Cristina Martín

Nanocomposite Hydrogels: 3D Polymer-Nanoparticle Synergies for On-Demand Drug Delivery.

Considerable progress in the synthesis and technology of hydrogels makes these materials attractive structures for designing controlled-release drug delivery systems. In particular, this review highlights the latest advances in nanocomposite hydrogels as drug delivery vehicles. The inclusion/incorporation of nanoparticles in three-dimensional polymeric structures is an innovative means for obtaining multicomponent systems with diverse functionality within a hybrid hydrogel network. Nanoparticle-hydrogel combinations add synergistic benefits to the new 3D structures. Nanogels as carriers for cancer therapy and injectable gels with improved self-healing properties have also been described as new nanocomposite systems.

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.

Influence of tungsten oxide on structural and surface properties of sol–gel prepared TiO2 employed for 4-nitrophenol photodegradation

A set of tungsten oxide/TiO2 polycrystalline samples (W/Ti) prepared by the sol–gel method has been characterised using several techniques, namely thermogravimetric analysis, gas-chromatography, mass spectrometry, thermogravimetric analysis combined with mass spectrometry or with gas chromatography/mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, determination of specific surface area, scanning electron microscopy, Fourier-transform infrared spectroscopy and monitorisation of pyridine adsorption for surface acidity. Moreover the samples have been empolyed as catalysts for 4-nitrophenol photodegradation in aqueous suspensions used as a ‘probe’ reaction. Characterisation results indicate that the surface of the W/Ti particles is enriched with homogeneously dispersed tungsten as well as microcrystalline or amorphous species. Maximum photoactivity for 4-nitrophenol photodegradation was achieved for a sample containing 1.7 mol W per 100 mol Ti.

Surface properties of iron-titania photocatalysts employed for 4-nitrophenol photodegradation in aqueous TiO2 dispersion

Iron(III) doped specimens (0.01–5% atomic Fe ∶ Ti) have been prepared by impregnating polycrystalline “home prepared” TiO2 (mainly anatase) and have been studied for photocatalytic degradation of 4-nitrophenol in aqueous dispersions. Some structural and surface properties have been studied by X-ray diffraction, specific surface area and porosity measurements and FTIR monitoring of pyridine, ammonia and methanoic acid adsorption for surface acidity and basicity. Their surface properties were compared with a corresponding series of photocatalysts prepared by a coprecipitation method. Adsorption of pyridine and ammonia indicates the presence of surface acid Lewis sites, a low concentration of surface Brønsted sites being present only in the samples prepared by impregnation. The photocatalytic experiments indicated that the presence of iron ions does not influence or is detrimental for the occurrence of the 4-nitrophenol photodegradation.

Preparation and characterisation of TiO2 (anatase) supported on TiO2 (rutile) catalysts employed for 4-nitrophenol photodegradation in aqueous medium and comparison with TiO2 (anatase) supported on Al2O3

Abstract In this paper the preparation of two sets of polycrystalline photocatalysts prepared by supporting TiO2 (anatase) on TiO2 (rutile) or Al2O3 is reported. The powders were prepared by a wet impregnation method using titanium(IV) isopropylate. The impregnation was followed by thermal treatment and this procedure was repeated several times in order to obtain samples with progressively increasing amounts of TiO2 (anatase). The photocatalytic activity of all of the specimens was tested by carrying out the 4-nitrophenol photodegradation, used as a “probe” reaction, in aqueous medium and in different kinds of batch photoreactors. The solids were characterised by X-ray diffraction (XRD), specific surface area (BET) and porosity determination, scanning electron microscopy observation (SEM) coupled with energy dispersive X-ray analysis (EDX), visible–ultraviolet diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR) monitoring of surface acidity. The characterisation results indicate an increase of TiO2 anatase phase with the number of impregnations. The porosity and the surface area of all the photocatalysts prepared by supporting TiO2 (anatase) on TiO2 (rutile) were always higher than that of the bare support, while those of the samples prepared by supporting TiO2 (anatase) on Al2O3 were lower than that of bare Al2O3. The FTIR measurements indicated that Lewis acid sites (Ti4+ or both Ti4+ and Al3+) were present on the surface of the two sets of supported samples, while no Bronsted acid sites were detected. The preparation method used allowed to obtain samples quite resistant to disaggregation when they were mixed in water. Moreover they showed to be easily decantable after the occurrence of the runs. Both sets of TiO2 (anatase) supported samples resulted photoactive and the photoactivity increased by increasing the content of the anatase phase, although it was less significant than that of a pure home prepared and Degussa P25 TiO2 samples, tested for the sake of comparison.

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.

A FTIR spectroscopic study of surface acidity and basicity of mixed Mg, Al-oxides obtained by thermal decomposition of hydrotalcite

Abstract A hydrotalcite with a Mg:Al ratio of 2.5:1 has been synthesized and characterized. The solids obtained upon calcination of this material at 770 and 1023 K have been also characterized, and have been found to be a mixture of MgAl 2 O 4 and MgO. Surface acidity and basicity of the solid calcined at 1023 K have been assessed by FTIR monitoring of pyridine and formic acid adsorption. It has been found that the surface is not acid, although a residual acidity, larger than that in pure MgO, exists. Adsorption of formic acid takes place dissociatively on surface, isolated hydroxyl groups, contrary to previous results with MgO, where dissociative adsorption took place through interaction with exposed oxide ions.

