Exploitation of Haloferax alexandrinus for Biogenic Synthesis of Silver Nanoparticles Antagonistic to Human and Lower Mammalian Pathogens

In the present study we report the use of cells of a Haloarchaeon for the green synthesis of silver nanoparticles. Biosynthesis of AgNPs occurred within 30 s on exposure of cells of Haloferax alexandrinus to silver nitrate in direct sunlight. Maximum AgNPs production was achieved within 4 min of exposure of silver nitrate (0.05 %) to cells (5 mg/ml), at pH 7, at ambient day temperature (26–34 °C). The AgNPs had characteristic surface plasmon resonance at 420 nm in UV–Vis spectra. Spherical and irregular crystals ranging from 2 to 60 nm in size with an average size of 18 nm were observed in TEM analysis. The FTIR spectral analysis indicated involvement of N–H, –OH, C=O, C–O functional groups present in cells of Haloferax alexandrinus MTCC 3265. The biogenic AgNPs exhibited broad spectrum antimicrobial activity against human and mammalian pathogens, in the order of Pseudomonas aeruginosa ATCC 9027 > Bordetella bronchiseptica ATCC 4617 > Bacillus subtilis ATCC 6633 > Staphylococcus aureus ATCC 6538P > Staphylococcus epidermidis ATCC 12228 > Escherichia coli ATCC 8739 > Salmonella typhimurium ATCC 14028.     

The role of sonic shocks between two- and three-phase states in porous media

Flowof threefluids in porousmedia is governed by a systemof two conservation laws. Shock solutions are described by curves in state space, which is the saturation triangle of the fluids. We study a certain bifurcation locus of these curves, which is relevant for certain injection problems. Such structure arises, for instance, when water and gas are injected in a mature reservoir either to dislodge oil or to sequestrate CO₂. The proof takes advantage of a certain wave curve to ensure that the waves in the flow are a rarefaction preceded by a shock, which is in turn preceded by a constant two-phase state (i.e., it lies at the boundary of the saturation triangle). For convex permeability models of Corey type, the analysis reveals further details, such as the number of possible two-phase states that correspond to the above mentioned shock, whatever the left state of the latter is within the saturation triangle.     

Photoresponsive Switches at Surfaces Based on Supramolecular Functionalization with Azobenzene–Oligoglycerol Conjugates

The synthesis, supramolecular complexation, and switching of new bifunctional azobenzene–oligoglycerol conjugates in different environments is reported. Through the formation of host–guest complexes with surface immobilized β‐cyclodextrin receptors, the bifunctional switches were coupled to gold surfaces. The isomerization of the amphiphilic azobenzene derivatives was examined in solution, on gold nanoparticles, and on planar gold surfaces. The wettability of functionalized gold surfaces can be reversibly switched under light‐illumination with two different wavelengths. Besides the photoisomerization processes and concomitant effects on functionality, the thermal cis to trans isomerization of the conjugates and their complexes was monitored. Thermal half‐lives of the cis isomers were calculated for different environments. Surprisingly, the half‐lives on gold nanoparticles were significantly smaller compared to planar gold surfaces.     

From Double‐Four‐Ring Germanosilicates to New Zeolites: In Silico Investigation

To date, the majority of zeolites have been prepared by the solvothermal route using organic structure directing agents. Two new zeolites with structural codes PCR and OKO were recently prepared from UTL germanosilicate by removal of the double‐four ring (D4R) connecting the dense two‐dimensional layers [Nature Chem. 2013 , 5, 628]. The corresponding experimental protocol, Assembly–Disassembly–Organization–Reassembly (ADOR), is explored in this contribution with an in silico investigation. The structure and properties of hypothetical zeolites that could be obtained from zeolites with IWW, IWV, IWR, ITR, and ITH topologies using the ADOR protocol are reported based on a computational investigation. A total of 20 new structures are presented together with their characteristics.     

A Study of the Effects of Aeration and Agitation on the Properties and Production of Xanthan Gum from Crude Glycerin Derived from Biodiesel Using the Response Surface Methodology

The effects of aeration and agitation on the properties and production of xanthan gum from crude glycerin biodiesel (CGB) by Xanthomonas campestris mangiferaeindicae 2103 were investigated and optimized using a response surface methodology. The xanthan gum was produced from CGB in a bioreactor at 28 °C for 120 h. Optimization procedures indicated that 0.97 vvm at 497.76 rpm resulted in a xanthan gum production of 5.59 g L^?1 and 1.05 vvm at 484.75 rpm maximized the biomass to 3.26 g L^?1. Moreover, the combination of 1.05 vvm at 499.40 rpm maximized the viscosity of xanthan at 0.5 % (m/v), 25 °C, and 25 s^?1 (255.40 mPa s). The other responses did not generate predictive models. Low agitation contributed to the increase of xanthan gum production, biomass, viscosity, molecular mass, and the pyruvic acid concentration. Increases in the agitation contributed to the formation of xanthan gum with high mannose concentration. Decreases in the aeration contributed to the xanthan gum production and the formation of biopolymer with high mannose and glucose concentrations. Increases in aeration contributed to increased biomass, viscosity, and formation of xanthan gum with greater resistance to thermal degradation. Overall, aeration and agitation of CGB fermentation significantly influenced the production of xanthan gum and its properties.     

Difluorinated analogues of shikimic acid

Investigations into the quinate to shikimate transformation have been carried out, the results of which have been exploited in the synthesis of a novel difluoromethylene homologue of shikimic acid from (−)-quinic acid. Martin's sulfurane {Ph₂S[OC(CF₃)₂Ph]₂} was the reagent of choice for the key dehydration step of this synthesis. The results of investigations into the synthesis of the important natural product analogue, 6,6-difluoroshikimic acid are also reported.     

Metal chloride-catalyzed acetylation of starch: Synthesis and characterization

Acylation of polysaccharides is a commercially important reaction and is usually performed in a process involving the polysaccharide, an acid anhydride, and an inorganic acid. As an alternative to inorganic acid, many catalysts, including some metal chlorides, have been previously reported as catalysts. In this work, we took a more comprehensive look at several metal chlorides to observe trends and reactivities among them, particularly relating to reaction temperature, time, and amount of acetic anhydride used. Iodine was also included for comparison. Almost all the metal chlorides studied were found to be active as catalysts for the acetylation of starch under suitable reaction conditions. However, each metal chloride had a somewhat different reactivity with a different optimal temperature needed for satisfactory reactions to take place. The molecular weight of the starch acetate products decreased in all cases observed. The reactivity trends among the metal halides seemed to correlate both with the ease of complexation between the halide and the substrate and with the acidity of the metal chloride. Characterization was achieved through ^13?C NMR, FT-IR, thermogravimetric analysis and size exclusion chromatography.     

Oil displacement by water and gas in a porous medium: the Riemann problem

In this work we present the construction of the Riemann solution for a system of two conservation laws representing displacement in immiscible three-phase flow. The porousmedium is initially filled with oil and small amounts of water and gas; then a fixed proportion of water and gas is injected. We use the wave curve method to determine the wave sequences in the Riemann solution for arbitrary initial and injection data in the above mentioned class. We show the L_Loc¹-stability of the Riemann solution with variation of data. We do not verify uniqueness of the Riemann solution, but we believe that it is valid.