Energetically favorable interactions between diclofenac sodium and cyclodextrin molecules in aqueous media

Journal of Colloid and Interface Science 326 (2008) 374–381

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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis

Energetically favorable interactions between diclofenac sodium and cyclodextrin molecules in aqueous media S.K. Mehta ∗ , K.K. Bhasin, Shilpee Dham Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh 160 014, India

a r t i c l e

i n f o

a b s t r a c t

Article history: Received 28 March 2008 Accepted 18 June 2008 Available online 21 June 2008

The effect of the addition of cyclodextrins (CD) viz., α -, β -, HPβ - and γ -CD to the aqueous solutions of the most widely prescribed anti-inflammatory drug, diclofenac sodium (DS), has been fully investigated by means of spectroscopic (UV–vis, steady-sate fluorescence, 1 H NMR and ROESY) and thermodynamic (conductivity) techniques. The global picture of the results indicates that diclofenac sodium penetrates the CD cavity. The apparent association constants for all the inclusion complexes were estimated from fluorescence data. Conductivity measurements of aqueous solutions of diclofenac sodium were performed both as a function of DS concentration and CD concentration, at different temperatures ranging from 15 to 40 ◦ C. Results suggested the existence of 1:1 complex between DS and CD. The thermodynamics of the system was discussed in terms of change in Gibbs free energy. Free energy of the DS/W system was found to decrease on addition of cyclodextrin, which points towards the energetically favorable interactions between drug and cyclodextrin molecules in solution phase. 1 H NMR chemical shift changes and ROESY spectra provide powerful means for probing CD:DS interactions. © 2008 Elsevier Inc. All rights reserved.

Keywords: Diclofenac sodium Cyclodextrin Conductivity UV–visible Fluorescence 1 H NMR ROESY

1. Introduction Cyclodextrins (nontoxic macrocyclic sugars) are well known in supramolecular chemistry as the most efficient molecular hosts [1–6] capable of encapsulating, with a degree of selectivity, a range of guest molecules via noncovalent interactions in hydrophobic cavities. The sequestration of a hydrophobic molecule or some part of it, inside the cavity usually alters the physicochemical properties of the encapsulated molecule, which is protected against the aqueous medium from light, oxidants or reactive attacks. CDs and their derivatives have received considerable attention in the pharmaceutical field [7–11] for the past few years due to their extensive use in drug delivery processes. In addition, they can be used to reduce or eliminate unpleasant smells or tastes, prevent drug–drug or drug–additive interactions. This stimulated a great deal of research toward the synthesis of new host–guest complexes and the structural characterization of the supramolecular adducts in terms of geometry and thermodynamics via a variety of physical methods. Most of the studies found in the literature regarding the CD formulation of drugs, have been carried out from a biomedical standpoint dealing mainly with pharmacokinetic assays, plasma level determinations, in vivo studies [1,9,10,12–14], etc. Few studies [3,6,15–17], however, are involved in physicochemical characteri-

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zation of microencapsulates. Thus it is necessary to analyze the colloidal behavior of drug both in absence and presence of cyclodextrins. The rational design of pharmaceutical CD formulations requires a good knowledge of the encapsulation process. Structural information, such as the stoichiometry and the geometry of the complex, and thermodynamic information of binding, are necessary to draw a complete picture of the driving forces governing the drug:CD interaction. The investigation of all these aspects is the main objective of this work, focused on the analysis of the interactions between different cyclodextrins and the drug diclofenac sodium. Diclofenac is one of the most widely prescribed NSAIDs (nonsteroidal antiinflammatory drug) for its analgesic, and anti-inflammatory indications. It is used to relieve pain and inflammation in a wide range of musculoskeletal conditions, including various forms of arthritis, gout, sprains, fractures, dislocations, back pain, tendinitis and frozen shoulder. Similar to other NSAIDs, diclofenac use is associated with rare, but serious and sometimes fatal, gastrointestinal (GI) side effects, including ulceration, and hemorrhage, so is an ideal candidate for incorporation in a controlled release device to diminish its adverse effects after oral administration. Different approaches have been taken to decrease NSAID-induced GI toxicity. For example, incorporation of NSAIDs with phospholipid has been suggested to improve GI safety of these drugs [18]. It is, therefore, expected that the formulation of diclofenac sodium as microencapsulate with cyclodextrin may show a better bioavailability. Keeping this in mind, it was planned to investigate the behavior of di-

