• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 71
  • 16
  • 12
  • 10
  • 8
  • 4
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 172
  • 30
  • 29
  • 23
  • 22
  • 19
  • 16
  • 14
  • 13
  • 13
  • 12
  • 11
  • 11
  • 10
  • 9
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Combustion Kinetics of Advanced Biofuels

Barari, Ghazal 01 January 2015 (has links)
Use of biofuels, especially in automotive applications, is a growing trend due to their potential to lower greenhouse gas emissions from combustion. Ketones are a class of biofuel candidates which are produced from cellulose. However, ketones received rather scarce attention from the combustion community compared to other classes such as, alcohols, esters, and ethers. There is little knowledge on their combustion performance and pollutant generation. Hence their combustion chemistry needs to be investigated in detail. Diisopropyl ketone (DIPK) is a promising biofuel candidate, which is produced using endophytic fungal conversion. A detailed understanding of the combustion kinetics of the oxidation of DIPK in advanced engines such as, the homogeneous charge compression ignition (HCCI) engine is warranted. This dissertation concentrates on the combustion kinetics of DIPK over a wide range of temperature and pressure with a focus on HCCI engine application. An existing DIPK kinetic mechanism has been reviewed and a single zone HCCI engine model has been modeled and validated against recent experimental data from Sandia National Lab. Therefore different HCCI modeling assumptions were tested and the DIPK reaction mechanism was modified with missing reactions and the required thermochemical data. As a result, the HCCI pressure trace, heat release rate and reactivity have been improved. In order to improve the ignition delay time simulation results, the low temperature oxidation of DIPK was studied as the fuel chemistry effects on the autoignition behavior becomes important in low temperature. Therefore DIPK low temperature oxidation experimental data was obtained from the synchrotron photoionization experiments conducted at the Advanced Light Source (ALS) so that the primary products as well as the dominant oxidation pathways are identified. Furthermore, the aldehydes oxidation, as a result of partial or incomplete combustion and as the primary stable intermediate products in oxidation and pyrolysis of biofuel were studied at low temperature in ALS. A high temperature reaction mechanism was created using the reaction class approach. The reaction mechanism for DIPK was improved using the experimental data along with quantum chemical calculation of activation energies and barriers as well as vibrational modes for the important reactions identified in ALS experiment. The rate constants for important reactions were calculated based on modified Arrhenius equation. DIPK oxidation and pyrolysis were studied at high temperature and pressure using UCF shock tube. The ignition delay times as well as the product (methane) time histories were investigated and used as validation targets for the new model.
92

Asymmetric Synthesis of Nitrogen Containing Bioactive Compounds via the Utilization of Enantiopure p-Toluenesulfinimines

Xu, Peng January 2013 (has links)
The research objective of this thesis research was to develop new methods for the asymmetric synthesis of amine derivatives using p-toluenesulfinimines. Enantiopure sulfinimines are versatile chiral building blocks for the asymmetric synthesis of alkaloids. Sulfinimines were prepared by the condensation of (S)- or (R)-p-toluenesulfinamide with aldehydes and ketones in good to excellent yields, which were prepared from the commercially available Anderson reagent. The first research project was the development of a new method for the preparation of enantiopure anti-anti- α-lkyl β-amino ketones and was accomplished by the stereoselective α-alkylation of enolates of sulfinimine derived β-amino esters. The anti- α-lkyl β-amino esters were transformed to their corresponding Weinreb amides by reacting with lithium dimethyl hydroxyl amine without epimerization. Reactions of the Weinreb amides with Grignard and organolithium reagents afforded the corresponding anti- α-lkyl β-amino ketones in modest yields and high optical purity. The modest yields are the results of competition between addition and reduction of the Weinreb amide. anti- α-lkyl β-amino ketones are important chiral building blocks for the asymmetric synthesis of nitrogen-containing biologically active molecules, such as pyrrolidines, piperidines and other alkaloids. To further illustrate the utility of sulfinimine -derived enantiopure N-sulfinyl anti- α-lkyl β-amino ketones, they was applied to the asymmetric synthesis of the unknown anti-C5, C6 derivative of 2,3,4,6-tetrasubsituted indolizidine 221-T. The key step in the synthesis was the stereoselective construction of the piperidine ring of the 5,6,8-tri-substituted indolizidine and was realized via the use of an acid-catalyzed intramolecular Mannich cyclization. The indolizidine was readily transformed in to the key intermediate 7-hydroxyl-2,3,4,6-tetrasubsituted indolizidine in high stereoselectivity and yield. Changing the sequence of chemical operation steps avoided the production of the side product β-pyrrole ketone. Reduction of the intermediate piperdinone, followed by ring-closing metathesis and reductive catalytic hydrogenation afford the bicyclic indolizidine with overall 76% yield of 3 steps. The C-2 branched cocaine analogs are thought to have varied bioactivities and potent therapeutical uses compared to other positions of substituted cocaine analogs. However, reports on the synthesis of such analogs are few. The first example of preparation of a cocaine analog having a dimethylphosphonate group at the C-2 position was reported. The key step in forming the required isoxazolidine intermediate, which controls the required cis stereochemistry at C-2 and C-3, was a novel microwave induce stereoselective [3+2] intramolecular cycloaddition of an α,β-unsaturated pyrrolidine nitrone. The use of the microwave irradiation techniques significantly reduce the time required for isoxazolidine formation from 96 hours to five hours. / Chemistry
93

