• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 380
  • 191
  • 56
  • 49
  • 22
  • 13
  • 13
  • 7
  • 4
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • Tagged with
  • 874
  • 178
  • 81
  • 69
  • 64
  • 59
  • 54
  • 52
  • 51
  • 51
  • 47
  • 47
  • 41
  • 40
  • 38
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
631

Chemické modifikace hydrogelů z přírodního polysacharidu / Chemical modifications of hydrogels from natural polysaccharide

Poštulková, Hana January 2014 (has links)
V teoretické části práce by shrnuty chemické a fyzikální vlastnosti, chemická struktura a využití přírodního polysacharidu gum karaya. Hlavním cíle diplomové práce byla alkalická modifikace původní nerozpustné gum karayi na rozpustný produkt, který může být v budoucnu využit pro další aplikace například v medicíně. Nerozpustnost gum karayi je způsobena přítomností acetylových skupin a vícemocných iontů ve struktuře polysacharidu. Byly zkoumány optimální podmínky pro modifikační proces. Pro modifikaci byl použit hydroxid sodný, draselný nebo amonný a čas modifikace od 1 minuty po 24 hodin pro roztok originální gum karayi s koncentrací od 0,1 do 3 %. Pro určení chemického složení originálního a modifikovaných vzorků byla využita FTIR. Bylo prokázáno, že vzorky A2, B1 - 7, C1 - 8 a E1 - 2 byly zcela deacetylovány, protože pás pro acetylovou skupinu nebyl v FTIR spektrech pozorován. Odstranění acetylových skupin alkalickou modifikací bylo taktéž potvrzeno 13C CP MAS NMR. Pomocí XRD byl prokázán amorfní charakter originálního vzorku. Množství vlhkosti a teplotní stabilita vzorků byly zkoumána pomocí TGA. Bylo zjištěno, že termální stability originální gum karayi je vyšší než u modifikovaných vzorků. Termální stabilita modifikovaných vzorků byla ovlivněna reakčními parametry. Entalpické změny vzorků byly studovány pomocí DSC, nicméně nebyly pozorovány žádné významné rozdíly mezi modifikovanými vzorky a originální gum karayou. Prvkové složení bylo určeno pomocí ICP-OES a byla potvrzena přítomnost vápníku, draslíku a hořčíku ve struktuře polysacharidu. Molekulová hmotnost modifikovaných vzorků byla měřena pomocí GPC a byla stanovena na 8 milionů g·mol-1. Reologické měření roztoků gum karayi bylo provedeno pro určení lineární viskoelastické oblasti. Dále byl sledován efekt NaCl na viskozitu originálního vzorku. Viskozita klesala s vyšším množstvím NaCl. Pokles viskozity originálního vzorku je způsoben výměnou vápenatých iontů za sodné, což vede k uvolnění fyzikálně vázané struktury a tím k vyšší rozpustnosti vzorku ve vodě.
632

Bioinformatický nástroj pro predikci rozpustnosti proteinů / Bioinformatics Tool for Prediction of Protein Solubility

Hronský, Patrik January 2016 (has links)
This master's thesis addresses the solubility of recombinant proteins and its prediction. It describes the subject of protein synthesis, as well as the process of recombinant protein creation. Recombinant protein synthesis is of great importance for example to pharmacologic industry. This synthesis is not a simple task and it does not always produce viable proteins. Protein solubility is an important factor, determining the viability of the resulting proteins. It is of course favourable for companies, that take part in recombinant protein synthesis, to focus their effort and their resources on proteins, that will be viable in the end. In this regard, bioinformatics is of great help, as it is capable, with the help of machine learning, of predicting the solubility of proteins, for example based on their sequences. This thesis introduces the reader to the basic principles of machine learning and presents several machine learning methods, used in the field of protein solubility prediction. It deals with the definition of a dataset, which is later used to test selected predictors, as well as to train the ensemble predictor, which is the main focus of this thesis. It also focuses on several specific protein solubility predictors and explains the basic principles upon which they are built, as well as the results of their testing. In the end, it presents the ensemble predictor of protein solubility.
633

