Thermodynamic Parameters of the Interactions between Lapachol and

Article pubs.acs.org/jced

Thermodynamic Parameters of the Interactions between Lapachol and Isolapachol Sodium Salts and Chitosan Flakes Paulo R. B. de Miranda,*,† Társila S. Silva,*,† Fabiane Caxico de Abreu,*,† Iara B. Valentim,*,‡ and Marília O. F. Goulart*,† †

Instituto de Química e Biotecnologia, Universidade Federal de Alagoas (UFAL), Av. Lourival Melo Mota, s/n, Tabuleiro do Martins, 57072-970 Maceió- AL, Brazil. ‡ Instituto Federal de Educaçaõ , Ciência e Tecnologia de Alagoas (IFAL), Rua Barão de Atalaia, s/n, Poço, 57020-510 Maceió-AL, Brazil ABSTRACT: The adsorption process of lapachol and isolapachol sodium salts (LSS and ISS, respectively) on chitosan flakes was investigated. The aim of this work is to analyze the interaction between chitosan flakes and LSS and ISS, bioactive quinones, looking for the enhancement of their stability and for their controlled release. The effects of contact time, quinone concentration, temperature, and ionic strength on the adsorption of LSS and ISS onto chitosan flakes were studied using a batch adsorption technique. The kinetics of adsorption follows the pseudo-second-order model. Isotherm data were analyzed using the Langmuir and Freundlich models. The adsorption process was found to be endothermic for LSS−chitosan and exothermic for ISS−chitosan. The results have shown the importance of the double bond position in the side chain of the quinone. The stability of both quinones was improved after adsorption on chitosan. An increase in ionic strength decreases the amount adsorbed for both quinones around 50 % for LSS and 20 % for ISS. Release studies of LSS and ISS from chitosan were investigated, indicating that the higher desorbed amount was in the buffered medium.

1. INTRODUCTION Quinones play vital roles in the biochemistry of living cells and exert relevant biological activities. Lapachol, a 2-hydroxynaphthoquinone isolated from plants of the Bignoniaceae family, is known to possess antitumor,1 antibiotic,1 antimalarial,1 antiinflammatory,2 antiulcer,2 leishmanicidal,3 molluscicidal,4,5 and larvicidal6 activities. Its low water solubility directly affects its application, making necessary to use more water-soluble derivatives, for example, its salts,4,6 or to use adequate formulations. There are additional problems related to its photochemical instability. Most drugs show very low bioavailability when administered orally and nasally, in comparison with the parenteral way, which is a result of different drawbacks, like enzymatic activity, absorption and others. The bioavailability of drugs has been improved using delivery systems that are able to cross over and transport associated molecules past these obstacles prolonging the residence time of the drugs at the absorption site, also furnishing sustained release.7,8 Several types of materials have been used as carriers in delivery systems. Liu and co-workers reported the use of lipid nanoparticles in pulmonary delivery of insulin.9 The use of protein nanoparticles as carrier of antitumor drugs was studied.10 Carbon nanotubes are also widely employed in controlled release of peptides, nucleic acids and other drugs,11−13 together with polymers, used as matrixes in drug delivery systems. Several works have reported the use of © 2014 American Chemical Society

cyclodextrins in immobilization/encapsulation of many compounds14 with low water solubility,15,16 anticancer,17 and anticonvulsivant18 drugs. Chitosan is another useful material for drug delivery. Many studies have reported its use in encapsulation for controlled release of several drugs.19−21 Chitosan has several advantages in comparison with other adsorbents. It is an abundant, biodegradable, biocompatible, and nontoxic natural polysaccharide produced from chitin by a deacetylation process.22,23 Several physicochemical characteristics, like degree of deacetylation, molecular weight, and distribution of acetamide groups in the molecule can influence chitosan applications.24 The deacetylation-resultant free amino groups enable the formation of positively charged chitosan salts at low pH values, which provide a good interaction with negatively charged drugs. Moreover, it is useful as an adsorbent for a large number of compounds, like amino acids and proteins,25,26 dyes,27,28 and metallic ions.29,30 In our research group, lithium, sodium, and potassium salts of lapachol and isolapachol have been studied and showed better biological activity than lapachol and isolapachol themselves, probably due to the increase in solubility although few papers have been found reporting the use of lapachol salts.3,4 Apart from the papers already cited, any other report Received: August 9, 2013 Accepted: February 27, 2014 Published: March 14, 2014 1181

dx.doi.org/10.1021/je400725n | J. Chem. Eng. Data 2014, 59, 1181−1192

Journal of Chemical & Engineering Data

Article

2.2.2. Stability of Quinone in Its Solid Form. The stability study was performed as follows: the synthesized salts were stored, and at different days (0, 3, and 6 weeks), solutions (LSS: 8.5·10−5 mol·kg−1 and ISS: 3·10−5 mol·kg−1) were prepared. The absorbance of the solutions was measured from UV−vis spectrophotometer Shimadzu Multispec 1501 at 274 nm for LSS and 294 nm for ISS. 2.3. Adsorption Kinetics. The kinetic plots were obtained at 298 K using 0.09 g of chitosan for LSS and 0.10 g for ISS, in erlenmeyer flasks with 15 mL of quinone solution, in three different concentrations [(3·10−5, 9·10−5, and 3·10−4) mol· kg−1] for each quinone at different time intervals (5 to 180) min at 170 rpm. The amount of adsorbed quinone was calculated in function of contact time. All experiments were performed in triplicate. 2.4. Adsorption Isotherms. The adsorption experiments were performed in a batch technique using 0.09 g of chitosan for LSS and 0.10 g for ISS in erlenmeyer flasks with 15 mL of acidified Milli-Q water (with few drops of diluted HCl), reaching a pH value of 4.0. Aliquots from a quinone stock solution were added to reach a concentration range (5·10−6 mol·kg−1 up to 6·10−4 mol·kg−1) for LSS and (5·10−6 mol·kg−1 up to 1.4·10−3 mol·kg−1) for ISS. Suspensions were stirred in a thermostatic incubator at 170 rpm for 1 h at different temperatures (298, 304, 310 and 316) K. After, chitosan was removed by filtration and the absorbance of the final solution was measured from UV−vis spectrophotometer. All experiments were performed in triplicate. 2.5. Ionic Strength Dependence. Isotherms at 310 K were obtained with ionic strength control through the addition of NaCl 1·10−2 mol.kg−1, with 0.09 g of chitosan for LSS and 0.1 g for ISS, in erlenmeyer flasks with 15 mL of quinone solution. The contact time was 1 h and stirred at 170 rpm. All experiments were performed in triplicate. 2.6. Desorption Studies. After the equilibrium studies with LSS and ISS at 3·10−4 mol·kg−1, the samples with quinone-loaded chitosan were transferred to different erlenmeyers, each one containing 15 mL of different media, according to Table 2. The flasks were stirred at 170 rpm and the desorbed quinone was determined at different time intervals.