Ketone Supplementation, Cardiometabolic Health, and Cognition in Humans

Reid, Glen Robertson 06 July 2022 (has links)
Cardiovascular disease (CVD) is the leading cause of death in the United States. Age is a primary risk factor for the development of CVD and middle-age is a vulnerable period where risk factors for the disease begin to exceed diagnostic thresholds. Interest has increased for the use of low carbohydrate high fat (LCHF) ketogenic diets due to their reported improvements for cardiometabolic health. Supplementation with exogenous ketone esters (KE) has been shown to increase plasma β-hydroxybutyrate (BHB) and mimic the metabolic effects of LCHF ketogenic diets. Evidence suggests elevated concentrations of plasma BHB may lower blood pressure, improve vascular function, attenuate hyperglycemic responses, and enhance cognitive function. The majority of research has been conducted in preclinical models, and whether exogenous KE supplementation has similar improvements in humans of any ages remains relatively unanswered. To address this we conducted a randomized, placebo controlled, crossover design study in healthy, sedentary, middle to older aged adults who received the exogenous KE (or placebo), and consumed the supplement for 2-weeks (3x/day, 15 minutes prior to each meal; breakfast, lunch, and dinner). Our first hypothesis was to test that KE supplementation would improve vascular function by increasing flow-mediated dilation, reducing arterial stiffness, and lowering blood pressure. Secondly, we hypothesized that KE supplementation would attenuate the glycemic response to an oral glucose tolerance test, improve glycemic variability, and show reductions in postprandial glucose levels. Thirdly, we tested the hypothesis that KE supplementation would improve cognitive performance by showing improvements in processing speed, memory, attention control, and executive functions. In support of our first hypotheses, KE supplementation increased flow-mediated dilation (8.1 ± 1.3 vs. 7.7 ± 1.2%, p = 0.023), but it did not show any difference in arterial stiffness or blood pressure. In contrast to our second hypotheses, following the KE supplementation intervention there were no significant difference from the placebo in terms of glycemic response, variability or mean 2-hour post-meal glucose. In support of our third hypotheses, we found a significant improvement in measures of working memory (7.55 ± 0.93 vs. 7.27 ± 0.29, p = 0.026) and inhibitory control (80 ± 38 vs. 87 ± 32ms, p = 0.035) following the 14-day KE supplementation. More research is needed to elucidate the effects of KE on cardiometabolic health and cognition. / Doctor of Philosophy / Recently there has been an increase in the popularity of low carbohydrate high fat (LCHF) ketogenic diets, with advocates for the diet claiming increased benefits in weight loss and blood glucose control, therefore leading to an increased interest for its use in the treatment for cardiovascular disease, obesity, and diabetes. As more evidence has accumulated much of the impact LCHF ketogenic diets are said to have, has been attributed to a state known as nutritional ketosis, which occurs in response to the restriction of carbohydrates from the diet. Ketone esters (KE) have been shown to effectively elevate ketone bodies (alternative energy produced by the body during times when glucose stores are low) without the need of altering one's own diet, however, this method of inducing ketosis is still lacking evidence for its impact on cardiometabolic health in humans. The purpose of these studies is to determine the effect of having sustained elevations of ketone bodies on our health and cognition in humans. Study 1 included healthy, sedentary middle to older aged adults who consumed a KE for 2-weeks (3x/day, prior to each meal) and a placebo. Following supplementation participants completed test to assess our vascular health and blood sugar control. Study 2 included healthy, sedentary middle to older aged adults who consumed a KE for the same 2-weeks (3x/day, prior to each meal) and a placebo. Participants underwent a series of tests to assess cognitive performance. Overall, after a 2-week supplementation period we found significant improvements in our blood vessel function and with cognitive performance where we saw improvements in working memory, and inhibitory control.
94

