Effect of cefoperazone sodium on the physicochemical ... - Springer Link

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Effect of Cefoperazone Sodium on the Physicochemical Properties of Surfactants Junhong Qiana,*, Jinghua Gua, and Jiding Xiab a School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, 225002 and bSchool of Chemical Engineering, Jiangnan University, Wuxi, 214036, People’s Republic of China

ABSTRACT: The effects of cefoperazone sodium (CS), a pharmaceutical compound, on the critical micelle concentration (CMC) of surfactants with different charges [cetyl trimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton X-100], the cloud point of Triton X-100, and the Krafft temperatures of SDS and CTAB were studied. The interaction of CS with differently charged surfactants was determined by ultraviolet and fluorescence spectrophotometry. The results show that with increasing CS concentration, the Krafft temperature increases and the CMC decreases in the SDS/H2O system, whereas the opposite results are obtained in the CTAB/H2O system. Both the cloud point and the CMC of Triton X-100 increase with the addition of CS. The above results are attributed to the different micellar interactions between CS and surfactants with different charges. Paper no. S 1464 in JSD 8, 241–246 (July 2005). KEY WORDS: Cefoperazone sodium, cloud point, CMC, Krafft temperature, surfactant.

Surfactants are widely used as solubilizers, emulsifiers, and detergents in many household and industrial situations owing to their unique physicochemical properties. The applications of micellar systems or other organized molecular assemblies have been recognized for many years, and they have been exploited in different areas including the chemical industry, materials science, the energy industry, and medicine (1–5). Interactions between drugs and surfactants in aqueous solutions have been investigated for more than two decades. Most of the studies in this field have emphasized the effects of surfactants on the stability, delivery, and controlled release of drugs (6–10). However, the number of studies on the effects of drugs on the physicochemical properties of surfactants is still limited. Previous work examined the effects of vitamin C, penicillin G potassium salt, and cephanone on the phase behavior of the cetyl trimethylammonium bromide (CTAB)/n-C5H11OH/H2O system and found that these *To whom correspondence should be addressed. E-mail: [email protected] Abbreviations: CMC, critical micelle concentration; CP, cloud point; CS, cefoperazone sodium; CTAB, cetyl trimethylammonium bromide; KT, Krafft temperature; SDS, sodium dodecyl sulfate; UV, ultraviolet. COPYRIGHT © 2005 BY AOCS PRESS

drugs can enhance the solubility of CTAB in water (11–13). Some interfacial properties of surfactants, such as critical micelle concentration (CMC), Krafft temperature (KT), and cloud point (CP), are very important for surfactant applications. In this regard, many efforts have been made to investigate the effects of various additives, such as inorganic electrolytes and organic compounds, on the physicochemical properties of surfactants (14–19). Cefoperazone sodium (CS), which inhibits the synthesis of mucopeptide of cell walls of gram-positive bacteria, is a βlactam with high medicinal value (20,21). In view of the lack of investigation of the effects of CS on the properties of common surfactants, it is necessary to study the effect of this medicine on certain physicochemical properties to expand its potential commercial application. In this paper, the effects of CS on the physicochemical properties of differently charged surfactants including CTAB, sodium dodecyl sulfate (SDS), and Triton X-100 were studied. These surfactants are cationic, anionic, and nonionic, respectively. Triton X-100 is the commercial name for octylphenolethoxylate containing an average of 10 ethylene oxide groups.

EXPERIMENTAL PROCEDURES Reagents and instruments. CS was purchased from Shandong Lukang Medicine Co. (Shandong, China), and its molecular structure is shown in Scheme 1. It has a complex ring structure and contains one charged carboxylate moiety. SDS (Sigma, St. Louis, Mo; 98%) was recrystallized twice in ethanol, and the surface tension curve of the SDS solution showed no minimum around the CMC, indicating its high purity. CTAB (Sigma, 99%), Triton X-100 (Aldrich, Milwaukee, WI; 99%), and pyrene (Aldrich, 99%) were used as received. Water used was twice distilled. Electrical conductivity was recorded on a DDS-11A data conductivity meter (Shanghai Second Instrument Co., Shanghai, China); fluorescence and ultraviolet (UV) spectra were measured using a RF-5301PC fluorescence spectrophotometer (Shimadzu Co., Tokyo, Japan) and a UV-2501 UV-visible spectrophotometer (Shimadzu Co.), respectively. Methods. (i) CMC. The CMC of SDS and CTAB were determined by the electroconductivity method, and the conductivity range was from 1 µS·cm−1 to 10 mS·cm−1 with a precision of JOURNAL OF SURFACTANTS AND DETERGENTS, VOL. 8, NO. 3 (JULY 2005)