had been published, except O2 reactivity data and pKa evaluation. It is interesting to study the controlled release of these salts using chitosan as a matrix, since this adsorbent is commercially available and also easily obtained locally. To the best of our knowledge, there has been no lapachol/isolapachol salt-chitosan interaction study, and it is relevant to understand the physicochemical parameters which affect this interaction, in order to further analyzing their behavior and biological activity in chitosan-controlled release systems. Thus, the main objective of this study is to perform a detailed analysis of the interaction between lapachol and isolapachol sodium salts (LSS and ISS, respectively; Figure 1), with

Figure 1. Lapachol sodium salt, LSS (A) and isolapachol sodium salt, ISS (B).

chitosan using pseudo-first-order, pseudo-second-order, and intraparticle diffusion adsorption kinetic models and thermodynamic parameters aiming to understand the adsorption mechanism and searching for the enhancement of stability of both compounds. Moreover, desorption kinetics was determined as a function of time at different pH levels and temperatures.

2. EXPERIMENTAL SECTION 2.1. Chemicals. Chitosan was purchased from TCI America, and used as received. Its textural characterization (BET surface area, pore volume and pore size) was performed by a surface area and porosity analyzer (Autosob I, Quantachrome Corporation, USA) using N2 adsorption at 77 K. The surface area characterization of chitosan is shown in Table 1. Table 1. Surface Area Determination of Chitosan chitosan BET surface area (m2·g−1) Langmuir surface area (m2·g−1) average pore diameter (Å) total pore volume (cm3·g−1)

Table 2. Different Media Used for Quinone Desorption

0.97 1.47 84.24 0.0026

LSS

Isolapachol [2-hydroxy-3-(3-methyl-1-butenyl)-1,4-naphthoquinone] was synthesized according to the procedure already described.31 Lapachol [2-hydroxy-3-(3-methyl-2-butenyl)-1,4naphthoquinone] and isolapachol sodium salts (LSS and ISS respectively, MW = = 264 g·mol−1), shown in Figure 1, were synthesized as reported, and their purities, tested by NMR, were 98 %.3 All of the compounds show analytical and spectral (IR and NMR) data in full accord with the indicated structures. 2.2. Stability Studies. Two types of stability studies were performed: (1) stability of the quinone solutions and (2) stability of the quinones in their solid forms. 2.2.1. Stability of Quinone Solutions. In this stability study, solutions of LSS and ISS were prepared at the concentrations 3· 10−5 mol·kg−1 and 4·10−5 mol·kg−1 respectively and stored for 15 days. After this period, the measurement was performed.

ISS

media

pH

T /K

media

pH

T/K

Milli-Q Milli-Q Milli-Q PBS

7.0 7.0 8.0 8.0

298 310 310 310

Milli-Q Milli-Q PBS

7.0 8.0 8.0

298 298 298

2.7. Stability of LSS/ISS-loaded Chitosan. After conducting the equilibrium studies with LSS and ISS (3·10−4 mol·kg−1), the quinone salts/chitosan were collected by filtration and used for stability experiments. The samples with quinone-loaded chitosan were transferred to different erlenmeyers, each containing 15 mL of Milli-Q water (without pH adjust) and stirred at 170 rpm. Aliquots were collected and measurements in UV−vis were performed at different time intervals (5 to 240) min. All experiments were performed in triplicate during 63 days, and each sample not yet used was left in the desiccator. 1182



Article

Figure 2. Absorption spectra in the UV−vis in function of time for freshly prepared solutions of LSS (A) and ISS (B) solid forms, kept without any protection, at time 0 (−), and after 3 weeks (- - -) and 6 weeks (···).

Figure 3. Absorption spectra in the UV−vis in function of time for (A) solution 3·10−5 mol·kg−1 of LSS and (B) solution 4·10−5 mol·kg−1 of ISS at time 0 (−) and after 15 days (- - -).

Figure 4. Amount of LSS (A) and ISS (B) adsorbed on chitosan at different time intervals with 0.09 g of chitosan for LSS and 0.10 g for ISS at 298 K, for concentrations 3·10−5 mol·kg−1 (■), 9·10−5 mol·kg−1 (●), and 3·10−4 mol·kg−1 (▲).

