1. Influence of supercritical carbon dioxide on the activity and conformational changes of α-amylase, lipase, and peroxidase in the solid state using white wheat flour as an exampleMilena Ivanović, Željko Knez, Maja Leitgeb, 2023, izvirni znanstveni članek Ključne besede: enzyme inactivation, supercritical carbon dioxide, a-amilaze, lipase, antioxidants, horseradish peroxidase, structural changes, CD spectroscopy
Objavljeno v DKUM: 22.04.2024; Ogledov: 183; Prenosov: 12
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2. P-x,y equilibrium data of the binary systems of 2-propanol, 1-butanol and 2-butanol with carbon dioxide at 313.15 K and 333.15 KDragana Borjan, Maša Knez Marevci, Željko Knez, 2022, izvirni znanstveni članek Opis: The ability to predict the behaviour of high-pressure mixtures of carbon dioxide and alcohol is important for industrial purposes. The equilibrium composition of three binary carbon dioxide-alcohol systems was measured at temperatures of 313.15 K and 333.15 K and at pressures of up to 100 bar for carbon dioxide-2-propanol, up to 160 bar for carbon dioxide-1-butanol and up to 150 bar for carbon dioxide-2-butanol. Different equilibrium compositions of carbon dioxide in alcohols were observed despite their similar molecular weight (M2-propanol = 60.100 g mol−1, M1-butanol = 74.121 g mol−1 and M2-butanol = 74.122 g mol−1) and place in the functional hydroxyl group (first or second carbon molecule). It is assumed that the differences in the phase equilibria are due to different vapor pressures, polarities and solute-solute interactions.
Ključne besede: high-pressure phase equilibrium, carbon dioxide, 2-propanol, 1-butanol, 2-butanol
Objavljeno v DKUM: 17.08.2023; Ogledov: 420; Prenosov: 43
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3. Determination of viscosity, density and interfacial tension of the carbon dioxide–isopropanol, argon–isopropanol, sulphur hexafluoride–isopropanol binary systems at 313.15 K and 333.15 K and at elevated pressuresDragana Borjan, Maja Gračnar, Željko Knez, Maša Knez Marevci, 2022, izvirni znanstveni članek Opis: Viscosity, density, and interfacial tension of three binary systems (carbon dioxide–isopropanol, argon–isopropanol, and sulphur hexafluoride–isopropanol) were measured at temperatures of 313.15 K and 333.15 K and at pressures up to 100 bar for carbon dioxide, and for argon and sulphur hexafluoride up to 500 bar. A vibrating tube densimeter method has been used for density measurements and a variable-volume high-pressure optical view cell with some modifications for the other measurements. The results showed that pressure does not have a high impact on viscosity. Density is found to be a linear function of pressure and temperature and the densities of the investigated binary systems increase with pressure and decrease with temperature. Interfacial tension decreased with the elevated pressure at a constant temperature for all the investigated systems. Accurate prediction of thermodynamic and mass transfer data is fundamental in various engineering and industrial operations to design processes with a higher yield of targeted compounds.
Ključne besede: viscosity, interfacial tension, carbon dioxide, argon, suplhur hexafluoride, isopropanol
Objavljeno v DKUM: 17.08.2023; Ogledov: 358; Prenosov: 44
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4. Hop (Humulus lupulus L.) essential oils and xanthohumol derived from extraction process using solvents of different polarityKatja Bizaj, Mojca Škerget, Iztok Jože Košir, Željko Knez, 2022, izvirni znanstveni članek Opis: This study evaluates the content of essential oils (EOs) and prenylated flavonoid Xanthohumol (XN) in extracts of Slovenian hops, cultivar Aurora, obtained by using fluids of different polarity. It is a continuation of our previous work, investigating the extraction of bitter acids from hops. Extraction was conducted semi-continuously, using sub- and supercritical fluids of different polarity, i.e., carbon dioxide (CO2) and propane as non-polar and dimethyl ether (DME) as the polar solvent. The experiments explored a temperature range between 20 °C and 80 °C and pressures ranging from 50 bar to 150 bar. The content of XN in extracts was analysed using high-performance liquid chromatography and experiments demonstrated the largest concentration of XN was obtained using DME. In order to analyse the EO components in extracts, connected with a distinct odour, the steam distillation of extracts was performed and GC analysis was employed. Hop oil derived from CO2 extracts at specific conditions, had the highest relative concentration of linalool, β-caryophyllene and α-humulene, and oil derived from propane extracts had the highest content of all other five selected components (myrcene, geraniol, farnesene, α-selinene and δ-cadinene). The relative content of the investigated EO components in DME extracts was similar to that in propane extracts.
