The mass spectrum of 2-cyclohexenol: Loss of CH3⋅ and H⋅ from the molecular ion

Methyl radical and hydrogen atom losses from the molecular ion of 2-cyclohexenol and deuterium labelled analogues have been studied. For fragmentations occurring in the first field free region, H? loss is a random process, whereas CH₃? loss is highly specific involving the C-1 hydrogen atom and the C-5 methylene group. A mechanism consistent with these results is proposed.     

Detection of trace levels of atrazine using surface-enhanced Raman scattering and information visualization

The detection of trace amounts of pesticides is essential for the quality control of waters, particularly with their inevitable increasing use with the growing demand for food. In this study, we report on the detection of atrazine, a highly toxic herbicide, down to 5?×?10^?12 M, which is sufficient to monitor the quality of drinking water even according to the most stringent international regulations. Such detection was performed with surface-enhanced Raman scattering (SERS) in atrazine incorporated into silver nanoparticles (AgNPs) colloids, with the SERS spectra being treated with Sammon’s mapping, an information visualization technique. In addition to providing a fingerprint of the atrazine molecules, SERS is advantageous in comparison with impedance spectroscopy and cyclic voltammetry applied to a sensor array of units made with layer-by-layer (LbL) films containing AgNPs and AuNPs. The combined use of SERS and information visualization methods is promising for monitoring water quality with regard to other pesticides, which may even approach single molecule detection.     

Effect of stoichiometry and pH on the structure and properties of Chitosan/Chondroitin sulfate complexes

This work reports the formation of chitosan (CHT)/chondroitin sulfate (CS) polyelectrolyte complexes and evaluates the changes in their complexation-stoichiometries, crystallinity, and mechanical properties at different pHs used for both complex preparation and swelling. Through high-performance liquid chromatography, the changes in CHT/CS complex stoichiometry due to CS release from CHT/CS complexes, which occurred mainly during swelling at pH ??6, were determined. In addition, strong evidences of self-assembling on CHT/CS complex network as swelled at pH?12 buffer were observed by WAXS patterns. Such a new rearrangement of the network increases the CHT/CS complexes rigidity as well as their elastic moduli, E, as observed through compressive tests. The results found in this work provide new information to allow the tailoring of the biofunctionalities of the CHT/CS complex for the development of physiological pH-compatible materials.     

Bactericidal activity of hydrogel beads based on N,N,N-trimethyl chitosan/alginate complexes loaded with silver nanoparticles

Polysaccharide-based composite materials (beads) containing silver nanoparticles (AgNPs) were successfully prepared. Hydrogel beads acted as an efficient vehicle for Ag⁺ delivery. Beads promoted the AgNPs protection and inhibited their aggregation. Antimicrobial assays showed that the beads/AgNPs concentration can be modulated to deliver an amount of Ag⁺ necessary for kill Escherichia coli cells.     

A robust and informative method for solving large-scale power flow problems

Solving power flow problems is essential for the reliable and efficient operation of an electric power network. However, current software for solving these problems have questionable robustness due to the limitations of the solution methods used. These methods are typically based on the Newton–Raphson method combined with switching heuristics for handling generator reactive power limits and voltage regulation. Among the limitations are the requirement of a good initial solution estimate, the inability to handle near rank-deficient Jacobian matrices, and the convergence issues that may arise due to conflicts between the switching heuristics and the Newton–Raphson process. These limitations are addressed by reformulating the power flow problem and using robust optimization techniques. In particular, the problem is formulated as a constrained optimization problem in which the objective function incorporates prior knowledge about power flow solutions, and solved using an augmented Lagrangian algorithm. The prior information included in the objective adds convexity to the problem, guiding iterates towards physically meaningful solutions, and helps the algorithm handle near rank-deficient Jacobian matrices as well as poor initial solution estimates. To eliminate the negative effects of using switching heuristics, generator reactive power limits and voltage regulation are modeled with complementarity constraints, and these are handled using smooth approximations of the Fischer–Burmeister function. Furthermore, when no solution exists, the new method is able to provide sensitivity information that aids an operator on how best to alter the system. The proposed method has been extensively tested on real power flow networks of up to 58k buses.     

