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Preparation of enantiomers using high pressure technologies
Paul Thorey, 2010, doktorska disertacija

Opis: The study of two different methods of obtaining chiral alcohols is proposed herein. The requirement of the relatively new paradigm of green chemistry associated with clean technologies such as biocatalysis or non-conventional solvents, dense gases, was focused at. Indeed, the two methods of production of chiral alcohols were: - the conversion of acetophenone into (R)-1-phenylethanol in dense gases catalysed by Lactobacillus brevis alcohol dehydrogenase and its coenzyme, NADP/H; - the resolution of (±)-trans-1,2-cyclohexanediol by cocrystal formation with tartaric acid followed by supercritical extraction. In both cases high enantiopurities were achieved (ee>99%).
Ključne besede: High-pressure technologies, enantiomers, green chemistry, R-1-phenylethanol, Lactobacillus brevis, alcohol dehydrogenase, NADP, liquid propane, enzyme deactivation, resolution, trans-1, 2-cyclohexanediol, tartaric acid, cocrystal, supercritical carbon dioxide, extraction, X-ray diffraction, differential scanning calorimetry
Objavljeno: 02.02.2011; Ogledov: 2105; Prenosov: 70
.pdf Celotno besedilo (6,25 MB)

Particle formation using supercritical fluids
Željko Knez, 2006, pregledni znanstveni članek

Opis: Particle formation and the design of solid particles and powdery composites with unique properties is at the moment one of major the developments of supercritical fluid (synonyms: dense gases, dense fluids, high pressure) applications. Conventional well-known processes for the particle-size redistribution of solid materials are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, in recrysfallization processes the product is contaminated with solvent and waste solvent streams are produced. The application of supercritical fluids may overcome the drawbacks of conventional processes, and powders and composites with special characteristics can be produced. Several processes for the formation and design of solid particles using dense gases have been studied intensively. The unique thermodynamic and fluid-dynamic properties of supercritical fluids can also be used for the impregnation of solid particles, for the formation of solid powderous emulsions, particle coatings, e.g. for the formation of solids with unique properties for use in different applications. This review will focus on the fundamentals and on recent advances of particle formation and design processes using supercritical fluids on their applications and the technological advantages and disadvantages of various processes.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno: 31.05.2012; Ogledov: 1404; Prenosov: 35
.pdf Celotno besedilo (514,21 KB)
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Supercritical fluids as solvents for enzymatic reactions
Maja Leitgeb, Mateja Primožič, Željko Knez, 2007, pregledni znanstveni članek

Opis: Enzymes may act in different solvent systems. Water as the solvent in vivo may be replaced partially or mostly with other solvents, such as micro-emulsions, organic solvents, reversed micelles, ionic liquids and supercritical fluids (SCFs).Several types of enzymatic reactions were performed in SCFs. Influence of SCFs on enzyme stability and activity is presented on different examples; on different reaction systems (hydrolysis, transesterification...) and on the use of non-immobilized (Subtilisin carlsberg, Aspergillus niger...) as well as immobilized enzymes. Several types of high-pressure enzymatic reactors (batch-, stirred-tank-, extractive semibatch-, recirculating batch-, semicontinuous flow-, continuous packed-bed-, and continuous-membrane reactors) have been used for the performance of enzymatic reactions. In the studies on stability of biocatalysts in a high-pressure batch-stirred tank reactor changes in biocatalysts activity due to pressurization/depressurization steps were observed. Interesting alternative to overcome this inconvenience is the use of the high-pressure continuous membrane reactors, where just single compression and expansion step is necessary.
Ključne besede: enzymatic reactions, supercritical carbon dioxide, high-pressure, enzyme stability, high-pressure reactors
Objavljeno: 31.05.2012; Ogledov: 1408; Prenosov: 58
.pdf Celotno besedilo (177,49 KB)
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Comparison of the esterification of fructose and palmitic acid in organic solvent and supercritical carbon dioxide
Saša Šabeder, Maja Leitgeb, Željko Knez, 2005, izvirni znanstveni članek