2.8. Statistical Analysis. Data were analyzed by analysis of variance (ANOVA), followed by Tukey’s test to detect significant differences between treatments. A probability value of p < 0.05 was considered statistically significant.

about 50 % of the initial mass of LSS decomposes. For ISS, similar results are observed with 71 % decomposition. After synthesis of the salts, aqueous solutions were prepared and their stabilities were verified by observation of their characteristic absorption bands in the UV−vis spectrophotometer, as shown in Figure 3. The spectrophotometric analyses of the solutions were performed at different days, and their spectra were evaluated according to the variation of absorbance. For the solution of LSS, after 40 days, the color of the solution apparently remained unchanged and slight changes were observed in the spectrum of UV−vis. At 274 nm, the decrease in absorbance was only 7.5 % (Figure 3A). However, for the solution of ISS, after 15 days, there was a loss of the characteristic violet color that changed to orange, with higher

3. RESULTS AND DISCUSSION 3.1. Stability Studies. Figure 2A,B displays the absorption spectra of solid forms LSS and ISS after (3 and 6) weeks. In studying the stability of the salts of quinones, it was revealed that LSS undergoes decomposition which can be observed through the decrease of its solubility and confirmed with the decrease of absorbance intensity. After 6 weeks of storage, 1183



Article

Table 3. Kinetic Data for Adsorption of LSS and ISS on Chitosan Flakes pseudo-first-order

pseudo-second-order

quinone

b/mol·kg−1

qe,exp/mg·g−1

qe,calc/mg·g−1

k1/min−1

R2

qe,calc/mg·g−1

k2/g·mg−1·min−1

R2

LSS

3·10−5 9·10−5 3·10−4 3·10−5 9·10−5 3·10−4

0.935 2.580 4.500 0.693 2.143 5.503

0.765 0.097 0.028 0.101 2.919 2.684

0.028 0.005 0.009 0.010 0.017 0.032

0.931 0.397 0.521 0.644 0.772 0.988

0.922 2.518 4.542 0.683 2.136 5.711

357.96 6.573 0.112 0.811 0.263 0.188

0.999 0.999 0.999 0.999 0.999 0.999

ISS

Figure 5. Comparison of pseudo-first-order (- - -) and pseudo-second-order () kinetic models with experimental data (●) where A (LSS 3·10−5 mol·kg−1), B (LSS 9·10−5 mol·kg−1), C (LSS 3·10−4 mol·kg−1), D (ISS 3·10−5 mol·kg−1), E (ISS 9·10−5 mol·kg−1), and F (ISS 3·10−4 mol·kg−1).

modification in the UV−vis spectrum, a decrease of 33.5 % in the absorbance at 294 nm (Figure 3B). This study had shown that both quinones are unstable and require formulation, for instance a solid matrix to stabilize them, increasing the residence time of the substance at the action site and therefore keeping their activity for longer time. 3.2. Adsorption Kinetics. The choice of concentration range was based on biological results earlier reported, where it

was verified that LSS and ISS had shown molluscicidal activities in concentrations in the order of 10−5 mol.kg−1.4 The adsorption of LSS and ISS at a fixed amount of chitosan flakes was studied as a function of time of contact in order to determine the equilibrium time. Figure 4A,B show that adsorption of LSS and ISS, respectively, on chitosan flakes takes place at a relatively fast rate for the three studied concentrations, revealing that the system attained a maximum 1184



Article

Figure 6. Plots of the intraparticle diffusion model for 3 different concentrations of LSS (A) and ISS (B) at 298 K, where (▲) 3·10−4 mol·kg−1, (●) 9·10−5 mol·kg−1, and (■) 3·10−5 mol·kg−1. () straight lines were used for obtention of the parameters listed in Table 4, for each concentration.

Table 4. Intraparticle Diffusion Rate Constants of LSS on Chitosan Flakes intraparticle diffusion −1

b/mol·kg LSS

ISS

−5

3·10 9·10−5 3·10−4 3·10−5 9·10−5 3·10−4

−1

ki1/mg·g ·min

−1/2

0.0176 0.0556 0.2099 0.0804 0.1898 0.8359

R12

ki2/mg·g−1·min−1/2

R2 2

c/mg·g−1

0.9976 0.9343 0.9993 0.9353 0.9661 0.9682

0.0016 0.0124 0.0193 8.82·10−4 7.05·10−4 0.0833

0.9269 0.7784 0.6932 0.6491 0.7014 0.9741

0.8389 2.2568 3.0575 0.3469 1.1815 1.3811

Figure 7. Comparison of the Langmuir () and Freundlich (- - -) isotherm models with experimental data (●) obtained from the adsorption of LSS with chitosan flakes in four different temperatures. The curves related to the experimental data (dependence on temperature) had been shown to be statistically different with value of p < 0.05.

3.2.1. Pseudo-First-Order and Pseudo-Second-Order Models. The pseudo-first-order (eq 1) and pseudo-second-order (eq 2) models and their respective linear forms (eqs 3 and 4) can be described according to the following equations

adsorption after 40 min, for all concentrations investigated. The relatively short adsorption time indicates the efficiency of chitosan flakes in their interaction with the quinones.32 Kinetic data of the systems LSS−chitosan and ISS−chitosan were correlated to linear forms of pseudo-first-order33 and pseudosecond-order models.34,35

∂qt ∂t 1185

= k1(qe − qt)

(1)



Article

Figure 8. Comparison of the Langmuir () and Freundlich (- - -) isotherm models with experimental data (●) obtained from the adsorption of ISS with chitosan flakes in four different temperatures. The curves related to the experimental data (dependence on temperature) had been shown to be statistically different with value of p < 0.05.

