| 1. |
- Schyman, Patric, et al.
(författare)
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Hydrogen Abstraction from Deoxyribose by a Neighbouring Uracil-5-yl Radical
- 2007
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 9, s. 5975-5979
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen abstraction from the C1 and C2 positions of deoxyadenosine by a neighbouring uracil-5-yl radical in the 5-AU-3 DNA sequence is explored using DFT. This hydrogen abstraction is the first step in a sequence leading to single or double strand break in DNA. The uracil-5-yl radical can be the result of photolysis or low-energy electron (LEE) attachment. If the radical is produced by photolysis the neighbouring adenine will become a cation radical and if it is produced by LEE the adenine will remain neutral. The hydrogen abstraction reactions for both cases were investigated. It is concluded that it is possible for the uracil-5-yl to abstract hydrogen from C1 and C2. When adenine is neutral there is a preference for the C1 site and when the adenine is a radical cation the C2 site is the preferred. If adenine is positively charged, the rate-limiting step when abstracting hydrogen from C1 is the formation of an intermediate crosslink between uracil and adenine. This crosslink might be avoided in dsDNA, making C1 the preferred site for abstraction.
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| 2. |
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| 3. |
- Schyman, Patric, et al.
(författare)
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Hydroxyl radical - thymine adduct induced DNA damages
- 2008
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Ingår i: Chemical Physics Letters. - Amsterdam : Elsevier. - 0009-2614 .- 1873-4448. ; 458:1-3, s. 186-189
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Tidskriftsartikel (refereegranskat)abstract
- DNA damages caused by a 5-hydroxy-5,6-dihydrothymine-6-yl radical (5-OHT-6yl) abstracting a C20 hydrogen from a neighboring sugar (inter-H abstraction) have been theoretically investigated using hybrid DFT in gas phase and in water solution. The inter-H abstraction was here shown to be comparable in energy (24 kcal mol 1) with the intra-H abstraction in which the 5-OHT-6yl abstracts a C20 hydrogen from its own sugar. The effect of a neutrally or a negatively charged phosphate group was also studied and the results show no significant impact on the activation energy of the hydrogen abstraction whereas base release and strand break reactions are affected.
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| 4. |
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| 5. |
- Maurina Morais, Eduardo, 1989, et al.
(författare)
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Solvent-free synthesis of protic ionic liquids. Synthesis, characterization and computational studies of triazolium based ionic liquids
- 2022
-
Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 360
-
Tidskriftsartikel (refereegranskat)abstract
- A series of triazolium and imidazolium based protic ionic liquids were synthesized using a solvent-free method designed to address several limitations encountered with other commonly used methods. Using this method, pure (98–99% m/m) and dry (128–553 ppm of water) protic ionic liquids were synthesized (in a laboratory scale) without the need for purification methods that require heating the ionic liquid, hence avoiding the common issue of thermal decomposition. This method was also designed to allow for the accurate measurement of acid and base, and for the controlled mixing of both compounds, which is essential to avoid producing impure protic ionic liquids with excess of either acid or base. The system is constructed of only glass and chemically resistant polymer (PTFE and PVDF) parts, which avoid other contaminants that can result from unwanted reactions involving the reagents with common laboratory tools (metallic objects, paper, plastic, etc.). This process is described in detail in the paper as well as in a video. The resulting ionic liquids were carefully analyzed by spectroscopic and thermal methods designed to avoid water absorption, which is known to affect their properties. To complement this experimental characterization, computational chemistry tools were used to assess the ionic liquids’ properties, as well as to assign vibrational modes.
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| 6. |
- Zhang, Ru Bo, et al.
(författare)
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Theoretical studies of damage to 3'-uridine monophosphate induced by electron attachment
- 2008
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley-VCH-Verl.. - 0947-6539 .- 1521-3765. ; 14:9, s. 2850-2856
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy electrons (LEE) are well known to induce nucleic acid damage. However, the damage mechanisms related to charge state and structural features remain to be explored in detail. In the present work, we have investigated the N1-glycosidic and C3'-O(P) bond ruptures of 3'-UMP (UMP=uridine monophosphate) and the protonated form 3'-UMPH with -1 and zero charge, respectively, based on hybrid density functional theory (DFT) B3 LYP together with the 6-31+G(d,p) basis set. The glycosidic bond breakage reactions of the 3'UMP and 3'UMPH electron adducts are exothermic in both cases, with barrier heights of 19-20 kcal mol(-1) upon inclusion of bulk solvation. The effects of the charge state on the phosphate group are marginal, but the C2'-OH group destabilizes the transition structure of glycosidic bond rupture of 3'-UMPH in the gas phase by approximately 5.0 kcal mol(-1). This is in contrast with the C3'-O(P) bond ruptures induced by LEE in which the charge state on the phosphate influences the barrier heights and reaction energies considerably. The barrier towards C3'-O(P) bond dissociation in the 3'UMP electron adduct is higher in the gas phase than the one corresponding to glycosidic bond rupture and is dramatically influenced by the C2'-OH group and bulk salvation, which decreases the barrier to 14.7 kcal mol(-1). For the C3'-O(P) bond rupture of the 3'UMPH electron adduct, the reaction is exothermic and the barrier is even lower, 8.2 kcal mol(-1), which is in agreement with recent results for 3'-dTMPH and 5'-dTMPH (dTMPH=deoxythymidine monophosphate). Both the Mulliken atomic charges and unpaired-spin distribution play significant roles in the reactions
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| 7. |
- Laarz, Eric, et al.
(författare)
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Colloidal processing of Al2O3-based composites reinforced with TiN and TiC particulates, whiskers and nanoparticles
- 2001
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Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 21:8, s. 1027-1035
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Tidskriftsartikel (refereegranskat)abstract
- A colloidal processing route has been developed for the preparation of dense and homogeneous Al2O3–TiN/TiC composites. The dispersion and rheological properties of mixtures of TiN or TiC particulates and Al2O3 particles were investigated using electrokinetics and steady-shear rheology. We found that well-dispersed aqueous suspensions with low viscosity could be prepared by adding a poly(acrylic acid) dispersant and controlling pH in the alkaline range. This processing scheme was also suitable for preparation of whisker and nanoparticle composite suspensions. The alumina-based composite suspensions with a secondary-phase concentration of 25 vol.% were freeze-granulated and hot-pressed, and the resulting bodies were fully densified with well-dispersed secondary phases. Homogeneous Al2O3–TiN nanoparticle composites could only be prepared with additions of up to 5 vol.% nanoparticles; higher additions resulted in agglomeration and subsequent grain growth of the nanoparticles.
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| 8. |
- Bushnell, Eric A. C., et al.
(författare)
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The first branching point in porphyrin biosynthesis : a systematic docking, molecular dynamics and quantum mechanical/molecular mechanical study of substrate binding and mechanism of uroporphyrinogen-III decarboxylase
- 2011
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Ingår i: Journal of Computational Chemistry. - New York : John Wiley & Sons. - 0192-8651 .- 1096-987X. ; 32:5, s. 822-834
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Tidskriftsartikel (refereegranskat)abstract
- In humans, uroporphyrinogen decarboxylase is intimately involved in the synthesis of heme, where the decarboxylation of the uroporphyrinogen-III occurs in a single catalytic site. Several variants of the mechanistic proposal exist; however, the exact mechanism is still debated. Thus, using an ONIOM quantum mechanical/molecular mechanical approach, the mechanism by which uroporphyrinogen decarboxylase decarboxylates ring D of uroporphyrinogen-III has been investigated. From the study performed, it was found that both Arg37 and Arg50 are essential in the decarboxylation of ring D, where experimentally both have been shown to be critical to the catalytic behavior of the enzyme. Overall, the reaction was found to have a barrier of 10.3 kcal mol−1 at 298.15 K. The rate-limiting step was found to be the initial protontransfer from Arg37 to the substrate before the decarboxylation. In addition, it has been found that several key interactions exist between the substrate carboxylate groups and backbone amides of various activesite residues as well as several other functional groups.
