Screening,Molecular Cloning,and Biochemical Characterization of an Alcohol Dehydrogenase from Pichia pastoris Useful for the Kinetic Resolution of a Racemic β‐Hydroxy‐β‐trifluoromethyl Ketone

The stereoselective synthesis of chiral 1,3‐diols with the aid of biocatalysts is an attractive tool in organic chemistry. Besides the reduction of diketones, an alternative approach consists of the stereoselective reduction of β‐hydroxy ketones (aldols). Thus, we screened for an alcohol dehydrogenase (ADH) that would selectively reduce a β‐hydroxy‐β‐trifluoromethyl ketone. One potential starting material for this process is readily available by aldol addition of acetone to 2,2,2‐trifluoroacetophenone. Over 200 strains were screened, and only a few yeast strains showed stereoselective reduction activities. The enzyme responsible for the reduction of the β‐hydroxy‐β‐trifluoromethyl ketone was identified after purification and subsequent MALDI‐TOF mass spectrometric analysis. As a result, a new NADP⁺‐dependent ADH from Pichia pastoris (PPADH) was identified and confirmed to be capable of stereospecific and diastereoselective reduction of the β‐hydroxy‐β‐trifluoromethyl ketone to its corresponding 1,3‐diol. The gene encoding PPADH was cloned and heterologously expressed in Escherichia coli BL21(DE3). To determine the influence of an N‐ or C‐terminal His‐tag fusion, three different recombinant plasmids were constructed. Interestingly, the variant with the N‐terminal His‐tag showed the highest activity; consequently, this variant was purified and characterized. Kinetic parameters and the dependency of activity on pH and temperature were determined. PPADH shows a substrate preference for the reduction of linear and branched aliphatic aldehydes. Surprisingly, the enzyme shows no comparable activity towards ketones other than the β‐hydroxy‐β‐trifluoromethyl ketone.     

Kinetic modeling of simultaneous polycondensation and free radical polymerization for polyurethane/poly(methyl methacrylate) interpenetrating polymer network

A comprehensive kinetic Monte Carlo algorithm has been developed to investigate the formation process of a polyurethane/poly(methyl methacrylate) (PU/PMMA) interpenetrating polymer network (IPN), in which a component independent strategy is proposed to perform the simulation of simultaneous polycondensation and free radical polymerization. An empiric diffusion model based on the mass fraction of polymer is used to quantify the effect of diffusional limitations on MMA polymerization. Results show that the presence of acrylic monomers has little impact on the formation rate of PU, but the presence of the PU network can accelerate the polymerization of MMA. In addition, the effects of component mass ratio, acrylic cross-linker concentration, and [NCO]/[OH] ratio on the IPN formation kinetics are investigated based on the kinetic model. It is believed that the as-developed modeling strategy can be extended to other IPN systems and provide a better understanding of the interactions between chemically independent networks.     

Kinetic study of liquid lipase-catalyzed glycerolysis of olive oil using Lipozyme TL 100L

Monoacylglycerol (MAG) and diacylglycerol (DAG) are two natural components found in most edible oils and fats. Conventional synthesis of MAG and DAG is usually conducted by glycerolysis of triacylglycerol (TAG) at high temperatures (above 200°C) in the presence of an alkaline catalyst. In this work, the synthesis of MAG and DAG using enzymatic glycerolysis of olive oil was investigated using Tween 80 as surfactant, n-butanol as co-surfactant and the novel lipase in free/liquid formulation Lipozyme TL 100L as catalyst. Experimental design was used to evaluate the effect of enzyme load and reaction temperature on the feedstock conversion. Enzyme load and system temperature were significant variables in the statistical design and the best condition was found at 35°C, 7.5 vol% of Lipozyme TL 100L and glycerol to oil volumetric ratio of 2:1 with conversion of TAG at approximately 98% after 2 h of process. A mathematical model based on the Ping-Pong Bi-Bi mechanism was used to describe the reaction kinetics. The model adequately described the behavior of the system and can be a useful tool for the design of reactors in larger scales.     

超重力强化AMP-PZ复合溶液脱碳技术及表观动力学

为提高工业上火电厂乙醇胺（MEA）吸收塔脱碳工艺中脱碳率和反应速率,提出了超重力技术耦合2-氨基-2-甲基-1-丙醇-对二氮己环（AMP-PZ）混合胺脱碳方法。正交实验表明：不同操作参数对脱碳率的影响显著性大小依次为：超重力因子、气液比、吸收剂质量浓度、主吸收剂含量、温度;最佳操作条件为：超重力因子为60,气液比为15,吸收剂质量分数为25%,主吸收剂质量分数为60%,温度为25℃,CO₂脱除率可达97.16%。相对传统的乙醇胺（MEA）吸收塔法,CO₂脱除率提高了7.16%。相同操作条件下,旋转填料床的脱碳反应速率常数比曝气反应装置高一倍。建立了超重力场中AMP-PZ脱碳表观动力学模型,不同操作参数对反应速率常数的显著性影响大小依次为：超重力因子>气液比>吸收剂质量浓度。     

Investigation of carbon dioxide photoreduction process in a laboratory-scale photoreactor by computational fluid dynamic and reaction kinetic modeling

The production of solar fuels via the photoreduction of carbon dioxide to methane by titanium oxide is a promising process to control greenhouse gas emissions and provide alternative renewable fuels. Although several reaction mechanisms have been proposed, the detailed steps are still ambiguous, and the limiting factors are not well defined. To improve our understanding of the mechanisms of carbon dioxide photoreduction, a multiphysics model was developed using COMSOL. The novelty of this work is the computational fluid dynamic model combined with the novel carbon dioxide photoreduction intrinsic reaction kinetic model, which was built based on three-steps, namely gas adsorption, surface reactions and desorption, while the ultraviolet light intensity distribution was simulated by the Gaussian distribution model and Beer-Lambert model. The carbon dioxide photoreduction process conducted in a laboratory-scale reactor under different carbon dioxide and water moisture partial pressures was then modeled based on the intrinsic kinetic model. It was found that the simulation results for methane, carbon monoxide and hydrogen yield match the experiments in the concentration range of 10⁻⁴ mol·m^–3 at the low carbon dioxide and water moisture partial pressure. Finally, the factors of adsorption site concentration, adsorption equilibrium constant, ultraviolet light intensity and temperature were evaluated.     

