Electron beam induced degradation of clopyralid in aqueous solutions

The degradation characteristics of clopyralid irradiated by electron beam (EB) was studied in aqueous solutions. The effects of factors, such as initial clopyralid concentrations, addition of radicals scavenger, initial solution pH and addition of H₂O₂, were investigated on clopyralid degradation efficiency and mechanism. It was found that the EB-radiolysis was an effective way to degrade clopyralid and its degradation rate decreased with the increasing of substrate concentration. In the investigated initial concentrations range of 100?C400 mg L^?1, the radiolytic degradation of clopyralid followed a pseudo-first kinetic order. The results from addition of radicals scavenger indicated that both ^?OH and e _aq ^? played significant roles in the degradation of clopyralid. Furthermore, the alkaline condition and addition of H₂O₂ (<10 mM) in the solution also slightly enhanced the efficiency of clopyralid degradation. The ion chromatography analysis showed that some organic acids (formic acid, acetic acid and oxalic acid) were formed, while the completely dechlorination of the substrate was achieved and organic nitrogen was recovered in the form of ammonium and nitrate ions during the irradiation process.     

Chemomechanics of surface stresses induced by DNA hybridization

When biomolecular reactions occur on one surface of a microcantilever beam, changes in intermolecular forces create surface stresses that bend the cantilever. While this phenomenon has been exploited to create label-free biosensors and biomolecular actuators, the mechanisms through which chemical free energy is transduced to mechanical work in such hybrid systems are not fully understood. To gain insight into these mechanisms, we use DNA hybridization as a model reaction system. We first show that the surface grafting density of single-stranded probe DNA (sspDNA) on a surface is strongly correlated to its radius of gyration in solution, which in turn depends on its persistence length and the DNA chain length. Since the persistence length depends on ionic strength, the grafting density of sspDNA can be controlled by changing a solution's ionic strength. The surface stresses produced by the reaction of complementary single-stranded target DNA (sstDNA) to sspDNA depend on the length of DNA, the grafting density, and the hybridization efficiency. We, however, observe a remarkable trend: regardless of the length and grafting density of sspDNA, the surface stress follows an exponential scaling relation with the density of hybridized sspDNA.     

Gamma-radiation induced decolorization and degradation on aqueous solutions of Indigo Carmine dye

Cesium uptake by natural zeolite clinoptilolite from Bulgaria was studied using batch technique and model solutions. The optimal conditions of interaction were determined. The pseudo-second-order rate model better describes the kinetic data obtained at different concentrations. The intraparticle diffusion and the surface diffusion models were tested to identify the rate-controlling step. The sites in the structure of clinoptilolite that are preferable for exchange were studied by application of Rietveld structural approach and the sequence of site occupation by cesium was followed. The Langmuir isotherm model provides a good fit of the equilibrium experimental data. The thermodynamic parameters for the system were calculated.     

Salting-in of alcohols in aqueous solutions by tetraalkylammonium bromides at the freezing temperature

The freezing-point depression of the ternary systems tetraalkylammonium bromides-t-butanol-water for the first five homologs of R₄NBr was measured. In the case of Bu₄NBr, the effect of size of the alcohol (methahol ton-butanol) was also investigated. From the corresponding freezing-point data for the binary systems the apparent salting constants were calculated. The true salting constantsk _s were obtained by extrapolation to infinite dilution. These are all very close to zero at the freezing temperature. From the corresponding thermochemical data the temperature dependence ofk _s was calculated, and above 5°C all the R₄NBr salts int-butanol; the salting-in increases with temperature and with the size of the hydrophobic cations. The scaled-particle theory is at present the only one which can account semiquantitatively for the temperature dependence of the salting-in effect. On leave of absence from Chemistry Department, The University, Sheffield S3 7HF, England To whom correspondence should be addressed.     

