Дисертації з теми "Chemical or enzymatic modification"
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1
Kriek, Marco. "Enzymatic synthesis of complex carbohydrates : approaches to the enzymatic synthesis and chemical modification of oligosaccharides." Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342146.
2
Canela, Xandri Anna. "Chemical and enzymatic valorization of polyols from biomass." Doctoral thesis, Universitat de Lleida, 2016. http://hdl.handle.net/10803/386443.
Анотація:
En les últimes dècades han augmentat els problemes derivats de la sobreproducció i acumulació de residus de la industria, així com els problemes mediambientals i la disminució de fonts de matèries primeres. En aquest sentit, ha incrementant l’interès en reutilitzar-los, per tal de re-valoritzar-los produint productes d’interès, acostant-nos cada cop més al concepte de residu zero.
Un dels majors subproductes de la industria agroalimentària és el conegut amb el terme de biomassa. En aquest treball, ens hem centrat en investigar la re-valorització d’una petita part dels poliols presents en la biomassa, entre ells alguns carbohidrats i el glicerol.En las últimas décadas han aumentado los problemas derivados de la sobreproducción y acumulación de residuos de la industria agroalimentaria, así como los problemas medioambientales y la disminución de fuentes de materias primas. Incrementando así el interés en reutilizarlos, revalorizándolos produciendo productos de interés, acercándonos cada vez más al concepto de residuo cero. Uno de los mayores subproductos de la industria es el conocido con el término de biomasa. En este trabajo, nos hemos centrado en investigar la revalorización de una pequeña parte de los polioles presentes en la biomasa, entre ellos algunos carbohidratos y el glicerol.
In the last decades, problems related with overproduction and industry waste accumulation have increased, causing environmental problems and depletion of raw material sources. Because of that, there has been an increasing interest in the reuse of wastes to prepare valuable products, getting closer to the zero waste concept. Biomass is one of the major agroindustrial by-products. In this work, we were focused on adding-value to a small portion of the polyols present in biomass, including some carbohydrates and glycerol.
3
Scholten, Matthew John. "Enzymatic and chemical modification of fatty acid methyl esters: enzymatic catalysis of methyl linoleate using soybean lipoxygenase and chemical catalysis of methyl oleate Using Hypobromination." Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/735.
Анотація:
Vegetable oils are a cheap and abundant chemical feedstock which can be readily broken down into fatty acid methyl esters (FAMEs) by transesterification using methanol and a base catalyst. These FAMEs contain reactive unsaturated double bonds which can be targeted for modification. In this study, enzymatic and chemical modifications of the unsaturated double bonds of FAMEs are explored with the goal of producing higher value products. Specifically the enzymatic modification of methyl linoleate using soybean lipoxygenase and the chemical modification of methyl oleate using hypobromantion are studied.
4
Gratzer, Paul F. "The effect of chemical modification on the enzymatic degradation of acellular matrix (ACM) processed biomaterials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0019/NQ45752.pdf.
5
Sweeney, Deacon John. "A Computational Tool for Biomolecular Structure Analysis Based On Chemical and Enzymatic Modification of Native Proteins." Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1316440232.
6
Rousseau, Dérick. "Modification of the physical and compositional properties of butter fat-canola oil blends by chemical and enzymatic interesterification." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24424.pdf.
7
Nemoto-Smith, Emi H. "Synthesis of cobalamin analogues using enzymatic and chemical modification methods, and subsequent identification of cobalamin localisation in a variety of organisms." Thesis, University of Kent, 2017. https://kar.kent.ac.uk/61694/.
Анотація:
Cobalamin, also known as vitamin B12, is an essential nutrient for many different organisms including mammals, fish, birds, nematodes, and a variety of bacteria. However, cobalamin is only synthesised by a few bacteria and archaea. Organisms that cannot synthesise cobalamin de novo must obtain it from their diet. In humans, the cobalamin uptake mechanism has been studied in detail, but in many organisms, such as Caenorhabditis elegans, no method of transport has been defined, and their need for cobalamin is recognised by a cobalamin deficiency phenotype. Corrin ring modified fluorescent analogues of cobyric acid and ribose conjugated fluorescent analogues of cobalamin were synthesised in order to follow the uptake and localisation of these corrinoids in a variety of organisms. Both the C5 corrin-ring modified and the ribose conjugated analogues were absorbed by Salmonella enterica, using the B12 uptake system (Btu) and could be converted into active coenzyme forms. The imaging of these fluorescent analogues enabled the identification of the coelomocytes in C. elegans as a possible storage cell for cobalamin. However, the C5 cobyric acid analogue was not recognised which suggests that the C. elegans cobalamin transport mechanism is specific for complete corrinoid molecules. Lepidium sativum, garden cress, was shown to take up both cobalamin analogues from the roots and store it in the vacuoles of the cotyledons in seedlings, even though plants have no cobalamin requirement. In contrast, Arabidopsis thaliana did not transport any of the cobalamin analogues. Cobalamin deficiency has been implicated in impeding disease progression in a number of diseases, such as tuberculosis. The Mycobacterium tuberculosis cobalamin uptake protein, BacA, has only recently been identified, and there is still much to learn about the relationship between M. tuberculosis and cobalamin. Incubations of a cobalamin dependent strain of M. tuberculosis, ΔmetE, with a selection of cobalamin biosynthesis intermediates showed that cobyric acid is the earliest intermediate to be taken up and converted into the cofactor form. The C5 corrin ring modified cobyric acid fluorescent analogue is also capable of rescuing this ΔmetE strain, and is taken up faster than the ribose conjugated cobalamin analogue. Overall, the research outlined in this thesis demonstrates that fluorescent corrinoid analogues can be used to follow the journey of cobalamin in a broad range of different organisms and systems.
8
Baron, Kim L. "Enzymatic and chemical modifications of erythrocyte surface antigens to identify Plasmodium falciparum merozoite binding sites." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/46043.
Анотація:
Malaria is a disease caused by the protozoan parasite Plasmodium where the species that causes the most severe form of malaria in humans is known as Plasmodium falciparum. At least 40% of the global population is at risk of contracting malaria with 627 000 people dying as a result of this disease in 2012. Approximately 90% of all malaria deaths occur in sub-Saharan Africa, where approximately every 30 seconds a young child dies, making malaria the leading cause of death in children under the age of five years old.
The malaria parasite has a complex life cycle utilising both invertebrate and vertebrate hosts across sexual and asexual stages. The erythrocyte invasion stage of the life cycle in the human whereby the invasive merozoite form of the parasite enters the erythrocyte is a central and essential step, and it is during this stage that the clinical symptoms of malaria manifest themselves. Merozoites invade erythrocytes utilising multiple, highly specific receptor-ligand interactions in a series of co-ordinated events. The aim of this study was to better understand the interactions occurring between the merozoite and erythrocyte during invasion by using modern, cutting-edge proteomic techniques. This was done in the hope of laying the foundation for the discovery of new key therapeutic targets for antimalarial drug and vaccine-based strategies, as there is currently no commercially available antimalarial vaccine and no drug to which the parasite has not at least started showing resistance.
In this study healthy human erythrocytes were treated separately with different protein-altering enzymes and chemicals being trypsin, the potent oxidant sodium periodate (NaIO4), the amine cross-linker tris(2-chloroethyl)amine hydrochloride (TCEA) and the thiol cross-linker 1,11-bis(maleimido)triethylene glycol (BM(PEG)3). The resulting erythrocyte protein alterations were visualised as protein band differences on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE), where treated and untreated control erythrocyte ghost protein fingerprints were visually compared to one another. The protein bands showing differences between treated and control samples were in-gel digested using trypsin then sequenced by liquid chromatography tandem mass spectrometry (LC-MS/MS) and identified using proteomics-based software. In this way, the erythrocyte proteins altered by each enzyme/chemical treatment were identified.