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| 9. |
- Erdtman, Edvin, et al.
(författare)
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Computational studies on Schiff-base formation : Implications for the catalytic mechanism of porphobilinogen synthase
- 2011
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Ingår i: Computational and Theoretical Chemistry. - Amsterdam : Elsevier. - 2210-271X .- 2210-2728. ; 963:2-3, s. 479-489
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Tidskriftsartikel (refereegranskat)abstract
- Schiff bases are common and important intermediates in many bioenzymatic systems. The mechanism by which they are formed, however,is dependent on the solvent, pH and other factors. In the present study we have used density functional theory methods in combination with appropriate chemical models to get a better understanding of the inherent chemistry of the formation of two Schiff bases that have been proposed to be involved in the catalytic mechanism of porphobilinogensynthase (PBGS), a key enzyme in the biosynthesis of porphyrins. More specifically, we have investigated the uncatalysed reaction of its substrate 5-aminolevulinic acid (5-ALA) with a lysine residue for theformation of the P-site Schiff base, and as possibly catalysed by the second active site lysine, water or the 5-ALA itself. It is found that cooperatively both the second lysine and the amino group of the initial 5-ALA itself are capable of reducing the rate-limiting energy barrier to14.0 kcal mol-1. We therefore propose these to be likely routes involved in the P-site Schiff-base formation in PBGS.
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| 10. |
- Halldin Stenlid, Joakim, 1987-
(författare)
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Computational Studies of Chemical Interactions: Molecules, Surfaces and Copper Corrosion
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chemical bond – a corner stone in science and a prerequisite for life – is the focus of this thesis. Fundamental and applied aspects of chemical bonding are covered including the development of new computational methods for the characterization and rationalization of chemical interactions. The thesis also covers the study of corrosion of copper-based materials. The latter is motivated by the proposed use of copper as encapsulating material for spent nuclear fuel in Sweden.In close collaboration with experimental groups, state-of-the-art computational methods were employed for the study of chemistry at the atomic scale. First, oxidation of nanoparticulate copper was examined in anoxic aqueous media in order to better understand the copper-water thermodynamics in relation to the corrosion of copper material under oxygen free conditions. With a similar ambition, the water-cuprite interface was investigated with regards to its chemical composition and reactivity. This was compared to the behavior of methanol and hydrogen sulfide at the cuprite surface.An overall ambition during the development of computational methods for the analysis of chemical bonding was to bridge the gap between molecular and materials chemistry. Theory and results are thus presented and applied in both a molecular and a solid-state framework. A new property, the local electron attachment energy, for the characterization of a compound’s local electrophilicity was introduced. Together with the surface electrostatic potential, the new property predicts and rationalizes regioselectivity and trends of molecular reactions, and interactions on metal and oxide nanoparticles and extended surfaces.Detailed atomistic understanding of chemical processes is a prerequisite for the efficient development of chemistry. We therefore envisage that the results of this thesis will find widespread use in areas such as heterogeneous catalysis, drug discovery, and nanotechnology.
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| 11. |
- Rahm, Martin, et al.
(författare)
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The Molecular Surface Structure of Ammonium and Potassium Dinitramide : A Vibrational Sum Frequency Spectroscopy and Quantum Chemical Study
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:21, s. 10588-10596
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Tidskriftsartikel (refereegranskat)abstract
- Vibrational sum frequency spectroscopy (VSFS) and quantum chemical modeling have been employed to investigate the molecular surface structure of ammonium and potassium dinitramide (ADN and KDN) crystals. Identification of key vibrational modes was made possible by performing density functional theory calculations of molecular clusters. The surface of KDN was found to be partly covered with a thin layer of the decomposition product KNO3, which due to its low thickness was not detectable by infrared and Raman spectroscopy. In contrast, ADN exhibited an extremely inhomogeneous surface, on which polarized dinitramide anions were present, possibly together with a thin layer of NH4NO3. The intertwined use of theoretical and experimental tools proved indispensable in the analysis of these complex surfaces. The experimental verification of polarized and destabilized dinitramide anions stresses the importance of designing surface-active polymer support, stabilizers, and/or coating agents, in order to enable environmentally friendly ADN-based solid-rocket propulsion.
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| 12. |
- Tejero, Ismael, et al.
(författare)
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Theoretical modeling of hydroxyl-radical-induced lipid peroxidation reactions
- 2007
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 111:20, s. 5684-5693
-
Tidskriftsartikel (refereegranskat)abstract
- The OH-radical-induced mechanism of lipid peroxidation, involving hydrogen abstraction followed by O2 addition, is explored using the kinetically corrected hybrid density functional MPWB1K in conjunction with the MG3S basis set and a polarized continuum model to mimic the membrane interior. Using a small nonadiene model of linoleic acid, it is found that hydrogen abstraction preferentially occurs at the mono-allylic methylene groups at the ends of the conjugated segment rather than at the central bis-allylic carbon, in disagreement with experimental data. Using a full linoleic acid, however, abstraction is correctly predicted to occur at the central carbon, giving a pentadienyl radical. The Gibbs free energy for abstraction at the central C11 is 8 kcal/mol, compared to 9 kcal/mol at the end points (giving an allyl radical). Subsequent oxygen addition will occur at one of the terminal atoms of the pentadienyl radical fragment, giving a localized peroxy radical and a conjugated butadiene fragment, but is associated with rather high free energy barriers and low exergonicity at the CPCM-MPWB1K/MG3S level. The ZPE-corrected potential energy surfaces obtained without solvent effects, on the other hand, display considerably lower barriers and more exergonic reactions.
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| 13. |
- Wojas, Natalia
(författare)
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The dynamic surface nature of calcite and its role in determining the adsorptive stability toward hydrophobizing carboxylic fatty acids
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Calcium carbonate has attracted a lot of interest over the centuries. Nowadays, mainly as mineral pigment and filler, it has a wide use in technological applications ranging from paper, construction, polymers, and environmental solutions to consumer goods. Amongst these uses, the filler pigment is required to display either hydrophilicity (for applications in aqueous colloidal systems, including, for example, in paper and emulsion paints), or, in contrast, oleophilicity (for applications in contact with oil-based systems, such as plastics and volatile solvent-containing sealants). To achieve oleophilicity, and resulting hydrophobicity, the filler is surface treated, typically using carboxylic fatty acids. In this thesis, effects of humidity and fatty carboxylic acids vapor on CaCO3 surface wettability and nanomechanical properties were studied, with the aim to gain knowledge on layer packing density and order, as well as resistance to water exposure and mechanical wear. A better understanding of the dynamic nature of the calcite surface presented in this work allows the industry to increase sustainable control over materials production and storage. First, a setup combining an atomic force microscope (AFM) with a humidifier was used to map nanomechanical properties of growing surface domains (hydrated form of CaCO3) formed by ion dissolution, diffusion, and redeposition, a process that is not reversible upon drying. Secondly, AFM and contact angle goniometer measurements showed that the stability of the calcite surface improves with increasing carboxylic acid chain length (C2 to C18). Meanwhile, X-ray photoelectron spectroscopy and vibrational sum frequency spectroscopy techniques demonstrated that a coherent layer with maximum packing density of carboxylate and carboxylic acid species was achieved with the use of stearic acid (C18) with high enough vapor pressure and exposure time. The AFM images successfully visualized that a complete C18 monolayer is capable of countering nano-wear of the calcite surface despite the humidity (under the range of loads investigated in this work) and the layer has self-healing properties, while calcite displayed high abrasive wear. Further, when calcite coated by a highly packed monolayer of C18 was covered with a water droplet, a large contact angle hysteresis resulted in a coffee ring effect (CRE). That is leading to formation of hillocks at the contact line consisting of dissolved fatty carboxylic acid and possibly calcium bicarbonate Ca(HCO3)2 molecules transported from the bare calcite region that also is created next to the droplet edge. Interestingly, C18 coated calcite remained considerably more stable in the case where a water droplet saturated with octanoic acid was used instead of water; thus, it was concluded that the CRE can be contained via reduction of the liquid surface tension and contact angle hysteresis.
