Perturbation analysis of coupled diffusion and reaction with high-order kinetics

Asymptotic solutions for the effectiveness factor and the concentration profile are obtained for mth-order chemical reactions inside a slab catalyst pellet with Robin boundary condition at the pellet's outer surface. Using perturbation analysis in the limit of large reaction order m, the effectiveness factor and the concentration profile are explicitly determined up to O(1/m). Higher-order solutions can be obtained in a systematic way if desired.     

Modeling enzyme immobilization in porous solid supports

Enzymes are often immobilized on the internal surfaces of porous solid by immersing enzyme-free particles in a well mixed solution of enzyme. The ensuing impregnation process involves coupled transient mass transfer and surface attachment of enzyme. A mathematical model is employed to explore the influences of process parameters on the amount of enzyme loaded and the distribution of immobilized enzyme within the support particles. Nonuniform loading of the support occurs under some conditions. This is significant since the distribution of enzyme within the support particle influences the overall activity and stability of the immobilized enzyme catalyst. The model developed here may also be used to describe removal of reversibly immobilized enzyme during washing or utilization of the immobilized enzyme catalyst.     

A semimechanistic mathematical model for growth of Rhizopus oligosporus in a model solid-state fermentation system

A Semimechanistic mathematical model is developed which describes the growth of Rhizopus oligosporus in a model solid-state fermentation system. Equations are presented for the release of glucoamylase, the diffusion of glucoamylase, the hydrolysis of starch, the generation and diffusion of glucose, and the uptake of glucose and conversion into new biomass. Good agreement of the model with the experimental data was obtained only after the glucoamylase diffusivity and the maximum specific glucose uptake rate were altered from their originally determined values. The model recognizes the distributed nature of the solid-state fermentation and therefore is able to predict the concentration profiles of the system components within the substrate. The model provides an insight into the possible rate-limiting steps in solid-state fermentation-the generation of glucose within the substrate and the resulting availability of glucose at the surface.     

Determination of total and active immobilized enzyme distribution in porous solid supports

The total and active immobilized enzyme (IME) distributions in porous supports are studied both theoretically and experimentally. In order to determine experimentally the enzyme distribution profiles within a single particle, we construct a diffusion cell containing controlled-pore glass particles such that the cell would mimic a large pellet support. Our purpose is to study the interplay between the diffusion process within the interparticle void space and immobilization process in the controlled-pore glass particles onto the evolution of the (total and active) enzyme distributions. A mathematical model is developed to describe the interaction of various processes within the diffusion cell. The immobilized enzymes are determined for a system of trypsin and controlled-pore glass particles. The total amount of enzymes are determined by the amino acid analysis, and the active fraction is obtained by an active-site titration. The experimentally measured total IME profiles compare very well with that predicted by the model. The determined active enzyme profile is found to be nonuniform one, and it represents about 40% of the total enzyme immobilized in the support particles.     

Anticlastogenic effect of flavonoids against mutagen-induced micronuclei in mice.

14 flavonoids, including flavone and flavonol derivatives, were tested for their anticlastogenic effect against induction of micronuclei by benzo[a]pyrene in polychromatic erythrocytes of mice. When each flavonoid was administered orally, together with intraperitoneally administered benzo[a]pyrene, most flavonol derivatives showed an anticlastogenic effect. The data suggest that the 2,3-double bond and 3,5,7-hydroxyl groups in the flavonoid molecules may be essential to produce anticlastogenic effects against benzo[a]pyrene. Galangin, one of the active compounds, and (-)-epicatechin, a weak one, were administered to mice in order to compare their anticlastogenic effect against 3 different kinds of carcinogens: ethyl methanesulfonate, 7,12-dimethylbenz[a]anthracene, and adriamycin. Galangin showed a stronger anticlastogenic effect than (-)-epicatechin against ethyl methanesulfonate and 7,12-dimethylbenz[a]anthracene. However, there was no significant effect against adriamycin-induced micronuclei by both compounds. Our study indicates that most flavonoids are anticlastogenic agents. Their anticlastogenic effects are apparently independent of their own clastogenic activities. Furthermore, their anticlastogenic activities do not apply universally to all types of genotoxic chemicals.     