Thermodynamics of aqueous solutions of orthophosphoric acid from the freezing point to 298.15°K

The osmotic coefficients of aqueous phosphoric acid have been determined at 298.15°K, at 273.15°K, and at the freezing point, and for concentrations from about 10^?4 m to 15 m. Phosphoric acid is incompletely dissociated even at very low concentrations, but it was possible to derived mean activity coefficients for the species H⁺ and H₂PO ₄ ^? by treating phosphoric acid as a 1-1 electrolyte.     

Enhanced protonation of cresol red in acidic aqueous solutions caused by freezing

The protonation degree of cresol red (CR) in frozen aqueous solutions at 253 or 77 K, containing various acids (HF, HCl, HNO3, H2SO4, and p-toluenesulfonic acid), sodium hydroxide, NaCl, or NH4Cl, was examined using UV/Vis absorption spectroscopy. CR, a weak organic diacid, has been selected as a model system to study the acid-base interactions at the grain boundaries of ice. The multivariate curve resolution alternating least-squares method was used to determine the number and abundances of chemical species responsible for the overlaying absorption visible spectra measured. The results showed that the extent of CR protonation, enhanced in the solid state by 2-4 orders of magnitude in contrast to the liquid solution, is principally connected to an increase in the local concentration of acids. It was found that this enhancement was not very sensitive to either the freezing rate or the type of acid used and that CR apparently established an acid-base equilibrium prior to solidification. In addition, the presence of inorganic salts, such as NaCl or NH4Cl, is reported to cause a more efficient deprotonation of CR in the former case and an enhanced protonation in the latter case, being well explained by the theory of Bronshteyn and Chernov. CR thus served as an acid-base indicator at the grain boundaries of ice samples. Structural changes in the CR molecule induced by lowering the temperature and a presence of the constraining ice environment were studied by the absorption and 1H NMR spectroscopies. Cryospheric and atmospheric implications concerning the influence of acids and bases on composition and reactivity of ice or snow contaminants were examined.     

Aligned porous materials by directional freezing of solutions in liquid CO2

We report here a method for generating structures with aligned macropores by templating solidified carbon dioxide. The CO2 template phase can be removed by direct sublimation to yield a dry, solvent-free porous material that may be useful in applications such as tissue engineering and aligned cell growth.     

Chemical degradation of polystyrene induced by chlorinated nitrosobenzene

Chemically induced degradation of polystyrene (PSt) in the presence of 2,4,6-tri-chloronitrosobenzene (TCNB) as radical generator was investigated in benzene solution by means of the electron spin resonance (ESR) method. The ESR spectra observed after the addition of TCNB to PSt in benzene solution were assigned to the nitroxide radicals (spin adducts) of the PSt radicals,

,

and

. These assignments were deduced from comparisons between observed and computer simulated spectra and were supported by experiments using α-deuterated PSt. It was found by analyses of ESR spectra that two kinds of type (B) radicals were produced, which were different in local conformation. The radicals (A) and (B) were thought to be produced by hydrogen abstraction by the chlorinated phenyl radical which results from homolytic scission of the CN bond of TCNB on slight warming. On the other hand, it was concluded that β-scission of radical (A) results in the formation of the chain scission radical (C). The mechanism of degradation of PSt induced by TCNB as radical initiator is discussed, together with the decrease in molecular weight observed after the addition of TCNB to a PSt-benzene solution. From the decrease of molecular weight it is concluded that TCNB acts as a scission inducer.     

Hydroxyl radical induced from hydrogen peroxide by cobalt manganese oxides for ciprofloxacin degradation

Advanced oxidation processes (AOPs) are promising technology to remove organic pollutant in water. However, the main problem in the AOPs is the low generation of hydroxyl radical (^?OH) owing to the low decomposition efficiency of hydrogen peroxide (H₂O₂). Herein, the spinel type cobalt acid manganese (MnCo₂O₄) with flower morphology was fabricated through a co-precipitation method. In situ Fourier transform infrared spectroscopy confirms that the MnCo₂O₄ with the optimal molar ratio of Co and Mn precursors (CM3, Co:Mn = 3) has more Lewis acid sites compared with single metal oxide catalysts (Co₃O₄ and Mn₂O₃), leading to the excellent performances for H₂O₂ decomposition rate constant on CM3, which is about 15.03 and 4.21 times higher than those of Co₃O₄ and Mn₂O₃, respectively. As a result, the obtained CM3 shows a higher ciprofloxacin degradation ratio than that of Co₃O₄ and Mn₂O₃. Furthermore, CM3 shows an excellent stability during several cycles. This work proposes effective catalysts for ciprofloxacin decomposition and provides feasible route for treating practical environmental problems.     