∂qt ∂t

= k 2(qe − qt)2

qt = k it 0.5 + c

(5)

(2)

ln(qe − qt) = ln qe − k1t

(3)

t 1 1 = + t 2 qt qe k 2qe

(4)

Figure 6A,B shows the double nature of the plots for three different concentrations of LSS and ISS, respectively. This multilinearity indicates that two or more phenomena occur successively. The first linear parts that do not go through the origin, represent the film diffusion, which is the transport of adsorbate from bulk solution to the surface of adsorbent. The final linear part represents the intraparticle diffusion effects. Table 4 shows some important data (correlation coefficient and rate constant) for adsorption of LSS on chitosan at three different concentrations. As observed, for both quinones, the linear correlation coefficient is higher than 0.90 and ki1 > ki2 indicating that the predominant adsorption step is the transfer of solute from bulk solution to the surface of the adsorbent, being this, a rapid process. This is in accordance with several reports in the literature.38,39 3.3. Adsorption Isotherms. The adsorption of LSS on chitosan flakes at different temperatures is shown in Figure 7. These results show that the adsorption capacity of chitosan increases (32 %) with a rise in temperature and suggest an endothermic process. Figure 8 illustrates the adsorption isotherms at 4 different temperatures for interaction between the ISS and chitosan. It is noticed that, unlike LSS, with increasing temperature there is a decrease in the amount adsorbed on chitosan. This suggests an exothermic process. Observing the isotherms obtained for the two quinones, it is possible to conclude that both are in agreement with the classification system proposed by Giles.40 Following this model, the two fit coherently in the L-type isotherm, suggesting that as the adsorbing sites are occupied, the next molecules to be adsorbed, find it difficult to find available sites. To calculate the thermodynamic parameters, experimental data for adsorption

where qt (mg·g−1) is the amount of quinone adsorbed at time t (min); qe (mg.g−1) is adsorption capacity at equilibrium; k1 (min−1) and k2 (g·mg−1·min−1) are pseudo-first-order and pseudo-second-order rate constants, respectively. In order to test the models, linear regression analysis was applied to ln(qe − qt) vs t data for pseudo-first-order and t/qt vs t data for pseudosecond-order. The rate constants of the respective models according to this analysis are given in Table 2 together with the regression coefficients. As seen in Table 3 and Figure 5, the pseudo-first-order model does not show good compliance with experimental data unlike the pseudo-second-order model for both quinones. With the linear correlation coefficient, tending to unit, and calculated qe near the experimental qe, it is possible to affirm that kinetics of adsorption preferentially follows the pseudo-second-order model over the whole experimental range of adsorption. This indicates that more than one-step may be involved in the adsorption process.36 3.2.2. Intraparticle Diffusion Model. The kinetic experimental data were also analyzed with the intraparticle diffusion model. According to Weber and Morris37 if the intraparticle diffusion is the rate-controlling factor, then the plot of qt vs t0.5 gives a straight line passing through the origin and the slope gives a rate constant ki. If not, the boundary layer diffusion controlled the adsorption to some degree. This model can be described by the following equation (eq 5): 1186



Article

Table 5. Parameters from Langmuir and Freundlich isotherms for adsorption of LSS and ISS on chitosan Langmuir T/K

quinone LSS

qe,max/mg·g−1

R2

KF/[(mg·g−1·(L·mg−1)1/n]

n

R2

40.782 70.142 43.417 44.434 63.504 41.925 43.833 37.036

6.849 6.955 9.068 11.677 11.329 10.461 9.053 6.906

0.984 0.994 0.969 0.984 0.997 0.998 0.994 0.996

34.302 39.357 84.532 109.572 66.200 65.435 62.213 35.754

1.450 1.514 1.167 1.119 1.343 1.374 1.338 1.391

0.961 0.937 0.924 0.937 0.922 0.915 0.914 0.889

298 304 310 316 298 304 310 316

ISS

Freundlich

KL/L·g−1

isotherm of LSS and ISS were treated according Langmuir41 and Freundlich42 models. The Langmuir model describes uniform energies of adsorption sites and a single monolayer of adsorbate is formed while Freundlich model describes heterogeneous surface and multilayers of the adsorbate are formed. The Langmuir (eq 6) and Freundlich (eq 7) equations and their linear forms (eqs 8 and 9) are, respectively, depicted by qe =

qe

ΔG°ads = −RT ln K

1 + KLCeq

=

1 qe,max KL

−ΔH °ads 1 (11) R T To calculate the entropy change (ΔS°ads), eq 12 was used. ln K = a +

(7)

log qe = log KF +

1 qe,max

(12)

ΔG° = ΔH ° − T ΔS°

The thermodynamic data obtained are shown in Table 6. The values of ΔG°ads are negative, indicating that the adsorptive

Ceq

1 log Ceq n

−1

where R is the universal gas constant (8.314 J·mol ·K ) and T is temperature in Kelvin and K is the equilibrium constant. For the enthalpy change of adsorption, ΔH°ads were calculated from the van’t Hoff equation (eq 11), where the plot of ln K vs 1/T was obtained.

(6)

+

(10) −1

KLqe,max Ceq

qe = KFCeq1/ n Ceq

should be negative. The free energy change was calculated from the equation

(8)

Table 6. Thermochemical Data of Chitosan/LSS and chitosan/ISS Interactions at Different Temperatures

(9)

quinone

where Ceq is the equilibrium concentration of quinone (g·kg−1), qe is the amount of quinone adsorbed on chitosan (mg·g−1), qe,max is the maximum amount of quinone adsorbed on a complete monolayer of chitosan (mg.g−1), and KL is the adsorption equilibrium constant or Langmuir constant (L·g−1), while KF is the Freundlich constant [mg·g−1·(L·mg−1)1/n] which is related to the adsorbent adsorption capacity and n is related to the adsorption affinity with the sorbate. Langmuir and Freundlich constants were determined from the plots of Ceq/qe vs Ceq and log qe vs log Ceq respectively. The obtained results are shown in Table 5. Table 5 and Figures 7 and 8 show that in the model proposed by Langmuir, at four studied temperatures, the linear correlation coefficients are above 0.96 for both quinones, while in the Freundlich model, lower values were obtained. Correlation coefficients situated above 0.96 can be considered for application of the model.43−45 Observing Figures 7 and 8, we note that both models are very similar, especially for the initial points of the experimental curves. Other isotherm models as Sips and Redlich-Peterson (nonlinear with three parameters) were used for this analysis (data not shown) and they also confirmed that the most appropriate model is the Langmuir. The values of Langmuir parameters listed in Table 5 were used to determine the standard free energy change (ΔG°ads; eq 10), the standard enthalpy variation (ΔH°ads) and then the standard entropy change (ΔS°ads). The change of Gibbs free energy (ΔG°ads) indicates the spontaneity of adsorption process, so that the adsorption occurs, the values of ΔG°

