| 39731. |
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| 39732. |
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| 39733. |
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| 39734. |
- Norell, Jesper, et al.
(författare)
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Ab initio simulations of complementary K-edges and solvatization effects for detection of proton transfer in aqueous 2-thiopyridone
- 2019
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:11
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Tidskriftsartikel (refereegranskat)abstract
- The nitrogen and sulfur K-edge X-ray absorption spectra of aqueous 2-thiopyridone, a model system for excited-state proton transfer in several recent time-resolved measurements, have been simulated from ab initio molecular dynamics. Spectral signatures of the local intra- and inter-molecular structure are identified and rationalized, which facilitates experimental interpretation and optimization. In particular, comparison of aqueous and gas phase spectrum simulations assesses the previously unquantified solvatization effects, where hydrogen bonding is found to yield solvatochromatic shifts up to nearly 1 eV of the main peak positions. Thereby, while each K-edge can still decisively determine the local protonation of its core-excited site, only their combined, complementary fingerprints allow separating all of the three relevant molecular forms, giving a complete picture of the proton transfer.
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| 39735. |
- Norell, Jesper, et al.
(författare)
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Interdependent Electronic Structure, Protonation, and Solvatization of Aqueous 2-Thiopyridone
- 2019
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 123:26, s. 5555-5567
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Tidskriftsartikel (refereegranskat)abstract
- 2-Thiopyridone (2-TP), a common model system for excited-state proton transfer, has been simulated in aqueous solution with ab initio molecular dynamics. The interplay of electronic structure, protonation, and solvatization is investigated by comparison of three differently protonated molecular forms and between the lowest singlet and triplet electronic states. An interdependence clearly manifests in the mixed-character T-1 state for the 2-TP form, systematic structural distortions of the 2-mercaptopyridine (2-MP) form, and photobase protolysis of the 2-TP- form, in the aqueous phase. In comparison, simplified continuum models for the solvatization are found to be significantly inaccurate for several of the species. To facilitate future computational studies, we therefore present a minimal representative solvatization complex for each stable form and electronic state. Our findings demonstrate the importance of explicit solvatization of the compound and sets the studies. stage for including it also in future studies.
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| 39736. |
- Norell, Jesper, et al.
(författare)
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Photoelectron shake-ups as a probe of molecular symmetry : 4d XPS analysis of I-3(-) in solution
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:30, s. 19916-19921
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Tidskriftsartikel (refereegranskat)abstract
- A combination of multi-configurational restricted active space calculations with a Dyson orbital formalism has been applied for accurate simulations of 4d photo-electron spectra of the I-3(-) molecular ion. The analysis based on the occupation numbers of natural orbitals allowed to predict and rationalize the spectral fingerprints of solvent-induced nuclear asymmetry. In particular, it demonstrates how the nuclear asymmetry directly causes an increase of shake-up intensity. The relative intensity of shake-up and main features of the I 4d XPS spectrum could therefore serve as a simplified experimental observable of structural asymmetry, complementary to changes in the shape of the main spectral features.
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| 39737. |
- Norén, Katarina, et al.
(författare)
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Adsorption mechanisms of EDTA at the water−iron oxide interface : implications for dissolution
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : ACS Publications. - 1932-7447 .- 1932-7455. ; 113:18, s. 7762-7771
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between chelating agents and metal oxide particles play important roles for the distribution and availability of metal ions in aquatic environments. In this work, the adsorption of ethylenediaminetetraacetate (EDTA) onto goethite (α-FeOOH) was studied as a function of pH, time, and background electrolyte concentration at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of infrared spectroscopy using the attenuated total reflectance sampling technique. The collective infrared spectroscopic results of this study show that two surface complexes consisting of HEDTA3− and H2EDTA2− predominate at the water−goethite interface within the pH range of 3−9. No direct interactions of these complexes with surface Fe(III) ions were detected; hence, most likely the surface complexes are stabilized at the interface by electrostatic and hydrogen-bonding forces. The formation of the EDTA surface complexes is fast (time scale of minutes), but a slower (time scale of hours to days) dissolution reaction also occurs. The dissolved iron in solution is in the form of the highly stable FeEDTA− solution complex, and the experimental evidence presented indicates that this complex can readsorb to the mineral surface. As dissolution proceeds, the concentration of FeEDTA− in the solution phase increases, and this in turn leads to a buildup of readsorbed FeEDTA− onto goethite. In the pH range of 4−7, this dissolution and readsorption process increases the total EDTA concentration at the surface. Under the experimental conditions in the present study, it is primarily the presence of uncomplexed EDTA in solution that drives the dissolution of goethite resulting in the subsequent readsorption of FeEDTA−, while the HEDTA3− and H2EDTA2− surface complexes are stable during this process.
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| 39738. |
- Norén, Katarina, et al.