242 J. QIAN ET AL.

SCHEME 1

0.5%. The CMC value was taken as the break in the conductivity vs. concentration plot at 25 ± 0.1°C. During the conductivity measurement, the sample solution was stirred gently and continuously with a magnetic stirrer. The CMC of Triton X-100 was determined by fluorescence spectrophotometry. The fluorescence intensity of Triton X100 around 302 nm was determined when it was excited at 279 nm. The CMC of Triton X-100 with different concentrations of CS in solution was determined as the break point in the fluorescence intensity vs. concentration plot at 25 ± 0.1°C. (ii) CP. CS solutions containing 1.0% Triton X-100 were prepared and placed in a thermostated water bath for equilibration. The temperature was increased at a rate of 1°C per 30 min near the CP until a change from a clear transparent solution to a turbid cloudy dispersion was observed. This transition temperature was recorded as the cloud point (CP) of Triton X-100. Reproducibility was ±0.5°C. (iii) KT. CS solutions containing 1.0% CTAB or SDS were prepared and placed in an ice-water bath mixture until precipitate appeared. The temperature was then increased at a rate of 1°C per 30 min. The temperature at which the sample changed from cloudy to clear was recorded as the Krafft temperature (KT) of CTAB or SDS. Reproducibility was ±0.5°C. (iv) Micropolarity. The micropolarity in micelles was determined by steady-state fluorimetry with pyrene (1.4 × 10−7 mol·L−1) as the probe molecule. Pyrene has five emission peaks when it is excited at 338 nm. The intensity ratio (I1/I3) at 373 nm to that at 384 nm indicates the polarity of the microenvironment around the probe molecule (22,23), from which the location of CS in micelles is derived (24). All the solutions were deoxygenated before measurement by bubbling pure nitrogen through for 15 min. The steadystate fluorescence spectra of pyrene in the micelles were determined at 25 ± 0.1°C. (v) Interaction of CS with surfactants. The UV absorbance spectra of CS aqueous solutions at different CTAB (or SDS) concentrations were measured. The interactions of CS with CTAB (or SDS) were verified by the change of UV spectrum of CS in CTAB (or SDS) micelles. The interaction between CS and Triton X-100 was determined by the change of fluorescence intensity of Triton X-100 with changes in CS concentration.

JOURNAL OF SURFACTANTS AND DETERGENTS, VOL. 8, NO. 3 (JULY 2005)

FIG. 1. Plots of conductivity vs. cetyl trimethyl ammonium bromide (CTAB) concentration (insert is the enlarged Figure). cCS, concentration of cefoperazone sodium (CS).

RESULTS AND DISCUSSION Effect of CS on the CMC of micelles with different charges. The specific conductivity of CS and surfactant solutions at various concentrations against surfactant concentration at 25 ± 0.1°C is plotted in Figures 1 and 2. These plots indicate that the conductivity increases with increasing surfactant concentration in three linear regions. The first marked break corresponds to the surfactant concentration at which the globular micelles form (CMC1), and the second, less marked break is attributed to a transition micellar concentration at which rodlike micelles begin to form (CMC2). The CMC1 and CMC2 of CTAB and SDS at various CS concentrations are shown in Tables 1 and 2, respectively. It can be seen from these two tables that both the CMC1 and CMC2 of CTAB micelles increase with increasing CS concentration whereas those of SDS decrease. These results indicate that the presence of CS

FIG. 2. Plots of conductivity vs. sodium dodecyl sulfate (SDS) concentration. For other abbreviation see Figure 1.