Hustotní a elektrostatické vlastnosti vody a jejich využití v termodynamice vodných specií a rozpustnosti minerálů za vysokých teplot a tlaků / Volumetric and electrostatic properties of water and their application to aqueous thermodynamics and mineral solubility at high temperatures and pressures

Hanková, Barbora January 2018 (has links)
Hydrothermal fluids are important mass and heat transfer agents in the Earth's crust and mantle. Aside from their transport role, the aqueous fluids act as reactants or products in rock environment during diverse processes ranging from partial melting, magmatic and metamorphic devolatilization. This study evaluates the effect of equations of state and thermodynamic data for aqueous species on prediction of mineral solubility in aqueous fluids at high temperatures and pressures employing the Helgeson-Kirkham-Flowers model (HKF). These calculations require: (i) volumetric properties of water; (ii) dielectric properties of water; (iii) aqueous species thermodynamic properties. A comparison of ten equations of state against the IAPWS scientific standard reveals that volumetric properties of water up to 1200 řC and 50 kbar are predicted within 5 %, except at low pressure (below 2 kbar), temperatures higher than 1000 řC, and the liquid-vapor equilibrium curve, particularly in the proximity of the critical point of water. The deviations of volumetric and electrostatic properties of water propagate into the mineral solubility calculations. For quartz and corundum these deviations lead to discrepancy in mineral solubility of up to half an order of magnitude for molal concentrations. These discrepancies...
634

Etude de la cristallisation d’une nouvelle molécule à efficacité cardiotonique dans un mélange liquide ionique - eau / Crystallization study of a new cardiotonic drug in an ionic liquid–water mixture

Resende de Azevedo, Jacqueline 25 March 2014 (has links)
La cristallisation par effet anti-solvant, comme technique de production de micro/nanoparticules, présente certains inconvénients. En effet, pour des molécules nouvellement synthétisées ou découvertes, comme le LASSBio-294, les solubilités dans l'eau et dans les solvants organiques sont faibles ce qui limite l'application de cette opération. L'utilisation de solvants alternatifs ouvre de nouvelles perspectives de recristallisation de ce type de molécules. Dans ce travail, nous nous sommes intéressés à la cristallisation du LASSBio-294 en utilisant un liquide ionique comme solvant. Ce sont des sels organiques fondus à température ambiante, qui ont la particularité d’avoir une tension de vapeur nulle. Ils constituent une nouvelle classe de solvants non volatiles et ininflammables qui présentent des propriétés originales. Dans un premier temps, des liquides ioniques (LIs) dérivés du cation imidazolium ont été utilisés comme solvant alternatif. La solubilité a été mesurée dans 5 LIs,dans l’eau et dans des mélanges eau/LI. Dans l’eau pure la solubilité est très faible (5 ppm). En revanche, dans certains LIs, elle est supérieure à 200 mg/g solution. Les résultats de solubilité dans des mélanges eau/LI ont permis de choisir le rapport eau/LI pour l’obtention d’un bon rendement en solide. En complément, une étude de la stabilité du solide en suspension a été menée dans différents systèmes aqueux. Cette étude a montré sa possible hydrolyse. Dans un deuxième temps, la recristallisation a été réalisée avec le 1-éthyl-3-méthylimidazolium méthyl phosphonate [emim][CH3O(H)PO2] comme solvant et l’eau comme anti-solvant. Deux approches sont présentées en vue de favoriser le mélange : l'utilisation de dispositifs de mélange et l'introduction des ultrasons pendant le processus de cristallisation. L’influence de paramètres tels que le rapport anti-solvant/solvant, la concentration initiale et la présence d'additifs a été étudiée. Les solides formés puis séchés en étuve ont été caractérisés par granulométrie laser, microscopie électronique à balayage, diffractométrie de rayons X, calorimétrie différentielle à balayage et test de dissolution. Malgré une diminution de la taille des particules élémentaires, l'état d'agglomération des cristaux obtenus n'a pas permis une augmentation de la vitesse de dissolution. En modifiant le mode de séchage (séchage par atomisation), cette agglomération est réduite et la dissolution améliorée. De plus, la présence d'un polymère entérique en solution lors du séchage par atomisation des cristaux synthétisés a eu un effet notable sur la structure des agglomérats formés. Ces derniers peuvent se désagréger, se disperser et se dissoudre rapidement. / The anti-solvent crystallization allows obtaining micro/nanoparticles, but it presents some disadvantages. In the case of new pharmaceutical molecules, as the LASSBio-294, the solubility in water or organic solvents is very low limiting the application of this operation. The use of Ionic Liquids (ILs) as alternative solvents opens new perspectives in pharmaceutical processing through anti-solvent crystallization process. Unlike conventional solvents, ILs are entirely composed of ions. ILs are organic salts, usually liquid at room temperature, and which are composed of a relatively large asymmetric organic cation and of an inorganic or organic anion. ILs derived from imidazolium cation are used as alternative solvents for this drug, water being used as anti-solvent. First, the solubility is measured in 5 ILs, in water and in water/IL mixtures. In pure water, the solubility is very low (5 ppm). However, for some ILs, it is greater than 200 mg/g solution. The results of solubility in water/IL mixtures permit to choose a water/IL ratio leading to a good solid theoretical yield. Then recrystallization is performed with 1-ethyl-3-methylimidazolium methyl phosphonate [emim][CH3O(H)PO2] as the preferred solvent. Antisolvent crystallization represents a class of process characterized by the mixing between a solution and an antisolvent to produce solid particles. The influence of solvent/anti-solvent ratio, initial concentration, and additives is studied. The solids formed and dried in an oven are characterized by laser granulometry, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, and dissolution test. Despite the decrease of elementary particles size, the agglomeration state of particles does not permit to improve the dissolution rate. The agglomeration is reduced and the dissolution improved by modifying the drying process (spray drying). Moreover, the presence of an enteric polymer during the spray drying process has a significant impact on the structure of the formed agglomerates. These are disaggregated, dispersed and dissolved very quickly.
635

