Daniela Berger

Box-Behnken experimental design for chromium(VI) ions removal by bacterial cellulose-magnetite composites

In this study bacterial cellulose-magnetite composites were synthesised for the removal of chromium(VI) from aqueous solutions. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the bacterial cellulose-magnetite composites and to reveal the uniform dispersion of nanomagnetite in the BC matrix. Magnetic properties were also measured to confirm the magnetite immobilization on bacterial cellulose membrane. The effects of initial Cr(VI) concentration, solution pH and solid/liquid ratio upon chromium removal were examined using the statistical Box-Behnken Design. Because of the possibility of magnetite dissolution during chromium(VI) adsorption, the degree of iron leaching was also analysed in the same conditions as Cr(VI) adsorption. From the factors affecting chromium(VI) adsorption the most important was solution pH. The highest Cr(VI) removal efficiency was observed at pH 4, accompanied by the lowest iron leaching in the solution. The adsorption experiments also indicated that the adsorption process of chromium(VI) is well described by Freundlich adsorption model. Our results proved that the BC-magnetite composites could be used for an efficient removal of chromium(VI) from diluted solutions with a minimum magnetite dissolution during operation.

Azobenzene functionalized mesoporous AlMCM-41-type support for drug release applications

AbstractA light-responsive material, aminoazobenzene functionalized AlMCM-41, was synthesized and characterized in order to be used as carrier for drug delivery devices. The light-induced hydrophobic-hydrophilic switching effect of azobenzene functionalized aluminosilicate was exploited in the release of irinotecan, a cytostatic drug. To obtain the functionalized mesoporous support, an azobenzene-silane precursor was synthesized by coupling 4-(4′-aminophenylazo) benzoic acid with 3-aminopropyl triethoxysilane and further grafted on AlMCM-41. The azobenzene functionalized mesoporous aluminosilicate exhibited no significant toxicity towards murine fibroblast healthy cells and a reduced toxicity towards murine melanocyte cells. The hybrid materials obtained by loading irinotecan on AlMCM-41 (wt. 35.4%) and aminoazobenzene modified AlMCM-41 (wt. 22%), respectively were characterized by FTIR, small and wide angle XRD, N2 adsorption-desorption isotherms and DSC analyses. A two-fold increase in the drug release rate from azobenzene functionalized aluminosilicate in phosphate buffer solution under UV irradiation was noticed, as compared with dark conditions. Moreover, the azobenzene functionalization of AlMCM-41 significantly increased the irinotecan delivery rate and total cumulative release in comparison with the pristine AlMCM-41 in similar conditions.

Mesostructured silica and aluminosilicate carriers for oxytetracycline delivery systems

Oxytetracycline delivery systems containing various MCM-type silica and aluminosilicate with different antibiotic content were developed in order to establish the influence of the support structural and textural properties and aluminum content on the drug release profile. The antibiotic molecules were loaded into the support mesochannels by incipient wetness impregnation method using a drug concentrated aqueous solution. The carriers and drug-loaded materials were investigated by small- and wide-angle XRD, FTIR spectroscopy, TEM and N2 adsorption-desorption isotherms. Faster release kinetics of oxytetracycline from uncalcined silica and aluminosilicate supports was observed, whereas higher drug content led to lower delivery rate. The presence of aluminum into the silica network also slowed down the release rate. The antimicrobial assays performed on Staphylococcus aureus clinical isolates showed that the oxytetracycline-loaded materials containing MCM-41-type mesoporous silica or aluminosilicate carriers inhibited the bacterial development.

Mesostructured silica matrix for irinotecan delivery systems

Three mesostructured silica-type carriers, MCM-41 and MCM-41 functionalized by a postsynthesis grafting procedure with hydrophilic aminopropyl groups (MCM-APTES) and hydrophobic vinyl moieties (MCM-VTES), respectively, were investigated in order to elaborate drug delivery systems (DDS) for irinotecan molecules. All studied drug delivery systems exhibited higher cytotoxicity on murine embrionary fibroblastic (MEF) cells than free irinotecan at the same content of the cytostatic agent, whereas no toxicity was observed for the three unloaded carriers. The cytotoxic effect of irinotecan loaded on MCM-41-type carriers continued to increase even 24 h after ceasing the cell exposure to the drug and remained significantly higher than that of free irinotecan. The cellular uptake of silica-type hybrids was investigated by labelling MCM-APTES with Rhodamine B. In the case of the studied DDS, an endocytotic mechanism was found to be involved in the cell uptake process, and it was used to explain the cytotoxicity differences between free irinotecan and drug loaded on MCM-41-type supports.

Tailoring the dissolution rate enhancement of aminoglutethimide by functionalization of MCM-41 silica: a hydrogen bonding propensity approach

The adsorption and in vitro release properties of the poorly soluble cytostatic agent DL-aminoglutethimide (AGT) on pristine MCM-41, 3-aminopropyl and a novel N-propyl-2-sulfanylacetamide functionalized MCM-41 material were studied. The mesostructured supports and hybrid samples were characterized by small- and wide-angle X-ray diffraction, FT-IR spectroscopy, thermogravimetric and calorimetric analyses, SEM-EDX and N2 adsorption–desorption isotherms. The drug uptake was found to be strongly influenced by its ionization state and solution pH. Drug release experiments show a spectacular increase in the dissolution rate of the therapeutic agent for all hybrid samples, indicating that aminoglutethimide encapsulation into the mesopores of MCM-41-type supports is a viable strategy for dissolution rate enhancement. Using a knowledge-based logit hydrogen bonding propensity model to assess the relative strengths of drug–support supramolecular interactions, we have proposed that a Si–OH⋯Cl− AGT+ mechanism is responsible for the increased drug adsorption in acid media and release rate enhancement at physiological pH.

