L’hydrogène est un vecteur énergétique qui peut être un atout pour nous aider à décarboner nos usages énergétiques. L’électrolyse de l’eau est un des moyens de production d’hydrogène qui présente un bon compromis pour obtenir un gaz en grande quantité tout en limitant le coût et l’impact environnemental. La compression est une des voies de stockage de l’hydrogène mais les électrolyseurs sont limités technologiquement pour atteindre des pressions de stockage satisfaisantes. Une des solutions pour pallier ce problème est l’électrolyse découplée. Il s’agit de séparer la production d’hydrogène et d’oxygène en deux étapes grâce à un intermédiaire oxydant/réducteur. La société Ergosup a développé le procédé ZHYNCELEC, un exemple de cette technologie qui utilise le zinc comme intermédiaire. La première étape est l’électrodéposition du zinc, ce qui acidifie la solution et permet la formation d’oxygène. Cette étape est inspirée de l’électrolyse industrielle du zinc. La deuxième étape est la réaction entre le dépôt et l’électrolyte produisant l’hydrogène et provoquant la dissolution du zinc en solution. Le sujet de cette étude est l’optimisation du procédé ZHYNCELEC.Ce travail peut être découpé en trois axes d’étude. Le premier axe concerne la sélection des différents matériaux d’électrode, choisi suivant leur performance électrochimique mais également suivant leur durabilité. Le deuxième axe a pour objectif d’optimiser la composition de l’électrolyte. Les éléments clés sont la concentration du zinc, la concentration de l’acide et la présence d’éventuels d’additifs en solution. Le troisième axe concerne l’aspect procédé et s’articule sur des conditions opératoires telles que la température, la densité de courant, la pression maximale en hydrogène ainsi que la géométrie du réacteur. Ces trois axes ne peuvent être étudiés séparément de par les interactions entre les différents paramètres, ce qui oblige à des compromis suivant l’application du procédé voulu. / Hydrogen is an energy carrier and a potential asset for helping to lower carbon levels of energetic uses. Water electrolysis is a way of production and a good compromise to generate a large quantity of cheap and low-environmental-impact hydrogen. Compression is used to store hydrogen but electrolysers are technologically limited to reach high pressures. One solution to overcome this problem is decoupling electrolysis. It aims at separating the hydrogen and oxygen production in two steps through mediation oxydizer/reducer. Ergosup company has developed ZHYNCELEC process, using different technologies such as zinc as mediator. The first step is zinc electrodeposition which increases the acidity of solution and lead to an oxygen formation. This step is inspired by industrial zinc electro winning. The second step is the reaction between the metallic deposition and electrolyte producing hydrogen and making the dissolution of zinc. The purpose of this study is the optimisation of ZHYNCELEC process.This work can be divided in three axes of study. First, the selection of the different electrode materials. They are chosen by electrochemical performances and durability. Secondly, electrolyte composition optimization. The key factors are zinc concentration, acid concentration and the possibility of additives presences. The final axe concerns the processing aspect and the operative conditions like temperature, current density, maximal hydrogen pressure and reactor geometry. These three axes cannot be studied separately because of the interaction between the different parameters, which forces at compromising following the aim of the application of the process.

Includes bibliographical references (leaves 234-280) / xxviii, 292, [72] leaves : ill. (some col.), plates (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 2002