Malaria invasion assays were performed where each treatment group of erythrocytes as well as the control erythrocytes were incubated separately with schizont stage malaria parasites for the duration of one complete life cycle. Using fluorescent staining and flow cytometry, the invasion inhibition efficiency for each treatment group was evaluated. By utilising these methods, the identification and the relative importance of the erythrocyte proteins involved in the invasion process were determined. Protein fingerprints of control and treated erythrocyte ghosts were visualised and optimised on SDS PAGE where induced protein band differences were successfully identified by LC-MS/MS. It was found that each treatment altered erythrocyte proteins with changes found in Band 3, actin, phosphoglycerate kinase 1, spectrin alpha, spectrin beta, ankyrin, haemoglobin, Bands 4.1 and 4.2, glycophorin A and stomatin. The invasion assays revealed that TCEA inhibited invasion to the greatest extent as compared to the other treatments, followed by BM(PEG)3 and trypsin. Sodium periodate-treated erythrocytes could not be assessed using the invasion assay due to auto-haemolysis. Band 3, glycophorin A, Band 4.1 and stomatin appear to be of higher relative importance in the invasion process as compared to the other altered erythrocyte proteins. These results confirmed the known roles of spectrin alpha, spectrin beta, glycophorin A, Band 3 and Band 4.1 in invasion, and suggested that ankyrin, Band 4.2 and stomatin may also be involved.
This study highlighted the potential that modern, cutting-edge proteomic techniques provide when applied to previous comparative studies found in older literature, as previously unidentified proteins that can be involved in invasion were revealed.
These results can be used as a foundation in future studies in order to identify new key targets for the development of new antimalarial drug- and vaccine-based strategies, with the hope of preventing the suffering of the millions of malaria-inflicted people worldwide, and ultimately eradicating this deadly disease.Dissertation (MSc)--University of Pretoria, 2014.
tm2015
Pharmacology
MSc
Unrestricted
9
Chooi, Kok Phin. "Synthetic phosphorylation of kinases for functional studies in vitro." Thesis, University of Oxford, 2014. https://ora.ox.ac.uk/objects/uuid:2adc517a-2876-4a0b-8ead-e9bf164ebc6f.
Анотація:
The activity of protein kinases is heavily dependent on the phosphorylation state of the protein. Kinase phosphorylation states have been prepared through biological or enzymatic means for biochemical evaluation, but the use of protein chemical modification as an investigative tool has not been addressed. By chemically reacting a genetically encoded cysteine, phosphocysteine was installed via dehydroalanine as a reactive intermediate. The installed phosphocysteine was intended as a surrogate to the naturally occurring phosphothreonine or phosphoserine of a phosphorylated protein kinase. Two model protein kinases were investigated on: MEK1 and p38α. The development of suitable protein variants and suitable reaction conditions on these two proteins is discussed in turn and in detail, resulting in p38α-pCys180 and MEK1-pCys222. Designed to be mimics of the naturally occurring p38α-pThr180 and MEK1-pSer222, these two chemically modified proteins were studied for their biological function. The core biological studies entailed the determination of enzymatic activity of both modified proteins, and included the necessary controls against their active counterparts. In addition, the studies on p38α-pCys180 also included a more detailed quantification of enzymatic activity, and the behaviour of this modified protein against known inhibitors of p38α was also investigated. Both modified proteins were shown to be enzymatically active and behave similarly to corresponding active species. The adaptation of mass spectrometry methods to handle the majority of project's analytical requirements, from monitoring chemical transformations to following enzyme kinetics was instrumental in making these studies feasible. The details of these technical developments are interwoven into the scientific discussion. Also included in this thesis is an introduction to the mechanism and function of protein kinases, and on the protein chemistry methods employed. The work is concluded with a projection of implications that this protein chemical modification technique has on kinase biomedical research.
10
Simiand, Cécile. "Modifications régio- et stéréosélectives du saccharose." Grenoble 1, 1993. http://www.theses.fr/1993GRE10180.
Анотація:
Les dextrane-saccharases utilisent le saccharose comme glucosyle donneur pour la biosynthese de dextranes. Des saccharoses modifies ont ete synthetises puis testes comme analogues de substrat de ces enzymes. Le 3-oxo-saccharose, obtenu par biooxydation du saccharose, a ete utilise comme compose precurseur pour les modifications en c-3. Les 3-oximino, 3-amino et 3-thio-saccharoses ont ete obtenus avec de bons rendements. La strategie developpee pour les modifications en position c-4 a permis d'obtenir, de facon stereoselective, les 4-amino, 4-thio et 4-fluoro-saccharoses. Des tests enzymatiques en presence de dextrane-saccharases ont mis en evidence le caractere inhibiteur des amino et thio-saccharoses
11
Eid, Georges. "Nouveaux dérivés lipophiles ou amphiphiles de composés phénoliques bio-sourcés à propriétés antioxydantes, anti-inflammatoires et/ ou anti-prolifératives." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0166.
Анотація:
La diminution des ressources pétrochimiques facilement accessibles, suscite, depuis ces dix dernières années, un intérêt croissant pour l'utilisation de matières première d'origine renouvelable. L'industrie de première transformation du bois génère chaque année des volumes importants de déchets qui sont à l'heure actuelle, soit recyclés vers d'autres filières comme la papeterie ou l'industrie des panneaux, soit utilisés comme source d'énergie, et donc vers des marchés de faible valeur ajoutée. Le projet se situe dans ce contexte de développement durable, d'économie circulaire et de valorisation des co-produits de l'industrie du bois par l'exploitation des métabolites secondaires présents dans le bois, comme les composés phénoliques, et plus précisément les flavonoïdes qui présentent en effet un intérêt dans différents domaines en raison de leurs activités biologiques. L'objectif de ce travail est de fonctionnaliser des composés accessibles et abondants afin d'obtenir des composés polyfonctionnels à propriétés 2 en 1 et pouvoir ainsi simplifier les formulations cosmétiques. La fonctionnalisation a été envisagée par deux voies : hémisynthèse chimique et/ou catalyse enzymatique. Par hemisynthèse chimique nous avons pu accéder à des composés bi-modulaires en associant un acide gras et un flavonoïde non glycosylé, en l'occurrence la catéchine. Des acylations directes au niveau des hydroxyles phénoliques de la catéchine ont été étudiées et la régiosélectivité a été demontrée par spectroscopie RMN et confirmée par modélisation moléculaire. Nous avons également préparé des composés tri-modulaires par hémisynthèse chimique en associant différents acides aminés, ainsi que des acides gras de longueur variable à la catéchine. Trois structures trimodulaires différentes ont ainsi été synthétisées, afin d'obtenir différents types de composés. Par hémisynthèse enzymatique nous avons synthétisé des composés tri-modulaires, à partir des flavonoïdes glycosylés, la rutine et la narignine, en visant le greffage d'acides gras de différentes longueurs de chaine mais cette fois ci sur la partie glycosidique des flavonoïdes. Nous avons également synthétisé des composés penta-modulaires issus du greffage d'un acide dicarboxylique sur la naringine ou la rutine. Ces composés comportent deux entités flavonoïdes greffées de part et d'autre de la chaine carbonée du diacide. A l'issue de ces synthèses, les propriétés physico-chimiques des produits ont été étudiées, notamment leur solubilité dans l'eau, leurs propriétés anti-radicalaires mais également les propriétés tensioactives. Certaines activités biologiques ont également été étudiées comme l'activité antiproliférative vis-à-vis de cellules CaCo2. Afin de comprendre l'effet de la structure des composés sur leur capacité antioxydante, des travaux de modélisation moléculaire ont été entrepris ; des corrélations entre l'activité antioxydante des composés déterminée expérimentalement et des descripteurs de réactivité chimique calculés in silico ont été recherchéesThe decrease in easily accessible petrochemical resources has given over the past ten years a growing interest in the use of raw materials of renewable origin. The primary wood processing industry generates large amounts of waste each year which are currently either recycled to other sectors such as paper mills or the panel industry, or used as a source of energy, and therefore to markets with low added value. The project is situated in this context of sustainable development, circular economy and valorization of co-products of the wood industry by the exploitation of secondary metabolites present in wood, such as phenolic compounds, and more precisely flavonoids, which are indeed of interest in various fields because of their biological activities.The objective of this work is to functionalize accessible and abundant compounds in order to obtain polyfunctional compounds with 2-in-1 properties and thus be able to simplify cosmetic formulations. Functionalization has been considered by two routes: chemical hemisynthesis and/or enzymatic catalysis.By chemical hemisynthesis we were able to obtain bi-modular compounds by combining a fatty acid and a non-glycosylated flavonoid, in this case we worked with catechin. Direct acylations on the phenolic hydroxyls of catechin have been studied and the regioselectivity has been demonstrated by NMR spectroscopy and confirmed by molecular modelling. We have also obtained tri-modular compounds by chemical hemisynthesis by combining different amino acids, as well as fatty acids of variable length with catechin. Three different trimodular structures have been synthesized.By enzymatic hemisynthesis we have synthesized tri-modular compounds, from glycosylated flavonoids, rutin and narignin, aiming for the grafting of fatty acids of different chain lengths but this time on the glycosidic part of the flavonoids. We have also synthesized penta-modular compounds resulting from the grafting of a dicarboxylic acid on naringin or rutin. These compounds comprise two flavonoid entities grafted on either side of the carbon chain of the diacid.At the end of these syntheses, the physico-chemical properties of the products were studied, in particular their solubility in water, their anti-radical properties but also the surfactant properties. Some biological activities have also been studied such as antiproliferative activity against CaCo2 cells. In order to understand the effect of the structure of the compounds on their antioxidant capacity, molecular modeling work has been undertaken; correlations between the antioxidant activity of compounds determined experimentally and chemical reactivity descriptors calculated in silico were sought
12
Kutacova, Pavla. "Enzymatic modification of kenaf pulp." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ33973.pdf.
