Academic literature on the topic 'Acid base equilibrium'

The equilibrium in the Ph2P(O)OC6H4OH-base system may be shifted by varying the base concentration, where base = imidazole, triethylamine, dimethyl sulfoxide, pyridine, and 1,4-dioxane. This equilibrium was studied by 31P and 1H NMR, and information about the symmetry of phosphorus-containing intermediates is provided by the 1H NMR spectrum of the catecholyl ring, with its ABCD spin system. The equilibrium is also affected by trifluoroacetic acid. A mechanism is proposed that involves protonation-deprotonation, cyclic-acyclic equilibria, and selective P-O bond cleavage, with all steps occurring rapidly on the NMR time scale.Key words: Ph2P(O)OC6H4OH-base system, cyclic-acyclic equilibrium, and selective P-O bond cleavage.

Acid–base reactions are ubiquitous in nature. Understanding their mechanisms is crucial in many fields, from biochemistry to industrial catalysis. Unfortunately, experiments give only limited information without much insight into the molecular behavior. Atomistic simulations could complement experiments and shed precious light on microscopic mechanisms. The large free-energy barriers connected to proton dissociation, however, make the use of enhanced sampling methods mandatory. Here we perform an ab initio molecular dynamics (MD) simulation and enhance sampling with the help of metadynamics. This has been made possible by the introduction of descriptors or collective variables (CVs) that are based on a conceptually different outlook on acid–base equilibria. We test successfully our approach on three different aqueous solutions of acetic acid, ammonia, and bicarbonate. These are representative of acid, basic, and amphoteric behavior.

Microscopic redox equilibrium constants and standard redox potential values were determined to quantify selenolate-diselenide equilibria of biological significance. The highly composite, codependent acid-base and redox equilibria of selenolates could so far be converted into pH-dependent, apparent parameters (equilibrium constants, redox potentials) only. In this work, the selenolate-diselenide redox equilibria of selenocysteamine and selenocysteine against dithiothreitol were analyzed by quantitative nuclear magnetic resonance (NMR) methods to characterize the interfering acid-base and redox equilibria. The directly obtained, pH-dependent, conditional redox equilibrium constants were then decomposed by our method into pH-independent, microscopic constants, which characterize the two-electron redox transitions of selenocysteamine and selenocysteine. The 12 different, species-specific parameter values show close correlation with the respective selenolate basicities, providing a tool to estimate otherwise inaccessible site-specific selenolate-diselenide redox potentials of related moieties in large peptides and proteins.

We developed mathematical models that predict equilibrium distribution of water and electrolytes (proteins and simple ions), metabolites, and other species between plasma and erythrocyte fluids (blood) and interstitial fluid. The models use physicochemical principles of electroneutrality in a fluid compartment and osmotic equilibrium between compartments and transmembrane Donnan relationships for mobile species. Across the erythrocyte membrane, the significant mobile species Cl−is assumed to reach electrochemical equilibrium, whereas Na+and K+distributions are away from equilibrium because of the Na+/K+pump, but movement from this steady state is restricted because of their effective short-term impermeability. Across the capillary membrane separating plasma and interstitial fluid, Na+, K+, Ca2+, Mg2+, Cl−, and H+are mobile and establish Donnan equilibrium distribution ratios. In each compartment, attainment of equilibrium by carbonates, phosphates, proteins, and metabolites is determined by their reactions with H+. These relationships produce the recognized exchange of Cl−and bicarbonate across the erythrocyte membrane. The blood submodel was validated by its close predictions of in vitro experimental data, blood pH, pH-dependent ratio of H+, Cl−, and HCO3−concentrations in erythrocytes to that in plasma, and blood hematocrit. The blood-interstitial model was validated against available in vivo laboratory data from humans with respiratory acid-base disorders. Model predictions were used to gain understanding of the important acid-base disorder caused by addition of saline solutions. Blood model results were used as a basis for estimating errors in base excess predictions in blood by the traditional approach of Siggaard-Andersen (acid-base status) and more recent approaches by others using measured blood pH and Pco2values. Blood-interstitial model predictions were also used as a basis for assessing prediction errors of extracellular acid-base status values, such as by the standard base excess approach. Hence, these new models can give considerable insight into the physicochemical mechanisms producing acid-base disorders and aid in their diagnoses.

Upon the addition of protons to an aqueous solution containing multiple buffers, the final H+concentration ([H+]) at equilibrium is determined by the partitioning of added H+among the various buffer components. In the analysis of acid-base chemistry, the Henderson-Hasselbalch equation and the Stewart strong ion formulation can only describe (rather than predict) the equilibrium pH following a proton load since these formulas calculate the equilibrium pH only when the reactant concentrations at equilibrium11 The term “equilibrium” refers to the steady state proton and reactant concentrations when the buffering of excess protons by the various buffers is complete. are already known. In this regard, it is simpler to directly measure the equilibrium pH rather than measure the equilibrium reactant concentrations to calculate the equilibrium pH. As these formulas cannot predict the final equilibrium [H+] following a proton load to a multiple-buffered aqueous solution, we developed a new quantitative approach for predicting the equilibrium [H+] that is based on the preequilibrium22 The term “preequilibrium” refers to the initial proton and reactant concentrations immediately upon addition of protons and before the buffering of excess protons by the various buffers. concentrations of all buffers in an aqueous solution. The mathematical model used to derive our equation is based on proton transfer buffer equilibria without requiring the incorporation of electroneutrality considerations. The model consists of a quartic polynomial equation that is derived based solely on the partitioning of H+among the various buffer components. We tested the accuracy of the model using aqueous solutions with various buffers and measured the equilibrium pH values following the addition of HCl. Our results confirmed the accuracy of our new equation ( r2= 1; measured pH vs. predicted pH), indicating that it quantitatively accounts for the underlying acid-base phenomenology.

