To see the other types of publications on this topic, follow the link: Chemical investigation.
Dissertations / Theses on the topic 'Chemical investigation'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Chemical investigation.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Porter, Joshua D. "A Chemical Investigation of Australian Winteraceae." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/419713.
Full textAbstract:
The Winteraceae are a small primitive family of angiosperms endemic to the cool rainforests and montane subtropics of South America, Melanesia, Australasia, and South-East Asia below the Wallace line.The medicinal value of Winteraceae plants branches from extensive use in traditional medicine regimens to use in modern clinical applications. Nonvolatile drimane sesquiterpenes do not occur broadly in nature. However, they are reported to be a chemotaxonomic characteristic of the Winteraceae. Many of those identified from the Winteraceae comprise structural features that are either unique to the family or
identified from a minimal number of natural sources.3 Biological investigations on the drimane structure class have identified several activities attractive for drug discovery and may be linked to their usefulness in traditional medicines.
Bubbia and Tasmannia are the only Winteraceae genera with species endemic to Australia. Except for Tasmannia lanceolata and studies on the essential oil content of both genera, the chemistry of the Australian Winteraceae is poorly studied and remains an unexploited source of potentially new biologically active natural products.The primary aim of this thesis was to investigate the chemistry of unexplored Australian Winteraceae species to identify new drimane sesquiterpene natural products and improve
the current knowledge of the chemistry of Australian Winteraceae. This was achieved by exploring the chemistry of two Australian Winteraceae species.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text
2
Ngai, Courtney L. "An Investigation of Chemical Identity Thinking." Thesis, University of Massachusetts Boston, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10265119.
Full textAbstract:
Chemical identity is a foundational crosscutting concept in chemistry and encompasses the knowledge, reasoning, and practices relevant for the classification and differentiation of substances. Substances are found everywhere – from the chemistry classroom to the kitchen at home – so classification and differentiation of substances is important for everyday decisions as well as challenges that are solved using chemistry. An understanding of chemical identity, then, is essential for scientifically literate citizens in addition to students training to be chemists. A better understanding of how chemical identity thinking develops could be used to inform instruction and education research, with the intent of producing students and citizens who can use their chemical knowledge to reason with in order to practice chemical identity thinking.
This thesis characterizes chemical identity thinking from the perspective of chemical identity knowledge and chemical identity practices, both of which contribute to chemical identity thinking. First, the literature is examined for existing research on how students perceive substances and chemical identity, and a hypothetical learning progression for chemical identity thinking is proposed. This is followed by the design of a qualitative instrument, the CSI Survey, to capture the chemical identity practices exhibited by students at a range of education levels (8th grade – 4th year university). The data collected using the CSI Survey are analyzed using content analysis. Eight unique themes corresponding to chemical identity practices (the application of chemical identity knowledge and reasoning) are revealed by this analysis (change, class, composition and structure, function, organism effect, sensory information, source, tests and experimental values). The application of chemical identity knowledge in biochemical contexts by both expert biochemists and biochemistry students is investigated in the final chapter, and the chemical identity knowledge observed in the biochemical contexts is characterized using the eight themes of chemical identity practices. Suggestions are offered on how the products of the research on chemical identity thinking can be used to inform decisions in both instruction and research.
3
Burton, Stephanie Gail. "A chemical investigation of Tulbaghia Violacea." Thesis, Rhodes University, 1990. http://hdl.handle.net/10962/d1015725.
Full textAbstract:
Tulbaghia violacea, a member of the family Alliaceae is indigenous to the Eastern Cape and is widely used as a herbal remedy for various febrile and gastro-enteric ailments, particularly in young children. Adverse effects, and even fatalities, have been reported following treatment with the plant extract. The project has involved synthesis of model compounds, chromatographic analysis of flavonoid and other constituents of the plant, and examination of the volatile components. Some fifteen flavones were synthesised as chromatographic models and in the course of this work, the development of a new method for synthesis of carboxylic anhydrides was completed. Use of the flavone standards permitted identification of the flavonols kaempferol and quercetin in hydrolysed glycosidic plant extracts. In addition, several sugars were identified, viz., D-glucose, D-fructose, L-arabinose and D-galactose as free sugars, and D-glucose, D-galactose , 1-rhamnose, D- fucose, D-xylose, 1-arabinose and D-fructose as glycosidic sugars, by g.l.c. and g. c. - m. s. analysis of derivatives of isolated sugar mixtures. The presence in the plant extracts of steroidal saponins was also demonstrated. The sulphur compounds, 2,4,5,7-tetrathiaoctane-2,2-dioxide and 2,4,5,7-tetrathiaoctane were isolated from the plant and characterised spectroscopically. This result, together with analysis of volatiles from the plant, has led to a proposal concerning the nature and origin of sulphur compounds in Tulbaghia violacea, showing close correlation with the sulphur compounds in Allium species. Investigation of the biological activity of Tulbaghia violacea extracts showed bacteriostatic activity, particularly of extracts which had not been heated, and which had been prepared from mature plants. Treatment of isolated smooth muscle preparations with Tulbaghia violacea extracts indicated the presence of a β-adrenergic agonist having an inhibitory effect on normal muscle contraction. The results of the investigations indicate that while there may be some basis for use of the plant as an antibacterial, or to treat colic, the adverse effects, caused possibly by the sulphur compounds and/or steroidal saponins present, may override the beneficial effects.
4
Hagos, Selam. "Chemical Investigation of Bioactive Marine Extracts." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7301.
Full textAbstract:
Natural products have been a fundamental source of medicinal scaffolds for decades; with sixty percent of marketed drugs. Many synthetic chemists are focused on synthesizing potent and nontoxic compounds for pharmaceutical targets, however, nature is still proving to be a source of new bioactive compounds. Produced by the host organism for defense, reproduction and communication, secondary metabolites also demonstrate promising bioactivity against human pathogens. Hence, natural product chemists continue their quest for new leads.
As a continuation of these efforts, this thesis attempts to explore fungi and sponges for new chemistry, and ultimately, new drug candidates. Antarctica is largely untapped; hence herein two Antarctic sponges were chemically investigated. This resulted in isolation and characterization of two metabolites. Concurrently, chemical investigation of fungus, from Floridian mangrove species, resulted in the isolation of two structurally diverse metabolites. Further, a dereplication process was applied to MPLC fractions, which lead to the identification of known metabolites and mycotoxins. This enabled prioritization of fractions for future studies.
5
Ge, Daozhi. "Chemical Investigation of Plant Taxodium ascendens." Thesis, Griffith University, 2018. http://hdl.handle.net/10072/380674.
Full textAbstract:
Anticancer activity screening of an extract library containing 152 traditional Chinese medicines (TCM) has identified one crude extract from Taxodium ascendens with potent activity. The overall aim of the project was to investigate the chemical composition of the TCM extract and to evaluate the activities of the natural products against cancer cell lines.
In Chapter1, it introduces the background of traditional medicines & natural products and also exemplifies several nature-derived-drugs. A review based on anticancer drugs derived from natural products and the importance of natural origin compounds against cancer were also discussed. A high throughput screening assay for 152 TCMs suggested the potential anti-breast cancer activities of MeOH and EtoAc extracts of Taxodium ascendens. Therefore, it was selected for large scale chemical investigation.
Chapter 2 details the large scale isolation and structure elucidation of pure natural products from Taxodium ascendens extract. A total of 15 compounds were isolated from 6.25 grams of crude extract. They represented four structural classes including diterpenes, flavonoids, terpene acids and aromatic acids. The structures of the compounds were elucidated via 1D- and 2D-NMR and Mass spectroscopic data. Cytotoxic assays of three compounds were tested against a breast cancer cell line, T-47D. One compound, 6-hydroxy-5,6-dehydrosugiol (2.23), showed potent activity against T-47D with an IC50 value of 8.24 M. The physical chemical properties of all the isolated compounds were also evaluated against Lipinski’s rule of five.
The detailed experimental procedures can be found in Chapter 3.
In conclusion, 15 pure natural products were isolated with 6-hydroxy-5,6-dehydrosugiol (2.23) showing potent anticancer activity.Thesis (Masters)
Master of Science (MSc)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text
6
Loehn, Clayton William. "Investigation of the monazite chemical dating technique." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/27688.