13
Mansfield, Shawn Denton. "Enzymatic modification of Douglas-fir pulp." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ27197.pdf.
14
Dalponte, Luca. "Chemo-enzymatic modification of cyclic peptides." Thesis, University of Aberdeen, 2018. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=239393.
15
Wirth, Petra. "Enzymes en solvants organiques." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37619244x.
16
簫乃志 and Nai-chi Siu. "Enzymatic modification of oat globulin by microbial transglutaminase." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31225147.
17
Siu, Nai-chi. "Enzymatic modification of oat globulin by microbial transglutaminase." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23234507.
18
Withers, Freddie. "Chemical modification of graphene." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/4081.
Анотація:
In this thesis investigations into chemically modified graphene structures are presented. Chemical functionalization of graphene is the chemical attachment of molecules or atoms to the graphene surface via covalent or Van der Waals bonds, this process offers a unique way to tailor the properties of graphene to make it useful for a wide range of device applications. One type of chemical functionalization presented in this thesis is fluorination of graphene which is the covalent attachment of fluorine to the carbon atoms of graphene and the resultant material is fluorographene which is a wide band-gap semiconductor. For low fluorine coverage the low temperature electron transport is through localized states due to the presence of disorder induced sub-gap states. For high fluorine coverage the electron transport can be explained by a lightly doped semiconductor model where transport is through thermal activation across an energy gap between an impurity and conduction bands. On the other hand, at low temperatures the disorder induced sub-gap density of states dominates the electrical properties, and the conduction takes place via hopping through these localized states. In this thesis it is also shown that electron beam irradiation can be used to tune the coverage of fluorine adatoms and therefore control energy gap between the impurity and conduction bands. Futhermore, electron beam irradiation also offers a valuable way to pattern conductive structures in fluorinated graphene \textit{via} the irradiation-induced dissociation of fluorine from the fluorinated graphene. This technique can be extended to the patterning of semiconducting nano-ribbons in fluorinated graphene where the spatial localization of electrons is just a few nm. The second type of chemical functionalization presented in this thesis is the intercalation of few layer graphene with ferric chloride which greatly enhances the electrical conductivity of few layer graphene materials making them the best known transparent conductors.
19
Holding, Finn Peter. "Chemical modification of streptavidin." Thesis, Open University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384989.
20
Cox, Owen. "Chemical modification of polysulfone." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665375.
Анотація:
The research presented herein is concerned with the chemical modification of polysulfone towards the synthesis of a hollow fibre boronic acid fixed carrier membrane system for saccharide separation. Chapter 1 firstly introduces the area of boronic acids as chemosensors, in particular for detecting saccharides. Secondly, membrane separation techniques are discussed focussing on hollow fibre membranes and their synthesis. Chapter 2 discusses the potential of boronic acid fixed carrier hollow fibre membranes for saccharide separation. Three general routes are highlighted to achieve the desired boronic acid appended polymers: electrophilic aromatic substitution, lithiation and functional monomer polymerisation. Chapter 3 describes the various attempts at achieving the target polymer via electrophilic aromatic substitution methodology. Chapter 4 describes the various attempts at achieving the target polymer via lithiation methodology. Chapter 5 investigates the ability to create functional monomers with which functional polymers can be polymerised from. Chapter 6 describes the synthesis and characterisation of the compounds discussed in chapters 3, 4 and 5.
21
Jin, Li. "Chemical modification of polymers." Thesis, Aston University, 1988. http://publications.aston.ac.uk/9706/.
Анотація:
Based on the knowledge of PVC degradation and stabilisation, chemical modifications were imposed on degraded PVC and raw PVC with the aim of obtaining non-migrating additives. The modifications were carried out mainly in the presence of dibutyl maleate (DBM), and the resulting polymer contained dibutyl maleic residues. Such modifications result in a polymer which contain substantive additives which resist migration under aggressive environments. Previous studies have shown that stable nitroxyl radicals function as stabilisers in polymer during processing (e.g. PP, PVC) by deactivating a large number of kinetic chains via a redox process whereby the concentrations of the nitroxyl and its reduced form, the hydroxylamine, fluctuate reciprocally and rhythmically. In order to understand the major reactions involved in such systems, a simulation method was used which resulted in a mathematical model and some rate constants, explaining the kinetic behaviour exhibited by such system. In the process of forming a suitable model, two nonlinear oscillators were proposed, which could be of interest in the study of nonlinear phenomenon because of their chaotic behaviour.
22
Liao, Rongzhen. "Quantum Chemical Cluster Modeling of Enzymatic Reactions." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-43026.
Анотація:
The Quantum chemical cluster approach has been shown to be quite powerful and efficient in the modeling of enzyme active sites and reaction mechanisms. In this thesis, the reaction mechanisms of several enzymes have been investigated using the hybrid density functional B3LYP. The enzymes studied include four dinuclear zinc enzymes, namely dihydroorotase, N-acyl-homoserine lactone hydrolase, RNase Z, and human renal dipeptidase, two trinuclear zinc enzymes, namely phospholipase C and nuclease P1, two tungstoenzymes, namely formaldehyde ferredoxin oxidoreductase and acetylene hydratase, aspartate α-decarboxylase, and mycolic acid cyclopropane synthase. The potential energy profiles for various mechanistic scenarios have been calculated and analyzed. The role of the metal ions as well as important active site residues has been discussed. In the cluster approach, the effects of the parts of the enzyme that are not explicitly included in the model are taken into account using implicit solvation methods. For all six zinc-dependent enzymes studied, the di-zinc bridging hydroxide has been shown to be capable of performing nucleophilic attack on the substrate. In addition, one, two, or even all three zinc ions participate in the stabilization of the negative charge in the transition states and intermediates, thereby lowering the barriers. For the two tungstoenzymes, several different mechanistic scenarios have been considered to identify the energetically most feasible one. For both enzymes, new mechanisms are proposed. Finally, the mechanism of mycolic acid cyclopropane synthase has been shown to be a direct methyl transfer to the substrate double bond, followed by proton transfer to the bicarbonate. From the studies of these enzymes, we demonstrate that density functional calculations are able to solve mechanistic problems related to enzymatic reactions, and a wealth of new insight can be obtained.
23
Qian, Xiangping. "Enzymatic and chemical synthesis of oligosaccharide analogs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0013/NQ60015.pdf.
24
Virden, Jane. "Chemical and enzymatic synthesis of #beta#-lactams." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253475.
25
Lind, Maria E. S. "Quantum Chemical Modeling of Asymmetric Enzymatic Reactions." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-116694.