Two approaches are applied to the clinical evaluation of acid--base equilibria: one is the traditional “Danish school” approach of Siggaard-Andersen et al., the other is the “modern” approach by Stewart and Fencl. The two theories are interlinked by what is called the balance approach, described in detail in [1]. A simulation model can be applied in order to model various pathogeneses of acid-base disorders and to monitor their mani-festations from both the traditional and the modern acid-base theory aspects.

The fundamental study of Lewis acid/base interactions presented in this dissertation demonstrates the role of these interactions in adhesive phenomena. The model systems investigated were representative of real substrates and soft, viscoelastic adhesives where, in one case, favorable acid/base interactions were possible which were not possible in the other. Inverse gas chromatography (IGC) and Infrared spectroscopy (IR) techniques were used to analyze the model adhesive in terms of its acid/base nature. The results of both experiments indicated, through negative enthalpies of acid/base interaction with acidic solvents, that the model adhesive poly(2-ethyl hexyl methacrylate) (PEHMA) exhibits the properties of a Lewis base. The near quantitative agreement of the results from both experiments validate these methods of determining acid/base interactions in polymeric systems. Fitting the enthalpies for acid/base interaction to Drago’s and Gutmann’s models brought out the importance of the electrostatic component of the interactions investigated. Furthermore, they illustrated the need to expand the existing datasets beyond organo-meta1lic compounds, and include more common organic solvents. Results from X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) analysis of the model substrate, grade 2 titanium, pretreated via chromic acid (CAA) or sodium hydroxide anodization (PSHA), confirmed that oxides of very similar topology can be produced. Indicator dye studies revealed the CAA-Ti had a surface pH of below 3.0 and the PSHA-Ti had a surface pH of above 8.0. Bonds constructed from these analyzed materials were tested in peel and both systems exhibited good adhesion. However, the bonds in which favorable interactions were possible demonstrated superior interfacial performance. This improvement was seen in the bond’s ability to resist adhesive (interfacial) failure at debond rates at which other bonds failed. When the test geometry was changed such that the stress intensity at the interface was increased, the bonds in which acid/base interactions were favorable supported a higher peel load.
Ph. D.

The possibility that an inadequate response of the pulmonary system might limit high intensity exercise in man has received increasing attention over the past few years. However, very few scientific investigations have focused systematically on pulmonary function during high intensity constant-load exercise. Furthermore, many studies have examined only one part of the pulmonary system during exercise and some have not included blood gas measurements as a measure of the adequacy of pulmonary function. The studies reported in this thesis were designed to investigate the possible failure of the gas exchanging and pump functions of the pulmonary system during high intensity constant-load exercise. In particular, the aim was to determine the extent to which the pulmonary system might be a factor causing fatigue during this form of exercise.

L'objectiu últim d’aquesta memòria és la descripció qualitativa i quantitativa de totes les transicions termodinàmiques i conformacionals lligades als equilibris àcid-base d’alguns polinucleòtids en ambients biològics de polaritat baixa. L’emulació d’aquests ambients especials s'ha dut a terme fent ús de mescles aigua-dioxa que mantenen la natura aquosa dels medis biològics i al mateix temps presenten la baixa polaritat desitjada gràcies a les propietats del cosolvent orgànic. La complexitat associada al caràcter macromolecular dels polinucleòtids i al fet d'utilitzar dissolvents mixtos ha aconsellat la realització de certs estudis fonamentals abans de tractar especificament el problema dels equilibris àcid-base dels polinucleòtids en mescles aigua-dioxa. Aquests estudis han inclòs, d'una banda, la caracterització detallada de les mescles aigua-dioxa i la interpretació de llur efecte sabre els equilibris àcid-base de soluts senzills d'altra banda, l'estudi de les unitats monòmeres dels polinucleòtids en aquestes mescles. Un punt constant d'interès en tot el treball que s'ha realitzat ha estat l’assoliment de la màxima qualitat en el tractament de les dades experimentals. En aquest sentit, han merescut una atenció especial els problemes associats a l’establiment de les relacions lineals d'energia de solvatació (LSER), que són els models que descriuen l'efecte del solvent sobre el comportament del solut, i la interpretació de les dades multivariants precedents del seguiment dels equilibris dels polinucleòtids. El primer problema s’ha solucionat amb l’aplicació de diversos mètodes de modelatge dur (hard-modelling) i de modelatge tou (soft­ modelling), mentre per al segon s’ha optat per l’aplicació de mètodes de resolució de corbes, que no necessiten la postulació de cap model químic per a interpretar la variació de les diferents espècies en solució.
The main goal of this project is the qualitative and quantitative description of all the thermodynamical and conformational transitions related to the acid-base behaviour of several polynucleotides in biological environments of low polarity. The emulation of these special environments has been carried out by using water-dioxane mixtures that keep the aqueous nature of the biological media and present the desired low polarity due to the features of their cosolvent. Owing to the complexity associated with the macromolecular nature of the polynucleotides and with the mixed character of the solvent used, some fundamental research must be carried out before facing specifically the research about the acid-base polynucleotide behaviour in water-dioxane mixtures. These previous studies include, on one hand, the detailed characterization of the water-dioxane mixtures and the interpretation of their effect on the acid-base behaviour of single solutes and, on the other hand, the study of the monomeric units of the polynucleotidesin these mixtures. In all the work performed, the careful treatment of the experimental data has been a constant concern. Special attention has been focused on the establishment of Linear Solvation Energy Relationships (LSER), behaviour models that relate the solute behaviour to the solvent effect, and on the interpretation of the multivariate data coming from the monitoring of the macromolecular equilibria of polynucleotides. The former problem has been tackled by using different kinds of bard-modelling and soft-modelling methods, whereas the latter has been solved with the application of curve resolution methods which do not need the postulation of any chemical model to interpret the variation of the different species in solution.