Full textAbstract:
In order to evaluate the electron microprobe (EMP) method for chemical dating of monazite, we chemically analyzed selected suites of monazite grains that were previously dated by standard U/Pb isotopic methods at three laboratories each equipped with a sensitive high resolution ion microprobe (SHRIMP). Representing diverse igneous and metamorphic lithologies, these grains yielded conventional isotopic ages ranging in age from Neoarchean to Devonian. Chemical dating was performed at Virginia Tech using a Cameca SX-50 EMP in which the analytical routines and settings were specifically optimized for monazite geochronology, including correction of analytical peaks for all major spectral interferences and correction of peak intensities for local background emission. Placement of cross-grain analytical traverses was based on backscattered electron (BSE) images together with wavelength-dispersive (WD) generated X-ray maps for Y, Th, U, and Ca, which revealed the internal compositional complexity of each grain. Shorter EMP traverses were selected adjacent to each SHRIMP pit in order to provide the best possible comparison of ages obtained by the two dating methods. Synthesis protocol for key elemental measurements (Y, Th, U, and Pb) was developed utilizing the 1Ï elemental errors associated with individual analyses, providing an objective approach for data synthesis. Analytical dates were either accepted or excluded based on analytical and spatial justifications. Isotopic dating techniques utilize three independent age calculations, provided the sample is old enough to have accumulated sufficient 207Pb (i.e., â ¥~1000 Ma). Similarly, the chemical dating method can utilize two independent age calculations (i.e., Th/Pb and U/Pb) and a U-Th-Pbtotal centroid age in Th/Pb vs. U/Pb space, verified independently against the calculated Th* or U* CHIME ages. Across the entire 2,200 m.y. age range represented by the sample set, the chemical ages calculated from the EMP data chemical ages are internally consistent (within 2Ï error) with the previously measured SHRIMP isotopic ages, except in one case where bulk mixing of discrete age domains within an ablation pit led to an isotopically discordant apparent age. Overall, this study illustrates that EMP chemical dating (1) represents both an accurate and precise primary method for dating monazite from igneous and polymetamorphic terrains; (2) provides superior spatial resolution for obtaining meaningful ages from small and/or irregular domains of discrete age that may be irresolvable or misinterpreted by other dating techniques that sample larger volumes; and (3) illuminates the geological meaning of isotopically discordant monazite ages obtained using conventional methods with lower spatial resolution (e.g., SHRIMP).Ph. D.
7
Park, Young Chul. "Chemical Investigation of Three Antarctic Marine Sponges." Scholar Commons, 2004. https://scholarcommons.usf.edu/etd/1190.
Full textAbstract:
This thesis describes the chemical investigation of three marine sponges from Antarctica and the total syntheses of natural products erebusinone (12) and its derivative, erebusinonamine (52). Investigation of the yellow Antarctic marine sponge Isodictya setifera resulted in the isolation of two secondary metabolites, purine analog (32) and 3-hydroxykynurenine (24). Chemical investigation of Isodictya setifera led to the isolation of six secondary metabolites which included 5-methyl-2-deoxycytidine (25), uridine (28), 2-deoxycytidine (31), homarine (37), hydroxyquinoline (33), 3-hydroxykynurenine (24). The latter two compounds were found to be intermediates of tryptophan catabolism in crustaceans. From the Antarctic marine sponge Isodictya antractica ceramide analog (39) was isolated and its chemical structure was assigned by a combination of spectroscopic and chemical analyses. Stereochemistry was determined by modified Mosher's method. Erebusinone (12), a yellow pigment isolated from the Antarctic marine sponge Isodictya erinacea has been implicated in molt inhibition and mortality against the Antarctic crustacean amphipod, Orchomene plebs, possibly serving as a precursor of a xanthurenic acid analog.
Thought to act as a 3-hydroxykynurenine 24 mimic, erebusinone (12) may be involved chemical defense. This appears to be the first example in the marine realm of an organism utilizing tryptophan catabolism to modulate molting as a defensive mechanism. To further investigate the bioactivity and ecological role of erebusinone (12), the synthesis of this pigment was carried out in an overall yield of 44% involving seven steps which were economical and convenient. Erebusinonamine (52) was also similarly synthesized in eight steps with an overall yield of 45%.
8
Phatak, Nisarga Laxman. "Chemical investigation of fungicolous and endophytic fungi." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/4719.
Full textAbstract:
Fungi have been an important source of many structurally diverse and biologically active secondary natural products. These secondary metabolites have found applications in pharmaceutical and agriculture industry. Fungi are estimated to be second only to insects in species diversity. It is estimated that there are at least 3.5 million species of fungi of which a less than 5% have so far been explored. Fungi are known to produce many secondary natural metabolites, however their role has still not been clearly understood. However it is possible that fungi which often thrive in competitive environments would experience evolutionary pressure to produce such metabolites for defensive or offensive functions.
Our research focusses on isolation and structure elucidation of secondary metabolites from endophytic and mycoparasitic/fungicolous fungi. Mycoparasitic and fungicolous fungi are those that colonize other fungi, and could be potential sources of antifungal agents because of the negative effects exerted on their hosts due to this colonization. Endophytic fungi are those that colonize the inner tissues of plants in a symbiotic or a non-symbiotic manner. They may or may not be necessary for the growth, defense and survival of the host. They may protect the plants from attack by other pathogens by producing secondary metabolites that inhibit the growth of other pathogenic organisms. Many biologically active secondary metabolites have been isolated from various members of these two classes of fungi.
During the course of this research fourteen new and several known compounds representing various biosynthetic classes including peptides, polyketides, terpenoids, and compounds with mixed biogenetic origins have been isolated and characterized using various tools such as NMR and MS. Details of the isolation, structure elucidation, and biological activity of these new compounds are presented in this thesis. Structure elucidation was performed mainly by analysis of various MS and NMR data, along with chemical derivatization reactions and/or X-ray diffraction analysis data. Absolute configuration assignments were made using, X-ray crystallography, and/or by ECD spectral analysis in combination with computational analysis.
9
Wang, Qianhe. "Investigation of Acrylated Alkyds." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1366047898.
Full text
10
Huang, Wei Hua. "Chemical investigation on root barks of Oplopanax horridus." Thesis, University of Macau, 2012. http://umaclib3.umac.mo/record=b2590373.
Full text
11
Meng, Xiaoli. "Chemical synthesis and investigation of reactive drug metabolites." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490798.
Full textAbstract:
Bioactivation of drugs to their chemically reactive metabolites (CRMs), often leading to protein-drug conjugates, is a widely-known hypothesis of adverse drug reactions. However the direct evidence of this hypothesis is lacking. Therefore highly pure CRMs are of great interest to both academia and industry, and substantial amounts of'highly pure CRMs are essential for the study of drug toxicity mechanisms. Thus the aims of this project are developing efficient methods to synthesize reactive drug metabolites in large quantity for thorough toxicological evaluation and investigating the chemical reactivity ofCRMs.towards proteins. Several efficient methods for the synthesis of CRMs of some important drugs have been developed. For example, acyl glucuronides, potentially reactive electrophilic metabolites implicated in adverse drug reactions, were obtained by selective acylation of benzyl or allyl glucuronate and subsequent deprotection under mild conditions. As demonstrated in chapter 2, highly pure acyl glucuronides (AGs) of various important drugs were synthesized through the selective acylation method, and their stabilities and reactivities were evaluated by LC-MS and NMR. Variable stabilities and reactivities of AGs were identified: AG of UK414, 495 is extremely unstable and underwent cyclisation to form a reactive imide at pH 7.4; whereas AG of UK505,749 is quite stable for several hours, then acyl migration rather than cyclisation occurred as shown by LC-MS. Furthermore, the chemical reactivities of the reactive imide towards various nucleophiles containing -NH2, -SH and -OH functional groups were investigated and the formed adducts were fully characterised. Benzyl penicillin (BP) is well-known to cause allergic reactions in 3-5% patients. Previous studies have shown that BP can covalently bind to albumin molecules and the resulting penicilloyl/albumin conjugates are considered to be the major antigenic determinants in penicillin allergy. Whether BP reacts directly with albumin or through penicillenic acid (PA), a highly reactive degradation product of penicillin, has been a debate for many years. Here we demonstrate a simple and sensitive method to characterize the modified protein as well as an efficient 4-step method to prepare the penicilllenic acid of benzyl penicillin for the study of penicillin allergy. Evaluation of protein reactivity of CRMs has been carried out both ill vitro and ill vivo. In chapter 3 and 4 we have investigated BP (or PA) modification of albumin in detail by ESIIMSIMS. BP and penicillenic acid have both shown high affinity binding to albumins ill vitro. 12 lysine residues on HSA and 7 lysine residues on RSA were found to be modified by both BP and PA, and PA appears to be more reactive than BP. In addition, BP or PA binding to albumins proved to be time and concentration dependent. Modification was also detected. in rats administered with a single intravenous dose of BP as well as multiple Lp. dose of BP. The modification also has been shown to vary in a dose- and time-dependent manner.