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| 14. |
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| 15. |
- Maurina Morais, Eduardo, 1989
(författare)
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Synthesis of protic ionic liquids. Challenges and solutions for the synthesis of pure compounds.
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The urgent need to diversify our energy matrix is responsible for a renewed interest in fuel cell technology, which can use hydrogen gas, a renewable green fuel, as an energy source. This technology is currently a commercially available option, however, it still requires technological improvements before it can be widely used for different applications. One way this technology could potentially be improved is by increasing its temperature range of operation by developing new, anhydrous proton conducting materials. Protic ionic liquids, which are organic salts with low melting temperatures, are interesting candidates for this application, since they can conduct protons in the operational conditions of fuel cells and without the need of water. These compounds can be synthesized by a simple acid-base neutralization reaction, but certain considerations must be taken in order to obtain high quality (dry and pure) protic ionic liquids. In this thesis, a series of triazolium and imidazolium based protic ionic liquids were synthesized using a solvent-free method designed to address several limitations encountered with other commonly used methods. Using this method, pure (98-99% m/m) and dry (128-553 ppm of water) protic ionic liquids were synthesized (in a laboratory scale) without the need for purification methods that require heating the ionic liquid, hence avoiding the common issue of thermal decomposition. This method was also designed to allow for the accurate measurement of acid and base, and for the controlled mixing of both compounds, which is essential to avoid producing impure protic ionic liquids with excess of either acid or base. The system is consists of only glass and chemically resistant polymer(PTFE and PVDF) parts, which avoids other contaminants that can result from unwanted reactions involving the reagents with common laboratory tools (metallic objects, paper, plastic, etc.). The resulting ionic liquids were carefully analyzed by spectroscopic and thermal analysis methods designed to avoid water absorption, which is known to affect their properties. To complement this experimental characterization, computational chemistry tools were used to assess the ionic liquids’ properties, as well as to assign vibrational modes.
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| 16. |
- Sauer, Christopher, 1993
(författare)
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Green Aromatics: Catalytic Valorisation of bio-derived 2,5-dimethylfuran over Zeolites and Zeotypes
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis discusses the use of biomass as a potentially green feedstock for the chemical industry in the urgent shift away from fossil resources. I elaborate on reasons why we cannot afford to burn virgin biomass for energy production, among them a variety of ecosystem services that forests and other lands provide. In addition, the utilisation of biomass should be focused on products that sequester and lock away carbon for more extended periods, e.g. timber, materials and chemicals. In particular, biomass can be used as an alternative "carbon neutral" feedstock for the chemical industry, where we can preserve the already existing chemical complexity in the bio-based molecules. One example is the upgrading of furans to benzene, toluene and xylene (BTX) aromatics with the help of zeolite catalysis. These aromatics are important commodity chemicals, where the shift to a bio-based resource could make use of already existing knowledge, catalyst and production infrastructure. However, research is necessary to understand these new feedstock molecules and their interaction with the catalysts and to enable the design of applicable catalysts. In order to study the interaction of the furans, in particular 2,5-dimethylfuran (2,5-dmf), I describe and discuss the development of an analytical methodology that utilises infrared spectroscopy and mass spectrometry for the on-line identification and quantification of product molecules during catalytic reactions. This on-line analysis method is then applied to the catalytic conversion of 2,5-dmf to aromatics over a range of zeolite and zeotype catalysts. In-depth studies with ammonia as a probe molecule of the catalytic active acid sites, as well as temperature programmed experiments with ammonia and 2,5-dmf give insights into product distribution, selectivity changes and deactivation of the catalyst. For example, olefins and aromatics are initially preferred products, while with increasing time on stream, the isomerisation of 2,5-dmf becomes dominant. The incorporation of Ga into the zeotype framework, resulting in a Ga-Silicate, shows how targeted catalyst design can increase overall aromatics production. This catalyst is also suitable for selective isomerisation of 2,5-dmf to 2,4-dimethylfuran, which has a rare substitution pattern. Finally, itwas found that the most valuable of BTX, p -xylene, can be produced more selectively when 2,5-dmf is pre-adsorbed onto zeolite ZSM-5 and then released during a temperature programmed product desorption.
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| 17. |
- Erdtman, Edvin, et al.
(författare)
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Modelling the behavior of 5-aminolevulinic acid and its alkyl esters in a lipid bilayer
- 2008
-
Ingår i: Chemical Physics Letters. - Amsterdam : North-Holland Publishing Co. - 0009-2614 .- 1873-4448. ; 463:1-3, s. 178-182
-
Tidskriftsartikel (refereegranskat)abstract
- 5-Aminolevulinic acid (5ALA) and ester derivates thereof are used as prodrugs in photodynamic therapy (PDT). The behavior of 5ALA and three esters of 5ALA in a DPPC lipid bilayer is investigated. In particular, the methyl ester displays a very different free energy profile, where the highest barrier is located in the region with highest lipid density, while the others have their peak in the middle of the membrane, and also displays a considerably lower permeability coefficient than neutral 5ALA and the ethyl ester. The zwitterion of 5ALA has the highest permeability constant, but a significant free energy minimum in the polar head-group region renders an accumulation in this region.
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| 18. |
- Damas, Giane Benvinda, et al.
(författare)
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Carbon dioxide reduction mechanism on Ru-based electrocatalysts [Ru(bpy)(2)(CO)(2)](2+) : insights from first-principles theory
- 2021
-
Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry. - 2398-4902. ; 5:23, s. 6066-6076
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Tidskriftsartikel (refereegranskat)abstract
- Solar fuel production through the so-called artificial photosynthesis has attracted a great deal of attention to the development of a new world energy matrix that is renewable and environmentally friendly. This process is characterized by light absorption with enough photon energy to generate conduction electrons, which drive the carbon dioxide reduction to produce organic fuels. It is also common to couple Ru-complex electrocatalysts to form a more efficient and selective hybrid system for this application. In this work, we have undertaken a thorough investigation of the redox reaction mechanism of Ru-based electrocatalysts by means of density functional theory (DFT) methods under the experimental conditions that have been previously reported. More specifically, we have studied the electrochemistry and catalytic activity of the [Ru(bpy)(2)(CO)(2)](2+) coordination complex. Our theoretical assessment supports the following catalytic cycle: (i) [Ru(bpy)(2)(CO)(2)](2+) is transformed into [Ru(bpy)(2)(CO)](0) upon two-electron reduction and CO release; (ii) [Ru(bpy)(2)(CO)](0) is protonated to form the [Ru(bpy)(2)(CO)H](+) hydride complex; (iii) CO2 is activated by the hydride complex through an electrophilic addition to form the [Ru(bpy)(2)(CO)(OCHO)](+) intermediate; (iv) the resulting formic acid ligand is released in solution; and, finally, (v) the CO ligand is reattached to the complex to recover the initial [Ru(bpy)(2)(CO)(2)](2+) catalyst.
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| 19. |
- Napolitano, C., et al.
(författare)
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Synthesis, kinase activity and molecular modeling of a resorcylic acid lactone incorporating an amide and a trans-enone in the macrocycle
- 2012
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 68:27-28, s. 5533-5540
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Tidskriftsartikel (refereegranskat)abstract
- Details for the synthesis of a resorcylic acid lactone (RAL) incorporating a trans-enone and an amide in the macrocyclic ring are provided herein. The sequence included the assembly of three fragments by esterification, olefination, and lactamization. The RAL with the lactam was less potent as an inhibitor of kinases than other RALs investigated. The biological results were rationalized by docking and molecular dynamics simulations of the lactam bound to human ERK2 and comparison with hypothemycin. (c) 2012 Elsevier Ltd. All rights reserved.
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| 20. |
- Bannan, T. J., et al.
