Production of Enzymes by Plant Cells Immobilized by Sol-Gel Silica

Ajuga reptans cells are cultivated and used for production of invertase. These plant cells are immobilized by a sol-gel SiO₂ membrane, which is built up directly on the cell surface by exposure to a gaseous flow of silicon alcoxide precursors. The immobilization modifies the metabolic activity of cells, resulting in a 40-fold increase in invertase production with respect of free cells. Results concerning total release of proteins, cell growth and produced invertase activity are discussed, considering the absence of breeding, induced by SiO₂ immobilization, the prominent factor promoting the observed exceptional increase in invertase productivity.     

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.     

Biosorption of Heavy Metals by Sol-Gel Immobilized Bacillus sphaericus Cells, Spores and S-Layers

Different types of biocers were prepared by dispersing vegetative cells, spores and surface layer proteins (S-layers) of Bacillus sphaericus JG-A12 in aqueous silica nanosols, gelling or coating on glass, and drying. The enzymatic activity of embedded B. sphaericus cells depends noticeably on the water content of the biocer. The cells are destroyed by drying and shrinkage of the silica network whereas embedded spores retain their ability for germination. The biosorption of uranium and copper of these biocomposites was investigated. Biocers with cells possess the highest metal binding capacity compared to matrices with spores or S-layers. An additional increasement of the metal binding capacity is achieved by using penetration reagents like sorbitol. For renewed use biosorpted uranium and copper can be completely removed from the biocers by using aqueous citric acid. The use of spores as biocomponent offers new interesting possibilities for the preparation of storage-stable bioactive biocers.     

SiO2溶胶凝胶固定的扑尔敏电极

SiO2溶胶凝胶固定的扑尔敏电极;四苯硼-扑尔敏缔合物;扑尔敏药物电极     

Catalysis in Organic Solvents with Lipase Immobilized by Sol-Gel Technique

A series of immobilized lipases were obtained by sol-gel process, using silica prepolymers prepared from tetramethoxysilane, methyltrimethoxysilane, propyltrimethoxysilane and (3-aminopropyl)triethoxysilane. The activities of these biocatalysts were compared with the lipase adsorbed on poly(methylhydroxysiloxane) and encapsulated into a silicone rubber, lipase entrapped in nanoporous silica matrix and commercial sol-gel lipase. Model reactions were the esterification of stearic acid and Corey lactone bisalcohol (an intermediate of prostaglandin synthesis). The positive effect of hydrophobic-hydrophilic interface, created by the addition of organosilanes, on the activity of biocatalysts was partially reduced by decreasing specific surface of mesopores. Hydrophobic solvents increased the activity of the lipase entrapped in tetramethoxysilane–methyltrimethoxysilane prepolymer in the sequence acetone < toluene < benzene < decane < hexane. The activity of silicone rubber-encapsulated biocatalysts was proportional to polymer swelling in organic solvents (hexane > toluene > acetone).     

Electrochromism in Materials Prepared by the Sol-Gel Process

Electrochromism is defined as the persistent but reversible optical change (usually transmission) produced electrochemically. The preparation by the sol-gel process of thin films made of amorphous or crystalline nanoparticles of WO₃, V₂O₅, Nb₂O₅, TiO₂, CeO₂, Fe₂O₃ and mixed compounds such as WO₃−TiO₂, CeO₂−TiO₂, CeO₂−SnO₂, have opened remarkable new opportunities for obtaining electrochromic layers exhibiting large optical transmission variation in the UV, visible or infrared range and acceptable kinetics under H⁺ or Li⁺ insertion. In this paper we give an overview of what has been recently achieved in this field, with emphasis for cathodic electrochromic coatings of Nb₂O₅ and TiO₂ composition. Finally we stress the future developments in this fast growing field.     

