1. Reaction mechanism and microkinetics of heterogeneously catalysed lignin depolymerisation and (de)functionalization : dissertationTina Ročnik, 2024, doktorska disertacija Opis: Lignin, a complex aromatic polymer derived from lignocellulosic biomass, is a renewable resource for the production of aromatic-like chemicals and materials. However, its complex nature, depolymerisation and valorisation remain a major challenge for the bio-based community within biorefinery concepts. For this reason, lignin model compounds have been used to understand and design lignin depolymerisation, but insufficient attention has been paid to linking knowledge between simpler systems and applying it to a more complex problem. The objectives of this thesis were formulated accordingly to address the aforementioned gap in the literature. The objectives included a systematic approach correlating studies of lignin model compounds with lignin. Hydrodeoxygenation, cleavage of the β-O-4 bond and depolymerisation were investigated to evaluate the process- and structure-dependent correlations, effects on product distribution and kinetic parameters.
The catalytic reactions were carried out in batch reactor and the conditions were applied and intensified according to the knowledge gained during the experimental work. The liquid samples for monomer yield evaluation were analysed by GC-MS, while the structural characteristics of lignin and oligomeric fragments, e.g. molecular weight, functionality/reactivity and structural features, were examined by SEC, quantitative 31P and 2D-HSQC NMR. Kinetic modelling was performed to determine the kinetic parameters (e.g. kinetic constants and activation energies) describing defunctionalisation, β-O-4 bond cleavage and depolymerisation.
The study with monomeric lignin compounds contributed to the understanding of the key parameters leading to condensation during hydrotreatment. The unsaturated alkyl side-chain of eugenol and the reactive hydroxyl groups bound irreversibly and formed the carbonaceous species, while 4-propylphenol and 4-propylguaiacol provided important insights into the contribution of steric hindrances to a favourable reaction mechanism. An initial assessment of β-O-4 cleavage was performed with β-O-4-model compound, 2-phenoxy-1-phenylethanol, and linked to the lignin macromolecule by process- and structure-dependent correlations. Although the lignin model compound lacks the structural complexity of lignin, important insights into possible reaction processes were gained and accurate kinetic parameters were determined. Furthermore, lignin isolated in 50 vol% EtOH/H2O solutions was depolymerised and the optimal
reaction conditions were defined at a temperature of 275 °C and a pressure of 1.5 MPa with regard to the product distribution and the changes in the structural characteristics of the corresponding oligomeric fragments. Depolymerisation of lignins isolated in different EtOH/H2O solutions showed the importance of the structural features, especially ethoxylation degree and the content of β-O-4 or α-ethoxylated β-O-4 bonds. A higher ethoxylation degree of lignin reduced its potential to depolymerise and achieve the theoretical monomer yield. Therefore, the structural characteristics of lignin play the main role in designing and prediction of lignin depolymerisation.
The thesis represents a systematic approach of increasing the complexity of structures exposed to hydrodeoxygenation and depolymerisation. The approach contributed to incorporating the knowledge gained from less complex model compounds to real lignin samples by tailoring and designing lignin depolymerisation to exploit the potential of lignin for biorefinery concepts. Ključne besede: model compounds, hydrodeoxygenation, organosolv lignin, depolymerisation, structural characteristics, kinetic modelling, dissertations Objavljeno v RUNG: 08.11.2024; Ogledov: 335; Prenosov: 4 Celotno besedilo (5,04 MB) |
