Pour pallier les inconvénients intrinsèques de l’amidon (hydrophilie, faibles propriétés mécaniques), deux voies de modification de ce polysaccharide ont été étudiées: la substitution des fonctions hydroxy par une fonction chimique hydrophobe de longueur variable d’une part, et le greffage par voie radicalaire de (co)polymères d’acrylate et de styrène d’autre part. Par la première voie, des degrés de substitution (DS) proches de 3 ont été visés conduisant à des matériaux hydrophobes dont la stabilité thermique est nettement améliorée par rapport à celle de l’amidon. Ces matériaux s’organisent sous forme de feuillets contenant les chaines amylacées séparés par les chaines alkyles qui peuvent s’interpénétrer et cristalliser si elles sont suffisamment longues. Le suivi de l’évolution structurale induite par déformation a révélé une orientation des chaînes amylacées parallèle à l’axe de sollicitation dans le cas des matériaux contenant les chaines alkyles les plus longues. La voie du greffage menée sur trois substrats amylacés de Mw distinctes a conduit à l’obtention de matériaux amorphes biphasés composés de chaines amylacés sur lesquelles ont été greffées quelques longues chaines de (co)polymères d’acrylate et de styrène. Ces matériaux hydrophiles liés à leur DS extrêmement faible présentent un comportement fragile dès que l’une des deux phases est à l’état vitreux. / In order to overcome the intrinsic disadvantages of starch (hydrophilicity, low mechanical properties), two modification ways of this polysaccharide have been studied: the substitution of the hydroxy groups by a hydrophobic chemical function of variable length on the one hand, and the radical grafting of (co)polymers of acrylate and styrene on the other hand.Using the first route, degrees of substitution (DS) near 3 were targeted leading to hydrophobic materials whose thermal stability is significantly improved over that of starch. These materials are organized into a sheet-like structure in which the starch chains are organized in planes separated by the alkyl chains which can interpenetrate and crystallize if they are long enough. The study of the structural evolution induced by deformation revealed an orientation of the starch chains towards the draw axis in the case of the materials containing the longest alkyl chains. The grafting way carried out on three starch substrates of different Mw led to the production of two-phase amorphous materials composed of starch chains onto which a few long chains of acrylate and styrene (co)polymers have been grafted. These hydrophilic materials linked to their extremely low DS exhibit a brittle behavior as soon as one of the two phases is in a glassy state.

No description available.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

<p> Fluorosulphonic acid has been employed to generate cyclohexadienyl cations by protonation of weak bases in order to study the affect of uv light on such systems which are variably substituted. Differing substitution has been obtained by selecting polymethylbenzenes, cyclohexadienones and polymethylphenols as cation precursors. </p> <p> The photoisomerization of the 1,2,4,5-te-tramethylcyclohexadienyl cation to the 1,2,4,5-tetramethylbicyclo-[3 .1.O.] hexenyl cation has been studied by nmr methods and is discussed mechanistically in terms of competitive electrocyclic and [ δ2a + π2a] mechanisms of ring closure. Investigations of a similar 1,2,3,5-tetrarnethylcyclohexadienyl cation failed to uncover an analogous photoisomerization. This result is briefly discussed in relation to the demonstrated instability of the supposed photo-product which has been produced by a non photo chemical route. </p> <p> Both the 1-hydroxy-6,6-dimethyl- and 1-hydroxy-4 1 4 dimethylcyclohexadienyl cations have been generated from the corresponding cyclohexadienones by low temperature protonation in FS03H. Photoisornerization of these systems produced the same 2-hydroxy-6,6-dimethylbicyclo[3.l.0.] hexenyl cation which underwent further photorearrangement to various protonated phenols, the nature of which depended upon the frequency of irradiation. </p> <p> A number of protonated polymethylphenols have been investigated with respect to their site(s) of protonation in fluorosulphonic acid and their tendency to undergo photochemical reaction. Several members of this series have been shown to rearrange photochemically to isomeric phenols through a bicyclo[3.l.O.] hexenyl cation intermediate. A necessary criterion for this reaction has been established as protonation of a methyl bearing ring carbon. </p> <p> An exceptional example of the phenol photo- isomerization was the photo-conversion of protonated 2,4,6-trimethy·lphenol·to protonated 1,3,5-trimethyl. bicyclo[3.1.o] hex-3-en-2-one. This, as well as additional evidence led to the conclusion that a significant amount of meta protonation occurred with this phenol. </p> / Thesis / Master of Science (MSc)

No description available.

Weathering of biotite supplies nutrients such as K+ and weathers into vermiculite/montmorillonite or kaolinite, which have varying influences on soil properties and characteristics. This study was conducted to determine if the weathering mechanisms of biotite are controlled by temperature, or if other factors, such as vegetation or leaching intensity dominantly influence the weathering process. A column study investigation was conducted to assess the influence of different acids, simulated rainfall rates, surface horizons, and temperature on the weathering and cation release of biotite. A field investigation was also conducted on the clay mineral fraction of soils in Grayson County, VA formed above biotite granite. Selected acid leachates did show a greater Al+3, Fe+2, and Si+4 release with organic acids (ascorbic, citric, and fulvic) than that with hydrochloric acid treatment at high leachate rates. Loss of K+ is greater with ascorbic acid than all other acids at high leachate rates. Leachate rate interaction with low temperature was an influencing factor in cation release. Field investigations revealed a greater weathering intensity at high elevations evidenced by; (i) higher clay content, (ii) a dominance of 2:1 minerals, (iii) greater surface area in the upper horizons, (iv) minerals indicative of later stages in the biotite weathering mechanism, and (v) precipitation of halloysite in the C horizon at the high elevation site where temperature is lower and a suspected higher leaching intensity occur. / Master of Science