LSS

ISS

T/K 298 304 310 316 298 304 310 316

ΔG°ads/kJ·mol−1 −23.0 −24.8 −24.1 −24.6 −24.1 −23.5 −24.1 −24.1

± ± ± ± ± ± ± ±

0.2 0.2 0.5 0.2 0.1 0.3 0.1 0.2

ΔS°ads/J·K−1·mol−1

ΔH°ads/kJ.mol−1

+90 ± 1 +94 ± 1 +90 ± 2 +90 ± 1 −9.7 ± 0.3 −12 ± 1 −9.4 ± 0.3 −9.2 ± 0.8

+3.8 ± 0.8

−27 ± 5

process occurs spontaneously. It can be also noted that these values are very close. The enthalpy change for the adsorption process of LSS has a positive value, showing that the process is endothermic. For the entropy change, positive values were obtained, demonstrating that the disorder of the system increased in the solid−liquid interface, due to adsorption process. It is possible to observe some peculiarities about the thermodynamic data comparing LSS and ISS in Table 6. The values of ΔG°ads obtained for the quinones are less than zero (∼ −24 kJ. mol−1), a result which indicates that both processes are favorable for the formation of pairs LSS−chitosan and ISS− chitosan. Structurally, the molecules of LSS and ISS are very similar, thus the values of ΔG°ads are also similar. The adsorption enthalpy change (ΔH°ads) is a relationship between the number and strength of interactions that are broken between the adsorbate-solvent and solvent-adsorbent and formed between the adsorbate−adsorbent.46,47 Observing the Table 6, it can be seen that for the LSS, the adsorption has 1187



Article

an endothermic behavior, with a value of ΔH°ads = +3.8 kJ· mol−1. As for the ISS, the adsorption process has an exothermic behavior with ΔH°ads = −27 kJ·mol−1. An increase of ∼31 kJ· mol−1 occurred when comparing the enthalpy changes of the two systems. A possible explanation can be given based on the chemical structures of quinones involved. Observing the Figure 9, there is possibility of conjugation of the double bond in the

The ISS has resonance structures that can contribute to the adsorption process, making the interaction with chitosan stronger, compared to chitosan−LSS system. While LSS has only one negative charge in its structure that can bind effectively to the positive sites of chitosan, the ISS has two negative charges with the possibility of a greater number of interactions with the positive sites of chitosan. This observation is important because the enthalpy change is influenced by the number of interactions. According to Table 6, the system chitosan−LSS showed a positive entropy change and the ISS−chitosan showed a variation of negative entropy. This change in behavior may be associated with limitation of translation, rotation and vibration movements of each quinone on the surface of chitosan, interfering in the degree of freedom of these molecules. Previously, it was admitted that the ISS on chitosan has a greater number of interactions than LSS, and it is plausible that the system ISS−chitosan has a negative entropy change, as

Figure 9. Resonance structures of ISS.

side chain of the quinone ring in the ISS, resulting in another negative charge, facilitating its interaction with chitosan.

Figure 10. Illustrative scheme representing possible interactions of LSS (A) and ISS (B) on chitosan. 1188



Article

Figure 11. Adsorption isotherms of quinones on chitosan flakes where: (A) LSS with (■) NaCl (1·10−2 mol·kg−1, I = 0.02) and without (●) added salt at 310 K; (B) ISS at 310 K with (■) NaCl (1·10−2 mol·kg−1, I = 0.02) and without (●) added salt.

Figure 12. Desorption kinetics at different media: (A) LSS at 298 K, pH 7.0 (■); 310 K, pH 7.0 (●); 310 K, pH 8.0 (▲); and 310 K PBS, pH 8.0 (◆) and (B) ISS at 298 K, pH 7.0 (■), pH 8.0 (●), and PBS, pH 8.0 (▲).

ionic environment. This suggests that Na+ and Cl− form a barrier preventing the LSS to adsorb on the surface with the same efficiency when compared in the absence of ions. The Cl− ions will compete with the enolate group of the quinone with the ammonium sites of chitosan, while Na+ ions will interact with the negative group (enolate) of the quinone. Both cases contribute to a lower degree of adsorption. These results prove that there is an influence of ionic strength on the adsorption process by decreasing the Coulombic attraction between the quinones and chitosan, indicating that the main interaction between them is of electrostatic nature. 3.5. Desorption Studies. Figure 12A illustrates the desorption of quinones from the chitosan flakes as a function of time at four different media: deionized water with adjusted pH to 7.0 at 298 and 310 K, deionized water with adjusted pH to 8.0 at 310 K, and phosphate buffer at pH 8.0 (I = 0.26) at 310 K. Using deionized water at 298 K, pH 7.0, the desorption process occurs in about 120 min, reaching a maximum at 30 %. This low desorption may be explained by the trapping of LSS inside the pores of chitosan (average pore diameter: 84.24 Å), thus LSS can interact with more than one group of chitosan at the same time, being avented a possible complex formation that turns its release difficult.48 At 310 K and pH 7 and 8, it is not possible to observe differences in the desorption percentage (around 40 % for both media). When the ionic strength is increased, using a phosphate buffer solution (PBS) at pH 8.0, a percentage of desorption of 100 % was observed after 60 min and remained constant for 4 h, confirming that LSS has a higher affinity with this medium than with the surface of chitosan, breaking the interactions of LSS−chitosan and so the release of

