Preparation and characterisation of ceria particles

Cerium dioxide (ceria) nanoparticles have been the subject of intense academic and industrial interest. Ceria has a host of applications but academic interest largely stems from their use in the modern automotive catalyst but it is also of interest because of many other application areas notably as the abrasive in chemical-mechanical planarisation of silicon substrates. Recently, ceria has been the focus of research investigating health effects of nanoparticles. Importantly, the role of non-stoichiometry in ceria nanoparticles is implicated in their biochemistry. Ceria has well understood non-stoichiometry based around the ease of formation of anion vacancies and these can form ordered superstructures based around the fluorite lattice structure exhibited by ceria. The anion vacancies are associated with localised or small polaron states formed by the electrons that remain after oxygen desorption. In simple terms these electrons combine with Ce4+ states to form Ce3+ states whose larger ionic radii is associated with a lattice expansion compared to stoichiometric CeO2. This is a very simplistic explanation and greater defect chemistry complexity is suggested by more recent work. Various authors have shown that vacancies are mobile and may result in vacancy clustering. Ceria nanoparticles are of particular interest because of the high activity and surface area of small particulates. The sensitivity of the cerium electronic band structure to environment would suggest that changes in the properties of ceria particles at nanoscale dimensions might be expected. Notably many authors report a lattice expansion with reducing particle size (largely confined to sub-10 nm particles). Most authors assign increased lattice dimensions to the presence of a surface stable Ce2O3 type layer at low nanoparticle dimensions. However, our understanding of oxide nanoparticles is limited and their full and quantitative characterisation offers serious challenges. In a series of chemical preparations by ourselves we see little evidence of a consistent model emerging to explain lattice parameter changes with nanoparticle size. Based on these results and a review of the literature it is worthwhile asking if a model of surface enhanced defect concentration is consistent with known cerium/cerium oxide chemistries, whether this is applicable to a range of different synthesis methods and if a more consistent description is possible. In Chapter one the science of cerium oxide is outlined including the crystal structure, defect chemistry and different oxidation states available. The uses and applications of cerium oxide are also discussed as well as modelling of the lattice parameter and the doping of the ceria lattice. Chapter two describes both the synthesis techniques and the analytical methods employed to execute this research. Chapter three focuses on high surface area ceria nano-particles and how these have been prepared using a citrate sol-gel precipitation method. Changes to the particle size have been made by calcining the ceria powders at different temperatures. X-ray diffraction methods were used to determine their lattice parameters. The particles sizes were also assessed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and BET, and, the lattice parameter was found to decrease with decreasing particle size. The results are discussed in light of the role played by surface tension effects. Chapter four describes the morphological and structural characterization of crystalline CeO2 nanoparticles prepared by forward and reverse precipitation techniques and compares these by powder x-ray diffraction (PXRD), nitrogen adsorption (BET) and high resolution transmission electron microscopy (HRTEM) analysis. The two routes give quite different materials although in both cases the products are essentially highly crystalline, dense particulates. It was found that the reverse precipitation technique gave the smallest crystallites with the narrowest size dispersion. This route also gave as-synthesised materials with higher surface areas. HRTEM confirmed the observations made from PXRD data and showed that the two methods resulted in quite different morphologies and surface chemistries. The forward route gives products with significantly greater densities of Ce3+ species compared to the reverse route. Data are explained using known precipitation chemistry and kinetic effects. Chapter five centres on the addition of terbia to ceria and has been investigated using XRD, XRF, XPS and TEM. Good solid solutions were formed across the entire composition range and there was no evidence for the formation of mixed phases or surface segregation over either the composition or temperature range investigated. Both Tb3+ and Tb4+ ions exist within the solution and the ratios of these cations are consistent with the addition of Tb8O15 to the fluorite ceria structure across a wide range of compositions. Local regions of anion vacancy ordering may be visible for small crystallites. There is no evidence of significant Ce3+ ion concentrations formed at the surface or in the bulk by the addition of terbia. The lattice parameter of these materials was seen to decrease with decreasing crystallite size. This is consistent with increased surface tension effects at small dimension. Chapter six reviews size related lattice parameter changes and surface defects in ceria nanocrystals. Ceria (CeO2) has many important applications, notably in catalysis. Many of its uses rely on generating nanodimensioned particles. Ceria has important redox chemistry where Ce4+ cations can be reversibly reduced to Ce3+ cations and associated anion vacancies. The significantly larger size of Ce3+ (compared with Ce4+) has been shown to result in lattice expansion. Many authors have observed lattice expansion in nanodimensioned crystals (nanocrystals), and these have been attributed to the presence of stabilized Ce3+ -anion vacancy combinations in these systems. Experimental results presented here show (i) that significant, but complex changes in the lattice parameter with size can occur in 2-500 nm crystallites, (ii) that there is a definitive relationship between defect chemistry and the lattice parameter in ceria nanocrystals, and (iii) that the stabilizing mechanism for the Ce3+ -anion vacancy defects at the surface of ceria nanocrystals is determined by the size, the surface status, and the analysis conditions. In this work, both lattice expansion and a more unusual lattice contraction in ultrafine nanocrystals are observed. The lattice deformations seen can be defined as a function of both the anion vacancy (hydroxyl) concentration in the nanocrystal and the intensity of the additional pressure imposed by the surface tension on the crystal. The expansion of lattice parameters in ceria nanocrystals is attributed to a number of factors, most notably, the presence of any hydroxyl moieties in the materials. Thus, a very careful understanding of the synthesis combined with characterization is required to understand the surface chemistry of ceria nanocrystals.

