Rise in the pH of an unfrozen solution in ice due to the presence of NaCl and promotion of decomposition of gallic acids owing to a change in the pH

Oxidative decomposition of gallic acid occurs in alkaline solutions but hardly arises in acidic solutions. We have found that the addition of sodium chloride promotes the decomposition of gallic acid caused by freezing even under neutral and acidic conditions. Even at pH 4.5, gallic acid was decomposed by freezing in the presence of NaCl; however, in the absence of NaCl, it was hardly decomposed by freezing at pH lower than 7. Chloride ions are more easily incorporated in ice than sodium ions when the NaCl solution is frozen. The unfrozen solution in ice becomes positively charged, and as a result, protons transfer from the unfrozen solution to the ice. We measured the pH in the unfrozen solution which coexists with single-crystal ice formed from a 5 mmol dm(-3) NaCl solution and determined the pH to be 8.6 at equilibrium with CO(2) of 380 ppm or 11.3 in the absence of CO(2) compared to pH 5.6 in the original solution. From the model calculation performed for gallic acid solution in the presence of 5 mmol dm(-3) NaCl, it can be estimated that the amount of OH(-) transferred from the ice to the solution corresponds to 1.26 x 10(-5) mol dm(-3). The amount of OH(-) transferred is concentrated into the unfrozen solution and affects the pH of the unfrozen solution. Therefore, the pH in an unfrozen gallic acid solution in ice becomes alkaline, and the decomposition of gallic acid proceeds. It is expected that other base-catalyzed reactions in weakly acidic solutions also proceed by freezing in the presence of NaCl without the need for any alkaline reagents.     

Radiation-Chemical Aspects of Radioactive Waste Management

Studies of radiation-chemical processes in model liquid radioactive waste are summarized. These processes are radiolytic transformations of various substances present in the waste (actinide ions (primarily, neptunium and plutonium ions), inorganic matter (for example, nitrate ions), and organic compounds (acetic acid, EDTA, etc.)) and radiolytic gas evolution. Attention was focused on the latter process. The volumes and compositions of gases formed in the -radiolysis of aqueous solutions that simulated intermediate-level and high-level liquid waste were determined. It was found that the nature and the radiation-chemical yields of released gases depend on the absorbed dose, the composition and concentration of solutions, the irradiation temperature, the presence of solid substances, etc. In a number of cases, data obtained with model solutions were compared to the results of studies of real liquid radioactive waste.     

The effect of pH on the room-temperature phosphorescence properties of several purine and pyrimidine derivatives

Room-temperature phosphorescence (RTP) spectra of eleven purines and pyrimidines adsorbed on Whatman No. 40 filter paper have been determined in acidic, neutral and basic media. RTP excitation and emission wavelengths do not vary significantly with pH. For most compounds, use of basic (pH approximately 13) solutions yields stronger RTP signals than use of neutral or acidic (pH approximately 1.6) solutions. Exceptions are adenine, theobromine and theophylline, which give larger RTP signals when in neutral than in basic conditions. The existence of differences in phosphorescence quantum yields between the various ionic species as well as of specific pH-related interactions with the substrate is discussed. Absolute limits of detection, ranging between 0.4 and 38 ng for selected compounds, depend on the pH of the analyte solution.     

Effect of selected scavengers on radiolytic degradation of 2,4-dichlorophenol for environmental purposes

The effect of pH of irradiated aerated solutions and the presence of various concentrations of bicarbonate and nitrate on radiolytic degradation of 2,4-dichlorophenol in aqueous solutions with γ-irradiation was examined using reversed phase HPLC and ion chromatography. The obtaining complete decomposition and dehalogenation of 2,4-dichlorophenol in the presence of naturally occurring inorganic scavengers may require to increase the irradiation dose in batch conditions up to 10 kGy. The presence of scavengers at different doses affects both efficiency of radiolytic degradation and its mechanism.     