Superabsorbent hydrogel nanocomposites based on starch-g-poly(sodium acrylate) matrix filled with cellulose nanowhiskers

Superabsorbents hydrogel nanocomposites based on starch-g-poly(sodium acrylate) and cellulose nanowhiskers (CNWs) were synthesized. A set of experiments was performed to evaluate the influence of some factors such as NaAc/starch mass ratio, crosslinker, and nanowhiskers amount in the swelling capacity and swelling kinetics. Increasing the NaAc/starch mass ratio up to 7 leads to an increase in the water uptake at a maximum value, however, higher ratios decreased that value due to the increase of crosslinking points. Similarly, the incorporation of CNWs up to 10 wt% provided an improvement in the swelling due to the hydrophilic groups from cellobiose units. Further, the incorporation of CNWs diminishes the water uptake. Besides, the CNWs improved the mechanical properties. SEM images showed that CNWs increase the average porous size of composites. The composites presented good responsive behavior in relation to pH and salt presence allowing those materials suitable for many potential applications.     

Kinetic Study of Bovine Serum Albumin (BSA) Released from Alginate-Ca2+/PNIPAAm Hydrogels

Summary: In this work the releasing of Bovine Serum Albumin (BSA) from thermosensitive hydrogels of alginate-Ca²⁺/PNIPAAm was investigated. The hydrogels are constituted of PNPAAm network interpenetrated in alginate-Ca²⁺ network, so the hydrogels are IPN-typed. The PNIPAAm network was synthesized in the first step in which the sodium alginate remained soluble. The alginate-Ca²⁺ network was formed in the second step by immersion the membrane obtained on the first step in aqueous calcium chloride. It was changed the amount of NIPAAm in the feed solution of the first step. The fractions of BSA released as a function of time were treated according to the mathematical model recently published by our lab [J. Coll. Interf. Sci. 2007 , 310, 128] that allows predicting the whole profile of solute released from polymer networks. This mathematical model is based in the partition phenomena. The amount of BSA released from alginate-Ca²⁺/PNIPAAm hydrogels changes inversely to both amount of PNIPAAm and temperature. Thus, the IPN-typed matrixes of alginate-Ca²⁺/PNIPAAm may be considered as smart hydrogels for release the BSA because the amount and rate of released BSA can be tailored by the amount of PNIPAAm in the hydrogel and by the control of temperature. Finally, the whole profile of released BSA can be adequately fitted by the model based in the partition phenomenon. From that model the kinetic parameter t_1/2 and rate constant of releasing, k_R, were calculated for the different hydrogels investigated in this work.     

Anthraquinone and Azo Dyes in Dyeing Processes of PET Films and PET Knitted Fabrics Using Supercritical CO2 Medium

Summary: Dyeing processes using supercritical fluid present advantages over the conventional dyeing process using aqueous medium. Previous works from our group on polymeric fibers such as N,N-dimethylacrylamide (DMAAm) modified poly(ethylene terephthalate), PET, showed higher sorption of disperse dyes in supercritical medium. Furthermore, recent studies showed that the association of UV radiation and DMAAm treatment leads to a better incorporation of dyes in modified PET soaked in aqueous medium. In this work, modified and non-modified PET knitted fabrics (KF) were dyed in supercritical CO₂ medium. Azo and anthraquinone dyes were used in order to compare the extent of incorporated dye in PET films and PET KF in supercritical CO₂. The dyeing process variables were studied by factorial design and by a response surface methodology (RSM) technique. The anthraquinone dye presented a better incorporation in PET than the azo dye. The UV light exposure and the dyeing times inputs showed positive main effects in the incorporation of dyes in PET films and PET KF. From the RSM data, DMAAm and UV light modified PET KF presented 7.43 mg of incorporated azo dye by g of PET if the optimized dyeing conditions, time: 135 min and pressure: 212 bar would be used. In the respective optimized dyeing conditions for the anthraquinone dye, time 150 min and pressure 229 bar, the incorporated dye would be 22.9 mg of dye by g of PET.