Optically active &amp / #945 / -hydroxy ketones are important subunits of many biologically active compounds and indispensable synthons for asymmetric synthesis. Benzaldehyde Lyase from Pseudomonas fluorescens Biovar I is a novel ThDP-dependent enzyme that catalyzes the synthesis of benzoin type chiral &amp / #945 / -hydroxy ketones starting from both benzaldehyde and racemic benzoin derivatives. Benzaldehyde Lyase is the first example of enzymes in the literature which leads to a chemical resolution of enantiomers of benzoin derivatives through a C-C bond cleavage reaction. Chiral 2-hydroxypropiophenone derivatives are formed by benzaldehyde lyase (BAL), catalyzing C-C bond formation after a selective C-C bond cleavage of a benzoin derivative accepted as a substrate. The enzyme uses only the (R)-benzoin derivatives as substrate for the formation of (R)-HPP derivatives and it is highly stereoselective. Thus, in the presence of the acetaldehyde as the acceptor aldehyde, the C-C bond cleavage of the benzoin molecule followed by the carboligation of the acetaldehyde to yield chiral 2-hydroxy propiophenone derivatives. Given the racemic benzoin to the enzyme as the substrate in the presence of acetaldehyde, both the racemic resolution of the substrate, revealing the unreacted (S)-Benzoin and the formation of the corresponding R-HPP occur.

Phosphorus (P), a necessary plant and animal nutrient, can also lead to eutrophication of fresh waters when in excess. Appropriate P management is necessary to prevent fresh water pollution. Mineralogy of soil clays has been shown to affect P adsorption, desorption, and movement through soils. Specifically, hydroxy-interlayered minerals have been shown to adsorb and retain inorganic P in soil systems. This study was designed to determine the sorption and desorption characteristics of inorganic, organic, and mixed forms of P interacting with soil hydroxy-interlayered vermiculites (HIV) and smectites (HIS), and compare the findings to sorption and desorption processes of natural aluminum (Al) and Iron (Fe) hydroxide minerals. Results indicate natural Al and Fe hydroxide minerals sorbed and retained P more strongly than hydroxy-interlayered minerals in our samples and inositol hexakisphosphate was more highly sorbed and retained than inorganic P.

Abstract The synthesis of α-hydroxy aldehydes and hydroxymethyl ketones as well as their interconversion to each other are discussed in this thesis. The literature survey of the monograph reviews the synthetic methods for the preparation of 1,2-bifunctionalized hydroxy aldehydes and ketones. The keto-aldehyde isomerisation reaction catalyzed by Triosephosphate isomerase enzyme (TIM) and organic compounds that interact with the TIM are also introduced. In addition, the microwave heating techniques in organic syntheses are reviewed. The practical work consists of two entities: The synthesis of new substrate candidates and transition state analogues for a mutated monomeric TIM. These compounds are model compounds for the catalytic activity and the structural studies of the mutated monomeric TIM. The synthesis of the sulphonyl α-hydroxy ketone-based substrate candidates consists of four successive syntheses. The microwave-activation was utilized in the preparation of a carbon-sulphur bond and the synthesis of hydroxymethyl ketones. The improved synthesis of the terminal α-hydroxy ketone functionality with microwave activation is presented. The formation of charged compounds was utilized to improve the absorption of microwave energy of reaction mixtures. The design and the synthetic work were carried out in accordance to principles of green chemistry. The second part of the practical work is the development of an organocatalytic α-oxybenzoylation reaction of aldehydes with high enantiomeric selectivity. This novel method generated enantiomerically pure α-hydroxy aldehydes in the stable benzoate-protected form from achiral starting materials under mild conditions at the presence of air and moisture.

Ketosis is a metabolic condition that occurs during heat stress, prolonged exercise, fasting, and in obese and diabetic individuals. The major ketone body, β-OH butyrate, affects cellular signaling pathways in a hormone-like manner through its receptor GPR109a. While physiological ketosis is often adaptive, chronic hyperketonemia may contribute to the metabolic dysfunction of diabetes. To understand how β-OH butyrate signaling affects hepatic metabolism we compared the fasting response in control and 3-hydroxy-3-methylglutaryl-CoA Synthase II (HMGCS2) knockdown mice that are unable to elevate β-OH butyrate production, and in GPR109a +/+ and -/- mice. To directly assess the response to ketone signaling we gave intraperitoneal injections of the GPR109a agonists niacin (0.8mmol/kg) and β-OH butyrate (5.7mmol/kg) to HMGCS2 knockdown mice over the final 9 hours of a 16 hour fast. Ketogenic deficient mice showed a more robust increase in hepatic carnitine palmitoyltransferase 1 (CPT1) and uncoupling protein 2 (UCP2) mRNA than control mice in response to fasting. Accordingly, niacin and β-OH butyrate administration decreased fasting CPT1 mRNA expression in knockdown mice, while fasting knockdown UCP2 mRNA and control HMGCS2 mRNA were lowered by β-OH butyrate. GPR109a knockout did not alter the hepatic response to fasting, although the effect of niacin on fasting HMGCS2 mRNA expression was dependent on GPR109a expression. While the role of GPR109a and how chronic hyperketonemia alters β-OH butyrate signaling require further study, these data suggest that endogenous β-OH butyrate signaling during a fast regulates the transcript levels of hepatic genes directly involved in its own synthesis.