243 CEFOPERAZONE SODIUM EFFECT ON SURFACTANT PROPERTIES TABLE 1 Effect of Cefoperazone Sodium on the CMC of CTAB Micellea Conc. of CS (10−4 mol/L)

CMC1

0 3.1 6.1 9.3 14.4 19.8

(10−5 mol/L)

90 191 294 390 543 596

TABLE 3 Effect of Cefoperazone Sodium on the CMC1 of Triton X-100a CMC2

Conc. of CS (10−4 mol/L)

2170 2410 2545 2519 2740 2938

0 4.0 6.0 8.0 10.0

a

CMC1 (10−4 mol/L) 2.84 3.30 3.67 4.30 4.78

a

For abbreviations see Table 1.

CS, cefoperazone sodium; CMC, critical micelle concentration; CTAB, cetyl trimethyl ammonium bromide.

is unfavorable to the formation of spherical and rod-like micelles of CTAB, but it enhances the formation of both types of micelles of SDS. Figure 3 shows that the fluorescence intensity of Triton X100 increases with increasing concentration, and that two linear regions are clearly evident. The break point in the top curve is 2.84 × 10−4 mol·L−1, which corresponds to the CMC1 of Triton X-100. Triton X-100 concentrations at the break points in the other curves can be regarded as the CMC1 of Triton X-100 at different CS concentrations, and they are listed in Table 3. It is clearly seen that the CMC1 increases with increasing CS concentration. The result shows that CS enhances the hydrophilicity of Triton X-100, and that more Triton X-100 molecules are therefore needed to form spherical micelles. The solubility of CS in water is about 3.62 mol·L−1. As shown in Scheme 1, there are several polar groups with lonepair electrons in the CS molecule, e.g., carbonyl and carboxylate groups, which can be easily attracted by electron-deficient atoms. Also, functional groups within the CS molecule with activated hydrogen, such as hydroxyl and amino groups, can contact those groups having lone-pair electrons. The hydrophilic group of the cationic surfactant CTAB, a quaternary ammonium salt, is an electron-deficient center. There exists electrostatic attraction between CTAB and CS. A CTAB⋅⋅⋅CS complex can therefore form by intermolecular action, and the hydrophilicity of CTAB is enhanced due to the larger solubility of CS. As a result, the CMC of CTAB also increases. In contrast, the hydrophilic group of SDS is an anionic radical OSO3− group. Because of its high charge density, electrostatic repulsion exists between SDS and CS, making the local concentration of SDS larger by a salting-out effect.

Thus, it is easier for SDS to form micelles, i.e., less SDS is needed to form micelles, and the apparent CMC of SDS becomes smaller. Finally, the hydrophilic oxyethylene group of the nonionic surfactant Triton X-100 has lone-pair electrons that can interact with CS through hydrogen bonding. The hydrophobic group of Triton X-100 has no obvious change in character. Thus, both the relative hydrophilicity and the solubility of Triton X-100 increase, which inhibits Triton X-100 from forming micelles and causing the CMC1 to increase. Effect of CS on the CP of Triton X-100. Figure 4 shows that the CP of Triton X-100 at a 1.0% concentration increases with the increasing concentration of CS. The addition of CS enhances the hydrogen bond interaction between Triton X-100 and water. This enhancement occurs because CS enlarges the effective hydrophilic chain of Triton X-100, thereby increasing both water solubility and the CP temperature. The effect of additive on the binding factor or critical packing parameter (f ) of micelles can be used to qualitatively explain the change of the CP (25). f = Vh/α⋅Lc

[1]

where Vh is the volume of the hydrophobic chain and α is the apparent area of the hydrophilic group. Lc is the length of the

TABLE 2 Effect of CS on the CMC of SDS Micellea Conc. of CS (10−4 mol/L)

CMC1

(10−5 mol/L)

CMC2

5672 941 0 5349 830 1.4 6.6 668 5078 11.4 623 4850 16.0 490 4793 a SDS, sodium dodecyl sulfate; for other abbreviations see Table 1.