Silica polymer bonding of stressed silica grains: An early growth of intergranular tensile strength

© 2015 Elsevier Ltd. All rights reserved.Laboratory tests on microscale are reported in which millimeter-sized amorphous silica cubes were kept highly compressed in a liquid environment of de-ionized water solutions with different silica ion concentrations for up to four weeks. Such an arrangement simulates an early evolution of bonds between two sand grains stressed in situ. In-house designed Grain Indenter-Puller apparatus allowed measuring strength of such contacts after 3-4 weeks. Observations reported for the first time confirm a long-existing hypothesis that a stressed contact with microcracks generates silica polymers, forming a bonding structure between the grains on a timescale in the order of a few weeks. Such structure exhibits intergranular tensile force at failure of 1-1.5 mN when aged in solutions containing silica ion concentrations of 200-to 500-ppm. The magnitude of such intergranular force is 2-3 times greater than that of water capillary force between the same grains.

Living in warmer, more acidic oceans retards physiological recovery from tidal emersion in the velvet swimming crab, Necora puber

The distribution patterns of many species in the intertidal zone are partly determined by their ability to survive and recover from tidal emersion. During emersion, most crustaceans experience gill collapse, impairing gas exchange. Such collapse generates a state of hypoxemia and a hypercapnia-induced respiratory acidosis, leading to hyperlactaemia and metabolic acidosis. However, how such physiological responses to emersion are modified by prior exposure to elevated CO2 and temperature combinations, indicative of future climate change scenarios, is not known. We therefore investigated key physiological responses of velvet swimming crabs, Necora puber, kept for 14 days at one of four pCO(2)/temperature treatments (400 mu atm/10 degrees C, 1000 mu atm/10 degrees C, 400 mu atm/15 degrees C or 1000 mu atm/15 degrees C) to experimental emersion and recovery. Pre-exposure to elevated pCO(2) and temperature increased pre-emersion bicarbonate ion concentrations [HCO3-], increasing resistance to short periods of emersion (90 min). However, there was still a significant acidosis following 180 min emersion in all treatments. The recovery of extracellular acid-base via the removal of extracellular pCO(2) and lactate after emersion was significantly retarded by exposure to both elevated temperature and pCO(2). If elevated environmental pCO(2) and temperature lead to slower recovery after emersion, then some predominantly subtidal species that also inhabit the low to mid shore, such as N. puber, may have a reduced physiological capacity to retain their presence in the low intertidal zone, ultimately affecting their bathymetric range of distribution, as well as the structure and diversity of intertidal assemblages.

Structural and functional analogs of the novel mammalian neuropeptide, neuromedin S (NmS), in the dermal venoms of Eurasian bombinid toads.

