Chemistry Commons^™

Stereoselective Synthesis Of Pseudosaccharide Derivative And Bisphosphoramidate Core Of Em2487, Saad Z. Mohammed Ali

Electronic Theses and Dissertations

HIV is among the leading causes of death worldwide resulting in over 1 million deaths annually according to the World Health Organization. Despite advances in the treatment of HIV, eradicating this pathogen remains a top priority in the medical and scientific communities. EM2487 is a natural product produced by Streptomyces sp. Mer-2487 that possesses promising activity against HIV. Specifically, EM2487 is a potent and selective inhibitor of HIV replication in both acutely and chronically infected cells. The observed HIV activity is hypothesized to be the result of targeting the Tat-TAR (trans-activation response) element which activates RNA polymerase II at the …

To Know The Land With Hands And Minds: Negotiating Agricultural Knowledge In Late-Nineteenth-Century New England And Westphalia, Justus Hillebrand

Electronic Theses and Dissertations

Ever since the eighteenth century, experts have tried to tell farmers how to farm. The agricultural enlightenment in Europe marked the beginning of a long arc of new experts aiming to change agricultural knowledge and practice. This dissertation analyzes the pivotal period in the late nineteenth and early twentieth century in Germany and the United States when scientists, improvers, and market agents began to develop comprehensive ways to communicate agricultural innovation to farmers. In a functional approach to analyzing the negotiation of agricultural knowledge through its communication in things, words, and practices, this dissertation argues that the process of change …

Synthesis And Photophysical Studies Of Nitrogen Heterocycles Containing Benzothiazines, Benzothiazoles, Indoles And Quinolines, Ealin N. Patel

Electronic Theses and Dissertations

Nitrogen heterocycles such as quinolines, benzothiazines, benzothiazoles, and indoles are widely found in nature and these compounds have significance in organic and medicinal chemistry, biochemistry as well as materials science. Monomeric units of eumelanin (brominated 5,6- dimethoxyindolecarboxylate derivatives) were synthesized and regioselectively functionalized to form three monobrominated, three dibrominated, and a tribrominated variant using thermally induced nitrene insertions. After deprotection, three monobrominated 5,6-dihydroxyindole carboxylate (DHICA) derivatives were synthesized, and their UV-Vis absorbance was compared to DHICA. Bominated DHICA derivatives showed similar λmax as DHICA (~330 nm) but did not show aerial oxidation as evident by absence of chromophore absorbance at …

An Intramolecular Method For The Formation Of Glycosidic Bonds, Sudeera Nadeeshani Kamburugamuwa Kamburugamuwe Loku Acharige

Electronic Theses and Dissertations

The improved understanding of carbohydrate functions in biological systems has increased the demand for well-characterized and pure carbohydrates in biomedical research. Chemical synthesis is the most feasible method to satisfy the scientific demand despite the inherent challenges of the glycosylation reaction. Therefore, it is essential to investigate novel methods for the formation of glycosidic bonds. In this work, an intramolecular method was developed using a thio-methylene-silyl linker to tether a glycosyl donor and acceptor. The glycosylation conditions resulted in the formation of both anomeric isomers with a preference for the inversion pathway, which is inconsistent with an entirely intermolecular glycosylation …

Phenolic Phytochemicals And Their Antioxidant Activities In Maine-Grown Asian, American-Hybrid, And European Plums, Hye Weon Hwang

Electronic Theses and Dissertations

Plum fruits of 16 plum cultivars derived from three species, Asian, American-hybrid, and European plums, and one cultivar of an interspecific hybrid between Asian plum and apricot were investigated to identify and quantify two major groups of phenolic phytochemicals, anthocyanins and hydroxycinnamic acids (HCAs) by HPLC–DAD/MS. The plums were harvested from 2014 to 2017. Some cultivars were analyzed through consecutive years to determine year-to-year differences and to evaluate the maturity impacts on the concentration of anthocyanins and HCAs from the partial-ripe stage and tree-ripe stage. Anthocyanins were present in red−purple colored plums, but their profiles varied among cultivars and species. …