Thesis (M.S.)--Georgia Southern University, 2007.
"A thesis submitted to the Graduate Faculty of Georgia Southern University in partial fulfillment of the requirements for the degree Master of Science." In Biology, under the direction of James B. Claiborne. ETD. Electronic version approved: December 2007. Includes bibliographical references (p. 77-85)

The current increase in the atmospheric CO2 concentration results in two major consequences in the marine environment: an increase of the sea surface temperature (0.7 °C since pre-industrial times) and a decreased seawater pH. This decrease is being measured continuously in different parts of the world and ranges from -0.0017 to -0.04 units per year according to the location considered. Based on CO2 emissions models provided by the IPCC, it was predicted that the average open ocean pH would decrease further by 0.4 units by 2100 and 0.8 by 2300 (corresponding to about a three-fold and six-fold increase of the proton concentration). Also, saturation states of seawater for the different forms of calcium carbonate, such as calcite, magnesium calcite and aragonite which are produced by calcifying marine organisms, are decreasing and consequently the saturation horizons of these minerals are shoaling. Today, some environments are characterized by pH values lower than the average open ocean pH. These are intertidal rock pools, upwelling zones, the deep-sea and CO2 vents. In these environments, pH is either constantly low or fluctuates. Those changes are either due to biological activity, geological CO2 leakage, or water masses movements. Within these environments, it has been hypothesized that organisms could be adapted or acclimatized to low pH values such as those predicted for the near-future.

Tolerance to ocean acidification in metazoans is linked to their acid-base regulation capacities when facing environmental hypercapnia (i.e. increased CO2 concentration in the surrounding environment). The latter may result in a hypercapnia of the internal fluids and a concomitant acidosis (i.e. reduced pH of the internal fluids due to the dissociation of CO2 in this case). Organisms have two buffer systems allowing the compensation of this acidosis: the CO2-bicarbonate and the non-bicarbonate buffers. Homeostasis of the internal fluids thanks to these systems is essential for the proper functioning of enzymes and processes. As hypometabolic calcifying osmoconformers, three of the characteristics conferring a relative vulnerability to ocean acidification, echinoderms are considered “at risk” for the near-future conditions. Nonetheless, post-metamorphic (juveniles and adults) echinoderms inhabit all environments showing naturally low pH. Furthermore, sea urchins which are highly calcified (compared to sea stars or sea cucumbers) are also found in these environments. This suggests that echinoderms have strategies to adapt or acclimate to low pH environments. Recent studies indicated that while sea urchins are able to regulate their coelomic (extracellular) fluid by accumulation of bicarbonate, sea stars seem to tolerate the acidosis linked to environmental hypercapnia. However, this information was obtained on a reduced number of species and significant interspecific differences were evidenced. Some taxa have not been investigated at all. Furthermore, several aspects of the acid-base physiology were unexplored, like the buffering capacity of the extracellular fluid and the origin of carbon within these fluids.

Accordingly, the goal of this study was to characterize the acid-base physiology in post-metamorphic echinoderms of different taxa in order to understand their response to ocean acidification.

The acid-base regulation capacities within the different echinoderm taxa were compared. A method was designed to measure the total alkalinity in small volumes (500 µl) of the main extracellular fluid (the coelomic fluid). This study showed that regular euechinoids have an increased buffer capacity in their coelomic fluid compared to seawater and the other echinoderm groups. In sea urchins, bicarbonate and non-bicarbonate buffers come into play, the former playing the major role. This buffer capacity was increased in fed individuals compared to fasted ones and increased further when seawater pH was lowered.

The acid-base regulation capacities of sea urchins from different taxa were investigated. Regular euechinoids possess an increased buffer capacity of the coelomic fluid allowing them to maintain a higher pH compared to cidaroids at current seawater pH. This pattern was found for temperate, tropical and Antarctic sea urchins. Data was also obtained for irregular echinoids which also showed a particularly low extracellular pH and a buffer capacity close to seawater like cidaroids. When exposed to reduced seawater pH (8.0, 7.7, and 7.4) for 4-6 weeks, regular euechinoids showed an increasing buffer capacity of the coelomic fluid accompanied by a homeostasis of the pH. On the contrary, cidaroids showed no changes in their acid-base status whatever the seawater pH (8.0 to 7.4). The origin of coelomic fluid carbon, investigated by stable carbon isotope analysis, also differs according to taxa. The δ13CDIC of regular euechinoids evidenced a mixing between CO2 from metabolic origin and that from the surrounding seawater. This is further supported by the correlation between the seawater signal of reduced pH conditions (modified by the addition of industrial gas, changing the δ13C to more negative values) and that of the coelomic fluid. On the other hand, cidaroids exhibit a signal reflecting principally metabolic CO2 (very negative δ13C), and the δ13C did not change under varying pH conditions (i.e. did not adapt to the seawater δ13CDIC signature). For irregular echinoids, the carbon origin is unclear as some species show signals close to that of regular euechinoids whereas others are similar to cidaroids.

The impact of acid-base regulation was investigated by testing the effect of ocean acidification on the mechanical properties of the skeleton (test plates) in the sea urchin Paracentrotus lividus. Individuals from intertidal pools, CO2 vents and a one year acidification experiment (pH 8.0, 7.9 and 7.7) were compared. Only the intertidal pool individuals showed a difference of the Young’s modulus and fracture forces of their plates. Sea urchins from the tide pool with the largest pH fluctuations showed a lower stiffness and strengthened test. On the contrary, sea urchins from CO2 vents and experimental acidification did not display any differences in the several mechanical properties tested. We suggest that the different food qualities (calcified vs. uncalcified algae) in the different tide pools significantly contributed to the observed difference.

The acid-base regulation ability of sea cucumbers was assessed in two species from contrasted habitats (mangrove intertidal vs. coral reef species). These organisms underwent acidosis of the coelomic fluid when exposed to reduced seawater pH for a short time (6 to 12 days). The δ13C signal of the coelomic fluid mirrored that of the surrounding seawater in all conditions, indicating that the CO2 accumulated (cause of the acidosis) comes also from the seawater. This is still unexplained to date. However, metabolic processes such as respiration and ammonium excretion rates were not affected. No difference was evidenced between the two species.

