R. Litrán

Sonogels and derived materials

Nowadays the sol–gel process is used by an increasing number of researchers for the preparation of various products, including bulk materials, films, membranes or fibers. The application of ultrasound (sonocatalysis) to the precursors gives rise to materials with new properties, known as sonogels. The absence of additional solvent and, mainly, the effects of ultrasonic cavitation create a unique environment for sol–gel reactions leading to particular features in the resulting gels: high density, fine texture, homogeneous structure etc. These properties determine the evolution of sonogels on further processing and the final material structure. In this sense, the full exploitation of sonocatalysis requires a thorough understanding of the processes involved and their sensitivity to reaction parameters. For this purpose, we have used diverse techniques to investigate the microstructural evolution during different steps in the sonogel process. The results of these studies are reported here. Finally, we present an overview of some applications for which the mechanical, textural and optical characteristics of sonogels are quite useful. Copyright

Size and surface effects in the magnetic properties of maghemite and magnetite coated nanoparticles

An increasing number of promising applications for future technology is arising from size constraints in nanoparticles (NPs) and from the chemical manipulation of their surfaces. In this work, we analyse the finite-size and surface effects on polyacrylic acid-coated Fe3O4 NPs and oleic acid-coated γ-Fe2O3 NPs by studying their magnetization curves at different temperatures. The measured thermal dependence of the saturation magnetization is no longer explained by the typical T3/2 Bloch law, yielding higher values than those expected for its exponent. When incorporated in polymeric matrixes to form magnetic transparent nanocomposites, the oleic acid-coated γ-Fe2O3 NPs also deviate from Bloch’s law, but following the opposite trend observed in free coated NPs.

Trapping Copper Phthalocyanine in a Silica Sono-Xerogel

A copper phthalocyanine (CuPc) has been encapsulated in silica. The trapping effects were studied comparing the UV-Vis absorption spectra of some CuPc solutions and composites prepared under different conditions. The trapped organic molecules’ stability was monitored during the gelation and drying processes. Leachability test have been carried out with the aim of checking the trapping efficiency. Hydrolysis water of pH=2 and a molar ratioRw=6 mol acid H2O/mol TMOS leads to a higher CuPc stacking angle homogeneity. The increase of Pc induces a narrower mesopore distribution and helps the stabilization of the composite.

Preparation and Characterization of Fluorescent CdS Quantum Dots used for the Direct Detection of GST Fusion Proteins

Advances in the life sciences are now closely linked to the availability of new experimental tools that allow for the manipulation of biomolecules and the study of biological processes at the molecular level. In this context, we have optimized a synthesis process to obtain glutathione-capped fluorescent CdS nanoparticles to specifically detect Glutathione S-Transferase (GST) -tagged proteins. Using our method, based on five different heating steps, brightly fluorescent and biocompatible CdS quantum dots of different sizes can be obtained. QD optical behaviour has been evaluated studying both absorbance and fluorescence. For all the samples, the excitonic absorption onset clearly shows a blue shift at 512nm in comparison with that of bulk CdS, due to the quantum confinement effect. At increased average sizes of the nanocrystal, the emission fluorescent band shows a red shift, from 440nm to 540nm. Among different QD solutions, we demonstrate an expansion of the emission range up to �˝ 100 nm, thus improving their features as biomarkers. Moreover we show that optimized glutathione- capped quantum dots can directly bind GST blotted onto polyvinylidene difluoride (PVDF) membranes, and thus are suitable for the direct detection of GST fusion proteins.