Graduation date: 1994

Marginal zinc deficiency (MZD) exists in children of industrialized societies and can impair growth and development. Presently there are no data available on its global prevalence. It is believed that MZD is one of the most common hidden deficiencies throughout the world. This is partly because of the lack of sensitivity and specificity of serum zinc, the most commonly used biomarker of zinc status, to detect MZD. This deficiency in children is always accompanied by a decrease in hair zinc. Although in research settings hair zinc is a recognized biomarker of MZD in children, health practitioners do not presently use it. These cross-sectional studies were designed to examine the hair zinc status of preschoolers in Vancouver. They also aimed at exploring some dietary and non-dietary factors associated with hair zinc status in an attempt to construct and validate a screening tool for detection of MZD. Our first study indicated a mean hair zinc of 75��30 ��g/g, with 46% below the cutoff (<70��g/g) for a group (n=87) of low-income preschoolers (Chapter II). Among these children we observed negative associations between the hair zinc and consumption of dairy (R�� =0.09, P=0 .01) and milk (R�� =0.08, P=0.01), being described as "often sick" (R�� =0.55, P=0 .00) and "eating unhealthy" (R�� =0.16 P=0.00), and prolonged breastfeeding (R�� =0.11, P=0.01). Our citywide survey (n=719) indicated a mean hair zinc of 116��43 ��g/g with 17% below the cutoff (Chapter III). Logistic regression analysis indicated sex, age, maternal education, the number of adults at home, consumption frequency of milk, "scores of activity level", "being described as frequently sick" and "taking supplements containing iron" as the significant predictors of hair zinc status. However, the final model had 16% sensitivity while having 98 .3% specificity, indicating its lack of usefulness as a screening tool. Our study provides important information on the hair zinc status of Vancouver preschoolers. Although we did not accomplish our primary goal of constructing and validating a screening tool, we did identify some factors in children and their environment associated with hair zinc, which may help in better understanding of hair zinc as a biomarker of MZD.

Zinc is an important micronutrient but the biological function of its labile form is poorly understood. Zinc selective fluorescence sensors, recognized as the major tool to gain information about the role of zinc in living systems, have been attracting more and more interest. The most promising solution currently being studied comes in the form of ratiometric sensors. Unlike sensors based on the switch-on mechanism, ratiometric sensors determine the free metal concentration directly from the ratio of the emission intensities at two wavelengths. The major restriction on the design of this type of sensor is from the necessity for a spectral-shift upon binding metal ions. To develop novel ratiometric sensors, we have developed designs based on excited-state intramolecular proton transfer (ESIPT). In the absence of ZnII at neutral pH, the 2-(2 -sulfonamidophenyl)benzimidazole family undergoes ESIPT to yield a highly Stokes-shifted emission from the proton-transfer tautomer. Coordination of ZnII inhibits the ESIPT process and yields a significant hypsochromic shift of the fluorescence emission maximum. By implementing structural modifications, we were able to gauge free ZnII concentrations in the millimolar to picomolar range. To tune the peak excitation towards lower energy, a property that is of particular importance in the light of biological applications, we modified the platform molecule with extended pi-conjugation and by substituent engineering. The position of the modification and the nature of the substituents strongly influenced the photophysical properties of the investigated derivatives. Several fluorophores revealed emission ratiometric properties with a large dynamic range combined with a peak absorption beyond 350 nm, rendering these probes promising candidates for applications. To further understand the origin of the substituent effect, we studied five derivatives for the solvatochromic shift analysis and quantum chemical studies. The results showed that the negative solvatochromic shift behavior was most pronounced in protic solvents presumably due to specific hydrogen-bonding interactions. The extrapolated gas-phase emission energies correlated qualitatively with the trends in Stokes shifts, suggesting that solute-solvent interactions do not play a significant role in explaining the divergent emission energy shifts. Detailed quantum chemical calculations not only confirmed the moderately polarized nature of the ESIPT tautomers but also provided a rationale for the observed emission shifts based on the differential change in the HOMO and LUMO energies. This study revealed the great potential of 2-(2 -arylsulfonamidophenyl)- benzimidazoles, such as tunable peak absorption and emission, a very wide dynamic range regarding to zinc binding, very little solvent polarity dependence, and especially, the emission ratiometric property. All these properties make this system a unique candidate to tackle the problems in the research of zinc biology.