Developing A Risk Assessment Protocol To Quantify Distribution And Uptake Of Persistent Organic Pollutants In Glacial Outflows, Kimberley Rain Miner

Electronic Theses and Dissertations

Pollutants released by industrialized nations between 1960 and 2004 have been transported northward through atmospheric processes and deposited into glaciated alpine ecosystems. Many of these chemicals retain their original structure and are absorbed into the biota thousands of miles away from where they were originally utilized. With a warming climate increasing the melt of alpine glaciers, these glaciers may be introducing growing amounts of toxins into the watershed. While studies have demonstrated the existence of resident pollutants within glaciated ecosystems, no one has developed a risk assessment to identify sources and quantity of risk posed by these compounds when released …

Extraction And Purification Of (E)-Resveratrol From The Bark Of Maine's Native Spruces, Panduka S. Piyaratne

Electronic Theses and Dissertations

Resveratrol is a plant secondary metabolite which protects plants from pathogenic invasions and acts as a remedial agent against injury, stress, and tissue damage by UV radiation. With its characteristic stilbene structure, resveratrol adopts (E) and (Z) isomeric forms. However, the (E) isomer is the most biologically active and abundant form of resveratrol in nature.

(E)- Resveratrol confers a variety of benefits to human health and well-being. Besides its antioxidant activity, the role of (E)-resveratrol as an anti-inflammatory, anti-aging, cardioprotection, and anticancer agent has been a widely explored research interest. …

Synthesis And Characterization Of Catalysts For The Selective Transformation Of Biomass-Derived Materials, Isaac Tyrone Ghampson

Electronic Theses and Dissertations

The experimental work in this thesis focuses on generating catalysts for two intermediate processes related to the thermal conversion of lignocellulosic biomass: the synthesis and characterization of mesoporous silica supported cobalt catalysts for the Fischer-Tropsch reaction, and an exploration of the reactivity of bulk and supported molybdenum-based nitride catalysts for the hydrodeoxygenation (HDO) of guaiacol, a lignin model compound. The first section of the work details the synthesis of a series of silicasupported cobalt Fischer-Tropsch catalysts with pore diameters ranging from 2-23 nm. Detailed X-ray diffraction measurements were used to determine the composition and particle diameters of the metal fraction, …

Exfoliated Graphite Nanoplatelet-Filled Impact Modified Polypropylene Nanocomposites, Alex Duguay

Electronic Theses and Dissertations

Exfoliated graphite nanoplatelets (xGnP)-filled polymer composites have demonstrated superior electrical, mechanical, physical and thermal properties and are becoming a major focus for both academic and industrial research and development (R&D) activities. The main objective of this study was to characterize the influence of xGnP particle diameter, filler loading and the addition of coupling agents on the mechanical, rheological and thermal properties of xGnP-filled impact modified polypropylene (IMPP) composites. IMPP is currently being used at the AEWC Advanced Structures and Composites Center in polymer impregnated (pre-preg) fiber reinforced polymer (FRP) tapes consisting of an IMPP matrix polymer and E-glass continuous fibers. …

The Removal Of Wood Components From Hardwood By Hot Water, Rory Jara

Electronic Theses and Dissertations

Hot-water extraction of hemicelluloses from wood is a promising technology in the integrated biorefmery concept. A particular case is where the pulp industry makes co-products such as ethanol and acetic acid besides pulp thereby maximizing the value of biomass. Similarly, the oriented strand board (OSB) industry appears to be suitable for this technical approach as it is composed of large centralized facilities. Many studies have been carried out on the kinetics and mechanism of hot-water extraction of lignocellulosics. However, most of these studies were performed in batch reactors which are not best suited to determine intrinsic kinetics of hemicellulose dissolution …

Biological Conversion Of Hemicellulose Extract Into Value-Added Fuels And Chemicals, Sara Lynn Walton

Electronic Theses and Dissertations

The research presented in this thesis describes the fermentation of hemicellulose extracts to produce ethanol and lactic acid. Hardwood hemicellulose extracts made at a variety of conditions using the green liquor and hot water extraction processes were characterized and then fermented by Escherichia coli K011 and Bacillus coagulans MXL-9. Hemicellulose extracts were found to contain a dilute amount of xylo-oligosaccharides and acetic acid as the major components, and many minor components including other organic acids, lignin-derived phenolics, and sugar degradation products. In order to generate ethanol economically, the fermentation must produce at least a 4% ethanol solution, which requires a …

