Method to Stop Geopolymer Reaction

The objective of this study was to develop a method to stop geopolymer reaction at early ages so that the molecular structure can be determined and its link to setting behavior probed. Solvent extraction, using a mixture of alcohol and acetone to remove water, was seen to suspend reaction up to at least 53 h, allowing enough time for nuclear magnetic resonance (NMR) tests to determine structure. However, this method caused precipitation of soluble species present at early ages, confounding interpretation of the spectra and thus making it suitable only for mature geopolymers. A combination of water treatment to extract soluble species and solvent treatment to extract water was seen to stop the geopolymer reaction long enough (> 1 week) for NMR tests in specimens with and without calcium.     

Evaluation of the Impact of Esterases and Lipases from the Circulatory System against Substrates of Different Lipophilicity

Esterases and lipases can process amphiphilic esters used as drugs and prodrugs and impact their pharmacokinetics and biodistribution. These hydrolases can also process ester components of drug delivery systems (DDSs), thus triggering DDSs destabilization with premature cargo release. In this study we tested and optimized assays that allowed us to quantify and compare individual esterase contributions to the degradation of substrates of increased lipophilicity and to establish limitations in terms of substrates that can be processed by a specific esterase/lipase. We have studied the impact of carbonic anhydrase; phospholipases A1, A2, C and D; lipoprotein lipase; and standard lipase on the hydrolysis of 4-nitrophenyl acetate, 4-nitrophenyl palmitate, DGGR and POPC liposomes, drawing structure–property relationships. We found that the enzymatic activity of these proteins was highly dependent on the lipophilicity of the substrate used to assess them, as expected. The activity observed for classical esterases was diminished when lipophilicity of the substrate increased, while activity observed for lipases generally increased, following the interfacial activation model, and was highly dependent on the type of lipase and its structure. The assays developed allowed us to determine the most sensitive methods for quantifying enzymatic activity against substrates of particular types and lipophilicity.     

Disrupting the methionine biosynthetic pathway in Candida guilliermondii: characterization of the MET2 gene as counter‐selectable marker

Candida guilliermondii (teleomorph Meyerozyma guilliermondii) is an ascomycetous species belonging to the fungal CTG clade. This yeast remains actively studied as a result of its moderate clinical importance and most of all for its potential uses in biotechnology. The aim of the present study was to establish a convenient transformation system for C. guilliermondii by developing both a methionine auxotroph recipient strain and a functional MET gene as selection marker. We first disrupted the MET2 and MET15 genes encoding homoserine‐O‐acetyltransferase and O‐acetylserine O‐acetylhomoserine sulphydrylase, respectively. The met2 mutant was shown to be a methionine auxotroph in contrast to met15 which was not. Interestingly, met2 and met15 mutants formed brown colonies when cultured on lead‐containing medium, contrary to the wild‐type strain, which develop as white colonies on this medium. The MET2 wild‐type allele was successfully used to transfer a yellow fluorescent protein (YFP) gene‐expressing vector into the met2 recipient strain. In addition, we showed that the loss of the MET2‐containing YFP‐expressing plasmid can be easily observed on lead‐containing medium. The MET2 wild‐type allele, flanked by two short repeated sequences, was then used to disrupt the LYS2 gene (encoding the α‐aminoadipate reductase) in the C. guilliermondii met2 recipient strain. The resulting lys2 mutants displayed, as expected, auxotrophy for lysine. Unfortunately, all our attempts to pop‐out the MET2 marker (following the recombination of the bordering repeat sequences) from a target lys2 locus were unsuccessful using white/brown colony colour screening. Nevertheless, this MET2 transformation/disruption system represents a new versatile genetic tool for C. guilliermondii. Copyright © 2014 John Wiley & Sons, Ltd.     

