Corresponding Values In Water Research Articles

Modeling of micellar‐catalyzed bimolecular ionic reactions by a nonlinear Poisson−Boltzmann equation and an electrostatic free energy model

AbstractThe hydrolysis reactions of crystal violet (CV) and p‐nitrophenyl acetate (PNPA) by sodium hydroxide in cetyltrimethylammonium bromide (CTAB) micellar solution were studied in this work. Combined with the Boltzmann probability of ionic species in an electrostatic potential field, a model with a numerical scheme was developed based on the nonlinear Poisson−Boltzmann equation in the micelle‐cell consisting of the reactants and the surfactant. The numerical solution gives the ionic species distribution in the micelle phase and the radius of the micelle‐phase. The dielectric constant of the micelle‐phase varies in the range of 39.8−54.4. The second‐order reaction rate constants in the micelle‐phase were determined using the electrostatic and dipolar free energy models. For the basic hydrolysis of CV and PNPA, the overall second‐order rate constants are three to five times and 1.4 times greater than the corresponding values in water, respectively. The rate enhancement occurs due to the distribution of the reactive ionic species in the cell region and the enhancement of the Coulombic and dipolar interactions among the ionic and polar reactants.

Solubilities of Amino Acids in Aqueous Solutions of Chloride or Nitrate Salts of Divalent (Mg2+ or Ca2+) Cations.

The solubilities of glycine, l-leucine, l-phenylalanine, and l-aspartic acid were measured in aqueous MgCl2, Mg(NO3)2, CaCl2,, and Ca(NO3)2 solutions with concentrations ranging from 0 to 2 mol/kg at 298.2 K. The isothermal analytical method was used combined with the refractive index measurements for composition analysis guaranteeing good accuracy. All salts induced a salting-in effect with a higher magnitude for those containing the Ca2+ cation. The nitrate anions also showed stronger binding with the amino acids, thus increasing their relative solubility more than the chloride anions. In particular, calcium nitrate induces an increase in the amino acid solubility from 2.4 (glycine) to 4.6 fold (l-aspartic acid) compared to the corresponding value in water. Amino acid solubility data in aqueous MgCl2 and CaCl2 solutions collected from the open literature were combined with that from this work, allowing us to analyze the relations between the amino acid structure and the salting-in magnitude.

Evaluation of the Perceptual Interactions among Aldehydes in a Cheddar Cheese Matrix According to Odor Threshold and Aroma Intensity.

To evaluate the contributions of 3-methylbutanal, 2-methylbutanal, 2-methylpropanal, and benzaldehyde in cheddar cheese models, the threshold values, optimal concentration ranges, and perceptual actions of these compounds were determined at various concentrations. The thresholds for 3-methylbutanal, 2-methylbutanal, 2-methylpropanal, and benzaldehyde in the cheese matrix were 150.31, 175.39, 150.66, and 500.21 μg/kg, respectively, which were significantly higher than the corresponding values in water. The optimal concentration ranges of these aldehydes were determined as 150–300, 175–325, 150–350, and 500–1500 μg/kg, respectively. Based on the results of the threshold method and Feller’s model, five binary mixtures were found to have synergistic effects, and only the pair of 2-methylpropanal and benzaldehyde was determined to have a masking effect. In addition, the synergistic olfactory effects between the four ternary mixtures and the quaternary mixture of these aldehydes were also assesSsed using Feller’s model. In a σ-τ plot analysis, synergism was usually observed when these odor pairs were at their threshold levels. In summary, the results suggested that perceptual interactions among these aldehydes exist in a cheese model variably with different concentrations and threshold ratios. This study will be helpful to a further understanding of the nutty aroma and improving the aroma quality of cheddar cheese.

Evaluation of the synergistic olfactory effects of diacetyl, acetaldehyde, and acetoin in a yogurt matrix using odor threshold, aroma intensity, and electronic nose analyses