Анотація:
Computational methods are very useful tools in the study of enzymatic reactions, as they can provide a detailed understanding of reaction mechanisms and the sources of various selectivities. In this thesis, density functional theory has been employed to examine four different enzymes of potential importance for biocatalytic applications. The enzymes considered are limonene epoxide hydrolase, soluble epoxide hydrolase, arylmalonate decarboxylase and phenolic acid decarboxylase. Besides the reaction mechanisms, the enantioselectivities in three of these enzymes have also been investigated in detail. In all studies, quite large quantum chemical cluster models of the active sites have been used. In particular, the models have to account for the chiral environment of the active site in order to reproduce and rationalize the experimentally observed selectivities. For both epoxide hydrolases, the calculated enantioselectivities are in good agreement with experiments. In addition, explanations for the change in stereochemical outcome for the mutants of limonene epoxide hydrolase, and for the observed enantioconvergency in the soluble epoxide hydrolase are presented. The reaction mechanisms of the two decarboxylases are found to involve the formation of an enediolate- or a quinone methide intermediate, supporting thus the main features of the proposed mechanisms in both cases. For arylmalonate decarboxylase, an explanation for the observed enantioselectivity is also presented. In addition to the obtained chemical insights, the results presented in this thesis demonstrate that the quantum chemical cluster approach is indeed a valuable tool in the field of asymmetric biocatalysis.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.
26
McMurray, Brian Thomas. "Chemical and enzymatic synthesis of organosulphur compounds." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359111.
27
Shepherd, S. D. "Chemical and enzymatic synthesis of organosulfur compounds." Thesis, Anglia Ruskin University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396225.
28
Manta, Bianca. "Quantum Chemical Studies of Enzymatic Reaction Mechanisms." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-141321.
Анотація:
Computer modeling of enzymes is a valuable complement to experiments. Quantum chemical studies of enzymatic reactions can provide a detailed description of the reaction mechanism and elucidate the roles of various residues in the active site. Different reaction pathways can be analyzed, and their feasibility be established based on calculated energy barriers. In the present thesis, density functional theory has been used to study the active sites and reaction mechanisms of three different enzymes, cytosine deaminase (CDA) from Escherichia coli, ω-transaminase from Chromobacterium violaceum (Cv-ωTA) and dinitrogenase reductase-activating glycohydrolase (DraG) from Rhodospirillum rubrum. The cluster approach has been employed to design models of the active sites based on available crystal structures. The geometries and energies of transition states and intermediates along various reaction pathways have been calculated, and used to construct the energy graphs of the reactions. In the study of CDA (Paper I), two different tautomers of a histidine residue were considered. The obtained reaction mechanism was found to support the main features of the previously proposed mechanism. The sequence of the events was established, and the residues needed for the proton transfer steps were elucidated. In the study of Cv-ωTA (Paper II and Paper III), two active site models were employed to study the conversion of two different substrates, a hydrophobic amine and an amino acid. Differences and similarities in the reaction mechanisms of the two substrates were established, and the role of an arginine residue in the dual substrate recognition was confirmed. In the study of DraG (Paper IV), two different substrate-binding modes and two different protonation states of an aspartate residue were considered. The coordination of the first-shell ligands and the substrate to the two manganese ions in the active site was characterized, and a possible proton donor in the first step of the proposed reaction mechanism was identified.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.
29
Chandra, Richard P. "Chemo-enzymatic modification of high-kappa kraft pulps with laccase." Diss., Available online, Georgia Institute of Technology, 2005, 2003. http://etd.gatech.edu/theses/available/ipstetd-1011/.
30
Washington, Benny Jr. "Enzymatic modification of synthetic mRNA's and their interaction with proteins." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 1985. http://digitalcommons.auctr.edu/dissertations/1244.
Анотація:
All eukaryotic mRNAs analyzed to date contain, at their 5' end, a cap structure consisting of a reversed 7-methyl guanosine residue linked at the 5' position of the ribose by a triphosphate to the 5'- position of the terminal residue. Since its discovery, the cap structure has been shown to play an important role in the control of initiation of protein synthesis. Further characterization of mRNAs has revealed other unique properties. Its 3' terminus in most eukaryotes is enriched with a sequence of adenylic acid residues called the poly(A) tail. Photoaffinity binding studies, using photoaffinity capped mRNAs and mRNAs polyadenylated with a photoaffinity label translated in a rabbit reticulocyte lysate system, suggest that proteins or initiation factors are associated with both the 5' and 3' ends. The ability for ribosomes to form complexes in a rabbit reticulocyte lysate system was tested by modi fying mRNAs using 8-azido-[32P]GTP and 8-azido-[32P]ATP. The extent of binding was measured by the total amount of photoaffinity label recovered from a 12% SDS-polyacrylamide gel cut into 1 mm stripes and counted in a LS 7000 scintillation counter. Several proteins labeled both at the 5' and 3' ends with the photoaffinity probe appear to be ribonuclear proteins.
31
Tack, Paul A. "Enzymatic production of oligosaccharides in centrifugal fields." Thesis, Aston University, 2001. http://publications.aston.ac.uk/9641/.
Анотація:
The aims of this work have been to identify an enzymatic reaction system suitable to investigate and develop the high-speed centrifuge as a novel reaction system for performing such reactions. The production of galacto-oligosaccharides by the trans-galactosyl activity of the enzyme β-galactosidase on lactose monohydrate was identified as a model enzymatic system to elucidate the principles of this type of process. Galacto-oligosaccharides have attracted considerable commercial interest as food additives which have been shown to be beneficial to the health of the human gastrointestinal tract. The development of a single unit operation capable of controlling the biosynthesis of galacto-oligosaccharides whilst simultaneously separating the enzyme from the reaction products would reduce downstream processing costs. This thesis shows for the first time that by using a combination of (a) immobilised or insolubilised β-galactosidase , (b) a rate-zonal centrifugation technique, and (c) various applied centrifugal fields, that a high-speed centrifuge could be used to control the formation of galacto-oligosaccharides whilst removing the enzyme from the reaction products. By layering a suspension of insolubilised β-galactosidase on top of a lactose monohydrate density gradient and centrifuging, the applied centrifugal fields generated produced sedimentation of the enzyme particles through the substrate. The higher sedimentation rate of the enzyme compared to those of the reaction products allowed for separation to take place. Complete sedimentation, or pelleting of the enzyme permits the possible recovery and re-use. Insolubilisation of the enzyme allowed it to be sedimented through the substrate gradient using much lower applied centrifugal fields than that required to sediment free soluble enzyme and this allowed for less expensive centrifugation equipment to be used. Using free soluble and insolubilised β-galactosidase stirred-batch reactions were performed to investigate the kinetics of lactose monohydrate hydrolysis and galacto-oligosaccharide formation. Based on these results a preliminary mathematical model based on Michaelis-Menten kinetics was produced. It was found that the enzyme insolubilisation process using a chemical cross-linking agent did not affect the process of galacto-oligosaccharide formation. Centrifugation experiments were performed and it was found that by varying the applied centrifugal fields that the yield of galacto-oligosaccharides could be controlled. The higher the applied centrifugal fields the lower the yield of galacto-oligosaccharides. By increasing the applied centrifugal fields the 'contact time' between the sedimenting enzyme and the substrate was reduced, which produced lower yields. A novel technique involving pulsing the insolubilised enzyme through the substrate gradient was developed and this was found to produce higher yields of galacto-oligosaccharide compared to using a single enzyme loading equivalent to the total combined activity of the pulses. Comparison of the galacto-oligosaccharide yields between stirred-batch and centrifugation reactions showed that the applied centrifugal fields did not adversely affect the transgalactosyl activity of the insolubilised enzyme.
32
Breakwell, I. K. "Chemical modification of smectite clays." Thesis, Aston University, 1992. http://publications.aston.ac.uk/9790/.
