Samples of zeolite ZSM-5 have been synthesized in both the sodium form (ZSM-5) and the acid activated form (H-ZSM-5). In addition, each of these two forms was prepared in the two molar SiO2/Al2O3 ratios of 169 and 15. All samples of these ZSM-5 derivatives were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, thermal gravimetric analysis (TGA), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). The samples were successfully loaded with the anticancer drug 5-fluorouracil (5-FU) with loading capacities varying from 22% (for the sodium form having the lower molar SiO2/Al2O3 ratio of 15, ZSM-5-(15)) to 43% (for the corresponding acid form, H-ZSM-5-(15)). Percent release of the drug-loaded ZSM-5 samples into simulated body fluid (SBF) was measured at pH 7.4 and 37°C. The results showed a slight variation in the % release within the range 84–93%, while the first-order rate constant (
Chemotherapy is the most commonly used route for cancer treatment employing organic- and inorganic-based drugs. However, most of these drugs are known for their poor physicochemical properties such as low solubility, low stability, short circulating half-life, and cytotoxicity [
Chemical structure and molecular dimensions of 5-fluorouracil (5-FU).
5-Fluorouracil (5-FU) is a water-soluble pyrimidine analogue which is widely used in the treatment of various kinds of cancer, especially colon, head, neck, and ovary cancers [
Different delivery systems have been used to ensure prolonged and sustained release of 5-FU. Examples include hydrogels [
In this study, zeolites ZSM-5 and H-ZSM-5, each prepared in two different molar SiO2/Al2O3 ratios (169 and 15), have been investigated as probable drug delivery systems for 5-FU. This choice of ZSM-5 zeolite derivatives for investigation as a possible drug carrier for 5-FU was dictated by their having a promising 3D-channel structure with a suitable pore size, in addition to its reasonable good acid and thermal stability, in comparison with low silica zeolites.
Tetrapropylammonium bromide (+98%, Acros Organics), aluminum sulfate Al2(SO4)3·16H2O (Interchem), sodium chloride (BDH), BaCl2·2H2O (Merck), CaCl2·2H2O (Merck), MgCl2·6H2O (SD Fine-Chem Limited), sodium metasilicate nonahydrate (Na2SiO3·9H2O) (Aldrich), sulfuric acid (98%, SD Fine-Chem Limited), ammonium nitrate (RPL), NaHCO3 (Merck), KCl (Riedel de Haën), K2HPO4·3H2O (Merck), sodium hydroxide pellets (BDH), Na2SO4 (Merck), hydrochloric acid (35%, SD Fine-Chem Limited), nitric acid (95%, Merck), 5-fluorouracil (Acros Organics, 99%), and tris(hydroxymethyl)aminomethane (Merck) were used as received. The simulated body fluid (SBF) was prepared following literature procedure [
X-ray powder diffraction spectra were measured using a Philips 2KW model X-ray diffractometer (Cu-K
Samples of zeolite ZSM-5 with two different molar SiO2/Al2O3 ratios were prepared following a literature procedure [
Solutions 2 and 3 were mixed, and then solution 1 was added dropwise. After vigorous stirring (~30.0 min), the pH was adjusted to the range 10.3–10.6 by adding concentrated sulfuric acid (98%). The hydrogel formed was transferred into an autoclave and heated for two days at 170°C. The solid product was filtered and washed with deionized water until the filtrate is sulfate-free (tested by BaCl2). The zeolite was dried at 110°C for one hour and then calcined at 550°C for 5 h to allow for the decomposition of the template.
The sodium zeolite ZSM-5 was acid activated into H-ZSM-5 using the following typical procedure: a sample of ZSM-5 (1.00 g) was added to a 2.0 M solution of ammonium nitrite (50.0 mL) and the mixture was placed in a thermostated water bath/shaker at 80°C for 24 h, to obtain the ammonium exchanged zeolite, NH4-ZSM-5. The ammonium form of the zeolite was transformed to the acid form (H-ZSM-5) by calcination at 500°C for 4 h [
5-FU was loaded into samples of ZSM-5 with two different molar SiO2/Al2O3 ratios via the following general procedure: 5-FU (≈0.400 g) was dissolved in water (25.0 mL) and then added to a flask containing ZSM-5 (~0.200 g). The mixture was stirred in the dark, at room temperature, for 24 h. The drug-loaded carrier was filtered and dried under vacuum (30 mmHg) for two hours at 60°C.
