Pore functioning of outer membrane protein PhoE of Escherichia coli: mutagenesis of the constriction loop L3

Each monomer of the trimeric outer membrane porin PhoE of Escherichia coli consists of a 16-stranded beta-barrel with short turns at the periplasmic side and large loops at the cell surface. One of these loops, L3, is folded inside the beta-barrel and forms a constriction within the channel. Therefore, it is assumed to play an important role in the permeability properties of this general diffusion pore. Several site-directed mutations were introduced in loop L3 to investigate its function. The loop L3 contains a short alpha-helix and, at the tip of the loop, a highly conserved PEFGG sequence. The alpha-helix was deleted and the two glycines in the PEFGG sequence were either replaced by alanines or deleted. A serine residue, supposed to play an indirect role in the anion selectivity of the pore, was removed. The mutant porins were analysed both in vitro and in vivo. The results suggest that flexibility of the third loop is important for solute passage and that this flexibility is determined by the two glycine residues in the PEFGG sequence. Furthermore, the alpha-helix is probably important for the folding of the protein. The supposed involvement of Ser115 (Ser121A in OmpF nomenclature) in anion selectivity was confirmed.      

Molecular dynamics simulations as a tool for improving protein stability

Haloalkane dehalogenase (DhlA) was used as a model protein toexplore the possibility to use molecular dynamics (MD) simulationsas a tool to identify flexible regions in proteins that canserve as a target for stability enhancement by introductionof a disulfide bond. DhlA consists of two domains: an     

Clean coal conversion options using Fischer-Tropsch technology

Material and energy balances were prepared for two coal conversion options for the co-production of liquid hydrocarbon products and electricity. The results are compared to the alternative approach of producing liquid hydrocarbons from natural gas. It is concluded that the capital cost for coal conversion must be higher but that cash operating costs may be similar. There are important synergistic effects so that facilities co-producing liquid hydrocarbons and electricity from coal are more efficient than facilities producing these products individually. There may be good strategic reasons to use clean coal conversion plants co-producing liquid hydrocarbons and electricity. Due to the huge capital investments required, some form of government assistance will be needed.     

Application of inline imaging for monitoring crystallization process in a continuous oscillatory baffled crystallizer

In this study, an in situ imaging system has been analysed to characterize the crystal size, the shape and the number of particles during a continuous crystallization process in a Continuous Oscillatory Baffled Crystallizer (COBC). Two image analysis approaches were examined for particle characterization in the suspension containing both small nuclei and larger grown crystals (nonspherical and irregular in shape). The pattern matching approach, in which the particles are approximated to be spherical, did result in an overestimation of the size. Alternatively, a segmentation‐based algorithm resulted in reliable crystal size and shape characteristics. The laser diffraction analysis in comparison to the image analysis overestimated the particle sizes due to the agglomeration of particles upon filtration and drying. The trend in the particle counts during the start of crystallization process, including nucleation, determined by the image analysis probe was comparable with the one measured by FBRM, highlighting the potential of in situ imaging for process monitoring. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2450–2461, 2018     

PREDICTION OF PINEAPPLE SORPTION ISOTHERMS USING THE ROSS EQUATION

ABSTRACT

A mathematical prediction of pineapple sorption isotherms was developed using Ross, Norrish and Henderson equations. The prediction considered to have the pineapple average composition oflhe main solutes: sucrose, glucose, fructose, citric acid, malic acid, NaCI, KC1 and cellulose as non-solute. Water activity of individual sugars and organic acids was obtained by Norrish's equation and for the two salts by Raoult's Law. Solute solubility at different temperatures was taken into account. Predicted isotherms were compared with the experimental isotherms obtained in laboratory at 30, 35, 40 and 45° C and with the isotherms reported in literature at 30 and 45° C. The generalized correlation coefficients ( r² ) between predicted and experimental isotherms were in the range of 0.8 - 0.98.     

Small Molecule Inhibitors of AI-2 Signaling in Bacteria: State-of-the-Art and Future Perspectives for Anti-Quorum Sensing Agents

Bacteria respond to different small molecules that are produced by other neighboring bacteria. These molecules, called autoinducers, are classified as intraspecies (i.e., molecules produced and perceived by the same bacterial species) or interspecies (molecules that are produced and sensed between different bacterial species). AI-2 has been proposed as an interspecies autoinducer and has been shown to regulate different bacterial physiology as well as affect virulence factor production and biofilm formation in some bacteria, including bacteria of clinical relevance. Several groups have embarked on the development of small molecules that could be used to perturb AI-2 signaling in bacteria, with the ultimate goal that these molecules could be used to inhibit bacterial virulence and biofilm formation. Additionally, these molecules have the potential to be used in synthetic biology applications whereby these small molecules are used as inputs to switch on and off AI-2 receptors. In this review, we highlight the state-of-the-art in the development of small molecules that perturb AI-2 signaling in bacteria and offer our perspective on the future development and applications of these classes of molecules.     

