Margarita del Arco

Layered double hydroxides as drug carriers and for controlled release of non-steroidal antiinflammatory drugs (NSAIDs): A review

Non-steroidal anti-inflammatory drugs constitute one of the groups most widely currently used, but show several problems for administration due to low solubility and delivery control. For this reason, several matrices have been tested to support them in order to overcome these drawbacks. Among them, layered double hydroxides have been used in recent years. The aim of this review is to update the current knowledge and findings on this hybrid system, namely, layered double hydroxides intercalated with different NSAIDs. The basic nature of the matrix introduces an additional advantage, i.e., to decrease ulceration damages. We have focused our review mostly on the preparation procedures, as these control, define and determine the performance of the systems in vitro and also in living organisms.

Cobalt–iron hydroxycarbonates and their evolution to mixed oxides with spinel structure

Cobalt(ii)–iron(iii) mixed hydroxides with hydrotalcite-like structure have been synthesized. Depending on the experimental conditions during synthesis, CoII becomes partially oxidized to CoIII . The solids have been characterized by X-ray diffraction, FTIR spectroscopy, temperature-programmed reduction and nitrogen adsorption at low temperature for specific surface area assessment. Reduction of FeIII takes place at lower temperatures than that of bulk Fe3O4 . Thermal treatment in air leads to oxidation of CoII to CoIII , in the same temperature range where collapsing of the layered structure by decarbonation is observed. The nature of the spinel phases formed upon calcination at high temperature depends both on the calcination temperature and the calcination time.

Effect of thermal treatments on the properties of V2O5/TiO2 and MoO3/TiO2 systems

The surface properties of TiO2 (anatase)-supported V2O5 and MoO3 have been studied, as well as the effect of calcination at 773 K on the porosity of the samples, before and after incorporation of the supported phase. While for the support and for the MoO3TiO2 samples a steady decrease in the surface area is observed with the thermal treatments and molybdena seems to have no effect on the pore structure of the carrier, incorporation of V2O5 has a dramatic effect on it, destroying the pore structure and sharply decreasing the surface area, irrespective of any thermal treatment on the support. No rutilization is observed in any case. The results are interpreted by assuming the formation of patches of vanadium pentoxide on the surface of the support and the formation of continuous films of MoO3 on the carrier.

Thermal behaviour of Zn–Cr layered double hydroxides with hydrotalcite-like structures containing carbonate or decavanadate

Hydrotalcite-like compounds containing ZnII and CrIII in the brucite-like layers have been prepared, containing carbonate or decavanadate in the interlayer, with the formulae [Zn0.67Cr0.33(OH)2](CO3)0.165· 1.34H2O and [Zn0.67Cr0.33(OH)2](CO3)0.165· 1.34H2O, respectively. The samples have been characterized by XRD, XAS, UV-VIS, FTIR and Raman spectrocopies, while the specific textuies of the samples were assessed by nitrogen adsorption, and reducibilities were studied by temperature-programmed reduction. A similar characterization study has been carried out on samples obtained after calcination of the parent samples in air at increasing temperatures. Thermal decomposition of the ZnCr hydrotalcite containing carbonate leads to oxidation of CrIII to CrO42– species at intermediate calcination temperatures, ZnII cations then retaining their original octahedral coordination; at higher calcination temperatures ZnO and ZnCr2O4 are formed. However, the presence of interlayer decavanadate species inhibits the CrIII→ CrO42– oxidation during thermal decomposition of the vanadate-containing hydrotalcite, owing to preferential formation of vanadates. In this case the final product is a mixture of Zn pyrovanadate, Zn2V2O7, and spinel ZnCr2O4, together with a phase consisting of a mixture of partially depolymerized decavanadate to β-VO3– chains, together with monomeric VO43– species.

Effect of consecutive and alternative oxidation and reduction treatments on the interactions between titania (anatase and rutile) and copper

Titania (anatase and rutile)-supported copper systems have been prepared by a conventional impregnation technique (2.5% CuTi atomic ratio). The effect of consecutive oxidation/reduction/ oxidation and reduction/oxidation treatments at 770 K on the final materials has been studied by X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, and visible-ultraviolet (diffuse reflectance) spectroscopy, as well as assessment of the texture of the solids by nitrogen adsorption at 77 K. Clustered CuO, detected by XRD, is formed on anatase, together with dispersed Cu2+ species, that are dominant on rutile. On this support, migration of copper species into the bulk of the support crystallites takes place, leading to unreactive copper species, and so, hydrogen consumption during reduction is lower in rutile-supported systems than the expected value to reduce all Cu2+ species to the metallic state.