Opis: Sugar fatty acid esters are nonionic surfactants, which are used for personal care products, cosmetic applications, and as emulsifiers for food. In recent years, enzymatic synthesis of sugar fatty acid esters is attracting keen attention as a new manufacturing method for future application. Reaction parameters of lipase-catalyzed synthesis of fructose fatty acid esters in organic solvent were optimized in a batch reactor at atmospheric pressure. Optimum conditions for reaction performed in organic solvent at atmospheric pressure were 10% (wžw of substrates) of lipase from Candida antarctica B, 12.14% (wžw of reaction mixture) of molecular sieves at 60 C, and stirring rate of 600 rpm. Esterification of fructose and palmitic acid was performed insupercritical carbon dioxide with and without addition of cosolvent (organicsolvent) at 60 C. Effect of pressure on enzyme activity was studied.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, esterification, organic solvent, lipase catalysed synthesis, fructose fatty esters, Candida antarctica B, enzyme activity
Objavljeno: 01.06.2012; Ogledov: 1321; Prenosov: 47
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Stability of proteinase from Carica papaya latex in dense gases
Maja Leitgeb, Mateja Primožič, Željko Knez, 2005, izvirni znanstveni članek

Opis: Proteinase from Carica papaya latex was tested on its thermal stability at atmospheric pressure and in supercritical carbon dioxide, near-critical propane and dimethyl-ether. In supercritical carbon dioxide at 300 bar thermalactivation of the examined proteinase was improved in the comparison toatmospheric pressure. In propane and dimethyl-ether (300 bar) activity of the examined proteinase decreased. Influence of compressionžexpansion cycles on residual activity of the same proteinase in supercritical carbon dioxide (300 bar and 50 °C) was studied, as well. Different ways of transition from supercritical to low-pressure-state were used which affected residual activityof the proteinase.Addition of water in the system increased activity of proteinase from C. papaya, which was incubated in supercritical carbon dioxide for 24 h. Optimum amount of water was found to be between 0.5 and 0.7 g/L.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno: 01.06.2012; Ogledov: 1028; Prenosov: 14
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Enzymatic reactions in dense gases
Željko Knez, 2009, pregledni znanstveni članek

Opis: The developments on applications of supercritical fluids as alternative solvents for biocatalytic processes that have taken place over the past two decades have been reviewed. An overview of process parameters influencing enzyme activity and stability, the influence of process parameters on reaction rates and productivity are presented. Applications of various types of reactors for enzymatic reaction in dense fluids, limitations of using enzymes as biocatalyst in supercritical fluids as well as future trends are presented. Main advantages of using dense gases as solvents for biocatalyzed reactions are the tunability of solvent properties and simple down stream processing features that can be readily combined with other unit operations. Although many enzymes are stable in supercritical fluids (SCFs) one should pay considerable attention to finding the correct reaction conditions for each substrate/enzyme/SCF system. One of the persistent problems is the instability and deactivation of enzymes under pressure and temperature. At present the most stable enzymes are hydrolases (lipases and esterases) for which pressure effect is lower than temperature deactivation.
Ključne besede: biocatalysis, supercritical fluids, enzyme bioreactors, heterogeneous biocatalysis
Objavljeno: 01.06.2012; Ogledov: 1361; Prenosov: 68
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The influence of enzymatic treatment on wool fibre properties using PEG-modified proteases
Suzana Jus, Marc Schroeder, Georg M. Gübitz, Elisabeth Heine, Vanja Kokol, 2007, izvirni znanstveni članek

Opis: The main contribution of the presented work was to introduce the use of proteases modified with the soluble polymer polyethylene glycol (PEG) in the bio-finishing process of wool fibres, to target enzyme action to the outerparts of wool fibres, i.e. to avoid the diffusion and consequent destroying of the inner parts of the wool fibre structure, in the case of native proteases using. Different proteolytic enzymes from Bacillus lentus and Bacillus subtilis in native and PEG-modified forms were investigated and their influence on the modification of wool fibres morphology surface, chemical structure, as well as the hydrolysis of wool proteins, the physico-mechanical properties, and the sorption properties of 1:2 metal complex dye during dyeing were studied. SEM images of wool fibres confirmed smoother and cleaner fibre surfaces without fibre damages using PEG-modified proteases. Modified enzyme products have a benefit effect on the wool fibres felting behaviours (14%) in the case when PEG-modified B. lentus is used, without markedly fibre damage expressed by tensile strength and weight loss ofthe fibre. Meanwhile the dye exhaustion showed slower but comparable level of dye uptake at the end of the dyeing.
Ključne besede: volnena vlakna, proteolitski encimi, encimske modifikacije, sorpcija barve, morfologija vlaken, wool fibres, proteolytic enzymes, enzyme modification, felting, dye sorption, protein hydrolysis, XPS-analysis, fibre morphology
Objavljeno: 01.06.2012; Ogledov: 1689; Prenosov: 66
URL Povezava na celotno besedilo