Hexabromocyclododecanes (HBCDs) in the environment and humans: a review

Hexabromocyclododecanes (HBCDs) are brominated aliphatic cyclic hydrocarbons used as flame retardants in thermal insulation building materials, upholstery textiles, and electronics. As a result of their widespread use and their physical and chemical properties, HBCDs are now ubiquitous contaminants in the environment and humans. This review summarizes HBCD concentrations in several environmental compartments and analyzes these data in terms of point sources versus diffuse sources, biomagnification potential, stereoisomer profiles, time trends, and global distribution. Generally, higher concentrations were measured in samples (air, sediment, and fish) collected near point sources (plants producing or processing HBCDs), while lower concentrations were recorded in samples from locations with no obvious sources of HBCDs. High concentrations were measured in top predators, such as marine mammals and birds of prey (up to 9600 and 19 200 ng/g lipid weight, respectively), suggesting a biomagnification potential for HBCDs. Relatively low HBCD concentrations were reported in the few human studies conducted to date (median values varied between 0.35 and 1.1 ng/g lipid weight). HBCD levels in biota are increasing slowly and seem to reflect the local market demand. One important observation is the shiftfrom the high percentage of the gamma-HBCD stereoisomer in the technical products to a dominance of the alpha-HBCD stereoisomer in biological samples. A combination of factors such as variations in solubility, partitioning behavior, uptake, and, possibly, selective metabolism of individual isomers may explain the observed changes in stereoisomer patterns. Recommendations for further work include research on how HBCDs are transferred from products into the environment upon production, use, and disposal. Time trends need to be analyzed more in detail, including HBCD stereoisomers, and more data on terrestrial organisms are needed, especially for humans. Whenever possible, HBCDs should be analyzed as individual stereoisomers in order to address their fate and effects.     

Development and Characterization of Continuous SiC Fiber‐Reinforced HfB2‐Based UHTC Matrix Composites Using Polymer Impregnation and Slurry Infiltration Techniques

This paper discusses the development of continuous SiC fiber‐reinforced HfB₂‐SiC composite laminates. A range of techniques, based on resin‐based precursors and slurries, for infiltrating porous SiC preforms with HfB₂ powder were developed. While resin‐based precursors proved to be ineffective due to low HfB₂ yield and poor adhesion, the slurry infiltration techniques were effective to varying degrees. The greatest pore filling and composite densities were achieved using pressure and vibration‐assisted pressure infiltration techniques. SiC_f/HfB₂‐SiC laminates were subsequently developed via lamination, cure and pyrolysis of fabrics using a HfB₂‐loaded polymeric SiC precursor, followed by HfB₂ slurry infiltration and preceramic polymer infiltration and pyrolysis (PIP). Repeated PIP processing, for 6–10 cycles, resulted in density increases, from the 3.03–3.22 g/cm³ range after HfB₂ slurry infiltration, to 3.97–4.03 g/cm³ after PIP processing. Correspondingly, there was a decrease in open porosity from approximately 52% to less than 11%. The matrix consisted of discreet, lightly sintered HfB₂ particles dispersed in SiC. The PIP SiC matrix was primarily nanocrystalline after 1300°C pyrolysis, but experienced grain growth with further heat treatment at 1600°C.     

Influence of dietary partially hydrogenated vegetable and marine oils on membrane composition and function of liver microsomes and platelets in the rat

The aim of the present study was to investigate the influence of partially hydrogenated vegetable and marine oils on membrane composition and function of liver microsomes and platelets with particular reference to the metabolism of linoleic acid and the production of arachidonic acid metabolites. Four groups of male weanling rats were fed linoleic acid supplemented diets containing 20% (w/w) of partially hydrogenated low erucic acid rapeseed oil (HLRSO), partially hydrogenated herring oil (HHO), olive oil (OO) and trierucin + triolein (TE) for 10 weeks. An additional two groups were fed partially hydrogenated low erucic acid rapeseed oil and partially hydrogenated herring oil without linoleic acid supplementation (HLRSO- and HHO-, respectively). Substantial amounts oftrans fatty acids were incorporated into liver microsomes (12.6% in group HLRSO) and platelets (7.0% in group HLRSO-). This incorporation was not dependent on the dietary linoleic acid level. Hepatic microsomal Δ⁵-desaturase activity was significantly increased after HLRSO feeding compared to OO feeding. Δ⁶-Desaturase activity did not vary in the linoleic acid supplemented groups. Both Δ⁵- and Δ⁶-desaturase activities were significantly increased in groups without linoleic acid supplementation. Docosenoic acid was incorporated into platelet phospholipids in contrast to liver microsomes. In the platelet, docosenoic acid seemed to have a special preference for phosphatidylserine. Very small amounts were incorporated into platelet phosphatidylinositol. Feeding diets HLRSO, HHO and OO did not influence rat platelet cyclooxygenase or 12-lipoxygenase activity. Platelets from rats fed TE, however, produced significantly less 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) than platelets from rats fed OO. Feeding of HLRSO- and HHO- resulted in a significantly diminished production of the arachidonic acid metabolites 12-HETE, 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 6-keto-prostaglandin F_1α in stimulated platelets and aorta. Thus, high dietary levels oftrans isomers of monoenoic acids do not interfere with platelet cyclooxygenase or lipoxygenase activity provided sufficient amounts of linoleic acid are available.     

