Transient Spark Discharge Generated in Various N2/O2 Gas Mixtures: Reactive Species in the Gas and Water and Their Antibacterial Effects

Reactive species generated in the gas and in water by cold air plasma of the transient spark discharge in various N₂/O₂ gas mixtures (including pure N₂ and pure O₂) have been examined. The discharge was operated without/with circulated water driven down the inclined grounded electrode. Without water, NO and NO₂ are typically produced with maximum concentrations at 50% O₂. N₂O was also present for low O₂ contents (up to 20%), while O₃ was generated only in pure O₂. With water, gaseous NO and NO₂ concentrations were lower, N₂O was completely suppressed and HNO₂ increased; and O₃ was lowered in O₂ gas. All species production decreased with the gas flow rate increasing from 0.5 to 2.2 L/min. Liquid phase species (H₂O₂, NO₂￣, NO₃￣, ^·OH) were detected in plasma treated water. H₂O₂ reached the highest concentrations in pure N₂ and O₂. On the other hand, nitrites NO₂￣ and nitrates NO₃￣ peaked between 20 and 80% O₂ and were associated with pH reduction. The concentrations of all species increased with the plasma treatment time. Aqueous ^·OH radicals were analyzed by terephthalic acid fluorescence and their concentration correlated with H₂O₂. The antibacterial efficacy of the transient spark on bacteria in water increased with water treatment time and was found the strongest in the air-like mixture thanks to the peroxynitrite formation. Yet, significant antibacterial effects were found even in pure N₂ and in pure O₂ most likely due to high ^·OH radical concentrations. Controlling the N₂/O₂ ratio in the gas mixture, gas flow rate, and water treatment time enables tuning the antibacterial efficacy.

     

Covalent Adaptable Networks with Tunable Exchange Rates Based on Reversible Thiol–yne Cross‐Linking

The design of covalent adaptable networks (CANs) relies on the ability to trigger the rearrangement of bonds within a polymer network. Simple activated alkynes are now used as versatile reversible cross‐linkers for thiols. The click‐like thiol–yne cross‐linking reaction readily enables network synthesis from polythiols through a double Michael addition with a reversible and tunable second addition step. The resulting thioacetal cross‐linking moieties are robust but dynamic linkages. A series of different activated alkynes have been synthesized and systematically probed for their ability to produce dynamic thioacetal linkages, both in kinetic studies of small molecule models, as well as in stress relaxation and creep measurements on thiol–yne‐based CANs. The results are further rationalized by DFT calculations, showing that the bond exchange rates can be significantly influenced by the choice of the activated alkyne cross‐linker.     

Barrier Dispersion-Based Coatings Containing Natural and Paraffin Waxes

Petroleum, synthetic, and natural waxes have been used as hydrophobic bases for dispersions intended for use as barrier coatings for packaging paper. Oil-in-water dispersions with alkaline pH were prepared by a two-step homogenization procedure containing paraffin wax, with various characteristics, the Fischer–Tropsch synthesis product or beeswax. The size of the dispersed particles determined by dynamic light scattering depended on the type of hydrophobic base used and was in the range of 350–440 nm. The ability of dispersion particles in aggregation driven by electrostatic attraction, evaluated by Zeta potential analysis by electrophoretic light scattering, was from −26 to −50 mV. Static multiply light scattering was used for 30 days of stability assessment and helped to select the dispersion with a Sarawax SX70 wax base as the most stable. Dispersions were further used for coating the backing of kraft paper by the Meyer rod method. Coated paper with an applied coating of 6 g/m² had very good hydrophobic properties (Cobb60 < 4 g/m²), sufficient strength properties, and air permeation, which enabled its application as a packaging material. The dispersions based on Sarawax SX70 wax were evaluated as the best coating for Mondi ProVantage Kraftliner 125 g/m² backing paper. Good hydrophobic properties and strength properties indicate the possibility of using the SX70-based wax dispersion coating as a replacement for PFAS coatings in some applications.     