The results obtained in this study compiled with data from the literature indicate that post-metamorphic echinoderms have contrasted acid-base physiology with most regular euechinoids compensating the coelomic fluid pH by accumulation of bicarbonate ions (and possibly ophiuroids also), cidaroids and at least one regular euechinoid (Arbacia lixula) having a naturally low coelomic fluid pH which is not affected by acidification, and sea stars and sea cucumbers which do not compensate their coelomic fluid pH when submitted to acidified seawater. In regular euechinoids, negative effects are linked to resource allocation with growth usually being reduced in favor of acid-base regulation mechanisms. Starfish and sea cucumbers appear as resilient to acidification, with very few functions being negatively impacted. In conclusion, it seems that post-metamorphic echinoderms studied so far will not be particularly at risk when facing ocean acidification levels expected by 2100. Furthermore, tolerance to ocean acidification does not seem linked to the present day ambient pH regime. Nevertheless, more studies need to be carried out on brittle stars and sea cucumbers to confirm preliminary results, as well as crinoids which have not been investigated to date. Long-term exposure experiments to estimate energy budget changes as well as more assessments of evolutionary potential in echinoderms are crucially needed./L’augmentation actuelle de la concentration en CO2 atmosphérique a deux conséquences majeures dans l’environnement marin :une augmentation de la température des eaux de surface (0.7°C depuis l’époque préindustrielle) et une diminution du pH de l’eau de mer. Cette diminution est mesurée continuellement dans différentes régions du monde et varie de -0.0017 à -0.04 unités de pH par an en fonction du site considéré. Basé sur des modèles d’émissions de CO2 du GIEC, il a été prédit que le pH moyen de l’océan diminuerait encore de 0.4 unités d’ici 2100 et 0.8 d’ici 2300 (correspondant à une augmentation de la concentration en protons d’environ 3 fois et 6 fois). De même, les états de saturation de l’eau de mer vis-à-vis des différentes formes de carbonate de calcium, telles que la calcite, la calcite magnésienne et l’aragonite produites par les organismes calcifiants, sont en train de diminuer et par conséquent, les horizons de saturation remontent vers les eaux de surface. Aujourd’hui, certains environnements sont caractérisés par des valeurs de pH plus basses que celle de l’océan. Ceux-ci sont les mares intertidales, les zones d’upwelling, l’océan profond et les évents volcaniques. Dans ces environnements, le pH est soit constamment bas ou fluctue. Ces changements sont soit dû à une activité biologique, une fuite de CO2 géologique, ou au mouvement des masses d’eau. Dans ces environnements, il a été suggéré que les organismes pourraient être adaptés ou acclimatés à des valeurs basses de pH, telles que celles prédites pour le futur proche.

La tolérance à l’acidification des océans chez les métazoaires est liée à leur capacité de régulation acide-base lorsqu’ils sont exposés à une hypercapnie environnementale (c’est-à-dire, une augmentation de la concentration en CO2 dans l’environnement entourant l’organisme). Ce phénomène peut résulter en une hypercapnie des liquides internes et une acidose concomitante (c’est-à-dire, un pH des liquides internes réduit dû à la dissociation du CO2 dans ce cas précis). Les organismes ont deux systèmes tampons leur permettant de compenser l’acidose :les tampons CO2-bicarbonate et non-bicarbonate. L’homéostasie des liquides internes grâce à ces systèmes est essentielle pour le fonctionnement correct des enzymes et processus. En tant qu’osmoconformes calcifiant hypométaboliques, trois caractéristiques menant à une certaine vulnérabilité face à l’acidification des océans, les échinodermes sont considérés « à risque » pour les conditions du futur proche. Cependant, les échinodermes post-métamorphiques (juvéniles et adultes) occupent tous les environnements montrant un pH faible naturellement. De plus, les oursins qui sont hautement calcifiés (par rapport aux étoiles de mer ou aux concombres de mer) sont également retrouvés dans ces environnements. Ceci suggère que les échinodermes ont des stratégies d’adaptation ou d’acclimatation à ces environnements à bas pH. Alors que des études récentes montrent que les oursins sont capables de réguler le pH du liquide cœlomique (extracellulaire) par l’accumulation de bicarbonates, les étoiles semblent tolérer l’acidose liée à l’hypercapnie environnementale. Néanmoins, ces informations ont été obtenues sur un petit nombre d’espèces et des différences interspécifiques significatives ont été mises en évidence. Certains taxa n’ont pas été étudié du tout. Par ailleurs, différents aspects de la physiologie acide-base sont inexplorés, tels que la capacité tampon du liquide extracellulaire et l’origine du carbone dans ces liquides.

Par conséquent, le but de cette étude était de caractériser la physiologie acide-base chez les échinodermes post-métamorphiques de différents taxa afin de comprendre leur réponse à l’acidification des océans.

Les capacités de régulation acide-base au sein des différents groupes d’échinodermes ont été comparées. Une méthode a été mise au point afin de mesurer l’alcalinité totale dans de petits volumes (500 µl) de liquide extracellulaire (le liquide cœlomique). Cette étude démontra que la capacité tampon du liquide cœlomique des euéchinoïdes réguliers est accrue comparée à celle de l’eau de mer ainsi que celle des autres groupes d’échinodermes. Dans les oursins, les tampons bicarbonate et non-bicarbonate entrent en jeux, le premier étant majoritaire. Cette capacité tampon est augmentée chez les individus nourris par rapport à ceux à jeuns et est augmentée plus encore lorsque le pH de l’eau de mer est diminué.