Chemical and Physical Modifications of Semicrystalline Gels to Achieve Controlled Heterogeneity

Anderson, Lindsey J. 07 February 2019 (has links)
Sulfonated polyaromatic hydrocarbon membranes have emerged as desirable candidates for proton exchange membranes (PEMs) due to their excellent mechanical properties, high thermal and chemical stability, and low cost. Specifically, sulfonated multiblock copolymers are attractive because their phase-separated morphologies aide in facile proton transport. In this work, the functionalization of semicrystalline gels of poly(ether ether ketone) (PEEK) is explored as a novel post-polymerization method to prepared blocky copolymers, and the effect of copolymer architecture on membrane physical properties, structure, and performance is extensively investigated. First, the blocky sulfonation of PEEK was explored to prepare blocky copolymers (SPEEK) with densely sulfonated domains and unfunctionalized, crystallizable domains. Compared to random SPEEK ionomers at similar ion content, blocky SPEEK exhibited enhanced crystallizability, decreased melting point depression, and faster crystallization kinetics. Phase separation between the hydrophilic sulfonated blocks and hydrophobic PEEK blocks, aided by polymer crystallization, resulted in enhanced water uptake, superior proton conductivity, and more closely associated ionic domains than random SPEEK. Furthermore, the random and blocky bromination of PEEK was investigated to prepare PEEK derivatives (BrPEEK) with reactive aryl-bromides. Spectroscopic evidence revealed long domains of unfunctionalized homopolymer for blocky BrPEEK, and this translated to an increased degree of crystallinity, higher melting temperature, and more rapid crystallization kinetics than random BrPEEK at similar degrees of bromination. The subsequent sulfonation of blocky BrPEEK resulted in a hydrophilic-hydrophobic blocky copolymer with clear multi-phase behavior. The phase-separated morphology contributed to decreased water uptake and areal swelling compared to random SPEEK and resulted in considerably higher proton conductivity at much lower hydration levels. Moreover, Ullmann coupling introduced superacidic perfluorosulfonic acid side chains to the BrPEEK backbone, which yielded membranes with less water content and less dimensional swelling than random SPEEK. Superior proton transport than random SPEEK was observed due to the superacid side chain and wider hydrophilic channels within the membranes, resulting in more continuous pathways for proton transport. Overall, this work provided a novel platform for the preparation of functionalized PEEK membranes using a simple post-polymerization functionalization procedure. The established methods produced blocky-type copolymers with properties reminiscent of multiblock copolymers prepared by direct polymerization from monomers/oligomers. / PHD / Block copolymers are an important class of polymers that are composed of two or more blocks of distinct polymeric segments covalently tethered to one another. Dissimilarity in the chemical nature of the blocks leads to self-organization into well-defined structures, and this unique structural order imparts material properties that are different from (and often superior to) the properties of the individual blocks alone. Thus, block copolymers are advantageous for a diverse array of applications including membranes, gas separation, water purification, medical devices, etc. Although considerable synthetic progress has been made towards discovering novel methods to prepare block copolymers, their widespread use is somewhat limited by the complex, energy-intensive procedures necessary to precisely control the block sequencing during polymerization. In this dissertation, a straightforward, inexpensive physical procedure is explored to synthesize blocky copolymers with controlled sequencing from commercially available polymers. This process relies on performing reactions in the gel state, whereby segments of the polymer chain are effectively shielded from the functionalizing chemistry. In particular, the gel state sulfonation and bromination of poly(ether ether ketone), a high performance polymer, is investigated to develop novel, blocky materials for membrane applications. This work not only expands the methodology towards the synthesis of block copolymers, but alaso provides critical insight into the effect of copolymer architecture on membrane physical properties, structure, and performance. Furthermore, this work provides an economically feasible method to prepare blocky copolymers from commercially derived materials, thereby providing a means to progress the widespread use of block copolymers in industry.
95

