Discrimination between ethanol inhibition models in a continuous alcoholic fermentation process using flocculating yeast

Discrimination between different rival models for describing the inhibitory effect of ethanol both on yeast growth and on fermentation was studied for a continuous process of alcoholic fermentation in a tower reactor with recycling of flocculating cells. Models tested include linear, parabolic, hyperbolic, exponential, and generalized nonlinear power-law types. The best expressions were identified under the criteria that all the kinetic parameters should assume acceptable values in a feasible range and should result in the best fit of the experimental data. The kinetic parameters were estimated from steady-state data of several sugar concentrations in feeding stream (S₀ = 160, 170, 180, 190, 200 g/L), constant dilution rate (D = 0.2 h^-1), recycle ratio (α = 13.6), and temperature (T = 30°C). The best model for the yeast growth was of power-law type, whereas for the product formation the best model was of linear type. These models were able to reproduce the trends of the process variables satisfactorily.     

Regioselective Condensation of Alkylidenephosphoranes to N-Methoxy- and N-Anilino-1H isoindole-1,3-(2H)-diones

Treatment of 2-methoxyisoindoline-1,3-dione with resonance-stabilized alkylidenephosphoranes afforded the corresponding monoalkenes as the sole reaction product, in ～58–63% yields, whereas more than 80% yields of the same monoolefin products were obtained when the reactions were carried out under microwave conditions. Similarly, 2-(phenylamino)isoindoline-1,3-dione reacted under either thermal or microwave conditions to give only the corresponding monoalkene derivatives. The alkene products from both substrates were further reduced to the corresponding isoindoles using Zn-dust in EtOH. Prediction of the designed compounds and the in vivo anti-inflammation activity of the products in the rat adjuvant model were also studied. The work is the first demonstration of the anti-inflammatory activity of phthalimide derivatives.     

Enzymatic kinetic of cellulose hydrolysis

The ethanol effect on the Trichoderma reesei cellulases was studied to quantify and clarify this inhibition type. To determine inhibition parameters of crude cellulase and purified exoglucanase Cel7A, integrated Michaelis-Menten equations were used assuming the presence of two inhibitors: cellobiose as the reaction product and ethanol as a possible bioproduct of cellulose fermentation. It was found that hydrolysis of cellulose by crude enzyme follows a model that considers noncompetitive inhibition by ethanol, whereas Cel7A is very slightly competitively inhibited. Crude cellulase is much more inhibited (K _iul=K _icl=151.9 mM) than exoglucanase Cel7A (K _icl=1.6 × 10¹⁵ mM). Also, calculated inhibition constants showed that cellobiose inhibition is more potent than ethanol inhibition both for the crude enzyme as well as exoglucanase Cel7A.     

Microcalorimetric studies on the non-competitive inhibition of bovine liver arginase

Two methods, e.g. initial rate method and thermokinetic reduced extent method were presented for studies on non-competitive inhibition. Arginase-catalyzed the hydrolysis of L-arginine toL-ornithine and urea and the inhibition of this reaction by sodium fluoride were studied in the absence and presence of exogenous of Mn²⁺at 37°C in 40 mM sodium barbiturate-hydrochloric acid buffer solution (pH 7.4). Both methods were successively used to determine the values of K₁. The advances and disadvantages of each method were compared in this paper. Exogenous Mn²⁺ could result in more sensitivity of arginase to F^-1. Since the inhibition of arginase by F^-1 depends on the pH values of the reaction system and behave as a non-competitive inhibition, it probably due to its small volume and high electronic density allow it access to the activity site of the enzyme and replaces of μ-OH₂ (or μ-OH) as the bridge ligand with Mn(II, II) cluster. However, further studies are necessary to determine the modes of interaction of F^-1 with bovine liver arginase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of substrate and product concentrations on the production of cyclodextrins by CGTase of Bacillus firmus,strain no. 37

The influence of substrate or product level on the initial velocity of cyclodextrin (CD) production by cyclodextringlycosyltransferase from a Brazilian isolate of Bacillus firmus was studied. Our results indicate that the product γ-CD is a stronger inhibitor to the reaction than β-CD. Small saccharides could also inhibit CD production, although to a lesser extent than the products, and maltose was the strongest inhibitor among small saccharides. Increasing substrate concentration resulted in greater reduction on enzyme activity for the formation of β-CD than for γ-CD. We modeled the kinetics of CD production with a set of four reversible reactions including the cyclization/coupling reaction that forms/opens CDs, and three disproportionation reactions. Our model on the initial velocity data explained well the substrate inhibition phenomenon. Kinetic parameters were determined by fitting the initial velocity data into our model.     