Paradoxical effect of n−3-containing vegetable oils on long-chain n−3 fatty acids in rat heart

Flaxseed, echium, and canola oils contain α-linolenic acid (18∶3n−3, ALA) in a range of concentrations. To examine their effect on elevating cardiac levels of long-chain n−3 FA, diets based on these n−3-containing vegetable oils were fed to rats for 4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the three n−3-containing vegetable oils, it was the most potent for elevating DHA (22∶6n−3) levels in rat hearts and plasma. However, the relative potencies of the dietary oils for elevation of EPA (20∶5n−3) in heart and plasma followed the same rank order as their ALA content, i.e., flaxseed>echium>canola>sunflower oil. This paradox may be explained by lower ALA intake leading to decreased competition for Δ6 desaturase activity between ALA and the 24∶5n−3 FA precursor to DHA formation.     

Investigation of polymer and nanoclay orientation distribution in nylon 6/montmorillonite nanocomposite

A method to determine the orientation distribution function of montmorillonite clay in nylon 6 nanocomposite films by a combination of infrared (FTIR) trichroic analysis and transmission electron microscopy (TEM) image analysis is described. The structural absorbance of the nanoclay Si-O vibrations was obtained by the sample tilting method described by Schmidt [Schmidt PG. J Polym Sci: Part A 1963;1:1271-1292]. A nonlinear least squares regression was performed to extract the absorbance of individual peaks. The montmorillonite clay orientation in spun cast nylon 6 films can be described by a Gaussian function having a standard deviation of 15° i.e. 95% of the clay platelets are tilted at an angle of within ±30° of the plane of the film. The transition dipole moment angles of the 1018 and 1046 cm⁻¹ clay vibrations are determined to be 18 and 16° relative to the clay surface, respectively. The orientation of nylon 6 in the nanocomposite was also investigated based on the NH stretching mode. The NH bonds are found to be less preferentially oriented along the plane of the film surface compared to pure nylon 6 film.     

The dynamics of HIV spread: a computer simulation model

Mathematical modeling of the AIDS pandemic has been limited by the difficulty of satisfactorily representing the marked behavioral heterogeneity that characterizes the various populations at risk. We propose an approach which models the spread of infection as a discrete-event simulation using SIMSCRIPT, a powerful simulation language. The program developed provides sufficient flexibility to adequately represent and study a wide range of risk-group dynamics. Using this tool we have verified the May-Anderson prediction relating contact rate heterogeneity to the rate of HIV spread. We have also been able to assess the sensitivity of the model to the particular choice of distribution for contact rates, disease stage durations, and intercontact intervals. It is thought that this approach will permit the empirical testing of hypotheses which do not lend themselves to a purely mathematical treatment.     

Sex- and Genotype-Dependent Nicotine-Induced Behaviors in Adolescent Rats with a Human Polymorphism (rs2304297) in the 3′-UTR of the CHRNA6 Gene

In human adolescents, a single nucleotide polymorphism (SNP), rs2304297, in the 3′-UTR of the nicotinic receptor subunit gene, CHRNA6, has been associated with increased smoking. To study the effects of the human CHRNA6 3′-UTR SNP, our lab generated knock-in rodent lines with either C or G SNP alleles. The objective of this study was to determine if the CHRNA6 3′-UTR SNP is functional in the knock-in rat lines. We hypothesized that the human CHRNA6 3′-UTR SNP knock-in does not impact baseline but enhances nicotine-induced behaviors. For baseline behaviors, rats underwent food self-administration at escalating schedules of reinforcement followed by a locomotor assay and a series of anxiety tests (postnatal day (PN) 25-39). In separate cohorts, adolescent rats underwent 1- or 4-day nicotine pretreatment (2×, 30 μg/kg/0.1 mL, i.v.). After the last nicotine injection (PN 31), animals were assessed behaviorally in an open-field chamber, and brain tissue was collected. We show the human CHRNA6 3′-UTR SNP knock-in does not affect food reinforcement, locomotor activity, or anxiety. Further, 4-day, but not 1-day, nicotine exposure enhances locomotion and anxiolytic behavior in a genotype- and sex-specific manner. These findings demonstrate that the human CHRNA6 3′-UTR SNP is functional in our in vivo model.