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1.
BIOAEROGELS: PROMISING MATERIALS FOR IMPREGNATION OF DRUGS : diploma thesis dissertation
Jorge Rodríguez Antolín, 2020, diplomsko delo

Opis: The following work examines the possibility of impregnating chosen model drug into bioaerogels to obtain final formulation with added value. The drug used in this study was esomeprazole, used to treat acid-related diseases. In the first part of the work, bioaerogels were prepared. Polysaccharide aerogels are lightweight biocompatible and biodegradable materials, suitable for applications in pharmaceutical industry. For this purpose, three different cores were prepared: pectin, alginate and their mixture, followed by coating with chitosan layer. The production of the bioaerogels follows a sol-gel synthesis and supercritical drying technique. All samples were characterised, and optimisation was performed based on examined properties. Aerogels having a pectin core and chitosan coating showed the highest surface area and the highest adsorption capacity. In the second part, the impregnation of esomeprazole was performed using two different methods: supercritical impregnation and diffusion via sol-gel synthesis. For supercritical impregnation, supercritical carbon dioxide was used as a solvent for impregnation of the drug. In the diffusion method, the model drug was added during sol-gel synthesis using ethanol as solvent. Finally, complete characterisation of prepared formulation followed by drug release studies was performed. The study showed successful impregnation of esomeprazole using either carbon dioxide or ethanol as a solvent. Bioaerogels proved to be promising as carriers for achieving the optimal release of the chosen drug.
Ključne besede: Bioaerogels, polysaccharides, supercritical impregnation, diffusion method, esomeprazole
Objavljeno v DKUM: 09.07.2020; Ogledov: 399; Prenosov: 37
.pdf Celotno besedilo (1,28 MB)

2.
High-Perssure process design for polymer treatment and heat transfer enhancement
Gregor Kravanja, 2018, doktorska disertacija

Opis: The doctoral thesis presents the design of several high-pressure processes involving »green solvents« so-called supercritical fluids for the eco-friendly and sustainable production of new products with special characteristics, fewer toxic residues, and low energy consumption. The thesis is divided into three main parts: polymer processing and formulation of active drugs, measurements of transport properties form pendant drop geometry, and study of heat transfer under supercritical conditions. In the first part, special attention is given to using biodegradable polymers in particle size reduction processes that are related to pharmaceutical applications for controlled drug release. The PGSSTM micronization process was applied to the biodegradable carrier materials polyoxyethylene stearyl ether (Brij 100 and Brij 50) and polyethylene glycol (PEG 4000) for the incorporation of the insoluble drugs nimodipine, fenofibrate, o-vanillin, and esomeprazole with the purpose of improving their bioavailability and dissolution rate. In order to optimize and design micronization process, preliminary transfer and thermodynamic experiments of water-soluble carriers (Brij and PEG)/ SCFs system were carried out. It was observed that a combination of process parameters, including particle size reduction and interactions between drugs and hydrophilic carriers, contributed to enhancing the dissolution rates of precipitated solid particles. In the second part, a new optimized experimental setup based on pendant drop tensiometry was developed and a mathematical model designed to fit the experimental data was used to determine the diffusion coefficients of binary systems at elevated pressures and temperatures. Droplet geometry was examined by using a precise computer algorithm that fits the Young–Laplace equation to the axisymmetric shape of a drop. The experimental procedure was validated by a comparison of the experimental data for the water-CO2 mixture with data from the literature. For the first time, interfacial tension of CO2 saturated solution with propylene glycol and diffusion coefficients of propylene glycol in supercritical CO2 at temperatures of 120°C and 150°C in a pressure range from 5 MPa, up to 17.5 MPa were measured. Additionally, the drop tensiometry method was applied for measuring systems that are of great importance in carbon sequestration related applications. The effect of argon as a co-contaminant in a CO2 stream on the interfacial tension, diffusion coefficients, and storage capacity was studied. In the third part, comprehensive investigation into the heat transfer performance of CO2, ethane and their azeotropic mixture at high pressures and temperatures was studied. A double pipe heat exchanger was developed and set up to study the effects of different operating parameters on heat transfer performance over a wide range of temperatures (25 °C to 90 °C) and pressures (5 MPa to 30 MPa). Heat flux of supercritical fluids was measured in the inner pipe in the counter-current with water in the outer pipe. For the first time, the heat transfer coefficients (HTC) of supercritical CO2, ethane and their azeotropic mixture in water loop have been measured and compared. A brief evaluation is provided of the effect of mass flux, heat flux, pressure, temperature and buoyancy force on heat transfer coefficients. Additionally, to properly evaluate the potential and the performance of azeotropic mixture CO2-ethane, the coefficients of performance (COP) were calculated for the heat pump working cycle and compared to a system containing exclusively CO2.
Ključne besede: supercritical fluids, PGSSTM, formulation of active drugs, biodegradable polymers, transport and thermodynamic data, pendant drop method, carbon sequestration, heat transfer coefficients
Objavljeno v DKUM: 28.05.2018; Ogledov: 1079; Prenosov: 163
.pdf Celotno besedilo (5,51 MB)

