A comprehensive study of the loss of enzyme activity in a continuous membrane reactor – application to starch hydrolysis

Loss of enzyme activity is a problem associated with enzymatic reactions in continuous recycled membrane reactors (CRMR). It may result from catalyst leakage and also enzyme denaturation due to the effects of pH, temperature, shear effects or adsorption/deposit on membrane. In this study, the relative importance of these various factors has been assessed in order to reduce their adverse effects on starch hydrolysis in a CRMR. The effects of temperature and denaturation by adsorption/deposit on membrane were the most limiting phenomena. Reducing the temperature to overcome thermal denaturation was not a practical solution since this increases viscosity and thereby decreases permeate flux and reactor performance. Insofar that adsorption/deposit of enzymes on the membrane is directly linked to membrane fouling, back‐flushing or regularly purging retentate should reduce this phenomenon by lowering accumulation of high molecular weight products. © 2001 Society of Chemical Industry     

Wall slip heating

When molten plastic is extruded, the upper limiting throughput is often dictated by fine irregular distortions of the extrudate surface. Called sharkskin melt fracture, plastics engineers spike plastics formulations with processing aids to suppress these distortions. Sharkskin melt fracture is not to be confused with gross melt fracture, a larger scale distortion arising at throughputs higher than the critical throughput for sharkskin melt fracture. Sharkskin melt fracture has been attributed to a breakdown of the no slip boundary condition in the extrusion die, that is, adhesive failure at the die walls, where the fluid moves with respect to the wall. In this article, we account for the frictional heating at the wall, which we call slip heating. We focus on slit flow, which is used in film casting, sheet extrusion, curtain coating, and when curvature can be neglected, slit flow is easily extended to pipe extrusion and film blowing. In slit flow, the magnitude of the heat flux from the slipping interface is the product of the shear stress and the slip speed. We present the solutions for the temperature rise in pressure‐driven slit flow and simple shearing flow, each subject to constant heat generation at the adhesive slip interface, with and without viscous dissipation in the bulk fluid. We solve the energy equation in Cartesian coordinates for the temperature rise, for steady temperature profiles. For this simplest relevant nonisothermal model, we neglect convective heat transfer in the melt and use a constant viscosity. We arrive at a necessary dimensionless condition for the accurate use of our results: Pé?1. We find that slip heating can raise the melt temperature significantly, as can viscous dissipation in the bulk. We conclude with two worked examples showing the relevance of slip heating in determining wall temperature rise, and we show how to correct wall slip data for this temperature rise. POLYM. ENG. SCI., 55:2042–2049, 2015. © 2014 Society of Plastics Engineers     

Dichlorophenylacrylonitriles as AhR Ligands That Display Selective Breast Cancer Cytotoxicity in vitro

Knoevenagel condensation of 3,4‐dichloro‐ and 2,6‐dichlorophenylacetonitriles gave a library of dichlorophenylacrylonitriles. Our leads (Z)‐2‐(3,4‐dichlorophenyl)‐3‐(1H‐pyrrol‐2‐yl)acrylonitrile ( 5 ) and (Z)‐2‐(3,4‐dichlorophenyl)‐3‐(4‐nitrophenyl)acrylonitrile ( 6 ) displayed 0.56±0.03 and 0.127±0.04 μm growth inhibition (GI₅₀) and 260‐fold selectivity for the MCF‐7 breast cancer cell line. A 2,6‐dichlorophenyl moiety saw a 10‐fold decrease in potency; additional nitrogen moieties (‐NO₂) enhanced activity (Z)‐2‐(2,6‐dichloro‐3‐nitrophenyl)‐3‐(2‐nitrophenyl)acrylonitrile ( 26 ) and (Z)‐2‐(2,6‐dichloro‐3‐nitrophenyl)‐3‐(3‐nitrophenyl)acrylonitrile ( 27 ), with the corresponding ‐NH₂ analogues (Z)‐2‐(3‐amino‐2,6‐dichlorophenyl)‐3‐(2‐aminophenyl)acrylonitrile ( 29 ) and (Z)‐2‐(3‐amino‐2,6‐dichlorophenyl)‐3‐(3‐aminophenyl)acrylonitrile ( 30 ) being more potent. Despite this, both 29 (2.8±0.03 μm ) and 30 (2.8±0.03 μm ) were found to be 10‐fold less cytotoxic than 6 . A bromine moiety effected a 3‐fold enhancement in solubility with (Z)‐3‐(5‐bromo‐1H‐pyrrol‐2‐yl)‐2‐(3,4‐dichlorophenyl)acrylonitrile 18 relative to 5 at 211 μg mL^?1. Modeling‐guided synthesis saw the introduction of 4‐aminophenyl substituents (Z)‐3‐(4‐aminophenyl)‐2‐(3,4‐dichlorophenyl)acrylonitrile ( 35 ) and (Z)‐N‐(4‐(2‐cyano‐2‐(3,4‐dichlorophenyl)vinyl)phenyl)acetamide ( 38 ), with respective GI₅₀ values of 0.030±0.014 and 0.034±0.01 μm . Other analogues such as 35 and 36 were found to have sub‐micromolar potency against our panel of cancer cell lines (HT29, colon; U87 and SJ‐G2, glioblastoma; A2780, ovarian; H460, lung; A431, skin; Du145, prostate; BE2‐C, neuroblastoma; MIA, pancreas; and SMA, murine glioblastoma), except compound 38 against the U87 cell line. A more extensive evaluation of 38 ((Z)‐N‐(4‐(2‐cyano‐2‐(3,4‐dichlorophenyl)vinyl)phenyl)acetamide) in a panel of drug‐resistant breast carcinoma cell lines showed 10–206 nm potency against MDAMB468, T47D, ZR‐75‐1, SKBR3, and BT474. Molecular Operating Environment docking scores showed a good correlation between predicted binding efficiencies and observed MCF‐7 cytotoxicity. This supports the use of this model in the development of breast‐cancer‐specific drugs.     