(författare)
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A method for extracting calibrated volatility information from the FIGAERO-HR-ToF-CIMS and its experimental application
- 2019
-
Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 12:3, s. 1429-1439
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Tidskriftsartikel (refereegranskat)abstract
- The Filter Inlet for Gases and AEROsols (FIGAERO) is an inlet specifically designed to be coupled with the Aerodyne High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS). The FIGAERO-HR-ToF-CIMS provides simultaneous molecular information relating to both the gas- and particle-phase samples and has been used to extract vapour pressures (VPs) of the compounds desorbing from the filter whilst giving quantitative concentrations in the particle phase. However, such extraction of vapour pressures of the measured particle-phase components requires use of appropriate, well-defined, reference compounds. Vapour pressures for the homologous series of polyethylene glycols (PEG) ((H-(O-CH 2 CH 2 ) n -OH) for n = 3 to n = 8), covering a range of vapour pressures (VP) (10 -1 to 10 -7 Pa) that are atmospherically relevant, have been shown to be reproduced well by a range of different techniques, including Knudsen Effusion Mass Spectrometry (KEMS). This is the first homologous series of compounds for which a number of vapour pressure measurement techniques have been found to be in agreement, indicating the utility as a calibration standard, providing an ideal set of benchmark compounds for accurate characterization of the FIGAERO for extracting vapour pressure of measured compounds in chambers and the real atmosphere. To demonstrate this, single-component and mixture vapour pressure measurements are made using two FIGAERO-HR-ToF-CIMS instruments based on a new calibration determined from the PEG series. VP values extracted from both instruments agree well with those measured by KEMS and reported values from literature, validating this approach for extracting VP data from the FIGAERO. This method is then applied to chamber measurements, and the vapour pressures of known products are estimated. © 2019 Author(s).
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| 21. |
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| 22. |
- Guo, Y. D., et al.
(författare)
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Identification of highly oxygenated organic molecules and their role in aerosol formation in the reaction of limonene with nitrate radical
- 2022
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 22:17, s. 11323-11346
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Tidskriftsartikel (refereegranskat)abstract
- Nighttime NO3-initiated oxidation of biogenic volatile organic compounds (BVOCs) such as monoterpenes is important for the atmospheric formation and growth of secondary organic aerosol (SOA), which has significant impact on climate, air quality, and human health. In such SOA formation and growth, highly oxygenated organic molecules (HOM) may be crucial, but their formation pathways and role in aerosol formation have yet to be clarified. Among monoterpenes, limonene is of particular interest for its high emission globally and high SOA yield. In this work, HOM formation in the reaction of limonene with nitrate radical (NO3) was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). About 280 HOM products were identified, grouped into 19 monomer families, 11 dimer families, and 3 trimer families. Both closed-shell products and open-shell peroxy radicals (RO2 center dot) 2 were observed, and many of them have not been reported previously. Monomers and dimers accounted for 47% and 47% of HOM concentrations, respectively, with trimers making up the remaining 6 %. In the most abundant monomer families, C10H15-17NO6-14, carbonyl products outnumbered hydroxyl products, indicating the importance of RO2 center dot termination by unimolecular dissociation. Both RO2 center dot autoxidation and alkoxy-peroxy pathways were found to be important processes leading to HOM. Time-dependent concentration profiles of monomer products containing nitrogen showed mainly second-generation formation patterns. Dimers were likely formed via the accretion reaction of two monomer RO2 center dot , and HOM-trimers via the accretion reaction between monomer RO2 center dot and dimer RO2 center dot. Trimers are suggested to play an important role in new particle formation (NPF) observed in our experiment. A HOM yield of 1.5%(+1.7%)(-0.7%) was estimated considering only first-generation products. SOA mass growth could be reasonably explained by HOM condensation on particles assuming irreversible uptake of ultra-low volatility organic compounds (ULVOCs), extremely low volatility organic compounds (ELVOCs), and low volatility organic compounds (LVOCs). This work provides evidence for the important role of HOM formed via the limonene +NO3 reaction in NPF and growth of SOA particles.
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| 23. |
- Guo, Y., et al.
(författare)
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Reversible Structural Isomerization of Nature's Water Oxidation Catalyst Prior to O-O Bond Formation
- 2022
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:26, s. 11736-11747
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic water oxidation is catalyzed by a manganese-calcium oxide cluster, which experiences five "S-states" during a light-driven reaction cycle. The unique "distorted chair"-like geometry of the Mn4CaO5(6)cluster shows structural flexibility that has been frequently proposed to involve "open" and "closed"-cubane forms from the S1 to S3states. The isomers are interconvertible in the S1 and S2states, while in the S3state, the open-cubane structure is observed to dominate inThermosynechococcus elongatus (cyanobacteria) samples. In this work, using density functional theory calculations, we go beyond the S3+Yzstate to the S3nYz•→ S4+Yzstep, and report for the first time that the reversible isomerism, which is suppressed in the S3+Yzstate, is fully recovered in the ensuing S3nYz•state due to the proton release from a manganese-bound water ligand. The altered coordination strength of the manganese-ligand facilitates formation of the closed-cubane form, in a dynamic equilibrium with the open-cubane form. This tautomerism immediately preceding dioxygen formation may constitute the rate limiting step for O2formation, and exert a significant influence on the water oxidation mechanism in photosystem II.
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| 24. |
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| 25. |
- Le Breton, Michael, 1986, et al.
(författare)
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Application of a FIGAERO ToF CIMS for on-line characterization of real-world fresh and aged particle emissions from buses
- 2019
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 53:3, s. 244-259
-
Tidskriftsartikel (refereegranskat)abstract
- © 2019, © 2019 The Author(s). Published with license by Taylor & Francis Group, LLC. On-line chemical characterization of real-world particle emissions from 13 transit buses was performed using a chemical ionization mass spectrometer (CIMS) equipped with a filter inlet for gases and aerosols (FIGAERO). In addition to the fresh emissions the emissions were artificially aged using a potential aerosol mass reactor (Go:PAM). The buses studied were running on different fuel types (diesel, compressed natural gas, and rapeseed methyl ester) and exhaust after-treatment systems (selective catalytic reduction (SCR), exhaust gas recirculation (EGR), and a three-way catalyst). When evaluating emissions from passing exhaust plumes using the FIGAERO ToF-CIMS, two technical features were highlighted from this work, the use of high mass calibrants and the factor enhancement method to be able to filter important compounds from mass spectra including hundreds of species. Here, acetate was used as the reagent ion to enable detection of highly oxygenated species in the exhaust particle emissions with potential high toxicity and/or secondary organic aerosol formation (SOA) potential. The acetate ionization scheme accounted for 4% to 46% of the total emitted particulate mass through identification of 61 species in the spectra. For aged emission the various fuel types provided overlapping species that could explain up to 19% of the aged emissions. This is hypothesized to come from the oxidation of engine lubrication oil, thus a common source for various fuels which was further supported by laboratory measurements. Specific markers from the SCR technology, such as urea oxidation products and further byproducts from hydrolysis were identified and attributed to reactions of isocyanic acid.
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| 26. |
- Le Breton, Michael, 1986, et al.
(författare)
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Chlorine oxidation of VOCs at a semi-rural site in Beijing: significant chlorine liberation from ClNO2 and subsequent gas- and particle-phase Cl-VOC production
- 2018
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:17, s. 13013-13030:18, s. 13013-13030
-
Tidskriftsartikel (refereegranskat)abstract
- Nitryl chloride (ClNO2) accumulation at night acts as a significant reservoir for active chlorine and impacts the following day's photochemistry when the chlorine atom is liberated at sunrise. Here, we report simultaneous measurements of N2O5 and a suite of inorganic halogens including ClNO2 and reactions of chloride with volatile organic compounds (Cl-VOCs) in the gas and particle phases utilising the Filter Inlet for Gas and AEROsols time-of-flight chemical ionisation mass spectrometer (FIGAERO-ToF-CIMS) during an intensive measurement campaign 40 km northwest of Beijing in May and June 2016. A maximum mixing ratio of 2900 ppt of ClNO2 was observed with a mean campaign nighttime mixing ratio of 487 ppt, appearing to have an anthropogenic source supported by correlation with SO2, CO and benzene, which often persisted at high levels after sunrise until midday. This was attributed to such high mixing ratios persisting after numerous e-folding times of the photolytic lifetime enabling the chlorine atom production to reach 2.3 x 10(5) molecules cm(-3) from ClNO2 alone, peaking at 09:30 LT and up to 8.4 x 10(5) molecules cm(-3) when including the supporting inorganic halogen measurements. Cl-VOCs were observed in the particle and gas phases for the first time at high time resolution and illustrate how the iodide ToF-CIMS can detect unique markers of chlorine atom chemistry in ambient air from both biogenic and anthropogenic sources. Their presence and abundance can be explained via time series of their measured and steady-state calculated precursors, enabling the assessment of competing OH and chlorine atom oxidation via measurements of products from both of these mechanisms and their relative contribution to secondary organic aerosol (SOA) formation.