Incremento da solubilidade e da cinética de dissolução do fármaco Efavirenz através da obtenção de misturas binárias amorfas com matrizes poliméricas / Improving the solubility and dissolution kinetics of the Efavirenz drug through formation of amorphous binary mixtures with polymeric matrixes / Amélioration de la solubilité et de la cinétique de dissolution de l'Efavirenz par des mélanges binaires amorphes Efavirenz-polymère

Maciel Lavra, Zênia Maria 12 September 2016 (has links)
L’amélioration de la solubilité des principes actifs peu solubles est devenue l’un des principaux challenges de l’industrie pharmaceutique. Bien que présentant une structure chimique potentiellement idéale pour interagir avec la cible, elles échouent dans l’efficacité in vivo : après administration, elles ne peuvent se dissoudre dans les milieux aqueux biologiques et par conséquent ne peuvent être transportées sur leur site d’action pour atteindre la concentration efficace, amenant à un échec thérapeutique. De nombreuses stratégies très intéressantes ont été proposées pour surmonter ce sérieux obstacle. Les dispersions solides sont étudiées depuis plus de 40 ans et ont conduit à de très nombreuses publications mais jusqu’à aujourd’hui peu de produits ont été commercialisés principalement pour des raisons de stabilité physico-chimique. Celles-ci ont pour but de présenter le principe actif sous sa forme amorphe car cette forme solide présente un état d’énergie plus élevé et par conséquent une solubilisation facilitée. Par ailleurs, le système doit rester stable durant le stockage, ainsi la recristallisation ou tout autre changement entraînant une modification du profil de libération doivent être évités. Différentes techniques de production peuvent être utilisées pour préparer les dispersions solides comme l’extrusion à chaud ou l’atomisation-séchage. Le principal objectif de ce travail a été d’améliorer la solubilité de l’Efavirenz (EFV), un principe actif peu soluble dans l’eau, par sa dispersion dans une matrice polymère en utilisant la technique d’atomisation-séchage. Différents polymères ont été utilisés : Soluplus®, PVPVA64 et HPMCAS. Des mélanges binaires EFV-polymère (Soluplus®, PVPVA64 et HPMCAS) ont été générées et caractérisées. Les techniques de caractérisation utilisées ont été la calorimétrique différentielle modulée, la diffraction des rayons X, l’analyse Raman et la spectroscopie infrarouge à transformée de Fourier et l’analyse de sorption de vapeur pour la caractérisation physicochimique de l’état solide des mélanges binaires. L’étude de caractérisation a été complétée par une étude de solubilité et de dissolution dans différents milieux aqueux ainsi que de stabilité dans différentes conditions de stress de température et humidité relative. Les résultats ont mis en évidence la formation de dispersions solides amorphes avec les trois polymères utilisés. Les différents profils de libération obtenus à partir des mélanges binaires générés dans ce travail montrent l’influence du type de polymère, de la concentration du principe actif dans les dispersions solides et de la composition du milieu de dissolution sur la fonctionnalité des produits (solubilité, dissolution). / Poor aqueous solubility has become a property of numerous new drug candidates causing major concern. Despite a potentially ideal chemical structure allowing for interaction with the target, these substances fail to be effective in vivo: upon administration, they cannot dissolve sufficiently in the aqueous fluids of the body and, thus, cannot be transported to their site of action to reach therapeutically effective concentrations. Various interesting