2. Yearlong measurements of monoterpenes and isoprene in a Mediterranean city (Athens) : natural vs anthropogenic originAnastasia Panopoulou, Eleni Liakakou, Stéphane Sauvage, Valérie Gros, Nadine Locoge, Iasonas Stavroulas, Bernard Bonsang, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2020, izvirni znanstveni članek Opis: Monoterpenes and isoprene are important constituents of the volatile organic compounds (VOCs) due to their high reactivity and participation in ozone and secondary aerosol formation. The current work focuses on the results of a 13-month intensive campaign of high resolution time-resolved measurements of these compounds, at an urban background site in Athens, Greece. On an annual basis, monoterpenes (α-pinene and limonene) surpass the isoprene levels presenting mean values of 0.70 ± 0.83 μg m−3, 0.33 ± 0.78 μg m−3 and 0.19 ± 0.36 μg m−3, respectively. The large standard deviation highlights the significant diurnal and day-to-day variability. Isoprene presents a typical seasonal cycle, with a photochemically induced summer-time maximum. Enhanced noon levels are observed during summer, whereas a morning peak in the autumn and winter profiles occurs, despite the generally low levels encountered during these seasons. The monoterpenes deviate from the expected biogenic pattern, presenting higher mean levels during the cold period and a night-to-early morning enhancement strongly related to local anthropogenic tracers such as BC, CO, NO or toluene, as well as increased levels under wind speeds lower than 3 m s−1. Estimations of the anthropogenic and biogenic fractions based on the enhancement ratios of α-pinene versus a variety of anthropogenic tracers, demonstrate a clear dominance of the anthropogenic sources in all studied seasons. Simultaneously, the biogenic fraction increased during summer relative to winter by more than 10 times. Both α-pinene and limonene significantly contribute to locally formed secondary organic aerosol (SOA), determined by means of an ACSM, accounting for at least 22% and 13% of their levels in summer and winter respectively. Additionally, monoterpenes and isoprene contribute 6% to the observed oxidants levels (O3 + NOx) during summer. Ključne besede: volatile organic compounds, biogenic compounds, monoterpenes, isoprene, Athens Objavljeno v RUNG: 10.05.2024; Ogledov: 899; Prenosov: 4 Povezava na datoteko Gradivo ima več datotek! Več... |
3. Exhaled volatile organic compounds and respiratory disease : recent progress and future outlookMaria Chiara Magnano, Waqar Ahmed, Ran Wang, Martina Bergant Marušič, Stephen J. Fowler, Iain R. White, 2024, pregledni znanstveni članek Opis: The theoretical basis of eVOCs as biomarkers for respiratory disease diagnosis is described, followed by a review of the potential biomarkers that have been proposed as targets from in vitro studies. The utility of these targets is then discussed based on comparison with results from clinical breath studies. The current status of breath research is summarised for various diseases, with emphasis placed on quantitative and targeted studies. Potential for bias highlights several important concepts related to standardization, including practices adopted for compound identification, correction for background inspired VOC levels and computation of mixing ratios. The compiled results underline the need for targeted studies across different analytical platforms to understand how sampling and analytical factors impact eVOC quantification. The impact of environmental VOCs as confounders in breath analysis is discussed alongside the potential that eVOCs have as biomarkers of air pollution exposure and future perspectives on clinical breath sampling are provided. Ključne besede: breath analysis, disease diagnosis, exhaled volatile organic compounds, respiratory disease, environmental exposure analysis, breath analysis Objavljeno v RUNG: 06.05.2024; Ogledov: 1482; Prenosov: 9 Celotno besedilo (1,36 MB) Gradivo ima več datotek! Več... |
4. Chemical composition of apple cider : a comparative study of Norwegian and French cidersIngunn Ovsthus, Mitja Martelanc, Tatjana Radovanović Vukajlović, Marko Lesica, Lorena Butinar, Branka Mozetič Vodopivec, Guillaume Antalick, 2024, objavljeni znanstveni prispevek na konferenci Opis: Norwegian apple ciders have recently gained attention at the levels of international competitiveness. Accordingly, a comparative study on the chemical composition of selected Norwegian and French apple ciders was conducted to gain knowledge on what ubiquitous chemical parameters make the Norwegian ciders different from ciders from well-established producing regions. A total of 43 ciders, 24 Norwegian and 19 French, in the category of acidic dominant ciders, were included in the study. Ethanol, individual sugars and organic acids, pH, total phenols, aroma compounds including esters, C6-alcohols, volatile phenols and terpenoids, were analysed. Norwegian ciders showed higher contents in ethanol, malic