Modeling the evolution of the dynamic mechanical properties of a commercial epoxy during cure after gelation

The cure kinetics for a commercial epoxy have been established and the influence of the degree of cure on the glass transition determined. Time‐temperature and time‐conversion superposition principles have been built into a model that successfully predicts the development of the viscoelastic properties of the epoxy during isothermal cure from gelation to after vitrification. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 495–508, 2000     

Electrokinetic remediation of metals and organics from historically contaminated soil

The electrokinetic remediation of an historically contaminated soil is described. The soil was contaminated with a range of metals including lead, zinc, manganese, copper and arsenic, polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene (BTEX). A small‐scale experiment (973.2 g dry weight soil), utilising a planar electrode configuration, investigated the potential for moving metals and organics. After 23 days treatment at a current density of 3.72 A /m⁻², 44% of calcium and 29% of manganese were removed from the soil at the cathode. Of the other contaminating metals, zinc and lead moved towards the cathode, but with no significant removal from the soil. Movement of PAHs was also observed, with a 94% reduction in concentration in the third of the soil closest to the anode after 23 days. A larger scale experiment (46.7 kg dry weight soil) utilised a hexagonal array of tubular anodes surrounding a central tubular cathode. Treatment for 112 days led to acidification of the soil to pH 2.59 closest to the anode in a direct line between the anode and cathode. Soil not directly in line between the electrodes was not acidified significantly. Movement of metal ions was observed, in line with the electrodes, with concentrations of lead and arsenic increasing to 162% and 171% of starting concentrations closest to the anode, respectively, and those of zinc, copper and manganese decreasing to 42%, 68% and 57%, respectively. At positions not directly in line with the electrodes, no significant metal movements were observed. Overall, there was no significant removal of contaminating metals from the soil. PAHs and BTEX compounds were moved by electroosmosis towards the cathode, with soil concentrations of PAHs reduced from 720 mgkg⁻¹ to 4.7 mgkg⁻¹ after 22 days. PAHS (28 mg) and benzene (9660 mg) were recovered in granular activated carbon (GAC) columns. © 2000 Society of Chemical Industry     

Poly(dimethylsiloxane)/poly(hexamethylene oxide) mixed macrodiol based polyurethane elastomers. I. Synthesis and properties

The compatibilizing effect of poly(hexamethylene oxide) (PHMO) on the synthesis of polyurethanes based on α,ω‐bis(6‐hydroxyethoxypropyl) poly(dimethylsiloxane) (PDMS) was investigated. The hard segments of the polyurethanes were based on 4,4′‐methylenediphenyl diisocyanate (MDI) and 1,4‐butanediol. The effects of the PDMS/PHMO composition, method of polyurethane synthesis, hard segment weight percentage, catalyst, and molecular weight of the PDMS on polyurethane synthesis, properties, and morphology were investigated using size exclusion chromatography, tensile testing, and differential scanning calorimetry (DSC). The large difference in the solubility parameters between PDMS and conventional reagents used in polyurethane synthesis was found to be the main problem associated with preparing PDMS‐based polyurethanes with good mechanical properties. Incorporation of a polyether macrodiol such as PHMO improved the compatibility and yielded polyurethanes with significantly improved mechanical properties and processability. The optimum PDMS/PHMO composition was 80 : 20 (w/w), which yielded a polyurethane with properties comparable to those of the commercial material Pellethane™ 2363‐80A. The one‐step polymerization was sensitive to the hard segment weight percentage of the polyurethane and was limited to materials with about a 40 wt % hard segment; higher concentrations yielded materials with poor mechanical properties. A catalyst was essential for the one‐step process and tetracoordinated tin catalysts (e.g., dibutyltin dilaurate) were the most effective. Two‐step bulk polymerization overcame most of the problems associated with reactant immiscibility by the end capping of the macrodiol and required no catalysts. The DSC results demonstrated that in cases where poor properties were observed, the corresponding polyurethanes were highly phase separated and the hard segments formed were generally longer than the average expected length based on the reactant stoichiometry. Based on these results, we postulated that at low levels (∼ 20 wt %) the soft segment component derived from PHMO macrodiol was concentrated mainly in the interfacial regions, strengthening the adhesion between hard and soft domains of PDMS‐based polyurethanes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2026–2040, 2000     

Preparation of 2,5‐Diamino‐3,6‐Dinitropyrazine (ANPZ‐i): A Novel Candidate High Energy Insensitive Explosive

2,5‐Diamino‐3,6‐dinitropyrazine (ANPZ‐i) has been prepared via the electrophilic nitration of 2,5‐diethoxypyrazine using nitronium tetrafluoroborate in sulpholane and subsequent amination under autoclave conditions. Molecular modelling studies have been carried out which indicate that ANPZ‐i should have a similar performance to RDX but with an expected higher insensitivity. ANPZ‐i ( 1 ) is therefore a novel candidate high energy insensitive explosive.     