Polarographic study on poly alpha-L-glutamic acid-Cd2+,Co2+ complexes in the helix-coil pH region

Interactions between poly alpha- L-glutamic acid (PGA) and metal ions Cd(2+), Co(2+) were studied by direct current polarography. The diffusion currents of these ions decreased sharply in the presence of PGA in the pH region from 5.0 through neutral. A corresponding increase in the helix content of the PGA-metal ion complex was revealed by CD measurements on the same solutions. Helix contents determined by polarography were in good agreement with those by CD in the neutral pH region. On the contrary, the decrease of current in lower acidic pH regions was independent of helix formation and suggested that metal ions coordinate to sporadically-dissociated carboxylate groups to cause aggregation of the intra and/or inter polymer chains. The diffusion current of the ions, therefore, is a parameter sensitive to the conformational changes of PGA from acidic through neutral pH region.     

Sample preparation procedure for PIXE elemental analysis on soft tissues

Neutral aqueous solutions of Nickel II-diethylenetriaminepentaacetate (DTPA) were irradiated using -rays both in the presence and in the absence of oxygen. A radiolytic mechanism has been proposed and discussed. It has been suggested that the radiolytic degradation of the ligand is due to the formation of OH^* during radiolysis.     

Copper release kinetics from a long-term contaminated acid soil using a stirred flow chamber: effect of ionic strength and pH

The effect of pH and ionic strength on copper release in a long-term Cu-polluted soil was studied using a stirred flow chamber. The presence of Ca(2+) and Na(+) was also evaluated. More copper was released as the ionic strength increased, and it was significantly higher in the presence of Ca(2+) than in the presence of Na(+). The maximum amount of Cu that could be released under experimental conditions increased logarithmically as the ionic strength increased, and the release rate parameters were not significantly correlated with ionic strength values. The maximum amount of Cu that could be released was similar for solutions with pH values between 5.5 and 8.5. For solutions with a pH value below 4.5, the amount of Cu released increased exponentially as the pH decreased. The release rate parameters and Cu release pattern were affected by pH, especially for more acidic solutions (pH values of 2.5 and 3.5).     

Interfacial Tension Measurements Between Oil Fractions of a Crude Oil and Aqueous Solutions with Different Ionic Composition and pH

Dynamic and equilibrium interfacial tensions between crude oil fractions and aqueous solutions of various compositions and pH were measured. The basic oil components seemed to determine the interfacial tensions at pH 2, while the non-dissociated and dissociated acidic components governed the interfacial tension at the natural pH and pH 9, respectively. The ionic composition of the aqueous phase influenced the degree of dissociation of the acidic components at pH 9: Na⁺ ions in the aqueous phase promoted dissociation of the interfacial acidic components (compared to pure water), while Ca²⁺ ions resulted in complexation with the dissociated acids and most likely formation of stable interfacial films. The amount of Ca²⁺ determined which of these phenomena that dominated when both ions were present in sea water solutions. Generally, the interfacial tensions of the oil fractions were lower when measured against the high salinity aqueous solutions than against the corresponding low salinity solutions.      

Raman spectroscopic study of the conformational order of octadecylsilane stationary phases: effects of electrolyte and pH

This study investigates effects of the electrolyte, of acidic and basic compounds, and of pH on the rotational and conformational order of octadecylsilane stationary phases with surface coverages of 3.09 and 6.45 mol/m². Both phases exhibit an increase in alkyl chain rotational and conformational order in 5–200 mM aqueous electrolyte solutions relative to water. These stationary phases are effectively salted-out of aqueous electrolyte solutions, thereby causing alkyl chain intermolecular interactions to increase with a concomitant increase in alkyl chain order. Although the presence of acidic and basic compounds generally has no effect on the conformational order of either stationary phase as a function of pH, the higher coverage stationary phase does exhibit pH-dependent changes in aqueous solutions of benzoic acid. At pH values below the pK_a of benzoic acid, the conformational order of this stationary phase is unchanged relative to that observed in the same pH solution in the absence of benzoic acid. In light of independent evidence that such monosubstituted aromatics interact with the octadecylsilane stationary phase under these conditions, the absence of a measurable effect on alkyl chain order for these conditions is attributed to benzoic acid self-association at the stationary phase-mobile phase interface. In contrast, at pH values above the pK_a of benzoic acid, slight disordering of the alkyl chains is observed and is attributed to repulsive interactions between retained benzoate anions.Electronic Supplementary Material Supplementary material is available for this article at     