Morphology-Property Relationships in Semicrystalline Aerogels of Poly(ether ether ketone)

Talley, Samantha J. 03 December 2018 (has links)
The phase diagrams for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in dichloroacetic acid (DCA) and 4-chlorophenol (4CP) were constructed over broad temperature and concentration ranges, revealing that PEEK is capable of dissolving and forming gels in DCA and 4CP up to a weight fraction of 25 wt.%. Highly porous aerogels of PEEK were prepared through simple solvent exchange and solvent removal of the PEEK/DCA or PEEK/4CP gels. Solvent removal utilized freeze-drying (sublimation) methods or supercritical CO2 drying methods. Varying the weight fraction of PEEK dissolved in solution determined PEEK aerogel density. Mechanical properties (in compression) were shown to improve with increasing density, resulting in equivalent compressive moduli at comparable density regardless of preparation method (concentration variation, gelation solvent, solvent removal method, or annealing parameters). Additionally, density-matched aerogels from various MW PEEK showed a correlation between increasing MW and increasing compressive modulus. Contact angle and contact angle hysteresis revealed that PEEK aerogels have a high contact angle, exceeding the conditions necessary to be classified as superhydrophobic materials. PEEK aerogel contact angle decreases with increasing density and a very low contact angle hysteresis that increases with increasing density, regardless of gelation solvent or drying method. Small angle neutron scattering (SANS) contrast-matching experiments were used to elucidate the morphological origin of scattering features, wherein it was determined that the origin of the scattering feature present in the small angle scattering region was stacked crystalline lamella. Ultra-small angle X-ray scattering (USAXS)/SAXS/Wide angle X-ray scattering (WAXS) was then used to probe the hierarchical nanostructure of PEEK aerogels across a broad range of length scales. The Unified Fit Model was used to extract structural information, which was then used to determine the specific surface areas of PEEK aerogels. Regardless of gelation solvent, gel concentration, or solvent removal method, all PEEK aerogels display high surface areas as determined by SAXS and high surface areas as determined by nitrogen adsorption methods. Surface area values determined from SAXS data were consistently higher than that measured directly using nitrogen adsorption, suggesting that pore densification diminishes the accessible aerogel surface area. / Ph. D. / Poly(ether ether ketone) (PEEK) is a semicrystalline polymer with high temperature thermal transitions and excellent mechanical strength, making it an ideal candidate for many high-performance polymer applications. When PEEK is dissolved in particular solvents, it will form a 3-dimensional network where crystalline polymer is the cross-linking unit of the network. Careful solvent removal does not significantly perturb the gel network structure and produces a low-density aerogel. This work details the first reported instance of the monolithic gelation of PEEK and the first examples of PEEK aerogels. The nanostructure of these gels and aerogels is fully characterized to relate structural features to physical properties such as mechanical stiffness and wettability.
96

The ionic liquid ethyltri-n-butylphosphonium tosylate as solvent for the acid-catalysed hetero-Michael reaction.