Анотація:
Today, speciality use organoclays are being developed for an increasingly large number of specific applications. Many of these, including use in cosmetics, polishes, greases and paints, require that the material be free from abrasive impurities so that the product retains a smooth `feel'. The traditional `wet' method preparation of organoclays inherently removes abrasives naturally present in the parent mineral clay, but it is time-consuming and expensive. The primary objective of this thesis was to explore the alternative `dry' method (which is both quicker and cheaper but which provides no refining of the parent clay) as a process, and to examine the nature of the organoclays produced, for the production of a wide range of commercially usable organophilic clays in a facile way. Natural Wyoming bentonite contains two quite different types of silicate surface (that of the clay mineral montmorillonite and that of a quartz impurity) that may interact with the cationic surfactant added in the `dry' process production of organoclays. However, it is oil shale, and not the quartz, that is chiefly responsible for the abrasive nature of the material, although air refinement in combination with the controlled milling of the bentonite as a pretreatment may offer a route to its removal. Ion exchange of Wyoming bentonite with a long chain quaternary ammonium salt using the `dry' process affords a partially exchanged, 69-78%, organoclay, with a monolayer formation of ammonium ions in the interlayer. Excess ion pairs are sorbed on the silicate surfaces of both the clay mineral and the quartz impurity phases. Such surface sorption is enhanced by the presence of very finely divided, super paramagnetic, Fe2O3 or Fe(O)(OH) contaminating the surfaces of the major mineral components. The sorbed material is labile to washing, and induces a measurable shielding of the 29Si nuclei in both clay and quartz phases in the MAS NMR experiment, due to an anisotropic magnetic susceptibility effect. XRD data for humidified samples reveal the interlamellar regions to be strongly hydrophobic, with the by-product sodium chloride being expelled to the external surfaces. Many organic cations will exchange onto a clay. The tetracationic cyclophane, and multipurpose receptor, cyclobis(paraquat-p-phenylene) undergoes ion exchange onto Wyoming bentonite to form a pillared clay with a very regular gallery height. The major plane of the cyclophane is normal to the silicate surfaces, thus allowing the cavity to remain available for complexation. A series of group VI substituted o-dimethoxybenzenes were introduced, and shown to participate in host/guest interactions with the cyclophane. Evidence is given which suggests that the binding of the host structure to a clay substrate offers advantages, not only of transportability and usability but of stability, to the charge-transfer complex which may prove useful in a variety of commercial applications.
33
Schofield, C. "Chemical and enzymatic synthesis of beta-lactam antibiotics." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355775.
34
Georgieva, Polina. "Quantum Chemical Modeling of Enzymatic Methyl Transfer Reactions." Doctoral thesis, Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9695.
35
Hamidi, Nor Hanimah. "Enzymatic depolymerization of lignin by laccases." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/14527/.
Анотація:
More than half of platform petrochemicals are aromatic, whereas the only large-scale, naturally-occurring, renewable source of aromatics is lignin. Chemical depolymerization of lignin requires extreme conditions, and results in extensive destruction of the aromatic rings and/or char formation. By contrast, enzymatic lignin depolymerization occurs under mild conditions with retention of the aromatic nuclei. Therefore, laccase from Agaricus bisporus (LAB) and from Trametes versicolor (LTV) with the mediator, ABTS (2,2'-azino-bis(3 ethyl benzthiazoline-6-sulphonic acid)) were used to depolymerize lignin (sodium Iignosulphonate) under mild reaction conditions with the aim to obtain high concentrations of value-added chemicals. The depolymerization in the presence of LTV was higher than LAB, which resulted from the high catalytic activity of LTV. Lignin degradation resulted in formation of complex product mixtures. Therefore the products were fractionated and analyzed by different analytical techniques including GPC (for preliminary screening), HPLC and GCMS (for product characterization and quantification), and NMR (for fingerprint analysis). Products included guaiacol, vanillin, acetovanillone, vanillic acid, homovanillyl alcohol, phenol, 4- methyl benzaldehyde, catechol, p-toluic acid, 4- hydroxybenzaldehyde, tyrosoI, isovaniIIin, and 3-hydroxy-1-(4-hydroxy-3 -methoxyphenyl) propan-1-one, and the total yield of monomers from lignin was 9.8 % in the presence of LTV. The parameters involved in the depolymerization process were optimized to increase the yield of monomers. The efficiency of laccase mediators was also explored by the use of 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO), 1-hydroxybenzotriazole (HBT), N-hydroxyphthalimide(HPI) and violuric acid (VLA) in the depolymerization of sodium lignosulphonate. However, the catalytic depolymerization in the presence of these mediators was lower than ABTS. In order to improve the solubility of the substrate for the depolymerization process, screening of ionic liquids that are compatible with LAB was deployed in order to find laccase-friendly ionic liquids for further use in lignin depolymerization. The study has found [C4mim] [L-tartrate] as the best ionic liquid tested, that increased the activity of LAB by 90 %. In conclusion, enzymatic depolymerization of lignin offers a greener process than the chemical methods, and also provides a more efficient method to obtain monomers of valuable specialty chemicals under mild reaction conditions.
36
Xiong, Chen. "Enzymatic modification of DNA and RNA 3'-termini for click ligation." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/367127/.
37
Holmes, Richard James. "Chemical modification of activated carbon adsorbents." Thesis, Brunel University, 1991. http://bura.brunel.ac.uk/handle/2438/5378.
Анотація:
Activated carbons have been modif fed using reactive chemicals to produce adsorbents of enhanced hydrophobic character which will also be resistant to surface oxidation that results from exposure to humid air ("ageing"). The intention was that modification would not disrupt the carbon pore structure. The adsorptive properties of the modified carbons have been investigated using probe molecules Including nitrogen, water, hexane, and chloropicrin, and the ageing characteristics of the carbons, and the factors controlling the adsorption of a model hydrophobic vapour from high humidity air have been studied. Directly fluorinated carbons were unstable, probably due to weakly adsorbed fluorine. Treatment of these adsorbents with other chemicals indicated the potential of the technique for Introducing specific functional groups onto the carbon surface. Carbons modified using selective fluorinating reagents (hexafluoropropene and 1,1-difluoroethene) were more hydrophobic, and adsorbed hydrophobic vapours more efficiently from humid air in comparison to controls. These adsorbents aged, but at a reduced rate in comparison to control carbon. Carbons modified using chlorinating reagents (carbonyl chloride and chlorine) and treated with solvents to remove adsorbed reagent and/or reaction products were of improved hydrophobic character, and adsorbed hydrophobic vapours from humid air at least as efficiently as the control samples. More importantly, these carbons offered resistance to ageing effects. A study of the factors controlling the efficiency with which hydrophobic vapours; are adsorbed from humid air revealed that the surface chemistry of the carbon is important, but that under typical conditions of use, filter performance was limited by the rate at which water displaced by the organic vapour could be carried away by the airstream. The results illustrate that filters containing chemically modified activated carbon offer advantages when volatile hydrophobic contaminant vapours are present, and where ageing effects are an important mechanism by which filtration efficiency is degraded.
38
Smith, Edward James. "The chemical modification of nylon 6,6." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405743.
39
Finch, Catherine Vanessa. "Chemical modification of skin mimic systems." Thesis, University of Huddersfield, 2017. http://eprints.hud.ac.uk/id/eprint/34645/.
