthe guest molecules are influenced by the encapsulation of ACV orFA in the �-CD cavity.

In the case of the ternary system spectra, it can be observedthat the characteristic adsorption bands for primary and secondaryamine, at (3312–3175) cm−1 and 1575 cm−1 are seen as very weakshoulders, C C adsorption band is shifted to higher wavenumbersand the C–H deformation vibrations of �-CD are shifted to higherfrequencies. These observations support the inclusion formationobserved in the DSC curves but it is difficult to identify which partof the APIs is enclosed in the cyclodextrin cavity.

Slight differences are observed in the spectra obtained for the1:1 and 1:2 mole ratio (one mole of binary mixture ACV–FA) andin the spectra of ternary systems obtained by physical and solventmethod. In the case where excess quantity of �-CD was used, inde-pendent from the obtaining method of the ternary mixtures, thespectra are more similar to that of pure �-CD, as expected. In thelight of these results we concluded that even the signals of ACV–FAbinary mixture are quite completely convoluted by the �-CD signalsthe FTIR spectra are a rich source of information on the structuralchanges due to physical interactions in binary and ternary mixtures.

4. Conclusions

In this study were obtained the physico-chemical and spectro-scopic characteristics of pure compounds and of physical mixturesof APIs with different molar fraction.

For the binary mixture of APIs, a eutectic reaction was observedin all DSC curves at 526 K, followed by decomposition, as also seenin HSM experiments. The eutectic temperature is influenced bythe solid–solid transitions of the FA in excess. The phase diagramand Tamman’s plot suggest a eutectic composition at xACV = 0.80.FT-IR spectra recorded before and after the dynamic temperaturetreatment confirms partial decomposition of mixtures. These data

suggests the use of this binary mixture below the eutectic temper-ature (526 K).

The DSC curves and the FT-IR spectra obtained for the binaryand ternary mixtures of APIs with �-CD suggest the inclusion

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[[21] C.P. Rossel, J.S. Carreno, M. Rodríguez-Baeza, J.B. Alderete, Química Nova 23

D.-C. Marinescu et al. / Thermo

omplexes formation for 1:1 mole ratio in the case of pure com-ound and also in the case of the binary mixtures of APIs, obtainedy mechanical activation or solvent evaporation method.

From physico-chemical point of view, this study highlights theotential use of a eutectic mixture of ACV and FA, below the eutecticemperature. Due to low solubility of FA and ACV, the formation of autectic mixture with a lower melting point using a simple mechan-cal activation (grinding), as also inclusion complexes formed with-CD, are two attractive methods for proper preparation of drugsith potential increased bioavailability.

cknowledgements

This work was possible with the financial support of the Sec-oral Operational Programme for Human Resources Development007–2013, co-financed by the European Social Fund, under theroject number POSDRU/107/1.5/S/80765.

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