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| 27. |
- Li, J. J., et al.
(författare)
-
Characterization of Aerosol Aging Potentials at Suburban Sites in Northern and Southern China Utilizing a Potential Aerosol Mass (Go:PAM) Reactor and an Aerosol Mass Spectrometer
- 2019
-
Ingår i: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 124:10, s. 5629-5649
-
Tidskriftsartikel (refereegranskat)abstract
- Aerosol mass spectrometry was used to characterize submicron aerosols before and after aging in a Gothenburg Potential Aerosol Mass (Go:PAM) reactor at two suburban sites in China, one in northern China at Changping (CP), Beijing, and a second in southern China at Hong Kong (HK). Organic aerosol (OA) dominated in the ambient nonrefractory particulate matter <1m (NR-PM1) for both CP (42-71%) and HK (43-61%), with a large contribution from secondary OA factors that were semivolatile oxygenated (SVOOA) and low-volatility oxygenated (LVOOA). Under constant OH exposure, OA enhancement (78-98%) dominated the NR-PM1 mass increment at both sites, while nitrate was enhanced the most among the inorganic species (7-9%). Overall, the CP site exhibited higher OA oxidation potential and more enhancement of SVOOA than LVOOA (7.5 vs. 2.7g/m(3)), but the reverse was observed in HK (0.8 vs. 2.6g/m(3)). In CP, more enhancement of the less oxygenated SVOOA suggests that aerosol aging was more sensitive to the abundant locally emitted primary OA and volatile organic compound precursors. On the contrary, the more formation of the highly oxidized LVOOA in HK indicates that aerosol aging mainly escalated the degree of oxygenation of OA as ambient aerosol was already quite aged and there was a lack of volatile organic compound precursors. The comparative measurements using the same oxidation system reveal distinct key factors and mechanisms that influence secondary aerosol formation in two suburban locations in China, providing scientific insights to assist formulation of location-specific mitigation measures of secondary pollution. Plain Language Summary Atmospheric submicron particles have significant impacts on the climate and human health. A large part of these particles are formed secondarily through successive aging of primary emissions. To study such aging processes, we used a reactor that can provide highly oxidizing conditions to simulate the oxidation of ambient aerosols at accelerated rates. An online mass spectrometer was connected after the reactor to measure changes in aerosol mass concentration and chemical composition between the ambient samples and the oxidized ones. We presented the first comparative measurements of the aging potentials of ambient aerosols in two suburban sites in northern and southern China (Changping District in Beijing, and Hong Kong). Results showed that generally aerosols at the Changping site had higher aging potentials after passing through the oxidation reactor, probably due to more local emissions of precursors, while air masses in Hong Kong were already in a higher oxidation state with lower aging potentials, mainly because of strong impacts from long-range transported pollution sources. Distinct aerosol aging pathways related to different ambient precursors were observed at the two sites. Understanding of the different characteristics of aerosol aging processes can lead to advances in air quality modeling and pollution management.
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| 28. |
- Mohr, Claudia, et al.
(författare)
-
Molecular identification of organic vapors driving atmospheric nanoparticle growth
- 2019
-
Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Particles formed in the atmosphere via nucleation provide about half the number of atmospheric cloud condensation nuclei, but in many locations, this process is limited by the growth of the newly formed particles. That growth is often via condensation of organic vapors. Identification of these vapors and their sources is thus fundamental for simulating changes to aerosol-cloud interactions, which are one of the most uncertain aspects of anthropogenic climate forcing. Here we present direct molecular-level observations of a distribution of organic vapors in a forested environment that can explain simultaneously observed atmospheric nanoparticle growth from 3 to 50nm. Furthermore, the volatility distribution of these vapors is sufficient to explain nanoparticle growth without invoking particle-phase processes. The agreement between observed mass growth, and the growth predicted from the observed mass of condensing vapors in a forested environment thus represents an important step forward in the characterization of atmospheric particle growth.
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| 29. |
- Barišić, Antun, et al.
(författare)
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Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media
- 2021
-
Ingår i: Colloids and interfaces. - : MDPI. - 2504-5377. ; 5:1
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrations showed that these surfaces acquired less charge from proton-related reactions than oxide minerals. The data from batch-type titrations for PTFE powder did not show an effect of ionic strength, which was also in contrast with results for classical colloids. In agreement with classical colloids, the electrokinetic results for inert surfaces showed the typical salt level dependence. In some cases, the point of zero net proton charge as determined from mass and tentatively from acid–base titration differed from isoelectric points, which has also been previously observed, for example by Chibowski and co-workers for ice electrolyte interfaces. Finally, we found no evidence for surface contaminations of our PTFE particles before and after immersion in aqueous solutions. Only in the presence of NaCl-containing solutions did cryo-XPS detect oxygen from water. We believe that our low isoelectric points for PTFE were not due to impurities. Moreover, the measured buffering at pH 3 could not be explained by sub-micromolar concentrations of contaminants. The most comprehensive explanation for the various sets of data is that hydroxide ion accumulation occurred at the interfaces between inert surfaces and aqueous solutions.
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| 30. |
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| 31. |
- Erdtman, Edvin, 1981-
(författare)
-
5-Aminolevulinic acid and derivatives thereof : properties, lipid permeability and enzymatic reactions
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 5-aminolevulinic acid (5-ALA) and derivatives thereof are widely usedprodrugs in treatment of pre-malignant skin diseases of the cancer treatmentmethod photodynamic therapy (PDT). The target molecule in 5-ALAPDTis protoporphyrin IX (PpIX), which is synthesized endogenously from5-ALA via the heme pathway in the cell. This thesis is focused on 5-ALA,which is studied in different perspectives and with a variety of computationalmethods. The structural and energetic properties of 5-ALA, itsmethyl-, ethyl- and hexyl esters, four different 5-ALA enols, and hydrated5-ALA have been investigated using Quantum Mechanical (QM) first principlesdensity functional theory (DFT) calculations. 5-ALA is found to bemore stable than its isomers and the hydrolysations of the esters are morespontaneous for longer 5-ALA ester chains than shorter. The keto-enoltautomerization mechanism of 5-ALA has been studied, and a self-catalysismechanism has been proposed to be the most probable. Molecular Dynamics(MD) simulations of a lipid bilayer have been performed to study themembrane permeability of 5-ALA and its esters. The methyl ester of 5-ALAwas found to have the highest permeability constant (PMe-5-ALA = 52.8 cm/s).The mechanism of the two heme pathway enzymes; Porphobilinogen synthase(PBGS) and Uroporphyrinogen III decarboxylase (UROD), have beenstudied by DFT calculations and QM/MM methodology. The rate-limitingstep is found to have a barrier of 19.4 kcal/mol for PBGS and 13.7kcal/mol for the first decarboxylation step in UROD. Generally, the resultsare in good agreement with experimental results available to date.
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| 32. |
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| 33. |
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| 34. |
- Erdtman, Edvin, et al.
