Catalytic olefin polymerisation at short times: Studies using specially adapted reactors

Despite the fact that the very early stages (several tens of seconds) of catalysed olefin polymerisation processes appear negligibly short with respect to the residence time of most industrial reactors, they are critical in terms of catalyst activation, obtaining good particle morphology, and avoiding irreparable problems caused by particle overheating. The different types of reactors that have been used over the course of the past few years are discussed in this feature article. It is shown that despite the difficulties encountered in finding the perfect experimental tool for this purpose, different configurations of stopped flow reactors can be used successfully to explore different aspects of what happens to the catalyst (supported and molecular) during these critical moments of polymerisation. © 2012 Canadian Society for Chemical Engineering     

Inhibition of Human α‐Methylacyl CoA Racemase (AMACR): a Target for Prostate Cancer

The enzyme α‐methylacyl CoA racemase (AMACR) is involved in the metabolism of branched‐chain fatty acids and has been identified as a promising therapeutic target for prostate cancer. By using the recently available human AMACR from HEK293 kidney cell cultures, we tested a series of new rationally designed inhibitors to determine the structural requirements in the acyl component. An N‐methylthiocarbamate (K_i=98 nM ), designed to mimic the proposed enzyme‐bound enolate, was found to be the most potent AMACR inhibitor reported to date.     

High‐solid‐content emulsions. V. Applications of miniemulsions to high solids and viscosity control

The use of miniemulsions of styrene and butyl acrylate to make high‐solid‐content, low‐viscosity latices was investigated. Products were obtained with solid concentrations greater than 70 wt % and viscosities as low as 350 mPa s at shear rates of 20 s^?1. This was possible with monomodal and bimodal latices. In addition, the compartmentalization of the reactive species in the miniemulsion systems was exploited to produce latices with high solid concentrations, low viscosities, and bimodal molecular weight distributions. This demonstrated a potentially interesting application for this sort of material. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 745–752, 2005     

Characterization of products from fast and isothermal hydrothermal liquefaction of microalgae

We investigated nonisothermal (fast) and nominally isothermal hydrothermal liquefaction (HTL) of Nannochloropsis sp. microalgae for the production of biocrude. Biocrude yields ranged from 36 to 45 wt % (dry weight), with fast HTL with low mass loading giving the highest yield. This condition also gave the biocrude with the lowest heating value, which indicates there are compromises to be made between biocrude quantity and quality. The aqueous phase and biocrude product fractions were characterized using elemental analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). This detailed level of analysis identified more than 30,000 unique molecular products. The aqueous phase products included compounds with the same molecular formulae as known herbicides, which may inform efforts in genetic engineering of algae and/or bacteria for cultivation on the aqueous phase. This detailed molecular‐level characterization provides some clues regarding the types of reactions that may take place during HTL. © 2016 American Institute of Chemical Engineers AIChE J, 62: 815–828, 2016     

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.     

Structure–Activity Relationships of Benzenesulfonamide‐Based Inhibitors towards Carbonic Anhydrase Isoform Specificity

Carbonic anhydrases (CAs) are implicated in a wide range of diseases, including the upregulation of isoforms CA IX and XII in many aggressive cancers. However, effective inhibition of disease‐implicated CAs should minimally affect the ubiquitously expressed isoforms, including CA I and II, to improve directed distribution of the inhibitors to the cancer‐associated isoforms and reduce side effects. Four benzenesulfonamide‐based inhibitors were synthesized by using the tail approach and displayed nanomolar affinities for several CA isoforms. The crystal structures of the inhibitors bound to a CA IX mimic and CA II are presented. Further in silico modeling was performed with the inhibitors docked into CA I and XII to identify residues that contributed to or hindered their binding interactions. These structural studies demonstrated that active‐site residues lining the hydrophobic pocket, especially positions 92 and 131, dictate the positional binding and affinity of inhibitors, whereas the tail groups modulate CA isoform specificity. Geometry optimizations were performed on each ligand in the crystal structures and showed that the energetic penalties of the inhibitor conformations were negligible compared to the gains from active‐site interactions. These studies further our understanding of obtaining isoform specificity when designing small molecule CA inhibitors.     

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     

Thermal pressure coefficient of a polyhedral oligomeric silsesquioxane (POSS)‐reinforced epoxy resin

The thermal pressure coefficients of a neat, unfilled, epoxy resin and a 10 wt % POSS (polyhedral oligomeric silsesquioxane)‐filled epoxy nanocomposite have been measured using a thick‐walled tube method. It is found that just below the glass transition temperature the thermal pressure coefficient is ～ 20% smaller for the polymer composite containing 10% POSS than for the neat, unfilled resin. The thermal expansion coefficient and thermal pressure coefficient of the uncured POSS itself are also reported. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Early observations on an emerging Great Lakes invader Hemimysis anomala in Lake Ontario

Hemimysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, Hemimysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of Hemimysis in the Great Lakes is scarce, the potential for food web disruption by Hemimysis cannot easily be predicted. Preliminary observations indicate widespread invasion of Hemimysis in Lake Ontario. In this study, we confirm the presence of Hemimysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0 mm and an average caloric density of 611 cal/g wet weight. The most effective methods for sampling Hemimysis were horizontal tows with either a zooplankton net in the water column or a benthic sled near the lake bottom. Although more quantitative data on the life history and distribution of this species is necessary, our preliminary observations support the prediction that the potential for Hemimysis to impact the nearshore food web in Lake Ontario appears high.     

Spatial and temporal variation in distribution of larval lake whitefish in eastern Lake Ontario: Signs of recovery?

The lake whitefish (Coregonus clupeaformis) is one of the native Lake Ontario fishes that declined severely over the past century. Recent evidence of larval lake whitefish production in a historic spawning area (Chaumont Bay) might signal a recovery of this species in New York waters. We surveyed coastal and open water areas to evaluate densities and estimate total abundance of larval lake whitefish in Chaumont Bay. Other historic spawning areas and embayments with appropriate spawning and nursery habitat were also surveyed, but only a few larvae were found outside of Chaumont Bay. Lake whitefish larvae were found in every embayment sampled within Chaumont Bay, with larval densities of nearly 600/1000 m² in some samples. Greatest abundances occurred in the northern sectors and near the mouth of the bay. Open water densities were generally less than half that of nearshore sites. The total bay-wide estimate for 2005 was approximately 644,000 lake whitefish larvae, but dropped to 230,000–400,000 in 2006 and 2007, respectively. Mean larval growth rates (0.36 mm/day) did not differ by year, but were consistently higher in early May than in late April. Lake whitefish production in Chaumont Bay is encouraging for this species, but the cause and persistence of the decline after 2005 can be determined only by continued monitoring. Other possible bottlenecks of survival may exist at juvenile and adult stages and could significantly affect recruitment dynamics. This species is sensitive to normal climatic fluctuations and increased variability associated with global climatic change could make winter nursery conditions unfavorable for this species.