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clofenac sodium in the presence of different cyclodextrins via spectroscopic and conductivity techniques. The information obtained from conductivity studies have been correlated with the observations of spectroscopic studies [15–17,19–21]. The analysis of the results will provide an insight into the thermodynamics of DS:CD association. Such systems may be used to improve the aqueous solubility of the drug, thus enhancing its dissolution rate, leading to a faster onset of action and less GI mucosal toxicity. It is believed that the findings will show the convenience of characterizing the drug:CD complexes from a physicochemical point of view, to improve our understanding of the drug:CD interaction and serve as the basis for further investigations of such systems. 2. Experimental 2.1. Materials Diclofenac Sodium having purity 98% was obtained from U.I.P.S., Panjab University, Chandigarh. β -Cyclodextrin (purity > 99%), HPβ -cyclodextrin (purity > 98%), γ -cyclodextrin (purity > 98%) and pyrene (purity  97%) were purchased from Fluka while α -cyclodextrin (purity > 98%) was obtained from Himedia. Potassium chloride (purity > 99%) and D2 O (99.9% atom D) was purchased from Merck and Aldrich respectively. All the chemicals were used without further purification. Water used for the preparation of samples was deionized and triply distilled (conductivity lower than 3 μS). 2.2. Methods 2.2.1. Conductivity studies The conductivity of mixtures was measured in a thermostatic glass cell with two platinum electrodes and Pico conductivity meter from Lab India. The conductivity meter was calibrated by measuring the conductivity of the solutions of potassium chloride of different concentrations (0.001, 0.01 and 0.1 M). Electrodes were inserted in a double walled glass cell containing the solution. The glass cell was connected to the thermostat controlled to better than ±0.01 K temperature variation. The cell constant of the cell used was 1.02 cm−1 . The measurement of conductivity was carried out with an absolute accuracy up to ±3% and the degree of precision was greater than ±0.1%. The solutions were prepared by weight using an electronic balance with an accuracy of ±1 × 10−4 g. The conductivity measurements were made at different temperatures viz. 15 to 40 ◦ C for drug/cyclodextrin/water (DS/CD/W) ternary system, as a function of drug concentration. 2.2.2. UV–visible spectroscopy The UV–vis spectra were recorded with JASCO V-530 spectrophotometer using quartz cells. In the experiments with DS/W binary system, the concentration of drug was varied from 0 to 0.3 mM while for the DS/CD/W ternary system cyclodextrin concentration was kept constant at 1.0 mM and drug concentration was varied from 0 to 0.3 mM, both in the sample and in the reference cell. 2.2.3. Fluorescence spectroscopy Fluorescence measurements were carried out with Varian spectrophotometer. A 1 cm rectangular silica cell was placed in a multicell holder whose temperature was kept constant at 25 ◦ C with a recirculating water circuit. Pyrene was used as luminescence probe and its concentration was kept constant at 10−3 mM. Both excitation and emission band slits were fixed at 5 nm and the scan rate was selected at 500 nm/min. The excitation wavelength was selected at 340 nm, while the emission spectra were collected in

Fig. 1. Effect of β -CD concentration (0.0–1.0 mM) on UV absorption spectra of DS (0.3 mM) in water.