Plant regeneration of NaCl-pretreated cells from long-term suspension culture of rice (Oryza sativa L.) in high saline conditions

Cells of a 2-year-old suspension culture of rice (Oryza sativa L.), grown under 1.5% NaCl stress for 3 months, gave rise to plants through embryogenesis in different saline conditions. The high regeneration potential (59.6%) on salt-free medium decreased rapidly with increasing concentration of salt in the regeneration medium. At 1.25% NaCl, healthy shoots were developed in 14.9% of the cultures. Under 1.5% salt stress, embryo formation and embryo germination (6.1%) was observed but further development into plants was inhibited. Cells not pretreated with salt produced plants at a low frequency (2.6–4.2%) both in salt-free and low saline condition (0.75–1% NaCl). Cells pretreated for 3 months with 0.75% salt did not give rise to plants on all tested media. Plants regenerated from the salt-stressed cultures were transferred to soil and grew to maturity in a greenhouse.Abbreviations BA 6-benzyladenine - CH casein hydrolysate - 2,4-D 2,4-dichlorophenoxyacetic acid - NAA 1-naphthaleneacetic acid     

Flavonoids of Derris araripensis

Nineflavonoids: a dihydrochalcone,a flavone,four 3-methylflavonols,a flavanone, a 3-methylflavanonol and a flavan were isolated from the roots of Derris araripensis. Eight of these compounds are reported for the first time. Structures were established by spectral analysis and chemical degradation.     

Possible anti-obesity therapeutics from nature – A review

Obesity is associated with many diseases, particularly diabetes, hypertension, osteoarthritis, and heart disease. The obesity incidence has increased at an alarming rate in recent years, becoming a worldwide health problem, with incalculable social costs. Two different obesity-treatment drugs are currently on the market: orlistat, which reduces intestinal fat absorption via inhibiting pancreatic lipase; and sibutramine, an anorectic or appetite suppressant. Both drugs have hazardous side-effects, including increased blood pressure, dry mouth, constipation, headache, and insomnia. For this reason, a wide variety of natural materials have been explored for their obesity treatment potential. These are mainly complex products having several components with different chemical and pharmacological features. This review aimed to survey the literature covering natural products with anti-obesity activity and to review the scientific data, including experimental methodologies, active components, and mechanisms of action against obesity.     

Human Health Risk Assessment of Soils Contaminated with Metal(loid)s by Using DGT Uptake: A Case Study of a Former Korean Metal Refinery Site

The human health risk of soils contaminated with As, Pb, Cu, and Zn was evaluated based on pseudo-total concentrations of metal(loid)s, the physiologically based extraction test (PBET), and diffusive gradients in thin films (DGT). Non-carcinogenic (NCR) and carcinogenic (CR) risks exceeded the U.S. Environmental Protection Agency criteria under both the residential and non-residential scenarios. Human bioavailable concentrations (PBET) were much lower than pseudo-total concentrations. The Hazardous Index of NCR (HI (NCR)) for the PBET in the studied soils was 67% and 94% less than that for pseudo-total concentration, respectively, under the non-residential and residential scenarios. Similarly, CR for the PBET was also 65% and 93% less for the two soils. The concentration of metal(loid)s accumulated in the DGT resin was highly correlated with the PBET-extractable concentration (R² > 0.649). Therefore, for both the CR and HI (NCR), the DGT-calculated risk was linearly related to the PBET-calculated risk for the studied soils under both scenarios. The results suggest that DGT uptake and PBET-extracted concentrations are good surrogates for risk estimation and that both J1 and J2 soils require remediation before their use for residential or non-residential purposes.