The purpose of the present study was to quantify the optimal zinc requirements of juvenile grouper (Epinephelus malabaricus). Basal diet contained 52 % crude protein from derived egg white and mackerel¡]Scomberomorus commerson¡^muscle. This semipurified basal diet which contained 10.0 mg Zn/kg was supplemented with ZnSO4 at levels of 0, 4, 8, 12, 24, 36 or 140 mg Zn/kg, respectively. The test diets were fed to juvenile groupers with an initial weight of about 5.9 g. All treatments were triplicated, each tank had 12 fish. After 18 weeks of rearing, dietary zinc levels have significant effects on the growth of fish. Weight gain and feed efficiency were significantly lower in grouper fed the unsupplemental diet than the supplemental groups. No significant difference among fish groups was found in survival rate, condition factor, muscle composition, ash contents of vertebra and scale, as well as some hematological parameters. Zinc concentrations in serum, muscle, vertebra and scale were affected by the supplemental zinc level. There was no significant difference in nonspecific immunity parameters including phagocytosis of macrophage, alternative complement pathway (ACH50) activity, agglutination titer and lysozyme activity among dietary treatments. The activity of the copper and zinc metalloenzyme superoxide dismutas in red blood cells was also not affected by dietary zinc intake. Broken-line regression analysis of weight-gain, feed efficiency as well as serum-, vertebra- and scale zinc concentrations against dietary zinc intake indicated requirement values of 33.7, 35.6, 32.5, 28.9 and 32.6 mg Zn/kg diet, respectively. Therefore, based on the results of growth performance and tissue zinc concentrations, the dietary zinc requirement of the juvenile groupers was between 28-36 mg Zn/kg diet.

No description available.

Zinc (Zn) fertilization is considered an important agronomic strategy for global food security. Lentil production in Saskatchewan not only provides significant economic benefit for growers, but is marketed in several countries where human Zn deficiencies are common. The impact of Zn fertilization on lentil yield and Zn concentration deserves attention. Field experiments were conducted in 2013 to determine if Zn fertilization of lentil could increase yield, grain Zn concentration and its bioavailability for humans in three popular lentil cultivars: CDC Maxim (red), CDC Imvincible (small green) and CDC Impower (large green). The effects of three rates (0, 2.5 and 5 kg Zn ha-1) of soil applied ZnSO4 were examined at a site in the Brown soil zone identified as Zn deficient and a site in the Dark Brown soil zone that was identified as sufficient in soil Zn. In 2014, hard red spring wheat was seeded to assess the residual effects on a rotational crop. A companion pot study was conducted in a polyhouse that compared single rates of soil and foliar applied forms of Zn fertilizer: soil applied ZnSO4, foliar applied Zn lignosulphonate, soil and foliar applied Zn chelated with EDTA. At the two field sites, soil applied ZnSO4 fertilizer had no significant effect on lentil yield, grain Zn concentration, and predicted bioavailability of Zn for humans. Significant differences in residual DTPA-extractable Zn were generally not found among rates of applied ZnSO4 fertilizer, and soil applied ZnSO4 did not have residual benefits for spring wheat grown at either location in 2014. Migration of Zn into less labile soil fractions was identified as a factor contributing to this general lack of response to soil applied ZnSO4 fertilizer. Based on results from the polyhouse study, chelated forms of Zn may be more effective than inorganic or organic-complexed forms of Zn in supplying Zn and improving predicted dietary bioavailability of lentils for humans. Phytate:Zn molar ratios were significantly decreased in all lentil cultivars fertilized with soil applied Zn that was chelated with EDTA (17.1) compared to when fertilized with soil applied ZnSO4 (24.7). Overall, the responses of lentil to Zn fertilization were small and variable, such that significant economic benefits were not observed.

