Aramis Rivera

Time evolution of a natural clinoptilolite in aqueous medium: conductivity and pH experiments

The chemical behavior in an aqueous medium of a natural zeolitic material, NZ (mainly consisting in crystals of the zeolites clinoptilolite/heulandite) has been studied through electrochemical techniques, complemented by atomic absorption spectrometry. The time dependence of the conductivity of the aqueous medium in the presence of NZ, showed a steep increase at the beginning followed by a slower increase for longer times until saturation of the system is reached. The release of the ions present in the zeolitic material at different times, was followed by means of atomic adsorption spectroscopy, which indicated that the sodium ion is the main responsible for the conductivity response. The interaction of NZ with the aqueous medium revealed a pH increase in the weakly acid region and a decrease in the basic region. The correlation between conductometric and pH-metric studies suggests that an ion-exchange mechanism takes place within the very first minutes of the interaction of NZ with the aqueous medium, followed by the temperature-dependent dissolution of minority phases up to several days. Finally, a comparative study between NZ and a modified form of this zeolite with sodium carbonate (NZ1), showed a faster pH increase with time for NZ1.

Interaction studies between drugs and a purified natural clinoptilolite

Taking into account the biological properties of the purified natural clinoptilolite, NZ, some studies were conducted to evaluate the physicochemical interaction between this zeolite and two drugs, metronidazole and sulfamethoxazole, which cause considerable gastric side effects. Two modified forms of NZ were also considered. We have studied the drug solutions before and after the contact with the zeolitic materials in a wide range of pH values by UV spectroscopy. The structure of the two drugs remains unaltered after interaction with the zeolitic products. It is demonstrated that metronidazole adsorption by the different materials is small in acidic pH, and that the zeolitic materials studied do not adsorb sulfamethoxazole at the considered pH values. The overall study suggests the possibility of parallel administration of these products. These results are coherent with a complementary investigation by transmission IR spectroscopy about the possible incorporation of drug on NZ and its modified forms.

Preliminary characterization of drug support systems based on natural clinoptilolite

Abstract The use of porous materials as host systems for medical applications has been considered in recent years. Taking into account the biological properties reported for the purified natural clinoptilolite, NZ, we study here the influence of different treatments on the structural behavior of the raw material, aiming at the future preparation of slow release systems. In particular, we study by 27 Al, 29 Si, 23 Na MAS NMR, and 13 C CPMAS NMR the evolution of these elements on clinoptilolite after acid treatments, and modifications involving a surfactant and three drugs. Our results confirm a small presence of octahedral aluminum, when NZ and AZ (Na-clinoptilolite) are submitted to modifications at pH 1.2, and also that a measurable amount of organic molecules incorporates to the clinoptilolite after adequate treatments. Finally, we study the influence of the treatments on the specific surface area of NZ through the use of the BET technique based on nitrogen adsorption.

Characterization and neutralizing properties of a natural zeolite/Na2CO3 composite material

Abstract A new zeolitic active principle called NZ* has been obtained, the neutralizing properties of which are better than those of its predecessor, Neutacid N. The new product is the result of hydrothermal transformations applied to purified natural clinoptilolite. NZ* and other related products have been characterized physically and chemically using atomic emission spectroscopy with inductively coupled plasma, X-ray fluorescence analysis, X-ray diffraction, IR spectroscopy, neutralizing capacity in the presence of synthetic gastric juice and UV spectroscopy. It was demonstrated that the structure of the zeolitic raw mineral remained unchanged after hydrothermal transformation, and that NZ* is structurally stable after interaction with synthetic gastric juice. The effect of NZ* dose on the gastric enzyme pepsin was evaluated.

Adsolubilization of drugs onto natural clinoptilolite modified by adsorption of cationic surfactants.

The combined adsorption onto purified natural clinoptilolite (NZ) of the cationic surfactant benzalkonium chloride (BC) and the model drugs metronidazole and sulfamethoxazole has been studied in order to design systems for the storage and release of drugs. The equilibrium adsorption of benzyldimethylalkylammonium chloride surfactants with hydrocarbon chain lengths corresponding to 12, 14 and 16 carbon atoms (BC12, BC14 and BC16) onto NZ from aqueous solutions was compared to that of BC. The effect of exchangeable cations on the NZ structure and that of acid-base pre-treatment of NZ on the adsorption capacity of BC was evaluated. It was shown that the nature of the exchangeable cations had little influence on the adsorption of BC onto NZ, and that acid-base treatments of NZ led to a decrease in the amount of surfactant adsorbed. The results indicated that the adsorption of the less polar drug, sulfamethoxazole, was enhanced by the presence of BC12 at the solid-liquid interface, whereas the uptake of metronidazole was independent of the surfactant adsorption.

Theoretical study of metronidazole adsorption on clinoptilolite

Abstract A possible combination of metronidazole–clinoptilolite has been studied by means of computational simulation, using AM1 semiempirical method, in order to know the adsorption of metronidazole on the zeolitic matrix, which could decrease the side-effects of this drug. Two different zeolite models were used, and the metronidazole molecule was oriented to them in several initial geometries. The nature of the interaction of metronidazole and zeolitic models depends on the size of the last one, which determines the kind of interaction, but in both cases the drug is adsorbed in the lattice structure.