We report the isolation and structural characterization of two neuromedin S (NmS) analogs, (NmS-17 and NmS-33), from the dermal venoms of Eurasian bombinid toads. NmS is a novel neuromedin U (NmU)-related peptide with potent anorexigenic and circadian rhythm-modulating properties recently discovered in mammals. Cloning of NmS precursor-encoding cDNAs from skin venom-derived libraries revealed the presence of a high degree of transcript splice variation comparable to that found previously for NmU in both amphibian skin and mammalian brain. Synthetic replicates of both amphibian NmS peptides evoked robust and dose-dependent transient increases in intracellular calcium ion concentrations in CHO cells that had been stably transfected with either FM-3/GPR66 or FM-4/TGR-1 human NmU receptors. The potency and efficacy of these amphibian skin peptides at such receptors were comparable to those observed with human NmS and rat NmS. These data show that NmS and NmU genes had already diverged at the level of the Amphibia and that differential splicing of their transcribed mRNAs has been highly conserved throughout tetrapod vertebrate evolution indicative of fundamental biological function. NmS is additionally a novel neuropeptide homolog that can be added to the biologically active peptide arsenal of amphibian venom/defensive skin secretions.

Temporal variation in the water chemistry of northern Victoria Land lakes (Antarctica)

Concentrations of major ions, silicate and nutrients (total N and P) were measured in samples of surface water from 28 lakes in ice-free areas of northern Victoria Land (East Antarctica). Sixteen lakes were sampled during austral summers 2001/02, 2003/04, 2004/05 and 2005/06 to assess temporal variation in water chemistry. Although samples showed a wide range in ion concentrations, their composition mainly reflected that of seawater. In general, as the distance from the sea increased, the input of elements from the marine environment (through aerosols and seabirds) decreased and there was an increase in nitrate and sulfate concentrations. Antarctic lakes lack outflows and during the austral summer the melting and/or ablation of ice cover, water evaporation and leaching processes in dry soils determine a progressive increase in water ion concentrations. During the five-year monitoring survey, no statistically significant variation in the water chemistry were detected, except for a slight (hardly significant) increase in TN concentrations. However, Canonical Correspondence Analysis (CCA) indicated that other factors besides distance from the sea, the presence of nesting seabirds, the sampling time and percentage of ice cover affect the composition of water in Antarctic cold desert environments.

Mammalian triokinase and dihydroxyacetone kinase are the same enzyme

It is widely accepted that the ATP-dependent phosphorylation of D-glyceraldehyde in the fructokinase pathway of fructose metabolism requires the enzyme “triokinase”. However, experimental data on this enzyme are remarkably scarce. The enzyme has been purified from a variety of sources and peptides derived from the pig kidney enzyme show high similarity to human dihydroxyacetone kinase – an enzyme which also has FMN cyclase activity in high manganese ion concentrations. The properties of the two enzymes are also highly similar. Therefore it is proposed that mammalian triokinase and dihydroxyacetone kinase are, in fact, the same enzyme. This has consequences for investigations of normal and aberrant fructose metabolism and for the teaching of biochemistry in medical and science courses.

Comparison of AGNES (absence of gradients and Nernstian equilibrium stripping) and SSCP (scanned stripping chronopotentiometry) for trace metal speciation analysis

The free metal ion concentrations obtained by SSCP (stripping chronopotentiometry at scanned deposition potential) and by AGNES (absence of gradients and Nernstian equilibrium stripping) techniques have been compared and the usefulness of the combination of both techniques in the same electrochemical cell for trace metal speciation analysis is assessed. The free metal ion concentrations and the stability constants obtained for lead(II) and cadmium(II) complexation by pyridinedicarboxylic acid, by 40 nm radius carboxylated latex nanospheres and by a humic acid extracted from an ombrotrophic peat bog were determined. Whenever possible, the free metal ion concentrations were compared with the theoretical predictions of the code MEDUSA and with the free metal ion concentrations estimated from ion selective electrodes (ISE). SSCP values were in agreement with the ones obtained by AGNES, and both of them agreed reasonably with the ISE values and the theoretical predictions. For the lead(II)-humic acid, it was not possible to obtain the stability constants by SSCP due to the heterogeneity effect. However, using AGNES it is possible to obtain, for these heterogeneous systems, the free bulk metal concentration, which allows us to retrieve the stability constant at bulk conditions.