(författare)
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Theoretical study of 5-aminolevulinic acid tautomerization : a novel self-catalyzed mechanism
- 2008
-
Ingår i: Journal of Physical Chemistry A. - Washington DC : American Chemical Society. - 1089-5639 .- 1520-5215. ; 112:18, s. 4367-4374
-
Tidskriftsartikel (refereegranskat)abstract
- 5-Aminolevulinic acid (5ALA) is the key synthetic building block in protoporphyrin IX (PpIX), the heme chromophore in mitochondria. In this study density functional theory calculations were performed on the tautomers of 5ALA and the tautomerization reaction mechanism from its enolic forms (5-amino-4-hydroxypent-3-enoic acid and 5-amino-4-hydroxypent-4-enoic acid) to the more stable 5ALA. The hydrated form 5-amino-4,4-dihydroxypentanoic acid was also studied. The lowest energy pathway of 5ALA tautomerization is by means of autocatalysis, in that an oxygen of the carboxylic group transfers the hydrogen atom as a "crane", with an activation energy of similar to 15 kcal/mol. This should be compared to the barriers of about 35 kcal/mol for water assisted tautomerization, and 60 kcal/mol for direct hydrogen transfer. For hydration of 5ALA, the water catalyzed activation barrier is found to be similar to 35 kcal/mol, approximately 5 kcal/mol lower than direct hydration.
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| 35. |
- Friedman, Ran
(författare)
-
Ions and the protein surface revisited : extensive molecular dynamics simulations and analysis of protein structures in alkali-chloride solutions
- 2011
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 115, s. 9213-9223
-
Tidskriftsartikel (refereegranskat)abstract
- Proteins interact with ions in various ways. The surface of proteins has an innate capability to bind ions, and it is also influenced by the screening of the electrostatic potential owing to the presence of salts in the bulk solution. Alkali metal ions and chlorides interact with the protein surface, but such interactions are relatively weak and often transient. In this paper, computer simulations and analysis of protein structures are used to characterize the interactions between ions and the protein surface. The results show that the ion-binding properties of protein residues are highly variable. For example, alkali metal ions are more often associated with aspartate residues than with glutamates, whereas chlorides are most likely to be located near arginines. When comparing NaCl and KCl solutions, it was found that certain surface residues attract the anion more strongly in NaCl. This study demonstrates that protein–salt interactions should be accounted for in the planning and execution of experiments and simulations involving proteins, particularly if subtle structural details are sought after.
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| 36. |
- Friedman, Ran, et al.
(författare)
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Surfactant Effects on Amyloid Aggregation Kinetics
- 2011
-
Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 414, s. 303-312
-
Tidskriftsartikel (refereegranskat)abstract
- There is strong experimental evidence of the influence of surfactants (e.g., fatty acids) on the kinetics of amyloid fibril formation. However, the structures of mixed assemblies and interactions between surfactants and fibril-forming peptides are still not clear. Here, coarse-grained simulations are employed to study the aggregation kinetics of amyloidogenic peptides in the presence of amphiphilic lipids. The simulations show that the lower the fibril formation propensity of the peptides, the higher the influence of the surfactants on the peptide self-assembly kinetics. In particular, the lag phase of weakly aggregating peptides increases because of the formation of mixed oligomers, which are promoted by hydrophobic interactions and favorable entropy of mixing. A transient peak in the number of surfactants attached to the growing fibril is observed before reaching the mature fibril in some of the simulations. This peak originates from transient fibrillar defects consisting of exposed hydrophobic patches on the fibril surface, which provide a possible explanation for the temporary maximum of fluorescence observed sometimes in kinetic traces of the binding of small-molecule dyes to amyloid fibrils.
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| 37. |
- Luong, N. Tan, 1995-
(författare)
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Water film-mediated mineralogical transformations and photocatalytic reactions
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mineral particles capture water vapor in the atmosphere in the form of water films that are only few monolayers thick. Water films form nanoscale hydration environments that mediate a wide range of important reactions in nature and technology. This thesis explored two important phenomena that commonly occur within the confines of water films: mineralogical transformations (Topic 1) and photocatalytic decomposition of organics (Topic 2). These transformations were chiefly identified by vibrational spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and (Transmission and Scanning) electron microscopy. Interpretations of reaction mechanisms were partially supported by chemometrics, kinetic and thermodynamic modeling, as well as molecular simulations.Mineralogical transformations (Topic 1) resolved in this thesis involved the hydroxylation (Papers I, II) and carbonation (Paper III) of periclase (MgO), and the oxidation of rhodochrosite (MnCO3) (Paper IV). Two types of MgO nanocubes with contrasting physical properties were used to resolve nucleation- and diffusion-limited hydroxylation reactions to brucite and carbonation reactions to amorphous magnesium carbonate (AMC). While nucleation-limited reactions completely transformed (8 nm) small and aggregated MgO nanocubes to brucite, the reactions became diffusion-limited in larger (32 nm) monodispersed MgO nanocubes because of brucite surface nanocoatings (Paper I). Additionally, brucite nanosheets grew under (GPa-level) crystallization pressures because of the important volumetric expansion of the reaction, which took place in a complex network of microporosity between the small and within the larger MgO nanocubes. Brucite stacking mechanisms, explored in Paper II, focused on the early stages of MgO-water interaction in water films of different thicknesses. These were suggested to involve the stacking and (epitaxial-like) growth of precursor Mg(OH)2 nanosheets in water films. Carbonation reactions explored in Paper III completely hampered hydroxylation reactions studied in Papers I and II, and produced AMC nanocoatings grown over an unreacted MgO core. Finally, oxidation-driven reactions involving rhodochrosite in Paper IV produced MnO2, Mn3O4, and MnOOH nanocoatings with growth rates being scaled with water loadings.Photocatalytic decomposition reactions of organics (Topic 2) were focused on the case of oxalate bound to TiO2 nanoparticles (Paper V). Photodecomposition rates scaled with humidity in oxygenated water films, and were explained by the combination of hole transfer (HT), ligand-to-metal charge transfer (LMCT), and the formation of hydroxyl radicals and reactive oxygen species. Decreasing rates in oxygen-free water films were, on the other hand, explained by water-driven charge localization, which eventually limited radical production and charge transfers via HT and LMCT. The reactions involved limited HT and LMCT processes which also competed with a charge recombination process across all humidity ranges.This thesis provides new insight into two key types of transformations mediated by water films on minerals. This knowledge can be used to understand the reactivity of mineral (nano)particles exposed to variations in atmospheric humidity and oxygen content, which are both highly relevant to a wide range of settings in nature and technology. It can also advance new ideas in the study of mineral growth, especially within the confines of nanometer-thick water films.
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| 38. |
- Xu, Yuan, et al.
(författare)
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Understanding intermolecular interactions of large systems in ground state and excited state by using density functional based tight binding methods
- 2021
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 154:19
-
Tidskriftsartikel (refereegranskat)abstract
- A novel energy decomposition analysis scheme, named DFTB-EDA, is proposed based on the density functional based tight-binding method (DFTB/TD-DFTB), which is a semi-empirical quantum mechanical method based on Kohn–Sham-DFT for large-scale calculations. In DFTB-EDA, the total interaction energy is divided into three terms: frozen density, polarization, and dispersion. Owing to the small cost of DFTB/TD-DFTB, DFTB-EDA is capable of analyzing intermolecular interactions in large molecular systems containing several thousand atoms with high computational efficiency. It can be used not only for ground states but also for excited states. Test calculations, involving the S66 and L7 databases, several large molecules, and non-covalent bonding complexes in their lowest excited states, demonstrate the efficiency, usefulness, and capabilities of DFTB-EDA. Finally, the limits of DFTB-EDA are pointed out.
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| 39. |
- Zhou, Yu, et al.