the range 350–450 nm. In the experiments with DS/CD/W ternary system drug concentration was kept constant at 0.3 mM and cyclodextrin concentration was varied from 0 to 4 mM, for all the systems. 2.2.4. NMR spectroscopy All the 1 H NMR and ROESY experiments were carried out in deuterated water (D2 O) on Bruker Avance II (400 MHz) spectrometer. Chemical shifts are given in ppm relative to tetramethylsilane as an internal standard (δ = 0 ppm). 3. Results and discussion Mode of host–guest interaction—UV–visible and fluorescence studies 3.1. UV–visible measurements In a previous study from our research lab [20], UV–vis spectrum of the aqueous solution of DS was recorded at different drug concentrations at room temperature. Molar absorption coefficient ε , at λmax = 275 nm was estimated to be 8221.14 ± 80 M−1 cm−1 . In the present work, UV–vis spectra of DS solution in presence of different CDs were recorded. An example is shown in Fig. 1. From these spectra it arises that DS λmax peak at 275 nm showed a hyperchromic effect with an intensity absorption increase in the presence of CD. The estimated molar absorption coefficient ε , for DS/α -CD/W, DS/β -CD/W, DS/HPβ -CD/W and DS/γ -CD/W systems at λ275 nm are 8338 ± 30, 8352.04 ± 29, 8725.25 ± 20 and 9845.38 ± 10 M−1 cm−1 respectively. The presence of molecular interactions among cyclodextrin and drug molecules induce structural modifications in the system that causes free movement of electrons into different energy levels and hence absorb more UV light. Thus increasing probability of electronic transitions of the excitable drug electrons in the presence of cyclodextrins causes increase in the magnitude of the absorbance and molar absorption coefficient. However, no significant shifts were observed in the characteristic peaks of drug by addition of CDs that indicates the absence of any strong bonding between drug molecule and CDs.

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Fig. 2. Emission fluorescence spectra of aqueous solution of diclofenac sodium at constant concentration (0.1 mM) at 25 ◦ C, in the absence and presence of different concentrations of β -CD and γ -CD (0.0–4.0 mM).

3.2. Fluorescence studies The investigation on the cyclodextrin (CD) derivative with fluorophore used as a sensor to detect foreign species via identifying the fluorescence intensity changes shows a profound meaning in the molecular recognition field [17,22–25]. Studies with pyrene as a fluorophore (fluorescence probe) have received a special consideration [26]. Pyrene is a strongly hydrophobic probe and its solubility in water is very low (2–3 μM). In the presence of cyclodextrins like macromolecular systems pyrene is preferentially solubilized in the interior hydrophobic regions of the systems. Thus its presence inside the CD cavity not only can alter the photochemical inert behavior of CD to active status but also can enhance its detective sensitivity. The fluorescence spectra were recorded for all the chosen cyclodextrin systems. Fig. 2 shows the effect of the addition of β -CD and γ -CD on the fluorescence emission spectra of an aqueous solution of DS at a constant concentration of 0.3 mM in pyrene [1 mM] at 25 ◦ C, as an example. An increase of the CD concentration results in clear emission intensity enhancements. Similar enhancements were observed for the other cyclodextrin systems. It is known that the intensification of luminescent processes of a fluorescent guest molecule partially or totally encapsulated by the CD cavity is due to shielding from quenching and nonradioactive decay processes (decay of stable compounds under the influence of external stimuli such as heat or the presence of other molecular compounds in the vicinity) occurring in the bulk solvent [27–29]. Thus, the evidences observed demonstrate that the self-inclusion complex has been formed under this condition and DS was able to get into the CD cavity spontaneously in aqueous solution. On encapsulation, the DS experiences a different chemical environment (geometric restrictions and reduced polarity) compared to that in aqueous solution. This alters the energetics and dynamics of the photophysical process of the drug molecule. These observations indicate the formation of DS:CD inclusion complex. 3.2.1. Apparent formation constant of D:CD inclusion complex The fluorescence intensity of a system can be increased by a variety of molecular interactions. This enhancement in intensity is useful in the estimation of the association constants [30–32]. Modified Stern–Volmer equation (Eq. (1)) has been used to analyze the fluorescence data. F0 F − F0

=

1 fa

+

1

[CD] f a K a

,

(1)

where F and F 0 are the steady state fluorescence intensities at 393 nm in the presence and absence of cyclodextrin (CD) respectively, K a is the association constant and f a is fluorophore assess-