would be with a larger limitation of their movements than for LSS. Figure 10 shows the illustrative scheme of the interaction of LSS and ISS on chitosan, with the release of water molecules from the surface of chitosan after adsorption. When the molecule of quinone reaches the surface of chitosan, a certain amount of water molecules must leave to make way for quinone molecule that adsorbs, and moreover, according to the Langmuir model the number of molecules that leave should be equivalent at cross-sectional areas. Looking at Figure 10A, it is possible to say that the number of interactions of the LSS on chitosan is lower, so the LSS still possesses a certain degree of freedom in the solid surface. Thus, the system entropy change becomes positive, because this organization created by the adsorption of LSS does not compensate the greater disorder caused by the release of water molecules. For the adsorption of the ISS (Figure 10B), it can be deduced that there is higher amount of interactions, so there are many restrictions on their movement, i.e., molecules of ISS are so firmly organized on the surface that the disorder caused by the release of water molecules is more than compensated, making the system entropy change negative.47 3.4. Ionic Strength Dependence. Aiming to determine whether the adsorption of LSS/ISS on chitosan is affected by ionic strength, a study was conducted by varying this parameter by adding sodium chloride. Figure 11A,B shows the adsorption isotherms with controlled ionic strength using NaCl 0.02 mol· kg−1. It is observed that an increase in ionic strength decreases the amount adsorbed for both quinones around 50 % for LSS and 20 % for ISS, showing that LSS is more affected by this 1189



Article

LSS in the buffered medium is increased. This also suggests how the ionic strength of the medium enhances the desorption process. Figure 12B shows the desorption of ISS from the chitosan flakes as a function of time in three different media at 298 K: deionized water with adjusted pH to 7.0, deionized water with adjusted pH to 8.0, and phosphate buffer in pH 8.0 (I = 0.26). According to Figure 11, at the same conditions (media, pH and temperature), the desorption of ISS (∼ 10 %) is lower than LSS (∼ 30 %), even in the buffered medium. This indicates, once again, than the ISS is more strongly bound to the surface of chitosan than LSS, while, in buffered medium, the desorption of ISS is around 80 %, showing that the influence of ionic strength is lower than that for LSS. These results further reaffirm the importance of conjugated double bonds present in the side chain of the ISS, with the enhancement of charges formation and electrostatic interaction increase. The presence of this conjugation (absent in the LSS) causes changes in several parameters: the values of qe for ISS were higher showing that it is present in greater quantities on the surface, the enthalpy change for ISS is higher, showing that there are more interactions between ISS and chitosan than that between LSS and chitosan, the largest number of interactions also caused a difference between the entropy values of the both quinones, and finally also favored a lower percentage of desorption. 3.6. LSS-Chitosan and ISS-Chitosan System Stability. In order to analyze the effect of chitosan in the stability of the LSS and ISS, the compounds were included in the biopolymer and desorbed during different times. Their stabilities were investigated through UV−vis spectra. Figure 13 shows the percentage of release of quinones from chitosan as a function of time (from 0 up to 240) min. This desorption experiment was repeated several times, from time 0 (LSS−chitosan or ISS− chitosan fresh preparations) up to day 5, 12, 21, 28, 49, 56, and 63. Figure 13A refers to the release of LSS. Note that this release was around 25 % for 0 and 21 days and was around 37 % for other days. Their UV−vis spectra are totally similar in absorbance, which allows us to conclude that LSS in chitosan has become more stable. Similar results were also obtained for the ISS−chitosan system. Figure 13B shows the release of ISS from the chitosan around 10 % for all days already commented. This system, when compared to figures 2 and 3, shows inequivocal higher stability for both salts, making both systems LSS−chitosan and ISS−chitosan perfectly viable in terms of the stabilization of quinones.

Figure 13. Release of LSS (A) and ISS (B) from LSS−chitosan and ISS−chitosan in different days. (■) 0 days, (□) 5 days, (●) 12 days, (○) 21 days, (▲) 28 days, (Δ) 49 days,(◆) 56 days, (◇) 63 days. Inset A (UV−vis spectra of LSS after desorption with 0 and 63 days. Inset B: the same with ISS.

be considered as a potential adsorbent for ISS and LSS, being pretty adequate for their stabilization. These results may be used for other biologically active hydroxyquinones and for controlled release at adequate sites.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. *Tel/Fax: + 55-82-3214-1393. E-mail: [email protected]; [email protected]. Funding

4. CONCLUSIONS The herein presented results show that LSS and ISS had been adsorbed on chitosan flakes and the adsorption equilibria for both compounds are reached rapidly. LSS and ISS adsorption kinetics on chitosan flakes were found to follow the pseudosecond-order model. The adsorption mechanism involved three stages: boundary layer diffusion, electrostatic interaction, and intraparticle diffusion. The adsorption of LSS on chitosan is an endothermic process, while for ISS−chitosan, the process is exothermic, showing the influence of the double bond in the side chain of the quinone ring. The ionic strength influences both the adsorption and desorption processes and the ISS is more strongly bound to the surface of chitosan than LSS. Both systems LSS−chitosan and ISS−chitosan were perfectly viable in terms of the stabilization of quinones. Chitosan is a low cost, biocompatible, biodegradable, and nontoxic material and could

Financial support from the Brazilian agencies CNPq, CAPES, PADCT/CNPq, FAPEAL, BNB (Banco do Nordeste do Brasil), CNPq/PNPD (Process 151636/2008-7), CAPES/ PNPD, and RENORBIO is gratefully acknowledged. The authors also acknowledge Selêude Wanderley da Nóbrega (UFAL, Maceio, AL) for the contribution in the discussions of this work. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Andrade-Neto, V. F.; Goulart, M. O. F.; Silva, J. F.; Silva, M. J.; Pinto, M. D.; Pinto, A. V.; Zallis, M. G.; Carvalho, L. H.; Krettli, A. U. Antimalarial activity of phenazines from lapachol, beta-lapachone and its derivatives against Plasmodium falciparum in vitro and Plasmodium berghei in vivo. Bioorg. Med. Chem. Lett. 2004, 14, 1145−1149.