An Improved Kinetic 5′Nucleotidase Assay

Abstract

5′nucleotidase activity was measured by a coupled optical assay in which adenosine, liberated by action of the primary enzyme, released ammonia which in turn formed L-glutamate from 2-oxoglutarate and NADH. Oxidation of the latter is monitored at 340 nm. Greater activity was obtained when triethanolamine buffer, pH 7.2, and Mn⁺⁺ were substituted for tris buffer, pH 7.9, and Mg⁺⁺. The concentration of substrate, 5′AMP, was altered to 1 mmole/liter and that of β-glycerophosphate to 50 mmoles/liter to achieve optimal activity of true nucleotidase and suppression of 5′AMP-hydrolysis by non-specific phosphatases.     

Conductimetric Measurement of Cholinesterase Inhibition by Some Pesticides

Abstract

In this present work, we have applied the conductimetric method to measure cholinesterase inhibition by pesticides.

When using acetylcholine as a substrate, we have demonstrated, that for a given incubation of 40 mn, the initial rate of the enzymatic hydrolysis can be related to pesticide concentration. In a given inhibitor concentration range, the activity/log (concentration) relationship is linear and may be used for pesticide quantitation.     

Ultra-stable Ni catalysts for methane reforming by carbon dioxide

Methane reforming by carbon dioxide has been studied over ultra-stable Ni catalysts. The catalyst was characterized by XRD, IR and TEM and temperature programmed hydrogenation. The nickel–magnesia solid solution catalyst containing low nickel has shown excellent stability (>3000 h) and no carbon deposition in the methane reforming by carbon dioxide. It was also found that the small nickel metal particle interaction with support surface is effective for the inhibition of carbon formation.     

Oxygen Inhibition and Coating Thickness Effects on Uv Radiation Curing of Weatherfast Clearcoats Studied by Photo-DSC

Radiation curing is an environmentally-friendly technology. Furthermore, radiation curing is a faster, energy saving and more efficient industrial process than the heat-curable process. One of the most important requirements for the widespread application of UV curable coatings in the coating industry is that they are stable vs. atmospheric degradation. Today's state of the art in oxidative drying and thermosetting coatings is the use of light stabilizers to protect polymers vs. the damage of outdoor exposure. Oxygen has a detrimental effect on the cure response of free radical systems, especially in thin-film coatings. Differential photocalorimetry (photo-DSC) was used to investigate the oxygen effect and the use of light stabilizers on UV curing of photocurable formulations based on acrylate materials. Coating thickness influence was also considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

新型不对称双季铵盐缓蚀剂在HCl中对Q235钢的缓蚀行为

采用静态失重法、极化曲线法和交流阻抗法研究了自制的含咪唑啉环不对称双季铵盐缓蚀剂(DBA)在1 mol•L^－1 HCl介质中对Q235钢的缓蚀性能, 并探讨了其在Q235钢表面的吸附行为. 结果表明, 缓蚀效率随DBA浓度增加而增大, 在25～55 ℃的实验温度范围内, 浓度为2.89×10^－4 mol•L^－1时, 缓蚀效率均在90%以上, 且缓蚀效率随温度升高而增大. 极化曲线测试显示DBA是一种阴极抑制为主的混合型缓蚀剂. 缓蚀剂在Q235钢表面的吸附过程为吸热过程, 其在Q235钢表面的吸附遵循Langmuir等温式, 属于化学吸附. 最后采用量子化学方法对DBA的缓蚀机理做了进一步分析.