Correlation of the intracellular reactive oxygen species levels with textural properties of functionalized mesostructured silica

Mesostructured silica is frequently used in biomedical applications, being considered nontoxic and biocompatible material, suitable for the development of drug delivery systems (DDS). Four functionalized MCM-41 silica materials with hydrophobic (methyl and vinyl) and hydrophilic (3-aminopropyl and 3-mercaptopropyl) groups were obtained by post-synthesis functionalization and characterized by small-angle X-ray diffraction, infrared spectroscopy, thermal analysis, and nitrogen adsorption-desorption isotherms. The main structural and textural parameters of the obtained silica were determined. The effect of the functionalized silica on fibroblast (NIH3T3) and melanocyte cells (B16F10) was studied with respect to the proliferation rate and the levels of reactive oxygen species (ROS). It was found that the textural properties of all samples influenced the levels of intracellular ROS and consequently, the proliferation rate. Both, healthy and malignant cells exhibited linear dependence of ROS levels with the specific surface area values, but with different response. The contribution of the methyl functionalized silica to the ROS level is apart to the general trend.

Influence of different templates on the morphology of mesoporous aluminas

AbstractMesoporous alumina has many environmental applications as catalysts support and adsorption or separation material. We studied the synthesis conditions for the mesoporous alumina formation from aluminum isopropoxide in the presence of anionic (lauric and stearic acid), cationic (cetyltrimethylammonium bromide, CTAB) and non-ionic (triblock poly(ethylene oxide)-poly(propylene oxide)-polyethyleneoxide, P123) templates. The X-ray diffraction data show that the alumina mesophases obtained at 550°C in the presence of fatty acids or P123 have amorphous walls, whereas the samples prepared at 500°C by using CTAB, in alkaline medium are crystalline with a γ-alumina structure. The solvothermal treatment caused the alumina mesophase with crystalline walls to be obtained at 550°C. The samples were investigated by nitrogen adsorption-desorption isotherms and scanning electron microscopy. The obtained alumina mesophases have specific surface areas in the range of 300–450 m2 g−1, narrow pore size distribution, and different morphology depending on the template used in the synthesis.

Controlling drug release from mesoporous silica through an amorphous, nanoconfined 1-tetradecanol layer

Graphical abstract Figure. No caption available. &NA; Mesoporous silica materials are promising nano‐carriers for drug delivery systems. Even though there are many strategies for controlling the drug release kinetics, these must be adapted through trial and error on a case‐by‐case basis. Here we explore the possibility of tailoring the release kinetics of hydrophilic, water soluble therapeutic agents from mesoporous silica through addition of a hydrophobic excipient, 1‐tetradecanol. In vitro drug release experiments performed at 37 °C, in phosphate buffer solution (pH 7.4) show that the addition of tetradecanol yields slower drug release kinetics, which was correlated with the presence of a liquid fatty alcohol interfacial layer. The layer mass is 11–23 wt.% of the metoprolol‐loaded silica sample, and it causes up to 1.6 times decrease of initial release rate with respect to materials without the fatty alcohol. This effect does not depend of carrier pore arrangement, being noticed for both hexagonal MCM‐41 and cubic KIT‐5 mesoporous silica. The toxicity of tetradecanol‐containing materials was evaluated by formazan‐based viability assay on Opossum kidney epithelial cell line, and no significant toxicity was observed.

Considerations about the Dependence of PEGylated ZnS Nanoparticles Properties on the Synthesis Method

Abstract We studied the dependence between properties and synthesis method for PEGylated ZnS nanoparticles. Thus, we proposed the PEGylation of ZnS nanopowder, in non-aqueous medium, by a facile one-pot synthesis in very mild conditions, as an alternative for the chemical precipitation of PEGylated ZnS in an aqueous solution, and we compared the properties of zinc sulfide obtained by both methods. The structure and morphology of PEGylated ZnS nanopowders were investigated by X-ray diffraction and transmission electron microscopy, and the FTIR spectra confirmed the PEGylation of ZnS nanoparticles. The values for band gap energy are in good accordance with the quantum confinement effect for nanocrystals. The mean dimension of particles was calculated, on the basis of UV–Vis spectra, by using the Brus equation and it is in good agreement with the crystallites size, determined from X-ray diffraction. The photocatalytic properties of synthesized nanopowders were tested in the degradation of Congo red azo dye, demonstrating a faster bleaching of dye in the presence of PEGylated ZnS prepared in non-aqueous medium. The photoluminescence properties are also dependent on the synthesis method and can be correlated with the surface modifications by PEG.

Low-Temperature synthesis and thermodynamic and electrical properties of barium titanate nanorods

Studies regarding the morphology dependence of the perovskite-type oxides functional materials properties are of recent interest. With this aim, nanorods (NRs) and nanocubes (NCs) of barium titanate (BaTiO3) have been successfully synthesized via a hydrothermal route at temperature as low as 408 K, employing barium acetate, titanium isopropoxide, and sodium hydroxide as reagents without any surfactant or template. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD), used for the morphology and structure analyses, showed that the NRs were formed by an oriented attachment of the NCs building-blocks with 20 nm average crystallites size. The thermodynamic properties represented by the relative partial molar free energies, enthalpies, and entropies of the oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressure of oxygen, indicated that NRs powders have lower oxygen vacancies concentration than the NCs. This NRs characteristic, together with higher tetragonallity of the structure, leads to the enhancement of the dielectric properties of BaTiO3 ceramics. The results presented in this work show indubitably the importance of the nanopowders morphology on the material properties.