12
Senanayake, Mahima. "A Chemical Investigation of New Zealand Unifloral Honeys." The University of Waikato, 2006. http://hdl.handle.net/10289/2665.
Full textAbstract:
The diethyl ether-extracted organic compounds of 155 samples of unifloral grade New Zealand kamahi and honeydew honeys, and New Zealand and Norwegian erica honeys, together with a series of active and inactive manuka honeys were analysed using combined gas chromatography/mass spectrometry. It was found that Kamahi honey is characterized by the presence of 2,6-dimethylocta-3,7-diene-2,6-diol, meliracemoic acid, and kamahines A-C and these compounds were typically present at average levels of 31, 14, and 73 mg/kg of honey, respectively. 2,6-Dimethylocta-3,7-diene-2,6-diol was isolated and the structure of this compound was defined using one- and two-dimensional NMR analyses. The only recognizably distinct peak present in the honeydew honey profile was indole acetic acid. In this honey, a relatively low to moderate level of indole acetic acid, ranging from 0.9 to 9.1 mg/kg honey was detected. In the New Zealand erica honey samples, ericinic acid, isoericinic acid isomers (average levels 363 and 34 mg/kg respectively), trans,cis and trans,trans-abscisic acid isomers (average levels 302 and 224 mg/kg respectively) and benzoic acid (average level 6950 mg/kg) were identified as floral marker compounds. Ericinic acid was isolated and the structure of this acid was defined using one-and two-dimensional NMR analyses. Low levels of ericinic and isoericinic acids (average levels of 1.1 and 0.32 mg/kg respectively) were detected in the Norwegian erica-rich honeys. The results presented here indicate that ericinic and isoericinic acids are likely to be universally present in erica honeys at levels which may range from as low as 1 mg/kg or less, as found in some Norwegian samples, to more than 100 mg/kg in some New Zealand samples. Two groups, namely a fingerprint pattern which characterized active manuka honeys, and a fingerprint pattern that characterized inactive manuka honeys were identified. Some substances contributing to the GCMS profile were found as marker compounds for the presence of unidentified substances responsible for the UMF activity. A statistically significant correlation was found between a small set of marker compounds (i.e. phenylacetic acid, 2-methoxyacetophenone, 2-methoxybenzoic, phenyllactic, octanedioic, cis-cinnamic, trans-cinnamic, nonanedioic, 4-methoxyphenyllactic and decanedioic acids and methyl syringate) and UMF activity of manuka honey. The best-fit marker compound regression equation (R = 0.92) was obtained for a set of pooled 30 moderate to high activity (UMF gt 14.1) samples. It was shown that the marker compound regression equation is capable of predicting the approximate UMF activity in both active and inactive manuka and kanuka honey samples. The leaf oil profiles of manuka (L. scoparium) plants that yielded active and inactive manuka honeys were characterized using an adaption of the micro-scale extraction and GC/FID or GC/MS, technique developed by Brophy et al. (1989). Six major groups of volatile (steam distillable) compounds (monoterpenes, sesquiterpene hydrocarbons, oxygenated sesquiterpenes [excluding eudesmols], eudesmols, triketones, and nor-triketones) and 3 groups of non-volatile or semi-volatile compounds (flavonoids, grandiflorone and nor-grandiflorone) were recognized in the leaf oil components. The active manuka honeys do not appear to be derived uniquely, or predominantly, from a single leaf oil chemotype.
13
Wang, XiuZhu. "Investigation of biological and chemical interactions by AFM." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615986.
Full text
14
Cadorette, Veronica R. "Chemical investigation of Dicranum fulvum for anticancer activity." Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/44706.
Full textAbstract:
Biological screening of extracts of various bryophytes showed that the species Dicranum fulvum gave extracts with activity in both in vitro and in vivo bioassays. This plant was thus selected for extraction and fractionation, monitored by iin vitro bioassays.
Isolation was guided by a combination of bioassay and chemical methods, and led to the isolation of three compounds, betulin, 9,l9- cyclolanostâ 23â eneâ 3,25â diol, and B-sitosterol. Purification was achieved by open column, flash column, gel filtration, thin layer chromatography, the chromatotron and crystallization.
The isolated compounds were identified by comparisons of spectroscopic data with those of authentic samples and the matching of experimental and literature melting points and optical rotations.
Master of Science
15
Phala, Noko Simon. "A theoretical investigation in heterogeneous gold catalysis." Thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/6767.
Full textAbstract:
Includes bibliographical references.Despite the nobleness of bulk gold metal in air, small supported gold particles have been shown experimentally to be active in a wide range of chemical reactions. The objective of this work was to study, theoretically, some of the fundamental aspects of the reactivity of gold catalysts. Using activation of CO, CO2 and H2 as a test case, periodic and cluster density functional theory (DFT) calculations, within the generalized-gradient approximation (GGA), were performed to investigate the change in nobility of gold from the extended surface to small clusters. Potential methanol synthesis intermediates were optimized on the Au(111) surface. It was found that the molecules that are stable as gasphase species generally adsorbed weakly on the surface. Surface hydrogenation of CO-derived species appeared to be easier than surface hydrogenation of CO2- derived species. On an AU13 cluster, the energetics of CO2 adsorption and hydrogenation remain unfavourable. The cluster-size dependency of hydrogen and carbon monoxide adsorption was investigated. It was found that small gold clusters (1 to 13 atoms in size) can bind both H and CO strongly. Due to the changes in the orbital spatial symmetries and the energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with cluster size in this small size range, the adsorption energies depend very strongly on the number of gold atoms present, i.e. each atom makes a difference. For H adsorption, there is a very marked oscillation in adsorption energies, with the clusters with an odd number of gold atoms (with lower LUMO energies) being generally more reactive than the even clusters, up to about 10 atoms when the HOMO-LUMO gap ceases to fluctuate strongly. The role of the support material in activating gold atoms was studied. A hybrid quantum mechanics/molecular mechanics (QMlMM) electronic embedding technique was employed to model the ZnO(000l) surface of zincite. The QM region of the surface, treated by density functional theory, consisted of a total of 13 zinc and oxygen atoms for the zinc-vacant site, and 14 atoms for the bulk-terminated island site. It was found that Au0 and Au+ could be stabilized at the zinc vacant site of this surface. The higher oxidation states are unstable with respect to auto-reduction by the ZnO surface (i.e. their LUMO energies were below the HOMO of a bare ZnO surface. However, gold hydroxyls, where gold has + 1 to +3 oxidation states, can be stabilized at the vacancy. As zinc-substitutional impurities on the bulk-terminated island site, Au+, Au2+ and Au3+ oxidation states can be stabilized. CO was used as a test molecule to probe the chemical reactivity of the gold atoms in different adsorption sites and oxidation states. It was found that supported Au+ was more reactive than Au0, Au2+, or Au3+. Furthermore, CO binds more strongly to supported Au0 than the free Au0 atom. This implies that the support does not simply disperse gold particles, but it also modifies their electronic properties. It was also found that the nucleation of gold atoms to clusters can be affected by the support. Supported charges Au clusters have shorter Au-Au distances than their gas-phase counterparts.
16
Jacobs, Kelvin Stephen. "Investigation of the activity and selectivity of the MoO3/AI2O3 catalyst and the structural investigation using in-situ raman." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/5314.