and citric acids, whereas total phenols, pH, glucose, and fructose were higher in French counterparts. Regarding the aromatic profile, no significant differences were observed for C6-alcohols. In contrast, differences were more expressed in the case of esters and volatile phenols. Norwegian ciders were characterised by higher average concentration for all the groups of esters, with the most important differences measured for higher alcohol acetates. Norwegian ciders also displayed higher contents of 4-vinylphenol and 4-vinylguaiacol while French ciders contained substantially higher levels of 4-ethylphenol and 4-ethylguaiacol. These results are in mutual correlation with the empirical observation reporting Norwegian apple ciders as more acidic, alcoholic and with lighter body but fruitier profile. Whereas French ciders are often perceived with more structure and animalistic profile. Ključne besede: alcohol, acidity, total phenols, aroma-compounds, apple cider Objavljeno v RUNG: 25.03.2024; Ogledov: 1815; Prenosov: 6 Povezava na datoteko Gradivo ima več datotek! Več... |
5. Functional characterization of Saccharomyces yeasts from cider produced in HardangerUrban Česnik, Mitja Martelanc, Ingunn Ovsthus, Tatjana Radovanović Vukajlović, Ahmad Hosseini, Branka Mozetič Vodopivec, Lorena Butinar, 2023, izvirni znanstveni članek Ključne besede: Saccharomyces, Hardanger, characterization, fermentation, cider, non-volatile compounds, volatile organic compounds, partial least squares regression Objavljeno v RUNG: 18.09.2023; Ogledov: 1690; Prenosov: 9 Celotno besedilo (4,79 MB) Gradivo ima več datotek! Več... |
6. Changes in exhaled volatile organic compounds following indirect bronchial challenge in suspected asthmaAdam Peel, Ran Wang, Waqar Ahmed, Iain R. White, Maxim Wilkinson, Yoon K. Loke, Andrew M. Wilson, Stephen J. Fowler, 2023, izvirni znanstveni članek Opis: Background Inhaled mannitol provokes bronchoconstriction via mediators released during osmotic degranulation of inflammatory cells, and, hence represents a useful diagnostic test for asthma and model for acute attacks. We hypothesised that the mannitol challenge would trigger changes in exhaled volatile organic compounds (VOCs), generating both candidate biomarkers and novel insights into their origin.
Methods Participants with a clinical diagnosis of asthma, or undergoing investigation for suspected asthma, were recruited. Inhaled mannitol challenges were performed, followed by a sham challenge after 2 weeks in participants with bronchial hyper-responsiveness (BHR). VOCs were collected before and after challenges and analysed using gas chromatography–mass spectrometry.
Results Forty-six patients (mean (SD) age 52 (16) years) completed a mannitol challenge, of which 16 (35%) were positive, and 15 of these completed a sham challenge. Quantities of 16 of 51 identified VOCs changed following mannitol challenge (p<0.05), of which 11 contributed to a multivariate sparse partial least square discriminative analysis model, with a classification error rate of 13.8%. Five of these 16 VOCs also changed (p<0.05) in quantity following the sham challenge, along with four further VOCs. In patients with BHR to mannitol distinct postchallenge VOC signatures were observed compared with post-sham challenge.
Conclusion Inhalation of mannitol was associated with changes in breath VOCs, and in people with BHR resulted in a distinct exhaled breath profile when compared with a sham challenge. These differentially expressed VOCs are likely associated with acute airway inflammation and/or bronchoconstriction and merit further investigation as potential biomarkers in asthma. Ključne besede: asthma, exhaled volatile organic compounds, pulmonology, breath metabolomics Objavljeno v RUNG: 31.07.2023; Ogledov: 2010; Prenosov: 4 Povezava na datoteko |
7. Electronic and chemical surface properties of Bi2Se3 derived compoundsZipporah Rini Benher, doktorska disertacija Ključne besede: Bismuth selenide derived compounds, surface chemical and electronic properties, topological insulators, single crystals, phase separation, inorganic bulk heterostructures, ix
Bridgman method, X-ray powder diffraction, scanning electron microscopy, photoelectron spectroscopy Objavljeno v RUNG: 16.12.2022; Ogledov: 2824; Prenosov: 30 Celotno besedilo (9,56 MB) |