Influence of temperature and photoperiod upon ionic regulation in rainbow trout Salmo gairdneri

Interactions of photoperiod and temperature upon waterelectrolyte balance were examined in rainbow trout acclimated to six combinations of two photoperiods {18h light: 6h dark, o 6h light: l8h dark) and three temperatures (2, 10 and 18 C). The influence of temperature and photoperiod upon plasma, skeletal muscle, cardiac muscle and liver levels of sodium, potassium, magnesi.um, calcium, chloride, water content, water distribution and cellular ion concentrations was determined by a one way analysis of variance. Significant (p < 0.05 or better) temperature effects at common photoperiods were observed in 70% of the analyses performed, showing no bias toward either photoperiod. Significant photoperiod effects occured in 57% of the analyses performed at common temperatures. The influence of photoperiod was most prevalent at reduced temperatures. Potassium and magnesium appeared to be particularly thermosensitive, while sodium and calcium were the most photosensitive of the electrolytes. The ionic composition of all tissues studied were relatively thermosensitive, with liver apparently being the most sensitive. On the other hand; the ionic composition of skeletal and cardiac muscle appear to be the mos.t photosensitive of the tissues examined. Water content and distribution in skeletal muscle and liver were significantly influenced by temperature in 50% of the analyses performed showing a very strong bias toward UwinterU animals. Photoperiod effects were significant in 56% of the water parameters measured with a strong bias toward the two lower temperatures. Body weight was of significant influence in 16% of the 174 analyses performed. These data are discussed in terms of the effect of temperature upon ionregulatory mechanisms and the possible impact of photoperiod variations on endocrine systems influencing water-electrolyte metabolism.

Ionic regulation in goldfish, Carassius auratus, acclimated to constant and diurnally-cycling temperature conditions

The effects of a diurnal sine-wave temperature cycle (250 +- 5° C) on the wa terI-e etc r o1 yt est a t us 0 f gol df1' Sh , Carassius auratus, was assessed through determination of Na+, K+, Mg2+, Ca2+, Cl- and water content in plasma, Red blood cells and muscle tissue. Animals were also acclimated to o 0 0 static temperatures (20 C, 25 c, 30 C) corresponding to the high, low and mid-ooint temperatures of the cycle. All groups were sampled at 03:00, 09:00, 15:00 and 21:00 hr. Hemoglobin content and packed cell volume, as well as electrolyte and 'water levels were determined for each animal and red cell ion concentrations and ion : hemoglobin ratios estimated. Cycled animals were distinct from those at constant temperatures in several respects. Hematological parameters were elevated above those of animals at constant temperature and were, on a diurnal basis, more stable. Red blood cell electrolyte levels varied in an adaptively appropriate fashion to cycle temperatures. This was not the case in the constant temperature groups_ Under the cycling regime, plasma ion levels were more diurnally stable than those of constant temperature fish. Although muscle parameters in cycled fish exhibited more fluctuation than was observed in plasma, these also tended to be relatively more stable than was the caseErythrocytic data are discussed in terms of their effects on hemoglobin-oxygen affinity while plasma and muscle observations were considered from the standpoint of overall water-electrolyte balance. In general, cycled fish appeared to be capable of stabilizing overall body fluid composition, while simultaneously effecting adaptively-appropriate modifications in the erythrocytic ionic microenvironment of hemoglobin. The sometimes marked diurnal variability of water-electrolyte status in animals held at constant temperature as opposed to the conservation of cycled fish suggests that this species is, in some fashion, programmed for regulation in a thermally-fluctuating environment. If this interpretation is valid and a phenomenon of general occurrence, some earlier studies involving constant acclimation of eurythermal species normally occupying habitats which vary in temperature on a daily basis may require reconsideration. at constant temperature.