MLC-kinase/phosphatase control of Ca[sup]2+ signal transduction in airway smooth muscles
Aleš Fajmut, Milan Brumen, 2008, izvirni znanstveni članek

Opis: In airway smooth muscles, kinase/phosphatase-dependent phosphorylation and dephosphorylation of the myosin light chain (MLC) have been revealed by many authors as important steps in calcium ▫$(Ca^{2+})$▫ signalling pathway from the variation of ▫$Ca^{2+}$▫ concentration in cytosol to the force development. Here, a theoretical analysis of the control action of MLC-kinase (MLCK) and MLC-phosphatase (MLCP) in ▫$Ca^{2+}$▫ signalling is presented and related to the general control principles of these enzymes, which were previously studied by Reinhart Heinrich and his co-workers. The kinetic scheme of the mathematical model considers interactions among ▫$Ca^{2+}$▫, calmodulin (CaM) and MLCK and the well-known 4-state actomyosin latch bridge model, whereby a link between them is accomplished by the conservation relation of all species of MLCK. The mathematical model predicts the magnitude and velocity of isometric force in smooth muscles upon transient biphasic ▫$Ca^{2+}$▫ signal. The properties of signal transduction in the system such as the signalling time, signal duration and signal amplitude, which are reflected in the properties of force developed, are studied by the principles of the metabolic control theory. The analysis of our model predictions confirms as shown by Reinhart Heinrich and his co-workers that MLCK controls the amplitude of signal more than its duration, whereas MLCP controls both. Finally, the simulations of elevated total content of MLCK, a typical feature of bronchial muscles of asthmatic subjects and spontaneously hypertensive rats as well as potentiation of MLCP catalytic activity, are carried out and are discussed in view of an increase in the force magnitude.
Ključne besede: cells, calcium, calcium oscillations, myosin light chains, enzyme activities, mathematical models
Objavljeno: 07.06.2012; Ogledov: 1171; Prenosov: 9
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Interakcije zdravil z zaviralci angiotenzinske konvertaze
Marjetka Pal, Polonca Ferk, 2012, pregledni znanstveni članek

Opis: V članku predstavljamo pregled potencialno klinično pomembnih interakcij zdravil (DDIs) z zaviralci angiotenzinske konvertaze (ACE). Na osnovi pregleda dveh knjig Stockleyʼs Drug Interactions in dveh preko spleta dostopnih podatkovnih zbirk o DDIs smo opisali več kot deset takih DDIs, razložili njihove mehanizme, opredelili njihov klinični pomen ter navedli možnosti za njihovo preprečevanje oz. ustrezno obravnavo. Večina DDIs z zaviralci ACE je farmakodinamičnih, le nekaj jih je na nivoju farmakokinetike. Največ DDIs z zaviralci ACE se odraža kot prekomerno znižanje krvnega tlaka, hiperkaliemija ali nefrotoksičnost. Dokazali so tudi, da zaviralci ACE zvečajo toksičnost litija in da lahko vplivajo na pojav hudih preobčutljivostnih reakcij pri bolnikih, ki so prejeli parenteralne pripravke železa, ali pri bolnikih, ki sočasno jemljejo alopurinol. Prav tako je zaviralce ACE zaradi njihove lastne hepatotoksičnosti potrebno previdno kombinirati z drugimi hepatoksičnimi zdravili. Zaradi velike porabe zaviralcev ACE je pogostost neželenih učinkov zdravil zaradi DDIs z zaviralci ACE visoka. Ugodno pa je, da lahko v večini primerov teh DDIs ustrezno ukrepamo že s primernim kliničnim in laboratorijskim spremljanjem bolnikov oz. s prilagoditvijo odmerkov sočasno predpisanih zdravil.
Ključne besede: angiotensin-converting enzyme inhibitors, drug-drug interactions, drug-interaction databases
Objavljeno: 10.07.2015; Ogledov: 1005; Prenosov: 30
URL Povezava na celotno besedilo

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