Fig. 3. Stern–Volmer plot for DS/HPβ -CD/W system at 25 ◦ C with 0.1 mM [DS] and at different concentrations of HPβ -CD (0.0–4.0 mM).

ability. The dependence of F 0 /( F − F 0 ) on the reciprocal value of the CD concentration is linear and K a values can be calculated from the slope. Fig. 3 shows the representative plot of DS:HPβ CD system. The K a values calculated for all the systems and are collectively presented in Table 1. Although association of DS with different CDs has not been reported in the literature, the K a values found in this work are comparable to those obtained for DS:β CD system by Manca et al. [33]. However, the values are different from those obtained for other NSAIDs [16,34,35]. The probable reason could be the use of different techniques for the calculation of association constants as it is a fact that the association constant between host–guest molecules significantly depends upon the technique/method used for their evaluation [36–38]. Moreover, the different sizes of drug molecules also affect the binding process and hence difference in K a values are observed. The affinity of DS by CDs is moderate with K a values in the range of 200–600 M−1 . These moderate values are favorable from pharmaceutical point of view, since it is known that a high affinity between the drug and CD can cause a difficult delivery of the therapeutic compound to the organism.

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Table 1 Values of association constant, K a for DS/CD/W at 25 ◦ C DS:CD

K a (M−1 )

DS/α CD/W DS/β CD/W DS/HPβ CD/W DS/γ CD/W

238.80 387.58 400.85 530.50

Fig. 5. Variation of specific conductivity (κ ) vs drug concentration for (a) DS/β CD/W and (b) DS/γ -CD/W system having constant concentration of CD (12 mM) and concentration of DS was varied (0.0–6.0 mM).

Fig. 4. Specific conductivity (κ ) plots for DS/W binary system at different temperatures.

The different CDs possessing hydrophobic cavities of different diameters (α -CD = 5.3 nm, β -CD ≈ HPβ -CD ≈ 6.5 nm, γ -CD = 8.3 nm) display obvious distinctions in association ability towards DS molecules (e.g. Table 1). We can thus deduce that the inclusion complexation behavior of CDs with DS is mostly related to the size-fit relationship between host and guest. As α -CD has smallest hydrophobic cavity, least association constant of DS:α -CD is reasonable. β -CD, HPβ -CD and γ -CD with larger cavities than α -CD form much more stable inclusion complexes with DS, resulting in highest association constant for DS:γ -CD system. This is due to the well size-fit between the larger cavity of γ -CD and DS molecule, thus γ -CD can carry the drug more strongly in comparison to other cyclodextrins. The results were comparable with those obtained by Liu and coworkers [4] where α -asarone (a traditional Chinese medicine) binds more strongly with γ -CD in comparison to α -CD and β -CD. 3.3. Thermodynamics of the system—Conductivity studies In Fig. 4, the values of the specific conductivity, κ for the binary DS/W solutions are plotted as a function of [DS] at various temperatures ranging from 15 to 40 ◦ C. At each temperature, the concentration dependence of the electrical conductivity shows a monotonic increase, which is due to an increase in the thermal energy of the molecular entities. Fig. 5 depicts the plot of specific conductivity κ , for the aqueous solution of drug in the presence of constant concentration (12 mM) of CDs viz., β -CD, and γ -CD respectively at different temperatures studied herein. Similar plots have been obtained for the DS/α -CD/W and DS/HPβ -CD/W ternary systems. On comparison, DS/CD/W system showed a lower conductivity than pure DS/W system. It points to the interaction of drug with cyclodextrin moiety, because the mobility of associated drug is expected to be less than that of the free drug (Fig. 6). Effect of temperature variation is insignificant for both binary and ternary systems. The critical aggregation concentration (cac) was determined in absence and

Fig. 6. Variation of specific conductivity (κ ) vs drug concentration in absence and presence of different cyclodextrins at 25 ◦ C with constant concentration of CD (12 mM) and concentration of DS was varied (0.0–6.0 mM).