Fluorescence properties of some 2-(4-amino-substituted-3-nitrophenyl)-3-hydroxyquinolin-4(1H)-ones

2-(4-Amino-substituted-3-nitrophenyl)-3-hydroxyquinolin-4(1H)-ones have been studied to evaluate their fluorescence properties and possible use as molecular fluorescent probes. The amino group was substituted with various alkyl moieties possessing a suitable terminal functional group (such as hydroxy or amino group) that could serve to bind a 3-hydroxyquinolin-4(1H)-one (3HQ) fluorescence label to a biomolecule. Besides simple hydrocarbon chains, ligands containing ethylenoxy units as optimal spacers were also tested. The structure-fluorescence properties and theoretical applicability of the studied molecules are discussed.     

Chlorination reaction behavior of Zircaloy-4 hulls: experimental and theoretical approaches

Chlorination reaction behavior of Zircaloy-4 (Zry-4) cladding hulls was demonstrated by using a quartz reactor system. By reacting at 380 °C for 3 h, mass of the Zry-4 hulls decreased by 65.8 wt% with Cl₂ utilization of 87.1 mol%. Composition of collected product was analyzed and it was revealed that concentration of Zr was higher than 99.97 wt%. The purity of Zr in the experimental result was higher than expectation when considering Sn (1.31 wt%) and Fe (0.25 wt%) contents which can produce gaseous SnCl₄ and FeCl₃ at the experimental condition. Theoretical calculations were performed to clarify the high purity of Zr by using the HSC code. The simulation results revealed that formation of ZrCl₄ is more preferred than SnCl₄, FeCl₃, and CrCl₃. The preference of chloride formation was confirmed by the theoretical calculation, and it was suggested that the major constituents of Zry-4 might react with Cl₂ to produce chlorides in an order of ZrCl₄ > CrCl₃ > SnCl₄ > FeCl₃. It was also suggested that continuous removal of ZrCl₄ and sufficient supply of Zr source during the chlorination reaction might have contributed to the high purity of Zr.     

Photoinitiated RAFT polymerization of vinyl acetate

A photoinitiation process was investigated to develop a rapid and well‐controlled RAFT polymerization method applied to vinyl acetate (VAc) using methyl (ethoxycarbonothioyl)sulfanyl acetate (MESA) and bis(2,4,6‐trimethylbenzoyl)phenylphosphine oxide as the RAFT agent and photoinitiator, respectively. MESA was selected as the photochemically inert RAFT agent to minimize photolysis of the thiocarbonylthio groups during polymerization. Poly(vinyl acetate) with a prespecified well‐controlled molecular weight (MW) and a narrow MW distribution was successfully synthesized. The polymerization reaction proceeded as a living polymerization and was remarkably rapid compared with approaches that use thermally initiated processes with a very short induction period. A detailed kinetic study of the mechanism underlying the polymerization reaction, however, revealed that the chain ends containing xanthate moieties were not perfectly stable upon UV‐irradiation, and they generated radicals via homolytic cleavage. This reaction appeared to proceed by a combination of a degenerative transfer RAFT mechanism and a dissociation‐combination mechanism. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Hydrolysis of carboxylate and phosphate esters using monopyridinium oximes in cationic micellar media

The reactions of p‐nitrophenyl acetate (PNPA) with a series of monopyridinium oximes, viz. 2‐PAM (2‐hydroxyiminomethyl‐1‐methylpyridinium iodide), 3‐PAM (3‐hydroxyiminomethyl‐1‐methylpyridinium iodide), and 4‐PAM (4‐hydroxyiminomethyl‐1‐methylpyridinium iodide) have been studied in the presence of cationic surfactants of same hydrophobic chain length (C₁₆) within the concentration range of 0.5–6.0 mM at pH 8.0 under the pseudo‐first‐order condition. The observed rate constant (k_obs) increases with increasing surfactant concentration culminating into a maximum, and this has been analyzed in detail following the concepts of micellar catalysis. The structure–activity relationship of the investigated oximes has been discussed, and 2‐PAM was found to be the most reactive among all the three investigated oximes for the cleavage of PNPA. Esterolytic decomposition of p‐nitrophenyldiphenyl phosphate with oximate ions (? CH?NO^?) was followed in cetyltrimethylammonium bromide micelles at pH 9.0, and 4‐PAM was the most reactive oxime for the micellar hydrolysis of phosphate ester. The apparent acid dissociation constants (pK_a) of the investigated oximes have been determined spectrophotometrically. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 569–578, 2011