Study by electron paramagnetic resonance and spectrophotometry of absorption of the primary processes in photochemistry of frozen aqueous solutions at 77 degree K of aromatic amino acids and polypeptides

Abstract— Neutral, acidic or basic frozen aqueous solutions of aromatic amino acids undergo photoionisation under u.v. irradiation, at 77°K. In neutral or basic solutions, photo-ejected electrons are trapped in the solvent matrix and exhibit a characteristic absorption band in the visible region. In acidic solutions electrons are trapped by protons and ESR signal spectrum of hydrogen atoms may be observed. Hydrogen atoms are also produced in low yield in neutral or basic frozen aqueous solutions, u.v. irradiated at 77°K. In basic media the ESR spectrum of 0^- radical ions is observed. Kinetic studies as a function of light intensity show that photoionisation takes place after absorption of a second photon by the phosphorescent molecule in its lowest triplet state. Recombination of trapped electrons in neutral or basic solutions may be induced using secondary excitation with visible light. In all instances we could record the absorption spectrum of photolytic products of aromatic amino acids and polypeptides which are u.v. irradiated at 77°K.     

Radiolytic decomposition of pesticide carbendazim in waters and wastes for environmental protection

The radiolytic degradation of widely used fungicide, carbendazim, in synthetic aqueous solutions and industrial wastewater was investigated employing γ-irradiation. The effect of the absorbed dose, initial concentration and pH of irradiated solution on the effectiveness of carbendazim decomposition were investigated. Decomposition of carbendazim in 100 μM concentration in synthetic aqueous solutions required irradiation with 600 Gy dose. The aqueous solutions of carbendazim have been irradiated in different conditions, where particular active radical species from water radiolysis predominate. The obtained data have been compared with the kinetic modeling. The reversed-phase high-performance liquid chromatography was used for the determination of carbendazim and its radiolytic decomposition products in irradiated solutions. The changes of toxicity of irradiated solutions were examined with different test organisms and human leukemia cells.     

Colloidal Regularities of the Interaction between Uranium(VI) and the Cells of Metal-Resistant Bacillus cereus AUMC 4368 Bacterial Culture

Sorption of uranium(VI) by the cells of metal-resistant Bacillus cereus AUMC 4368 bacterium was studied in aqueous solutions as a function of pH, equilibrium concentration of metal, and the presence of co-ions with account of the changes in phase state of metals and biocolloids. Experimental data indicate that the sorption of uranium(VI) by negatively charged biocolloids is maximal at pH 4.2–4.5 (1.2 mM per 1g of dry biomass), when metal is present in the form of positively charged hydroxocomplexes. At pH 8, the interaction between uranium(VI) and the cells is inhibited due to the formation of negatively charged water-soluble hydroxocarbonate complexes and uranate ions. Co, Sr, Cu, Ca, Mg, and Zn ions do not influence the efficiency of sorption of uranium(VI) in a weakly acidic medium, but can cause inhibiting effect in neutral pH region. The most pronounced effect expressed in broadening of sorption range and in the heterocoagulation of uranyl is observed in the presence of Fe³⁺ ions. It was established that the binding of uranium(VI) occurs by the carboxyl surface groups of Bacillus cereuscell surface. Uranium(VI) is irreversibly bound by the carboxyl groups of cell surface and its efficient desorption is possible only during the interaction with citric acid or sodium hydrocarbonate with the formation of water-soluble complexes transferred to aqueous phase. It was shown that uranyl in the form of organocomplexes (citric, humatic, and fulvatic) is not sorbed by biocolloids.     

