Alginate Microspheres Loaded with Animal Cells and Coated by a Siliceous Layer

Animal cells or cell aggregates are suspended in Na-alginate solution and extruded under a flow of air saturated with silicon alcoxides. The immediate formation of a sol-gel siliceous membrane on the microdrop surface allows the reaction with Ca²⁺⁺, leading to solid Ca-alginate, and yields homogeneous, stable microcapsules 200 m in diameter. The cell function of the encapsulated biomass were tested in specific protein production, which is not affected by the siliceous membrane protection of Ca-alginate microcapsules. This fact, and the observed increase in mechanical stability and chemical durability, indicate that valuable features of silica encapsulation are added to those proper to Ca-alginate.     

Guest Editorial

Journal of Sol-Gel Science and Technology -     

Rh Inclusion in Sol-Gel SiO2. Effects of Rh Precursors on Metal Dispersion and SiO2-Rh Thermal Behavior

RhCl₃·nH₂O and [RhCl(C₂H₄)₂]₂ are used as precursors for the preparation of 1%Rh in sol-gel derived SiO₂. The gelling process of Si(OEt)₄ is carried out in the absence of solvent and under strong acid catalysis. The thermal behavior of Rh precursors, of SiO₂ gel and Rh-SiO₂ composites is independently studied by analysing organic species released at definite temperature intervals and concomitantly collecting infrared, XPS, TEM, XRD and porosity data. Results indicate that nanometric Rh particles may be obtained from [RhCl(C₂H₄)₂]₂, their dispersion being homogeneous, dense and stable up to 250°C, whereas RhCl₃·nH₂O affords less metallic dispersion with other crystalline Rh-species; in both cases, well-shaped Rh metal crystallites are obtained at 650°C. The different synthetic approaches used for the preparation of RhCl₃- and [RhCl(C₂H₄)₂]₂-derived samples, are invoked to account for the features of Rh dispersion obtained by mild temperature treatment. Moreover, the particular procedures for sol-gel SiO₂ synthesis are related to the high-temperature maintenance of great porosity and elevated specific surface area.     

Physical and chemical evolutions occurring in glass formation from alkoxides of silicon,aluminum and sodium

A multicomponent glass was obtained on using the new method of glass preparation from gel. The reactions occurring in the ethanolic solution of the parent alkoxides give condensation of the monomers so that hydrolysis of the remaining alkoxides groups followed by polycondensation appears to proceed on preformed oligomers. DTA, TGA, density and chemical durability measurements indicate that the transition from gel to the final glass is a continuous process. During the gel to glass conversion, scanning electron microscopy results show considerable compacting of the material.     

Immobilization of plant cells in hybrid sol-gel materials

Cells of three different plant species were immobilized on a glass fiber fabric by sol-gel deposition. The process involved the following steps: (1) reinforcement of glass-fiber supports by coating with a gelling solution of hybrid-SiO₂ precursors, (2) entrapment of cells by stuffing the voids of the support with a suspension cell culture, (3) achievement of a definite immobilization by a primary treatment with SiO₂-sol, followed by gas phase reaction of tetraethoxysilane and diethoxymethylsilane with OH groups of cell wall and of surface silica. Immobilized cells maintained their viability as tested by the positive reaction to TTC and by the development of calli from stretched samples. The samples did not release cells in solution over a time period of four months, at least. The biosynthetic capability of one of immobilized species, Coronilla vaginalis, was studied by periodically monitoring the production of umbelliferone and marmesin which constituted the major secondary metabolites produced by in vitro cultured cells of this species. The results were evaluated in order to determine the versatility of the method and its potential for exploitation in continuous industrial-scale production of rare and fine chemicals.Abbreviations 2,4-D = 2,4-dichlorophenoxyacetic acid - K = kinetin - IAA = indol-3-acetic acid - NAA = naphthalenacetic acid - B5 = Gamborg's medium - MS = Murashige and Skoog medium - TEOS = tetraethoxysilane - DEMS = diethoxymethylsilane - DEDMS = diethoxydimethylsilane - TTC = tetrazolium salt     

Production of Valuable Drugs from Plant Cells Immobilized by Hybrid Sol-Gel SiO2

Catharantus roseus cells are supported on a polyester fiber mat and encapsulated by a porous layer of SiO2 modified by Si–CH3 and Si–H bonds. This layer is obtained by reaction of Si-alkoxides in the gas phase with H2O adsorbed on the cell surface or with exposed –OH groups of cellulosic cell membrane. Viability and alkaloid production of cells are maintained after encapsulation. An experimental reactor allows study of secondary metabolite productivity, which is increased by two orders of magnitude with respect to that of free cells.Sucrose consumption kinetics are also studied and related to the viability of encapsulated cells.     

Optical Study of The Matrix Effect on the ESIPT Mechanism of 3-HF Doped Sol-Gel Glass

In this work we report our preliminary results on the synthesis and characterization of the optical properties of 3-hydroxyflavone (3-HF) doped sol-gel derived glass, to be applied as a wavelength shifting medium in GaAs based near UV-VIS detectors in order to extend the device response down to 350 nm. As already reported by several authors, the intramolecular excited-state proton transfer process (ESIPT) in the 3-HF molecule is strongly affected by the chemical environment. For this reason the evolution of the emission features of the synthesized glasses was investigated by changing the chemical nature of precursor alkoxides used in the sol-gel process. The influence of chemical surroundings on the ESIPT process was studied by analysing the samples with fluorescence spectroscopy. FT-IR spectroscopy was performed in order to study the chemical interactions between the host matrix and the encapsulated dye molecule. The main result of this work is that the Stokes-shifted emission from the 3-HF tautomeric form is enhanced at increasing trifunctional alkoxide amount and at decreasing polarity of the non-hydrolizable groups.     

Formation of silver nanoclusters in transparent polyimides by Ag-K ion-exchange process

Silver nanoclusters embedded in two transparent fluorinated polyimides, 4,4'-hexafluoroisopropylidene diphthalic anhydride – 2,3,5,6-tetramethyl paraphenylene diamine (6FDA-DAD) and 3,3',4,4' – biphenyltetracarboxylic acid dianhydride – 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (BPDA-3F), have been produced by surface modification with KOH aqueous solution followed by K-assisted Ag doping and thermal reduction in hydrogen atmosphere. The reaction rate of the nucleophilic hydrolysis in KOH, studied by Fourier transform infrared spectroscopy (FT-IR) and Rutherford backscattering spectrometry (RBS), depends on the polyimide chemical structure. After ion-exchange in AgNO₃ solution and subsequent annealing, the polyimide structure recovery was monitored by FT-IR whereas the characteristic surface plasmon absorption band of silver nanoparticles was evidenced by optical absorption measurements. The structure of silver nanoclusters as related to size and size distribution in the different polyimide matrices was thoroughly investigated by Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The collected data evidenced a uniform distribution of Ag clusters of nanometric size after thermal treatment at 300 ^○C in both polyimides. For the same ion-exchange treatment parameters and annealing temperature, XRD analyses evidenced the presence of crystallites with similar sizes.     

Hybrid Gels as Host Matrices of Perfumed Essences

The variety of SiO₂-gel structures allows the use of sol-gel derived materials as host matrices for prolonged release of chemicals. In this work, the release of perfumed essences is studied in the case of hybrid SiO₂ materials obtained from alkyl-modified silicon alkoxides. Thermogravimetric analysis in isothermal conditions at various temperatures provide data on the kinetic release process. The effects of physical parameters (porosity reduction, vapour pressure) and chemical interactions (organic molecules with matrix) are discussed for the interpretation of the results.