Infrared Reflection Spectroscopy and Effective Medium Modeling of As-Anodized and Oxidized Porous Silicon Carbide

We present a study of the infrared reflectance of porous silicon carbide (PSC) formed by the electrochemical dissolution of silicon carbide substrates of both 6H and 4H polytypes. The reflectance from n-PSC, both as-anodized and passivated, is reported for the first time. The passivation of PSC has been accomplished using a short thermal oxidation. Fourier transform infrared (FTIR) reflectance spectroscopy is employed ex situ after different stages of the thermal oxidation process. The characteristics of the reststrahlen band normally observed in bulk SiC are altered by anodization; further changes in the reflectance spectra occur following oxidation for different periods of time. An effective medium theory model that includes air, SiC and SiO₂ as component materials is shown to characterize the observed changes in the reflectance spectra after different stages of PSC oxidation.     

Discovery of Selective Luteinizing Hormone Receptor Agonists Using the Bivalent Ligand Method

Two series of dimeric ligands for a G‐protein‐coupled receptor were prepared that differ by the interconnecting spacer system. Biological evaluation revealed that both dimeric series exhibit unique biological properties relative to their monomeric counterparts.

     

Continuous operation of membrane bioreactor treating toluene vapors by Burkholderia vietnamiensis G4

A laboratory-scale biofilm membrane bioreactor inoculated with Burkholderia vietnamiensis G4 was examined to treat toluene vapors in a waste gas stream. The gas feed side and nutrient solution were separated by a composite membrane consisting of a porous polyacrylonitrile (PAN) support layer coated with a very thin (0.3 μm) dense polydimethylsiloxane (PDMS) top layer. After inoculation, a biofilm developed on the dense layer. The biofilm membrane bioreactor was operated continuously at different residence times (28–2 s) and loading rates (1.2–26.7 kg m⁻³ d⁻¹), with inlet toluene concentrations ranging from 0.21 to 4.1 g m⁻³. The overall performance of the membrane bioreactor was evaluated over a period of 165 days. Removal efficiencies ranging from 78% to 99% and elimination capacities from 4.2 to 14.4 kg m⁻³ d⁻¹ were observed after start-up period depending on the mode of operation. A maximum elimination capacity of 14.4 kg m⁻³ d⁻¹ was observed at a loading rate of 17.4 kg m⁻³ d⁻¹. Overall, the results illustrate that biofilm membrane reactors can potentially be more effective than conventional biofilters and biotrickling filters for the treatment of air pollutants such as toluene.     

Stability of lead(II) complexes of alginate oligomers

The current work reports on the Pb(ll) complexes formed with oligomeric uronic acids (carboxylated saccharide residues) found polymerized in the cell walls and envelopes of algae and bacteria alike. The application of partial acid hydrolysis, size-exclusion chromatography (SEC), 1H NMR, and scanned deposition stripping chronopotentiometry (SSCP) has permitted the determination of stability constants for Pb(II) with both mannuronic (M) and guluronic (G) acid oligomers ranging from the dimer to the pentamer. The determined logarithm of the stability constants range between 4.11 +/- 0.05 and 5.00 +/- 0.04 mol(-1) x dm3 for the eight oligomers studied (pH 6; I = 0.1 mol x dm(-3)). Additional experiments under the same experimental conditions employing galacturonic and glucuronic acid oligomers yielded slightly lower values (2.19 +/- 0.10 to 4.02 +/- 0.07 mol(-1) x dm3) that were expected based on their structure, whereby the monomers which were not included in the alginate oligomer series (unavailable by SEC), yielded the lowest stability constants. This work demonstrates the applicability of the SSCP technique for the determination of stability constants for metal-ligand complexes in which the ligands display relatively low molecular mass. Previous studies on heavy metal interaction with the matrix polysaccharide alginate have largely been restricted to the whole polymer that forms a gel upon binding to network bridging ions such as calcium. The results will be discussed in this context with the emphasis being placed on the relevance of these findings to processes occurring at the biointerface and results from the relevant literature.