Immobilization systems more frequently used are calcium alginate spheres. These biocatalysts have many potential applications in the immobilization of enzymes, prokaryotic cells, vegetal and animal cells, algae, organ...Immobilization systems more frequently used are calcium alginate spheres. These biocatalysts have many potential applications in the immobilization of enzymes, prokaryotic cells, vegetal and animal cells, algae, organelles and mixtures of these living components. Other applications of immobilized cells imply the use of non aqueous systems. Some bioconversions are carried out in the presence of solvents such as hexane acetone or acetonitrile, or mixtures water-solvents. The aim of this work was to investigate the behaviour of Ca-alginate spheres when put in contact with different solvents (water, diesel, ethanol, methanol, acetone, n-hexane, isopropyl alcohol, THF, acetonitrile, and toluene), or solvent-water mixtures (i.e., ethanol-water), regarding the resistance of the alginate spheres after days of contact. Calcium alginate particles suffered different damages, depending on the solvent they were put in contact. Water did not damaged the Ca-alginate structure with or without Ca present. On the other hand different solvents lost a proportion of volume, i.e., n-hexane (16%), methanol (19%), ethanol (19.5%), toluene (22%), diesel (34%), acetone (765), isopropyl alcohol (80%), THF and acetonitrile (total loss, total destruction). Nor the dielectric constant nor the polarity indexes were capable of explaining the difference on the volume loss or total sphere destruction, except for water-ethanol mixtures.展开更多
Micro-environmental restriction effects to yeast cell growth obtained within Ca-alginate microbeads are considered. It is complex phenomenon influenced by: (1) relaxation of expanded polymer network around the cellula...Micro-environmental restriction effects to yeast cell growth obtained within Ca-alginate microbeads are considered. It is complex phenomenon influenced by: (1) relaxation of expanded polymer network around the cellular clusters, (2) forces generated by cell growth inside the beads and (3) interactions between solvent, network parts and cells. The resulting effects are measured experimentally by estimating volume of microbeads and yeast cell concentration as function of time of cultivation. Comparative analysis of dynamics of cell growth and increase of microbead volume through four regimes indicates that reversible and irreversible local structural changes of Ca-alginate hydrogel induces micro-environmental restrictions to cell growth. The mechanism of restrictions includes both mechanical and electrostatic effects.展开更多
An equation of diffusion for microcapsules（hollow sphere）was developed,employing the mathematicalmodel for the diffusion characteristics of solid sphere.In the proposed equation,a combination diffusion coeffi-cient ...An equation of diffusion for microcapsules（hollow sphere）was developed,employing the mathematicalmodel for the diffusion characteristics of solid sphere.In the proposed equation,a combination diffusion coeffi-cient was introduced as a substitute for the diffusion coefficient in the solid sphere mathematical model and ex-pressed as a function of the diffusion coefficient inside solution of hollow sphere,as well as in the polymer mem-brane.With this modified model,the diffusion coefficients of glucose in NaCS（sodium cellulose sulfate）-PDADMAC（Poly-diallyl-dimethyl-ammonium chloride）membrane and in Ca-alginate gel membrane were deter-mined.The diffusion coefficient in NaCS-PDADMAC membrane was found to be 2.12×10<sup>-11</sup>m<sup>2</sup>·s<sup>-1</sup>and thatin Ca-alginate membrane 2.62×10<sup>-10</sup>m<sup>2</sup>·s<sup>-1</sup>.展开更多
文摘Immobilization systems more frequently used are calcium alginate spheres. These biocatalysts have many potential applications in the immobilization of enzymes, prokaryotic cells, vegetal and animal cells, algae, organelles and mixtures of these living components. Other applications of immobilized cells imply the use of non aqueous systems. Some bioconversions are carried out in the presence of solvents such as hexane acetone or acetonitrile, or mixtures water-solvents. The aim of this work was to investigate the behaviour of Ca-alginate spheres when put in contact with different solvents (water, diesel, ethanol, methanol, acetone, n-hexane, isopropyl alcohol, THF, acetonitrile, and toluene), or solvent-water mixtures (i.e., ethanol-water), regarding the resistance of the alginate spheres after days of contact. Calcium alginate particles suffered different damages, depending on the solvent they were put in contact. Water did not damaged the Ca-alginate structure with or without Ca present. On the other hand different solvents lost a proportion of volume, i.e., n-hexane (16%), methanol (19%), ethanol (19.5%), toluene (22%), diesel (34%), acetone (765), isopropyl alcohol (80%), THF and acetonitrile (total loss, total destruction). Nor the dielectric constant nor the polarity indexes were capable of explaining the difference on the volume loss or total sphere destruction, except for water-ethanol mixtures.
文摘Micro-environmental restriction effects to yeast cell growth obtained within Ca-alginate microbeads are considered. It is complex phenomenon influenced by: (1) relaxation of expanded polymer network around the cellular clusters, (2) forces generated by cell growth inside the beads and (3) interactions between solvent, network parts and cells. The resulting effects are measured experimentally by estimating volume of microbeads and yeast cell concentration as function of time of cultivation. Comparative analysis of dynamics of cell growth and increase of microbead volume through four regimes indicates that reversible and irreversible local structural changes of Ca-alginate hydrogel induces micro-environmental restrictions to cell growth. The mechanism of restrictions includes both mechanical and electrostatic effects.
基金Supported by the National Natural Science Foundation of China(No.29676069),the Foundation of the National Education committee of China and Mr.Chao Guangbiao advanced Technology Foundation of Zhejiang University.
文摘An equation of diffusion for microcapsules（hollow sphere）was developed,employing the mathematicalmodel for the diffusion characteristics of solid sphere.In the proposed equation,a combination diffusion coeffi-cient was introduced as a substitute for the diffusion coefficient in the solid sphere mathematical model and ex-pressed as a function of the diffusion coefficient inside solution of hollow sphere,as well as in the polymer mem-brane.With this modified model,the diffusion coefficients of glucose in NaCS（sodium cellulose sulfate）-PDADMAC（Poly-diallyl-dimethyl-ammonium chloride）membrane and in Ca-alginate gel membrane were deter-mined.The diffusion coefficient in NaCS-PDADMAC membrane was found to be 2.12×10<sup>-11</sup>m<sup>2</sup>·s<sup>-1</sup>and thatin Ca-alginate membrane 2.62×10<sup>-10</sup>m<sup>2</sup>·s<sup>-1</sup>.