Benzalkonium chloride and sulfamethoxazole adsorption onto natural clinoptilolite: effect of time, ionic strength, pH and temperature.

The influence of different physical factors on the adsorption of the cationic surfactant benzalkonium chloride (BC) and the model drug sulfamethoxazole by a purified natural clinoptilolite (NZ) has been studied in order to employ zeolite-surfactant-drug composites as drug deliverer. It has been demonstrated that the adsorption of BC and sulfamethoxazole onto NZ depends of the time, the temperature, the ionic strength and the pH of the aqueous medium. The optimal conditions for the preparation of the zeolite-surfactant and zeolite-surfactant-drug composite materials are established. The results of the composite characterization support the presence of BC and sulfamethoxazole, as well as the structural stability of NZ during the treatments performed. The release experiments in acid medium demonstrate that the adsorption of sulfamethoxazole is reversible. It is also confirmed that the drug release profile corresponds to a diffusion or zero-order mechanism as a function of the compression pressure.

Advantages of base exchanged natural clinoptilolite as a catalyst for the Knoevenagel reaction

Abstract The potential use of natural zeolites as base catalysts was ascertained by studying the catalytic behavior of a purified natural clinoptilolite (NZ) and its sodium carbonate modified form (NZC) in the aldol condensation reaction of benzaldehyde with methyl cyanoacetate (Knoevenagel reaction). The natural zeolites activities were compared to that of cesium modified X and Y faujasite type zeolites (CsFAUX and CsFAUY). It was observed that the activity of the NZC zeolite was five times higher than that of NZ. The normalized activity per surface area of the modified clinoptilolites was higher than that shown by synthetic FAUs zeolites. The higher activity of NZC is attributed to the presence of single and double carbonate species, such as Na2CO3 and Na2Ca(CO3)2, occluded in the internal cavities of the clinoptilolite zeolite, as confirmed by XRD and IR diffuse reflectance. The CO2 and NH3 TPD analysis corroborated the presence of stronger basic sites in the natural zeolites in good agreement with the catalytic behavior shown by these solids in the Knoevenagel condensation reaction.

Acid natural clinoptilolite: structural properties against adsorption/separation of n-paraffins.

The employment of an acid natural clinoptilolite (AZH-1) in the adsorption and separation of n-paraffins has been evaluated. Natural clinoptilolite, NZ, was the raw material used to prepare the sodium-exchanged clinoptilolite (AZ) starting from which the AZH-1 sample was obtained by acid treatment. The structural stability of the samples after the applied treatments was demonstrated. The nitrogen adsorption experiments indicated that the acid sample has a homogeneous porous distribution and a considerable increase in the micropore volume with respect to NZ and AZ. The employment of the inverse gas chromatography at infinite dilution (IGCID) allowed studying the adsorption and separation of n-paraffin mixtures on AZH-1. It was also confirmed that the diffusion on AZH-1 took place in an unblocked structure through the A channel of ten members with minimal interactions. The IGCID results demonstrated the capacities of the acid Cuban natural zeolite in the adsorption and separation of n-paraffin mixtures.

A simple way for targeted delivery of an antibiotic: In vitro evaluation of a nanoclay-based composite

The sodium-modified form of fluorohectorite nanoclay (NaFh) is introduced as a potential drug carrier, demonstrating its ability for the controlled release of the broad-spectrum antibiotic Ciprofloxacin through in vitro tests. The new clay-drug composite is designed to target the local infections in the large intestine, where it delivers most of the incorporated drug thanks to its pH-sensitive behavior. The composite has been conceived to avoid the use of coating technology and to decrease the side-effects commonly associated to the burst-release of the ciprofloxacin at the stomach level. NaFh was obtained from lithium-fluorohectorite by ion exchange, and its lack of toxicity was demonstrated by in vivo studies. Ciprofloxacin hydrochloride (Cipro) was encapsulated into the clay at different values of the pH, drug initial concentration, temperature and time. Systematic studies by X-ray diffraction (XRD), infrared and visible spectrophotometry (FT-IR and UV-vis), and thermal analysis (TGA) indicated that the NaFh host exhibits a high encapsulation efficiency for Cipro, which reaches a 90% of the initial Cipro in solution at 65 oC, with initial concentration of drug in solution of 1.36 x 10−2 mol L-1 at acid pH. XRD revealed that a true intercalation of Cipro takes place between clay layers. TG showed an increased thermal stability of the drug when intercalated into the clay, as compared to the “free” Cipro. IR suggested a strong clay-Cipro interaction via ketone group, as well as the establishment of hydrogen bonds between the two materials. In vitro drug release tests revealed that NaFh is a potentially efficient carrier to deliver Cipro in the large intestine, where the release process is mediated by more than just one mechanism.