1190



Article

solvents for nutrient delivery applications. Food Hydrocol. 2013, 31, 332−339. (22) Gupta, V. K.; Suhas. Application of low-cost adsorbents for dye removal − a review. J. Environ. Manage. 2009, 90, 2313−2342. (23) Crini, G. Non-conventional low-cost adsorbents for dye removal: a review. Bioresour. Technol. 2006, 97, 1061−1085. (24) Kofuji, K.; Qian, C.; Nishimura, M.; Sugiyama, I.; Murata, Y.; Kawashima, S. Relationship between physicochemical characteristics and functional properties of chitosan. Eur. Polym. J. 2005, 41, 2784− 2791. (25) Grenha, A.; Remuñań -López, C.; Carvalho, E. L. S.; Seijo, B. Microspheres containing lipid/chitosan nanoparticles complexes for pulmonary delivery of therapeutic proteins. Eur. J. Pharm. Biopharm. 2008, 69, 83−93. (26) Bai, P.; Cao, F.; Lan, X.; Zhao, F.; Ma, Y.; Zhao, C. Chitosan gel beads immobilized Cu (II) for selective adsorption of amino acids. J. Biochem. Biophys. Methods 2008, 70, 903−908. (27) Wen, Y.; Shen, C.; Ni, Y.; Tong, S.; Yu, F. Glow discharge plasma in water: a green approach to enhancing ability of chitosan for dye removal. J. Hazard. Mater. 2012, 201/202, 162−169. (28) Asgher, M. Biosorption of Reactive Dyes: A Review. Water, Air, Soil Pollut. 2012, 223, 2417−2435. (29) Paulino, A. T.; Santos, L. B.; Nozaki, J. Removal of Pb2+, Cu2+ and Fe3+ from battery manufacturing wastewater by chitosan produced from silkworm chrysalides as a low-cost adsorbent React. React. Funct. Polym. 2008, 68, 634−642. (30) Ghaee, A.; Shariaty-Niassar, M.; Barzin, J.; Zarghan, A. Adsorption of copper and nickel ions on macroporous chitosan membrane: Equilibrium study. Appl. Surf. Sci. 2012, 258, 7732−7743. (31) Hooker, S. C. The constitution of lapachol and its derivatives. The structure of Paterno’s isolapachol. J. Chem. Soc. 1936, 59, 1190− 1195. (32) Carvalho, T. E. M.; Fungaro, D. A.; Izidoro, J. C. Adsorçaõ do corante reativo laranja 16 de soluções aquosas por zeólita sintética. Quim. Nova 2010, 33, 358−363. (33) Lagergren, S. Zur theorie der sogenannten adsorption gelöster stoffe. Kungliga Svenska Vetenskaps-Akademiens. Handlingar 1898, 24, 1−39. (34) Ho, Y. S.; Mckay, G. Pseudo-second order model for sorption processes. Process. Biochem. 1999, 34, 451−465. (35) Blanchard, G.; Maunaye, M.; Martin, G. Removal of heavy metals from waters by means of natural zeolites. Water Res. 1984, 18, 1501−1507. (36) Ho, Y. S.; Mckay, G. Sorption of dye from aqueous solution by peat. Chem. Eng. J. 1998, 70, 115−124. (37) Weber, W. J.; Morris, J. C. Kinetics of adsorption on carbon solution. J. San. Eng. Div. ASCE 1963, 89, 31−59. (38) Doğan, M.; Ö zdemir, Y.; Alkan, M. Adsorption kinetics and mechanism of cationicmethyl violet and methylene blue dyes onto sepiolite. Dyes Pigm. 2007, 75, 701−713. (39) Yalçin, M.; Gürses, A.; Doğar, Ç .; Sözbilir, M. The adsorption kinetics of cethyltrimethylammonium bromide (CTAB) onto powdered active carbon. Adsorption 2004, 10, 339−348. (40) Giles, C. H. Studies in adsorption: part XI. A system of classification of solution adsorption isotherms, and its use in diagnosis of adsorption mechanism and in measurement of specific surface areas of solids. J. Chem. Soc. 1960, 111, 3973−3993. (41) Langmuir, I. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 1918, 40, 1361−1403. (42) Freundlich, H. M. F. Over the adsorption in solution. Z. Phys. Chem. 1906, 57, 385−470. (43) Tan, I. A. W.; Ahmad, A. L.; Hameed, B. H. Adsorption isotherms, kinetics, thermodynamics and desorption studies of 2,4,6trichlorophenol on oil palm empty fruit bunch-based activated carbon. J. Hazard. Mater. 2009, 164, 473−482. (44) Piccin, J. S.; Vieira, M. L. G.; Golçalves, J. O.; Dotto, G. L.; Pinto, L. A. A. Adsorption of FD&C Red N°. 40 by chitosan: isotherms analysis. J. Food Eng. 2009, 95, 16−20.

