Interactions of binary liquid mixtures with polysaccharides studied using multi-dimensional NMR relaxation time measurements

Nuclear magnetic resonance transverse T₂ relaxation time has proven to be a valuable parameter for characterizing liquid/polymer interactions. This measurement is applicable to many food, personal care, and cosmetic products that contain multi-component liquid mixtures. Here, we investigate the interactions of corn starch with water/glycerol mixtures of different weight compositions and explore liquid exchange dynamics; such a system is relevant to the personal care industry. We use a combination of chemical shift resolved ¹H T₂ relaxation measurements and corresponding two-dimensional T₂ relaxation exchange experiments using both a conventional experimental protocol and a modified method with the addition of NMR chemical shift selectivity. Two relaxation regimes were evident for the hydroxyl ¹H (found in both water and glycerol) whilst three relaxation regimes are evident for the aliphatic glycerol ¹H associated here with strongly bound, weakly bound, and free (bulk) liquid, respectively. At higher water contents preferential absorption of glycerol was evident. T₂-T₂ exchange maps with a range of storage times reveal molecular exchange rates between all three regimes due to self-diffusion. Rapid exchange of water between the bulk and bound locations was evident in the case of pure water. Exchange rates for hydroxyl ¹H was considerably reduced by the inclusion of glycerol.     

Reinforcement of model filled elastomers: characterization of the cross-linking density at the filler-elastomer interface by H NMR measurements

The cross-linking density at the filler-elastomer interface is analyzed by ¹H NMR measurements in model reinforced elastomers composed by grafted nanosilica particles and cross-linked ethylacrylate chains. We have focused our attention on the effect of introducing fillers on the relaxation of the bulk polymer matrix which is observed at long times (t>100 μs). Measurements performed at high temperature (T>T_g+120 K) have revealed that its relaxation is affected by the topological constraints existing at the particle surface. We deduce that the effect of particles in the bulk matrix can be interpreted as that of an homogeneous additional constraint density which increases proportionally to the surface area introduced in the matrix.     

Fate of the 15N-labelled faeces fraction of dairy farm effluent (DFE) irrigated onto soils under different water regimes

Irrigation of dairy farm effluent (DFE) onto pasture is the preferred treatment method in New Zealand for this very dilute organic effluent. Whereas the dynamics of the urine fraction is comparatively well understood, there is a lack of data on the fate of the mainly organic faecal fraction. To improve our understanding of the complex turnover processes, we labelled both the inorganic and organic N compounds of the faecal fraction of DFE with ¹⁵N. We then measured the ¹⁵N dynamics in various soil and plant fractions in a laboratory experiment at two water contents for up to 254 days. Feeding a dairy cow with ¹⁵N-labelled pasture yielded faeces that had a mean ¹⁵N abundance of 2.95 atom%. Unlabelled urine and water were added to the labelled faeces to construct the DFE, which contained 90.4% of the ¹⁵N in the organic nitrogen fraction (2.87 atom%) and 9.6% in the ammonium fraction (1.23 atom%). As N turnover and losses depend on the method of application and the soil structure, we simulated field conditions by surface-applying our DFE onto intact soil cores with pasture. Two soil water treatments were imposed; dry (30% water content) and wet (water table at 17 cm below the soil surface). The surface application resulted in filtration of the DFE, with a high proportion of the ¹⁵N remaining on the soil surface, where it was relatively unavailable for plant uptake but prone to gaseous and physical losses. Of the applied ¹⁵N, 9.9% in the dry and 13.5% in the wet treatment were still recovered as DFE on the soil surface at day 254. Plant uptake of faecal ¹⁵N accounted for 9.3% and 13.0% in the dry and wet treatments, respectively. The bulk of the ¹⁵N was recovered in the soil organic nitrogen fraction (35.1% in dry, 42.5% in wet), whereas ¹⁵N in inorganic and microbial nitrogen accounted for only very small amounts (< 2%). Total recoveries of the applied ¹⁵N in plant, soil and DFE remaining on the surface at day 254 were 58.4% in the dry, and 71.5% in the wet treatment. Separate analysis of the total and ammonium nitrogen contents and ¹⁵N enrichments of the constructed DFE and filtered subsamples (0.5 mm, 0.2 m) showed that the faecal fraction was not labelled homogeneously. Due to this heterogeneity, which was exacerbated by the filtration of DFE on the soil surface, it was difficult to calculate the turnover of the total faecal fraction based on ¹⁵N results.     

