Theory of asymmetric organocatalysis of Aldol and related reactions: rationalizations and predictions

Computational studies have led to models to understand some classic and contemporary asymmetric reactions involving organocatalysts. The Hajos-Parrish-Eder-Sauer-Wiechert reaction and intermolecular aldol reactions as well as Mannich reactions and oxyaminations catalyzed by proline and other amino acids, and Diels-Alder reactions catalyzed by MacMillan's chiral amine organocatalysts have been studied with density functional theory. Quantitative predictions for several new catalysts and reactions are provided.     

The effect of aluminum alkyls and BHT‐H on reaction kinetics of silica supported metallocenes and polymer properties in slurry phase ethylene polymerization

In slurry and gas phase catalytic ethylene polymerization processes, aluminum alkyl (AlR₃) compounds are usually present inside the reactor and their role either as co‐catalyst or scavenger is of considerable importance. Silica supported metallocene/methyl aluminoxane (MAO) catalysts show specific interactions with AlR₃ compounds. Therefore, this study shows an attempt to analyze and compare the effect of concentration as well as type of commonly used AlR₃ on slurry phase ethylene homopolymerization kinetics of silica supported (n‐BuCp)₂ZrCl₂/MAO catalyst. The obtained results indicate that the lower the concentration of smaller AlR₃ compounds, the higher the instantaneous catalytic activity. Concerning the polymer particle size distributions, a rise in fines generation has been observed with increasing AlR₃ content inside the reactor. Finally, it has been shown that the addition of 2,6‐di‐tert‐butyl‐4‐methylphenol (a substituted phenol) into the reactor containing AlR₃ reduces the influence of AlR₃ compounds on the reaction kinetics of silica supported metallocene/MAO catalysts. Polyethylene properties remain similar in all the studied scenarios. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45670.     

Construction of microbial cell factories for industrial bioprocesses

The development of industrial microbial processes is gaining unprecedented momentum. Increased concern for environmental issues and the prospect of declining petroleum resources has shifted the industrial focus increasingly to microorganisms as biocatalysts. At the same time systems biology and synthetic biology supply industry and academia with new tools to design optimal microbial cell factories. Among the tools are systems biology approaches allowing the modelling of cellular networks for rational strain design, single cell analyses methods for gaining insight into population hetereogeneity, and an exciting combination of tools from structural biology and synthetic biology, permitting the catalysis of new (unnatural) enzymatic reactions or the production of new (unnatural) chemicals. This perspective article outlines recent advances and new developments within the field of microbial cell factory design. Copyright © 2012 Society of Chemical Industry     

Experimental proof of the existence of mass‐transfer resistance during early stages of ethylene polymerization with silica supported metallocene/MAO catalysts

The size of a silica supported metallocene/MAO (methylaluminoxane) catalyst plays an important role in determining its productivity during ethylene polymerization. From a chemical engineering point of view, this size dependency of catalytic activity of supported metallocenes is mathematically connected with the different levels of mass‐transfer resistance in big and small catalyst particles but no experimental evidence has been provided to date. The results of this systematic experimental study clearly demonstrate that the intraparticle monomer diffusion resistance is high in bigger catalyst particles during initial instants of ethylene polymerization and diminishes with the polymer particle growth. Two different silica supported metallocene/MAO catalysts provided the same results while highlighting the fact that catalyst chemistry should be carefully considered while studying complex chemical engineering problems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4476–4490, 2017     

Two‐dimensional modeling of an absorbing falling film in its development zone

This work presents the modeling of a vertical falling film expanding or shrinking from the inlet manifold. Considering a stationary approach, the film shape, the flow field and the absorption rate of an ambient gas are computed. For the flow field, one dimensional (1‐D) second‐order weighted integral boundary layer (WIBL) model is shown to accurately reproduce the film deformations. The gas transfer is then solved in a 2‐D predeformed domain to investigate the impact of the film deformations on the gas absorption rate. It is found that a significant mass transfer enhancement, as compared to a flat film, is obtained when the film is expanding due to the concomitant increase of the concentration gradient perpendicular to the interface. On the contrary, a slight hindrance of the mass transfer is observed when the film is shrinking, although it remains in this case very close to the flat film analytical solution. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4370–4378, 2017     