Diffusion process in enzyme–metal hybrid catalysts

Enzyme–metal hybrid catalysts bridge the gap between enzymatic and heterogeneous catalysis, which is significant for expanding biocatalysis to a broader scope. Previous studies have demonstrated that the enzyme–metal hybrid catalysts exhibited considerably higher catalytic efficiency in cascade reactions, compared with that of the combination of separated enzyme and metal catalysts. However, the precise mechanism of this phenomenon remains unclear. Here, we investigated the diffusion process in enzyme–metal hybrid catalysts using Pd/lipase-Pluronic conjugates and the combination of immobilized lipase (Novozyme 435) and Pd/C as models. With reference to experimental data in previous studies, the Weisz–Prater parameter and efficiency factor of internal diffusion were calculated to evaluate the internal diffusion limitations in these catalysts. Thereafter, a kinetic model was developed and fitted to describe the proximity effect in hybrid catalysts. Results indicated that the enhanced catalytic efficiency of hybrid catalysts may arise from the decreased internal diffusion limitation, size effect of Pd clusters and proximity of the enzyme and metal active sites, which provides a theoretical foundation for the rational design of enzyme–metal hybrid catalysts.     

含氰基聚酰亚胺薄膜的制备及其热分解动力学

以4-[3,5-双(4-氨基苯氧基)苯氧基]邻苯二甲腈和3,3′,4,4′-联苯四甲酸二酐为原料,经聚酰胺酸热酰亚胺化制备含氰基的聚酰亚胺(CN-BP-PI)薄膜。采用傅里叶变换红外光谱、热重分析、差示扫描量热法对CN-BP-PI薄膜进行了分析。采用动态热重法研究了CN-BP-PI的分解动力学,用积分法结合常见固相热分解反应动力学函数来判断热分解的动力学函数。由Ozawa,KAS,Kissinger,Achar,Coats-Redfern,MacCallum-Tanner,van Krevelen方程求热分解反应的动力学参数。转化率为0.2~0.8时所得CN-BP-PI在氮气中热分解反应的表观活化能为119.68~215.61 kJ/mol,平均活化能为136.35 kJ/mol,指前因子平均值为8.52×107 s-1。     

MBR处理制药废水中动力学参数测定

根据膜生物反应器的特点,利用Lawrence-McCarty模式建立了膜生物反应器处理废水时的污泥增殖动力学模型和底物降解动力学模型,并根据MBR处理诺氟沙星制药废水的试验运行数据计算出了动力学常数Y、Kd、Vmax、和Ks,分别为0.31、0.01、0.32、270.22。     

天然气非催化部分氧化转化炉模拟

O2/CH4比、操作压力和气化炉长度等因素对天然气非催化部分氧化转化炉的运行至关重要。研究建立了基于反应动力学的反应器网络模型和平衡模型。考察了O2/CH4摩尔比、压力与停留时间对合成气出口温度和组成的影响。结果表明,反应器网络模型的预测结果与工业运行数据吻合较好。随着O2/CH4摩尔比增大、压力的上升或停留时间的变长,两种模型模拟结果的差异逐渐变小。反应器网络模型模拟结果表明,O2/CH4摩尔比上升,合成气温度逐渐升高,出口甲烷含量逐渐降低,H2/CO摩尔比逐渐下降。在停留时间较短时,压力的上升会促进甲烷的转化,而在停留时间较长时,较高的压力会抑制甲烷的转化。     

Fe‐mediated ICAR ATRP of styrene and acrylonitrile in polyethylene glycol

In this contribution, random copolymers of p(styrene‐co‐acrylonitrile) via initiators for continuous activator regeneration (ICAR) in atom transfer radical polymerization (ATRP) (ICAR ATRP) of styrene and acrylonitrile (SAN) were synthesized at 90°C in low molecular weight polyethylene glycol (PEG‐400) using CCl₄ as initiator, FeCl₃·6H₂O as catalyst, succinic acid as ligand and thermal radical initiator azobisisobutyronitrile (AIBN) as thermal free radical initiator. In this system, well‐defined copolymer of SAN was achieved. The kinetics results showed that the copolymerization rate obeyed first‐order kinetics model with respect to the monomer concentration, and a linear increase of the molecular weights with the increasing of monomer conversion with narrow molecular weight distribution was observed in the range of 1.1–1.5. The conversion decreased with increasing the amount of FeCl₃·6H₂O and increased with increasing the molar ratio of [St]₀/[AN]₀/[CCl₄]₀ and temperature. AIBN has a profound effect on the polymerization. The activation energy was 55.67 kJ mol^?1. The living character of copolymerization was confirmed by chain extension experiment. The resultant random copolymer was characterized by ¹H‐NMR and GPC. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40135.