Despite intensive analyses of yogurt flavor, the synergistic effects of the key aroma compounds on sensory responses and their optimum concentration ranges remain less well-documented. This study investigated the odor thresholds, optimum concentration ranges, and perceptual actions of diacetyl, acetaldehyde, and acetoin in a yogurt matrix. Our results show that the odor thresholds of diacetyl, acetaldehyde, and acetoin in the yogurt matrix were 5.43, 15.4, and 29.0 mg/L, respectively, which were significantly higher than the corresponding values in water. The optimum diacetyl, acetaldehyde, and acetoin concentration ranges were found to be 6.65 to 9.12, 25.9 to 35.5, and 37.3 to 49.9 mg/L, respectively. In Feller's additive model, the addition of each compound led to a significant reduction in their odor threshold in the yogurt matrix, thus demonstrating the synergistic effects of the compounds. In the σ-τ plot, various concentrations of compounds were associated with various degrees of additive behavior with respect to the aroma intensity of the yogurt matrix, thus demonstrating the synergism among these compounds in increasing the overall aroma intensity. The optimal simultaneous concentration ratio of diacetyl:acetaldehyde:acetoin was determined to be 4.00:16.0:32.0 mg/L. The specific synergistic effects were also confirmed by an electronic nose analysis and aroma profile comparison. In summary, these 3 aroma compounds exhibited synergistic effects in a yogurt matrix, thus providing a theoretical basis for the enhancement of flavors in dairy products.

A simple method for estimating the absolute solvation free energy of monovalent ions in different solvents.

The solvation Gibbs free energies (SGFE) of 39 ions were estimated in protic and aprotic solvents including methanol, ethanol, N,N-dimethylformamide (DMF) and acetonitrile (ACN) using a proposed approach. In this method, the error of the applied computational method, used for estimating the SGFE of a specific ion in water and dimethyl sulfoxide (DMSO) solvents, was used as a reference value to correct the calculated SGFE of the ion in other protic and aprotic solvents, respectively. The estimated values of SGFE of ions, obtained in this work, show good agreement with those obtained using the other methods reported in literature. New correlation equations were also proposed for correlating the estimated values of SGFE of ions in a specific solvent to the corresponding values in water and DMSO for protic and aprotic solvent. By using the proposed method in this work, it is possible to estimate the values of SGFE of ions in the solvents that there are no experimental and theoretical reports on them in literature provided that the appropriate and correct reference solvent is selected. Typically, this method was applied on two most popular solvents in organic chemistry including acetone and 1-propanol to estimate the SGFE of the considered ions in them for the first time.

Universal Charge Quenching and Stability of Proteins in 1-Methyl-3-alkyl (Hexyl/Octyl) Imidazolium Chloride Ionic Liquid Solutions

This study reports pH dependent stability of protein dispersions of five common proteins, bovine serum albumin (BSA), human serum albumin (HSA), immunoglobulin (IgG), β-lactoglobulin (β-Lg), and gelatin-B (Gel-B), all having isoelectric pH, pI ≈ 5, in room temperature ionic liquid solutions of 1-methyl-3-alkyl (hexyl/octyl) imidazolium chloride (concentration 0-0.2% w/v). Molecular hydrophobicity index, (H-index = hydrophobicity/hydrophilicity) of these molecules spanned the range 0.43-0.87. Electrophoretic characteristics, surface tension data and hydrodynamic size information revealed that IL solutions provide dispersion stability owing to specific protein-IL binding which did not alter their pI values though their surface charge was considerably screened. Change in maximum (ζ(max)) and minimum (ζ(min)) zeta potential values observed at pH ~3 (maximum protonated state) and pH ~8 (maximum deprotonated state) could be described universally as function of IL concentration, c as Δζ(x) = [1 - exp(-ac)] where Δζ(x) is either |(ζ(max) - ζ(w))|/ζ(w) or |(ζ(min) - ζ(w))|/ζ(w), and ζ(w) is the corresponding value in water. Tensiometry data showed two major stages of protein-IL interactions: (i) for c < cmc of IL, the IL molecules selectively bind with imidazolium cation through electrostatic forces forming protein-IL (complex) and (ii) for c> cmc free IL-aggregates begin to form. Similarly, we can define Δγ(x) as either |(γ(max) - γ(w))|/γ(w) at pH 3 or |(γ(min) - γ(w))|/γ(w) at pH 8. Both Δζ(x) and Δγ(x) showed linear dependence with c, Δγ(min, max) (or Δζ(min, max)) = (1 - K(γ) (or K(ζ)) H-index), where the slopes K(ζ) and K(γ) defined intermolecular interactions. Hydrodynamic radii data revealed protein stabilization, circular dichroism spectra implied retention of secondary structures, and Raman spectra confirmed a marginal increase in water structure. Results concluded that selective binding of IL molecules to protein surface in the form of bilayer screen protein surface charge, thereby, contributing to its dispersion stability.