Evaluation of Simple and Inexpensive High-Throughput Methods for Phytic Acid Determination

High‐throughput/low‐cost/low‐tech methods for phytic acid determination that are sufficiently accurate and reproducible would be of value in plant genetics, crop breeding and in the food and feed industries. Variants of two candidate methods, those described by Vaintraub and Lapteva (Anal Biochem 175:227–24, 1988 ; “VL” methods) and Huang and Lantzsch (J Sci Food Agric 34:1423–1426, 1983 ; “HL” methods), were evaluated. The primary concern with these methods is that, due to interference of matrix constituents including inorganic P, they can overestimate phytic acid and are ineffective at low levels of phytic acid. Twelve seed flours, representing lines of soybean, maize, barley and dry bean, containing a wide range of phytic acid levels, were analyzed by a minimum of eight cooperating laboratories using three variants of the VL method and two variants of the HL method. No method had consistently acceptable (?2.0”) “Horwitz ratios”, a measure of reproducibility, although some treatments approached that. For example, one variant of the VL method when used to assay a soybean flour with a “standard” level of phytic acid had a Horwitz ratio of 2.15. Some variants of the VL method were adequate for analyses of cereal grains regardless of phytic acid level but none accurately measured phytic acid when at low levels in soybean flours. One variant of the HL method in which the 0.2 N HCl extraction media is modified to contain 10% Na₂SO₄, did accurately measure phytic acid levels in both cereal and legume flours regardless of endogenous phytic acid levels or matrix constituents.     

Effects of urban coarse particles inhalation on oxidative and inflammatory parameters in the mouse lung and colon

Background

Air pollution is a recognized aggravating factor for pulmonary diseases and has notably deleterious effects on asthma, bronchitis and pneumonia. Recent studies suggest that air pollution may also cause adverse effects in the gastrointestinal tract. Accumulating experimental evidence shows that immune responses in the pulmonary and intestinal mucosae are closely interrelated, and that gut-lung crosstalk controls pathophysiological processes such as responses to cigarette smoke and influenza virus infection. Our first aim was to collect urban coarse particulate matter (PM) and to characterize them for elemental content, gastric bioaccessibility, and oxidative potential; our second aim was to determine the short-term effects of urban coarse PM inhalation on pulmonary and colonic mucosae in mice, and to test the hypothesis that the well-known antioxidant N-acetyl-L-cysteine (NAC) reverses the effects of PM inhalation.

Results

The collected PM had classical features of urban particles and possessed oxidative potential partly attributable to their metal fraction. Bioaccessibility study confirmed the high solubility of some metals at the gastric level. Male mice were exposed to urban coarse PM in a ventilated inhalation chamber for 15 days at a concentration relevant to episodic elevation peak of air pollution. Coarse PM inhalation induced systemic oxidative stress, recruited immune cells to the lung, and increased cytokine levels in the lung and colon. Concomitant oral administration of NAC reversed all the observed effects relative to the inhalation of coarse PM.

Conclusions

Coarse PM-induced low-grade inflammation in the lung and colon is mediated by oxidative stress and deserves more investigation as potentiating factor for inflammatory diseases.

     

Strain-based anisotropic damage modelling and unilateral effects

A new continuum damage mechanics model is developed to describe the behaviour of quasi-brittle materials under general path loading. The induced damage is represented by a second rank symmetric tensor. The constitutive equations are based on irreversible thermodynamics theory. The strain-based model covers in an unified way the unsymmetrical behaviour in tension and in compression and the unilateral response due to crack closure effect. Uniaxial stress tests (in tension as in compression) show realistic non-linear responses in the stress–strain space. The different behaviour in both domains is covered by a single set of equations. A significant volume dilatation is noticed in compression. The model can be generalised to time-dependent phenomena.