Bioaccumulation, biotransformation, and biochemical effects of brominated diphenyl ethers in juvenile lake trout (Salvelinus namaycush)

Juvenile lake trout (Salvelinus namaycush) were exposed to three dietary concentrations (0, approximately 2.5, and approximately 25 ng/g per BDE congener) of 13 BDE congeners (3-10 Br atoms) in the laboratory for 56 days, followed by 112 days of clean food, to examine bioaccumulation parameters and potential biochemical effects. The bioaccumulation of BDEs by the trout was highly influenced by biotransformation, via debromination, which resulted in bioaccumulation parameters that were much different than would be expected based on studies of chlorinated organic compounds (e.g., PCBs). Half-lives (t1/2's) for some BDE congeners (e.g., BDE-85 and -190) were much lower than expected based on their Kow, which was likely due to biotransformation, whereas t1/2's of other BDE congeners (e.g., BDE-66, -77, -153, and -154) were much longer than anticipated based on Kow. This was likely because the metabolites of BDE formed via debromination had the same chemical structure of these BDE congeners, which supplemented measured concentrations. The detection of three BDE congeners (an unknown penta, BDE-140, and an unknown hexa) in the fish that were not present in the food or in the control fish provide further evidence forthe debromination of BDEs. Half-lives of BDEs ranged from 38 +/- 9 to 346 +/- 173 days and biomagnification factors ranged from 1.6 (BDE-190) to 45.9 (BDE-100), but these bioaccumulation parameters need to be viewed with caution because they were highly influenced by debromination and relative abundance of individual BDEs that the fish were exposed to. CYP1A enzyme activity, measured as EROD, and free tri-iodothyronine (T3) concentrations in the plasma of lake trout varied significantly throughout the experiment but were not related to BDE exposure. In contrast, plasma levels of thyroxine levels (T4) were lower in both groups of PBDE-exposed fish compared with control fish after 56 days of exposure, and after 168 days in the high dose, suggesting that PBDEs may influence thyroid homeostasis at levels that are higher than what is normally found in the environment.     

Transformations for early reply and forward message passing mechanisms

Message passing notations (language, package, etc.) typically include some form of asynchronous or synchronous invocation. In a synchronous invocation, the invoker waits for the invocation's servicer to pass back results. Some message passing notations also include early reply or deferred reply (including forwarding), which alters how and when the servicer passes back its results; this additional flexibility is useful in realistic applications. It is well known how to transform a synchronous invocation into only asynchronous invocations. This paper extends such transformations to early reply and forward. This paper also describes the use of these transformations within the implementations of programming notations. Using the transformation simplifies the implementation without significantly affecting run‐time costs. Copyright © 2015 John Wiley & Sons, Ltd.     

Biophysical Modulation of Mesenchymal Stem Cell Differentiation in the Context of Skeletal Repair

A prominent feature of the skeleton is its ability to remodel in response to biophysical stimuli and to repair under varied biophysical conditions. This allows the skeleton considerable adaptation to meet its physiological roles of stability and movement. Skeletal cells and their mesenchymal precursors exist in a native environment rich with biophysical signals, and they sense and respond to those signals to meet organismal demands of the skeleton. While mechanical strain is the most recognized of the skeletal biophysical stimuli, signaling phenomena also include fluid flow, hydrostatic pressure, shear stress, and ion-movement-related electrokinetic phenomena including, prominently, streaming potentials. Because of the complex interactions of these electromechanical signals, it is difficult to isolate the significance of each. The application of external electrical and electromagnetic fields allows an exploration of the effects of these stimuli on cell differentiation and extra-cellular matrix formation in the absence of mechanical strain. This review takes a distinctly translational approach to mechanistic and preclinical studies of differentiation and skeletal lineage commitment of mesenchymal cells under biophysical stimulation. In vitro studies facilitate the examination of isolated cellular responses while in vivo studies permit the observation of cell differentiation and extracellular matrix synthesis.     

