Large-scale in vivo synthesis of the carbohydrate moieties of gangliosides GM1 and GM2 by metabolically engineered Escherichia coli

Two metabolically engineered Escherichia coli strains have been constructed to produce the carbohydrate moieties of gangliosides GM2 (GalNAcbeta-4(NeuAcalpha-3)Galbeta-4Glc; Gal = galactose, Glc = glucose, Ac = acetyl) and GM1 (Galbeta-3GalNAcbeta-4(NeuAcalpha-3)Galbeta-4Glc. The GM2 oligosaccharide-producing strain TA02 was devoid of both beta-galactosidase and sialic acid aldolase activities and overexpressed the genes for CMP-NeuAc synthase (CMP = cytidine monophosphate), alpha-2,3-sialyltransferase, UDP-GlcNAc (UDP = uridine diphosphate) C4 epimerase, and beta-1,4-GalNAc transferase. When this strain was cultivated on glycerol, exogenously added lactose and sialic acid were shown to be actively internalized into the cytoplasm and converted into GM2 oligosaccharide. The in vivo synthesis of GM1 oligosaccharide was achieved by taking a similar approach but using strain TA05, which additionally overexpressed the gene for beta-1,3-galactosyltransferase. In high-cell-density cultures, the production yields for the GM2 and GM1 oligosaccharides were 1.25 g L(-1) and 0.89 g L(-1), respectively.     

Bond strengths of toluenes, anilines, and phenols: to hammett or not

The Hammett equation correlates the effects of Y on many different chemical properties of YC(6)H(4)ZX families of compounds. One of the most surprising is that the Z-X bond dissociation enthalpy (BDE), a homolytic property, can be correlated for some 4-YC(6)H(4)ZX families with electrophilic substituent constants, sigma(p)(+)(Y), which were largely derived from the rates of the heterolytic S(N)1 solvolyses of para-substituted cumyl chlorides. Although there is no Hammett correlation of the C-X BDEs in 4-YC(6)H(4)CH(2)X (X = H, halide, OPh) families, there are good correlations of N-X BDEs with sigma(p)(+)(Y) in 4-YC(6)H(4)NHX (X = H, CH(3), OH, F) and excellent correlations of O-X BDEs with sigma(p)(+)(Y) in 4-YC(6)H(4)OX (X = H, CH(3), CH(2)Ph) families. The reasons for this varied behavior are discussed.     

Partitioning of polymers into pores with surface interactions at dilute solution limit

The partitioning of a single polymer chain into a slit in a good solvent with different surface interactions is examined through Monte Carlo simulations from subcritical regime to adsorptive regime. The chain conformation in the subcritical regime is not perturbed by the surface interactions significantly. In the adsorptive regime, the conformation of the chain is strongly perturbed by the surface interactions. The confinement free energy in the two regimes maybe written in a uniform formula, βΔμ_conf∼c₁N(a/D)^xε_w+c₂N(a/D)^1/ν with x∼2.0 or larger in the subcritical regime and ∼1.0 in the adsorptive regime, where ν is the Flory exponent, D is the slit width, N is the chain length, a is the monomer size, and ε_w is the surface interaction energy between the polymer beads and the slit. This formula is valid for a long chain in the narrow slit in the subcritical regime or when the adsorption layer h>D in the adsorptive regime. A critical behavior occurs when ε_w is at the critical adsorption point and x=1/ν, then Δμ_conf will have little dependence on N or D. Higher order terms that are neglected in the above equation, however, may be present that could lead to a weak dependence of K on N and D even in the critical adsorption point.     

Toward optimisation of electrolytic reduction of solid chromium oxide to chromium powder in molten chloride salts

Electrochemical reduction of solid Cr₂O₃, in the form of an assembled cathode of porous pellets attached to a current collector, to chromium powder was investigated in molten CaCl₂ and a molten equimolar mixture of CaCl₂ and NaCl. The study focused on the influence of pellets preparation conditions, cell voltages and temperatures on the reduction process. Analyses were reported of the characteristics of the current-time plots of the constant voltage electrolysis under different conditions, cyclic voltammograms of solid Cr₂O₃ in the molten equimolar mixture of CaCl₂ and NaCl, the microstructures and elemental compositions of the reduced pellets. Particularly, attention was given to the intermediate product of the electrolysis, calcium chromites of various stoichiometries, aiming to achieve a better understanding and optimisation of the reduction process.     