Full textAbstract:
Bibliography: leaves 89-94.Metathesis is a very versatile reaction, which allows the conversion of Simple, relatively inexpensive olefins into specialty, high-purity olefins which are useful intermediates in the fragrance, agricultural and many other specialty chemical industries. Supported molybdenum on alumina is an active heterogeneous catalyst for the metathesis of olefins. Its activity, as a function of time, passes a maximum. It is known that the activity of molybdenum-based catalyst increases up to monolayer capacity. Catalysts with various Mo-Ioadings were prepared by controlled adsorption method using ammonium heptamolybdate as a precursor. A catalyst using a new slurry impregnation method was also prepared for comparative reasons. Before the metathesis process, the molybdenum catalysts are activated at 550°C under N2 in a fixed bed reactor. The loading of the prepared catalysts was below and above monolayer capacity. It was observed that up to a loading 0.3 g Mo03 per g Ab03 the initial conversion increases more than proportional to the Mo03- loading. The catalysts with a Mo03-loading higher than 0.3 g Mo03 per gram AIz03 show initially a lower activity, ie. The activity per molybdenum atom in the catalyst decreases. With increasing time-on-stream the activity of the catalysts declines. The decline is much stronger over the catalysts with a rligher initial activity.
17
Ostler, Richard Bruce. "An investigation of intracellular PDT mechanisms." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301122.
Full text
18
Segraves, Nathaniel Lee. "Chemical investigation of biologically active alkaloids from marine sponges /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2005. http://uclibs.org/PID/11984.
Full text
19
Glowacki, David Ryan. "Investigation of Atmospheric Chemical Mechanisms Using Experiments and Theory." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485587.
Full textAbstract:
This thesis IS divided into two parts. Part I provides a detailed discussion of the design ami construction of a highly instrumented reactor for atmospheric chemistry (HlRAC). The main analytical tool'constraining HlRAC's design is its multipass FTIR absorption spectroscopy optical system. Apart from the FTIR system, HIRAC features an extensive suite of instrumentation en'abling simultaneous measurement of several different atmospheric trace gases. This capability allows experimental flexibility, and potentially provides multiple constraints in the development and testing of atmospheric oxidation mechanisms. The initial experimental results obtained from the system show HlRAC's capacity to facilitate atmospheric chemistry research at Leeds, linking laboratory and theoretical investigations of elementary reactions with VOC mechanism development. Part II discusses theoretical work conducted in order to -explore reaction kinetics and product yields of elementary reactions that are significant to the chemistry of planetary atmospheres. The tools for theoretical analysis include: (1) electronic structure theory, (2) statistical theories for describing reaction rates and product energy partitioning, (3) the energy grained master equation (EGME), and (4) trajectory simulations. In conjuction with experimental data, .these techniques permit a detailed' understanding of reaction mechanisms under a range of conditions that are relevant to the chemistry of planetary atmospheres. They also facilitate experimental design in: (1) laboratory studies of elementary reactions and (2) chamber studies of more complex oxidation systems, such as may be carried out in HIRAC.
20
Ingham, Angela M. "Models in chemical education : an investigation into their uses." Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/771366/.
Full textAbstract:
This thesis is concerned with the use of models in chemical education, in particular the way chemistry students use models in understanding chemistry. The study begins with an outline of the reasons for my interest in the subject of models in chemistry. The report describes some of the problems encountered by undergraduate chemistry students in dealing with three dimensional structures, and surveys literature relating to visualization skills in chemistry. Preliminary broad areas for investigation are identified including the relevance of models to students, problems of representing 3D structures, and students' use of models to solve chemical problems. A pilot study to gather information in these areas and to develop a suitable research instrument for investigation is described. The pilot study proved useful in highlighting errors in understanding chemical concepts, assessing practical model use, and considering students' perceptions of the relevance of models. This is followed by a consideration of the role of models in understanding chemistry in relation to the nature of model, chemistry and understanding, and the links and interactions between them. It discusses issues such as the match between the currently perceived roles of models in chemical practice and in chemistry teaching and the desirability of bringing these into line. It surveys the literature concerning purpose of model use in chemistry and describes the features of chemical structure models used in the research. Criteria for selecting appropriate data collection and analysis methods in a research study are considered and 80me of the methods adopted in recent chemical education research described. The chapter concludes with a description and justification of the particular research methods used in the study. The report gives details of the interviews carried out with selected scientists to consider the notion of 'the good chemist'. It then describes the videorecorded workshop interviews with forty five chemistry students relating to their appreciation and use of models in chemistry, and the follow up int.erviews with eight of the participants. Data from these interviews are analysed in an attempt to answer the research questions posed initially, including individual chemists' purposes in using models, patterns in model appreciation, perceptions of the good chemist, fiexibility of model use as an indicator of competence as a chemist, and the potential of the workshop interview in higher education assessment. The research findings are discussed in relation to existing literature, and the study concludes with a discussion of the implications for chemistry curricula, chemical education and for future research.
21
Lebar, Matthew D. "Antarctic Tunicates and Endophytic Fungi: Chemical Investigation and Synthesis." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3638.
Full textAbstract:
Drug discovery is reliant on new developments in natural product chemistry as well as advances in chemical synthesis. The interconnectivity and interdependence of natural and synthetic investigation in drug discovery is evident. The chemical exploration reported herein elaborates the relationship between natural product chemistry and chemical synthesis. Of particular interest are chemicals from organisms residing in less accessible environments, particularly Antarctica and endophytic microbial communities. Degradation via reductive ozonolysis of palmerolide A, a macrocyclic polyketide isolated from the Antarctic tunicate Synoicum adareanum, and subsequent synthetic preparation of the resulting polyols (1,2,6-hexanetriol and 1,2,3,6-hexanetetraol) led to a revision in the absolute configuration of the bioactive natural product (7R, 10R, 11R to 7S, 10S, 11S). A partial synthesis of palmerolide A (C3-14) was completed using Grubb’s 2nd generation catalyst to couple fragments formed using the previously developed methodology from the degradation study. Isolation of indole-pyrimidine containing alkaloids meridianins A, B, C, and E from the Antarctic tunicate Synoicum sp. prompted a synthetic investigation of psammopemmin A, a related alkaloid from the Antarctic sponge Psammopemma sp. resulting in reassignment of the structure of psammopemmin A to that of meridianin A. Both meridianin A and psammopemmin A were synthesized through a Suzuki coupling of the same 4-indolol nucleophile to the apposite pyrimidine electrophile. Several synthetic 3-pyrimidylindole analogs were also prepared and investigated for central nervous system, antimalarial, and cytotoxic activity. Chemical investigation of extracts from mangrove fungal endophytes that displayed antimalarial properties in vitro resulted in the isolation of several potent but cytotoxic and cytostatic compounds: cytochalasin D, roridin E, and 12,13-deoxyroridin E.
22
Powell, Mark William. "An investigation of chemical factors influencing bitumen-mineral adhesion." Thesis, University of Hertfordshire, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314732.
Full text
23
Rao, Vikram Mohan. "Investigation of Decision Processes in Chemical Substitution Decision Making." Thesis, The George Washington University, 2021. http://pqdtopen.proquest.com/#viewpdf?dispub=28261055.
Full textAbstract:
In recent years, new regulatory guidance has spurred organizations to replace hazardous chemicals with safer alternatives. The factors and influences that shape decisions to transition to safer chemicals are of interest to decision scientists. Previous studies have examined the role that various factors, such as regulation, health impacts, and environmental impacts, have played in shaping such decisions. However, two key research gaps have been identified. First, existing semi-quantitative-based studies do not adequately capture the complexity of decision-making. Second, no in-depth qualitative study of a current substitution process, elucidating decision-making mechanisms at various stages of the design process, has yet been performed. The current research addresses these gaps. The first component of the study is an extensive survey of product and chemical manufacturers to elicit potential tradeoffs concerning final product design and redesign decisions. Such tradeoffs are characterized by a set of six factors affecting product design, which are further disaggregated into thirty-three attributes distributed across these factors. Statistical methods including Bayesian Dirichlet modeling and Principal Component Analysis were used to show: 1) two factors were statistically significantly different than other factors, 2) how features such as company size and time of decision affected factor weighting, and 3) that nine principal components explain 79% of the variance in the attribute scores. The second component of the study was a phenomenological assessment of a current substitution process: replacement of cadmium with Zn-Ni for aircraft components, undertaken by the U.S. Navy and Air Force. This study synthesized existing research in cognition, decision-making, and knowledge management. Semi-structured interviews were conducted with participants representing engineering, environmental, safety, and management disciplines. Qualitative analysis was used to identify and characterize the underlying mechanisms guiding the decision process, including external/internal influences, organizational structure and inertia, and innovative team problem solving. The results from this research contribute to theoretical knowledge in decision-making and cognition, as well as practical knowledge for organizations and policymakers. The broader implications of this research study include a realization that decision tradeoffs vary based on decision contexts, indicating that sector-specific future policy and guidance efforts are needed.