Les capacités de régulation acide-base ont été étudiées plus spécifiquement dans les différents groupes d’oursins. Les euéchinoïdes réguliers possèdent une capacité tampon accrue du liquide cœlomique leur permettant de maintenir un pH élevé comparé aux oursins cidaroïdes, au pH de l’eau de mer actuel. Ce patron se retrouve dans les oursins tempérés, tropicaux et antarctiques. Des données ont également été obtenues pour les oursins irréguliers qui ont également un pH extracellulaire particulièrement bas et une capacité tampon proche de celle de l’eau de mer comme les cidaroïdes. Lorsqu’ils sont exposés à un pH de l’eau de mer réduit (7.7 et 7.4 par rapport à 8.0) pour 4 à 6 semaines, les euéchinoïdes réguliers ont montré une augmentation de la capacité tampon du liquide cœlomique accompagnée d’une homéostasie du pH de ce liquide. A l’inverse, les cidaroïdes n’ont montré aucune modification de leur statut acide-base quel que soit le pH (8.0 à 7.4). L’origine du carbone du liquide cœlomique, étudié par analyse des isotopes stables du carbone, diffère également en fonction du groupe. Le δ13CDIC des euéchinoïdes réguliers met en évidence un mélange entre du CO2 d’origine métabolique et celui de l’eau environnante. Ceci est également démontré par la corrélation entre le signal de l’eau de mer dont le pH est réduit (modifié par l’ajout de CO2 industriel, changent le δ13C vers des valeurs plus négatives) et celui du liquide cœlomique. En revanche, les cidaroïdes montrent un signal reflétant principalement celui du CO2 métabolique (δ13C très négatif), et le δ13C n’est pas influencé par des conditions de pH variées (c’est-à-dire, qu’il ne s’adapte pas à la signature du δ13CDIC de l’eau de mer). Pour les oursins irréguliers, l’origine du carbone est incertaine puisque certaines espèces montrent un signal proche de celui des euéchinoïdes réguliers et d’autres similaire à celui des cidaroïdes.

L’impact de la régulation acide-base a été étudié en testant l’effet de l’acidification des océans sur les propriétés mécaniques du squelette (plaques squelettiques) de l’oursin Paracentrotus lividus. Des individus de mares intertidales, d’évents volcaniques et d’une expérience d’acidification d’un an (pH 8.0, 7.9 et 7.7) ont été comparés. Seuls les individus des mares intertidales montrèrent une différence pour le module de Young et la force des fractures des plaques. Les oursins venant de la mare intertidale montrant les plus grandes variations de pH avaient une rigidité plus faible et un squelette renforcé. A l’inverse, les oursins des évents volcaniques et de l’expérience d’acidification n’ont montrés aucune différence dans les diverses propriétés mécaniques étudiées. Nous suggérons que les variations en termes de qualité de nourriture (algues calcifiées vs. non-calcifiées) dans les différentes mares intertidales ont contribués de manière significative à la différence observée.

L’habilité des concombres de mer à réguler leur balance acide-base a été évaluée dans deux espèces d’habitats contrastés (espèce intertidale des mangroves vs. subtidale des récifs coralliens). Ces organismes ont subis une acidose du liquide cœlomique lorsqu’ils ont été exposés à un pH réduit de l’eau de mer pour une courte durée (6 à 12 jours). Le signal δ13C du liquide cœlomique reflétait celui de l’eau environnante dans toutes les conditions, indiquant que le CO2 accumulé (cause de l’acidose) venait de l’eau. Ceci est encore inexpliqué à l’heure actuelle. Cependant, les processus métaboliques tels que la respiration ou l’excrétion d’ammonium n’ont pas été affecté. Aucune différence n’a été observée entre les deux espèces.

Les résultats obtenus dans cette étude compilés avec ceux de la littérature indiquent que les échinodermes post-métamorphiques ont une physiologie acide-base contrastée avec la plupart des euéchinoïdes réguliers qui compensent le pH du liquide cœlomique par l’accumulation d’ions bicarbonates (et peut-être les ophiures aussi), les cidaroïdes et au moins un euéchinoïde régulier (Arbacia lixula) qui ont naturellement un pH du liquide cœlomique bas et qui ne sont pas affectés par l’acidification, et les étoiles de mer et les concombres de mers qui ne compensent pas le pH du liquide cœlomique lorsqu’ils sont soumis à une eau acidifiée. Chez les euéchinoïdes réguliers, des effets négatifs sont liés à un changement de l’allocation des ressources avec souvent un taux de croissance réduit en faveur des mécanismes de régulation acide-base. Les étoiles de mer et les concombres de mer apparaissent plus tolérants à l’acidification, avec peu de fonctions négativement impactées. En conclusion, il semble que les échinodermes post-métamorphiques étudiés jusqu’à présent ne seront pas particulièrement à risque lorsqu’ils seront exposés au niveau d’acidification attendu pour 2100. De plus, la tolérance à l’acidification des océans ne semble pas liée au régime de pH subit actuellement. Cependant, plus d’études doivent être menées sur les ophiures et les concombres de mer afin de confirmer les résultats préliminaires, ainsi que sur les crinoïdes qui n’ont à l’heure actuelle pas encore été étudiés. Des expériences à long terme afin d’estimer le budget énergétique des organismes ainsi que plus d’évaluations du potentiel d’évolution chez les échinodermes sont absolument nécessaires.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Orientador: Lizandra Amoroso
Resumo: A urolitíase é enfermidade com importância econômica para a ovinocultura, que causa a saída prematura de ovinos machos destinados à reprodução, custos com tratamento e morte. A associação entre avaliação hemogasométrica, pesquisa de proteínas de fase aguda (PFA) como biomarcadores precoces e o estudo morfométrico do trato urinário pode ser empregada como método de auxílio diagnóstico precoce para a doença. Com esse objetivo, foram utilizados 14 ovinos hígidos, machos (não castrados), da raça Santa Inês com idade aproximada de 90 dias. Os ovinos receberam dieta experimental hiperfosfórica durante todo o período experimental, foram examinados semanalmente e após desenvolvimento da urolitíase, reorganizados em dois grupos experimentais distintos D1 (sem urolitíase) e D2 (com urolitíase) para análise comparada dos dados. No período pré-experimental e no dia do abate foram coletadas amostras de sangue venoso para avaliação hemogasométrica. Para mensurar as imunoglobulinas (A e G) e as PFA, analisaram-se as amostras dos ovinos que desenvolveram a urolitíase (D2). As coletas de sangue foram realizadas semanalmente até a manifestação clínica da enfermidade, totalizando 16 amostras. Ao término do experimento foi realizado o abate e necropsia dos ovinos, para descrição das alterações patológicas e a análise morfométrica. Fragmentos do trato urinário e fígado foram coletados e submetidos à rotina histológica e as lâminas histológicas foram descritas, seguindo-se a histomorfometria. Embo... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Urolithiasis is an economically important disease for male sheep production that causes the premature calving of sheep for breeding, treatment costs and death. The association between hemogasometric evaluation, acute phase protein (APP) research as early biomarkers and urinary tract morphometric study can be employed as an early diagnostic aid for the disease. For this purpose, 14 healthy male (non-castrated) Santa Inês sheep, approximately 90 days old, were used. Sheep received a hyperphosphoric experimental diet throughout the experimental period, were examined weekly and after development of urolithiasis, reorganized into two distinct experimental groups D1 (without urolithiasis) and D2 (with urolithiasis) for comparative analysis of the data. In the pre-experimental period and on the day of slaughter, venous blood samples were collected for hemogasometric evaluation. To measure immunoglobulins (A and G) and APP, samples from sheep that developed urolithiasis (D2) were analyzed. Blood samples were collected weekly until the clinical manifestation of the disease, totaling 16 samples. At the end of the experiment, sheep were slaughtered and necropsied to describe the pathological changes and the morphometric analysis. Urinary tract and liver fragments were collected and submitted to histological routine and histological slides were described, followed by histomorphometry. Although blood pH was not different (P < 0.05) between groups, sheep that developed urolithiasis had com... (Complete abstract click electronic access below)
Doutor