Investigation in the Series of Substituted Butan- and Butenolides: XV. Transformations of 4-Hydroxy-2-butenolide in Water Media at Various pH Values

The 4-hydroxy-2-butenolide was established by polarographic method to undergo in water solutions fast tautomeric and acid-base transformations. Depending on pH of the medium the compound is present either as a cyclic irreducible form (at pH 0-4) or in the open-chain (carbonyl-containing) reducible forms (at pH > 4 and < 0). It is presumed that in going from the basic to strongly acidic medium and backwards occur consecutive equilibrium transitions of four species: cis--formylacrylic acid anion (A^-), its neutral molecule (HA) existing as linear and cyclic tautomers, and protonated forms (H₂A⁺ and H₃A⁺). The formation mechanism thereof is considered.     

Radiation decomposition of Co(acac)3 in alcohol-water matrices

The reduction yields of Co(acac)₃ in methanol-water (11) solutions and also the formation yields of the radiolysis products Co(acac)₃Co(acac)₂ + acac have been determined. These yields were found to depend considerably on the acidity and also on the initial complex concentration. Solvated electrons, transformed in acidic solutions into atomic hydrogen, less effective in reducing acetyloacetonate, are of basic significance in the reduction process of Co(acac)₃. Studies of the methanol-glycol Co(acac)₃ solutions showed that the type of radiolytic products formed depends on the composition of the matrix.     

Radiolysis of nitrate-alcohol binary mixtures at pH 12

Gamma-radiolysis of alkaline binary mixtures of nitrate-alcohol (1-propanol and 1-butanol) has been investigated at a fixed pH of 12. The products of radiolysis, mainly nitrite, aldehyde and hydrogen peroxide were estimated. Also the effect of concentration of each species present in the mixture on the G-values of the products formed has been examined. The G-values of each of the products are found to be lower in basic medium in binary mixtures as compared to those obtained at neutral pH; other conditions being kept constant. However, the yields of products in nitrate solutions show higher values at basic pH in comparison with their counterparts at neutral pH. Results are explained on the basis of reaction mechanism that operates during the process of radiolysis, leading to the formation of the different products.     

Electrospray ionization of alkali and alkaline earth metal species. Electrochemical oxidation and pH effects

The utility of electrospray ionization mass spectrometry (ESI-MS) for characterizing dissolved metal species has generated considerable interest in the use of this technique for metal speciation. However, the development of accurate speciation methods based on ESI-MS requires a detailed understanding of the mechanisms by which dissolved metal species are ionized during electrospray. We report how the analysis of alkali and alkaline earth metal species provides new information about some of the processes that affect electrospray ion yield. Selected metal ions and organic ligands were combined in 50 : 50 water-acetonitrile buffered with acetic acid or ammonium acetate and analyzed by flow injection ESI-MS using mild electrospray conditions. Species formed by alkali metal ions with thiol and oxygen-donating ligands were detected in acidic and neutral pH solutions. Electrochemical oxidation of N, N-diethyldithiocarbamate and glutathione during electrospray was indicated by detection of the corresponding disulfides as protonated or alkali metal species. The extent of ligand oxidation depended on solution pH and the dissociation constant of the thiol group. Tandem mass spectrometric experiments suggested that radical cations such as [NaL](+.) (where L=N,N-diethyldithiocarbamate) can be generated by in-source fragmentation of disulfide species. Greater complexation of alkali metals at neutral pH was indicated by a corresponding decrease in the relative abundance of the free metal ion. The number of alkali metal ions bound by glutathione and phthalic acid also increased with increasing pH, in accordance with thermodynamic equilibrium theory. Alkaline earth metal species were detected only in acidic solutions, the absence of 8-hydroxyquinoline complexes being attributed to their relative instability and subsequent dissociation during electrospray. Hence, accurate speciation by ESI-MS depends on experimental conditions and the intrinsic properties of each analyte. Copyright 2000 John Wiley & Sons, Ltd.     