Inverse freezing in α-cyclodextrin solutions probed by quasi elastic neutron scattering

Solutions of α-cyclodextrin, 4-methylpyridine and water undergo a reversible liquid–solid phase transition on heating (“inverse freezing”). In this paper quasi elastic neutron scattering (QENS) measurements are reported, from which the diffusive dynamics of different components in the liquid and solid phases is determined. Results imply that, in solution, α-cyclodextrin is contained in a solvation shell of 4-methylpyridine molecules, while in the crystal phase, the majority of the cell contents are immobilized on the nanosecond timescale. This information will be important in evaluating the entropy of the system in its different phases and in understanding the unusual phase transition.     

Study on the radiation degradation of polyether-polyurethane induced by electron beam

Polyether-urethane samples were irradiated at the dose range from 10 to 2000 kGy by 2 MeV electron beams. Volatile species from the polymer degradation were analyzed quantitatively and qualitatively with GC/MS. Thermal properties and micro-phase separation of the samples were examined by TG and the morphology was studied by TEM and SEM. The results show that the irradiated polyether-polyurethane evolves CO₂, H₂, CH₄ and C₂H₆, etc. The thermal stabilities between the hard and soft segments in the irradiated samples are different. At high doses, the phase separation in the sample is predominant and the hard segment of sample is more stable. The dose rate affects the soft segment of the irradiated sample much more.     

Recovery of phenols from water by extraction freezing

A procedure was developed for the recovery of phenol from aqueous solutions into acetonitrile using extraction freezing. Experimental results and the revealed regularities were discussed in the context of the proposed theoretical model. The low temperature used in the sample preparation advantageously distinguishes this procedure from the conventional versions of the extraction recovery of organic compounds from water. Moreover, the procedure does not require special glassware or expendable materials.     

Radiation induced degradation of EPR by IR oxidation profiling

Infrared absorption spectroscopy has been used to investigate the effect of γ-radiation on ethylene-propylene copolymer loaded with different amount of antioxidant. The oxidation profiles were obtained analyzing slices of the samples by an IR microscope. The IR spectra have shown that the antioxidant content does not affect the shape of the oxidation profiles; their dependence on thickness and dose rate is in good agreement with the Clough and Gillen model. Our results indicate that the antioxidant does not affect the reactions involved in the oxidation process and the oxygen distribution on the sample.     

Ion release from vesicles induced by pardaxin and its analogues

The mechanism of pore formation employed by pardaxin, a shark-repellent neurotoxin, and three of its charge-modified analogues, (N¹,Lys⁸,Lys¹⁶-trisuccinylamido)pardaxin, (N¹,Lys⁸,Lys¹⁶-triacetyl) pardaxin and (C³³-di-ethanolamido)pardaxin, was investigated. The kinetics of Tl⁺ and IO₃⁻ release from large unilamellar phospholipid vesicles was measured under acidic, neutral and basic conditions. Both the kinetics of pore formation and the ability of the analogues to release ions increase when the N-terminal amino acid residue and the peptide backbone are either neutrally or positively charged. Moreover, five- or sixfold higher concentrations of the polypeptides are required for IO₃⁻ release than for Tl⁺ release. Our results are consistent with the “barrel stave” model by which pardaxin and its analogues exert their pore-forming activities. The smallest pore permeable to Tl⁺ is impermeable to IO₃⁻, for which larger pores obtained at higher polypeptide concentrations are required.