strategies have been proposed to overcome this crucial hurdle. Solid dispersions have been studied for more than 40 years and lead to numerous interesting research articles. However, today, only a few products have reached the market principally due to problems with the physico-chemical stability. The idea is to transform the crystalline raw material into a physical state having a greater energy in order to increase the driving force for drug dissolution. At the same time, the system should be stable during long term storage, thus, re-crystallization or other system changes, resulting in altered drug release rates, must be avoided. Different manufacturing techniques can be used to prepare such polymeric systems, including hot-melt extrusion and spray-drying. The main objective of this work has been to improve Efavirenz (EFV) solubility by forming solid dispersions using the spray-drying technique. In this study EFV has been incorporated into hydrophilic polymeric matrices Soluplus®, PVPVA64 and HPMCAS to increase its aqueous solubility. Binary mixtures EFV-Soluplus®, EFV-PVPVA64 and EFV-HPMCAS) were produced and characterized using SEM, X-ray diffraction, DSC, RAMAN, Infrared spectroscopy and water vapor sorption. This physicochemical characterization was completed by solubility and in vitro dissolution studies at different stress conditions (temperature, RH). The results obtained confirmed the formation of amorphous solid dispersions for all studied drug-polymer combinations. The different kinetic profiles obtained from the various solid dispersions generated in this work showed the influence of the type and polymer and drug-polymer binary mixture composition and in vitro dissolution medium on the functionality of spray-dried solid dispersions produced in this work (solubility and dissolution kinetics).
636

Development of synthetic methodology for non-symmetric fullerene dimers

Barnå, Fredrik January 2019 (has links)
This bachelor thesis covers the initial development of a synthesis of fullerene dimers using two different types of linking reactions. Different setups for [3+2] cycloadditions to fullerenes (Prato reaction) were tested, and for that purpose, an N-alkylated amino acid was synthesised. Hydroarylation of fullerene using Rh-catalysis was also studied, using both MIDA protected and unprotected boronic acids, as well as by using cycloaddition products. A range of model compounds in form of fulleropyrrolidenes were synthesised. Products were puried with HPLC and analysed with MALDI-MS and 1H NMR. A range of new compounds were synthesised and characterisation of them was begun. With MALDI-MS, indications that the fullerene dimer had formed were found. Using synthesised model compounds, by-products of the hydroarylation reaction were identied. / Denna kandidatuppsats behandlar påborjandet av syntesutvecklingen för bildandet av fullerendimerer genom användandet av två olika sorters länkningskemi. Olika förhållanden och reagens for [3+2]-cykloaddition till fullerener (Pratoreaktionen) studerades, och i samband med det syntetiserades en N-alkylerad aminosyra. Hydroarylering av fullerener med hjälp utav rodiumkatalys studerades även, genom reaktioner med både skyddade och oskyddade borsyror, inklusive fulleropyrrolidiner. Produkter har renats upp med HPLC och analyserats med MALDI-MS och 1H NMR. En uppsättning nya substanser har syntetiserts, men karaktäriseringen av dessa har inte slutförts. Genom användning av MALDI-MS har indikationer att fullerendimer bildats framkommit. Genom att använda syntetiserade modellsubstanser har biprodukter från hydroaryleringsreaktionen identierats.
637