presence of CD from plots of the molar conductance, Λ vs [DS] (Fig. 7). The formation of the inclusion complex DS:CD can be more clearly observed in Fig. 8, which shows the plots of difference between the specific conductivity of drug in absence and presence of CD (β -CD and γ˜ -CD) as a function of [CD]. The decrease in κ when CD is added points to the inclusion of the DS− anion into the CD cavity, because the mobility of the associated anion is expected to be less than that of the free anion. Similar trends were observed in other D:CD systems [15]. An attempt has been made to estimate the stoichiometry of inclusion complex that is defined as the ratio between [CD] and [DS− ] (Fig. 8), where [CD] being the concentration at which two straight lines intercept at each temperature and [DS− ], the initial drug concentration, kept constant in the experiment (6 mM) [16]. A value of 1.0 ± 0.3, averaged over the results obtained at all the temperatures for all the systems, indicates that the complex is formed by the association of a molecule

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Table 2 Values of critical aggregation concentration, cac for DS/W and DS/CD/W at various temperatures with [CD] = 12 mM T (◦ C)

15 20 25 30 35 40

cac (mM) DS/W

DS/α -CD/W

DS/β -CD/W

DS/HPβ -CD/W

DS/γ -CD/W

1.05 1.11 1.17 1.18 1.25 1.31

0.94 0.95 0.96 0.97 0.98 1.12

0.85 0.86 0.88 0.92 0.94 1.05

0.84 0.85 0.88 0.90 0.93 1.02

0.79 0.80 0.85 0.87 0.90 0.95

Table 3 0 Values of free energy G m , for DS/W and DS/CD/W at various temperatures with [CD] = 12 mM T (◦ C)

Fig. 7. Variation of molar conductivity (Λ) vs drug concentration for (a) DS/β -CD/W and (b) DS/γ -CD/W system where concentration of CD was kept constant (12 mM) and concentration of DS was varied (0.0–6.0 mM).

of CD per molecule of drug, which is most common for cyclodextrin/drug complexes [7,8,16,17,23,27,33,34]. Surface energetic was analyzed in terms of standard Gibbs energy change. The standard Gibbs energy change for aggregation of drug is represented by

G 0 = R T ln X cac ,

(2)

where R is the universal gas constant, T the temperature and X cac is the mole fraction of cac. Tables 2–3 list the cac and G 0 values for diclofenac sodium both in absence and presence of α -, β -, HPβ - and γ -cyclodextrins at different temperatures respectively. The decrease in free energy

15 20 25 30 35 40

0

G m (kJ mol−1 )

DS/W

DS/α -CD/W

DS/β -CD/W

DS/HPβ -CD/W

DS/γ -CD/W

−26.06 −26.37 −26.70 −27.12 −27.42 −27.74

−26.31 −26.74 −27.16 −27.60 −28.02 −28.15

−26.56 −26.99 −27.40 −27.75 −28.15 −28.32

−26.60 −27.02 −27.40 −27.80 −28.18 −28.40

−26.74 −27.18 −27.48 −27.89 −28.26 −28.58

of the system on addition of CD indicates that the DS:CD system is more stabilized. Since

α -, β -, HPβ - and γ -cyclodextrins have

similar structures with similar constituent atoms, any differences in the thermodynamic parameters will be due to difference in their hydrophobicity, which in this case is related to increase in cavity size. Thus, this structural difference gives rise to lower standard Gibbs energies for

γ -cyclodextrin system as expected due to its

larger cavity size. This behavior is similar to that observed for the

β -CD:Orange G system [29].

Fig. 8. Plot of the difference between the specific conductivity ( κ ) of DS/CD/W and DS/W as a function of [CD], at different temperatures for (a) DS/β -CD/W and (b) DS/γ CD/W system.