Transplanting is a common practice for many horticultural crops and some field crops. Recently, transplanted oilseed rape (Brassica napus L.) crops have been reported to be sensitive to zinc (Zn) deficiency. However, Zn nutrition in transplanted field crops has not been investigated in detail. The objectives of this present research were to investigate whether transplanting increases external Zn requirements of transplanted oilseed rape, and the mechanisms of root function, growth and Zn uptake after transplanting including rhizosphere modification capacity by plant roots. The second objective was to examine the relative effects of root pruning and transplanting on Zn responses of oilseed rape, and the third objective was to determine external and internal Zn requirements of transplanted oilseed rape for diagnosing and predicting Zn deficiency. An experiment on a low Zn sand (DTPA extractable Zn 0.14 mg kg-1) was set up to determine whether transplanted oilseed rape had a higher Zn requirement than that of direct-sown plants. Low Zn supply depressed shoot dry weight, however, root growth was relatively more strongly suppressed than shoots. Maximum root dry weight required much higher external Zn for transplanted plants compared to direct-sown plants, whilst shoot dry weight required a similarly low external Zn supply. In addition, transplanted plants were sensitive to zinc deficiency during the early post-transplanting growth, and the response weakened as the plants recovered from root injury or transplanting stress. However, the transplanted plants also experienced root pruning before transplanting and so in this experiment the higher Zn requirement could have been due to root pruning or transplanting or both. A further experiment was undertaken to determine the comparative external Zn requirements of direct-sown and transplanted plants in well-stirred chelate-buffered solution culture where a rhizosphere effect on plant availability of Zn forms is absent and the effects of poor root-soil contact on post-transplanting growth are minimized. In solution culture at the same level of Zn supplied, direct- sown plants produced higher shoot and root dry matter and greater root length than those of transplanted plants. However, since a higher external Zn requirement was found for transplanted plants in buffered solution culture than for direct- sown plants, it was concluded that the higher Zn requirement was not related to decreased rhizosphere modification, to greater demand for Zn or to poor root-solution contact, but rather to the time required for transplanted plants to recover from transplanting and root injury. The recovery of root function in solution culture was more rapid than that in soil culture and expressed as a higher Zn requirement for shoot as well as root growth. It suggested that the delay in root recovery in soil culture was due to slower absorption of Zn from the soil after transplanting than was the case in solution culture. Chelate-buffered nutrient solution culture and harvesting plants successively at 5 day intervals until 25 days after transplanting was used to examine the mechanisms of the recovery of root growth and function. In this experiment, the external Zn requirement of transplanted plants was investigated with unpruned or pruned root systems. Plants with unpruned root system and sufficient Zn supply exhibited faster recovery from transplanting than those with pruned root system plants. The results suggest that root pruning impaired Zn uptake by plant roots and slowed down the root and shoot growth after transplanting. Increased solution Zn partly alleviated the effects of root pruning and presumably this is a major reason why transplanted oilseed rape had a high external Zn requirement. However, root pruning also appeared to impair water uptake, and may have suppressed shoot growth through sequestering carbon for new root growth and through decreased phytohormone production by roots. Since rapid root recovery of transplanted plants is essential for successful of growth in the field, Zn application to the nursery bed was explored as a starter fertilizer to stimulate root growth after transplanting. The objective of this experiment was to determine whether increasing the seedbed Zn would stimulate new root growth of transplanted oilseed rape, and therefore would alleviate the need for increased external Zn for post-transplanting growth. Results showed that adequate Zn concentration in the seedbed promoted the post-transplanting growth by stimulating the new root growth especially increased root length, and also hastened the recovery of root systems. However, high Zn concentration at transplanting still had a more dominant effect in stimulating the new root growth of oilseed rape after transplanting. The final experiment was set up using rhizobags with three rates of Zn supply and unpruned or pruned root systems. The purpose of this study was to investigate the chemical change in the rhizosphere and non-rhizosphere or bulk soil and its relationship to the recovery of root function after transplanting, and also to identify and quantify the organic acids in soil extracts of direct-sown and transplanted plants. The rhizosphere soil pH was lower than that of non-rhizosphere soil, and the decrease of soil pH was suggested as the mechanism of the increase of Zn availability and mobility in the rhizosphere soil. Direct-sown plants were more efficient in utilizing Zn than those of transplanted plants especially compared to those of plants with pruned root system. Zinc deficient plants excreted higher concentration of organic acids particularly citric acid, suggesting this was a mechanism of Zn mobilization and Zn uptake by roots of oilseed rape. The main implications of the present study for the management of Zn nutrition of transplanted crops were: the need to increase the Zn application to crops in the nursery and at transplanting compared to direct-sown plants; the possibility that external requirements of other nutrients will be greater in transplanted crops also requires further consideration; and in cropping systems where transplanting is practised, greater attention should be given to the avoidance of root damage during the transplanting.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.