Synthesis And Oxidation Of Lignin-Carbohydrate Model Compounds, Mai Thanh Thi Nguyen

Electronic Theses and Dissertations

To decrease our dependence on foreign oil supply and in an effort to decrease the amount of green house gases into the atmosphere, researchers are focusing on ways of producing fuels and chemicals from renewable resources. A renewable source such as wood has great potential for the production of biofuels and biochemicals. An integrated biorefinery process that maximizes the usage of wood and complements existing pulp and paper technology was proposed to extract underutilize hemicelluloses and covert them into bioethanol. In this process, not only hemicelluloses are extracted; lignin, since it is covalently bonded to hemicelluloses is extracted as well. …

Technical Evaluation Of Hardwood Biorefinery Using The "Near-Neutral" Hemicellulose Extraction Process, Haibo Mao

Electronic Theses and Dissertations

A technical analysis was performed for a new process that produces ethanol and acetic acid from hardwood in addition to bleached hardwood Kraft pulp. The new process, termed the "near neutral" hemicellulose extraction process, involves the extraction of wood hemicellulose using green liquor prior to conventional Kraft pulping. This thesis assumes that the new process is located at an existing kraft pulp mill. Ancillary unit operations in the process include hydrolysis of the extracted carbohydrates using sulfuric acid, filtration of the extract to remove lignin that was extracted with the carbohydrates, liquid-liquid extraction of acetic acid and by-product furfural, liming …

Kinetics And Mechanism Of Oxygen Delignification, Yun Ji

Electronic Theses and Dissertations

Considerable research has been conducted into the kinetics and selectivity of the oxygen delignification process to overcome limitation in its use. However most studies were performed in a batch reactor whereby the hydroxide and dissolved oxygen concentrations are changing during the reaction time in an effort to simulate tower performance in pulp mills. This makes it difficult to determine the reaction order of the different reactants in the rate expressions. Also the lignin content and cellulose degradation of the pulp are only established at the end of the experiment when the sample is removed from the batch reactor. To overcome …

Production Of Ethanol From Hardwood, Jay Mitchell

Electronic Theses and Dissertations

Diminishing crude oil and natural gas supplies, along with concern about greenhouse gas are major driving forces in the search for efficient renewable energy sources. The conversion of lignocellulosic biomass to energy and useful chemicals is a component of the solution. Ethanol is most commonly produced by enzymatic hydrolysis of complex carbohydrates to simple sugars followed by fermentation using yeast.

C₆H_l0O₅ + H₂O −Enxymes→ C₆H₁₂O₆ −Yeast→ 2CH₃CH₂OH + 2C0₂

In the U.S. corn is the primary starting raw material for commercial ethanol production. …

Ir Studies Of The Interaction Of Surfactants And Polyelectrolytes Adsorbed On Tio2 Particles, Haiyan Li

Electronic Theses and Dissertations

Polymers/surfactants are used to control and modify the interfacial properties of particulate suspensions. The resulting properties are dependent on the amount of adsorbed surfactants/polymers on the surface as well as the nature of the aggregated structures. Often these interactions are complex and not well understood. In this thesis we have used Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) to identify surfactant, mixed surfactant, polyelectrolyte and mixed polyelectrolyte surfactant structures formed on charged Ti0₂ particles. In addition, the change occurring to the structure of an adsorbed polymer layer on Ti0₂ to flowing suspension of silica particles was studied. A …

Mechanistic Studies Of The Oxidation Of Lignin And Cellulose Models, Oh-Kyu Lee

Electronic Theses and Dissertations

Oxygen delignification is an environmentally friendly pulp bleaching system. To develop a selective delignification process that results in high DP retention of carbohydrate with lignin being removed, obtaining better knowledge of reactions occurring during oxygen delignification is essential.