Rapid [Gamma]-amino acid synthesis and the inhibition of the growth and development of oblique banded leaf-roller larvae

The hypothesis that rapid y-aminobutyric acid (GABA) accumulation is a plant defense against phytophagous insects was investigated. Simulation of mechanical damage resulting from phytophagous insect activity increased soybean (Glycine max L.) leaf GABA 10- to 25-fold within 1 to 4 min. Pulverizing leaf tissue resulted in a value of 2. 15 (±O. 11 SE) ~mol GABA per gram fresh weight. Increasing the GABA levels in a synthetic diet from 1.6 to 2.6 Jlffiol GABA per gram fresh weight reduced the growth rates, developmental rates, total biomass (50% reduction), and survival rates (30% reduction) of cultured Oblique banded leaf-roller (OBLR) (Choristonellra rosacealla Harris) larvae. In field experiments OBLR larvae were found predominantly on young terminal leaves which have a reduced capacity to produce GABA in response to mechanical damage. Glutamate decarboxylase (GAD) is a cytosolic enzyme which catalyses the decarboxylation of L-Glu to GABA. GAD is a calmodulin binding enzyme whose activity is stimulated dramatically by increased cytosolic H+ or Ca2 + ion concentrations. Phytophagous insect activity will disrupt the cellular compartmentation of H+ and Ca2 +, activate GAD and subsequent GABA accumulation. In animals GABA is a major inhibitory neurotransmitter. The possible mechanisms resulting in GABA inhibited growth and development of insects are discussed.

Thermoaclimatory variations in the microenvironment of hemoglobin in the rainbow trout, Salmo gairdneri and the carp, Cyprinus carpio

Several inorganic substances (e.g., C£ , Mg , Ca , H ) are potent negative modulators of hemoglobin-oxygen affinity. To evaluate the possibility that potentially adaptive changes in the red cell ionic environment of hemoglobin may take place during acclimation of fishes to increased environmental temperature, hematological status (hemoglobin, hematocrit, red cell numbers, mean erythrocytic volume and hemoglobin content), plasma + + 2+ 2+ and packed red cell electrolyte levels (Na , K , Ca , Mg , C£ ) were evaluated in summer and winter populations of the stenothermal rainbow trout, Salmo gairdneri, following acclimation to 2°, 10°, 18°C, and in a spring population of eurythermal carp, Cyprinus carpio, held at 2°, 16° and 30°C. From these data cell ion concentrations and ion:hemoglobin ratios were estimated. In view of the role of red cell carbonic anhydrase in the reductions of blood C02 tensions and the recruitment of Na and C£~ lost by fishes, a preliminary investigation of thermoacclimatory changes in the activity of this system in rainbow trout erythrocytes was conducted. Few changes in hematological status were encountered following acclimation. There was, however, some evidence of weight-specific differential hematological response in carp. This lead to markedly greater increases in hemoglobin, hematocrit and red cell numbers in smaller rather than in larger specimens at higher temperatures; variations which were 2+ well correlated with changes in plasma Ca . Plasma composition in summer trout was not altered by acclimation. In winter trout plasma Na and K increased at higher temperatures. Carp were characterized by increases in plasma calcium, and reductions in sodium and magnesium under these conditions. Several significant seasonal differences in plasma ion levels were observed in the trout. (n) In trout, only erythrocytic K and K :Hb were altered by acclimation, rising at higher temperatures. In carp Na , Na :Hb, C£~ and C£~:Hb in- 2+ 2+ creased with temperature, while Mg and Mg :Hb declined. Changes in overall ionic composition in carp red cells were consistent with increases in H content. In both species significant reciprocal variations in C£~ 2+ - + and Mg were found. In mammalian systems increases in C£ and H reduce hemoglobin-oxygen affinity by interaction with hemoglobin. Reduction in 2+ 2+ Mg maximizes organophosphate modulator availability by decreasing ATP»Mg complex formation. Thus, the changes observed may be of adaptive value in reducing hemoglobin-oxygen affinity, and facilitating oxygen release to cells at higher temperatures. Trout appear to maintain a high chloridelow magnesium state over the entire thermal tolerance zone. Carp, however, achieved this state only at higher temperatures. In both species mean erythrocytic volume was decreased at higher temperatures and this may facilitate branchial oxygen loading. Since mean erythrocytic volume was inversely related to red cell ion content, it is hypothesized that reductions in cell volume are achieved by export of some unidentified solute or solutes. Variations in the carbonic anhydrase activity that could be attributed to the thermoacclimatory process were quite modest. On the other hand, assays performed at the temperature of acclimation showed a large temperature effect where under in vivo conditions of temperature fish acclimated to higher temperatures might be expected to have higher activities. Furthermore, since hematocrit increased with temperature in these fish, while carbonic anhydrase is present only in the erythrocyte, the whole blood levels of this enzyme are expected to increase and further augment the temperature effect. This, in turn, could aid in the reduction of C02 (111) tension and increase the production of H and HC0~~ used in the active uptake of Na and C£ at higher temperatures.