Exploring the interaction between functional carbohydrate polymers and small-molecule active compounds

Jingfan Chen (6369032) 30 April 2021 (has links)
<p>Naturally occurring carbohydrates polymers and their functional derivatives play important roles in the research and technology development in the food, nutrition, and pharmaceutical areas. A major property of these polymeric materials is to associate, enable, enhance, and/or deliver small-molecule active compound such as phytochemicals, nutraceuticals, and active pharmaceutical ingredients (APIs). The goal of this project was to synthesize and characterize phytoglycogen-based materials and study their structure-function relationships in association with selected small-molecule active compounds, including resveratrol, a food-related poorly water-soluble phenolic compound, griseofulvin, an insoluble API, and CCVJ (9-(2-carboxy-2-cyanovinyl) julolidine) a molecular rotor used as a structural probe of polymeric materials. </p><p>In this study, phytoglycogen (PG) was derivatives to phytoglycogen octenyl succinate (PG-OS), hydroxypropyl phytoglycogen (HPP), and octenylsuccinate hydroxypropyl phytoglycogen (OHPP). PG, HPP, and OHPP were evaluated for their efficacy in improving the solubility and Caco-2 permeation of resveratrol and griseofulvin, and using CCVJ, PG-OS was evaluated on its performance at oil-water interface in comparison with OSA-starch, acacia gum, and sodium caseinate. The results showed that: 1) PG, HPP, and OHPP substantially improved the soluble amount and Caco-2 monolayer permeation of resveratrol and griseofulvin, and anti-fungal efficacy of griseofulvin in the aqueous system were significantly enhanced; suggesting that the active ingredients were effective solubilized and released to become bioavailable, 2) among all PG-based biopolymers, OHPP showed superior performance in solubilizing resveratrol and griseofulvin, and 3) in the oil-water two-layer model system, PG-OS, OSA-starch, acacia gum, and sodium caseinate all affected the transferring of CCVJ from oil to aqueous phase, and the effect was monitored and interpreted by the emission spectra of molecular rotor; in the emulsion system, the emission peak wavelength of CCVJ was correlated with the amount of biopolymer adsorbed at the interface of emulsion droplets, and the molecular rotor-based method can be used to characterize the interfacial adsorption of biopolymer at the interface in oil-in-water emulsion.</p><p>This study provides information on the interactions between phytoglycogen-based biopolymers and poorly water-soluble active ingredients, and may potentially supports the study of new functional ingredients interaction with phytoglycogen-based biopolymers in aqueous system. Furthermore, this work allowed us to advance the use of molecular rotor as new analytical tool to study the physicochemical properties of biopolymer.</p>
638

Élaboration et application d’agents fixateurs de colorants à base de chitosane pour l’industrie papetière / Elaboration of chitosan-based dyes fixing agents for paper applications

