Sharif Digital Repository

Nonporous and mesoporous silica-coated magnetite cluster nanocomposites particles were fabricated with various silica structures in order to develop a desired carrier for the lipase immobilization and subsequent biodiesel production. Lipase from Pseudomonas cepacia was covalently bound to the amino-functionalized particles using glutaraldehyde as a coupling agent. The hybrid systems that were obtained exhibited high stability and easy recovery regardless of the silica structure, following the application of an external magnetic field. The immobilized lipases were then used as the recoverable biocatalyst in a transesterification reaction to convert the soybean oil to biodiesel with methanol.... 

In this research work, different devices made of glutaraldehyde cross-linked chitosan hydrogels loaded by amoxicillin, have been prepared using freeze-drying method. Effects of system parameters such as cross-linker concentration, pH, and gel structure on the morphology and release behavior of devices have been investigated using standard methods. Morphological studies were performed using SEM instrument and controlled releases are followed via spectrophotometeric method. Reaction of glutaraldehyde with chitosan has been studied using FTIR instrument. SEM micrographs have shown that with increasing cross-linker percentage in hydrogel, pore sizes increased where pore size distribution... 

Chitosan was crosslinked with different amount of glutaraldehyde to prepare appropriate hydrogels to be used as drug delivery system. The swelling behavior of freeze-dried hydrogels in aqueous media at different temperature and pHs has been examined. The swelling, porosity and biocompatibility behavior of samples were investigated to check effects of polymer/polymer and polymer/drug interactions on these system characteristics. Obtained experimental results illustrates that with increasing crosslinking agent from 0.068 to 0.30, swelling of the prepared samples degrees from 1200% to 600% and pore diameters change from 100 to 500 μm. To investigate systems biocompatibility in gastric... 

Porous scaffolds composed of gelatin/poly (vinyl alcohol), (Gel/PVA), were prepared using combination of freeze gelation and freeze drying methods. The effect of polymer concentration, gelatin/PVA ratio, and glutaraldehyde/gelatin ratio (GA/Gel) was investigated on morphology of pores, swelling ratio, biodegradation, and skin cell culture. At optimum preparation conditions the scaffolds had uniform pore size distributions showing high swelling ratio of 23.6. The scaffolds were of biodegradable nature and almost degraded in 28 days. Human dermal fibroblast cells (HDF) were cultured on the scaffolds and MTS assay was conducted to evaluate the influence of PVA on growth and proliferation of the... 

Enzymatic removal of Bisphenol A (BPA), acknowledged as an environmentally friendly approach, is a promising method to deal with hard degradable contaminants. However, the application of “enzymatic treatment” has been limited due to lower operational stability and practical difficulties associated with recovery and recycling. Enzyme immobilization is an innovative approach which circumvents these drawbacks. In this study, laccase from Trametes hirsuta was used for BPA removal. Amino-functionalized magnetic Fe3O4 nanoparticles were synthesized via the co-precipitation method followed by surface modification with (3-aminopropyl)trimethoxysilane (APTMS). The as-prepared nanoparticles were... 

The immobilization of cellulase onto non-porous ultrafine silica particles was studied. Cellulase was extracted from a Trichoderma reesei culture after partial purification with ammonium sulfate (pH = 5.0), which was then immobilized onto non-porous ultrafine silica particles, with or without the use of glutaraldehyde as a crosslinking agent. Cellulase was immobilized by adsorption onto ultrafine silica particles efficiently, as well as by covalent cross-linking with glutaraldehysde. Increasing the concentration of the free form of enzyme increased the amount of immobilized cellulase. The maximum enzyme immobilization happened at the free enzyme concentration of 0.48 mg/ml. In general, the... 

In this paper, immobilization of penicillin G aclylase onto non-porous ultrafine silica particles has been studied. The amount of penicillin G acylase immobilized was increased by increasing the free enzyme concentration and, at 0.45 mg/ml concentration of the free enzyme, 80% of the enzyme was immobilized. The optimum pH for immobilization was found to be 7.0, close to the pl of the enzyme. Although immobilization of the enzyme on ultrafine silica particles with and without glutaraldehyde showed almost the same activities, the enzyme immobilized with glutaraldehyde retained its initial activity much longer during 40 cycle-repeated batches with a half life of 163.2 h. © Sharif University of...