The loading capacities of drug-loaded samples were determined by TGA measurements within the temperature range 25–1100°C, under nitrogen. The drug loading capacity was also determined by UV-Visible absorption spectrophotometer, in which a predetermined amount of drug-loaded carrier (around 0.0100 g) was stirred with water (100.00 mL) for 24 hours at room temperature, the solution was then filtered, and the concentration of 5-FU was determined by measuring the absorbance at 266 nm. The total amount of drug contained in the sample was calculated with reference to a calibration curve.
The
At predetermined time intervals (1/60, 5/60, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, and 13 hours), an aliquot (1.000 mL) was withdrawn from the flask and replaced by a fresh sample of SBF (1.000 mL, 37.0°C) to maintain a constant volume. The release experiments were conducted in triplicate.
The concentration of 5-FU released was determined by measuring the absorbance at 266 nm relative to a calibration curve of 5-FU in SBF. The calibration curve covered the concentration range of 0.50 to 20.00 ppm.
ZSM-5 (sodium form) was prepared with two molar SiO2/Al2O3 ratios (169 and 15) by using a constant amount of sodium silicate and changing the aluminum content in the hydrogel (Table
ZSM-5 sample preparation with molar SiO2/Al2O3 ratios of 169 and 15.
Sample |
NaSiO3·9H2O mass (g) | Al2(SO4)3·16H2O mass (g) | SiO2/ |
---|---|---|---|
ZSM-5-(169) | 25.25 | 0.400 | 169 |
ZSM-5-(15) | 25.25 | 3.000 | 15 |
The XRD spectra of ZSM-5 samples having the molar SiO2/Al2O3 ratios of 15 and 169 appear almost exactly the same. Similarly, the XRD spectra for the acid activated samples were in agreement with the typical pattern for zeolite ZSM-5, thus confirming that the zeolite keeps its structure and crystallinity upon acid activation as shown in the spectra of ZSM-5-(15) and H-ZSM-5-(15) depicted in Figure
XRD spectra of ZSM-5 and H-ZSM-5 having a molar SiO2/Al2O3 ratio of 15.
In an ideal case, microporous materials should exhibit type I isotherm according to IUPAC classification [
A typical nitrogen adsorption-desorption isotherm for ZSM-5-(15).
The specific surface areas of ZSM-5 derivatives were estimated from the adsorption branch using the Brunauer-Emmett-Teller (BET) theory [
Specific surface area (
Zeolite sample | SiO2/Al2O3 (molar ratio) |
|
---|---|---|
ZSM-5-(15) | 15 | 194 |
ZSM-5-(169) | 169 | 326 |
H-ZSM-5-(169) | 169 | 369 |
H-ZSM-5-(15) | 15 | 247 |
As to the effect of variations in acid activation and/or molar SiO2/Al2O3 ratio on the specific surface area of ZSM-5 zeolite, the following three observations are evident: For the acid activated form H-ZSM-5, increasing the molar SiO2/Al2O3 ratio from 15 to 169 raises the specific surface area by ≈50% (247 up to 369 m2/g). For the sodium form ZSM-5, increasing the molar SiO2/Al2O3 ratio from 15 to 169 raises the specific surface area by ≈70% (194 up to 326 m2/g). For the sodium form ZSM-5, a combination of acid activation and increase in the molar SiO2/Al2O3 ratio, from 15 to 169, raises the specific surface area by ≈90% (194 up to 369 m2/g). Therefore, a combination of increasing molar SiO2/Al2O3 ratio and acid activation of ZSM-5 yields the highest specific surface area.
Estimates of the sizes of ZSM-5 and H-ZSM-5 particles, and their morphologies, were obtained through SEM micrographs. All micrographs depict homogeneous distribution of particles, with no significant effect of molar SiO2/Al2O3 ratio or acid activation on their size or shape. Some of the particles have elongated cubic shapes while others have hexagonal prismatic units with particle size distributions in the range of 0.4–0.8
SEM micrographs of (a) ZSM-5-(15) and (b) H-ZSM-5-(169).
With the dimensions shown in Figure
XRD of (a) 5-FU, (b) ZSM-5-(15) loaded with 5-FU, and (c) unloaded ZSM-5-(15).
The zeolite loading capacity for 5-FU was determined from the TGA thermograms of pure ZSM-5 and ZSM-5 loaded with 5-FU. Figure
TGA thermograms of (a) 5-FU, which shows a residual mass of 6.95%, (b) 5-FU-ZSM-5-(15), with a residual mass of 50.02%, (c) 5-FU-ZSM-5-(169), with a residual mass of 58.69%, (d) 5-Fu-H-ZSM-5-(169), with a residual mass of 64.72%, and (e) 5-Fu-H-ZSM-5-(15), exhibiting a residual mass of 71.96%.