3.
Formation, characterization and application of polysaccharide aerogels
Gabrijela Horvat, 2018, doktorska disertacija

Opis: The aim of this PhD dissertation was to describe and analyze the preparation and characterization of polysaccharide aerogels and their future pharmaceutical and medical application. For the research, we used four types of polysaccharides: pectin, alginate, xanthan and guar. We used two types of pectin, high-methoxyl and low-methoxyl pectin, because of their different gelation mechanisms. The first part of the dissertation describes the preparation and characterization of pure polysaccharide aerogels. First, we prepared pectin spherical aerogels, cross-linked with three different ions, and we investigated their final properties. Later, we developed a new method for the preparation of alginate, pectin, xanthan and guar aerogels. We used only ethanol and no other cross-linkers. Ethanol was removed in the later processes of supercritical drying, and the remaining final material was thus only porous polysaccharide. By this method, we were able to prepare pure xanthan and guar aerogels. Prior to this study, xanthan and guar aerogels were prepared only as composites. Pectin aerogels prepared by the new method have amazing properties. On the other hand, alginate aerogels show poor characteristics, and thus the methods need to be optimised. We tried different alginate viscosities, different alcohols (methanol, ethanol, 1-propanol and 1-butanol), and we investigated longer (24h) and shorter (1h) gel setting times. The second part of this dissertation describes the pharmaceutical and medical applications of prepared aerogels. The release of diclofenac sodium from spherical pectin aerogels was investigated in vitro. Calcium cross-linked aerogels were not able to retain the drug, and its release was immediate. In order to achieve controlled release of diclofenac sodium, zinc ions had to be used as cross-linkers. Later, a low water-soluble drug, nifedipine, was used as a model drug for the monolithic aerogels prepared by the new method. The release of nifedipine from pectin and alginate aerogels was highly increased, compared to the crystalline drug. This result is promising for future evaluation of these materials for increasing the bioavailability of poorly water-soluble drugs. Nifedipine release from xanthan and guar aerogels was prolonged up to two weeks. This result reveals a new perspective on such materials for their potential use in medicine as implants and local drug delivery. According to these results, we then developed a new coating material for medical-grade stainless steel from xanthan and pectin. An aerogel coating was loaded with diclofenac sodium and indomethacin, and their release profiles were investigated in vitro. Electrochemical analysis and cell tests proved the safety of such materials for use in medicine. Using aerogel coatings, the drug can be introduced locally into the body; therefore, the need for intravenous, post-operational treatment is greatly reduced.
Ključne besede: polysaccharides, aerogels, supercritical drying, drug carriers
Objavljeno v DKUM: 09.04.2018; Ogledov: 1141; Prenosov: 217
.pdf Celotno besedilo (5,84 MB)

4.
5.
Use of non-conventional cell disruption method for extraction of proteins from black yeasts
Maja Čolnik, Mateja Primožič, Željko Knez, Maja Leitgeb, 2016, izvirni znanstveni članek