Анотація:
This thesis investigates the effect of various physical and chemical surface modification methods on the permeation of topically applied pharmaceutical compounds through poly(dimethylsiloxane) (PDMS), a polymer frequently employed as a model barrier in in vitro skin permeation studies. Such studies are essential for safety, risk assessment, and quality control purposes, in addition to assisting in the design and development of efficacious topically applied medicines. The commercial availability, legal status, ease of handling, and the reproducibility of the permeation data associated with polymeric skin mimics renders them an attractive alternative to biological tissue. However, over-predictions of percutaneous absorption observed following the use of such membranes are a significant disadvantage when attempting to obtain quantitative toxicological data. Accordingly, the aims of the work presented in this thesis were to both reduce the permeability of PDMS to pharmaceutical compounds, and to increase correlation between permeation data obtained using the synthetic substitute and data obtained similarly using suitable biological tissue. Primarily, the potential of an air plasma pre-treatment to produce a lamellae-type structure in PDMS, endeavouring to more accurately model the architectural, physical, and chemical properties of the human stratum corneum, was investigated. Reductions in the permeability coefficient of up to 54.4 % were observed, rendering the modified system promising. Correlation analysis revealed an increase in correlation between the data collected using the modified synthetic substitute (R 2 = 0.86) and a selfcollated library of literature-derived epidermal tissue permeability data, relating to eighteen compounds and spanning a range of typical penetrants, compared to similar analysis using data obtained using the native substitute ( R 2 = 0.75), suggesting an increase in the predictive capability. It was hypothesised that an N2 plasma treatment may provide suitable surface functional groups on the PDMS substrate, namely amine groups, for the covalent attachment of biomolecules via an N,N'- dicylohexylcarbodiimide (DCC) coupling reaction, enabling the production of a skin mimic displaying enhanced biorelevance. Therefore, the effect of an N2 plasma pre-treatment on the permeation of a subset of the eighteen compounds investigated. It was found that the N2 plasma pre-treatment was advantageous in terms of offering a greater reduction in permeability, since longer treatment times could be employed i.e. reductions of up to 61.8 % were observed. However, significant surface oxidation was still observed, with only a marginal increase in nitrogen containing functionalities compared with the air plasma analogue i.e. 0.31 %. Furthermore, the treatment did not offer any additional increase in correlation between epidermal-derived data than previously observed. Further chemical methods of biomolecule attachment were pursued for use in the development of a lipidproteinaceous bilayer model, initiated in both cases by surface amination using an alkoxysilane. This was followed by a DCC coupling to an amino acid in the former approach, and use of a glutaraldehyde III linker molecule to attach the same amino acid, namely lysine, in the latter approach. In either case, no further reductions in the permeation of the pharmaceutical compounds tested were observed, with respect to that through plasma treated PDMS. In summary, the air plasma treatment of PDMS was found to be a promising approach to simultaneously reducing the permeability of a silicone skin mimic and increasing correlation with data obtained in similar studies employing biological tissue. Further, the covalent coupling of biomolecules to the surface of PDMS following surface amine group generation, via both plasma and wet chemical methods, appeared not to compromise the integrity the PDMS membranes relating to such applications, rendering the techniques compatible with the production of biorelevant semi-synthetic skin mimics.
40
Erdas, Yonca. "Novel chemical modification of cellulosic substrates." Thesis, University of Manchester, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488431.
Анотація:
Constrained by lack of availability of suitable land the consumption of cotton has leveled off while that of polyester has increased rapidly, the demand for clothes, which are made from cotton is increasing in the highly sophisticated countries. Cotton production is criticised as it is a polluting process and the land could be used for food production in the poor countries. Therefore much attention has been directed towards re-engineering of synthetic fibres aimed at mimicking cotton properties such as breathability, comfort, antistatic and dyeability. Even so world cotton production is still growing slowly; it is expected to increase to 20.1 m tonnes for 2003/04, according to the International Cotton Advisory Committee. It is likely that there will always be a demand for cotton, and more research will be directed to environmentally friendly cotton production, coloration and finishing. Coloration of cotton is carried out by using vat, sulphur, azoic, direct and reactive dyes. Reactive dyes are a very important group of dyestuffs for colouring cotton because of their desirable properties which include unrestricted shade range, ease of application, low cost and good fastness to light, washing and rubbing. When they are applied to cellulose by an exhaustion process, they require relatively high levels of electrolyte (salt) to increase the substantivity of the anionic dyestuff for cellulose and thereby achieve high visual colour yields. Discharge of highly saline effluent is becoming environmentally less acceptable, as increased salinity in rivers upsets the delicate balance of aquatic flora and fauna. Hence some recent developments in cotton dyeing with reactive dyes have focused on reduced salt usage. This thesis evaluates one of the options for low salt cotton reactive dyeing; chemical modification (pre-treatment) of cellulose with cationic agents. This has the effect of eliminating the inherent electrostatic repulsion between the anionic (negative) dye and the fibre, so that the use of electrolyte can either be reduced or eliminated. The (negative) surface charge of cotton was modified to a positive charge by using initially a commercial polymeric cationic fixing agent. The amount of cationic agent applied by an exhaustion technique to a cotton fabric, was quantitatively determined using Congo Red, the method being based on the titration of a known concentration of Congo Red with a solution of the treatment agent. The application of this procedure to determine the exhaustion properties of potential cationic pre-treatment agents for cotton was then studied. The pre-treated cotton was dyed to evaluate the effect of the treatment on both dye exhaustion and fixation under three different sets of dyeing conditions and a comparison was made with untreated cotton dyed conventionally. Lower colour yield, inferior wash and light fastness, shade change, ring dyeing and poor migration (levelness) were obtained on the pre-treated fabric. Therefore, pre-treatment of cotton with polymeric cationic agents was adjudged to be of no further interest. To avoid the technical problems associated with the use of polymeric pre-treatment agents, further modification of cotton was carried out with low molecular weight (monomeric) species. A systematic study of the introduction of different amino groups into cotton, via reaction with a commercially available reactive, water soluble dichlorotriazine agent followed by amination with different amines, was undertaken. Where possible, the characterization of the reaction products was made by using a variety of analytical methods. Once the resulting adducts had been characterised, the dyeing behaviour of reactive dyes on the derived substrate was evaluated. The present study also involved the synthesis and application of other pre-treatment agents, e.g. 2,4-bis(4-sulphophenylamino-)-6-chlorotriazine and dyes with a view to obtaining a better understanding of the causes of the shade changes arising from the use of cationic agents to cotton.
41
Kallitsis, Konstantinos. "Chemical modification of fluorinated electroactive polymers." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0094.
Анотація:
L'électronique organique est une alternative peu coûteuse à l'électronique classique (à base de silicium) qui permet la fabrication de dispositifs flexibles, élargissant le champ d'application de l'électronique au-delà des limites imposées par le silicium. Pour que l'électronique organique trouve des applications plus larges dans le monde réel, trois classes de matériaux doivent être optimisées. Il s’agit des conducteurs, des semi-conducteurs et des diélectriques, qui constituent les trois éléments de tout appareil électronique. Alors que les conducteurs et les semiconducteurs organiques ont attiré une attention particulière au cours des 40 dernières années, la recherche sur des isolants à constante diélectrique élevée et donc de haute performance est en retard. La famille de matériaux isolants organiques ayant la constante diélectrique la plus élevée sont les polymères électroactifs fluorés (FEPS). Les FEPS peuvent être classés en deux groupes différents avec des propriétés électroniques très différentes. Ces groupes sont les ferroélectriques et les férroélectriques relaxeurs. Les polymères ferroélectriques, dont le plus connu est le copolymère P(VDF-TrFE), trouvent des applications dans des dispositifs électroniques tels que les capteurs, les actionneurs, les mémoires non volatiles et les générateurs d'énergie. D'autre part, les polymères relaxeurs-ferroélectriques, dont le système le plus connu est le terpolymère P(VDFTrFE- CTFE), sont des matériaux isolants à haute performance et trouvent, entre autres, une application dans l'électronique comme couches diélectriques, dans des dispositifs tels que les condensateurs, les transistors organiques à effet de champ, les écrans souples et dans des dispositifs de refroidissement électrocaloriques. Bien que les polymères mentionnés ci-dessus soient compatibles avec une grande variété de techniques d’impression, leur compatibilité limitée avec la photolithographie, qui est la méthode de choix pour la production d’électronique à grande échelle, limite leur potentiel de réalisation. L'un des principaux objectifs de cette thèse était de modifier la chimie de ces polymères, de manière à les rendre directement compatibles avec la photolithographie, tout en maintenant leurs propriétés électroniques. Pour ce faire, il a fallu mettre au point une méthode permettant d’introduire des groupes fonctionnels supplémentaires sur les FEP. Cependant, en raison de l’excellente stabilité chimique des polymères fluorés, la mise au point d’un tel procédé était une tâche ardue. Pour contourner cette difficulté, l’idée est d’exploiter l’existence de groupes susceptibles de réagir lors d’une substitution nucléophile sur le squelette du polymère, tout en utilisant des FEPS disponibles dans le commerce. Tout d'abord, des