Controlled Production of Exopolysaccharides from Enterobacter A47 as a Function of Carbon Source with Demonstration of Their Film and Emulsifying Abilities

The bacterium Enterobacter A47 has demonstrated the ability to synthesise distinct exopolysaccharides (EPS) as a function of the substrate used. The culture's performance was evaluated in experiments using either glucose or xylose, as single carbon sources, and compared with the substrate (glycerol) used in previous studies. The highest EPS production (13.23 g L^?1) was obtained in the glucose fed assay, with a volumetric productivity of 3.38 g L^?1 day^?1. The use of xylose resulted in lower productivity (1.39 g L^?1 day^?1). The synthesised polymers have the same main sugar monomers (fucose, glucose, galactose and glucuronic acid), but their relative proportion varied with the substrate used. The acyl groups' content and composition were also affected by the substrate used. The polymers produced from glycerol (EPS-s) and glucose (EPS-g) had identical shear-thinning behaviour and good emulsion-stabilising capacity and their films had similar mechanical and water vapour properties. However, the emulsions stabilised with EPS-g were less stable and destabilised within short periods of time or when subjected to heat and freezing/thawing procedures. On the other hand, the polymer produced from xylose had little emulsion-stabilising capacity and lower apparent viscosity than EPS-s and EPS-g, but its films were considerably more elastic.     

Microchip Electrophoretic Analysis of Phaseolin Patterns and Its Comparison with Currently Used SDS-PAGE Techniques

The goal of this work was to compare reproducibility of phaseolin patterns of common bean obtained by two electrophoretic protein separation techniques including the conventional SDS-PAGE and an automated chip electrophoresis system. Five standard cultivars of common bean provided by the United States Department of Agriculture (Beltsville, Maryland) that represented five phaseolin types, T (Tendergreen), C (Contender) and S (Sanilac), B (Boyaca) and P (Pampa), were used in this study. Comparison of the phaseolin patterns revealed that the chip-on-a-lab electrophoresis provided a good reproducibility. The phaseolin polymorphism included four to seven polypeptides typical for the pattern composition of the T, C and S types. The polymorphism of the B and P patterns was also established. Phaseolin polypeptides separated by the microchip electrophoresis exhibited differences with respect to the molecular weights and electrophoretic mobility as compared to the SDS-PAGE technique. This phenomenon could be attributed to the absence of a solid separation phase in the microchip electrophoresis. Moreover, this technique has potential to substantially accelerate screening of large bean germplasm collections since it allows for the accurate analysis of the higher number of individual plants within accessions than the conventional, tedious and time consuming SDS-PAGE method.     

Formation of hybrid nano-crystals in organic–inorganic films from a basic sol

Organic–inorganic films containing hybrid nanocrystals have been prepared by sol–gel processing in controlled conditions. We have systematically changed the temperature and the aging time of a precursor sol containing an organically modified alkoxide bearing an epoxy group, 3-glycidoxypropyltrimethoxysilane, to obtain a controlled crystallization of hybrid layered structures in hybrid films. The precursor sol has been aged at different temperatures, from 5 to 60 °C, and for 1, 2 or 3 days; the films have been deposited from the aged sol and immediately after characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. We have observed that the formation of the hybrid crystals can be obtained only when at least 50% of the epoxies are opened and a larger silica condensation is achieved. These conditions are reached after aging at 60 °C for 1 day, or at longer aging times when the sol is aged at lower temperatures. Transmission electron microscopy and optical polarized images have confirmed the formation of the hybrid crystals.     

The flyby anomaly and the effect of a topological torsion current

A new variational technique determines the general condition of equilibrium of a rotating gravitational or electromagnetic system (or both) and provides a modified dynamical equation of motion from where it emerges a so-far unforseen topological torsion current (TTC) (Pinheiro, 2013) [63]. We suggest that the TTC may explain, in a simple and direct way, the anomalous acceleration detected in spacecrafts during close planetary flybys. In addition, we theorize that TTC may represent a novel relationship between linear momentum and angular motion through the agency of a vector potential.     

Dinuclear iridium(III) complexes consisting of back-to-back tpy-(ph)n-tpy bridging ligands (n = 0, 1, or 2) and terminal cyclometallating tridentate N-C-N ligands