Spectroscopic investigations of the water pool in lecithin reverse micelles

The nature of the water pool formed in the reverse micellar system, lecithin/nonpolar solvent/water, has been investigated by means of near infrared, ultraviolet, fluorescence emission and visible spectroscopic techniques. The three nonpolar solvents chosen in this study were benzene, carbon tetrachloride and cyclohexane. Near infrared spectroscopic studies revealed that the amount of water present in the bulk organic phase is negligible at all water concentrations studied in all three solvents. The results of the polarity probe and 8-anilinonaphthalene sulfonic acid (ANSA) fluorescence emission maxima studies indicate that the polarity of the water pool is much lower than that of bulk water. The difference in polarity between the water pool and bulk water decreases with increasing water concentration in benzene and carbon tetrachloride systems. However, in the cyclohexane system, at a water content of 6 moles of water per mole of lecithin, where the system is known to change from isotropic reverse micelle to anisotropic liquid crystalline state, the polarity of the water pool is found to decrease.     

Detectability of15N-depleted fertilizer N in soil and plant tissue during a corn-rye crop rotation

Use of¹⁵N-depleted fertilizer materials have been primarily limited to fertilizer recovery studies of short duration. The objective of this study was to determine if¹⁵N-depleted fertilizer N could be satisfactorily used as a tracer of residual fertilizer N in plant tissue and various soil N fractions through a corn (Zea mays L.) -winter rye (Secale cereale L.) crop rotation. Nitrogen as¹⁵N-depleted (NH₄)₂SO₄ was applied at five rates (0, 84, 168, 252, and 336 kg N ha^–1) to corn. Immediately following corn harvest a winter rye cover crop treatment was initiated. Residual fertilizer N was easily detected in the soil NO ₃ ^- -N fraction following corn harvest (140-d after application). Low levels of exchangeable NH ₄ ⁺ -N (<2.5 mg kg^–1) did not permit accurate isotope-ratio analysis. Fertilizer-derived N recovered in the soil total N fraction following corn harvest was detectable in the 0 to 30-cm depth at each N rate and in the 30 to 60 and 60 to 90-cm depths at the 336 kg ha^–1 N rate. Atom %¹⁵N concentrations in the nonexchangeable NH ₄ ⁺ -N fraction did not differ from the control at each N rate. Nitrogen recovery by the winter rye cover crop reduced residual soil NO ₃ ^- -N levels below the 10 kg ha^–1 level needed for accurate isotope-ratio analysis. Atom %¹⁵N concentrations in the soil total N fraction (approximately one yr after application) were indistinguishable from the control plots below the 168, 252, and 336 kg ha^–1 N rate at the 0 to 30, 30 to 60, and 60 to 90-cm depths, respectively. Recovery of residual fertilizer N by the winter rye cover crop was verified by measuring significant decreases in atom %¹⁵N concentrations in rye tissue with increasing N rates. The greatest limitation to the use of¹⁵N-depleted fertilizer N as a tracer of residual fertilizer N in a corn-rye crop rotation appears to be its detectibility from native soil N in the total N pool.Research partially supported by grants from the National Fertilizer and Environmental Research Center/TVA and the Virginia Division of Soil and Water Conservation.     

Glycine–nitrate synthesis of Sr doped La2Zr2O7 pyrochlore powder

Abstract

Abstract

Materials with A₂B₂O₇ (pyrochlore) structure have received significant attention for their applications as new protonic conductors and materials used in electronic devices. One of the unique synthesis routes for La₂Zr₂O₇ (pyrochlore) powders is the glycine–nitrate combustion method, which shows superior properties of the synthesised powder using glycine as a complexing agent. The Sr doped La₂Zr₂O₇ powders in pure pyrochlore structure were produced using this approach. Selected characteristics of the synthesised powders, such as crystal structure, lattice parameters, crystallite size, the vibrational properties, the morphology of the particles, along with the specific surface area and particle size, have been investigated. The dependence of some properties on annealing temperatures of the powders has been studied.     

Nano Structured Metal Oxides as Potential Sorbents for 188W/188Re Generator: A Comparative Study

Nanostructured oxides of Ti, Zr, and Al were synthesized to evaluate their efficacy as sorbent matrices for the preparation of ¹⁸⁸W/¹⁸⁸Re generator. These oxides, in many respects, can improve the efficiency of the generator by providing better selectivity and enhanced capacity for ¹⁸⁸W, which arises from a higher surface area, surface energy, and surface charge, compared to the attributes of conventionally used bulk alumina. The performance of these materials, in the context of preparation of ¹⁸⁸W/¹⁸⁸Re generators, were compared with respect to sorption capacity for ¹⁸⁸W, shelf-life of the generator, purity, and quality of ¹⁸⁸Re for radiopharmaceutical applications.     