FIG. 3. Plots of fluorescence intensity I vs. concentration of Triton X100 [excitation wavelength (ex) = 279 nm, emission wavelength (em) = 302 nm]. For other abbreviation see Figure 1.


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FIG. 4. Effect of CS on the cloud point (CP) of Triton X-100 (wTriton X-100 = 1.0%). For other abbreviation see Figure 1.

hydrophobic group. If the addition of additive results in an increased f value, the hydrophobicity of the surfactant molecule is enhanced and the CP of the surfactant solution decreases. Smaller f values indicate an increase in CP temperature would occur. As mentioned, CS is a water-soluble substance and it can link with the hydrophilic group of Triton X-100, which leads to the larger apparent area of hydrophilic group α, while the apparent volume (Vh) and the length (Lc) of the hydrophobic group are unchanged. Therefore, the f value obtained by Equation 1 becomes smaller, and the CP rises. Effect of CS on the KT of CTAB and SDS. Figure 5 shows that with an increasing concentration of CS, the KT of 1.0% SDS rises sharply initially and then at a slower rate. In contrast, the KT of CTAB drops with increasing CS concentration, as shown in Figure 6. The above results reveal that the formation of the complex CS⋅⋅⋅CTAB enhances the solubility of CTAB and therefore lowers the KT. The electrostatic repulsion between CS and SDS results in a “salting-out” effect,

FIG. 5. Effect of CS on the Krafft temperature (KT) of SDS (wSDS = 1.0%). For other abbreviation see Figure 1. JOURNAL OF SURFACTANTS AND DETERGENTS, VOL. 8, NO. 3 (JULY 2005)

FIG. 6. Effect of CS on the KT of CTAB (wCTAB = 1.0%). For other abbreviations see Figures 1 and 5.

causing the local SDS concentration to increase and the KT of SDS to rise. Location of CS in the micelles of differently charged surfactants. The interactions of CS with differently charged surfactants can be understood by studying the location of CS in the micelles. This parameter can be determined by the I1/I3 value of the microenvironment in which a pyrene probe exists. Since pyrene is a strongly hydrophobic molecule, it is barely soluble in water. In the presence of micelles, pyrene is preferentially solubilized in the palisade of these aggregates. When pyrene transfers into the inside of the micelles, the polarity of the microenvironment decreases, causing a decrease in the I1/I3 value. In a surfactant/H2O micellar system, pyrene exists in the palisade of surfactant micelles where the polar

FIG. 7. Effect of CS on the micropolarity of the microenvironment where pyrene exists in differently charged micelles (ex = 338 nm, em1 = 373 nm, em3 = 384 nm; pyrene concentration = 1.4 × 10−7 mol·L−1). For abbreviations see Figures 1 and 3. Surfactant concentration (10−3 mol·L−1): SDS, 11.35; CTAB 9.55; Triton X-100, 9.89. For abbreviations see Figures 1–3.

245 CEFOPERAZONE SODIUM EFFECT ON SURFACTANT PROPERTIES

FIG. 9. Effect of CS on the fluorescence intensity of Triton X-100 (Triton X-100 concentration = 4 × 10−5 mol·L−1; ex = 279 nm). FIG. 8. Influence of SDS and CTAB on the ultraviolet spectrum of CS (CS concentration = 1.35 × 10−4 mol·L−1, λ = 275 nm). For abbreviations see Figures 1–3.