fonctions azotures, connues pour réticuler lors d'une irradiation UV, ont été fixés sur des terpolymères de relaxeur ferroélectrique P(VDF-TrFE-CTFE). Les terpolymères portant ces fonctions ont pu être directement utilisés comme résine photosensible négative dans les procédés de photolithographie classiques et ont conservé une constante diélectrique très élevée. Dans un second temps, pour des raisons de sécurité et de stabilité, une approche plus générale a été développée. Cette approche consiste à greffer des photo-amorceurs de type II (basés sur des arylcétones) sur le relaxeur-ferroélectrique P(VDF-TrFE-CTFE) et le ferroélectrique P(VDF-TrFE). Des polymères exceptionnellement stables ont été obtenus, avec dans certains cas, des propriétés électro-actives bien meilleures que celles des matériaux purs. Ces modifications chimiques nous ont conduits à une étude de cas particulière où des FEP comportant des doubles liaisons (réaction secondaire de la modification chimique) ont montrés une amélioration remarquable des propriétés électro-actives. Cette méthode très simple de fonctionnalisation de FEPs ouvre la voie à de nombreuses avancées dans le domaineOrganic electronics are a low cost alternative to silicon based electronics that nable the fabrication of flexible devices, broadening the scope of electronics beyond the limitations imposed by silicon. For organic electronics to find wider real world applications, three classes of materials have to be optimized. Those classes are conductors, semiconductors and insulators, which are the three building blocks for any electronic device. While organic conductors and semiconductors have attracted significant attention during the past 40 years, research in high dielectric constant and thus high performance insulators is lagging far behind. The class of organic insulating materials with the highest dielectric constant are the Fluorinated Electroactive Polymers (FEPs). FEPs can be categorized in two different groups with vastly different electronic properties. Those groups are the ferroelectrics and the relaxor-ferroelectrics. The ferroelectric polymers, with main representative the copolymer P(VDF-TrFE) find application in electronic devices such as sensors, actuators, non volatile memories and energy generators. On the other hand, relaxorferroelectric polymers, with main representative the P(VDF-TrFE-CTFE) terpolymer are high performance insulating materials and find application in electronics as dielectric layers, in devices such as capacitors, organic field effect transistors, flexible displays and electrocaloric cooling devices amongst others. Although the polymers mentioned above are compatible with a large variety of printing techniques, their limited compatibility with photolithography, which is the method of choice for large throughput electronics production limits their potential of realization. One of the main aims of this thesis was to alter the chemistry of such polymers, in a way that would make them directly compatible with photolithography, while maintaining their desirable electronic properties. To do so, a method allowing the introduction of additional functional groups on FEPs had to be developed. However, due to the excellent chemical stability of fluorinated polymers, developing such a method was a challenging task. The methods developed, use nucleophilic substitution to attach different functional groups on commercially available FEPs by leveraging the existence of groups prone to substitution on the polymer backbone, bypassing the innate chemical stability of such polymers. First, azido groups, known to cross-link upon irradiation with UV light were attached on relaxor ferroelectric P(VDF-TrFE-CTFE) terpolymers. The terpolymers bearing azido groups were directly used as negative photoresists in conventional photolithography process while maintaining a very high dielectric constant. Second, due to safety and stability issues, a more general approach was followed, consisting in grafting type II photoinitiators (based on aryl ketones) on the relaxorferroelectric P(VDF-TrFE-CTFE) and the ferroelectric P(VDF-TrFE) polymers. In those cases exceptionally stable polymers were obtained, with in some cases improved electroactive properties as compared to the pristine materials. These chemistries led us to an extraordinary case study, where FEPs bearing unsaturation were showing remarkable enchancement in electroactive properties. his very simple method of functionalizing FEPS paves the way to many more advances in the field
42
Windle, Claire Louise. "Altering enzyme activities using chemical modification." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/11808/.
Анотація:
In Nature there are twenty proteogenic amino acid ‘building blocks’, from which proteins and enzymes are constructed. These proteogenic amino acids confer activity to enzymes; however there are many instances where the chemistries provided by these ‘building blocks’ are expanded upon. Nature recruits an array of cofactors, post translational modifications and post translationally generated cofactors, all which help to provide function or activity. Until recently the protein engineer was restricted to the use of the twenty proteogenic amino acids, and so access to this increased chemical diversity was highly challenging. In this thesis, chemical modification has been used to insert a variety of non canonical amino acids (ncAAs) throughout the active site of the enzyme N acetylneuraminic acid lyase (NAL). This modification method incorporates ncAAs site specifically into a protein, via a dehydroalanine intermediate and conjugate addition with a thiol compound. Initial work using this method replaced the catalytic lysine at position 165 with the non canonical analogue γ thialysine. It was possible to obtain homogenously modified protein in high yields for detailed kinetic and X ray crystallographic studies, and therefore possible to elucidate the catalytic and structural consequences of this modification. The work to replace Lys165 with a non canonical analogue provided a starting point to expand the incorporation of ncAAs into NAL. A total of thirteen different non canonical side chains were incorporated, individually, at thirteen different positions within the active site of NAL. These modified enzymes were then screened for activity with ten different substrates to determine the effects of ncAA incorporation. It was seen that the ncAAs were well tolerated by the enzyme, as active modified enzymes were produced. By incorporating ncAAs it was possible to alter the substrate specificity of the enzyme. The modified enzyme F190Dpc, containing a dihydroxypropyl cysteine side chain, was found to have an increased activity with an altered substrate, erythrose. This activity was higher than the wild type enzyme with both the altered substrate and the wild type substrate, and the non canonical Dpc side chain outperformed any of the proteogenic amino acids when inserted at the same position in the protein, for the substrate erythrose. This research begins to explore the possibilities of what may be achieved by use of ncAAs. Facile incorporation of ncAAs will allow protein engineers to take inspiration from Nature and expand the chemistries provided by the proteogenic amino acids, hopefully to engineer novel activities or catalysis.
43
Liu, Z. "Insight into chemical reactions : from heterogeneous to enzymatic reactions." Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398116.
44
Gadre, S. R. "Bioactive molecules: chemical and enzymatic approaches to their synthesis." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1993. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3072.
45
Ramos, Luiz Pereira. "Steam pretreatment and enzymatic hydrolysis of Eucalyptus viminalis chips." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7749.
Анотація:
The steam pretreatment of Eucalyptus viminalis chips was characterized. Pretreatment parameters such as steam temperature, residence time, addition of SO$\sb2$ as an acid catalyst, and initial moisture content of the chips were evaluated in order to optimize recovery, fractionation and enzymatic hydrolysis of pretreated materials. In the absence of an acid catalyst, the best pretreatment was obtained at 230$\sp\circ$C for 120 s using chips with a moisture content of 50% (w/w). Pretreatment by steam explosion showed no variation resulting from differences in the initial moisture content of the chips. However, when the substrate was steam-treated without explosion, the initial moisture content of the chips had a significant influence on the recovery yield and the degree of enzymatic hydrolysis. When the chips were impregnated with sulfur dioxide (1% SO$\sb2$, w/w) prior to steaming, milder pretreatment conditions of 210$\sp\circ$C for 50 s were sufficient because of the catalytic action of the SO$\sb2$ gas. SO$\sb2$ catalysis was shown to be particularly beneficial for the steam explosion of green chips. More than 95% of the original cellulose could be hydrolysed to glucose with more than 90% of the original pentosan recovered as xylose in the water-soluble fraction. It appeared that the efficient uptake of the SO$\sb2$ catalyst was dependent on the initial moisture content of the chips. Enzymatic hydrolysis of SO$\sb2$-impregnated, steam-treated E. viminalis was carried out with increasing substrate concentrations and enzyme loadings. Removal of the alkali-soluble lignin had a minor effect on the hydrolysis yield when both the substrate concentration and enzyme loading were calculated in relation to the cellulose content. The mode of action of Trichoderma cellulases was further investigated by looking at changes which occurred in the morphology and fine structure of the cellulosic substrate during hydrolysis. A rapid reduction in fiber length (fragmentation), followed by an almost complete saccharification of cellulose, was observed for several fractions derived from pretreated eucalyptus. A gradual decrease in the degree of polymerisation (DP) of the SO$\sb2$-SEE-WIA/$\rm H\sb2O\sb2$ fraction reflected the high susceptibility of this substrate to hydrolysis. However, when the influence of hydrolysis on the DP of a fully bleached kraft pulp derived from eucalyptus was investigated, there was no noticeable change in the DP distribution of the residue until 24 h of hydrolysis. It seemed that the mode of action of Trichoderma cellulases varied depending on the type of pretreated substrate that was hydrolysed. As hydrolysis resulted in a gradual decrease in both the degree of polymerisation (DP) and the degree of crystallinity of the F-150 fraction, it was apparent that the depolymerisation of this substrate was predominantly due to exoglucanase activity. By contrast, the enzymatic hydrolysis of the FBEP-48 fraction resulted in little change in either the cellulose DP or the degree of crystallinity of the substrate. This suggested a "peeling off" type of mechanism. The susceptibility of the pretreated substrates to enzymatic hydrolysis could not be easily predicted from the differences in their cellulose DP or crystallinity. (Abstract shortened by UMI.)