INFLUENCE OF PROCESSING INDUCED TEXTURAL EFFECT ON AGGREGATION LEVEL IN CUPC–SIO2 SONOGEL COMPOSITES

Abstract Aggregation effects in metallophthalocyanine/SiO 2 composites play an important role in the optical properties of these materials. With the aim to decrease phthalocyanine self-association induced in aqueous solution into the network pores, alternative processing methods for trapping the organic in the matrices have been carried out. Monolithic xerogels have been obtained by three chemically different processing routes, preserving their homogeneity and transparency, even under extremely acid conditions. Micro, meso and non-porous silica xerogels have been obtained, depending on processing method. However, the organic doping highly modifies the textural features of the final composite, increasing the pore volume of composites even in more than 50%. Phthalocyanine aggregation degree has been tested by UV–VIS absorption spectroscopy and correlated to the textural parameters and pore size distribution of the composites. The effect of the textural features on molecular self-association level is evaluated.

Confinement of CdS Nanocrystals in a Sonogel Matrix

CdS/silica xerogel composites have been prepared using a sonocatalytic method. The confinement effects of CdS semiconductor nanocrystallites have been analyzed through UV-VIS absorption and Raman scattering. The blue shift of the absorption band and the shape of the Low Frequency Inelastic Raman Scattering (LOFIRS) spectra make it possible to evaluate the size of nanocrystallites, which are contrasted with previous results obtained through other techniques. Moreover, in the 200–700 cm−1 region of Raman shift, resonant effects are discussed, through the longitudinal optical mode lines.

Photoluminescence from CdS Quantum Dots in Silica Gel

CdS semiconductor nanocrystals were grown as quantum dots (QDs) inside a silica matrix obtained by the sol-gelmethod and assisted in the mother liquid by high powerultrasounds. Small-angle neutron scattering (SANS) accountsfor a 3.6 nm crystal size homogeneously distributed. Optical excitation from the third harmonic of a Nd:YAG ns laser wasfocused on the sample to study the photoluminescence (PL) atroom temperature. The PL spectrum shows radiative processfrom intrinsic transitions and a broad band corresponding tothe traps. Variable stripe length (VSL) method was used to measure the optical gain spectra by the growth of theamplified luminescence. A broad optical gain spectrumproduced by the biexciton-exciton transitions revealing thestimulated emission from the CdS QDs. It is also observed ared-shift of the PL emission crystal size-dependent.

CdS semiconductor nanoparticles in silica sonogel matrices: Code: F12

SiO2 gels obtained by sonocatalytic method combined with DCCA were used as host-matrices for extremely fine dispersions of CdS semiconductor particles. Small crystallites were produced “in situ” by H2S gas diffusion method. The particles were characterized by TEM and HRTEM, EXAFS, UV-Vis and Raman spectroscopies. The size of crystallites ranged from 5 to 10 nm. The optical transmission spectra showed the characteristic blue shift as a function of the particles size, as predicted by the theory. The optical and mechanical qualities of the samples were substantially improved by an infiltration method using a sono-sol which sealed the superficial pores thus ensuring greater longevity and the possibility of obtaining transparent gels by polishing.

Immune modulation by the hepatitis C virus core protein

Hepatitis C virus (HCV) infection is currently the most important cause of chronic viral hepatitis in the world and one of the most frequent indications for liver transplantation. HCV uses different strategies to evade the innate and adaptive immune response, and this evasion plays a key role in determining viral persistence. Several HCV viral proteins have been described as immune modulators. In this review, we will focus on the effect of HCV nucleocapsid core protein in the function of immune cells and its correlation with the findings observed in HCV chronically infected patients. Effects on immune cell function related to both extracellular and intracellular HCV core localization will be considered. This review provides an updated perspective on the mechanisms involved in HCV evasion related to one single HCV protein, which could become a key tool in the development of new antiviral strategies able to control and/or eradicate HCV infection.

Microstructural and Mechanical Properties of Sono-Ormosils

Monolithic pieces and films of ormosils were obtained from ultrasound-assisted polycondensation of tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS). These sono-Ormosils were studied by means of high resolution Brillouin spectroscopy and their textures analyzed from adsorption isotherms. Evidence is given for the occurrence of organic and inorganic micro-phase separation in samples with high polymer concentrations. Nitrogen isotherms show that the texture of the samples is highly dependent on the composition.