24
Patel, Vinodkumar H. "Chemical kinetic investigation of a commercial batch reactor process." Thesis, Aston University, 1987. http://publications.aston.ac.uk/10185/.
Full textAbstract:
The aim of this investigation was to study the chemical reactions occurring during the batchwise production of a butylated melamine-formaldehyde resin, in order to optimise the efficiency and economics of the batch processes. The batch process models are largely empirical in nature as the reaction mechanism is unknown. The process chemistry and the commercial manufacturing method are described. A small scale system was established in glass and the ability to produce laboratory resins with the required quality was demonstrated, simulating the full scale plant. During further experiments the chemical reactions of methylolation, condensation and butylation were studied. The important process stages were identified and studied separately. The effects of variation of certain process parameters on the chemical reactions were also studied. A published model of methylolation was modified and used to simulate the methylolation stage. A major result of this project was the development of an indirect method for studying the condensation and butylation reactions occurring during the dehydration and acid reaction stages, as direct quantitative methods were not available. A mass balance method was devised for this purpose and used to collect experimental data. The reaction scheme was verified using this data. The reactions stages were simulated using an empirical model. This has revealed new information regarding the mechanism and kinetics of the reactions. Laboratory results were shown to be comparable with plant scale results. This work has improved the understanding of the batch process, which can be used to improve product consistency. Future work has been identified and recommended to produce an optimum process and plant design to reduce the batch time.
25
Okpoko, Egwono Kelvin. "Chemical-looping combustion : investigation of Cu-based oxygen carriers." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/11749.
Full textAbstract:
Chemical looping combustion (CLC) is a process developed to efficiently combust hydrocarbon fuels and at the same time capture CO2 without an additional energy intensive separation unit. CLC is a two-stage process which involves supplying oxygen to the fuel for combustion with an oxygen carrier and the same oxygen carrier is regenerated back to its original state with air in a subsequent reactor, prior to recycling. CLC is potentially economically and financially viable, and depending on the design, a variety of products can be obtained. Hydrogen and syngas are two very important products useful for power generation and intermediates in the chemical industry. This project focuses on studying the CLC process, with issues related to the development of suitable oxygen carriers for complete fuel combustion as well as assessing their performances under different process conditions. A 500 W laboratory-scale fixed-bed reactor was designed and built, and was used to investigate the reaction kinetics and performance of suitable oxygen carriers. Particles composed of 40, 60 and 80 wt.% CuO supported on Al2O3 were prepared by co-precipitation methods with Na2CO3 and NH4OH. Ideal pH conditions ranged between 8.5 – 9.7 and 4.4 – 6.0 for precipitation with Na2CO3 and NH4OH respectively. X-ray diffraction analyses (XRD) revealed the presence of CuO and CuAl2O4, and both species were reducible as observed from the CO/CH4-TPR analysis. The reduction and oxidation kinetics were investigated in a Thermal Gravimetric Analyser (TGA) for particle sizes < 355 μm. Reaction orders with CO, CH4 and O2 were ~ 2, 1.5 and 0.7 respectively and activation energies were in the order O2 > CO > CH4 at T ≤ 700 oC. The reaction mechanism for the reduction and oxidation was investigated, as well as the rate-limiting steps. The reactivities of the Cu-based oxygen carriers over 20 redox cycles were investigated in a TGA and also in a fixed-bed reactor at temperatures ≤ 800 oC. SEM analysis revealed no sign of sintering with the carriers prepared with Na2CO3, but sintering effects were observed with carriers prepared with NH4OH. Overall, the conducted experiments suggest that Cu-based oxygen carriers prepared by co-precipitation are potentially suitable for a CLC system.
26
Hong, Baoyu. "Investigation on chemical steps of thymidylate synthase catalyzed reaction." Diss., University of Iowa, 2007. http://ir.uiowa.edu/etd/125.
Full text
27
Von, Stein Ferdinand. "A chemical investigation of Dendrobium discolor and Senecio madagascariensis." Thesis, Queensland University of Technology, 2002.
Find full text
28
Moore, Peter Nathaniel 1974. "A fundamental investigation of surface-induced skin irritation." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8532.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2002.Includes bibliographical references.
Surfactants frequently come in contact with the skin in the form of personal care products, where they are used to improve the wetting and oil solubilizing qualities of the products. Surfactants are also known to induce skin irritation by damaging the barrier properties of the stratum corneum, the outer layer of the skin, and denaturing proteins in the epidermis and the dermis. The goal of this thesis has been to understand the relationship between the physicochemical properties of surfactant solutions and their skin irritation potential. In vitro tests were developed to measure: (1) the effect of surfactants on the barrier properties of the skin, (2) the concentration of surfactant in the skin, and (3) surfactant-induced protein denaturation, all of which can be related to skin irritation. The physicochemical properties of the surfactant solution, specifically, the concentration of the surfactant monomers (unmicellized surfactant), the composition of the surfactant monomers, and the size and shape of the surfactant micelles, were related to the results of these tests. An in vitro skin irritation test was developed that measures the electrical conductivity of pig skin to quantify the reduction in the barrier properties of the skin, or the skin damage, induced by surfactant solutions. Skin conductivity was found to be directly related to the transdermal water permeability, directly relating the skin conductivity to in vitro skin irritation. Skin conductivity was used to measure the in vitro skin irritation potential of mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant dodecyl hexa(ethylene oxide) (C12E6), and a relationship was observed between the surfactant monomer concentration and
(cont.) the skin conductivity. The in vitro skin irritation test correctly ranked the in vivo irritation potential of three mild commercial soap bars-Dove, Lever 200, and Ivory. In order to understand the relationship between the micelle concentration and the surfactant-induced damage to the skin, a method was developed to measure the penetration of 14C-radiolabeled SDS surfactant into pig skin. It was found that both monomeric and micellar SDS are able to penetrate into the skin, and that the contribution of the micellar SDS to the concentration of SDS in the skin is comparable to the contribution of the monomeric SDS. SDS penetration into the skin was also measured in the presence of poly(ethylene oxide) (PEO), which forms PEO-bound SDS micelles, and C12E6, which forms SDS/C12E6 mixed micelles. In mixtures of PEO-bound and free SDS micelles, the PEO-bound SDS micelles were found not to penetrate into the skin while the free SDS micelles were found to penetrate. Mixing SDS with C12E6 led to a reduction in the penetration of SDS into the skin by reducing the SDS monomer concentration, as well as by reducing, or preventing altogether, the penetration of micellar SDS. The hydrodynamic radii of the free SDS micelles (21 A), the PEO-bound SDS micelles (25 A), and the SDS-C12E6 mixed micelles (24-30 A) were measured using dynamic light scattering. Based on these results, a new model of surfactant penetration into the skin was proposed, in which the penetration of micellar surfactant into the skin is limited by the size of the micelles...
by Peter Nathaniel Moore.
Ph.D.
29
Harding, Jonathon R. (Jonathon Robert). "Investigation of oxidation in nonaqueous lithium-air batteries." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98707.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 161-177).