AbstractThis chapter presents acid-base equilibria and simple methods to calculate the pH of solutions. The inorganic carbon system in water is introduced, including the concept of alkalinity, and methods to solve carbon dioxide equilibria in water are discussed. Earth system science relevant examples such as rainwater, surface waters in equilibrium with calcium carbonate minerals, soda lakes and the physical chemistry of karst systems are presented.

AbstractHerein, we introduce the pKa concept as a strategy for proceeding with unfavorable reactions in the total synthesis of palau’amine. The cascade reaction aimed at constructing palau’amine’s ABDE tetracyclic ring core initially encountered poor reproducibility due to an unfavorable equilibrium reaction. However, the addition of 1.0 equivalent of AcOH enabled the progression of the unfavorable equilibrium reaction. In the second-generation synthesis, the improved cascade reaction to construct CDE ring core also initially did not proceed due to an unfavorable equilibrium reaction, but using Ph2NLi as a base was later found to enable the reaction to proceed smoothly. The conjugate acid of Ph2NLi proved to be a suitable acid in the unfavorable equilibrium mixture. These investigations of the cascade reactions revealed that the coexistence of an appropriate acid played an important role in allowing the unfavorable equilibrium reaction to proceed. The authors propose a general equation for proceeding with an unfavorable equilibrium reaction.

The spectral and luminescent properties of trans-2-(4’-dimethylaminebenzylideneacetyl)-5,5-dimethylcyclohexane-1,3-dione and 10-hydroxy-3,3,6,6,9-pentamethyl-1,2,3,4,5,6,7,8,9,10-decahydroacridine-1,8-dione have been studied depending on the acid-base properties of the medium. It has been shown that the first compound can exist in the form of three different structural forms, while the second compound exhibits dual fluorescence in solvents with a high basicity parameter. These properties of chromophores can be used in chemical analysis to indicate the acid-base equilibrium of the medium.

Abstract Scale inhibitor (SI) squeeze treatments are widely used for the prevention of inorganic scale deposition in oil and gas production operations. This may be an expensive operation and its efficiency depends on the degree of SI retention in the formation. Carbonate formations are known to be highly reactive, where the SI retention is driven by both adsorption and precipitation of SI and SI-Ca/Mg complexes. To design and carry out this type of squeeze treatment, a comprehensive model capable of simulating SI retention in carbonate formations is required. In this study, a model has been developed to fully characterize the retention of DETPMP in a carbonate system. This model considers all the equilibrium reactions coupled with precipitation and adsorption processes to simulate the equilibrium of a DETPMP-Calcite-brine system containing free Ca2+ and Mg2+ cations. To equilibrate this system, the following coupled reactions were considered: (i) the full aqueous carbonate system, (ii) SI speciation by dissociation (SI is considered as a weak n-poly acid, HnA), (iii) SI impurities and their reactions, (iv)SI-Ca and SI-Mg complexation, (v)the associated adsorption and precipitation of the SI/Ca/Mg complexes. These reactions may be coupled together through the equilibrium equations, the mass balance of base species and the system charge balance. After some algebra, the system of equations is reduced and solved by Newton Raphson to find the concentration of key primary species from which the concentration of all other species is calculated and the equilibrium of the entire couple system is characterized. In the entire system, there may be up to ~100 species involved in the chemical equilibrium equation set. The adsorption process is characterized by an adsorption isotherm, Γ(C), which can be a reversible process. In the examples presented, the adsorption is considered to proceed in both directions of adsorption and desorption. Precipitation (denoted Π) is coupled with the adsorption (and the rest of the system) to satisfy the SI solubility by removing further SI from the solution, if required, through the complex SI species that may physically precipitate. Finally, the proposed model was validated against coupled adsorption-precipitation experiments. The results showed very good agreement between the model and experiments and confirmed the reliability and validity for various conditions and DETPMP concentrations.