(författare)
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Unveiling the Interfacial Effects for Enhanced Hydrogen Evolution Reaction on MoS2/WTe2 Hybrid Structures
- 2019
-
Ingår i: Small. - : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 15:19
-
Tidskriftsartikel (refereegranskat)abstract
- Using the MoS2-WTe2 heterostructure as a model system combined with electrochemical microreactors and density function theory calculations, it is shown that heterostructured contacts enhance the hydrogen evolution reaction (HER) activity of monolayer MoS2. Two possible mechanisms are suggested to explain this enhancement: efficient charge injection through large-area heterojunctions between MoS2 and WTe2 and effective screening of mirror charges due to the semimetallic nature of WTe2. The dielectric screening effect is proven minor, probed by measuring the HER activity of monolayer MoS2 on various support substrates with dielectric constants ranging from 4 to 300. Thus, the enhanced HER is attributed to the increased charge injection into MoS2 through large-area heterojunctions. Based on this understanding, a MoS2/WTe2 hybrid catalyst is fabricated with an HER overpotential of -140 mV at 10 mA cm(-2), a Tafel slope of 40 mV dec(-1), and long stability. These results demonstrate the importance of interfacial design in transition metal dichalcogenide HER catalysts. The microreactor platform presents an unambiguous approach to probe interfacial effects in various electrocatalytic reactions.
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| 40. |
- Hedlund, Artur, et al.
(författare)
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Microstructures of cellulose coagulated in water and alcohols from 1-ethyl-3-methylimidazolium acetate : contrasting coagulation mechanisms
- 2019
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 26:3, s. 1545-1563
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract: Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations. Graphical abstract: [Figure not available: see fulltext.].
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| 41. |
- Moth-Poulsen, Kasper, 1978
(författare)
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Molecular Systems for Solar Thermal Energy Storage and Conversion
- 2013
-
Ingår i: Organic Synthesis and Molecular Engineering. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. ; , s. 179-196
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Using a synthetic approach to organic materials chemistry, this book sets forth tested and proven methods and practices that make it possible to engineer organic molecules offering special properties and functions. Throughout the book, plenty of real-world examples demonstrate the countless possibilities of creating one-of-a-kind molecules and supramolecular systems to support a broad range of applications. The book explores applications in both materials and bioorganic chemistry, including molecular electronics, energy storage, sensors, nanomedicine, and enzyme engineering.Organic Synthesis and Molecular Engineering consists of fourteen chapters, each one contributed by one or more leading international experts in the field. The contributions are based on a thorough review and analysis of the current literature as well as the authors' firsthand experience in the lab engineering new organic molecules. Designed as a practical lab reference, the book offers:Tested and proven synthetic approaches to organic materials chemistryMethods and practices to successfully engineer functionality into organic moleculesExplanations of the principles and concepts underlying self-assembly and supramolecular chemistryGuidance in selecting appropriate structural units used in the design and synthesis of functional molecules and materialsCoverage of the full range of applications in materials and bioorganic chemistryA full chapter on graphene, a new topic generating intense researchOrganic Synthesis and Molecular Engineering begins with core concepts, molecular building blocks, and synthetic tools. Next, it explores molecular electronics, supramolecular chemistry and self-assembly, graphene, and photoresponsive materials engineering. In short, it offers everything researchers need to fully grasp the underlying theory and then build new molecules and supramolecular systems.
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| 42. |
- Sun, Bing, et al.
(författare)
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Ion transport in polycarbonate based solid polymer electrolytes : experimental and computational investigations
- 2016
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:14, s. 9504-9513
-
Tidskriftsartikel (refereegranskat)abstract
- Among the alternative host materials for solid polymer electrolytes (SPEs), polycarbonates have recently shown promising functionality in all-solid-state lithium batteries from ambient to elevated temperatures. While the computational and experimental investigations of ion conduction in conventional polyethers have been extensive, the ion transport in polycarbonates has been much less studied. The present work investigates the ionic transport behavior in SPEs based on poly(trimethylene carbonate) (PTMC) and its co-polymer with epsilon-caprolactone (CL) via both experimental and computational approaches. FTIR spectra indicated a preferential local coordination between Li+ and ester carbonyl oxygen atoms in the P(TMC20CL80) co-polymer SPE. Diffusion NMR revealed that the co-polymer SPE also displays higher ion mobilities than PTMC. For both systems, locally oriented polymer domains, a few hundred nanometers in size and with limited connections between them, were inferred from the NMR spin relaxation and diffusion data. Potentiostatic polarization experiments revealed notably higher cationic transference numbers in the polycarbonate based SPEs as compared to conventional polyether based SPEs. In addition, MD simulations provided atomic-scale insight into the structure-dynamics properties, including confirmation of a preferential Li+-carbonyl oxygen atom coordination, with a preference in coordination to the ester based monomers. A coupling of the Li-ion dynamics to the polymer chain dynamics was indicated by both simulations and experiments.
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| 43. |
- Lyubartsev, Alexander, 1962-, et al.
(författare)
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Hierarchical multiscale modelling scheme from first principles to mesoscale
- 2009
-
Ingår i: Journal of Computational and Theoretical Nanoscience. - : American Scientific Publishers. - 1546-1955 .- 1546-1963. ; 6:5, s. 951-959
-
Tidskriftsartikel (refereegranskat)abstract
- We present a straight-forward implementation of a practical hierarchical multiscale modelling scheme which enables us to start from first-principles atomistic computer simulation and successively coarse-grain the model by leaving out uninteresting degrees of freedom. Using the Car-Parrinello method or our recently developed highly efficient tight-binding-like approximate density-functional quantum mechanical method,w e first perform first-principles simulations we obtain a set of atomistic pair-wise effective interaction potentials to be used as a force field with scaling up the system size 2–3 orders of magnitude. The atomistic simulations similarly provide a new set of effective potentials but at a chosen coarse-grain level suitable for large-scale mesoscopic or soft-matter simulations beyond the atomic resolution. Show several examples are shown of how this scheme is done based on effective interaction potentials to tie together the various scales of modelling.
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| 44. |
- Tong, Yujin, et al.
(författare)
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Preferential Adsorption of Amino-Terminated Silane in a Binary Mixed Self-Assembled Monolayer
- 2011
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:9, s. 5420-5426
-
Tidskriftsartikel (refereegranskat)abstract
- The composition and structure of a binary mixed self-assembled monolayer (SAM) of 3-aminopropyltiethoxysilane (APS, NH2(CH2)(3)Si-(OCH2CH3)(3)) and octadecyltrimethoxysilane (ODS, CH3(CH2)(17)Si(OCH3)(3)) on a silicon oxide surface have been characterized by water contact-angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. XPS demonstrated that APS in the mixed SAM is significantly enriched in comparison to that in solution, indicating the preferential adsorption of APS during the SAM formation. AFM observations showed that the mixed SAM becomes rougher. SFG revealed that the coadsorption of APS induced a conformation disordering in the ODS molecules present in the mixed SAM. The surface enrichment of APS has been explained in terms of differences in the surface adsorption rates of the two components as well as in the self-congregation states of APS molecules in the bulk solution. Furthermore, the structure of the water molecules on the mixed SAM surface in contact with the aqueous solutions at different pH's has also been studied. The results indicate that the mixed-SAM modified surface is positively charged at pH < 5 and negatively charged at pH > 7.