Partitioning and Localization of Fragrances in Surfactant Mixed Micelles

The localization and dynamics of fragrance compounds in surfactant micelles are studied systematically in dependence on the hydrophobicity and chemical structure of the molecules. A broad range of fragrance molecules varying in octanol/water partition coefficients P _ow is employed as probe molecules in an aqueous micellar solution, containing anionic and nonionic surfactants. Diffusion coefficients of surfactants and fragrances obtained by Pulsed Field Gradient (PFG)-NMR yield the micelle/water distribution equilibrium. Three distinct regions along the log(P _ow) axis are identified: hydrophilic fragrances (log(P _ow) < 2) distribute almost equally between micellar and aqueous phases whereas hydrophobic fragrances (log(P _ow) > 3.5) are fully solubilized in the micelles. A steep increase of the incorporated fraction occurs in the intermediate log(P _ow) region. Here, distinct micelle swelling is found, while the incorporation of very hydrophobic fragrances does not lead to swelling. The chemical structure of the probe molecules, in addition to hydrophobicity, influences fragrance partitioning and micelle swelling. Structural criteria causing a decrease of the aggregate curvature (flattening) are identified. ²H-NMR spin relaxation experiments of selectively deuterated fragrances are performed monitoring local mobility of fragrance and leading to conclusions about their incorporation into either micellar interface or micelle core. The tendencies of different fragrance molecules (i) to cause interfacial incorporation, (ii) to lead to a flattening of the micellar curvature and (iii) to incorporate into micelles are shown to be correlated.     

Usefulness of the carbon-13 tracer technique for characterizing terrestrial carbon pools

Application of the carbon-13 (¹³C) tracer technique to soil organic carbon emission is relatively new to many researchers and only a few results have been reported to date. This mini-review paper cites some well-documented research in organic carbon pool studies using the ¹³C tracer technique. The ¹³C abundance in soil usually remains at a stable level under a set of natural conditions. Variations in ¹³C reflect different sources and types of organic components from natural environments. An important feature of ¹³C discrimination in the soil C pool has permitted researchers to assess the dynamic nature of the pool. This discrimination may reflect a selective preference at early stage of residue decomposition by soil microbes. Crop rotation and residue input to humic substances can change the ¹³C abundance, which is a possible way to estimate soil C emission. However, the dynamic relationship between ¹³C abundance in the soil C pool and C emission is still in an early stage of development. Restrictions due to requirement of long-term experiments and duration of vegetation changes may affect its wide-spread adoptions in C emission studies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Treatment of Cs liquid wastes by reverse osmosis Part I. Preliminary tests

As a consequence of an accidental fusion of a ¹³⁷Cs source in a steel production factory, 40 m³ of radioactive liquids were generated in the plant decontamination process. This radioactive liquid waste was treated by a reverse osmosis plant, managing to declassify more than 36 m³. The remaining 4 m³ were treated by evaporation reducing the final volume to less than 1 m³. Prior to the waste treatment at the steel factory, preliminary tests were done in order to determine reverse osmosis membrane performance with ¹³⁷Cs effluents. The influence ofgamma and electron irradiation on structure and transport properties of reverse osmosis membranes was studied; and reverse osmosis performance with a ¹³⁷Cs-contaminated liquid obtained from contaminated ashes was assessed. The aim of this paper is to describe and show the results of these preliminary tests.     

Membrane Interactions of Latarcins: Antimicrobial Peptides from Spider Venom

A group of seven peptides from spider venom with diverse sequences constitute the latarcin family. They have been described as membrane-active antibiotics, but their lipid interactions have not yet been addressed. Using circular dichroism and solid-state ¹⁵N-NMR, we systematically characterized and compared the conformation and helix alignment of all seven peptides in their membrane-bound state. These structural results could be correlated with activity assays (antimicrobial, hemolysis, fluorescence vesicle leakage). Functional synergy was not observed amongst any of the latarcins. In the presence of lipids, all peptides fold into amphiphilic α-helices as expected, the helices being either surface-bound or tilted in the bilayer. The most tilted peptide, Ltc2a, possesses a novel kind of amphiphilic profile with a coiled-coil-like hydrophobic strip and is the most aggressive of all. It indiscriminately permeabilizes natural membranes (antimicrobial, hemolysis) as well as artificial lipid bilayers through the segregation of anionic lipids and possibly enhanced motional averaging. Ltc1, Ltc3a, Ltc4a, and Ltc5a are efficient and selective in killing bacteria but without causing significant bilayer disturbance. They act rather slowly or may even translocate towards intracellular targets, suggesting more subtle lipid interactions. Ltc6a and Ltc7, finally, do not show much antimicrobial action but can nonetheless perturb model bilayers.     