8. Untargeted molecular analysis of exhaled breath as a diagnostic test for ventilator-associated lower respiratory tract infections (BreathDx)Pouline M. van Oort, Tamara M. E. Nijsen, Iain R. White, Hugo Knobel, Timothy Felton, Nicholas J. W. Rattray, Oluwasola Lawal, Murtaza Bulut, Waqar Ahmed, Antonio Artigas, 2021, drugi znanstveni članki Opis: Patients suspected of ventilator-associated lower respiratory tract infections (VA-LRTIs) commonly receive broad-spectrum antimicrobial therapy unnecessarily. We tested whether exhaled breath analysis can discriminate between patients suspected of VA-LRTI with confirmed infection, from patients with negative cultures. Breath from 108 patients suspected of VA-LRTI was analysed by gas chromatography-mass spectrometry. The breath test had a sensitivity of 98% at a specificity of 49%, confirmed with a second analytical method. The breath test had a negative predictive value of 96% and excluded pneumonia in half of the patients with negative cultures. Trial registration number: UKCRN ID number 19086, registered May 2015. Ključne besede: ventilator-associated pneumonia, breath analysis, volatile organic compounds, metabolomics, intensive care, hospital acquired infections Objavljeno v RUNG: 07.09.2021; Ogledov: 5205; Prenosov: 0 Gradivo ima več datotek! Več... |
9. Secondary organic aerosol formation from anthropogenic air pollution : rapid and higher than expectedRainer Volkamer, Jose L. Jimenez, F. M. San Martini, Katja Džepina, Q. Zhang, Dara Salcedo, Luisa T. Molina, D. Worsnop, 2006, izvirni znanstveni članek Opis: The atmospheric chemistry of volatile organic compounds (VOCs) in urban areas results in the formation of 'photochemical smog', including secondary organic aerosol (SOA). State-of-the-art SOA models parameterize the results of simulation chamber experiments that bracket the conditions found in the polluted urban atmosphere. Here we show that in the real urban atmosphere reactive anthropogenic VOCs (AVOCs) produce much larger amounts of SOA than these models predict, even shortly after sunrise. Contrary to current belief, a significant fraction of the excess SOA is formed from first-generation AVOC oxidation products. Global models deem AVOCs a very minor contributor to SOA compared to biogenic VOCs (BVOCs). If our results are extrapolated to other urban areas, AVOCs could be responsible for additional 3 - 25 Tg yr(-1) SOA production globally, and cause up to - 0.1 W m(-2) additional top-of-the-atmosphere radiative cooling. Ključne besede: atmospheric aerosol, atmospheric chemistry, volatile organic compounds, secondary organic aerosols Objavljeno v RUNG: 12.04.2021; Ogledov: 4620; Prenosov: 0 Gradivo ima več datotek! Več... |
10. Atmospheric peroxyacetyl nitrate (PAN) : a global budget and source attributionE. V. Fischer, D. J. Jacob, R. M. Yantosca, M. P. Sulprizio, D. B. Millet, Jiandong Mao, F. Paulot, H. B. Singh, A. Roiger, Katja Džepina, 2014, izvirni znanstveni članek Opis: Peroxyacetyl nitrate (PAN) formed in the atmospheric oxidation of non-methane volatile organic compounds (NMVOCs) is the principal tropospheric reservoir for nitrogen oxide radicals (NOx = NO + NO2). PAN enables the transport and release of NOx to the remote troposphere with major implications for the global distributions of ozone and OH, the main tropospheric oxidants. Simulation of PAN is a challenge for global models because of the dependence
of PAN on vertical transport as well as complex and uncertain NMVOC sources and chemistry. Here we use an improved representation of NMVOCs in a global 3-D chemical
transport model (GEOS-Chem) and show that it can simulate PAN observations from aircraft campaigns worldwide.
The immediate carbonyl precursors for PAN formation include acetaldehyde (44 % of the global source), methylglyoxal (30 %), acetone (7 %), and a suite of other isoprene and
terpene oxidation products (19 %). A diversity of NMVOC
emissions is responsible for PAN formation globally including isoprene (37 %) and alkanes (14 %). Anthropogenic
sources are dominant in the extratropical Northern Hemisphere outside the growing season. Open fires appear to play
little role except at high northern latitudes in spring, although
results are very sensitive to plume chemistry and plume rise.
Lightning NOx is the dominant contributor to the observed
PAN maximum in the free troposphere over the South Atlantic. Ključne besede: peroxyacetyl nitrate, non-methane volatile organic compounds, global 3-D chemical transport model, GEOS-chem Objavljeno v RUNG: 11.04.2021; Ogledov: 3463; Prenosov: 0 Gradivo ima več datotek! Več... |