Three dinuclear iridium(III) complexes consisting of a conjugated bis-tpy type bridging ligand and cyclometallating capping tridentate ligands of the 1,3-di-2-pyridylbenzene family have been prepared (tpy, 2,2',6',2' '-terpyridine). The two tpy units of the bridge are connected via their back-positions (4') either directly or with a p-phenylene or p-biphenylene spacer. The synthesis relies on the reaction between the dinuclear [Ir(dpb)Cl2]2 complex (dpb-H =1,3-dipyridyl-4,6-dimethylbenzene) and the corresponding bis-tpy ligand. Electrochemical measurements afford metal-centered oxidation and ligand-centered reduction potentials; from the oxidation steps, no evidence is obtained for a strong coupling between the two iridium(III) subunits of the dinuclear species. For all complexes, ground-state absorption data in the 380 nm to visible region show a trend which is consistent with the presence of charge-transfer (CT) transitions involving different degrees of electronic delocalization at the bridging ligands. (dpb)Ir(tpy-tpy)Ir(dpb)4+ exhibits an appreciable luminescence at room temperature (phi = 3.0 x 10(-3); tau = 3.3 ns), whereas no emission from the other binuclear complexes is detected. All binuclear complexes luminesce at 77 K, and a metal-to-ligand CT nature for (dpb)Ir(tpy-tpy)Ir(dpb)4+ is suggested, whereas a ligand-centered (LC) emission is proposed for (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+ on the basis of the comparison with the phosphorescence properties of the free bridging ligand, tpy-(ph)2-tpy. Transient absorbance experiments at room temperature afford the absorption spectra and lifetimes of the non-emissive excited states. For (dpb)Ir(tpy-ph-tpy)Ir(dpb)4+ and (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+, the spectra exhibit a broad profile peaking around 780 nm, quite intense in the case of (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+, and lifetimes of 160 and 440 ps, respectively.     

Vibrational and electron paramagnetic resonance properties of free and MgO supported AuCO complexes

The bonding, spin density related properties, and vibrational frequency of CO bound to single Au atom in the gas-phase or supported on MgO surfaces have been investigated with a variety of computational methods and models: periodic plane waves calculations have been compared with molecular approaches based on atomic orbital basis sets; pseudopotential methods with all electron fully relativistic calculations; various density functional theory (DFT) exchange-correlation functionals with the unrestricted coupled-cluster singles and doubles with perturbative connected triples [CCSD(T)]. AuCO is a bent molecule but the potential for bending is very soft, and small changes in the bond angle result in large changes in the CO gas-phase vibrational frequency. At the equilibrium geometry the DFT calculated vibrational shift of CO with respect to the free molecule is about -150 cm(-1), whereas smaller values -60-70 cm(-1) are predicted by the more accurate CCSD(T) method. These relatively large differences are due to the weak and nonclassic bonding in this complex. Upon adsorption on MgO, the CO vibrational shift becomes much larger, about -290 cm(-1), due to charge transfer from the basic surface oxide anion to AuCO. This large redshift is predicted by all methods, and is fully consistent with that measured for MgOAuCO complexes. The strong influence of the support on the AuCO bonding is equally well described by all different approaches.     

Ab initio molecular dynamics simulation of NO reactivity on the CaO(001) surface

Ab initio molecular dynamics (MD) is used to investigate NO reaction processes on the (001) surface of CaO. A novel path is proposed for the first steps of nitrogen oxides reactivity catalyzed by the CaO surface. The mechanism consists of the formation of anionic dimers, adsorbing on the surface cations, at the expense of oxidized NO species adsorbed on surface anions. The complete charge-transfer process takes place in two steps, producing first monovalent anionic dimers (NO)2- and, later on, divalent anionic dimers (NO)2(2-). These redox processes cause spin quenching and are observed in the short time scale of the ab initio MD simulation at 300 K. The results presented provide a rationalization of a recent electron spin resonance (ESR) investigation indicating that the spectroscopy is silent to most of the nitrogen oxide species adsorbed on CaO powders, despite deposition of paramagnetic NO molecules at room temperature.     

Approximations to the Log-Likelihood Function in the Nonlinear Mixed-Effects Model

Abstract

Nonlinear mixed-effects models have received a great deal of attention in the statistical literature in recent years because of the flexibility they offer in handling the unbalanced repeated-measures data that arise in different areas of investigation, such as pharmacokinetics and economics. Several different methods for estimating the parameters in nonlinear mixed-effects model have been proposed. We concentrate here on two of them—maximum likelihood and restricted maximum likelihood. A rather complex numerical issue for (restricted) maximum likelihood estimation in nonlinear mixed-effects models is the evaluation of the log-likelihood function of the data, because it involves the evaluation of a multiple integral that, in most cases, does not have a closed-form expression. We consider here four different approximations to the log-likelihood, comparing their computational and statistical properties. We conclude that the linear mixed-effects (LME) approximation suggested by Lindstrom and Bates, the Laplacian approximation, and Gaussian quadrature centered at the conditional modes of the random effects are quite accurate and computationally efficient. Gaussian quadrature centered at the expected value of the random effects is quite inaccurate for a smaller number of abscissas and computationally inefficient for a larger number of abscissas. Importance sampling is accurate, but quite inefficient computationally.