The Diurnal Rhythms in Plasma Glycine Pool Sizes and Turnover Rates: 15N-Glycine Single Dose Experiments Employing Gas Chromatographic — Mass Spectrometric Analysis

Gas liquid chromatography–mass spectrometry of trifluoroacetyl n-butyl ester derivatives of plasma amino acids has been used to determine directly the ¹⁵N-enrichment of plasma glycine in rabbits, following the intravenous administration of a single dose of ¹⁵N-glycine. The isotope enrichment time decay curves of plasma glycine were linear over the course of the measurements (5–45 min). Glycine pool sizes and turnover rate constants were obtained from the intercepts and slopes of non weighted least-squares lines, describing the isotope enrichment time decay curve. In fed animals, glycine pool sizes showed only modest variations over a 24 h period, while glycine turnover rate constants showed a statistically significant daily variation with a minimum at 10 PM. In fasted animals, the glycine pool sizes decreased and turnover rate constants increased with the duration of the fast. The turnover rate constants appeared to represent the utilization of glycine, as an energy or nitrogen source in the liver, rather than uptake of glycine into the free amino acid pool of muscle. These data indicate that physiologically significant variations in amino acid dynamics can be obtained from single dose tracer experiments, when GC-MS is used to determine directly the isotope enrichments of plasma amino acids.     

NMR study of temperature-induced phase separation and polymer-solvent interactions in poly(vinyl methyl ether)/D2O/ethanol solutions

The changes in the dynamic structure during temperature-induced phase transition in D₂O/ethanol solutions of poly(vinyl methyl ether) (PVME) were studied using NMR methods. The effect of polymer concentration and ethanol (EtOH) content in D₂O/EtOH mixtures on the appearance and extent of the phase separation was determined. Measurements of ¹H and ¹³C spin-spin and spin-lattice relaxations showed the presence of two kinds of EtOH molecules: besides the free EtOH expelled from the PVME mesoglobules there are also EtOH molecules bound in PVME mesoglobules. The existence of two different types of EtOH molecules at temperatures above the phase transition was in solutions with polymer concentration 20 wt% manifested by two well-resolved NMR signals (corresponding to free and bound EtOH) in ¹³C and ¹H NMR spectra. With time the originally bound EtOH is slowly released from globular-like structures. From the point of view of polymer-solvent interactions in the phase-separated PVME solutions both EtOH and water (HDO) molecules show a similar behaviour so indicating that the decisive factor in this behaviour is a polar character of these molecules and hydrogen bonding.     

Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag²⁺ from Ag⁺ in 6 M HNO₃ anolyte has been studied with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO₃ is generally used as catholyte, which, however, produces NO _x gases in the cathode compartment. The performance of the cell with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag⁺ to Ag²⁺ conversion efficiency in the anolyte, (iii) the migration of Ag⁺ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H₂SO₄ catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H₂SO₄ concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H₂SO₄ as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.     

Experimental and modeling analysis of the formation of cuprous intermediate species formed during the copper deposition on a rotating disk electrode

Two comprehensive kinetic models reported in the literature for the copper deposition in sulfate media are modeled and compared with experimental data (linear sweep voltammetry) in order to disclose the role and phase of the cuprous species as intermediates. Differences in the phase of these species are considered for each model, i.e. Cu(I)_ads and Cu⁺. Modeling considers the formation of copper in two mono-electronic steps and account for mass transport by diffusion and convection in a RDE. Reasonable fits were obtained for both models at different experimental conditions (e.g. Cu²⁺ bulk concentration, rotation rate). It was found that this behavior is possible due to the low concentrations of cuprous species and their rapid consumption to form metallic copper, i.e. not rate-controlling step. Further insights of the kinetic and mass transport contributions of this system were obtained for both models by computing some variables that cannot be experimentally measured (i.e. surface concentrations). The first reaction in the mechanism was found to be the rate-determining step. A set of optimum kinetic parameters and constants obtained from the analysis of the models are also reported in this study.     