Inclusion and Release of Fenbufen in Mesoporous Silica

This work reports the immobilization of Fenbufen, a nonsteroidal anti-inflammatory drug, into two different hexagonal mesoporous silicas (MCM-41) which exhibit some differences in terms of morphology and pore size, and their behavior as systems for sustained release at pH 7.5. The drug/mesoporous silica systems have been characterized by powder X-ray diffractometry (PXRD), Fourier transform infrared spectroscopy (FT-IR), N(2) adsorption-desorption, and transmission electron microscopy (TEM). The results show that the drug is mainly incorporated inside the pores, and its loading is dependent on both the pore size and the impregnation temperature. The Fenbufen/mesoporous-silica systems give a well-sustained release profile, releasing 100% of the initially loaded drug at the end of the in vitro assays.

Surface structure and reactivity of molybdena–titania catalysts prepared by different methods

MoO3–TiO2 samples have been prepared from aqueous solutions of ammonium heptamolybdate and titania (by conventional impregnation and equilibrium adsorption) and by mechanically mixing both oxides (with and without further hydrothermal treatment). The samples have been characterized by X-ray diffraction, specific surface area assessment, Fourier-transform infrared (FTIR) and ultraviolet–visible diffuse refectance (UV–VIS DR) spectroscopies and temperature-programmed reduction (TPR). Surface properties have been studied following the adsorption of probe molecules by FTIR spectroscopy. Dispersed phases are formed preferentially in samples prepared by equilibrium adsorption and in physical mixtures submitted to hydrothermal treatment; in all other cases crystalline MoO3 is mainly formed. Dispersed phases are more easily reduced. They have been identified as surface molybdenyl species bonded to Ti cations through bridging oxygens, and their overall coordination depends on the degree of surface hydration. These species predominate quantitatively on the catalyst surfaces and have been found to be strong Lewis and Bronsted acids. They are also more easily reduced than bulk MoO3 under TRP conditions, and very active as oxidizing agents for methanol.

Surface dispersion of molybdena supported on silica, alumina and titania

Surface species formed upon impregnation of silica, alumina and titania with aqueous solutions of ammonium molybdate and calcination at 770 K have been studied by X-ray diffraction, specific surface area assessment, scanning electron microscopy, laser Raman spectroscopy and temperature-programmed reduction. Dispersion decreases in the order TiO2> Al2O3SiO2. Polymolybdate species are formed for low loadings, that lead to bulk MoO3 for loadings of 0.4 monolayer on SiO2, but persist for higher loadings on titania and alumina. On this last support, isolated molybdate species have been also found.

An FT-IR study of the adsorption and reactivity of ethanol on systems derived from Mg2Al–W7O246− layered double hydroxides

A FT-IR spectroscopy study on the surface reactivity of MgAl-paratungstate LDHs calcined at 500 and 700 °C, prepared by anion exchange from a Mg2Al-nitrate hydrotalcite and precursor salt (NH4)10H2W12O42, for ethanol dehydrogenation, is reported. Calcination at 300 °C of Mg2Al–W7O246− LDH leads to amorphous species, and crystallisation of MgWO4 is observed at 700 °C. The solids calcined at 500 and 700 °C exhibit surface Lewis acid sites and are selective to acelaldehyde formation during ethanol dehydrogenation or to oxidative dehydrogenation, especially in the sample calcined at 500 °C, where carboxylate species are not detected in the temperature range tested (room temperature to 300 °C).

Characterization of Chromate-Intercalated Layered Double Hydroxides

PXRD (powder x-ray diffraction), FT-IR (Fourier Transform infrared), N2 adsorption at - 196 °C and TG/DTA (thermogravimetric and differential thermal analyses) techniques have been used for characterisation of MgAl- and ZnAl-CrO4 LDHs, which had been prepared by the ion exchange method from the corresponding chloride LDH (layered double hydroxides) precursors. The results indicates that the oxometalate intercalation in both systems produces interlayer microporosity and a basal spacing of 8.7 Å; This gallery height decreases when the samples are calcined in the temperature range 100-300 °C, due to a grafting process. A larger thermal stability is detected for MgAl-CrO4 sample than for the zinc-containing one.