Intramolecular Michael reaction of tert-butylsulfinyl ketimines: asymmetric synthesis of 3-substituted indanones

Aromatic tert-butylsulfinyl ketimines bearing a suitable Michael acceptor at the ortho position readily undergo an intramolecular conjugate addition achieving indanone derivatives in good yields and complete diastereoselectivity.     

A note on asymptotic values of quasiregular maps

In this note we give an example of a quasiregular map in ? ⁿ (n ≥ 3) of order of growth n ? 1 and whose set of asymptotic values is A ∪ {∞} for a given Suslin analytic set A ? ? ⁿ . Our example is a modification of Drasin’s construction in [4] of a quasiregular map with order of growth n ? 1 and set of asymptotic values ? ⁿ ∪ {∞}.     

Development of electrospun EVOH fibres reinforced with bacterial cellulose nanowhiskers. Part I: Characterization and method optimization

In the present study, hybrid electrospun EVOH fibres reinforced with bacterial cellulose nanowhiskers (BCNW) were developed and characterized. The nanowhiskers, obtained by sulphuric acid digestion of native bacterial cellulose mats generated by Gluconacetobacter xylinum, were morphologically characterized by SEM and optical microscopy with polarized light and revealed a highly crystalline structure of nanofibrils aggregates. XRD analyses suggested a crystalline structure corresponding to the cellulose I allomorph. It was also confirmed by means of FT-IR spectroscopy that amorphous regions were preferentially digested by the acid treatment, whereas TGA analyses showed a decrease in the thermal stability of the nanowhiskers most likely due to incorporation of sulphate groups and the inherent acidity remaining in the filler even after extensive washing cycles. A method was developed for improving the incorporation of BCNW within the EVOH electrospun fibres, consisting on the addition of the BCNW in the form of a centrifuged precipitate, versus the most conventionally employed freeze-dried nanowhiskers. DSC analyses showed a significant increase in the glass transition temperature of the composites during the second heating run, which may be related to the acidic character of the nanofiller. Finally, sonication was seen to enhance interfacial interaction but to reduce the incorporation of the filler in the matrix in the case of the centrifuged material.     

Forced synchronization of a self-sustained chaotic oscillator

This work presents a forced synchronization phenomenon like the asymptotic correlated behavior between chaotic oscillators forced by an external signal. Different kinds of forced synchronization are presented and given a theoretical justification explaining why it is possible to find some of them. Numerical results are presented for different cases such as antisymmetric, lag, phase, and identical forced synchronization.     

Green Extracellular Synthesis of Silver Nanoparticles by Pseudomonas alloputida,Their Growth and Biofilm-Formation Inhibitory Activities and Synergic Behavior with Three Classical Antibiotics

Bacterial resistance to antibiotics is on the rise and hinders the fight against bacterial infections, which are expected to cause millions of deaths by 2050. New antibiotics are difficult to find, so alternatives are needed. One could be metal-based drugs, such as silver nanoparticles (AgNPs). In general, chemical methods for AgNPs’ production are potentially toxic, and the physical ones expensive, while green approaches are not. In this paper, we present the green synthesis of AgNPs using two Pseudomonas alloputida B003 UAM culture broths, sampled from their exponential and stationary growth phases. AgNPs were physicochemically characterized by transmission electron microscopy (TEM), total reflection X-ray fluorescence (TXRF), infrared spectroscopy (FTIR), dynamic light scattering (DLS), and X-ray diffraction (XRD), showing differential characteristics depending on the synthesis method used. Antibacterial activity was tested in three assays, and we compared the growth and biofilm-formation inhibition of six test bacteria: Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis. We also monitored nanoparticles’ synergic behavior through the growth inhibition of E. coli and S. aureus by three classical antibiotics: ampicillin, nalidixic acid, and streptomycin. The results indicate that very good AgNP activity was obtained with particularly low MICs for the three tested strains of P. aeruginosa. A good synergistic effect on streptomycin activity was observed for all the nanoparticles. For ampicillin, a synergic effect was detected only against S. aureus. ROS production was found to be related to the AgNPs’ antibacterial activity.