Axe et rotaxane parapluie : vers de nouveaux transporteurs transmembranaires de chlorures et de médicaments cycliques

La membrane cellulaire est principalement une bicouche phospholipidique constituant une barrière qui régule les échanges entre la cellule et son environnement. Son intérieur hydrophobe empêche le passage d’espèces hydrophiles, chargées, de grande masse moléculaire et polaires, qui sont généralement transportées par des protéines à travers la bicouche. Dans certains cas de systèmes défectueux (e.g. les canalopathies), l’équilibre des concentrations en ions à l’intérieur et à l’extérieur des cellules est perturbé et les cellules sont compromises. C’est pourquoi le développement de transporteurs transmembranaires synthétiques est nécessaire. De nombreux travaux ont été faits dans le développement de transporteurs synthétiques d’anions (particulièrement du chlorure). Dans cette thèse, nous présentons nos travaux sur un nouveau transporteur d’anion appelé axe parapluie, capable de changer de conformation dépendamment de la polarité de son environnement. Dans un premier temps, nous avons conçu le design, puis synthétisé ces axes parapluie qui montrent une importante activité en tant que transporteur de chlorures. Ces composés réunissent deux concepts : - Le parapluie, constitué d’acides biliaires amphiphiles (une face hydrophile, une face hydrophobe). La flexibilité des articulations combinée à la grande surface des acides choliques permettent d’empêcher les interactions défavorables entre les parties hydrophiles et hydrophobes, ce qui facilite l’insertion dans la bicouche. - Un site ammonium secondaire en tant que site de reconnaissance, capable de former des ponts hydrogène avec des ions chlorure. De plus, l’axe peut complexer une roue de type éther couronne pour former un pseudo-rotaxane ou rotaxane parapluie ce qui résulte en l’inhibition partielle de leurs propriétés de transport. Ceci nous mène au second objectif de cette thèse, le développement d’un nouveau moyen de transport pour les médicaments cycliques. Certains macrocycles polaires et biologiquement actifs tels que les nactines ont besoin d’atteindre leur objectif à l’intérieur de la cellule pour jouer leur rôle. La membrane cellulaire est alors un obstacle. Nous avons imaginé tirer profit de notre axe parapluie pour transporter un médicament cyclique (en tant que roue d’un rotaxane parapluie). Les assemblages des rotaxanes parapluie furent accomplis par la méthode de clipage. Le comportement de l’axe et du rotaxane parapluie fut étudié par RMN et fluorimétrie. Le mouvement du parapluie passant d’une conformation fermée à exposée dépendamment du milieu fut observé pour le rotaxane parapluie. Il en fut de même pour les interactions entre le rotaxane parapluie et des vésicules constituées de phospholipides. Finalement, la capacité du rotaxane parapluie à franchir la bicouche lipidique pour transporter la roue à l’intérieur de la vésicule fut démontrée à l’aide de liposomes contenant de la α-chymotrypsine. Cette dernière pu cliver certains liens amide de l’axe parapluie afin de relarguer la roue.