Anti-Reflective Coatings for CRTs by Sol-Gel Process

Two types of anti-reflective coatings composed of nano-particles were developed for cathode ray tubes (CRTs). The anti-reflective and anti-static coating is composed of two layers. An outer SiO₂ layer is formed over a porous inner layer composed of titanium oxynitride (TiO _x N_y), antimony-doped tin oxide (ATO) and SiO₂. To control the reflection of the film, a porous structure is formed using a mixed sol composed of TiO _x N _y -ATO particles and hydrolyzed-polymerized tetraethoxy-silane (TEOS). The resulting double layered coating is shown to consist in a nanocomposite pseudo three-layer structure. The antireflective electromagnetic-wave-shielding coating is also composed of two layers. An outer SiO₂ layer is formed over an electric-conductive inner layer composed of silver colloids, TiO _x N _y nano particles. Silver colloids are used to obtain a film having low surface resistivity and TiO _x N _y nano-particles contained in the inner layer enhance the durability of the film. To reduce the plasma-resonance absorption caused by silver colloids, silver ions are added to the outer layer solution. The silver ions diffuse into the inner layer from the outer layer when the film is cured, touch to the surface of silver colloids, suppress the silver colloid growth and reduce the specific absorption of the film. These coatings are successfully applied to the panel glass for CRTs on an industrial scale.     

Anti-Reflective Coatings for CRTs by Sol-Gel Process

Anti-reflective and electromagnetic shielding double-layered coatings were developed for cathode ray tubes (CRTs) by wet chemical process. An outer SiO₂ layer is formed over a porous inner tin-doped indium oxide (ITO) particle layer. ITO particles used in the inner layer lower the sheet resistance below 10³ohm/sq. and an electromagnetic shielding property is attained. To improve the abrasion wear resistance of the film, the structure of the film and hydrolysis-polymerization condition of tetraethoxy-silane (TEOS) are estimated. An outer SiO₂ layer component penetrates into the inner layer and adheres to the glass surface. As the extent of hydrolysis of TEOS proceeds and the molecular weight of hydrolyzed TEOS becomes small, the abrasion wear resistance of the film enhances. The relation between the curing condition of the film and surface resistance of the film is investigated. The surface resistance of the film lowers by curing the film in reductive atmosphere. The transmittance of the film in the near-infrared region shows that the lowering of surface resistance of the film is caused by the increase of carrier concentration of ITO particles. The double layered coatings are successfully applied to the panel glass for CRTs on an industrial-scale.     

Sol-Gel Immobilized Glucose-Oxidase: Calorimetric Investigations of Enzyme Activities

Using the sol-gel process, the enzyme glucose-oxidase was immobilized in modified SiO2 layers. The tetraethoxysilane based sol was varied by veratrylaldehyde, aminopropyltriethoxysilane and an azomethine compound, which was synthesized from both molecules. Changes in reaction kinetics of the sol-gel process by addition of veratrylaldehyde were observed by 29Si NMR measurements. The fixation of this additive in the final gel was clarified by FTIR spectroscopy.The influence of inserted functional groups on the enzyme activity was determined by calorimetry. The Enzyme Thermistor is a fast and uncomplicated method to obtain comparative results of sol-gel immobilized enzyme activity. Differences in immobilization effects were found dependent on structure and concentration of additives.     

溶胶—凝胶法制备有机—无机纳米复合材料

溶胶－凝胶法以其温和的反应条件，尤其是低的反应温度成为有机－无机纳米复合材料制备的最有效的方法．本文根据合成路线的不同，分５个方面对用溶胶－凝胶法制备复合材料进行概要介绍．     

溶胶-凝胶法制备掺钙铬酸镧超细粉的工艺研究

采用柠檬酸作螯合剂、乙二醇作分散剂,用溶胶-凝胶法制备了掺杂Ca元素的铬酸镧超微粉末,通过XRD和HTEM检测手段对粉体的物相和颗粒粒径进行了检测.试验结果表明通过Ca离子单独络合的方法,经700℃煅烧可以得到La1-xCaxCrO3纳米颗粒,向溶胶中添加乙二醇分散剂可以明显减少杂相的生成和颗粒的团聚现象,颗粒粒径达到30 nm左右.煅烧温度高于800℃会使颗粒之间以晶界结合.     