The demand for clean energy in portable applications is driving the development of high specific energy batteries, which will enable automobiles powered by electricity derived from renewable energy sources such as solar and wind. Lithium-air batteries are a promising avenue for advancing the energy storage capabilities beyond that of current lithium-ion technology. These batteries face a number of challenges which prevent their practical implementation in devices. This thesis explores possible mitigations for two of these challenges: (1) the high charging overpotential and (2) the volatility and poor oxygen conduction of liquid electrolytes in Li-air batteries. In the first part, Vulcan carbon-based electrodes were developed where chemically-synthesized lithium peroxide was included during the electrode preparation process. Variants of these electrodes which further included noble metal catalyst nanoparticles (Au, Pt, and Ru) were also prepared, and Pt and Ru were both demonstrated to begin oxidizing Li₂O₂ 500 mV lower than required for carbon-only or Au-containing electrodes. Using a differential electrochemical mass spectrometer (DEMS) designed and built over the course of this thesis, we showed that Ru-containing electrodes produce oxygen throughout the oxidation of Li₂O₂, while Pt generated both carbon dioxide and oxygen, indicative of electrolyte decomposition. These results served as a foundation for future efforts to develop solid catalysts for the oxidation of Li₂O₂ in Li-air batteries. In the second part, Li-O₂ devices using a solid electrolyte based on poly(ethylene oxide) (PEO) were developed. The discharge performance at room temperature and 60 °C was characterized, with dramatically higher discharge capacity and rate capability achievable at the elevated temperature. DEMS was used to show that the gases evolved during charging in argon were sensitive to the temperature of charging, with additional carbon dioxide observed at and above 50 °C. Finally, the autoxidation of PEO at 60 °C in Li-O₂ environments was studied, where NMR and DEMS measurements showed that the rate of PEO autoxidation increases with increasing applied potential, and that this reaction has a significant impact after only one charging cycle, identifying another condition that must be met for stable and practical Li-air batteries.
by Jonathon R. Harding.
Ph. D.
30
Chung, Elena Yin-Yin. "Investigation of Chemical Looping Oxygen Carriers and Processes for Hydrocarbon Oxidation and Selective Alkane Oxidation to Chemicals." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469182957.
Full text
31
Elliot, Mark. "An investigation of propellant stabiliser degradation products." Thesis, University of the West of Scotland, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259888.
Full textAbstract:
Chemical stabilisers are incorporated into nitrate ester based propellant formulations to react with the initial propellant decomposition products, preventing the onset of autocatalytic deterioration of these energetic constituents. As a result of these interactions the stabiliser forms a number of derivatives. Sources of these propellant stabiliser degradation products are vital for investigating the course of propellant breakdown and for the validation of several established stability tests. Synthetic methodologies have been developed which yield targeted derivatives of diphenylamine via catalysed and uncatalysed nucleophilic aromatic substitutions in conjunction with standard nitrosating techniques. Ethylcentralite, used in double or triple base propellants, reacts depending on stabiliser concentration, to give two distinct groups of degradation products. Those based on the N-ethylaniline nucleus and those based on the parent stabiliser. The derivatives based on N-ethylaniline have been synthesised utilising a variety of synthetic approaches including phase transfer catalysed N-alkylation, while the utility of urea synthesis employing the reaction between anilines and isocyanates has been evaluated as a possible route towards the second group of ethylcentralite propellant stabiliser degradation products. High performance liquid chromatographic techniques have been developed for the quantitative assay of the diphenylamine and ethylcentralite stabiliser derivatives synthesised. Preliminary analysis of different single base propellants, stabilised by diphenylamine, indicate markedly different degrative product profiles for each of the samples studiedFinally an investigation of a resorcinol stabilised model propellant system has provided evidence that 2-nitroresorcinol, 4-nitroresorcinol and lacmosol are propellant stabiliser degradation products of the aforementioned stabiliser
32
Simmons, B. "A shock tube investigation in soot formation." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371060.
Full text
33
Moes, Sebastian. "Investigation into Potential Mosquitocides for Future Development." Thesis, Umeå universitet, Kemiska institutionen, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-150542.
Full text
34
Tamuli, Roktima. "Chemical Investigation of Clerodendrum polycephalum for Anti-Malarial Compounds and its Chemical Diversity with Australian Clerodendrum." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/414921.
Full textAbstract:
The use of indigenous plants by native healers has been in healthcare system for a long time. It is prevalent in many developing countries because of its wide benefits and rising popularity. But less is known about the chemistry behind the medicinal properties of those indigenous plants. Unraveling the knowledge helps develop drugs based on the indigenous plants and understand their mechanisms of the action. Malaria happens to be a vector borne protozoan parasitic disease which has been reported to affect 229 million people in 2019. Use of indigenous plant for treating malaria is widely practiced and this had led to the development of two anti-malarial drugs, artemisinin, and quinine. Clerodendrum polycephalum, also known as ‘egungun eja’ or ‘ewe agbosa’ or ‘aporo’ by different tribes of Nigeria, is used by native healers as an anti-malarial treatment. However, the anti-malarial effect is not well studied and the chemical compounds responsible for its activity is unknown. The understanding of the chemical composition and their antimalarial activities will provide scientific evidence for its traditional application in malaria treatment. This project was a collaborative research between A/Prof Yunjiang Feng at Griffith Institute for Drug Discovery and Prof. Francis B. Adewoyin at Drug Research and Production Unit, Obafemi Awolowo University, and Prof. Alexander B. Odaibo at Department of Zoology, University of Ibadan; mediated by BIO Ventures for Global Health (BVGH). The Nigerian group analysed the crude extract of Clerodendrum polycephalum based on its traditional use; but lack of expertise in natural product chemistry led to this collaboration. The overall objective was to use bioassay as a guide to isolate antimalarial natural products against Plasmodium falciparum 3D7 drug resistant cell lines. Any novel/new compounds will also be targeted by using 1H NMR guided isolation strategy. Knowing the wide distribution of Clerodendrum around the world, several Australian Clerodendrum sp. were investigated by LC-MS to understand the chemical compositions of samples from different geographic locations. The thesis was started with an introduction chapter which included different concepts such as traditional medicine, malaria, Clerodendrum, bioassay guided fractionation, NMR guided isolation and a brief outline of the project. Traditional medicine (TM) was introduced with a detailed description on African traditional medicine (ATM). It then proceeded with a brief discussion on malaria, its causes, and the current treatment. The chapter then provided a detailed description of genus Clerodendrum, its geographical distribution, traditional use and the biological activity of the plant extract and secondary metabolites. The chapter continued with a brief of bioassay guided fractionation. Finally, the chapter ended with a description of NMR guided isolation of compounds with biological activity. Chapter 2 described detailed experimental procedures involved in this project, including isolation and purification of natural products from the plant species. The chapter also detailed the biological assays as well as the spectroscopic data of the pure compounds. Chapter 3 started with an introduction of Clerodendrum polycephalum, then moved on to the bioassay guided isolation which resulted in four pure compounds, including the new clerodane diterpene lactone A. Considering the difficulties in the isolation process due to the presence of large amount of methyl pheophorbide a, the next batch of crude extract was purified using a revised strategy where the fractionation procedure was modified and 1H NMR was utilized to guide the isolation. This resulted in ten compounds, including four new clerodane diterpene lactone (A-D), one new 12,16-Epoxy-11,14,17-trihydroxy-17(15→16)-abeo- 5,8,11,13,15-abietapentaen-7-one, as well as 5 known compounds, namely, acacetin, methyl pheophorbide a, loliolide, bis (2-ethylhexyl) phthalate and 12,16-Epoxy-6,11,14,17- tetrahydroxy-17(15→16)-abeo-5,8,11,13,15-abietapentaen-7-one. The chemical structures were elucidated by comprehensive analysis of 1D-, 2D-NMR and MS spectroscopic data assisted by density functional theory (DFT) calculated NMR and circular dichroism (CD). The in-vitro activity evaluation against P. falciparum 3D7 revealed that methyl pheophorbide a was active with IC50 values of 4.49 M. The compound showed no cytotoxicity against neonatal foreskin fibroblast (NFF) mammalian cells. Our results provided scientific evidence for the traditional use of Clerodendrum polycephalum in malarial treatment. Chapter 4 aims to investigate whether Clerodendrum sp. collected from different geographic location contain similar chemistry. The chapter started with an introduction of Australian Clerodendrum sp., Griffith University’s NatureBank and the use of LC-MS for screening compounds in plant extracts. Fifteen Australian Clerodendrum were extracted and analyzed by LC-MS. Our results suggested that every compound isolated from Clerodendrum polycephalum was detected in the Australian species. Large scale isolation of Nature Bank sample NB020858 yielded verbascoside, diosmetin-5-o-glucuronide, 4-hydroxywogonin-5-oglucuronide and acacetin-5-o-8-hydroxyglucuronide; among these four compounds verbascoside and an analogue of acacetin-5-o-8-hydroxyglucuronide were also detected in the Nigerian plant extract. Based on the results, we conclude that Clerodendrum plant species from Nigeria and Australia contained same classes of compounds, and chemistry can be used as a tool for plant taxonomic identification.Thesis (Masters)
Master of Science (MSc)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text
35
Razi, Javeed. "Investigation of the structure of coal using ultrasonic energy." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28519.