Opis: The influence of pressure and treatment time on cells disruption of different black yeasts and on activities of extracted proteins using supercritical carbon dioxide process was studied. The cells of three different black yeasts Phaeotheca triangularis, Trimatostroma salinum, and Wallemia ichthyophaga were exposed to supercritical carbon dioxide (SC $CO_2$) by varying pressure at fixed temperature (35°C). The black yeasts cell walls were disrupted, and the content of the cells was spilled into the liquid medium. The impact of SC $CO_2$ conditions on secretion of enzymes and proteins from black yeast cells suspension was studied. The residual activity of the enzymes cellulase, $beta$-glucosidase, $alpha$-amylase, and protease was studied by enzymatic assay. The viability of black yeast cells was determined by measuring the optical density of the cell suspension at 600 nm. The total protein concentration in the suspension was determined on UV–Vis spectrophotometer at 595 nm. The release of intracellular and extracellular products from black yeast cells was achieved. Also, the observation by an environmental scanning electron microscopy shows major morphological changes with SC $CO_2$-treated cells. The advantages of the proposed method are in a simple use, which is also possible for heat-sensitive materials on one hand and on the other hand integration of the extraction of enzymes and their use in biocatalytical reactions.
Ključne besede: P. triangularis, W. ichtyophaga, T. salinum, supercritical carbon dioxide, enzyme activity, cells
Objavljeno v DKUM: 10.07.2017; Ogledov: 969; Prenosov: 332
.pdf Celotno besedilo (2,13 MB)
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6.
Phase equilibrium measurements and data correlation for the ternary system oleic acid + 1-octanol + carbon dioxide
Chiara Giulia Laudani, Mateja Primožič, Željko Knez, Maja Leitgeb, 2009, izvirni znanstveni članek

Opis: A study of the high-pressure phase equilibria in the ternary system oleic acid/1- octanol/supercritical CO2 was performed to obtain information for optimization of enzymatic synthesis of n-octyl oleate. Equilibrium data were measured at temperatures of 308.15, 323.15 and 343.15 K over a pressure range from 1 to 25 MPa. Two different apparatuses: a Variable Volume View Cell and a Batch Stirred Tank were used employing synthetic and static-analytic measurement methods, respectively. The measured solubility of dense CO2 in the binary liquid mixture oleic acid/1-octanol covered the range from 0.0781 to 0.7686 of CO2 molar fraction. CO2 solubility increased with increasing pressure up to 10 MPa. At higher pressures, no significant increase was observed. The Soave-Redlich-Kwong equation-of-state (SRK-EoS) with quadratic mixing rules was successfully used for data correlation in the whole P-T-x region studied.
Ključne besede: data correlation, 1-octanol, oleic acid, supercritical carbon dioxide, Soave-Redlich-Kwong equation-of-state, vapor-liquid equilibria
Objavljeno v DKUM: 05.07.2017; Ogledov: 890; Prenosov: 81
.pdf Celotno besedilo (3,35 MB)
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7.
OLEORESINI IZ RDEČE PEKOČE PAPRIKE - EKSTRAKCIJA IN UPORABA
Jana Simonovska, 2016, doktorska disertacija

Opis: Pepper (Capsicum annuum L.) as widely distributed vegetable crop in the world is an excellent source of nutritive and biologically active compounds. The characteristic compounds, capsaicinoids and carotenoids, highlight the importance of the red hot pepper varieties and their oleoresin extracts in the food and pharmaceutical industry. In the Ph.D. thesis was studied the possibility for a separate and integral utilization of the red hot pepper for obtaining the oleoresins from pericarp, placenta, seeds and stalk. Pre-treatment of the raw material (drying, separation of anatomical structures i.e. pericarp, placenta and seeds, and determination of theirs physico-chemical characteristics and determination of the he characteristic bioactive compounds: capsaicinoids, carotenoids and volatiles was studied, also. The second part of the Ph.D. thesis was focused of the determination of the optimal conditions for isolation of the bioactive capsaicinoids and coloured compounds, through comparative following of the thermodynamical parameters by application of organic solvents and supercritical fluids. Influence of the working parameters: temperature, time, pressure, solid to liquid phase ratio, density, type of solvents, and particle size of raw material on the yield of extract and content of capsaicinoids, colour compounds and volatiles was studied. Modelling of the experimental phase data by application of mathematical methods was performed. Re-utilization of seed and stalk from red hot pepper in form of extracts for development of new formulations as edible films, biopesticides and nanoemulsions was studied, also.
Ključne besede: red hot pepper, pericarp, placenta, seed, stalk, extraction, sub- and supercritical fluids, bioactive compounds, volatiles, re-utilization, edible films, biopesticides, nanoemulsions
Objavljeno v DKUM: 08.11.2016; Ogledov: 1399; Prenosov: 117
.pdf Celotno besedilo (4,71 MB)