group links to the hydrocarbon chain. In this situation without added CS, I1/I3 is 1.320, 1.165, and 1.367 in CTAB, SDS, and Triton X-100 micellar systems, respectively. When CS concentration is increased from 0 to 8.9 × 10−4 mol⋅L−1, the I1/I3 value decreases from 1.320 to 1.285 in CTAB micelles, from 1.165 to 1.155 in SDS micelles, and from 1.367 to 1.350 in Triton X-100 micelles (Fig. 7). This trend suggests that CS is solubilized among the polar groups of surfactant micelles, which causes pyrene transfer to the inside of micelles and decreases the I1/I3 value. These results suggest that CS combines with surfactants by intermolecular interaction and is located in the palisade of micelles. The degree of change of I1/I3 decreases in the following order: CTAB > Triton X-100 > SDS, suggesting that there are more CS molecules locating in CTAB micelles than in Triton X-100 or SDS micelles. In general, the electrostatic attraction is stronger than the hydrogen bonding, so more CS molecules can reside in CTAB micelles than in Triton X-100 micelles. CS molecules may be solubilized in SDS micelles by hydrophobic interaction, but this force is weaker than the hydrogen bonding. This difference results in fewer CS molecules being located in SDS micelles as compared with those solubilized within CTAB and Triton X-100 micelles. Interactions between CS and surfactants with different charges. The interaction of CS with differently charged surfactants also can be verified by the change of UV spectrum of CS in different micelles. Figure 8 shows that the addition of SDS increases the absorbance of CS slightly, which indicates that SDS interacts with CS to some extent. In contrast, the addition of CTAB decreases the absorbance of CS first; then the absorbance increases slightly when the CTAB concentration exceeds 3.3 × 10−3 mol·L−1 (this value is larger than the CMC1 of CTAB). The effect of CTAB on the UV spectrum of CS suggests that a supramolecular structure forms between CS and CTAB through electrostatic attraction. In the CTAB micellar system, three forms of CS exist with different absorptivities: CS mole-

cules in water (free CS), complex of CTAB⋅⋅⋅CS, and CS molecules located in micellar aggregates (binding CS). When the CTAB concentration is lower than CMC1, free CS molecules and CTAB⋅⋅⋅CS complexes coexist in solution, and the absorbance of CS decreases at a faster rate. When the CTAB concentration is higher than CMC1, spherical micelles form and some CS molecules begin to solubilize into CTAB micelles. This causes both the numbers of CTAB⋅⋅⋅CS complexes and free CS molecules to decrease and binding CS molecules to increase. As a result, the absorbance decreases at a lower rate. As the CTAB concentration continues to increase, more micelles form, meaning more CS molecules go into the micelles, and the UV absorbance increases slightly. The results shown in Figure 8 suggest that the molar absorptivity decreases in the following order: free CS > binding CS > CTAB⋅⋅⋅CS complex. The UV spectrum of Triton X-100 is similar to that of CS. The effect of CS on the fluorescence spectrum of Triton X100 was studied by assessing the interaction between Triton X-100 and CS (Fig. 9). It can be seen from Figure 9 that with increasing CS concentration, the fluorescence intensity of Triton X-100 decreases, and the peak position shifts to the red, from 302 to 304 nm. These results suggest that supramolecular interaction occurs between CS and Triton X-100 through hydrogen bonding. These interactions between CS and different surfactants undoubtedly influence the stability and controlled release of the drug. Based on these reported results, CTAB and Triton X-100 may enhance the stability of CS and reduce its release rate, whereas SDS may reduce the stability and increase the release rate of CS. Further study is needed to support this hypothesis.

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Junhong Qian was born in 1970 in Yangzhou, Jiangsu Province, People’s Republic of China (P.R. China). She received her B.S. degree in fine chemistry from Dalian University of Technology in 1991 and her master’s degree in fine chemistry from Wuxi Institute of Light Industry in 1993. From 1994 to August 2004, she worked in Yangzhou University. In the fall of 2003, she was appointed as an assistant professor in the School of Chemical & Chemistry Engineering at Yangzhou University. She began her Ph.D. study in September 2004 at East China University of Science & Technology. Her research work mainly focuses on the interaction between drugs and surfactants, such as stability, controlled release of drugs in micellar systems, and the effects of drugs on the physicochemical properties of surfactants. Jinghua Gu was born in 1983 in Suzhou, Jiangsu Province, P.R. China. She received her B.S. degree in applied chemistry from Yangzhou University in 2004. Her research work focuses on the effects of drugs on the physicochemical properties of surfactants. Jiding Xia is a professor of Jiangnan University, the P.R. China. His specialty is in the area of surfactants and detergents. His research work mainly focuses on the synthesis and the physicochemical properties of surfactants.