Design, synthesis and biological evaluation of Trypanosoma brucei trypanothione synthetase inhibitors

Trypanothione synthetase (TryS) is essential for the survival of the protozoan parasite Trypanosoma brucei, which causes human African trypanosomiasis. It is one of only a handful of chemically validated targets for T. brucei in vivo. To identify novel inhibitors of TbTryS we screened our in-house diverse compound library that contains 62,000 compounds. This resulted in the identification of six novel hit series of TbTryS inhibitors. Herein we describe the SAR exploration of these hit series, which gave rise to one common series with potency against the enzyme target. Cellular studies on these inhibitors confirmed on-target activity, and the compounds have proven to be very useful tools for further study of the trypanothione pathway in kinetoplastids.     

Enzymatic degradation of polyacrylamide in aqueous solution with peroxidase and H2O2

Polyacrylamides are often used in water‐based hydraulic fracturing for natural gas and oil production. However, residual polymer remaining in the fractured rock can limit production. A novel approach for degrading partially hydrolyzed polyacrylamide (HPAM) was investigated using hydrogen peroxide and horseradish peroxidase (HRP). This sustainable HRP/H₂O₂ system degraded the polymer in solution, reducing its viscosity in both pure water and brine solutions. Molecular weight measurements confirmed that the viscosity reduction was due to a significant degradation of the polymer backbone and not primarily by other mechanisms such as amide hydrolysis or rearrangement, and so forth. The reduction in viscosity and molecular weight was first order with respect to H₂O₂ concentration. The kinetics of viscosity reduction and molecular weight are closely correlated which would allow the quicker and simpler viscosity method to help engineer future processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44560.     

Quasi-spherical focal spot in two-photon scanning microscopy by three-ring apodization

We present a beam-shaping technique for two-photon excitation (TPE) fluorescence microscopy. We show that by inserting a properly designed three-ring pupil filter in the illumination beam of the microscope, the effective optical sectioning capacity of such a system improves so that the point spread function gets a quasi-spherical shape. Such an improvement, which allows the acquisition of 3D images with isotropic quality, is obtained at the expense of only a small increase of the overall energy in the axial sidelobes. The performance of this technique is illustrated with a scanning TPE microscopy experiment in which the image of small beads is obtained. We demonstrate an effective narrowing of 12.5% in the axial extent of the point spread function, while keeping the 82% of the spot-fluorescence efficiency.     

Thermal stability of morpholine additive in the steam-water cycle of CANDU-PHW nuclear power plants

The thermal decomposition of morpholine, an additive used in the steam-water cycles of nuclear power plants, was studied using a laboratory high-pressure reactor. The measured decomposition rate constants are 2.67, 8.73 and 21.25 × 10^?7 s^?1 at 260, 280 and 300°C respectively. The kinetics were found to be first-order and the activation energy was 131.9 kJ/mol. Ammonia, ethanolamine, 2-(2-aminoethoxy) ethanol, methylamine, ethylamine, ethylene glycol, and acetic and glycolic acids were identified as the major breakdown products. The decomposition route proposed was validated in the field by tracking these breakdown products in water samples taken at Gentilly 2 power plant.     

Sintering of Industrial Mullites in the Presence of Magnesia as a Sintering Aid

The sinterability of two industrial mullite powders, in the presence of MgO as a sintering aid, was investigated. A glassy phase, which was generated during preparation, was present in both powders; this glassy phase had a strong influence on sintering, depending on its content, composition, and spatial distribution. MgO promoted sintering in the presence of a liquid phase, both in the as-received materials and in samples washed with HF, in which most of the pre-existing glassy phase was eliminated. Investigations using transmission electron microscopy, coupled with energy-dispersive spectroscopy, as well as dilatometric measurements and X-ray diffraction data, on washed and unwashed materials and on quenched and slow-cooled samples allowed a better understanding of the influence of MgO and the glassy phase on the sintering behavior and the formation of new phases. Most of the phases, in fact, can be explained by using the MgO–Al₂O₃–SiO₂ phase diagram, even in such complex systems.