Karodia, Nazira, Liu, Xihan, Ludley, Petra, Pletsas, Dimitrios, Stevenson, Grace January 2006 (has links)
No / A new and convenient method for the acid-catalysed Michael addition reactions of alcohols, thiols and amines to methyl vinyl ketone has been developed using the ionic liquid ethyltri-n-butylphosphonium tosylate. The reaction conditions are mild and obviate the need for toxic and expensive Lewis acid catalysts, offering advantages over more commonly used systems.
97

Élévation aigüe de la cétonémie : effets cétogènes de produits alimentaires dérivés de l’huile de noix de coco et influence d’une combinaison avec de l’exercice de type aérobie / Acute plasma ketone stimulation : ketogenic effects of products derived from coconut oil and influence of a combination with aerobic exercise

Vandenberghe, Camille January 2017 (has links)
Depuis maintenant plus de 30 ans, il est reconnu qu’au début de la maladie d’Alzheimer, le cerveau utilise moins bien le glucose, son principal carburant. Cependant, ce problème énergétique précoce dans la maladie semblerait limité au glucose et ne concernerait pas un autre carburant, celui-ci dérivé des gras, les cétones. Ces dernières sont produites par le corps après un exercice physique d’intensité modérée. Leur production est également stimulée avec la prise de suppléments alimentaires à base d’huile de noix de coco, un aliment riche en triglycérides de moyennes chaînes (MCT). La capture des cétones au cerveau augmente proportionnellement à leur concentration plasmatique. Ainsi, des conditions élevant la cétonémie augmentent aussi la capture cérébrale des cétones. Par conséquent, l’élévation de l’apport en cétones pourrait constituer une approche novatrice qui permettrait de potentiellement ralentir le développement de la maladie d’Alzheimer. Notre objectif général était d’optimiser le type de supplément MCT à utiliser afin d’élever la cétonémie de manière aigüe et, en second lieu, d’employer ce dernier en combinaison avec une seconde stratégie cétogène, l’exercice physique de type aérobie (EA). Lors de la première phase de ce projet, l’effet cétogène de différents produits alimentaires dérivant de l’huile de noix de coco (acide caprylique [C8], acide caproïque [C10], mélange de MCT typique [C8+C10]) était comparé chez 9 participants jeunes sains. Des échantillons sanguins étaient récoltés toutes les 30 min pendant 8 h. Lors de la seconde phase, le potentiel cétogène de la combinaison d’EA à une supplémentation MCT était évalué chez 10 femmes âgées saines pendant 5 jours. Les cétones plasmatiques sous ces différentes conditions étaient mesurées. Lors de cette étude, le C8 était le produit le plus cétogène testé suivi du supplément C8+C10. L’huile de noix de coco n’a pas induit une cétonémie plus élevée qu’un 8 h sans MCT. De plus, l’ajout de 5 jours d’EA a potentialisé la cétonémie observée suite à la prise de MCT C8+C10 seul. Ainsi, la combinaison de stratégies cétogènes, tant au niveau de la diversité des molécules utilisées ou des stratégies cétogènes employées, permet d’augmenter la présence de cétones dans le sang. / Abstract : Brain glucose consumption deteriorates with age, a situation that worsens with the onset of Alzheimer's disease. However, this early energy problem in the disease is limited to glucose and does not affect brain ketone uptake. Ketones are the main alternative fuel for the brain when glucose concentrations are decreased. They are produced endogenously after moderate aerobic exercise (AE) or with a medium chain triglyceride (MCT) exogenous supplement. Ketone brain uptake increases in proportion to their plasma concentration. Thus, providing a daily ketogenic fuel could help support brain energy needs during aging. Our aim was to optimize the type of MCT to use in a ketogenic supplementation and to combine this supplement with another ketogenic strategy, AE. In the first phase of this project, the acute ketogenic effect of products derived from coconut oil was compared. Nine healthy adults took various MCT supplements (coconut oil, caprylic acid [C8], capric acid [C10], classic MCT mix [C8+C10]). Blood was sampled every 30 min over 8 h. In the second phase, we evaluated the acute ketogenic potential of the combination of AE and MCT supplementation. Ten healthy older women took C8+C10 MCT supplement for 5 days combined with a 5-days AE program. Automated spectrophotometric assays where used to measure plasma ketones under these different conditions. Our results show that in this 8 h experimental design, C8 was the most ketogenic MCT followed by C8+C10. Coconut oil alone did not induce more net ketosis than an 8 h visit with no added MCT. Furthermore, the combination of AE and MCT supplementation enhanced the ketogenic response over 4 h compared to the control day. Thus, the combination of ketogenic strategies, both in terms of the diversity of the molecules or the ketogenic strategy employed, makes it possible to increase the presence of ketones in the blood.
98

