Absolute emission quantum yield determination of self-assembled mesoporous titania films grafted with a luminescent zinc complex

A luminescent zinc complex was successfully incorporated to mesostructured porous titania films through a grafting process. The resulting films show an intense blue-emission increasing with functionalization time. The emission quantum yield of these newly synthesized films was quantitatively and accurately determined by measurements carried by an integrating sphere.     

Amphiphilic poly(Ala)-b-poly(Sar) microspheres loaded with hydrophobic drug

Amphiphilic block polypeptides, (Ala)m(Sar)n, were synthesized. Transmission electron microscopy showed that three kinds of block polypeptides, (Ala)42(Sar)21, (Ala)34(Sar)22, and (Ala)34(Sar)27, formed spherical aggregates in water. Dynamic light scattering measurement revealed that the average diameters of (Ala)42(Sar)21 and (Ala)34(Sar)22 aggregates were in the range of 80-90 nm, whilst that of (Ala)34(Sar)27 was about 30 nm. The polypeptides in aqueous solution took a beta-sheet structure, while they took an alpha-helical conformation in trifluoroethanol. These polypeptide aggregates took up 8-anilinonaphthalene-1-sulfonate (ANS), and the capacity of the aggregates for ANS decreased in the order of (Ala)42(Sar)21 > (Ala)34(Sar)22 > (Ala)34(Sar)27. Sumithion, which is a commercial agricultural insecticide, was also taken up by the polypeptide aggregates. When increasing amounts of Sumithion were introduced, (Ala)42(Sar)21 aggregates kept their shape, but (Ala)34(Sar)27 aggregate increased in size. These different behaviors of the polypeptide aggregates were discussed in terms of different structure of aggregates.     

pH-responsive release from polypeptide microcapsules

Microcapsules were prepared from [Glu(OMe)]_m(Sar)_n (m = 21, n = 19) and [Lys(Z)]_m(Sar)_n (m = 27, n = 15), and were chemically modified to obtain a pH-responsive releasing membranes. One membrane was prepared by partially deprotecting the ester groups of [Glu(OMe)]_m(Sar)_n. The other membrane was prepared by connecting of poly(Glu) to side chain amino groups that were generated by a partial deprotection of [Lys(Z)]_m (Sar)_n. Consequently, two types of polypeptidic microcapsules were prepared; Glu residues in the main chain, and Glu residues in the graft chains on the positively charged main chain. Both microcapsules showed pH-responsive release of FITC-dextran encapsulated in the microcapsules. The release rate became slower in the medium at pH 3.0 than pH 7.5. Optical microscope observation revealed that partially deblocked [Glu(OMe)]_m(Sar)_n microcapsules swelled more at pH 7.5 than at pH 3.0; hence, enhanced permeation through the polypeptide membrane at pH 7.5. However, the shape of poly(Glu)-grafted [Lys(Z)]_m(Sar)_n microcapsules changed a little by changing pH of the medium. It is suggested that ion-pairing between carboxylate groups of poly(Glu) and ammonium groups of Lys acts as crosslinking to give the shape stability. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 453–458, 1997     

Mesostructured self-assembled silica films with reversible thermo-photochromic properties

A spiropyran molecule has been introduced via one-pot synthesis into mesostructured silica films, which have been obtained through a micelle templating self-assembling process. The mesostructure has been characterized by transmission electron microscopy and small-angle X-ray scattering performed with synchrotron light. The final material exhibited a p6mm 2d-hexagonal organization and the mesostructure has not been affected by the introduction of spiropyrans in the precursor solution. A comparative characterization of the optical properties of the spiropyrans dissolved in different solvents and after incorporation in the mesostructured films has been done by UV–Vis absorption spectroscopy, fluorescence spectroscopy and ellipsometric spectroscopy. The spiropyran-doped films appeared transparent before external stimuli had applied, a colour change to yellow (thermally induced) or to red (light induced) has been observed. Both the colour changes have been observed to be reversible under room temperature or visible light exposure; the colour transitions have been attributed to different equilibria among the various forms of merocyanine of spiropyrans.     