Altounian, Anais 18 December 2018 (has links)
Au cours des dernières années, des progrès ont été faits dans le domaine papetier. De plus, le développement de nouveaux matériaux biosourcés a fait l’objet de nombreux sujets de recherche. L’élaboration de fixateurs de colorants alimentaires anioniques à base de chitosane destinés à l’industrie papetière, s’inscrit donc dans ce contexte R & D. Ce projet, proposé par la société Colorey et mené à bien en collaboration avec le laboratoire d’Ingénierie des Matériaux Polymères (IMP, UMR 5223), a consisté en l’utilisation de chitosane (unique polycation naturel) tel quel pour la coloration en surface du papier, ou modifié avec le chlorure de glycidyltriméthylammonium (GTMAC) sous la forme de chitosane quaternarisé (Chi-GTMAC), pour la coloration dans la masse. Ce dernier procédé de coloration requiert un pH neutre ou légèrement alcalin, ce qui est incompatible avec la solubilisation du chitosane, qui nécessite un milieu aqueux acide. C’est pourquoi le Chi-GTMAC, comportant des fonctions triméthylammonium comme charges positives indépendantes du pH, a été mis au point. La stabilité thermique et la solubilité à tout pH de chaque échantillon, ont été évaluées afin de déterminer leur capacité à supporter ou non les températures de séchage du processus papetier, et leur potentiel d’utilisation au sein du pulpeur pour la coloration dans la masse. Puis, l’efficacité de certains dérivés à colorer la pâte et à fixer le colorant a été étudiée à l’aide d’un plan d’expérience. Le chitosane a, quant à lui, été testé en solution aqueuse acide comme agent fixateur pour la coloration de surface du papier préformé / Over the past years, progresses have been achieved in the field of the paper industry. Moreover, the development of biosourced materials has been studied under intense investigations.The elaboration of chitosan-based fixing agents of anionic food dyes intended to paper industry is in line with this R & D context. This project, proposed by the company Colorey and carried out in collaboration with IMP laboratory (UMR 5223), consisted in using chitosan (the only natural polycation) as such for the surface dyeing of paper or, modified with the glycidyltrimethylammonium chloride (GTMAC) as quaternized chitosan (Chi-GTMAC), for the mass dyeing of the pulp. This last process required a neutral or slightly alkaline pH within the pulper, which cannot allow the solubilization of chitosan. Hence, chitosan was derivatized into Chi-GTMAC, bearing trimethylammonium moieties as pH-independent functional groups. The thermal stabilities and the aqueous solubilities as a function of pH of these derivatives were investigated in order to determine whether they could support the drying temperature of the papermaking process or whether they could be used within the pulper for mass coloration. Then, the efficiency of some of the obtained derivatives to color the pulp and to fix dyes was determined thanks to a designed of experiments. Chitosan, for its part, has been tested as fixing agent for surface coloration of paper
639

Investigation of solubility and dissolution of famotidine from solid glass dispersions of xylitol

Mummaneni, Vanaja 01 January 1988 (has links)
The solubility and dissolution of famotidine from solid glass dispersions of xylitol, prepared by the fusion method, were investigated. Preliminary stability studies revealed that famotidine was stable for 72 hours (< 0.5% decomposition) in water at 37° ± 0.5° C. Both the drug and the carrier were stable and did not decompose during the fusion process. About 4% decomposition of famotidine was observed after 72 hours in an aqueous solution of famotidine:xylitol glass dispersion at 37° ± 0.5° C. Solubility of famotidine from solid glass dispersions and physical mixtures with famotidine:xylitol ratios of 1:1, 1:20 and 1:40 was studied at 37° ± 0.5° C and found to be higher than that of famotidine alone in water. The solubility of famotidine from physical mixtures increased linearly with the increase in xylitol concentration, but the relationship was not linear for glass dispersions. The dispersions were more effective in enhancing the solubility of famotidine as compared to physical mixtures of corresponding drug:carrier ratios. A 1:40 glass dispersion increased the solubility by up to 32% while the solubility increase from a 1:40 physical mixture was 14%. Dissolution studies were carried out on glass dispersions with famotidine:xylitol ratios of 1:1, 1:10 and 1:20 in water at 37° ± 0.5° C. Results revealed a marked increase in the dissolution rate of famotidine from solid glass dispersions when compared to the dissolution rate of plain famotidine powder alone. The increase was greatest at the lowest drug level (1:20 drug:carrier ratio) with 100% of the drug dissolving within one minute. The glass dispersions were subjected to thermal analysis. Thermograms obtained by differential scanning calorimetry showed no evidence of chemical interaction between famotidine and xylitol. Phase diagrams were constructed for famotidine:xylitol solid glass dispersions and physical mixtures from melting temperatures determined by the capacity tube method. The phase diagram of the dispersion system suggested the formation of a eutectic mixture of famotidine and xylitol near a drug:carrier ratio of 1:40.
640

Theoretical Prediction of Changes in Protein Structural Stability upon Cosolvent or Salt Addition and Amino-acid Mutation / 共溶媒や塩の添加およびアミノ酸置換に伴う蛋白質立体構造安定性変化の理論的予測

Murakami, Shota 23 March 2017 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第20481号 / エネ博第350号 / 新制||エネ||70(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 木下 正弘, 教授 森井 孝, 教授 片平 正人 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Page generated in 0.0672 seconds