Ključne besede: hop extract, hop essential oils, flavonoids, carbon dioxide, propane, dimethyl ether
Objavljeno v DKUM: 17.08.2023; Ogledov: 364; Prenosov: 60
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5. Improvements to the quality of underground water by introducing carbon dioxideMojca Poberžnik, Ludvik Trauner, Albrecht Leis, Aleksandra Lobnik, 2008, izvirni znanstveni članek Opis: The presented research work is focused on the development of an innovative way of economically improving the quality of underground water by the application of carbon dioxide.
The basic pilot plant was developed with the idea of applying carbon dioxide in order to maintain the carbonate equilibria in water, pumped from under the ground. The optimal content of this natural component in underground water, used in urban areas for different purposes (e.g. drinking water, heating systems etc), simultaneously prevents corrosion and precipitated mineral deposits. The adaptation of an existing pilot plant started with operational testing and preliminary measurements. An appropriate sensor system for the online monitoring of the tap waterćs heating process measuring parameters such as the temperature, the concentration of dissolved carbon dioxide, the conductivity and the pH value was built in. Different amounts of carbon dioxide were applied during the two experimental stages. The composition of the water was regularly analysed using automatic titration and ionic chromatography. The gas-dosing control in the first phase was volumetric. Due to an observed inaccuracy in the gasdosing system, the volumetric dosing control was replaced with a system for the mass control of the introduced gas. Closing the system was considered to be suitable, as the water composition remained almost constant during the entire experiment. Improvements to the gas-dosing control and the closing of the system were carried out in the final phase of the pilot plant's adaptation. Further measurements were made in different seasons to test the seasonal influences on underground water's composition and the efficiency of the carbon dioxide supply.
Ključne besede: underground water, drinking water quality, pilot plant, carbonate equilibria, carbon dioxide, precipitation, scale
Objavljeno v DKUM: 05.06.2018; Ogledov: 1645; Prenosov: 79
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6. Use of non-conventional cell disruption method for extraction of proteins from black yeastsMaja 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: 1546; Prenosov: 399
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7. Phase equilibrium measurements and data correlation for the ternary system oleic acid + 1-octanol + carbon dioxideChiara 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: 1558; Prenosov: 120
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8. The dynamic pattern of end-tidal carbon dioxide during cardiopulmonary resuscitation - difference between asphyxial cardiac arrest and ventricular fibrillation/pulseless ventricular tachycardia cardiac arrestKatja Lah, Miljenko Križmarić, Štefek Grmec, 2011, izvirni znanstveni članek Opis: Introduction: Partial pressure of end-tidal carbon dioxide (PetCO2) during cardiopulmonary resuscitation (CPR) correlates with cardiac output and consequently has a prognostic value in CPR. In our previous study we confirmed that initial PetCO2 value was significantly higher in asphyxial arrest than in ventricular fibrillation/pulseless ventricular tachycardia (VF/VT) cardiac arrest. In this study we sought to evaluate the pattern of PetCO2 changes in cardiac arrest caused by VF/VT and asphyxial cardiac arrest in patients who were resuscitated according to new 2005 Guidelines.
Methods: The study included two cohorts of patients: cardiac arrest due to asphyxia with initial rhythm asystole or pulseless electrical activity (PEA), and cardiac arrest due to arrhythmia with initial rhythm VF or pulseless VT. PetCO2 was measured for both groups immediately after intubation and repeatedly every minute, both for patients with or without return of spontaneous circulation (ROSC). We compared the dynamic pattern of PetCO2 between groups.
Results: Between June 2006 and June 2009 resuscitation was attempted in 325 patients and in this study we included 51 patients with asphyxial cardiac arrest and 63 patients with VF/VT cardiac arrest. The initial values of PetCO2 were significantly higher in the group with asphyxial cardiac arrest (6.74 +/- 4.22 kPa versus 4.51 +/- 2.47 kPa; P = 0.004). In the group with asphyxial cardiac arrest, the initial values of PetCO2 did not show a significant difference when we compared patients with and without ROSC (6.96 +/- 3.63 kPa versus 5.77 +/- 4.64 kPa; P = 0.313). We confirmed significantly higher initial PetCO2 values for those with ROSC in the group with primary cardiac arrest (4.62 +/- 2.46 kPa versus 3.29 +/- 1.76 kPa; P = 0.041). A significant difference in PetCO2 values for those with and without ROSC was achieved after five minutes of CPR in both groups. In all patients with ROSC the initial PetCO2 was again higher than 1.33 kPa.