Effect of NaCl and NaNO3 on the Partial Molar Volumes and Partial Molar Isentropic Compressibilities of Some Amino Acids at Several Different Temperatures (298.15–328.15) K

The partial molar volumes, \(\varphi_{v}^{\mathrm{o}}\), and partial molar isentropic compressibilities, \(\varphi_{k}^{\mathrm{o}}\), values have been computed using density and speed of sound values of L-phenylalanine/ L-leucine/L-glutamic acid/L-proline in 2 mol ⋅ L−1 aqueous NaCl or NaNO3 solutions, measured as a function of the amino acid concentration at temperatures of 298.15, 303.15, 308.15, 313.15, 318.15, 323.15 and 328.15 K. The variation of \(\varphi_{v}^{\mathrm{o}}\) values among the amino acids studied was found to follow the order proline < glutamic acid < leucine < phenylalanine. The increase in the partial molar volume of an amino acid with increasing in temperature has been attributed to the volume expansion of the hydrated zwitterions. The \(\varphi_{v}^{\mathrm{o}}\) and \(\varphi_{k}^{\mathrm{o}}\) values of L-phenylalanine, L-leucine, L-glutamic acid, and L-proline in 2 mol ⋅ L−1 aqueous NaCl and NaNO3 solutions have been found to be larger than the corresponding values in water. The larger partial molar volumes of L-phenylalanine, L-leucine, L-glutamic acid, and L-proline in 2 mol ⋅ L−1 aqueous NaCl and NaNO3 solutions have been ascribed to the possible formation of ‘zwitterion–\(\mbox{Na}^{+}/\mbox{Cl}^{-}/\mathrm{NO}_{3}^{ -}\)’ and ‘\(\mbox{Na}^{+}/\mbox{Cl}^{-}/\mathrm{NO}_{3}^{ -}\)–water dipole’ entities in solutions. The formation of these entities in solutions causes the release of water associated with zwitterions to the bulk water. The larger partial molar compressibilities of L-phenylalanine, L-leucine, L-glutamic acid and L-proline in 2 mol ⋅ L−1 aqueous NaCl NaNO3 solutions compared to the corresponding values in water has been attributed to the formation of these ‘zwitterion–ion’ and ‘ion–water dipole’ entities.

Investigation of radiological properties and water equivalency of PRESAGE® dosimeters

PRESAGE is a dosimeter made of polyurethane, which is suitable for 3D dosimetry in modern radiation treatment techniques. Since an ideal dosimeter is radiologically water equivalent, the authors investigated water equivalency and the radiological properties of three different PRESAGE formulations that differ primarily in their elemental compositions. Two of the formulations are new and have lower halogen content than the original formulation. The radiological water equivalence was assessed by comparing the densities, interaction probabilities, and radiation dosimetry properties of the three different PRESAGE formulations to the corresponding values for water. The relative depth doses were calculated using Monte Carlo methods for 50, 100, 200, and 350 kVp and 6 MV x-ray beams. The mass densities of the three PRESAGE formulations varied from 5.3% higher than that of water to as much as 10% higher than that of water for the original formulation. The probability of photoelectric absorption in the three different PRESAGE formulations varied from 2.2 times greater than that of water for the new formulations to 3.5 times greater than that of water for the original formulation. The mass attenuation coefficient for the three formulations is 12%-50% higher than the value for water. These differences occur over an energy range (10-100 keV) in which the photoelectric effect is the dominant interaction. The collision mass stopping powers of the relatively lower halogen-containing PRESAGE formulations also exhibit marginally better water equivalency than the original higher halogen-containing PRESAGE formulation. Furthermore, the depth dose curves for the lower halogen-containing PRESAGE formulations are slightly closer to that of water for a 6 MV beam. In the kilovoltage energy range, the depth dose curves for the lower halogen-containing PRESAGE formulations are in better agreement with water than the original PRESAGE formulation. Based on the results of this study, the new PRESAGE formulations with lower halogen content are more radiologically water equivalent overall than the original formulation. This indicates that the new PRESAGE formulations are better suited to clinical applications and are more accurate dosimeters and phantoms than the original PRESAGE formulation. While correction factors are still needed to convert the dose measured by the dosimeter to an absorbed dose in water in the kilovoltage energy range, these correction factors are considerably smaller for the new PRESAGE formulations compared to the original PRESAGE and the existing polymer gel dosimeters.

