SIMPLE ENTRAPMENT OF ALCALASE IN DIFFERENT SILICA XEROGELS USING THE TWO STEPS SOL-GEL METHOD

The present study has focused on the entrapment of Alcalase in different xerogels obtained by using various molar ratios of methyltriethoxysilane, dimethyldietoxisilane and tetraethoxysilane. Silica and their derivatives were characterized with regard to specific surface area (nitrogen adsorbtion), chemical composition (Fourier transform infrared spectroscopy (FT-IR)), weight loss upon heating (thermogravimetric analysis (TGA)) and catalytic activity

PRELIMINARY STUDY FOR USING VINYLTRIACETOXYSILANE AS PRECURSOR IN ENZYME IMMOBILIZATION BASED ON SOL-GEL METHOD

During the last years, sol-gel technology has become a well-established method for the preparation of catalytic active monoliths, bulk, particles and thin films. One reason for the increasing research activities in this field is the opportunity to obtain versatile hybrid materials by incorporation of different molecules, like dyes, enzymes, whole cells, chemicals and drugs. The aim of this research was to evaluate the suitability of vinyltriacetoxysilane (VTAS) as precursor in sol-gel enzyme immobilization and the physicochemical characterization of the final products (silica xerogels)

Entrapment of glucoamylase by sol-gel technique in PhTES/TEOS hybrid matrixes

Mesoporous silica particles were prepared by the sol-gel method from different alkoxysilane precursors and used as a host matrix for encapsulation of glucoamylase, an enzyme widely used in fermentative industry. The aim was to investigate the physico-chemical properties of the different silica powders and their effect on the enzyme kinetics. The encapsulated enzymes followed Michaelis-Menten kinetics. The Michaelis constant (KM) and the maximum rate of starch hydrolysis reaction (Vmax) were calculated according to the Michaelis-Menten and Lineweaver-Burke plots. The values of the Michaelis constant (KM) of the encapsulated enzymes were higher than those of the free enzyme. The temperature and pH infl uence on the activity of free and immobilized glucoamylase were also compared. The results of this study show that the enzymes immobilized in organic/inorganic hybrid silica matrixes (obtained by the sol-gel method), allowing the entrapped glucoamylase to retain its biological activity, are suitable for many different applications, (medicinal, clinical, analytical)

MICROBIAL HYDROLASES IMMOBILIZED ON POROUS MATRICES

Starch degrading enzymes are used as feed additives to increase the digestibility of corn meal based dietin livestock and poultry. To be efficient, these enzymes have to present a good activity and stability.Immobilization by physical bonding of enzymes on a porous support is a simple and efficient method topreserve enzyme molecules in an active form and retain their activity for a period of time.The aim of this study was to stabilize an enzymatic preparation with amylase activity produced by a nativestrain of Bacillus amyloliquefaciens in submerged culture. The immobilization technique used wasphysical bonding on a porous ceramic support. The enzymatic preparation with amylase activity was usedin immobilization in a liophylized form. By using the same method we immobilized also a purifiedAspergillus niger amylase. For both enzymes, the optimal temperature and pH of the native andimmobilized enzymes did not vary significantly. At temperature and pH values lower than the optimum,the relative activities have been higher for the immobilized Bacillus amyloliquefaciens enzyme comparedto the native one. The immobilization has led to an enzymatic compound with stability at pH 3 and 37°Cand in time higher than that of the free one

Structure Effects over Behavior of Graphite Gray Iron in Running

The work aims at emphasizing the structure changes of graphite gray iron, as a result of make-casting conditions and their effects over behavior in running of several cast items. Researches consisted of complex characterization of several gray iron specimens sampled from damaged items comparatively to other suitable ones. Chemical composition, crack aspect, tensile strength, structure, kind, micro hardness of structural constituent were analyzed. Laboratory researches made by optical and electronic microscopy emphasized the showing up of some unsuitable structures with fragile structural constituents and areas unpurified by exogenous inclusions as well as degenerated graphite. All of these steady structural changes had a powerful fragility effect over the material. This fact was confirmed by mechanical characteristics and analysis of cracking area. Results corroborating allowed finding the causes of graphite gray iron cast items damage as a result of a faulty make-casting technological management and incomplete heating treatment

Chromium Substituted Cobalt Ferrites by Glycine-Nitrates Process

Chromium substituted cobalt ferrites (CoFe2–xCrxO4, 0 ≤ x ≤ 2) were synthesized through solution combustion method using glycine as fuel, named glycine-nitrates process (GNP). As evidenced by X-ray diffraction data (XRD), single cubic spinel phase was formed for all CoFe2–xCrxO4 (0 ≤ x ≤ 2) series. The cubic lattice parameter (a) decreases with increasing chromium content. Room temperature 57Fe Mössbauer spectra revealed the Fe3+ and Cr3+ site occupancy, the local hyperfine magnetic fields and the substitution of Fe3+ by Cr3+ in the lattice. Scanning electron microscopy (SEM) showed a refinement of particle size with the increase of Cr3+ content. Magnetic measurements from 5 K to 120 K have shown a dropping in the saturation magnetization as the chromium content increases. This behaviour has been explained in terms of substitution of Fe3+ by Cr3+ in the cubic lattice of cobalt ferrite

Bioorganically doped sol-gel materials containing amyloglucosidase activity

Amyloglucosidase (AMG) from Aspergillus niger was encapsulated in various matrices derived from tetraethoxysilane, methyltriethoxysilane, phenyltriethoxysilane and vinyltriacetoxysilane by different methods of immobilization. The immobilized enzyme was prepared by entrapment in two steps, in one-step and entrapment/deposition, respectively. The activities of the immobilized AMG were assayed and compared with that of the native enzyme. The effects of the organosilaneprecursors and their molar ratios, the immobilization method, the inorganic support (white ceramic, red ceramic, purolite, alumina, TiO2, celite, zeolite) and enzyme loading upon the immobilized enzyme activity were tested. The efficiency of the sol-gel biocomposites can be improved through combination of the fundamental immobilization techniques and selection of the precursors