Conclusions: The dynamic pattern of PetCO2 values during out-of-hospital CPR showed higher values of PetCO2 in the first two minutes of CPR in asphyxia, and a prognostic value of initial PetCO2 only in primary VF/VT cardiac arrest. A prognostic value of PetCO2 for ROSC was achieved after the fifth minute of CPR in both groups and remained present until final values. This difference seems to be a useful criterion in prehospital diagnostic procedures and attendance of cardiac arrest.
Ključne besede: end-tidal carbon dioxide, ETCO2, cardiopulmonary resuscitation, CPR, asphyxial cardiac arrest, ventricular fibrillation, pulseless ventricular tachycardia, cardiac arrest
Objavljeno v DKUM: 29.06.2017; Ogledov: 1298; Prenosov: 423
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9. Partial pressure of end-tidal carbon dioxide successful predicts cardiopulmonary resuscitation in the field - a prospective observational studyMiran Kolar, Miljenko Križmarić, Petra Klemen, Štefek Grmec, 2008, izvirni znanstveni članek Opis: Introduction: The prognosis among patients who suffer out-of-hospital cardiac arrest is poor. Higher survival rates have been observed only in patients with ventricular fibrillation who were fortunate enough to have basic and advanced life support initiated early after cardiac arrest. The ability to predict outcomes of cardiac arrest would be useful for resuscitation. Changes in expired end-tidal carbon dioxide levels during cardiopulmonary resuscitation may be a useful non-invasive predictor of successful resuscitation and survival from cardiac arrest, and help in the termination of cardiopulmonary resuscitation in the field.
Methods: This is a prospective observational study of 737 cases of victims who suffered sudden out-of-hospital cardiac arrest. The patients were intubated and the measurements of end-tidal carbon dioxide were performed. Data according to the Utstein criteria, demographic information, medical data and partial pressure of end-tidal carbon dioxide (petCO2) values were collected for each patient in cardiac arrest, by the emergency physician. We presumed that an end-tidal carbon dioxide level of 1.9 kPa (14.3 mmHg) or more after 20 minutes of standard advanced cardiac life support would predict restoration of spontaneous circulation (ROSC).
Results: Partial pressure of end-tidal carbon dioxide after 20 minutes of advanced life support averaged 0.92+/- 0.29 kPa (6.9mmHg +/- 2.2 mmHg) in patients who did not have ROSC and 4.36 +/-1.11 kPa (32.8 mmHg +/- 9.1 mmHg) in those who did (p<0,001). End-tidal carbon dioxide values of 1.9 kPa (14.3 mmHg) or less discriminated between the 402 patients with ROSC and 335 patients without ROSC. When a 20-minute end-tidal carbon dioxide value of 1.9 kPa (14.3 mmHg) or less was used as a screening test to predict ROSC, the sensitivity, specificity, positive predictive value, and negative predictive value were all 100 percent.
Conclusions: Measurements of end-tidal carbon dioxide levels of more than 1.9 kPa (14.3 mmHg) after 20 minutes should be used to accurately predict ROSC. End-tidal carbon dioxide levels should be monitored during cardiopulmonary resuscitation and considered a useful prognostic value for determining the outcome of resuscitative efforts and termination of cardio-pulmonary resuscitation in the field.
Ključne besede: out-of-hospital cardiac arrest, cardiopulmonary resuscitation, CPR, partial pressure of end-tidal carbon dioxide, PetCO2
Objavljeno v DKUM: 29.06.2017; Ogledov: 1968; Prenosov: 171
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10. Enzymatic esterification of glycerol and stearic acid in non-conventional mediaZsófia Csanádi, Katalin Bélafi-Bakó, Eszter Szentgyörgyi, László Gubicza, Željko Knez, Maja Leitgeb, 2010, izvirni znanstveni članek Opis: Ionic liquids as trihexyl-tetradecyl-phophonium-dicyanamide (Cyphos 105) and cocosalkyl-pentaethoxi-methyl-ammonium-methosulfate (Ammoeng 100) were applied for the esterification of stearic acid and glycerol using Candida antarctica lipase (Novozyme 435). When only ILs were applied as solvents at 1:15 initial substrate molar ratio the conversion was 76 and 78 % in the case of two kinds of ILs, respectively. Mixed the ILs and supercritical $CO_2$ the conversion reached 79 and 86 %. The conversion was found highest in supercritical $CO_2$, reached 90 %. Moreover formation of glycerol-di-stearate is much lower in the case of ILs comparing with $SCCO_2$.
Ključne besede: glycerol-mono-stearate, Lipase, ionic liquids, supercritical $CO_2$, carbon dioxide
Objavljeno v DKUM: 10.07.2015; Ogledov: 1488; Prenosov: 189
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