Metabolic Profiling of VOCs Emitted by Bacteria Isolated from Pressure Ulcers and Treated with Different Concentrations of Bio-AgNPs

Considering the advent of antibiotic resistance, the study of bacterial metabolic behavior stimulated by novel antimicrobial agents becomes a relevant tool to elucidate involved adaptive pathways. Profiling of volatile metabolites was performed to monitor alterations of bacterial metabolism induced by biosynthesized silver nanoparticles (bio-AgNPs). Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae and Proteus mirabilis were isolated from pressure ulcers, and their cultures were prepared in the presence/absence of bio-AgNPs at 12.5, 25 and 50 µg mL⁻¹. Headspace solid phase microextraction associated to gas chromatography–mass spectrometry was the employed analytical platform. At the lower concentration level, the agent promoted positive modulation of products of fermentation routes and bioactive volatiles, indicating an attempt of bacteria to adapt to an ongoing suppression of cellular respiration. Augmented response of aldehydes and other possible products of lipid oxidative cleavage was noticed for increasing levels of bio-AgNPs. The greatest concentration of agent caused a reduction of 44 to 80% in the variety of compounds found in the control samples. Pathway analysis indicated overall inhibition of amino acids and fatty acids routes. The present assessment may provide a deeper understanding of molecular mechanisms of bio-AgNPs and how the metabolic response of bacteria is untangled.     

Retention of gallium ions from acidic solutions by pyridine strong‐base anion exchangers

Using the batch method, the retention of Ga(III) from HCl solutions by two gel‐type pyridine strong‐base anion exchangers containing 1‐methyl‐ or 1‐butyl‐4‐vinylpyridinium chloride structural units, called S₁ and S₂ resins, respectively, was studied. The influence of the HCl and Ga(III) concentrations as well as of the contact time between the resin and the liquid phase was investigated. The parameters, which characterize the retention process, were estimated using Langmuir and Freundlich isotherms. Both resins exhibited a higher affinity for gallium ions from a 6M HCl solution. According to Langmuir isotherms, maximum retention capacities of 44.44 and 60 mg Ga(III)/g dry resin for the S₁ and S₂ resins, respectively, were obtained. Freundlich isotherms provide additional proof for a higher affinity of the S₂ resin for Ga(III) from HCl solutions. It is clear that the substituent length increase on N⁺ atoms led to an increasing affinity of the pyridine strong base anion exchangers toward Ga(III). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3440–3444, 2002     

The stacked lamellar texture on the fracture surfaces of fibre composites

A fracture surface texture, which has been variously termed as lacerations, hackles or serrations, is often observed on the matrix surface of fibre composites, most often in resin-rich regions. This texture, referred to here as a stacked lamellar texture to emphasize its plate-like nature, was studied in an E-glass/epoxy composite. Scanning electron fractographs of these materials suggest that the stacked lamellar texture arises from crack fingers due to a meniscus instability mechanism interacting with a reorienting stress field.     

Synthesis of poly(urethane-urea) varnish bearing azobenzene chromophoric pendants

A new diol with azoaromatic pendant was prepared by N-phenyl-4-amido-3,4-dichloromaleimide with 2-mercaptoethanol in the presence of NaOH, and used to obtain photosensible poly(urethane-urea) varnish. A poly(urethane-urea) varnish bearing azobenzene chromophores, based on a poly(ethylene adipate)diol (average molecular weight—2000), 4,4′-dibenzyldiisocyanate, diethylene glycol, trimethylolpropane, and afore-mentioned diol, were prepared and characterized. The polymers were characterized by FTIR spectroscopy, thermal analysis (DMA, DSC, and TGA), and the photochromic behavior by UV irradiation of thin films was discussed.     