Full textAbstract:
The aim of the research was to find out more about the structure of bituminous coal by studying the rate of mass transfer in coal particles. Previous investigations had shown that small molecules could be trapped in the coal matrix in two different ways. A procedure was developed to keep the various extracts separate from one another.Each of the extracts were analyzed in the following ways: (a) Ultimate analysis; (b) Molecular weight determination; (c) FT-IR spectra; (d) Differential scanning calorimetry; and (e) Thermogravimetric analysis.
In the extraction process the first extraction was simple Soxhlet extraction. The residue from this was irradiated with ultrasonic energy and then re-extracted. The residue of the second extraction was ground to a small size and re-extracted without using ultrasonics. The fourth extraction was on the residue of the third extract, using ultrasonics.
In general the molecular weight of each successive extract increased while the amount of extract decreased. From the chemical analysis and the molecular weights it appears that the successive extracts are, by and large, members of a family of addition polymers. This finding, coupled with the fact that over 60% of the total coal could be extracted by the procedures used, shows that the bulk of this coal does not consist of a cross-linked polymer.
As was shown in previous research the rate of extraction using ultrasonic energy did not rupture and chemical bonds and the extraction rate curve approximated that predicted by Fick's Law, being slightly lower initially and slightly higher later. This work confirmed this. It can be concluded that the only effect of the ultrasonic irradiation was to speed up the relaxation of the glassy coal matrix and release the small molecules so that they could diffuse.
The diffusivities of the molecules being extracted was determined for different sized particles. The apparent diffusivity became smaller as the particle size became smaller. This is the opposite of what would be expected if the molecules were diffusing out of small pores.
To explain this anomalous effect it has been hypothesized that many of the coal molecules are trapped inside a molecular cage or clathrate, which has been formed from fossilized lignin of the original plants.
Some auxiliary experiments were carried out to ascertain the practicability of shattering the coal by soaking the coal particles in a liquid at high pressure and temperature and then suddenly releasing the pressure to let the liquid flash to vapor. The process worked well to produce small coal particles, but there were difficulties in recovering all the coal particles when pyridine was used as the liquid.
36
Mao, Kangyi. "Microstructural investigation of tablet compaction and tablet pharmacological properties." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62108.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
In current tablet manufacturing processes, there is a knowledge gap concerning material transformation and the subsequent impact on tablet properties; this gap presents a barrier to rational formulation / process design. In this study, it was hypothesized that the understanding of tablet microstructure is pivotal in bridging our knowledge about the materials, the manufacturing process, and the tablet properties. A series of X-ray micro computed tomography (microCT) characterization methods were developed to untangle material interactions during tablet manufacturing process, leading to an interpretation of tablet compaction mechanisms through 3-D representation of microstructural features. Numerical simulation of liquid intrusion based on microCT data was utilized in calculating tablet microstructure permeability, introducing a novel parameter for characterization of tablet dissolution properties. A tablet holder was designed and used in combination with paddle dissolution test to investigate tablet dissolution process, enabling the classification of dissolution mechanisms and identification of correspondent formulation design strategies. When incorporated with permeability results, a quantitative dissolution model capable of separating the contributions from disintegration and surface dissolution was derived. The dissection of the dissolution process provides a scientific framework supporting the Quality by Design paradigm for product and process development. . This work provides a strategy for building an integrated formulation design and characterization system incorporating microstructural analysis. It opens up an approach in which microstructure becomes a critical target for design and optimization.
by Kangyi Mao.
Ph.D.
37
Beckham, Gregg Tyler. "A computational investigation of nucleation processes in organic crystals." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42433.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2008.Includes bibliographical references.
Nucleation processes are ubiquitous in nature and technology. For instance, cloud formation in the atmosphere, the casting of metals, protein crystallization, biomineralization, the production of porous materials, and separation of pharmaceutical compounds from solution are a few examples of relevant nucleation processes. One pathway for nucleation to occur is homogeneous nucleation, in which an embryo of a more stable phase forms within an original metastable medium. Homogeneous nucleation is an activated process, meaning that a free energy barrier must be overcome for the transition to take place, and the height of the free energy barrier determines the rate at which the process will occur. Despite considerable advances in both theoretical and experimental techniques to date, determining nucleation mechanisms for real systems remains a considerable technical challenge. The aim of this thesis is therefore to apply molecular simulation techniques to elucidate nucleation mechanisms in organic crystals. Specifically, the newly developed methods of aimless shooting and likelihood maximization are applied for the first time to study nucleation processes in complex and technically relevant systems. The first portion of the thesis examines polymorphism, or the ability of a material to pack in different crystal lattices whilst retaining the same chemical composition. Transformation to a more stable polymorph can readily occur in the solid state, which has broad implications in pharmaceutical processing. To date, over 160 mechanisms have been proposed for polymorph transitions in the solid state, but none have been definitively verified. A model compound, terephthalic acid, is chosen for computational studies because it is similar in size to a small molecule therapeutic and exhibits a common bonding motif for organic crystals. Using aimless shooting and likelihood maximization, the mechanism of the solid state polymorph transformation in terephthalic acid is shown to be comer nucleation. The mechanism shows that for a given nucleus size, the interfacial area between the crystalline domains is minimized, thus reducing the unfavorable surface free energy penalty required for nucleation to occur.
(cont.) Furthermore, based on the results presented, it is anticipated that corner nucleation may be a common mechanism for many polymorph transformations in hydrogen bonded crystalline materials. The second portion of the thesis investigates the mechanism of freezing a subcooled liquid to form a crystal. This phenomenon has widespread application across many technical domains. Similar studies to date on freezing have been limited to model systems, such as Lennard-Jones particles or hard spheres. Benzene is chosen as a model compound. A periodic system is constructed and aimless shooting and likelihood maximization are applied to determine the nature of the critical nucleus. Local order analysis is implemented to distinguish among solid and liquid-like molecules. Preliminary results indicate that the critical nucleus is on the order of 200-300 molecules at 50 K subcooling. This thesis demonstrates that the complementary molecular simulation techniques of aimless shooting and likelihood maximization offer fundamental insight into nucleation mechanisms in molecular crystals. Knowledge of the mechanism from likelihood maximization is essential for accurate free energies and pathway optimization methods, and it should therefore be applied in computational studies of rare events prior to free energy or rate constant calculations. Moreover, these methods provide quantitative understanding of the important physical variables that determine experimentally observable rates and can further aid in experimental design.
by Gregg Tyler Beckham.
Ph.D.
38
Von, Holt Sean Thomas. "An investigation into column flotation of South African coals." Master's thesis, University of Cape Town, 1992. http://hdl.handle.net/11427/21992.
Full textAbstract:
Bibliography: pages 245-254.The high efficiency of separation of fine (typically the -150 μm fraction) particles achievable with column flotation technology is well established. The principal aim of this thesis is to investigate whether column flotation can be used to recover saleable, particularly low-ash quality, coal from South African coal fines which are presently discarded. Samples of thickener underflow fines from the Durnacol, Kleinkopje and Greenside Collieries were used in laboratory column testwork. In addition, on-line column trials were performed at the Kleinkopje Colliery. The effects of co 1 umn operating parameters were established using both one-variable-at-a-time testing and fractional factorial design experiments. An investigation into coal slurry conditioning using oil and oil-water dispersions was also undertaken. The results of laboratory and plant column testwork showed that it was possible to recover the desired quality products from all three of the coal fines samples investigated. For all the coals tested, better grades were obtained at any given yield from column cell flotation than with conventional (batch) froth flotation. The test results also demonstrated that the column cell is best suited to recovering and upgrading the finer (< 75 μm) size fractions. Column performance was found to be strongly affected by the petrographic composition of the coal fines feed, i.e. by coal TYPE. Coals with high vitrinite and, conversely, low inertinite contents were found to be the most easily floatable. Depending on the coal TYPE, the rate of mass transport in either the pulp or froth phase was found to be rate limiting; this in turn dictated which operating parameters affected product yields and grades. Existing methods of conditioning coal slurries were found to be inadequate. Considerable scope for improvement in coal conditioning lies in better choice of collector and "promotor" reagents as well as in designing more energetically efficient conditioning vessels.