Anomalous profile of a self-reversed resonance line from Ba+ in a laser produced plasma from YBa2Cu307

A laser produced plasma from the multielement solid target YBa2Cu3O7 is generated using 1.06 μm, 9 ns pulses from a Q-switched Nd:YAG laser in air at atmospheric pressure. A time resolved analysis of the profile of the 4554.03 Å resonance line emission from Ba II at various laser power densities has been carried out. It has been found that the line has a profile which is strongly self-reversed. It is also observed that at laser power densities equal to or exceeding 1.6×1011 W cm−2, a third peak begins to develop at the centre of the self-reversed profile and this has been interpreted as due to the anisotropic resonance scattering (fluorescence). The number densities of singly ionized barium ions evaluated from the width of the resonance line as a function of time delay with respect to the beginning of the laser pulse give typical values of the order of 1019 cm−3. The higher ion concentrations existing at smaller time delays are seen to decrease rapidly. The Ba II ions in the ground state resonantly absorb the radiation and this absorption is maximum around 120 ns after the laser pulse.

Extraction behavior of the synergistic system 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine and 2-bromodecanoic acid using Am and Eu as radioactive tracers

In this study, the extraction properties of a synergistic system consisting of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine (BODO) and 2-bromodecanoic acid (HA) in tert-butyl benzene (TBB) have been investigated as a function of ionic strength by varying the nitrate ion and perchlorate ion concentrations. The influence of the hydrogen ion concentration has also been investigated. Distribution ratios between 0.03-12 and 0.003-0.8 have been found for Am(III) and Eu(HI), respectively, but there were no attempts to maximize these values. It has been shown that the distribution ratios decrease with increasing amounts of ClO4-, NO3-, and H+. The mechanisms, however, by which the decrease occurs, are different. In the case of increasing perchlorate ion concentration, the decrease in extraction is linear in a log-log plot of the distribution ratio vs. the ionic strength, while in the nitrate case the complexation between nitrate and Am or Eu increases at high nitrate ion concentrations and thereby decreases the distribution ratio in a non-linearway. The decrease in extraction could be caused by changes in activity coefficients that can be explained with specific ion interaction theory (SIT); shielding of the metal ions, and by nitrate complexation with Am and Eu as competing mechanism at high ionic strengths. The separation factor between Am and Eu reaches a maximum at similar to1 M nitrate ion concentration. Thereafter the values decrease with increasing nitrate ion concentrations.

Buffering of recovery from acidification by organic acids

In the United Kingdom, as in other regions of Europe and North America, recent decreases in surface water sulphate concentrations, due to reduced sulphur emissions, have coincided with marked increases in dissolved organic carbon (DOC) concentrations. Since many of the compounds comprising DOC are acidic, the resulting increases in organic acidity may have the potential to offset the benefits of a decrease in mineral (sulphate) acidity. To test this, we used a triprotic model of organic acid dissociation to estimate the proportional organic acid buffering of reduced mineral acidity as measured in the 22 lakes and streams monitored by the UK Acid Waters Monitoring Network. For an average non-marine sulphate decrease of 30 μeq l− 1 over 15 years from 1988–2003, we estimate that around 28% was counterbalanced by rising strong organic acids, 20% by rising alkalinity (partly attributable to an increase in weak organic acids), 11% by falling inorganic aluminium and 41% by falling non-marine base cations. The situation is complicated by a concurrent decrease in marine ion concentrations, and the impact this may have had on both DOC and acidity, but results clearly demonstrate that organic acid increases have substantially limited the amount of recovery from acidification (in terms of rising alkalinity and falling aluminium) that have resulted from reducing sulphur emissions. The consistency and magnitude of sulphate and organic acid changes are consistent with a causal link between the two, possibly due to the effects of changing acidity, ionic strength and aluminium concentrations on organic matter solubility. If this is the case, then organic acids can be considered effective but partial buffers to acidity change in organic soils, and this mechanism needs to be considered in assessing and modelling recovery from acidification, and in defining realistic reference conditions. However, large spatial variations in the relative magnitude of organic acid and sulphate changes, notably for low-deposition sites in northwestern areas where organic acid increases apparently exceed non-marine sulphate decreases, suggest that additional factors, such as changes in sea-salt deposition and climatic factors, may be required to explain the full magnitude of DOC increases in UK surface waters.