Thermoresponsive release from poly(Glu(OMe))-block-poly(Sar) microcapsules with surface-grafting of poly(N-isopropylacrylamide)

We have designed a synthetic cornea that has a transparent hydrogel optic and a porous skirt. The device has been implanted in rabbit corneas. We have shown that keratocytes migrate into the device and deposit a complex extracellular matrix. The immediate response is detected in the surrounding stroma, and the secondary response is seen after cells have deposited a matrix in the disc. After implantation, a decrease in keratan sulfate accompanied by an increase in dermatan sulfate was detected in the surrounding tissue compared to the unwounded corneal stroma. The glycosaminoglycans in the disc resemble that of an injured stroma. The appearance of heparan sulfate and growth factors, bFGF and TGFbeta, was not detected until 6 weeks after implantation. The growth factors were detected at the interface between the device and the tissue and become more diffuse over time. Methods of controlled release in vivo were used to enhance the rate of fibroplasia and wound repair. While these were successful in the cornea itself, when combined with the synthetic cornea the response was magnified and the initial attempts yielded neovascularization and edema. Currently, efforts are being directed at controlling the release within the porous haptic so that fibroplasia is enhanced while minimizing an inflammatory response.     

An alternative sol-gel route for the preparation of thin films in CeO2-TiO2 binary system

Thin films of titania-ceria have been prepared via sol-gel processing by employing titanium and cerium chloride compounds in highly acidic conditions for the precursor sol. This sol-gel route allows obtaining titania-ceria and cerium titanate films, CeTi₂O₆, after thermal treatment in air. The films exhibit a high optical transparency which is modulated by controlling the composition and the thermal treatment. The materials have been characterized by X-ray diffraction, UV-visible spectroscopy, ellipsometric spectroscopy and atomic force microscopy. The titania-ceria films show, as a function of the composition, the formation of different phases after thermal treatment in air at 800 °C. In particular, with the composition Ce25-Ti75 we have obtained a pure cerium titanate phase, CeTi₂O₆, which can be formed only in a very strict range of compositions.     

Liquid-Phase Preparation and Characterization of Zinc Oxide Nanoparticles

Zinc oxide (ZnO) nanoparticles have been prepared by a wet chemical method, from zinc acetate and LiOH ethanol-based solutions. The resulted nanoparticles were dispersed in a solvent. The effect of solvent (ethanol or butanol) and surfactant (polyethylene glycol-PEG 200) on the average size and size distribution of the nanoparticles was investigated by light scattering measurements. Smaller size was observed for ZnO nanoparticles dispersed in butanol and PEG 200. The statistical parameters of the Gaussian size distribution curves were calculated. ZnO nanoparticles have been prepared to be used as seeds on a substrate for the growth of ZnO nanowires. The morphology, surface roughness, crystalline structure, and orientation of the nanoparticles deposed on silicon substrate were characterized by atomic force microscopy and x-ray diffraction, respectively.     

Formation of Monoclinic Hafnium Titanate Thin Films Via the Sol–Gel Method

Hafnium titanate films are generating increasing interest because of their potential application as high- k dielectrics materials for the semiconductor industry. We have investigated sol–gel processing as an alternative route to obtain hafnium titanate thin films. Hafnia-titania films of different compositions have been synthesized using HfCl₄ and TiCl₄ as precursors. The HfO₂–TiO₂ system composition with 50 mol% of TiO₂ and 50 mol% of HfO₂ has allowed the formation of a hafnium titanate film after annealing at 1000°C. The films exhibited a homogeneous nanocrystalline structure and a monoclinic hafnium titanate phase that has never been obtained before in thin films. The films resulted in the formation of homogeneously distributed nanocrystals with an average size of 50 nm. Different compositions, with higher or lower hafnia contents, produced anatase crystalline films after annealing at 1000°C.