39
Abdallah, Suaad Audat. "Investigation of Oxidative DNA Damage from Ionizing Radiation." University of Toledo Health Science Campus / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=mco1349377002.
Full text
40
Endres, Derek. "Numerical Investigation of pulsed chemical vapor deposition of aluminum nitride." Connect to resource, 2010. http://hdl.handle.net/1811/44821.
Full text
41
McOwen, Dennis Wayne. "Investigation of solid fuel conversion in the chemical looping process." Connect to resource, 2010. http://hdl.handle.net/1811/45381.
Full text
42
Chaulk, Steven George. "New chemical approaches for the investigation of RNA structural dynamics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63597.pdf.
Full text
43
Nave, Andy [Verfasser]. "Physico-chemical investigation of plasma induced deposition processes / Andy Nave." Greifswald : Universitätsbibliothek Greifswald, 2017. http://d-nb.info/1141405997/34.
Full text
44
Mitchell, James. "An investigation of the physico-chemical properties of clay suspensions." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.647445.
Full text
45
Phipps, Mark. "A physico-chemical and microcalorimetric investigation of an antibacterial drug." Thesis, University of Kent, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262353.
Full text
46
DENG, LEI. "Investigation of Electric Arc Furnace Chemical Reactions and stirring effect." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-109248.
Full textAbstract:
Chemical energy plays a big role in the process of modern Electric Arc Furnace (EAF). The objective of this study is to compare the results of chemical reaction enthalpies calculated by four different methods. In general, the “PERRY-NIST-JANAF method” is used to calculate the chemical energies. However, this method heavily depend on heat capacities of the substances which have to be deduced from “Perry’s Chemical Engineers’ Handbook” and “NIST-JANAF Thermochemical Tables”, even the calculation process is complicated. Then, some other methods are introduced: Total enthalpy method, HT (High Temperature) enthalpy method and Atomic energy method. In this thesis, the above four methods have been used to calculate the enthalpies of chemical reactions in EAF process. Both of “Total enthalpy method” and “HT enthalpy method” are not complicated, but some basic data are not available. The calculation for chemical reaction enthalpies cannot be completely made by these two methods. “Atomic energy method” is more complicated than “Total enthalpy method” and “HT enthalpy method”, even almost all data are available, but some results of these methods are far from those of the other three methods’. The results show that values of enthalpies obtained by “PERRY-NIST-JANAF method” are more reasonable, though the calculation process is more complicated. In this study, it is also discussed two influencing factors on EAF process: electric power and electromagnetic stirring (EMS).
47
Hance, Glen W. "The chemical and electrochemical investigation of the glassy carbon surface /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487324944215524.
Full text
48
Yeh, Thomas M. "Syngas chemical looping particle production scale up and kinetics investigation /." Connect to resource, 2009. http://hdl.handle.net/1811/36976.
Full text
49
Li, Hang, and n/a. "Chemical investigations of Natural Products from Australian Marine Sponge-Derived Fungi." Griffith University. Eskitis Institute for Cell and Molecular Therapies, 2007. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20081103.091038.
Full textAbstract:
This thesis described the chemical investigations of natural products from Australian marine sponge-derived fungi. Sponge samples were collected from the Great Barrier Reef, Queensland, Australia, by Queensland Museum. The thesis is divided into eight chapters and can be devided into two major parts. The first three chapters comprised the first part of the thesis: Chapter 1 outlined the research background, literature review of marine fungal secondary metabolites; Chapter 2 introduced fungal culture and storage background knowledge, and the list of isolated marine fungal strains. Chapter 3 introduced the background of the thrombin inhibition assay and assay results.
The second part (Chapter 4 to 7) of this thesis is focused on chemical isolation and structure elucidation of secondary metabolites from isolated fungal strains, mostly active strains against thrombin. An unidentified fungal strain, FS-G315858 (T)-Y, isolated from the frozen sponge sample Dysidea sp.1400 produced five peptide compounds (chapter 4, 16-20). Compound 16 is a polypeptide which features the same relative configuration with a known compound unguisine A, and compounds 17-20 are diketopiperazines.
Active fungal strains FS-G315695 (T)-Y and FDPS-61732-YB were isolated from different sponge samples. However, they were identified to be the identical fungal strain Eurotium rubrum; the chemical isolation of FS-G315695 (T)-Y from its mycelia EtOAc extract resulted in three compounds (chapter 5, 17-19). Compounds 18 and 19 were identified to be flavoglaucin and iso-dihydroauroglaucin. Compound 17 was identified to have the same relative configuration with a known compound neo-echinulin A. The chemical isolation of FDPS-61732-YB from its broth EtOAc extract resulted in several diketopiperazines (chapter 5, 27-29).
Another active fungal strain FS-G315695 (T)-WY was identified as Aspergillus ochraceous, the chemical isolation of its mycelia EtOAc extract resulted in one benzodiazepine compound (chapter 6, 18), together with two fatty acids (chapter 6, 16-17). The structure of compound 18 was elucidated and identified to have same relative configuration with the known compound circumdatin E.
Media comparison for active fungal strain FS-G315695 (T)-Y was conducted and this work resulted in producing several neo-echinulin analogues (chapter 7, 1-3). The isolation and structure elucidation of these compounds were reported in chapter 7.
50
Li, Hang. "Chemical investigations of Natural Products from Australian Marine Sponge-Derived Fungi." Thesis, Griffith University, 2007. http://hdl.handle.net/10072/367548.
Full textAbstract:
This thesis described the chemical investigations of natural products from Australian marine sponge-derived fungi. Sponge samples were collected from the Great Barrier Reef, Queensland, Australia, by Queensland Museum. The thesis is divided into eight chapters and can be devided into two major parts. The first three chapters comprised the first part of the thesis: Chapter 1 outlined the research background, literature review of marine fungal secondary metabolites; Chapter 2 introduced fungal culture and storage background knowledge, and the list of isolated marine fungal strains. Chapter 3 introduced the background of the thrombin inhibition assay and assay results.
The second part (Chapter 4 to 7) of this thesis is focused on chemical isolation and structure elucidation of secondary metabolites from isolated fungal strains, mostly active strains against thrombin. An unidentified fungal strain, FS-G315858 (T)-Y, isolated from the frozen sponge sample Dysidea sp.1400 produced five peptide compounds (chapter 4, 16-20). Compound 16 is a polypeptide which features the same relative configuration with a known compound unguisine A, and compounds 17-20 are diketopiperazines.
Active fungal strains FS-G315695 (T)-Y and FDPS-61732-YB were isolated from different sponge samples. However, they were identified to be the identical fungal strain Eurotium rubrum; the chemical isolation of FS-G315695 (T)-Y from its mycelia EtOAc extract resulted in three compounds (chapter 5, 17-19). Compounds 18 and 19 were identified to be flavoglaucin and iso-dihydroauroglaucin. Compound 17 was identified to have the same relative configuration with a known compound neo-echinulin A. The chemical isolation of FDPS-61732-YB from its broth EtOAc extract resulted in several diketopiperazines (chapter 5, 27-29).
Another active fungal strain FS-G315695 (T)-WY was identified as Aspergillus ochraceous, the chemical isolation of its mycelia EtOAc extract resulted in one benzodiazepine compound (chapter 6, 18), together with two fatty acids (chapter 6, 16-17). The structure of compound 18 was elucidated and identified to have same relative configuration with the known compound circumdatin E.
Media comparison for active fungal strain FS-G315695 (T)-Y was conducted and this work resulted in producing several neo-echinulin analogues (chapter 7, 1-3). The isolation and structure elucidation of these compounds were reported in chapter 7.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Eskitis Institute for Cell and Molecular Therapies
Full Text