Study of dosimetric water equivalency of PRESAGE® for megavoltage and kilovoltage x-ray beams

PRESAGE is a dosimeter that is suitable for 3D dosimetry. To be used as an ideal dosimeter, however, it should present radiologically water equivalent properties. In this work, we have investigated the radiological properties of three different PRESAGE® formulations. The radiological water equivalence was assessed by comparing the photon cross sections and radiation dosimetry properties of the three different PRESAGE® formulations with the corresponding values for water. Relative depth doses were calculated using Monte Carlo methods for 75, 125, 180 and 280 kVp and 6 MV x-ray beams. Based on the results of this study, the PRESAGE® formulations with lower halogen content are more dosimetrically water equivalent.

Ultrasound transmission gel as a bolus device for skin irradiation of irregular surfaces: technical note

This paper describes an uncommon radiation treatment of the external ear, with ultrasound (US) transmission gel used as bolus device to compensate for the irregularity of the target surface. Postoperative radiotherapy for cutaneous carcinoma was performed with a single high-energy electron beam directed over the ear auricle. Due to the irregular surface of the target, a "missing tissue" compensator was employed. Daily, after patient positioning, the concha was filled and flattened with US gel, and a dose of 54 Gy in 27 fractions was delivered. Water equivalence of the gel was verified by comparing the gel's computed tomography (CT) number [Hounsfield units (HU)] and density with the corresponding values for water and another commercial bolus device. Whereas ultrasound gel and water had comparable values (HU: 0; density 1 g/cm(3) for both), the corresponding values for the commercial device were slightly higher (HU: 80; density 1.02 g/cm(3)). Ultrasound gel proved to be an easy, fast and cheap compensating tool. Its water equivalence allows it to be used as an alternative to water, though easier to position and with lower risk of displacement. Thus, it is recommendable as a practical tool for most irregular sites. Further investigations are warranted to validate this solution in more complex irradiation techniques.

Study of interactions of l-histidine/ l-glutamic acid/ l-tryptophan/glycylglycine with KCl/KNO 3 at different temperatures: 298.15, 303.15, 308.15, 313.15, 318.15, 323.15 K

Density ( ρ) and ultrasonic velocity ( u) values of amino acid/peptide: l-histidine, l-glutamic acid, l-tryptophan and glycylglycine in 2 M aqueous KCl and 2 M aqueous KNO 3 solutions have been measured as a function of amino acid/peptide concentration at different temperatures: 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15 K. Using the ρ and u data, the partial molar volumes ( ϕ v o ) and partial molar isentropic compressibilities ( ϕ k o ) have been computed. The increase in partial molar volume with an increase in temperature has been attributed to the volume expansion of hydrated zwitterions. The ϕ v o and ϕ k o values of l-histidine, l-glutamic acid, l-tryptophan and glycylglycine in 2 M aqueous KCl and 2 M aqueous KNO 3 solutions have been found to be larger than the corresponding values in water. The larger partial molar volumes of l-histidine, l-glutamic acid, l-tryptophan and glycylglycine in 2 M aqueous KCl and 2 M aqueous KNO 3 solutions have been ascribed to the probable formation of ‘zwitterion–K +/Cl −/NO 3 −’ and ‘K +/Cl −/NO 3 −–water dipole’ aggregates in solutions. The zwitterions–ions interactions in solutions may cause the release of water associated with zwitterions to the bulk water. The larger partial molar isentropic compressibilities of l-histidine/ l-glutamic acid/ l-tryptophan/glycylglycine in 2 M aqueous KCl/2 M aqueous KNO 3 solutions than the corresponding values in water have been attributed to the zwitterions–ions and ions–waters dipoles interactions in solutions.