Contactless Spin Switch Sensing by Chemo-Electric Gating of Graphene

Direct electrical probing of molecular materials is often impaired by their insulating nature. Here, graphene is interfaced with single crystals of a molecular spin crossover complex, [Fe(bapbpy)(NCS)₂], to electrically detect phase transitions in the molecular crystal through the variation of graphene resistance. Contactless sensing is achieved by separating the crystal from graphene with an insulating polymer spacer. Next to mechanical effects, which influence the conductivity of the graphene sheet but can be minimized by using a thicker spacer, a Dirac point shift in graphene is observed experimentally upon spin crossover. As confirmed by computational modeling, this Dirac point shift is due to the phase-dependent electrostatic potential generated by the crystal inside the graphene sheet. This effect, named as chemo-electric gating, suggests that molecular materials may serve as substrates for designing graphene-based electronic devices. Chemo-electric gating, thus, opens up new possibilities to electrically probe chemical and physical processes in molecular materials in a contactless fashion, from a large distance, which can enhance their use in technological applications, for example, as sensors.     

Polyimides with 3,3’-Bipyrrolidine-2,2’,5,5’-Tetrone Units

Summary New linear polymers with 3,3’-bipyrrolidine-2,2’,5,5’-tetrone units were prepared by the ring-coupling reaction of α,α’-bis(chlorosuccinimide)s under the action of dust zinc and iodine. Bis(α-chlorosuccinimide)s were synthesized by the dehydrocyclization of the bismaleamic acids in the presence of thionyl chloride. The IR, ¹H-NMR and ¹³C-NMR spectroscopy and elemental analysis confirmed the structure of monomers and polymers. The thermal behaviour of the polymers was monitored using dynamic thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).     

Chemical modification of chloromethylated polysulfones via click reactions

A new approach to the modification of azidomethyl polyethersulfones using click reactions with acetylenic derivatives in the presence of CuBr as catalyst is presented. An azidomethyl polyethersulfone was prepared by the reaction of chloromethylated polysulfone with sodium azide in dimethylformamide. By the Cu(I)‐catalysed Huisgen 1,3‐dipolar cycloaddition reaction of the azidomethyl polyethersulfone to acetylenic derivatives, new polyethersulfones containing 1,2,3‐triazole rings were obtained. The structures of the polymers were confirmed using attenuated total reflectance Fourier transform infrared and NMR spectroscopy. The polymers were characterized using dynamic mechanical analysis, thermogravimetric analysis, stress‐strain and water contact angle measurements and solubility tests. The polymers bearing 1,2,3‐triazole rings having OH or COOH as substituents exhibited static contact angles smaller than that of the parent polyethersulfone. Copyright © 2010 Society of Chemical Industry     

Adsorption of Zn(II) by crosslinked acrylic copolymers with amine functional groups

Adsorption of Zn(II) ions from diluted aqueous solutions by the acrylic copolymer based on ethylacrylate : acrylonitrile : divinylbenzene matrix with different crosslinking degrees and ethylenediamine and triethylenetetramine functional groups was investigated. Adsorption experiments were carried out by batch method. The effects of the pH, initial concentration of zinc, time of contact, and the crosslinking degree of the copolymers were studied. On the basis of Langmuir and Freundlich isotherms, the parameters that characterize the adsorption were determined. The maximum Zn(II) retention capacity value (500 mg g^?1) was obtained for the acrylic copolymer with 2% crosslinking degree and ethylenediamine, as functional groups. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 803–808, 2004     

Mathematical models of optimization problems under creep conditions

This paper concerns the optimization of structures, the state of which is in general determined by the creep of the material. The material of the structure is in the state of steady creep. The relationship of the creep flow rates and the stresses is determined by the exponential function according to the flow theory. The mathematical models of the optimization problem in the static formulation is derived on the basis of the extremum energy principle of the minimum plastic dissipation. The mathematical model of the problem in the kinematic formulation is obtained by way of formal consideration on the basis of the duality theory of mathematical programming. This corresponds to the extremum energy principle of the maximum external power. The mathematical models of the optimization problem in the static and kinematic formulations are a dual pair of mathematical programming problems. The problems for the determination of the minimum volume, the minimum theoretical cost and the period of failure of the structure may be looked upon as particular cases of the problems presented. The design of circular plates with simply supported and clamped edges is presented as numerical examples.