Palladium(II)-Catalysed Heck and Addition Reactions : Exploring Decarboxylative and Desulfitative Processes

Skillinghaug, Bobo January 2016 (has links)
Palladium complexes have the ability to catalyse cross-coupling of two organic moieties through the formation of transient metal-carbon bonds, thus bringing them closer to each other to facilitate the formation of a new bond. Palladium-catalysed coupling reactions are one of the most important carbon-carbon forming reactions available to organic chemists and many of these reactions rely on the reactivity of aryl-palladium complexes. The investigation of new aryl-palladium precursors is thus of great interest, especially as more sustainable and economic methods can be developed. This thesis describes the use of carboxylic acids and sodium arylsulfinates as such new arylating agents. Protocols for microwave-assisted palladium(II)-catalysed decarboxylative synthesis of electron-rich styrenes and 1,1-diarylethenes were developed. However, these transformations had very limited substrate scopes which prompted the investigation of sodium arylsulfinates as alternative arylating agents. These substrates were employed in the microwave-assisted palladium(II)-catalysed desulfitative addition to nitriles, and the substrate scope was demonstrated by combining a wide array of sodium arylsulfinates and nitriles to yield the corresponding aryl ketones. The application of the desulfitative reaction in a continuous flow setup was demonstrated, and aluminium oxide was identified as safe alternative to borosilicate glass as a reactor material. The mechanisms of the decarboxylative and desulfitative transformations were investigated by density functional theory (DFT) calculations. The desulfitative reaction was also investigated by direct electrospray ionization mass spectrometry (ESI-MS), providing further mechanistic insight. Finally, a protocol for the safe and convenient synthesis of a wide range of sodium arylsulfinates was developed.
99

Development of an adductomic approach to identify electrophiles in vivo through their hemoglobin adducts

Carlsson, Henrik January 2016 (has links)
Humans are exposed to electrophilically reactive compounds, both formed endogenously and from exogenous exposure. Such compounds could react and form stable reaction products, adducts, at nucleophilic sites in proteins and DNA. The formation of adducts constitutes a risk for effects, such as cancer and contact allergy, and plays a role in ageing processes. Adducts to proteins offer a possibility to measure electrophilic compounds in vivo. Adductomic approaches aim to study the totality of adducts, to specific biomolecules, by mass spectrometric screening. This thesis describes the development and application of an adductomic approach for the screening of unknown adducts to N-terminal valine (Val) in hemoglobin (Hb) by liquid chromatography tandem mass spectrometry (LC/MS/MS). The adductomic approach is based on the FIRE procedure, a modified Edman procedure for the analysis of adducts to N-terminal Val in Hb by LC/MS/MS. The adduct screening was performed by stepwise scanning of precursor ions in small mass increments and monitoring four fragments common for derivatives of detached Val adducts, in the multiple reaction monitoring mode. Samples from 12 smokers/nonsmokers were screened with the adductomic approach, and seven previously identified adducts and 19 unknown adducts were detected. A semiquantitative approach was applied for approximate quantification of adduct levels. A strategy for identifying unknown Hb adducts using adductome LC/MS/MS data was formulated and applied for the identification of unknown adducts. Identifications were based on the observed m/z of precursor ions and retention times combined with databases and Log P calculations. Hypothesized adducts were generated in vitro for comparison and matching with the corresponding unknown adducts. Five identified adducts correspond to the precursor electrophiles ethyl vinyl ketone (EVK), glyoxal, methylglyoxal, acrylic acid, and 1-octen-3-one. These adducts, except the adducts corresponding to glyoxal and methylglyoxal, have not been observed as protein adducts before.  Probable exposure sources to these electrophiles are diet and/or endogenous formation. The observation of these adducts motivate further studies to evaluate possible contributions to health risks, as well as their potential as biomarkers of exposure. The adduct from EVK was quantitatively assessed through different experiments to estimate the daily internal dose (area under the concentration-time-curve, AUC). EVK is about 2 × 103 more reactive than the reference compound acrylamide. The EVK adduct was shown to be unstable, with a relatively short half-life. The daily AUC in humans of EVK was estimated to be about 20 times lower than the corresponding AUC of acrylamide from intake via food. To confirm the observation of the detected unknown adducts and obtain a statistical foundation, analysis of unknown adducts were performed in large sets of blood samples (n = 50–120) from human cohorts. The majority of the previously detected unknown adducts were found in all analyzed samples, and the levels of many adducts showed large variations between individuals. The cause and significance of these observed variations are not yet clarified, but are of importance for the directions of future studies. In conclusion, a new approach for identification of unknown human exposure to electrophiles was developed and successfully applied. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.</p>
100