A Kinetic Study of the Photodynamic Effect on Tryptophan Methyl Ester and Tryptophan Octyl Ester in DOPC Vesicles

The photodynamic effect on tryptophan methyl ester (trpME) and tryptophan octyl ester (trpOE), using the O(2)((1)Delta(g))-photosensitizers Rose Bengal (RB) and Perinaphthenone (PN) has been studied in large unilamellar vesicles (LUVs) of the phospholipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) by stationary photolysis and time-resolved methods. This work reports on the influence of both the site (O(2)((1)Delta(g))) generation and the location of the tryptophan derivatives (trpD), on the photo-oxidation process in a compartmentalized system. The apparent rate constant values for chemical quenching of O(2)((1)Delta(g)) by trpOE (k(r,app)), was higher in vesicles than in water. Also, the ratio between apparent reactive and overall rate constant values for the deactivation of O(2)((1)Delta(g)) (k(r,app)/k(t,app)), increases in vesicles as compared with water, when the oxidative species is generated in the lipidic region or at the interface. Nevertheless, this quotient is lower than the corresponding value in water when O(2)((1)Delta(g)) is generated in the aqueous pseudophase. For trpME, the k(r,app)/k(t,app)values in vesicles and in water are quite similar, confirming the fact that trpME is located in the water pseudophase. Results are discussed in terms of relative protection against O(2)((1)Delta(g)) attack in a microheterogeneous medium as compared with water.

Effect of KCl and KNO3 on Partial Molal Volumes and Partial Molal Compressibilities of Some Amino Acids at Different Temperatures

Density (ρ) and ultrasonic velocity (u) values of amino acids l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and 2M aqueous KNO3 solutions have been measured as a function of amino acid concentration at different temperatures (298.15 K, 303.15 K, 308.15 K, 313.15 K, 318.15 K, and 323.15 K). Using the ρ and u data, partial molal volume (\({\phi_{\rm v}^{\rm o}}\)) and partial molal isentropic compressibility (\({\phi_{\rm k}^{\rm o} }\)) values have been computed. The increase in partial molal volume with temperature has been attributed to the volume expansion of hydrated zwitterions. The \({\phi_{\rm v}^{\rm o}}\) and \({\phi_{\rm k}^{\rm o}}\) values of l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and KNO3 solutions have been found to be larger than the corresponding values in water. The larger partial molal volumes of l-alanine, l-proline, l-valine, and l-leucine in 2M aqueous KCl and KNO3 solutions have been ascribed to the formation of ‘zwitterion-K+/Cl−/NO3−’ and ‘K+/Cl−/NO3−–water dipole’ aggregates in solutions. The formation of these entities in solutions causes the release of water associated with zwitterions to the bulk water. The larger partial molal compressibilities of l-alanine-/l-proline-/l-valine-/l-leucine–2M aqueous KCl/KNO3 solutions than the corresponding values in water have been attributed to the formation of ‘zwitterion–ion’ and ‘ion–water dipole’ incompressible entities in solutions.

Analysis of Thermal Effects in Cavitating Liquid Hydrogen Inducers

Evaporative cooling effects due to cavitation can significantly improve the performance of liquid rocket turbomachinery that operate with cryogenic fluids, in which the fluid is operating close to its critical temperature and the thermal effects resulting from phase change become important. A detailed numerical analysis to quantify these thermal effects of cavitation and to better understand their impact on cavitation flow physics in liquid hydrogen inducers is presented. Simulations were performed on a helical flat-plate inducer that was extensively tested in both liquid hydrogen and cold water. Predictions of cavitating performance over the operational range of inlet pressures were conducted and compared with experimental data. Fundamental differences were observed in the cavity for liquid hydrogen compared with the cold-water inducer; the cavity in liquid hydrogen shows far less vapor content, although spreading out further in the spanwise direction, which may generate blade-to-blade interactions. Thermal effects result in a more gradual breakdown of the head in liquid hydrogen resulting in improved overall performance; the liquid hydrogen inducer performed to a suction specific speed (N SS number) of 75,000 and the corresponding value in water is 35,000. The temperature depressions due to evaporative cooling in the liquid hydrogen fluid are found to be only on the order of 0.5-1.0 K, highlighting the strong coupling of thermodynamic properties and the phase-change process at these flow conditions.