A lysine to arginine substitution at position 146 of rabbit aldolase A changes the rate-determining step to Schiff base formation

Lys146 of rabbit aldolase A [D-fructose-1,6-bis(phosphate):D-glyceraldehyde-3-phosphate lyase, EC 4.1.2.13 [EC] ] was changedto arginine by site-directed mutagenesis. The k_cat of the resultingmutant protein, K146R, was 500 times slower than wild-type insteady-state kinetic assays for both cleavage and condensationof fructose-1,6-bis(phosphate), while the Km for this substratewas unchanged. Analysis of the rate of formation of catalyticintermediates showed K146R was significantly different fromthe wild-type enzyme and other enzymes mutated at this site.Single-turnover experiments using acid precipitation to trapthe Schiff base intermediate on the wild-type enzyme failedto show a build-up of this intermediate on K146R. However, K146Rretained the ability to form the Schiff base intermediate asshown by the significant amounts of Schiff base intermediatetrapped with NaBH₄. In the single-turnover experiments it appearedthat the Schiff base intermediate was converted to productsmore rapidly than it was produced. This suggested a maximalrate of Schiff base formation of 0.022 s^–1, which wasclose to the value of k_cat for this enzyme. This observationis strikingly different from the wild-type enzyme in which Schiffbase formation is >100 times faster than k_cat. For K146Rit appears that steps up to and including Schiff base formationare rate limiting for the catalytic reaction. The carbanionintermediate derived from either substrate or product, and theequilibrium concentrations of covalent enzyme-substrate intermediates,were much lower on K146R than on the wild-type enzyme. The greaterbulk of the guanidino moiety may destabilize the covalent enzyme-substrateintermediates, thereby slowing the rate of Schiff base formationsuch that it becomes rate limiting. The K146R mutant enzymeis significantly more active than other enzymes mutated at thissite, perhaps because it maintains a positively charged groupat an essential position in the active site or perhaps the Argfunctionally substitutes as a general acid/base catalyst inboth Schiff base formation and in subsequent abstraction ofthe C4-hydroxyl proton.     

New intramolecular effect observed for polyesters: An anomeric effect

A series of polyesters was prepared to evaluate hydrolytic stability as a function of cyclohexyl dibasic acid content. The three cyclohexyl dibasic acids: 1,2; 1,3; and 1,4 were formulated into polyesters with two glycols. The proportion of cis and trans isomers was evaluated via ¹H NMR. The hydrolytic stability of short chain polyesters was evaluated in an acetone/water mixture which solubilized the polyesters to mimic oligoester behavior within a thermosetting polyester coating environment. The rate of hydrolysis was monitored by acid titration and corroborated by GPC. Surprisingly, 1,2-cylohexyl diacid-based polyesters were robust, and 1,3-cyclohexyl diacid-based polyesters were the most susceptible to hydrolysis. Evidently, a 1,2-anchimeric effect for cyclohexyl dibasic acid polyesters was not an important consideration, while the 1,3-cyclohexyl ester interaction was. Consequently, an anomeric effect was proposed. Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia, PA.     

Kinetic study of crude oil-to-chemicals via steam-enhanced catalytic cracking in a fixed-bed reactor

This study presents new experimental results on the direct conversion of crude oil to chemicals via steam-enhanced catalytic cracking. We have organized the experimental results with a kinetics model using crude oil and steam co-feed in a fixed-bed flow reactor at reaction temperatures of 625, 650, and 675°C over the Ce-Fe/ZSM-5 catalyst. The model let us find optimum conditions for crude oil conversion, and the order of the steam cracking reaction was 2.0 for heavy oil fractions and 1.0 for light oil fractions. The estimated activation energies for the steam cracking reactions ranged between 20 and 200 kJ/mol. Interestingly, the results from kinetic modelling helped in identifying a maximum yield of light olefins at an optimized residence time in the reactor at each temperature level. An equal propylene and ethylene yield was observed between 650 and 670°C, indicating a transition from dominating catalytic cracking at a lower temperature to a dominating thermal cracking at a higher temperature. The results illustrate that steam-enhanced catalytic cracking can be utilized to effectively convert crude oil into basic chemicals (52.1% C2-C4 light olefins and naphtha) at a moderate severity (650°C) as compared to the conventional high-temperature steam cracking process.     

Use of Numerical Calculations to Simulate the Sampling Efficiency Performance of a Personal Aerosol Sampler

Numerical calculations were conducted to simulate air and particle behavior near and into the inlet of an aerosol sampler in order to determine sampling efficiency performance. This was done with the pre-verified commercial computational fluid dynamics (CFD) software package, FLUENT (Fluent, Inc., Lebanon, NH, US). Air flow behavior was calculated for steady-state conditions approaching and flowing into 3D geometries of an aerosol sampler free in the air that was similar in dimension to two commercial samplers, namely the Gesamtstaubprobenahme sampler (GSP) and the conical inhalable sampler (CIS). Particle trajectories were calculated in a Lagrangian reference frame on the resulting velocity fields. Based on the particle trajectories, sampling efficiencies were calculated and compared to those reported in the literature for a CIS aerosol sampler. They were found to have similar overall trends for particle sizes up to 21 μ m. Using a correction factor, agreement was observed to be very good for smaller particles, but less so for larger particles.