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3.4. NMR studies 3.4.1. 1 H NMR—Inclusion mechanism The interactional behavior which correlates with different interactions occurring between the components of the system of the components was investigated by 1 H NMR spectroscopy, since this technique provides direct and detailed information on the physicchemical interactions indicative of the formation of an inclusion complex [39–43]. Cyclodextrin and diclofenac sodium structures are shown in Fig. 9 with the numbering systems used to 1 H assignment. The 1 H NMR spectra for DS and cyclodextrins both in free and complexed form were recorded (see Figs. I–IX in Supplementary material). The addition of cyclodextrin to the drug solution gives significant shift to the system protons. Remarkable upfield shifts in H3, H5 (inner face protons) of cyclodextrin were observed, however the signals for H1, H2 and H4 (exterior protons) signal scarcely changes. The results were more pronounced for γ -CD systems. Similarly significant shifts were seen in H5’, H6’, H4’ (aromatic protons) of drug molecule. Tables 4–5 list the chemical shift values for DS hydrogens: H4’, H5’, H6’ (aromatic protons) and H3, H5 protons signal of CD for both binary and ternary systems in which changes in chemical shifts were observed. Thus, the largest differences in the chemical shifts for CD protons in all systems are observed for the protons situated inside the hydrophobic cavity (H3, H5), demonstrating the reality of inclusion processes. Moreover, the changes in chemical shift values are useful in identification of the part of drug that is included in the CD cavity. On the basis of the results the following scheme (Scheme 1) can be presumed for the inclusion process occurring in the solution phase. 3.4.2. ROESY studies—Structural features The ROESY (Rotating-frame Overhauser Enhancement Spectroscopy) experiment provides structural information and allows the study of the geometry of the inclusion complex in aqueous solution. The intensities of the cross-peaks in a ROESY spectrum

(a)

(b) Fig. 9. Structures of (a) cyclodextrin and (b) diclofenac sodium molecules.

depend on the distance between the interacting nuclei. The crosspeaks intensity decreases with the internuclear distance. To infer the geometry of the inclusion complex 400 MHz ROESY spectra were recorded for all the ternary systems. Assigning H5 as 3.70 ppm, H3 as 3.76 ppm and in the opposite direction, the aromatic region of the drug. Cross-peaks are displayed between the inner protons of cyclodextrin, H3 and H5 (Fig. 10), and the aro-

Table 4 1 H-chemical shifts (400 MHz) of H4’, H5’, H6’, aromatic protons signals for DS/D2 O and DS/CD/D2 O systems Pure DS hydrogens δ (ppm)

H4’, 7.3538 H5’, 6.3416 H6’, 7.3336

DS/CD hydrogens δ (ppm)

δ (ppm)

α -CD

β -CD

HPβ -CD

γ -CD

α -CD

β -CD

HPβ -CD

γ -CD

7.4070 6.3210 7.3866

7.3648 6.3364 7.3444

7.4161 6.3044 7.3960

7.2781 6.1614 7.2580

0.053 (downfield) 0.021 (upfield) 0.053 (downfield)

0.011 (downfield) 0.005 (upfield) 0.011 (downfield)

0.062 (downfield) 0.037 (upfield) 0.062 (downfield)

0.076 (upfield) 0.18 (upfield) 0.076 (upfield)

Table 5 1 H-chemical shifts (400 MHz) of H3, H5 protons signals for CD/D2 O and DS/CD/D2 O systems

α -CD

β -CD

Pure CD hydrogens δ (ppm)

DS/CD hydrogens δ (ppm)

δ (ppm)

Pure CD hydrogens δ (ppm)

H3, 3.8134 H5, 3.6895

3.7980 3.6827

0.015 (upfield) 3.7609 0.007 (upfield) 3.7008

γ -CD

HPβ -CD DS/CD hydrogens δ (ppm)

δ (ppm)

Pure CD hydrogens δ (ppm)

3.7188 3.6832

0.042 (upfield) 3.8787 0.018 (upfield) 3.7265

DS/CD hydrogens δ (ppm)

δ (ppm)

3.8630 3.7131

0.020 (upfield) 3.7673 0.013 (upfield) 3.6973

Scheme 1. Representation of the possible inclusion route for DS:CD system in solution.