Structural and surface characterization of the polycrystalline system CrxOy · TiO2 employed for photoreduction of dinitrogen and photodegradation of phenol

The polycrystalline system CrxOy-TiO2, used as a catalyst for photoreactions, was studied by X-ray diffractometric method, visible-ultraviolet diffuse reflectance and infrared spectroscopic methods, surface area determination, and porosimetry to characterize its structural and surface features. Two series of catalysts were prepared by two different methods, namely by coprecipitation and by impregnation. The first series was tested as photocatalysts for the dinitrogen photoreduction in a gas-solid regime and for the phenol photodegradation in a liquid-solid regime. The results indicate that the interaction of chromium ions with OH groups modifies the surface properties of the supports and consequently influences the photocatalytic activity. The addition of Cr ions was found to accelerate the photoreduction reaction, while it is detrimental to the photodegradation of phenol.

ADSORPTION AND DESORPTION OF N-METHYL 8-HYDROXY QUINOLINE METHYL SULFATE ON SMECTITE AND THE POTENTIAL USE OF THE CLAY-ORGANIC PRODUCT AS AN ULTRAVIOLET RADIATION COLLECTOR

The interaction between N-methyl 8-hydroxy quinoline methyl sulfate, a drug that absorbs erymathogenic near-ultraviolet radiation, and smectite was studied by X-ray powder diffraction (XRD) and adsorption and desorption techniques. From the adsorption studies, (1) the amount of the drug adsorbed by Na-smectite increased with the pH of the solution to pH 6.5 and then decreased as the pH was further increased; (2) the maximum amount adsorbed at pH 6.5 was 102 meq/100 g of clay; and (3) the maximum amount of drug adsorbed, according to the adsorption isotherms at pH 4, was close to the cation-exchange capacity of the smectite (80 meq/100 g). The XRD studies showed that the drug molecules were adsorbed in the interlayer space of smectite and that cation exchange was the chief mechanism responsible for these interactions. The results of the adsorption-desorption cycles of the drug by smectite showed that this clay is a good support for this compound. In addition, an alternative method was developed to obtain the intercalation compound to avoid the standard method of exchange by impregnation. The method consisted of grinding a mixture of the drug with the clay. The characteristics of the complex thus formed were similar to those of the complex formed by exchange at pH 4 to 7.To gain insight into the pharmacological properties of the intercalation compound studied, its capacity for absorption of visible and near-ultraviolet light was investigated. The diffuse reflectance spectrum of the complex showed intense absorption bands, absent or weak in the spectra of the pure drug or the untreated clay, at 250, 290, and ~390 nm.ResumenSe ha estudiado mediante difracción de rayos X (DRX) y técnicas de adsorción-desorción la interacción entre el metil-sulfato de N-metil 8-hidroxiquinolina, una droga que absorbe las radiaciones erimatógenas de la zona ultravioleta próxima, con la esmectita. A partir de los estudios de adsorción se ha encontrado que: (1) la cantidad de droga adsorbida por la esmectita sódica aumenta con el pH hasta 6.5 y luego disminuye; (2) la máxima cantidad adsorbida a pH 6.5 fue de 102 meq/100 g de arcilla; y (3) la cantidad máxima adsorbida, según los datos de la isoterma medida a pH 4, es similar a la capacidad de cambio de la esmectita (80 meq/100 g). Los estudios de DRX señalan que las moléculas de droga se adsorben en el espacio interlaminar de la esmectita y que el mecanismo principal de la interacción esmectita-droga es el cambio catiónico. Los resultados de los estudios de ciclos de adsorción-desorción señalan que esta arcilla es un buen soporte para este compuesto. Además, se ha desarrollado un método alternativo para obtener compuestos de intercalación que evitan el método convencional de intercambio por impregnación. El método consiste en la molienda de una mezcla de la droga y de la arcilla. Las características del complejo así formado son similares a las del complejo formado por intercambio a pH entre 4 y 7.Con objeto de profundizar en el conocimiento de las propiedades farmacológicas del compuesto de intercalación estudiado, se ha ivestigado su capacidad de absorción de luz en la zona visible y ultravioleta próxima. El espectro de reflectancia difusa del complejo pretensa intensas bandas de absorción, ausentes o débiles en los espectros de la droga pura o de la arcilla, sola, a 250, 290, y ~390 nm.

An FT-IR study of the adsorption of pyridine, formic acid and acetic acid on magnesia and molybdena-magnesia

Abstract The adsorption of pyridine, formic acid, and acetic acid on MgO, MoO3 and MoO3/MgO (Mo:Mg=1:15) samples calcined at 773 K (where no extensive reaction between the two oxides seems to take place) or 1100 K (where the MgMoO4 species is formed) has been monitored by FT-IR spectroscopy. The adsorption of pyridine indicates the formation of Lewis sites on MgO upon incorporation of molybdena. However, this change in the surface acidity does not modify the adsorption of the two carboxylic acids, which takes place dissociatively, probably because the formation of surface MgMoO4 still leaves exposed Mg2+, where adsorption of the carboxylate ions takes place.