Solid-state NMR and FT-IR investigation of 12-tungstophosphoric acid on TiO2

The chemical and dynamic nature of the tungstophosphoric acid (TPA) species adsorbed on pressed, extruded, and powdered TiO₂ support was studied by ³¹P and ¹H solid-state NMR spectroscopy and diffuse reflectance FT-IR. From ³¹P NMR and FT-IR results the TPA appeared to be present in at least five forms on the titania surface: a bulk salt phase, two weakly bound intact Keggin species, a range of partially fragmented clusters such as the 11-“defect” Keggin ion, and a range of species formed by high or complete fragmentation of the Keggin ion. The relative amount of these species varied depending on the form of the support. Adsorption was incomplete on extruded titania resulting in bulk salt formation. There was almost complete adsorption on pressed titania pellets, yielding predominantly fragmented Keggin units, along with a small amount of bulk salt. However, complete adsorption (and fragmentation) without bulk salt formation was attained by impregnation of powdered TiO₂. The acidic nature of the catalysts and the degree of TPA dispersion were investigated by solid-state ¹H high-speed MAS-NMR. Pure TPA salt yielded resonances at about 6.5 ppm. The catalysts yielded acidic proton resonances at about 7–8 and 10–11.5 ppm. The broad resonance observed at 7–8 ppm is due to a dispersion of acidic sites on the surface. The intensity of the acidic resonance at around 11 ppm increased with adsorption effectiveness and could, therefore, be related to the formation of hydroxonium ions upon fragmentation of adsorbed Keggin ions. This revised version was published online in July 2006 with corrections to the Cover Date.     

6. Ammonium dynamics of puddled soils in relation to growth and yield of lowland rice

The release of non-exchangeable (fixed) NH ₄ ⁺ and the importance of exchangeable NH ₄ ⁺ at transplanting (initial exchangeable NH ₄ ⁺ ) for rice (Oryza sativa L.) growth was studied in representative lowland rice soils of the Philippines.The experiments showed that initial exchangeable ammonium behaved like fertilizer N and thus may serve as a valuable guideline for nitrogen fertilizer application rates when calculated on a hectare basis. By using the¹⁵N tracer technique it was found that nonexchangeable ammonium in soil may contribute to the nitrogen supplying capacity of lowland rice soils. Fixation and release of NH ₄ ⁺ seem to be more dependent on the form of clay minerals than on clay content. In soils rich in vermiculite non-exchangeable ammonium should be considered together with other available N sources such as exchangeable ammonium for N fertilizer recommendations for lowland rice.     

Selective Separation and Preconcentration of Arsenite from Arsenic Enriched Natural Waters with Three Different Adsorbents

Arsenite (AsO₃^3-) is the dominant arsenic (As) oxyanion in most of As rich groundwaters, generating serious health problems worldwide. It is assumable that the isotopic composition of the associated oxygen may broaden our understanding about the causes, which led to the appearance of this kind of contamination. The aim of this study was to work out an efficient method for the selective extraction of arsenite from natural water samples, in a form adequate for isotopic measurements. Three adsorbents,

i. basic yttrium carbonate (BYC),

ii. porous polymer beads loaded with monoclinic hydrous zirconium oxide (MHZR), and

iii. nanoparticlate Fe₂O₃ (NFO) were tested for their suitability to separating AsO₃^3- from coexisting anions that may interfere with the isotopic measurement.

Results show that 95.1%, 99.3%, and 98.2% of AsO₃^3- were adsorbed selectively and separated from SO₄^2- and Cl^- in water by BYC, MHZR, and NFO, respectively. Using different desorption agents, 95.0% and 87.5% of AsO₃^3- were stripped from BYC in 0.05 M HNO₃ and NFO in 2 M NaOH, respectively, but only 27.5% from MHZR. By adding AgNO₃ in excess to these solutions, 98.3 ± 1.28% (n = 4) and 95.7 ± 4.81% (n = 4) of the AsO₃^3-, desorbed from the BYC and NFO, were precipitated as Ag₃AsO₃, respectively. The purity of the precipitates was checked with SEM-EDX.     

Study of the reactions taking place at the ‘GaAs electrode/SiMo12O40 solution’ interface

The electrochemical response of GaAs, n- and p- type, in the presence of a Keggin-type heteropolyanion—SiMo₁₂O₄₀⁴⁻—has been studied in order to determine the reactions which take place at the GaAs/SiMo₁₂O₄₀⁴⁻ solution interface. The behavior of the GaAs electrodes, in the dark and under illumination, allowed us to determine the nature of the semiconductor carriers involved in the charge transfer. All the charge transfers occur via the GaAs valence band (VB). At open circuit potential, the SiMo₁₂O₄₀⁴⁻ ions are reduced at the GaAs surface which therefore undergoes an anodic dissolution process. Under polarization, when the reduction current is maximum, no GaAs oxidation reaction takes place. The SiMo₁₂O₄₀⁴⁻ reduction current densities are the same at a platinum electrode and at a GaAs electrode. These observations imply that at a GaAs/SiMo₁₂O₄₀⁴⁻ solution interface, under electroless conditions, the GaAs anodic dissolution occurs via a purely electrochemical process, by consumption of the holes injected during SiMo₁₂O₄₀⁴⁻ reduction.