Miscible blends of biobased poly(lactide) with poly(methyl methacrylate): Effects of chopped glass fiber incorporation

Poly(lactide) (PLA) and poly(methyl methacrylate) (PMMA) are melt compounded with chopped glass fiber using laboratory scale twin‐screw extrusion. Physical properties are examined using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), tensile testing, impact testing, X‐ray computed tomography (CT) scanning, and field emission scanning electron microscopy (FE‐SEM). Molecular weight is determined using gel permeation chromatography (GPC). Miscibility of the blends is implied by the presence of a single glass transition temperature and homogeneous morphology. PLA/PMMA blends tend to show positive deviations from a simple linear mixing rule in their mechanical properties (e.g., tensile toughness, modulus, and stress at break). The addition of 40 wt % glass fiber to the system dramatically increases physical properties. Across all blend compositions, the tensile modulus increases from roughly 3 GPa to roughly 10 GPa. Estimated heat distortion temperatures (HDTs) are also greatly enhanced; the pure PLA sample HDT increases from 75 °C to 135 °C. Fiber filled polymer blends represent a sustainable class of earth abundant materials which should prove useful across a range of applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44868.     

Extraction Behavior of Americium and Curium on Selected Extraction Chromatography Resins from Pure Acidic Matrices

Due to the similar chemical properties between the neighboring trivalent actinide elements americium and curium, their extraction behavior is often perceived as indistinguishable. In this work, the characterization of seven extraction chromatography resins (TEVA, TRU, DGA(N), Actinide, Ln, Ln2, and Ln3) for these trivalent actinides from acidic matrices (HNO₃, HCl, and HBr) has provided some evidence to the contrary. In most cases, Am(III) and Cm(III) exhibit identical extraction properties. However, separation is possible with TRU and DGA(N) resins as demonstrated in this study. The extraction shows a strong dependency on the specific anion in solution that follows the order NO₃^?>Br^?>Cl^?.     

Flow and Pressure Balancing in a Fluid Interface Impactor

Fluid interface impactors, such as virtual and opposing jet impactors, require particular attention to flow and pressure balance in the incoming and outgoing airstreams. The relationship of flow rate to pressure drop has been studied in an opposing jet aerosol classifier of rectangular design. In tests of the sensitivity of classifier operation, changes in pressure differences across the inlets and the outlets were associated with changes in the flow balances of 0.5 and -1.0%/mm w.g., respectively. These flow sensitivities may be used in conjunction with cut size sensitivities to conclude that the appropriate measurements to use for classifier control are the static pressure differences between the two inlets and between the two outlets, rather than the mass flow rates of the four jets. For aerosol size classification tests, a nebulizer-virtual impactor polydisperse aerosol generator was designed to reduce the concentration of small particles and make the generator compatible with dynamic optical particle counting. The aerodynamic cut diameter is Stk ^1/2 ₅₀ = 0.49 ± 0.08 for the standard pressure balance condition. Classification sharpness, using 84 and 16% efficiency sizes, is 1.43 ± 0.03 at the standard condition and can be reduced to 1.11 ± 0.02 at other conditions.     

An Ultrafine,Water-Based Condensation Particle Counter and its Evaluation under Field Conditions

An ultrafine, water-based condensation particle counter (U-WCPC, TSI Model 3786) has been compared to a butanol-based ultrafine counter (U-BCPC, TSI Model 3025) for measurement of atmospheric and freeway-tunnel aerosols. The U-WCPC utilizes a warm, wet-walled growth tube to activate and grow particles through water condensation in a laminar-flow. It has an aerosol sampling rate of 0.3 L/min, and a nominal detection limit near 3 nm. Several field comparisons were made to the butanol-based instrument with the same nominal detection limit. For measurements of size-selected aerosols with diameters of 5 nm and larger the two instruments generally agreed, with a mean response within 5%. At 3 nm particle size differences were observed, and these differences varied with the data set. Measurements of ambient aerosol in Boulder, Colorado showed higher counting efficiency at 3 nm with the U-BCPC, while in a California freeway tunnel the opposite trend was observed, with higher counting efficiencies at 3 nm observed by the U-WCPC. For direct measurement of atmospheric aerosols, the two types of instruments yielded equivalent concentrations, independent of particle number concentration.