Pure CD hydrogens δ (ppm)

DS/CD hydrogens δ (ppm)

δ (ppm)

3.7215 3.6120

0.046 (upfield) 0.085 (upfield)

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Fig. 10. ROESY spectrum for a stoichiometric (1:1) aqueous solution of DS:γ -CD system.

matic protons of diclofenac sodium, confirming the formation of a true inclusion complex. The aromatic region of the spectrum shows three and four bond correlations that include a TOCSY type component in dispersive phase and negative pure phase signals for correlations between ring systems. The ROESY of the complex indicates a correlation between H3 and H5 of sugar with the aromatic protons of the drug in the complex, thus providing information about the connectivity and coupling allowing a full assignment based on through-space correlations and hence complete assignment of the proton spectrum.

which indicates the increased stability of DS/CD/W system. Thus, these results confirmed that there is possibility of energetically favorable interactions between drug and cyclodextrin molecules in aqueous media. Further the structural evidence for the host–guest complex was elucidated by 1 H NMR and ROESY results. Acknowledgment The authors are grateful to CSIR for financial assistance. Supplementary material

4. Summary This paper constitutes a physicochemical characterization of the interaction of cyclodextrins and an anti-inflammatory drug, diclofenac sodium. Detailed spectroscopic and thermodynamic studies have been done in order to study the possibility of interactions between the drug and cyclodextrin molecules. UV–vis and fluorescence spectroscopy results confirmed the drug cyclodextrin inclusion. The conductivity measurements were performed with variation in temperature. The cac value calculated for DS/W system was less than that for DS/CD/W system. The delay in cac infers drug cyclodextrin interaction. The stoichiometry of DS:CD was found to be 1:1. The association in DS/γ -CD/W system was found to be more stable. The change in Gibbs free energy was determined to study the thermodynamics of these systems. It was observed that free energy of the DS/W system decreases on addition of cyclodextrin,

Supplementary material for this article may be found on ScienceDirect, in the online version. Please visit DOI: 10.1016/j.jcis.2008.06.039. References [1] M.E. Brewster, R. Vandecruys, G. Verreck, M. Noppe, J. Peeters, J. Inclusion Phenom. Macro. Chem. 44 (2002) 35. [2] C.P. Rossel, J.S. Carreno, M.R. Baeza, J.B. Alderete, Quim. Nova 6 (2000) 23. [3] E. Junquera, L. Pena, E. Aicart, J. Pharm. Sci. 87 (1998) 86. [4] A.D. Qi, L. Li, Y. Liu, J. Inclusion Phenom. Macro. Chem. 45 (2003) 69. [5] H. Ueda, J. Inclusion Phenom. Macro. Chem. 44 (2002) 53. [6] N. Martinez, E. Junquera, E. Aicart, Phys. Chem. Chem. Phys. 1 (1999) 4811. [7] S.F. Badawy, A.L. Marshall, M.M. Ghorab, C.M. Adeyeye, Drug Dev. Ind. Pharm. 22 (1996) 959. [8] J.R. Moyano, M.J. Arias, J.M. Gines, J.I. Perez, A.M. Rabasco, Drug Dev. Ind. Pharm. 23 (1997) 379.