Permeability of bacterial cellulose membranes

Mass transfer experiments were conducted to determine the transport and interaction parameters of selected molecules in hydrated bacterial cellulose (BC) membranes. The objective was to determine physiochemical characteristics and elucidate the mechanisms governing transport in relation to the membrane structure. Pore and sorption models developed previously for the analysis of transport in hydrogel membranes were relevant to the cellulose membrane system, including: (1) interfacial phenomena between the bulk fluid and the outer membrane surfaces and/or along a pore wall, (2) sorption into the membrane matrix itself with diffusion possibly affected by immobilization at specific interactive sites, (3) free and/or fixed site diffusion within the matrix and if appropriate, through the porous regions, whether as distinct pores, micro-channels or other non-homogeneous/discrete areas and (4) chemical reactions that could alter the nature of the diffusing species or the media itself. Since all these mechanisms may be active, our classification, and thus characterization, was based upon whichever mechanism dominates. The diffusion coefficients of various dextrans (44–260 kDa), measured using a horizontal flow diffusion chamber, were compared to their corresponding values in water to demonstrate hindered diffusion. The degree of hindrance, ψ, was the same for all four dextrans indicating that the parameter is not a function of pore or micro-channel size but rather due to the presence of membrane fibers. Three representative marker molecules (Vitamin B12, lysozyme and bovine serum albumin) were evaluated using the same apparatus combined with desorption experiments to measure permeation ( P) and effective diffusion ( D eff) coefficients. Partition coefficients, H, were subsequently calculated and verified experimentally. Estimates of D eff in the BC membranes were made through a weighted average using literature values for the diffusion of the three molecules in water and regenerated cellulose along with measured H and ψ values. The experimental results are in excellent agreement with these estimates indicating the presence of dual transport mechanisms, for solute transport through the continuous water phase and cellulose matrix, with some hindrance of molecular diffusion via fiber obstruction. With Vitamin B12 and lysozyme (the two smallest solutes), equilibrium interactions such as adsorption and solubility are also important. These results help clarify the potential utility of these novel bio-derived membranes in a variety of possible separations scenarios.

Diffusive and convective transport through hollow fiber membranes for liver cell culture

For an efficient membrane bioreactor design, transport phenomena determining the overall mass flux of metabolites, catabolites, cell regulatory factors, and immune-related soluble factors, need to be clarified both experimentally and theoretically. In this work, experiments and calculations aimed at discerning the simultaneous influence of both diffusive and convective mechanisms to the transport of metabolites. In particular, the transmembrane mass flux of glucose, bovine serum albumin (BSA), APO-transferrin, immunoglobulin G, and ammonia was experimentally measured, under pressure and concentration gradients, through high-flux microporous hydrophilic poly-ether-sulphone (PES-HFMs) and poly-sulphone hollow fiber membranes (PS-HFMs). These data were analyzed by means of a model based on the mechanism of capillary pore diffusion, assuming that solute spherical molecules pass through an array of solvent-filled cylindrical pores with a diffusive permeation corrected for friction and steric hindrances. Additionally, resistances to the mass transfer were taken into account. Convective permeation data were discussed in terms of morphological properties of the polymeric membranes, molecular Stokes radius, and solute-membrane interactions according to information given by contact angle measurements. The observed steady-state hydraulic permeance of PS-HFMs was 0.972 L/m 2 h mbar, about 15.6-fold lower than that measured for PES-HFMs (15.2 L/m 2 h); in general, PS-HFMs provided a significant hindrance to the transport of target species. Diffusion coefficients of metabolites were found to be similar to the corresponding values in water through PES-HFMs, but significantly reduced through PS-HFMs ( D Glucose Membrane = 2.8 × 10 − 6 ± 0.6 × 10 − 6 c m 2 / s , D BSA Membrane = 6.4 × 10 − 7 ± 1 × 10 − 7 c m 2 / s , D Apotransferrin Membrane = 2.3 × 10 − 7 ± 0.25 × 10 − 7 c m 2 / s ).

Auger parameter of hafnium in elemental hafnium and in hafnium oxide

X-ray photoelectron spectroscopy has been used to determine the Auger parameters in elemental hafnium and in hafnium oxide (HfO 2). The zirconium L α line has been used as a source of excitation to study the 3d core levels of hafnium, the 1s core level of oxygen, and the X-ray excited MNN Auger region of hafnium and KVV Auger region of oxygen. The Auger parameters for hafnium and oxygen have been determined from these spectral data. In case of oxygen, the Auger parameter has been compared with the corresponding value in water. The change in the Auger parameter is observed to be negative for hafnium and positive for oxygen. We have shown that the opposite signs of the Auger parameters in binary systems can be utilized to determine the direction of charge transfer between the constituents. This is consistent with the chemical shift due to charge transfer. This chemical shift in the core level has been evaluated by subtracting the relaxation shift from the experimentally observed core level shift. It is found to be positive for the 3d 5/2 core level of hafnium in the oxide indicating a charge transfer from hafnium to oxygen in the oxide. The observations are consistent with Pauling’s electronegativity criterion.