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| 45. |
- Wallqvist, Viveca, 1977-
(författare)
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Interactions between non-polar surfaces in water: Fokus on talc, pitch and surface roughness effects
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work was to gain understanding of the interactions between talc mineral and surfaces, liquids and chemicals relevant for industrial applications, such as pulp and paper. Talc is used in the pulp and paper industry as a filler pigment, in control of pitch (lipophilic extractives) deposits and as a coating pigment. A deeper understanding of talc interactions will be beneficial in optimizing its use. Long-range attractive interactions between talc and hydrophobic model probes, as well as pitch probes, have been measured using the atomic force microscope (AFM) colloidal probe method. Two procedures for preparation of pitch colloidal probes were developed to allow these studies. Model hydrophobic, nanorough surfaces with surface energy characteristics similar to talc have also been prepared and their interactions with hydrophobic model probes compared to interactions between hydrophobic model probes and talc. It is demonstrated that talc mineral interacts with model hydrophobic particles, as well as with pitch, by long-range attractive forces, considerably stronger than the expected van der Waals force. The possible origin of the measured interaction forces is discussed, and the conclusion is that the main cause is an attractive capillary force due to formation of a gas/vapor capillary between the surfaces. Force measurements using model hydrophobic, nanorough surfaces show that a large-scale waviness does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. It is demonstrated that a large variation in adhesion force corresponds to a small variation in local contact angle of the capillaries at the surfaces. The nature of the surface topographical features influences the capillary attraction by affecting the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on the size of the surface features and whether they exist in the form of crevices or as extending ridges. Entrapment of air also affects the imbibition of water in pressed talc tablets. The effects of wetting and dispersion agents on the interactions between talc and hydrophobic probes have also been investigated. It is demonstrated that a common dispersing agent used for talc, poly(acrylic acid), does not affect the capillary attraction between talc and non-polar probes. In fact, the results strongly suggest that poly(acrylic acid) does not adsorb on the basal plane of talc. From this finding it is inferred that the stabilizing effect of this additive most likely is due to adsorption to the edges of talc. In contrast, a wetting agent (the non-ionic triblock copolymer Pluronic PE6400) removes the long-range capillary attraction. It is suggested that such an ability to replace air at the talc surface is of great importance for an efficient wetting agent. The Hamaker constant for talc has also been estimated by using optical data obtained from spectroscopic ellipsometry. It is demonstrated that a nanocrystalline talc mineral, cut in different directions displays very small differences in Hamaker constant between the different crystallographic orientations, whereas a microcrystalline sample displays a significantly higher value. The estimated Hamaker constants are discussed for different material combinations of relevance for the pulp- and paper industry, such as cellulose and calcium carbonate.
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| 46. |
- Sörensen, Malin H., et al.
(författare)
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Improved enzymatic activity of Thermomyces lanuginosus lipase immobilized in a hydrophobic particulate
- 2010
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier Inc.. - 0021-9797 .- 1095-7103. ; 343:1, s. 359-365
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Tidskriftsartikel (refereegranskat)abstract
- Lipase from Thermomyces lanuginosus has been immobilized within particulate mesoporous silica carriers, with either hydrophilic or hydrophobic supporting surfaces, produced by the newly developed emulsion and solvent evaporation (ESE) method. The Michaelis-Menten model was used to calculate the parameters related to the enzymatic activity of lipase i.e. the turnover number, kcat, and the specific activity. The specific activity was improved by immobilization of lipase onto the hydrophobic support, compared to lipase immobilized onto the hydrophilic support and lipase free in solution. The enhanced enzymatic activity of lipase onto a hydrophobic support was attributed to interfacial activation of the Thermomyces lanuginosus lipase when it is attached to a hydrophobic surface and a reduced denaturation. Confocal scanning laser microscopy (CLSM) studies, of fluorescently tagged lipase, showed that leakage of the lipase from the mesoporous particles was limited to an initial period of only a few hours. Both the rate and the amount of lipase leached were reduced when the lipase was immobilized onto the hydrophobic support.
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| 47. |
- Kiraev, Salauat
(författare)
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Unravelling Sensitisation and Quenching Pathways in Lanthanide Luminophores
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lanthanide (Ln) ions find use in cellular detection and probing of many analytes, owing to their unique photophysical properties. However, to make the Ln emission efficient, one has to develop a light-harvesting antenna, which is an organic chromophore that absorbs and transfers energy to the Ln. By exciting the Ln complex, photoinduced electron transfer (PeT) from the antenna to the readily reducible Ln might occur. Usually, PeT is quenching Ln emission intensity. Thus, the work herein aims to evaluate and distinguish sensitising and quenching pathways in Ln emission to improve the brightness of Ln luminophores for biological applications.After presenting an introduction to Ln photophysics and sensitisation in chapter 1, chapter 2 describes our work on Ln octa- and nonacoordinate complexes bearing the same antenna. We demonstrated that the azide and alkyne reactive groups could be attached to the antenna to make Ln complexes bioconjugable. The saturation of the Ln coordination environment resulted in intraligand PeT, which cancelled out the benefits of eliminated quenching from the coordinated water molecule.To study the effect of photoredox quenching in Eu emission, we focused on tuning reduction potentials for a possible response in luminescence properties in chapter 3. Increasing positive charges of complexes destabilised Eu3+ and decreased Ln emission quantum yields. This behaviour was due to PeT quenching of the more readily reducible Eu under similar sensitisation conditions. Fluoride binding boosted Ln emission intensity in the least Eu3+-stabilising ligand field.In chapter 4, the role of a tertiary amide linker between the antenna and the metal binding site was examined. For poorly emissive coumarin-appended complexes quenching via photoinduced reduction of Eu from the antenna was unlikely, while in carbostyril-sensitised complexes PeT was efficient.Ln compounds with lower ligand denticity allowed better fluoride detection via the increased effect of PeT quenching and the larger number of water molecules, as shown in chapter 5. However, the presence of cyanide significantly quenched Eu emissions of the same complexes, making it possible to distinguish cyanide from fluoride.Chapters 6‒7 were devoted to the sensitisation of Yb luminescence. The NIR emission intensity increased marginally in the complexes with efficient PeT. The main sensitising effect originated from phonon-assisted energy transfer favourable in our Yb complexes. When picolinate donors stimulated intraligand PeT, detrimental to the ligand fluorescence in Yb compounds, Yb emission was noticeably more intense than in the first series without picolinates.
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| 48. |
- Sznitko, L., et al.
(författare)
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Low-threshold stimulated emission from lysozyme amyloid fibrils doped with a blue laser dye
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 106:2
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Tidskriftsartikel (refereegranskat)abstract
- © 2015 AIP Publishing LLC. Amyloid fibrils are excellent self-assembling nanotemplates for organic molecules such as dyes. Here, we demonstrate that laser dye-doped lysozyme type fibrils exhibit significantly reduced threshold for stimulated emission compared to that observed in usual matrices. Laser action was studied in slab planar waveguides of the amyloids doped with Stilbene 420 laser dye prepared using a film casting technique. The lowering of the threshold of stimulated emission is analyzed in the context of intrinsic structure of the amyloid nanotemplates, electrostatic interaction of different microstructures with dye molecules, as well as material properties of the cast layers. All these factors are considered to be of importance for introducing gain for random laser operation.
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| 49. |
- Erdtman, Edvin, et al.
(författare)
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Computational insights into the mechanism of porphobilinogen synthase
- 2010
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Ingår i: Journal of Physical Chemistry B. - Washington : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:50, s. 16860-16870
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Tidskriftsartikel (refereegranskat)abstract
- Porphobilinogen synthase (PBGS) is a key enzyme in heme biosynthesis that catalyzes the formation of porphobilinogen (PBG) from two 5-aminolevulinic acid (5-ALA) molecules via formation of intersubstrateC-N and C-C bonds. The active site consists of several invariant residues, including two lysyl residues (Lys210 and Lys263; yeast numbering) that bind the two substrate moieties as Schiff bases. Based on experimental studies, various reaction mechanisms have been proposed for this enzyme that generally can be classified according to whether the intersubstrate C-C or C-N bond is formed first. However, the detailed catalytic mechanism of PBGS remains unclear. In the present study, we have employed density functional theory methods in combination with chemical models of the two key lysyl residues and two substrate moieties in order to investigate various proposed reaction steps and gain insight into the mechanism of PBGS. Importantly, it is found that mechanisms in which the intersubstrate C-N bond is formed first have a ratelimiting barrier (17.5 kcal/mol) that is lower than those in which the intersubstrate C-C bond is formed first (22.8 kcal/mol).
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| 50. |
- Börjesson, Karl, 1982, et al.
(författare)
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Conjugated anthracene dendrimers with monomer-like fluorescence
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:38, s. 19846-19850
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Tidskriftsartikel (refereegranskat)abstract
- Two generations of highly emissive conjugated anthracene dendrimers containing up to 9 anthracene units are presented. In these dendrimers, anthracene-like absorption and emission properties are preserved due to the relatively weak electronic coupling between the anthracene units, while evidence of fast crosstalk within the molecular framework is still observed.
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