8.
Supercritical fluid chromatography and scale up study
Miha Oman, Petra Kotnik, Mojca Škerget, Željko Knez, 2014, izvirni znanstveni članek

Opis: The influence of process parameters on supercritical fluid chromatography (SFC) and scale-up on to the preparative scale was investigated. In this scope, dependency of pressure, temperature, type and concentration of modifier, and type of stationary phase on the separation were examined separately. Experiments were performed on silica stationary phases in the range of pressures from 100 bar to 250 bar and temperatures from 30°C to 65°C, with use of ethanol and methanol as modifier. Results obtained on analytical scale were used for scale up on preparative (to production) scale. The aim of this study is presentation of the state-of-the-art of SFC through separate effects of process parameters on the separation and investigation of development, benefits and drawbacks of scaling-up process of the SFC.
Ključne besede: supercritical fluids, supercritical fluid chromatograpy, chromatography, scale up study, SFC
Objavljeno v DKUM: 21.12.2015; Ogledov: 1017; Prenosov: 107
.pdf Celotno besedilo (842,20 KB)
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9.
Pressure stability of lipases and their use in different systems
Maja Leitgeb, Željko Knez, 2001, izvirni znanstveni članek

Opis: For the investigation of the solvent impact on the enzymes, lipases from different sources (Pseudomonas fluorescences, Rhizopus javanicus, Rhizopus niveus, Candida rugose and Porcine pancreas) were used. Stability and activity of these lipases in aqueous medium in supercritical $CO_2$ and liquid propane at 100 bar and 40°C were studied. On the basis of previous results lipases were used for their application in two different systems. The application of the polysulphone membrane in the continuous stirred tank membrane reactor was studied on the model system of the hydrolysis of oleyl oleate in propane at high pressure. As a catalyst the Candida rugosa lipase was used. The next utilization of lipases was the use of on silica arerogel self-immobilized lipase from Porcine pancreas as catalyst for esterification reaction in near-critical propane at 40°C and 100 bar.
Ključne besede: chemical processing, supercritical fluids, lipases, enzyme stability, high pressure membrane reactor
Objavljeno v DKUM: 10.07.2015; Ogledov: 985; Prenosov: 140
.pdf Celotno besedilo (608,04 KB)
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10.
Extraction of lutein diesters from tagetes erecta using supercritical $CO_2$ and liquid propane
Mojca Škerget, Miran Bezjak, Katja Makovšek, Željko Knez, 2010, izvirni znanstveni članek

Opis: The efficiency of high pressure extraction of lutein diesters from marigold (Tagetes erecta) flower petals has been investigated. The solvents used for extraction were supercritical carbon dioxide and liquid propane. Operating parameters were 300 bar and 40, 60 and 80 °C for $CO_2$ and 100, 150, 200 bar and 40 and 60 °C for propane, respectively. The influence of process parameterson the total yield of extraction and content of lutein diesters in the extracts was investigated. The results show, that solvent power of propanefor lutein diesters is approximately 3.5 times higher than of $CO_2$. The calculation procedure based on the Fick's second law was applied to determine the diffusivities of lutein diesters during extraction from marigold flower petals for both extraction stages: a constant rate stage followed by a stage of decreasing rate. The mathematical model based on the Fick's second law well described the experimental extraction results.
Ključne besede: lutein diesters, Tagetes errecta, extraction, supercritical $CO_2$, subcritical propane
Objavljeno v DKUM: 10.07.2015; Ogledov: 1026; Prenosov: 65
.pdf Celotno besedilo (156,17 KB)
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