(författare)
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Adsorption of monocarboxylates at the water/goethite interface : The importance of hydrogen bonding
- 2007
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 71:23, s. 5717-5730
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of monocarboxylates (acetate, benzoate and cyclohexanecarboxylate) at the water/goethite interface was studied as a function of pH and ionic strength by means of quantitative adsorption measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR spectra were obtained of suspensions prepared in both H2O and D2O. In order to identify the number of predominating surface complexes and to improve the resolution of overlapping peaks the ATR-FTIR spectra were subjected to a 2D correlation spectroscopic analysis. The adsorption envelopes of acetate, benzoate and cyclohexanecarboxylate are similar and depend strongly on pH and ionic strength, but the pH dependence is also correlated to the slightly different pKa values of the monocarboxylic acids. At the molecular level, the ATR-FTIR spectroscopic results reveal two surface complexes: one solvent-surface hydration-separated ion pair and one surface hydration-shared ion pair. The former predominates at circumneutral pH values while the latter forms mainly in the acidic pH range. We find no evidence for direct inner-sphere coordination between the carboxylic oxygens and the Fe(III) ions present at the surface. The identification of surface hydration-shared ion pairs emphasizes the importance of comparatively strong ionic hydrogen-bonding interactions for adsorption processes at the water/goethite interface.
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| 39739. |
- Norén, Katarina, et al.
(författare)
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Co-adsorption of Ga(III) and EDTA at the water/goethite interface : spectroscopic evidence for the formation of ternary surface complexes
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:39, s. 16547-16555
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Co-adsorption reactions between metal ions and anionic ligands play important roles in controlling availability and transport of chemical species in natural aquatic environments as well as in industrial processes. A molecular understanding of the properties of the surface species formed provides means to model these reactions in a predictive manner and to exploit them in synthetic routes of modified surfaces. In this study, we have used EXAFS and infrared spectroscopies in combination with quantitative adsorption measurements to investigate the coadsorption of Ga(III) and EDTA on α-FeOOH (goethite) as a function of pH. The quantitative results showed a 1:1 stoichiometry between adsorbed Ga(III) and EDTA and a maximum in total adsorption around pH 5. EXAFS and infrared data showed that the molecular structures displayed pH-dependent characteristics, and within the studied pH range, these results were concurrent and indicated that Ga(III)EDTA formed ternary surface complexes on goethite. The collective results were fully consistent with the occurrence of both outer sphere Ga(III)EDTA and inner sphere ternary surface complexes of type A (i.e., a surface−Ga(III)−EDTA structure), where the latter was favored by increasing pH. This study showed that despite a macroscopic adsorption behavior that was seemingly ligand-like, a substantial fraction of Ga(III) may bond directly to surface hydroxyl groups.
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| 39740. |
- Norén, L., et al.
(författare)
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Purification of crime scene DNA extracts using centrifugal filter devices
- 2013
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Ingår i: Investigative Genetics. - : Springer Science and Business Media LLC. - 2041-2223. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: The success of forensic DNA analysis is limited by the size, quality and purity of biological evidence found at crime scenes. Sample impurities can inhibit PCR, resulting in partial or negative DNA profiles. Various DNA purification methods are applied to remove impurities, for example, employing centrifugal filter devices. However, irrespective of method, DNA purification leads to DNA loss. Here we evaluate the filter devices Amicon Ultra 30 K and Microsep 30 K with respect to recovery rate and general performance for various types of PCR-inhibitory crime scene samples. Methods: Recovery rates for DNA purification using Amicon Ultra 30 K and Microsep 30 K were gathered using quantitative PCR. Mock crime scene DNA extracts were analyzed using quantitative PCR and short tandem repeat (STR) profiling to test the general performance and inhibitor-removal properties of the two filter devices. Additionally, the outcome of long-term routine casework DNA analysis applying each of the devices was evaluated. Results: Applying Microsep 30 K, 14 to 32% of the input DNA was recovered, whereas Amicon Ultra 30 K retained 62 to 70% of the DNA. The improved purity following filter purification counteracted some of this DNA loss, leading to slightly increased electropherogram peak heights for blood on denim (Amicon Ultra 30 K and Microsep 30 K) and saliva on envelope (Amicon Ultra 30 K). Comparing Amicon Ultra 30 K and Microsep 30 K for purification of DNA extracts from mock crime scene samples, the former generated significantly higher peak heights for rape case samples (P-values <0.01) and for hairs (P-values <0.036). In long-term routine use of the two filter devices, DNA extracts purified with Amicon Ultra 30 K were considerably less PCR-inhibitory in Quantifiler Human qPCR analysis compared to Microsep 30 K. Conclusions: Amicon Ultra 30 K performed better than Microsep 30 K due to higher DNA recovery and more efficient removal of PCR-inhibitory substances. The different performances of the filter devices are likely caused by the quality of the filters and plastic wares, for example, their DNA binding properties. DNA purification using centrifugal filter devices can be necessary for successful DNA profiling of impure crime scene samples and for consistency between different PCR-based analysis systems, such as quantification and STR analysis. In order to maximize the possibility to obtain complete STR DNA profiles and to create an efficient workflow, the level of DNA purification applied should be correlated to the inhibitor-tolerance of the STR analysis system used.
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