(2) Hussain, H.; Krohn, K.; Ahmad, V. U.; Miana, G. A.; Green, I. R. Lapachol: an overview. Arkivoc. 2007, 2, 145−171. (3) Lima, N. M. F.; Correia, C. S.; Leonor, L. L.; Machado, G. M. C.; Madeira, M. F.; Sant’Ana, A. E. G.; Goulart, M. O. F. Antileishmanial activity of lapachol analogues. Mem. Inst. Oswaldo Cruz. 2004, 99, 757−761. (4) Lima, N. M. F.; Santos, A. F.; Porfírio, Z.; Goulart, M. O. F.; Sant’Ana, A. E. G. Toxicity of lapachol and isolapachol and their potassium salts against Biomphalaria glabrata, Schistosoma mansoni cercariae, Artemia salina and Tilapia nilotica. Acta Trop. 2002, 83, 43− 47. (5) Lima, N. M. F.; Correia, C. S.; Ferraz, P. A. L.; Pinto, A. V.; Pinto, M. C. R. F.; Sant’Ana, A. E. G.; Goulart, M. O. F. Molluscicidal Hydroxynaphthoquinones and Derivatives. Part 1: Correlation between their redox potentials and activity against Biomphalaria glabrata. J. Braz. Chem. Soc. 2002, 13, 822−829. (6) Ribeiro, K. A. L.; Carvalho, C. M.; Molina, M. T.; Lima, E. P.; Montero, E. L.; Reys, J. R. M; Oliveira, M. B. F; Pinto, A. V.; Sant’Ana, A. E. G.; Goulart, M. O. F. Activities of naphthoquinones against Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae), vector of dengue and Biomphalaria glabrata (Say, 1818), intermediate host of Schistosoma mansoni. Acta Trop. 2009, 111, 44−50. (7) Goulart, M. O. F.; Freitas, L. R.; Tonholo, J.; de Abreu, F. C.; Raslan, D. S.; Starling, S.; Zani, C. L.; Oliveira, A. B.; Chiari, E. Trypanocidal Activity and Redox Potentials of Heterocyclic and 2Hydroxy-Naphthoquinones. Bioorg. Med. Chem. 1997, 7, 2043−2048. (8) Issa, M. M.; Köping-Höggård, M.; Artursson, P. Chitosan and the mucosal delivery of bio-technology drugs. Drug Discovery Today: Technol. 2005, 2, 1−6. (9) Liu, J.; Gong, T.; Fu, H.; Wang, C.; Wang, X.; Chen, Q.; Zhang, Q.; He, Q.; Zhang, Z. Solid lipid nanoparticles for pulmonary delivery of insulin. Int. J. Pharm. 2008, 356, 333−344. (10) Hawkins, M. J.; Soon-Shiong, P.; Desai, N. Protein nanoparticles as drug carriers in clinical medicine. Adv. Drug Delivery Rev. 2008, 60, 876−885. (11) Hilder, T. A.; Hill, J. M. Carbon nanotubes as drug delivery nanocapsules. Curr. Appl. Phys. 2008, 8, 258−261. (12) Bianco, A.; Kostarelos, K.; Prato, M. Applications of carbon nanotubes in drug delivery. Curr. Opin. Chem. Biol. 2005, 9, 674−679. (13) Zanella, I.; Fagan, S. B.; Mota, R.; Fazzio, A. Ab initio study of pristine and Si-doped capped carbon nanotubes interacting with nimesulide molecules. Chem. Phys. Lett. 2007, 439, 348−353. (14) Brewster, M. E.; Loftsson, T. Cyclodextrins as pharmaceuticals solubilizers. Adv. Drug Delivery Rev. 2007, 59, 645−666. (15) Trichard, L.; Fattal, E.; Besnard, M.; Bochot, A. α-Cyclodextrin/ oil beads as a new carrier for improving the oral bioavailability of lipophilic drugs. J. Controlled Release 2007, 122, 47−53. (16) Cappello, B.; De Rosa, G.; Giannini, L.; Rotonda, M. I.; Mensitieri, G.; Miro, A.; Quaglia, F.; Russo, R. Cyclodextrin-containing poly(ethylene oxide) tablets for the delivery of poorly soluble drugs: potential as buccal delivery system. Int. J. Pharm. 2006, 319, 63−70. (17) Bilensoy, E.; Gürkaynak, O.; Doğan, A. L.; Hıncal, A. A. Safety and efficacy of amphiphilic beta-cyclodextrin nanoparticles for paclitaxel delivery. Int. J. Pharm. 2008, 347, 163−170. (18) Teixeira, L. R.; Sinisterra, R. D.; Vieira, R. P.; Scarlatelli-Lima, A.; Moraes, M. F. D.; Doretto, M. C.; Denadai, A. M.; Beraldo, H. An inclusion compound of the anticonvulsant sodium valproate into acyclodextrin: physico-chemical characterization. J. Incl. Phenom. Macro. Chem. 2006, 54, 133−138. (19) Soo, P. L.; Cho, J.; Grant, J.; Ho, E.; Piquette-Miller, M.; Allen, C. Drug release mechanism of paclitaxel from a chitosan-lipid implant system: Effect of swelling, degradation and morphology. Eur. J. Pharm. Biopharm. 2008, 69, 149−157. (20) Fang, J.; Chen, J.; Leu, Y.; Hu, J. Temperature sensitive hydrogels composed of chitosan and hyaluronic acid as injectable carriers for drug delivery. Eur. J. Pharm. Biopharm. 2008, 68, 626−636. (21) Luo, Y.; Teng, Z.; Wang, X.; Wang, Q. Development of carboxymethyl chitosan hydrogel beads in alcohol-aqueous binary 1191



Article

(45) Alagumuthu, G.; Rajan, M. Equilibrium and kinetics of adsorption of fluoride onto zirconium impregnated cashew nut shell carbon. Chem. Eng. J. 2010, 158, 451−457. (46) Somasundaran, P.; Huang, L. Adsorption/aggregation of surfactants and their mixtures at solid−liquid interfaces. Adv. Colloid Interf. Sci. 2000, 88, 179−208. (47) Espinosa-Jiménez, M.; Padilla-Weigand, R.; Ortega, A. O.; Perea-Carpio, R. Electrokinetic and thermodynamic analysis of the adsorption process of N-cetylpyridinium chloride on polyester fabric. J. Colloid Interface Sci. 2002, 252, 42−49. (48) Weber, W. J.; Smith, E. H. Simulation and design models for adsorption processes. Environ. Sci. Technol. 1987, 21, 1040−1050.

1192


Thermodynamic Parameters of the Interactions between Lapachol and

Recommend Documents