Direct Synthesis of Ceramic Membranes by Sol-Gel Process

Ceramic ultrafiltration and nanofiltration membranes (TiO₂) are prepared by sol-gel route using a special arrangement which allows the reaction of the reactants directly in the pores of a tubular Al₂O₃ support or on its surface, respectively. By this direct synthesis the number of technological steps can be reduced which is the main advantage of the method. The produced layers are well joined with the Al₂O₃ support and the reaction can be adjusted by various technological parameters. The dried and sintered coatings are characterized by X-Ray diffraction, FESEM and AFM. In addition, pore size distribution and filtration properties are investigated and discussed.     

溶胶-凝胶工艺制备发光薄膜研究进展

本文综述了通过深胶－凝胶工艺制备发光薄膜的基本过程、薄膜的表征方法、发光薄膜的当前发展及应用情况。依据组成特点,对溶胶－凝胶法制备的发光薄膜乾地了分类阐述,并预言了今后该法制备发光薄膜的发展趋势。     

Fluoroalkoxides as Molecular Precursors of Fluoride Materials by the Sol-Gel Process

Numerous works have reported the preparation of pure oxide materials using the sol-gel process. The purpose of this paper is to show that it is possible to obtain pure fluoride homometallic or heterometallic materials at room temperature by the hydrolysis of tailored molecular precursors.The work is focussed on alkaline-earth and lanthanide fluoroalkoxides ([M(OR)n]n where OR = fluoroalkoxo group) and the characterization of the final products of their hydrolysis. The molecular precursors were characterized by FT-Raman and the final powders by XRD and EDXRMA.The formation of these fluoride materials involves fluoride organic by-products. The reactivity of these organic compounds on various substrates in terms of surface modification has been studied.     

Encapsulation of Tetraazaannulenato Compounds in Matrix by Sol-Gel Process

The hybrid organic-inorganic catalyst constituted by {5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraaza[14]annulenato} nickel (II), NiTMTAA, encapsulated in an alumina matrix has been prepared. NiTMTAA was synthesized by the reaction of nickel acetate with o-phenylenediamine in the presence of 2,4-pentanedione under argon atmosphere. The alumina hybrid material was obtained by a non hydrolytic sol-gel route, through the condensation of aluminum chloride with diisopropylether in the presence of NiTMTAA. The material has been prepared through precipitation from a gel. Characterization of the alumina hybrid material has been performed by ultra violet-visible spectroscopy, electron spectroscopic imaging, surface area, atomic absorption, infrared spectroscopy, and thermogravimetric analysis. The ultra violet-visible absorption spectrum of the hybrid material has bands characteristic of the NiTMTAA compound showing that the structure of NiTMTAA has been preserved in the hybrid material. The new material has a surface area of 300 m²/g. The electron image was that of a non-crystalline microstructure. Comparison between the leaching of NiTMTAA from NiTMTAA adsorbed on commercial neutral alumina confirm that in the non-hydrolytic materials the NiTMTAA is entrapped and not only adsorbed on the alumina surface. The use of conventional hydrolytic sol-gel process leads to the complete leaching of NiTMTAA from matrix, underlining the importance of the non-hydrolytic alumina gel process in the matrix preparation. The new catalysts prepared were tested for their ability to catalyze the epoxidation of (Z)-cyclooctene using iodosylbenzene as oxygen donor, giving moderate yields in the epoxidation (40%), while the homogeneous NiTMTAA is inactive due to NiTMTAA bleaching. These results emphasize the effect of the non-hydrolytic alumina matrix to prevent chemical degradation of NiTMTAA.     