Identification and kinetic analysis of a functional homolog of elongation factor 3, YEF3 in Saccharomyces cerevisiae

Yeast and other fungi contain a soluble elongation factor 3 (EF-3) which is required for growth and protein synthesis. EF-3 contains two ABC cassettes, and binds and hydrolyses ATP. We identified a homolog of the YEF3 gene in the Saccharomyces cerevisiae genome database. This gene, designated YEF3B, is 84% identical in protein sequence to YEF3, which we will now refer to as YEF3A. YEF3B is not expressed during growth under laboratory conditions, and thus cannot rescue growth of YEF3A deletion strains. However, YEF3B can take the place of YEF3A in vivo when expressed from the YEF3A or ADH1 promoters. The products of the YEF3A and YEF3B genes, EF-3A and EF-3B, respectively, were expressed from the ADH1 promoter and purified. Both factors possessed basal and ribosomal-stimulated ATPase activity, and had similar affinity for yeast ribosomes (103 to 113 nm). K_m values for ATP were similar, but the K_cat values differed significantly. Ribosome-dependent ATPase activity of EF-3A was more efficient than EF-3B, since the K_cat and K_cat/K_m values for EF-3A were about two-fold higher; however, the difference in K_cat/K_m values between the two factors was small for basal ATPase activity. © 1998 John Wiley & Sons, Ltd.     

Polyurethane elastomers with low modulus and hardness based on novel copolyether macrodiols

A series of copolyether macrodiols was prepared from either 1,10-decanediol or 1,6-hexanediol, by acid-catalyzed condensation polymerization using several comonomers to investigate the effect of copolymerization on reducing macrodiol crystallinity. The comonomers used to disrupt crystallinity included 2,2-diethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, and 1,7-heptanediol. The product copolyethers were identified as hydroxy terminated copoly(alkylene oxides) by ¹H- and ¹³C-NMR spectroscopy. Based on NMR results, the structures of the copolyethers were established as consisting of blocks of the principal monomer with comonomer 2,2-diethyl-1,3-propanediol incorporated to form only the end structural unit, whereas 1,4-cyclohexanedimethanol incorporated to form the end unit as well as part of the main chain. DSC results confirmed that the copolymerization produced macrodiols with lower crystallinity and lower T_g than those of the corresponding homopolyethers of the principal monomers, with two exceptions. The exceptions were 1,6-hexanediol/1,10-decanediol, and 1,10-decanediol/1,7-heptanediol copolyethers where no reduction in crystallinity was observed. A series of polyurethane elastomers with a constant hard segment percentage (40 wt %) was prepared using 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol as the hard segment. Tensile test results and Shore hardness measurements demonstrated that copolyether macrodiols produced several polyurethanes with lower modulus and hardness than those of polyurethanes based on homopolyethers of the principal monomers. Of the comonomers studied, 2,2-diethyl-1,3-propanediol-based copolyether produced the polyurethane with the lowest hardness and modulus. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1373–1384, 1997     

Origin of Increased Solvent Accessibility of Peptide Bonds in Mutual Synergetic Folding Proteins

Mutual Synergetic Folding (MSF) proteins belong to a recently discovered class of proteins. These proteins are disordered in their monomeric but ordered in their oligomeric forms. Their amino acid composition is more similar to globular proteins than to disordered ones. Our preceding work shed light on important structural aspects of the structural organization of these proteins, but the background of this behavior is still unknown. We suggest that solvent accessibility is an important factor, especially solvent accessibility of the peptide bonds can be accounted for this phenomenon. The side chains of the amino acids which form a peptide bond have a high local contribution to the shielding of the peptide bond from the solvent. During the oligomerization step, other non-local residues contribute to the shielding. We investigated these local and non-local effects of shielding based on Shannon information entropy calculations. We found that MSF and globular homodimeric proteins have different local contributions resulting from different amino acid pair frequencies. Their non-local distribution is also different because of distinctive inter-subunit contacts.     

Multivariate Calibration of Semi‐Synthetic Data Sets: Gun Powder Analysis

Quantitative analysis of multi‐component mixtures such as propellant powders is not trivial since it usually requires separation of the mixture constituents. Multivariate calibration combined to the use of semi‐synthetic data sets can eliminate the need for standard solutions preparation, and therefore allow the rapid determination of mixtures provided no intermolecular interactions occur in the systems. Multivariate compositional analyses of FTIR spectra of low‐vulnerability (LOVA), high‐energy low‐vulnerability (HELOVA) and energetic thermoplastic elastomer (ETPE) propellant powder systems were performed using the partial least‐squares (PLS) regression algorithm. All constituents except ethyl centralite (EC) were quantified. Concentrations were predicted within 1% error for the major component (1,3,5‐trinitro‐1,3,5‐triazacyclohexane or RDX), and within 5% error for the minor components (between 12 and 2% nominally by weight). LOVA, HELOVA, and ETPE gun powder samples concentrations were estimated and compared to expected compositions.     

Influence of Risk Factors for Male Infertility on Sperm Protein Composition

Male infertility is a common health problem that can be influenced by a host of lifestyle risk factors such as environment, nutrition, smoking, stress, and endocrine disruptors. These effects have been largely demonstrated on sperm parameters (e.g., motility, numeration, vitality, DNA integrity). In addition, several studies showed the deregulation of sperm proteins in relation to some of these factors. This review inventories the literature related to the identification of sperm proteins showing abundance variations in response to the four risk factors for male infertility that are the most investigated in this context: obesity, diabetes, tobacco smoking, and exposure to bisphenol-A (BPA). First, we provide an overview of the techniques used to identify deregulated proteins. Then, we summarise the main results obtained in the different studies and provide a compiled list of deregulated proteins in relation to each risk factor. Gene ontology analysis of these deregulated proteins shows that oxidative stress and immune and inflammatory responses are common mechanisms involved in sperm alterations encountered in relation to the risk factors.