46
Bond, Stephen P. "Interlamellar modification of smectite clays." Thesis, Aston University, 1991. http://publications.aston.ac.uk/9741/.
Анотація:
Clay minerals, both natural and synthetic, have a wide range of applications. Smectite clays are not true insulators, their slight conductivity has been utilized by the paper industry in the development of mildly conducting paper. In particular, the synthetic hectorite clay, laponite, is employed to produce paper which is used in automated drawing offices where electro graphic printing is common. The primary objective of this thesis was to modify smectite clays, particularly laponite, to achieve enhanced conductivity. The primary objective was more readily achieved if the subsidiary objective of understanding the mechanism of conductivity was defined. The cyclic voltammograms of some cobalt complexes were studied in free solution and as clay modified electrodes to investigate the origin of electroactivity in clay modified electrodes. The electroactivity of clay modified electrodes prepared using our method can be attributed to ion pairs sorbed to the surface of the electrode, in excess of the cationic exchange capacity. However, some new observations were made concerning the co-ordination chemistry of the tri-2-pyridylamine complexes used which needed clarification. The a.c. conductivity of pressed discs of laponite RD was studied over the frequency range 12Hz- 100kHz using three electrode systems namely silver-loaded epoxy resin (paste), stainless-steel and aluminium. The a. c. conductivity of laponite consists of two components, reactive (minor) and ionic (major) which can be observed almost independently by utilizing the different electrode systems. When the temperature is increased the conductivity of laponite increases and the activation energy for conductivity can be calculated. Measurement of the conductivity of thin films of laponite RD in two crystal planes shows a degree of anisotropy in the a.c. conductivity. Powder X-ray diffraction and 119Sn Mossbauer spectroscopy studies have shown that attempts to intercalate some phenyltin compounds into laponite RD under ambient conditions result in the formation of tin(IV) oxide pillars. 119Sn Mossbauer data indicate that the order of effectiveness of conversion to pillars is in the order: Ph3SnCl > (Ph3Sn)2O, Ph2SnCl2 The organic product of the pillaring process was identified by 13C m.a.s.n.m.r. spectroscopy as trapped in the pillared lattice. This pillaring reaction is much more rapid when carried out in Teflon containers in a simple domestic microwave oven. These pillared clays are novel materials since the pillaring is achieved via neutral precursors rather than sacrificial reaction of the exchangeable cation. The pillaring reaction depends on electrophilic attack on the aryl tin bond by Brønsted acid sites within the clay. Two methods of interlamellar modification were identified which lead to enhanced conductivity of laponite, namely ion exchange and tin(IV) oxide pillaring. A monoionic potassium exchanged laponite shows a four fold increase in a.c. conductivity compared to sodium exchanged laponite RD. The increased conductivity is due to the appearence of an ionic component. The conductivity is independent of relative humidity and increases with temperature. Tin(IV) oxide pillared laponite RD samples show a significant increase in conductivity. Samples prepared from Ph2SnCl2 show an increase in excess of an order of magnitude. The conductivity of tin(IV) oxide pillared laponite samples is dominated by an ionic component.
47
Overton, Nigel. "Enzyme catalysed modification of polymers." Thesis, Aston University, 1998. http://publications.aston.ac.uk/9608/.
Анотація:
The aim of this project was to investigate the enzyme catalysed modification of synthetic polymers. It was found that an immobilised lipase from Candida antartica (Novozyme 435) catalysed the selective epoxidation of poly(butadiene) in the presence of hydrogen peroxide and catalytic quantities of acetic acid. The cis and trans double bonds of the backbone were epoxidised in yields of up to 60 % whilst the pendent vinyl groups were untouched. The effect of varying a number of reaction parameters was investigated. These studies suggested that higher yields of epoxide could not be obtained because of the conformational properties of the partially epoxidised polymer. Application of this process to the Baeyer-Villiger reaction of poly(vinyl phenyl ketone) and poly(vinyl methyl ketone) were unsuccessful. The lack of reactivity was found to be a property of the polymer rather than the enzymatic system employed. Attempts to modify hydroxyl containing polymers and polymers bearing active esters close to the polymer backbone were unsuccessful. Steric factors appear to be the most important influence on the outcome of the reactions.
48
Nobes, Geoffrey A. R. "In vitro enzymatic synthesis and degradation of polyhydroxyalkanoates." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37549.
Анотація:
Studies of the use of enzymes to both produce and degrade polyhydroxyalkanotes (PHAs) under in vitro conditions are presented in this thesis. PHAs were produced using a lipase-catalyzed ring-opening polymerization of the corresponding lactones. Poly(3-hydroxybutyrate), PHB, was obtained in up to 89% yield with a degree of polymerization of 3--12. Polymerization of other lactones, including beta-propiolactone, gamma-butyrolactone, and e -caprolactone, also yielded the corresponding polyesters in good yields with degrees of polymerization up to 25. MALDI-TOF mass spectroscopy was used to characterize the polymer products. The growth and kinetics of PHB granules produced in an in vitro polymerization were studied using TEM and CRYO-TEM in conjunction with image analysis. The in vitro reaction was confirmed to be a pseudoemulsion polymerization. The average granule diameter and volume increased with reaction time while the number of granules fell throughout the reaction due to coalescence. Basic kinetic parameters including KM, Vmax, and the rate constants of polymerization were determined and compared to those obtained for the in vivo biosynthesis of poly(3-hydroxybutyrate).With the aim of improved understanding of the mechanism of depolymerase action on water insoluble crystalline PHAs, folded chain lamellar single crystals of PHAs were partially degraded with PHA depolymerases and examined using TEM. Enzymatically degraded single crystals of bacterial PHB were found to be splintered by PHB-depolymerase A from Pseudomonas lemoignei parallel to their long axes into a needle-like morphology. These results support an "edge attack" model for the degradation of PHB single crystals and suggest that PHB-depolymerase A has both endo and exo activity. A further study was performed using single crystals of a number of PHAs which were partially degraded with depolymerases from Pseudomonas lemoignei and examined by TEM. In contrast to previous results with single crystals of bacterial PHB, the predominant effect observed with all crystals was a significant narrowing of the lamellae. This suggests an edge attack mechanism which because of lateral disorder of the crystals (caused by the introduction of valerate or repeat units of opposite stereochemistry) leads to a narrowing of the crystalline lamellae as opposed to the splintering effect previously observed.
49
Cetin, Nihat S. "Surface activation of lignocellulosics by chemical modification." Thesis, Bangor University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298633.
50
Hagan, Andrew Kevin. "The chemical modification of the lantibiotic mersacidin." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496643.
Анотація:
Lantibiotics are antibiotic natural products that are synthesised ribosomally and undergo extensive post-translational modification, resulting in multiple thioether bridges and dehydro amino acids in the mature peptide. One such lantibiotic is mersacldin, which is produced by Bacillus sp. and exhibits extremely promising in vitro and in vivo efficacy versus a number of clinically relevant pathogens, most notably methicillin-resistant Staphylococcus aureus. Mersacidin is believed to function by binding to the bacterial cell wall precursor lipid II, thereby preventing its incorporation into the growing peptidoglycan network.