Bicarbonate surfoxidants: micellar oxidations of aryl sulfides with bicarbonate-activated hydrogen peroxide.

The mechanism and kinetics of bicarbonate-catalyzed oxidations of sulfides by H(2)O(2) at the aqueous /cationic micellar interface have been investigated. The general term surfoxidant is introduced to describe the combination of an ionic surfactant with a reactive counterion that is itself an oxidant or activates an oxidant from the bulk solution to form an oxidant counterion. It is shown that the new catalytic cationic surfoxidant CTAHCO(3) (cetyltrimethylammonium bicarbonate) significantly enhances the overall oxidation rates as compared to the addition of bicarbonate salts to CTACl and CTABr, for which the halide counterions must undergo equilibrium displacement by the oxidant anion (peroxymonocarbonate, HCO(4)(-)). General equations based on the classic pseudophase model have been derived to account for the preequilibrium reaction in the aqueous and micellar phases, and the resulting model can be used to describe any micellar reaction with associated preequilibria. Rate constants and relevant equilibrium constants for HCO(4)(-) oxidations of aryl sulfides at micellar surfaces have been estimated for CTAHCO(3), CTACl, and CTABr. The second-order rate constants in the Stern layer (k(2)(m)) for sulfide oxidations by HCO(4)(-) are estimated to be approximately 50-fold (PhSEtOH) and approximately 180-fold (PhSEt) greater than the background rate constant k(m)(0) for oxidation by H(2)O(2) at the micellar surface. The estimated values of k(2)(m) are lower than the corresponding values in water by a factor of 20-70 depending on the substrate, but the high local concentration of the bicarbonate activator in the surfoxidant and the local accumulation of substrate as a result of strong binding to the micelle lead to a net increase in the observed reaction rates. Comparisons of CTAHCO(3)-activated peroxide to other highly reactive oxidants such as peroxymonosulfate (HSO(5)(-)) in aqueous surfactant media suggest a wide variety of potential applications for this green oxidant.

THERMAL AND RHEOLOGICAL PROPERTIES OF BRINE FROM FERMENTED AND SULFITE‐PRESERVED CUCUMBERS1

ABSTRACTPickling cucumbers may be temporarily preserved by fermentation in brine (6–8% NaCl) or without fermentation in salt‐free, sulfite solution (300 ppm sulfite, pH 3.5). Brines obtained from preservation processes are often discarded. Due to environmental concerns, there is increasing consideration for further use of the brine solutions by recycling for use in bulk storage or filtration and incorporation into finished products. Thermal and rheological properties are fundamental to the reuse of the brine. The effect of temperature was determined on the rheological (5–45C) and thermal properties (5–75C) of brine. The properties of the brine samples were found to be significantly different (P &lt; 0.05) from each other and from water. Salt content was the most important factor affecting the thermal and rheological properties of brine. At the same conditions, the values of the properties (thermal conductivity, specific heat, and thermal diffusivity, viscosity) were about 5 to 23% less than the corresponding values for water.

Singlet molecular oxygen [O2(1Δg)] production and quenching by hydroxybiphenyls in micellar media

The role of cationic and anionic surfactants on the kinetics of hydroxybiphenyls (OH‐BPs) photooxidation in alkaline medium (pH =11) has been studied. We evaluate, in a quantitative fashion, the interaction surfactants (CTAC, SDS) — OH‐BPs as well as the rate constants for the eosin‐sensitized aerobic photooxidation, in these media, of two representative members of the OH‐BPs family: 2‐hydroxybiphenyl and 2,2‐dihydroxibiphenyl, employing static photolysis. The characterization of solute‐micelle interaction from the spectral changes, indicates that OH‐BPs bind CTAC and SDS micelles in a different extent, depending on the charge of the surfactant. The binding constants are higher for CTAC. The rate constants, kr , for the chemical reaction O2(1Δg) — OH‐BPs follows the order: kr (SDS) > kr (H2O) ∼ kr (CTAC). This behavior can be rationalized on the basis of two effects: higher local substrate concentration in the anionic micellar medium and polarity of the substrate microenvironment. The quantum yields for the production of O2(1Δg)(øδ), in the range of 0.07 to 0.25 in micellar media, are considerably higher than the corresponding values in water.