Modificação da D-glicose em produtos de interesse industrial (C-glicosídeo e derivados) buscando preferencialmente o emprego de processos sustentáveis / Modification of D-glucose in products of industrial interest (Cglycoside and derivatives) preferentially seeking the use of sustainable processes

Rodrigues, Bruna Green 10 December 2018 (has links)
Nos últimos anos a química é apontada como solução para diversos problemas globais originados por um modo de vida não sustentável, em virtude disso o desenvolvimento econômico e social ficam vinculados aos conhecimentos em ações sustentáveis embasadas na química verde. Neste contexto emerge a indústria química baseada em matérias-primas renováveis, dentre as biomassas renováveis destacam-se os carboidratos com cerca de 75% da biomassa da terra. Os glicosídeos são moléculas orgânicas nas quais o açúcar está ligado à uma porção não-carboidrato (aglicona), dentre eles os C-glicosídeos se destacam por apresentarem tanto resistência à hidrólise ácida quanto à enzimática, característica que confere interesse a indústria de fármacos e às ciências dos materiais apresentando-se como excelentes blocos de construção. A condensação de Knoevenagel é a reação entre um grupo metileno ativado e um aldeído ou cetona levando à formação de um composto &beta;, &beta;-insaturado e é muito relevante na derivatização de C-glicosídeos. O objetivo principal deste trabalho é empregar a D-glicose, como fonte de matéria-prima renovável, na obtenção de Cglicosídeos e potenciais derivados de interesse industrial, visando oferecer ao ambiente uma opção através de processos mais sustentáveis, para isso dividiu-se o trabalho em três etapas: a primeira de preparação da cetona &beta;-C-glicosídeos e reações de proteções, a segunda, de derivações diretas dessas moléculas, por meio das preparações das oximas, das aril cetonas C-glicosídeos, da cicloexenona C-glicosídeo e do metil pentenol C-glicosídeo e a terceira consistiu de derivação de moléculas, obtidas na segunda etapa, em gem halo-nitro, oxima aril e isoxazol aril. Na primeira etapa, síntese da cetona &beta;-C-glicosídeo, fez-se alterações metodológicas e obteve-se um rendimento médio de 92%, o composto foi confirmado por TGA, FT-IR e RMN 13C, nas reações de proteção à cetona &beta;-C-glicosídeo, acetilação e benzoilação, obteve-se rendimentos de 60% e 31,4% respectivamente, os compostos foram confirmados por FT-IR e RMN 13C. Na segunda etapa sintetizou a aril cetona C-glicosídeo, desprotegida e protegida, com 91% e 78% de rendimentos respectivamente, a cicloexenona C-glicosídeo acetilada com 60% de rendimento e o metil pentenil C-glicosídeo acetilado com até 71% de rendimento, oximas a partir da cetona &beta;-C-glicosídeo desprotegida e posterior proteção (economizando uma etapa) e oximas a partir da cetona &beta;-C-glicosídeo acetilada obtendo rendimentos de 73,6 % e 83%, também foi sintetizada a oxima da glicose e sua acetilação gerou o nitrilo da glicose em 60% de rendimento, os compostos foram confirmados por FT-IR e RMN 13C. Na terceira etapa foram obtidos os derivados, gem bromo-nitro C-glicosídeo acetilado 30% (rota desprotegida) e 73% (rota protegida), gemcloro C-glicosídeo acetilados 30% (rota desprotegida) e 72% (rota protegida). A aril cetona C-glicosídeo acetilada, a oxima aril C-glicosídeo acetilada e isoxazol C-glicosídeo acetilado apresentaram rendimentos 45%, 78% e 31% respectivamente, todos confirmados por FT-IR e RMN 13C. A síntese da cetona &beta;-C-glicosídeo desprotegida em meio aquoso alcalino apresenta um alto rendimento e demonstrou uma