Osmotic coefficients and activity coefficients of lodic acid at high concentrations

Isopiestic vapor pressure measurements have been used to determine the osmotic coefficients of aqueous solutions of iodic acid at molalities from 0.1 to 17 mole-kg^?1 at 25°C. The isopiestic standards were solutions of sodium chloride and solutions of sulfuric acid. Because of the corrosive nature of iodic acid, platinum cups were used. Stoichiometric activity cofficients of iodic acid were derived by a Gibbs-Duhem integration. The activity coefficients for solutions of molality greater than 0.5 mole-kg^?1 cannot be accounted for in terms of the two equilibria, namely, the acidic dissociation of iodic acid and formation of the ion H(IO₃) ₂ ^? , shown by Pethybridge and Prue to explain adequately the behavior in dilute solutions. The activity coefficient is unexpectedly small in concentrated solutions, suggesting the formation of neutral aggregates of iodic acid. The presence of dimers and tetramers, or alternatively trimers and tetramers, can explain the observed results up to a molality of 7 mole-kg^?1.     

Selective solid phase extraction of platinum on an ion imprinted polymers for its electrothermal atomic absorption spectrometric determination in environmental samples

An ion-imprinted polymer (IIP) was obtained by copolymerization of methacrylic acid (as a functional monomer) and ethylene glycol dimethacrylate (as a crosslinking agent) in the presence of various chelators for Pt(II) ion and using 2,2??-azo-bis-isobutyronitrile as the initiator. Specifically, acetaldehyde thiosemicarbazone (AcTSn) and benzaldehyde thiosemicarbazone (BnTSn) were used as chelators. The IIPs were applied as sorbents for solid-phase extraction of Pt(II) and Pt(IV) ions from aqueous solutions. The effects of acidity and flow rate of the sample, of elution conditions and of potentially interfering ions were investigated. The imprinting effect of analyte is clearly demonstrated by the fact that only the IIP is capable of quantitative retention of Pt(II) and Pt(IV) ions. The method works best in the pH range from 0.5 to 1 and from 3.5 to 9.5. The ions can be recovered with an acidic solution of thiourea. The Pt-AcTSn polymer displays better sorption properties for the separation of analytes. The selectivity coefficients of the Pt-AcTSn and control polymers for Pt(IV) in the presence Pd(II), Rh(III), Ru(III), Al(III) and Cu(II) were calculated, and the sorbent capacity for Pt(IV) was found to be 4.56???g?g?^-1. The method was successfully applied to the determination of Pt(IV) by electrothermal atomic absorption spectrometry in tap water, tunnel dust and anode slime samples.

pH-dependent magnetic phase transition of iron oxide nanoparticles synthesized by gamma-radiation reduction method

In this study, the influence of pH variation on structural and magnetic phase transition of gamma radiolytic synthesized iron oxide nanoparticles is investigated. The structure and magnetic properties of irradiated samples are characterized using X-ray diffraction, Fourier transfer infrared spectroscopy, transmission electron microscopy, and vibrating sample magnetometer. It was found that, in acidic irradiated solution, Fe³⁺ ions make various complexes with polyvinyl alcohol and water molecules which exhibit a multiphase magnetic property as a mixture of dia and paramagnetic materials. On the other hand, in basic condition, rate of radiation induced reduction of Fe³⁺ ions increased which leads to the formation of superparamagnetic Fe₃O₄ nanoparticles. By increasing pH value, in strong basic condition, the tendency of paramagnetic iron (III) oxy-hydroxide formation was high compared to other phases. This variation in the magnetic properties was explained based on iron ions reduction mechanism and the variation of the ligands’ properties during formation of nanoparticles under irradiation.