Sulphide (H2S, HS- and S2-) is an undesired by-product of biogas production processes. This modelling work in Aquasim was carried out to study three parallel processes related to sulphide in AD processes: 1) H2S liquid-gas mass transfer; 2) Acid-base equilibrium; and 3) Sulphide oxidation with three different electron acceptors; nitrate, oxygen, and a biotic anode with a given potential. Multiplicative Monod (biotic processes) and Nernst-Monod kinetics (bioelectrochemical process) provide the basis for the sulphide bio-oxidation processes. At the current stage, the model can be used to study sulphide bio-oxidation and the effect of relevant parameters, including initial biomass concentration, uptake rates, temperature, and pH. The model can be improved further by implementing anaerobic microbial processes as competing reactions. With the proposed improvements, the model can be a useful tool for calculating the chemical dosage or electrode potential required for sulphide removal. These calculations can be based on both the concentration of H2S(g) in the headspace (ppm) often available at full-scale plants and the concentration of sulphide (HS-(liq)) in effluent streams from the plants.

Carboxylic peroxy acids are organic oxidants of relevance in the cosmetic, food, and agrochemical industries. However, they are traditionally used as intermediaries in a process known as Prileschajew epoxidation and synthesized using sulfuric acid as a catalyst, promoting undesirable reactions on the final epoxides. Therefore, the study of selective catalysts such as enzymes is a topic of interest. In this work, peroctanoic acid synthesis was carried out using n-hexane as the solvent and an immobilized Candida Antarctica Lipase B commercial preparation as the catalyst. On the other hand, the oxidant, hydrogen peroxide was supplied as an aqueous solution, comprising the disperse phase of the reacting system. The reaction progression was quantified by iodometric and cerimetric titration of the peroctanoic acid concentration in the hexane phase. Four different initial amounts of octanoic acid were tested (0.74, 1.57, 10, and 20 millimoles). Substrate inhibition by octanoic acid was observed having at 1.57 millimoles the maximum initial reaction rate. The experimental data were fitted to a ping-pong bi-bi enzymatic kinetic model to estimate the initial reaction rate. Since this system constituted a liquid-liquid (organic-aqueous) two-phase system, the model was evaluated employing the thermodynamic activities of all species involved, assuming phase equilibria with time. The activities of all species were estimated using UNIFAC. As a result, the model was able to reproduce the trend of the initial rate with the change of the initial amount of octanoic acid.

Rhizoferrin, a siderophore produced by Rhizopus arrhizus, has been shown in previous studies to be an outstanding Fe carrier to plants. However, calculations based on stability constants and thermodynamic equilibrium lead to contradicting conclusions. In this study a kinetic approach was employed to elucidate this apparent contradiction and to determine the behavior of rhizoferrin under conditions representing soil and nutrient solutions. Stability of Fe3+ complexes in nutrient solution, rate of metal exchange with Ca, and rate of Fe extraction by the free ligand were monitored for rhizoferrin and other chelating agents by 55Fe labeling. Ferric complexes of rhizoferrin, desferri-ferrioxamine-B (DFOB), and ethylenediamine-di(o-hydroxyphenylacetic acid) (EDDHA) were found to be stable in nutrient solution at pH 7.5 for 31 days, while ferric complexes of ethylenediaminetetraacetic acid (EDTA) and mugineic acid (MA) lost 50% of the chelated Fe within 2 days. Fe-Ca exchange in Ca solutions at pH 8.7 revealed rhizoferrin to hold Fe at non-equilibrium state for 3-4 weeks at 3.3 mM Ca and for longer periods at lower Ca concentrations. EDTA lost the ferric ion at a faster rate under the same conditions. Fe extraction from freshly prepared Fe-hydroxide at pH 8.7 and with 3.2 mM Ca was slow and followed the order. DFOB > EDDHA > MA > rhizoferrin > EDTA. Based on these results we suggest that a kinetic rather than equilibrium approach should be the basis for predictions of Fe-chelates efficiency. We conclude that the non-equilibrium state of rhizoferrin is of crucial importance for its behavior as a Fe carrier to plants.