In this work, mixtures of guaiacol (model lignin) and methyl-ß-D-glucoside (model cellulose) were reacted in a pressurized oxygen reaction system (pH 12,65 psi O₂, and 95°C in a glass reaction vessel). In the results, methyl-ß-D-glucoside degraded only in the presence of lignin. This indicates that hydroxyl radicals, that subsequently react with methyl-ß-D-glucoside, are generated in the system. Unfortunately, we could …

Effects Of Fiberimatiux Interactions On The Interfacial Deformation Micromechanics Of Cellulose-Fiberipolymer Composites, William Tai-Yin Tze

Electronic Theses and Dissertations

The overall objective of this dissertation was to gain an understanding of the relationship between interfacial chemistry and the micromechanics of the cellulose-fiber/polymer composites. Regenerated cellulose (lyocell) fibers were treated with amine-, phenylamine-, phenyl-, and octadecyl-silanes, and also styrene-maleic anhydride copolymer. Inverse gas chromatography was conducted to evaluate the modified surfaces and to examine the adsorption behavior of ethylbenzene, a model compound for polystyrene, onto the fibers. Micro-composites were formed by depositing micro-droplets of polystyrene onto single fibers. The fiber was subjected to a tensile strain, and Raman spectroscopy was employed to determine the point-to-point variation of the strain- and …

Oxygen Delignification Kinetics And Selectivity Improvement, Steven M. Violette

Electronic Theses and Dissertations

Pulp strength loss during oxygen delignification is caused by cellulose chain cleavage resulting fiom attack by oxygen-based radicals generated through reactions with lignin. The objective of this research was to improve the lignin-to-cellulose selectivity during oxygen delignification by using radical-scavenging polymeric additives that adsorb on the cellulose surfaces where protection fiom radicals is needed. Among the polymers evaluated were starch, carboxymethyl-cellulose, galactomannan, xylan, and glucomannan. Oxygen delignification experiments were conducted on Northeast softwood Kraft pulps at different temperatures, sodium hydroxide charges, reaction times, and pretreatments. The effect of polymer additives on the selectivity and kinetics was studied. Polymer adsorption on …

Relationship Between Alkaline Pulp Yield And The Mass Fraction And Degree Of Polymerization Of Cellulose In Pulp, Mehmet Sefik Tunc

Electronic Theses and Dissertations

Wood as a raw material is generally the dominant cost factor for the production of chemical pulp. Therefore, an increase in pulp yield has a major impact on the competitiveness of a mill. In order to optimize pulp yield, for example by changing operating conditions, a mill must be able to monitor the yield accurately. However, an accurate "real-time" pulp yield measurement method is not available at the present time. Pulping yield is presently measured from the amount of pulp produced from a given quantity of wood consumed over a 3 to 6 month time frame. This method is obviously …

Effect Of Kraft Pulping On Oxygen Delignification, Haixuan Zou

Electronic Theses and Dissertations

The objective of the study reported here was to investigate experimentally the effect of the major Kraft pulping variables on the response of brownstock pulps to medium consistency oxygen delignification. Kraft pulping was performed on mixed Northeastern hardwood chips in a laboratory rocking digester. Kraft pulps of kappa number 16 and 20 mL KMnO₄ were produced by pulping under a variety of conditions. The effective alkali (EA) charged to the digester was varied over the range of 12 to 21% while the sodium sulfide content of the pulping liquor was varied between 0 to 30% sulfidity. Cooking temperatures of …

Photostabilization Of High-Yield Pulps Reaction Of Thiols And Quinones With Pulp, Jonathan Spender

Electronic Theses and Dissertations

Some thiols have been shown to be efficient in both bleaching and stabilizing the brightness of mechanical pulps. Two thiols, thioglycerol and glycol dimercaptoacetate, have received considerable attention due to their photostabilization effects. Their reactions with 1,4-benzoquinone, a model lignin compound, were investigated. In the first part of this study, reaction products were isolated using preparative HPLC and were fully characterized using GC-MS as well as ^l3C-NMR Both thiols were found to undergo Michael addition with the model quinone (in methanol) to yield a substituted hydroquinone. Further reaction with excess quinone in the presence of UVlight facilitated subsequent redox …