Crystallization Behavior of Sol-Gel Derived Films by Self-Seeding Process

We propose the novel preparation method, Self-seeding Process, based on the following concept for low temperature crystallization of oxide films. Introduction of desirable inhomogeneity should give lowering of a crystallization temperature through heterogeneous nucleation accompanied with reduced activation energy. We carried out inspection of the above concept through use of PZT films. PZT gel films with the desirable inhomogeneity of microstructure were prepared, and their crystallization behaviors was examined. The PZT film was successfully crystallized at 500°C by the self-seeding process. The single phase (001) oriented PZT film with 0.55 m in thickness was obtained at 550°C for 5 min. The self-seeding process by microstructure control is efficient for the low temperature process of the oxide thin film.     

Fabrication of Sol-Gel Optical Waveguide by Hot-Dip Coating Process

The TiO₂: Sb nanoscale thin films were deposited on glass substrates by the sol–gel dip-coating method. The influence of the dopant density on the structure and the phase transformation of the thin films were investigated by X-ray diffraction (XRD) and Raman spectra. From the results of XRD, the thin films were in a majority of anatase state. The results of Raman spectra indicated that the non-doped TiO₂ thin film composed of not only anatase but also brookite phase. Dopant Sb enhances the transformation of the TiO₂ from brookite to anatase phase. After doping proper amount of Sb, the thin films show more superhydrophilicity than the non-doped TiO₂ thin film as well. The crystal size of the TiO₂ : Sb is about 13.3–20 nm calculated from the XRD patterns.     

Aluminum Sol-Gel Immobilized Amperometric Biosensor for H2O2

The determination of hydrogen peroxide is of practical importance in chemical, biological, clinical and many other fields. Enzyme electrodes have been studied widely for the past two decades and many research papers have been devoted to them. A very important factor in enzyme electrode development is the enzyme immobilization. Since Braun et al reported the first attempts to encapsulate proteins inside silica glasses in 1990, the low temperature sol-gel process has become an attractive avenue for the immobilization of biomolecules in connection with the development of new biosensors. A sufficient amount of trapped interstitial water contained in gels played an important role in the retention of the tertiary structure and reactivity of the immobilized enzymes.     

A Trypsin Immobilized Sol-Gel for Protein Indentification in MALDI-MS Applications

The proteolytic enzyme trypsin was chemically immobilized to an amine-functionalized sol-gel using adipoyl chloride under nonaqueous conditions and a nitrogen atmosphere. In the synthesis of the sol-gel, tetraethyl orthosilicate (TEOS), and 3-(2-aminoethylamino) propyldimethoxymethylsilane (AEAPMS) (50:50, v/v) were used, which provided convenient physical and chemical conditions to maintain catalytic activity of immobilized trypsin molecules for the digestion of proteins in proteomics applications. Bovine serum albumin was used as a model protein to perform enzymatic digestion using the trypsin immobilized sol-gel. The resulting peptides were analyzed by matrix-assisted laser desorption/ionization-mass spectrometry to evaluate the digestion performance and specificity of the sol-gel material. The trypsin immobilized sol-gel showed superior enzymatic activity in protein digestion and it was determined that the sol-gel material could be repeatedly used at least 25 times without significant activity loss in long-term use. Additionally, autocatalysis was prevented by immobilization of trypsin. The peptide digest having the highest purity was obtained for protein identification studies.     

High Purity Glass Forms by a Colloidal Sol-Gel Process

Novara Technology (NTECH) has developed its own process for bulk silica glass based on Sol-Gel chemistry. The process is characterized by its thermomechanical ideal isotropy of the aerogel and the glass it forms. Remarkable glass properties are: ultrapurity up to 1 ppb or better for single metal contaminant, optical compatibility with high-temperature treatments up to 2000°C, precision mouldability without intrinsic dimensional limitations.The process, that makes large use of the fumed silica Aerosil® in combination with TEOS, is characterized by the synthesis of monolithic material, i.e. a chemically manufactured body with shape and dimensions defined at reaction time, when the whole material is generated as a unit. Process implementation was achieved with the operation of a pilot plant. The road to industrialization besides volume scale-up, readily achieved for the chemical and hypercritical drying sector of the plant, was focused on getting a cost effective procedure.