Beneficial use of reclaimed wastewater (RW) and biosolids (BS) in soils is accompanied by large input of sewage-originated P. Prolonged application may result in P accumulation up to levelsBeneficial use of reclaimed wastewater (RW) and biosolids (BS) in soils is accompanied by large input of sewage-originated P. Prolonged application may result in P accumulation up to levels that impair plant nutrition, increase P loss, and promote eutrophication in downstream waters. This study aims to shed light on the RW- and BS-P forms in soils and to follow the processes that determine P reactivity, solubility, availability, and loss in RW and BS treated soils. The Technion group used sequential P extraction combined with measuring stable oxygen isotopic composition in phosphate (δ18OP) and with 31P-NMR studies to probe P speciation and transformations in soils irrigated with RW or fresh water (FW). The application of the δ18OP method to probe inorganic P (Pi) speciation and transformations in soils was developed through collaboration between the Technion and the UCSC groups. The method was used to trace Pi in water-, NaHCO3-, NaOH-, and HCl- P fractions in a calcareous clay soil (Acre, Israel) irrigated with RW or FW. The δ18OP signature changes during a month of incubation indicated biogeochemical processes. The water soluble Pi (WSPi) was affected by enzymatic activity yielding isotopic equilibrium with the water molecules in the soil solution. Further it interacted rapidly with the NaHCO3-Pi. The more stable Pi pools also exhibited isotopic alterations in the first two weeks after P application, likely related to microbial activity. Isotopic depletion which could result from organic P (PO) mineralization was followed by enrichment which may result from biologic discrimination in the uptake. Similar transformations were observed in both soils although transformations related to biological activity were more pronounced in the soil treated with RW. Specific P compounds were identified by the Technion group, using solution-state 31P-NMR in wastewater and in soil P extracts from Acre soils irrigated by RW and FW. Few identified PO compounds (e.g., D-glucose-6-phosphate) indicated coupled transformations of P and C in the wastewater. The RW soil retained higher P content, mainly in the labile fractions, but lower labile PO, than the FW soil; this and the fact that P species in the various soil extracts of the RW soil appear independent of P species in the RW are attributed to enhanced biological activity and P recycling in the RW soil. Consistent with that, both soils retained very similar P species in the soil pools. The HUJ group tested P stabilization to maximize the environmental safe application rates and the agronomic beneficial use of BS. Sequential P extraction indicated that the most reactive BS-P forms: WSP, membrane-P, and NaHCO3-P, were effectively stabilized by ferrous sulfate (FeSul), calcium oxide (CaO), or aluminum sulfate (alum). After applying the stabilized BS, or fresh BS (FBS), FBS compost (BSC), or P fertilizer (KH2PO4) to an alluvial soil, P availability was probed during 100 days of incubation. A plant-based bioassay indicated that P availability followed the order KH2PO4 >> alum-BS > BSC ≥ FBS > CaO-BS >> FeSul-BS. The WSPi concentration in soil increased following FBS or BSC application, and P mineralization further increased it during incubation. In contrast, the chemically stabilized BS reduced WSPi concentrations relative to the untreated soil. It was concluded that the chemically stabilized BS effectively controlled WSPi in the soil while still supplying P to support plant growth. Using the sequential extraction procedure the persistence of P availability in BS treated soils was shown to be of a long-term nature. 15 years after the last BS application to MN soils that were annually amended for 20 years by heavy rates of BS, about 25% of the added BS-P was found in the labile fractions. The UMN group further probed soil-P speciation in these soils by bulk and micro X-ray absorption near edge structure (XANES). This newly developed method was shown to be a powerful tool for P speciation in soils. In a control soil (no BS added), 54% of the total P was PO and it was mostly identified as phytic acid; 15% was identified as brushite and 26% as strengite. A corn crop BS amended soil included mostly P-Fe-peat complex, variscite and Al-P-peat complex but no Ca-P while in a BS-grass soil octacalcium phosphate was identified and o-phosphorylethanolamine or phytic acid was shown to dominate the PO fraction that impair plant nutrition, increase P loss, and promote eutrophication in downstream waters. This study aims to shed light on the RW- and BS-P forms in soils and to follow the processes that determine P reactivity, solubility, availability, and loss in RW and BS treated soils. The Technion group used sequential P extraction combined with measuring stable oxygen isotopic composition in phosphate (δ18OP) and with 31P-NMR studies to probe P speciation and transformations in soils irrigated with RW or fresh water (FW). The application of the δ18OP method to probe inorganic P (Pi) speciation and transformations in soils was developed through collaboration between the Technion and the UCSC groups. The method was used to trace Pi in water-, NaHCO3-, NaOH-, and HCl- P fractions in a calcareous clay soil (Acre, Israel) irrigated with RW or FW. The δ18OP signature changes during a month of incubation indicated biogeochemical processes. The water soluble Pi (WSPi) was affected by enzymatic activity yielding isotopic equilibrium with the water molecules in the soil solution. Further it interacted rapidly with the NaHCO3-Pi. The more stable Pi pools also exhibited isotopic alterations in the first two weeks after P application, likely related to microbial activity. Isotopic depletion which could result from organic P (PO) mineralization was followed by enrichment which may result from biologic discrimination in the uptake. Similar transformations were observed in both soils although transformations related to biological activity were more pronounced in the soil treated with RW. Specific P compounds were identified by the Technion group, using solution-state 31P-NMR in wastewater and in soil P extracts from Acre soils irrigated by RW and FW. Few identified PO compounds (e.g., D-glucose-6-phosphate) indicated coupled transformations of P and C in the wastewater. The RW soil retained higher P content, mainly in the labile fractions, but lower labile PO, than the FW soil; this and the fact that P species in the various soil extracts of the RW soil appear independent of P species in the RW are attributed to enhanced biological activity and P recycling in the RW soil. Consistent with that, both soils retained very similar P species in the soil pools. The HUJ group tested P stabilization to maximize the environmental safe application rates and the agronomic beneficial use of BS. Sequential P extraction indicated that the most reactive BS-P forms: WSP, membrane-P, and NaHCO3-P, were effectively stabilized by ferrous sulfate (FeSul), calcium oxide (CaO), or aluminum sulfate (alum). After applying the stabilized BS, or fresh BS (FBS), FBS compost (BSC), or P fertilizer (KH2PO4) to an alluvial soil, P availability was probed during 100 days of incubation. A plant-based bioassay indicated that P availability followed the order KH2PO4 >> alum-BS > BSC ≥ FBS > CaO-BS >> FeSul-BS. The WSPi concentration in soil increased following FBS or BSC application, and P mineralization further increased it during incubation. In contrast, the chemically stabilized BS reduced WSPi concentrations relative to the untreated soil. It was concluded that the chemically stabilized BS effectively controlled WSPi in the soil while still supplying P to support plant growth. Using the sequential extraction procedure the persistence of P availability in BS treated soils was shown to be of a long-term nature. 15 years after the last BS application to MN soils that were annually amended for 20 years by heavy rates of BS, about 25% of the added BS-P was found in the labile fractions. The UMN group further probed soil-P speciation in these soils by bulk and micro X-ray absorption near edge structure (XANES). This newly developed method was shown to be a powerful tool for P speciation in soils. In a control soil (no BS added), 54% of the total P was PO and it was mostly identified as phytic acid; 15% was identified as brushite and 26% as strengite. A corn crop BS amended soil included mostly P-Fe-peat complex, variscite and Al-P-peat complex but no Ca-P while in a BS-grass soil octacalcium phosphate was identified and o-phosphorylethanolamine or phytic acid was shown to dominate the PO fraction.