The zeolite loading capacity was also estimated by UV-Visible spectrophotometry, according to the following equation:
The measured % loading of 5-FU into the four zeolite samples.
Sample | % loading (TGA data) | % loading (UV data) |
---|---|---|
ZSM-5-(169) | 38 | 38.0 |
H-ZSM-5-(169) | 40 | 39.1 |
ZSM-5-(15) | 21 | 22.0 |
H-ZSM-5-(15) | 45 | 43.0 |
In view of data presented in Table
The
At predetermined time intervals (as specified in the experimental section), aliquots were withdrawn from the release medium and were readily replaced by fresh samples of SBF at the same conditions, in order to maintain a constant SBF volume. The release experiments were conducted in triplicate, and corresponding data averages of the three experiments were used for nonlinear regression analysis.
The withdrawn samples were analyzed for 5-FU concentration by measuring the absorbance at
The first-order kinetic model was used to simulate the kinetics of the drug release process. Nonlinear regression analysis was used to fit the experimental cumulative drug release
Both
Percent release profiles of 5-FU from 5-FU-ZSM-5-(15) (triangles), 5-FU-H-ZSM-5-(15) (squares), and 5-FU-ZSM-5-(169) (circles). Solid lines passing through experimental data represent nonlinear regression into first-order release kinetics.
The kinetic parameters for the release of 5-FU from the three carriers ZSM-5-(15), H-ZSM-5-(15), and ZSM-5-(169) are listed in Table
Kinetic parameters of 5-FU release from sodium zeolite (ZSM-5) and the corresponding acid activated form (H-ZSM-5). Modeling of % release (
5-FU loading data | 5-FU kinetic release models’ data | |||||||
---|---|---|---|---|---|---|---|---|
Zeolite |
|
|
|
|||||
|
% loading |
|
|
% release |
|
|
|
|
ZSM-5-(15) | 49.2 | 22 | 10.8 | 10.47 | 97 | 2.2 | 1.2 | 11.0 |
H-ZSM-5-(15) | 50.2 | 43 | 21.6 | 19.8 | 92 | 3.9 | 1.4 | 22.5 |
ZSM-5-(169) | 50.6 | 38 | 19.2 | 16.2 | 85 | 2.9 | 1.1 | 2.4 |
The Higuchi square root time model [
A plot of the % release, against
In addition, estimates of the individual contributions of drug diffusion (
Table Successful use of zeolite ZSM-5 as a carrier for 5-FU with a relatively high loading capacity (≥40%) can be partially attributed to the close matching between the size of ZSM-5 micropores and that of the 5-FU molecule. Enhancements on the loading capacity and the first-order rate constant A relatively high % release of 5-FU was achieved with the highest % release exhibited by ZSM-5 having a molar SiO2/Al2O3 ratio of 169 (≥85%). The Diffusion is the principal process governing 5-FU release from zeolite ZSM-5.
A comparison of % loading, % release, and kinetic model parameter data of 5-FU obtained in this work, as well as related data on siliceous carriers published literature, for comparison.
5-FU kinetic release models’ data | |||||
---|---|---|---|---|---|
Siliceous material |
|
|
Reference | ||
% loading | % release |
|
|
||
ZSM-5-(15) | 22 | 97% after 3 hrs | 2.2 | 1.2 | This work |
H-ZSM-5-(15) | 43 | 92% after 3 hrs | 3.9 | 1.4 | |
ZSM-5-(169) | 38 | 85% after 3 hrs | 2.9 | 1.1 | |
|
|||||
Zeolite NaX-FAU | 16 | 83% after 3 min (0.1 M HCl) | — | — | [ |
|
|||||
Zeolite HY-60 | 9 | 63% after 5 hrs | 90 | — | [ |
|
|||||
MCM-41 | 86 | 45% after 1 hr, 95% after 26 hrs | 0.24 | 3.3 |
[ |
Thiol-functionalized MCM-41 | 99 | 20% after 2 hrs, 95% after 18 hrs | 0.1 | 206 |
In this research work, zeolite ZSM-5 was synthesized with two different molar SiO2/Al2O3 ratios, which were both acid activated. The acid activated ZSM-5 with a molar SiO2/Al2O3 ratio of 169 shows the highest % loading and % release. As shown in Table
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors acknowledge the fruitful discussions of kinetic data with Professor M. Zughul. The authors gratefully acknowledge the financial support provided by the Deanship of Academic Research, The University of Jordan, Amman, Jordan, and Scientific Research Support Fund (Grant no. Bas/2/02/2012), Amman, Jordan.