enorme versatilidade podendo ser empregada na obtenção de muitos derivados, no entanto as reações de proteção são necessárias para derivação dessas moléculas e facilitação da análise. / In recent years, chemistry has been identified as a solution to several global problems caused by an unsustainable way of life, as economic and social development are linked to the knowledge of sustainable actions based on green chemistry. In this context emerges the chemical industry based on renewable raw materials, among the renewable biomasses stand out the carbohydrates with about 75% of the earth\'s biomass. Glycosides are organic molecules in which sugar is bound to a non-carbohydrate (aglycone) moiety, among them the C-glycosides stand out because they have both resistance to acid and enzymatic hydrolysis, which is of interest to the pharmaceutical industry and sciences of materials presenting themselves as excellent building blocks. The Knoevenagel condensation is the reaction between an activated methylene group and an aldehyde or ketone leading to the formation of an &beta;, &beta;-unsaturated compound and is very relevant in the derivatization of Cglycosides. The main objective of this work is to use D-glucose, as a source of renewable raw material, to obtain C-glycosides and potential derivatives of industrial interest, aiming to offer the environment an option employing more sustainable processes, for this the work was divided in three stages: the first one of preparation of the ketone &beta;-C-glycosides and reactions of protections, the second, of direct derivations of these molecules, through the preparations of oximes, aryl ketones C-glycosides, cyclohexenone C-glycoside and methyl pentenol C-glycoside and the third step consisted of derivation of molecules obtained in the second step in gem halo-nitro, aryl oxime and isoxazole aryl. In the first step, synthesis of the &beta;-C-glycoside ketone made methodological changes and obtained an average yield of 92%, the compound was confirmed by TGA, FT-IR and 13C NMR, in the protection reactions to &beta;-C-glycoside ketone, acetylation and benzoylation, yields of 60% and 31.4% respectively were obtained, the compounds were confirmed by FT-IR and 13C NMR. In the second step, the unprotected and protected C-glycoside aryl ketone was synthesized in 91% and 78% yields respectively, the acetylated C-glycoside cyclohexenone in 60% yield and the acetylated methyl pentenyl C-glycoside in up to 71% yield, oximes from the deprotected &beta;-C-glycoside ketone and subsequent protection (saving one step) and oximes from acetylated &beta;-C-glucoside ketone yielding 73.6% and 83% yields, the glucose oxime was also synthesized and its acetylation generated the glucose nitrile in 60% yield, the compounds were confirmed by FT-IR and 13 C NMR. In the third stage the derivatives were obtained, gem bromo-nitro C-glycoside acetylated 30% (unprotected route) and 73% (protected route), gem-chloro C-glycoside acetylated 30% (route deprotected) and 72% (protected route). The acetylated C-glycoside aryl ketone, the acetylated C-glycoside aryl oxime and the acetylated C-glycoside isoxazole presented yields of 45%, 78% and 31% respectively, all confirmed by FT-IR and 13C NMR. The synthesis of &beta;-C-glycoside ketone deprotected in alkaline aqueous medium presents a high yield and demonstrated an enormous versatility that can be used to obtain many derivatives, however the protection reactions are necessary for derivation of this molecules and facilitation of the analysis.

Page generated in 0.039 seconds