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[9] G. Trapani, A. Latrofa, M. Franco, M.R. Pantaleo, E. Sanna, F. Massa, F. Tuveri, G. Liso, J. Pharm. Sci. 89 (2000) 1443. [10] E. Stefansson, T. Loftssonn, J. Inclusion Phenom. Macro. Chem. 44 (2002) 23. [11] M.L. Skiba, A. Coquard, F. Bounoure, P. Verite, P. Arnaud, M. Skiba, J. Inclusion Phenom. Macro. Chem. 57 (2007) 197. [12] N. Nasongkla, A.F. Wiedmann, A. Bruening, M. Beman, D. Ray, W.G. Bornmann, D.A. Boothman, J. Gao, Pharm. Res. 20 (2003) 1626. [13] Z. Zuo, Y.K. Tam, J. Diakur, L.I. Wiebe, J. Pharm. Pharm. Sci. 5 (2002) 292. [14] I. Nandi, M. Bateson, M. Bari, H.N. Joshi, AAPS Pharm. Sci. Technol. 4 (2003) 1. [15] T. Fergoug, E. Junquera, E. Aicart, J. Inclusion Phenom. Macro. Chem. 47 (2003) 65. [16] E. Junquera, F. Mendicuti, E. Aicart, Langmuir 15 (1999) 4472. [17] C. Merino, E. Junquera, J. Barbera, E. Aicart, Langmuir 16 (2000) 1557. [18] T. Khazaeinia, F. Jamali, J. Pharm. Pharm. Sci. 6 (2003) 352. [19] G. Gonzalez-Gaitano, A. Guerrero-Martinez, F. Ortega, G. Tardajos, Langmuir 17 (2001) 1392. [20] S.K. Mehta, K.K. Bhasin, N. Mehta, S. Dham, Colloid Polym. Sci. 283 (2005) 532. [21] S.K. Mehta, N. Bala, S. Sharma, Colloids Surf. A 268 (2005) 90. [22] E. Junquera, J.C. Romero, E. Aicart, Langmuir 17 (2001) 1826. [23] A.D. Qi, L. Li, Y. Liu, J. Inclusion Phenom. Macro. Chem. 45 (2003) 69. [24] W. Hui, M. Minghua, X. Hongzhi, F. Yu, Z. Xiaohong, W. Shikang, Arkivoc (2003) (ii), 173. [25] E.I. Martinez, I. Brandariz, F. Penedo, J. Inclusion Phenom. Macro. Chem. 57 (2007) 573. [26] K. Kalyanasundaram, J.K. Thomas, J. Am. Chem. Soc. 99 (1977) 2039.

381

[27] L.M.A. Pinto, L.F. Fraceto, M.H.A. Santana, T.A. Pertinhez, S.O. Junior, E. de Paula, J. Pharm. Biomed. Anal. 39 (2005) 956. [28] A. Harada, F. Ito, I. Tomatsu, K. Shimoda, A. Hashidzume, Y. Takashima, H. Yamaguchi, S. Kamitori, J. Photochem. Photobiol. 179 (2006) 13. [29] H.Y. Wang, J. Han, X.G. Feng, Spectrochim. Acta 66 (2007) 578. [30] M.R. Eftink, C.A. Ghiron, Anal. Biochem. 114 (1981) 199. [31] Y.J. Hu, Y. Liu, L.X. Zhang, R.M. Zhao, S.S. Qu, J. Mol. Struct. 750 (2005) 174. [32] S.M.T. Shaikh, J. Seetharamappa, S. Ashoka, P.B. Kandagal, Chem. Pharm. Bull. 54 (2006) 422. [33] M.L. Manca, M. Zaru, G. Enas, D. Valenti, C. Sinico, G. Loy, A.M. Fadda, AAPS Pharm. Sci. Technol. 6 (2005) E464. [34] E. Junquera, E. Aicart, J. Phys. Chem. 101 (1997) 7163. [35] E. Junquera, M.M. Pastor, E. Aicart, J. Org. Chem. 63 (1998) 4349. [36] E. Junquera, L. Pena, E. Aicart, Langmuir 13 (1997) 219. [37] E. Junquera, L. Pena, E. Aicart, Langmuir 11 (1995) 4685. [38] I. Satake, T. Ikenoue, T. Takeshita, K. Hayakawa, T. Maeda, Bull. Chem. Soc. Jpn. 58 (1985) 2746. [39] N. Funasaki, S. Ishikawa, S. Neya, J. Phys. Chem. B 107 (2003) 10094. [40] Y. Saito, H. Ueda, M. Abe, T. Sato, S.D. Christian, Colloids Surf. A 135 (1998) 103. [41] C. Andrade-Dias, B.J. Goodfellow, L. Cunha-Silva, J.J.C. Teixeira-Dias, J. Inclusion Phenom. Macro. Chem. 57 (2007) 151. [42] A.M.L. Denadai, M.M. Santoro, L.H. Da Silva, A.T. Viana, R.A.S. Santos, R.D. Sinisterra, J. Inclusion Phenom. Macro. Chem. 55 (2006) 41. [43] A. Syed Mashhood, A. Fahmeena, Chin. J. Chem. 24 (2006) 665.