| 1. |
- Ali, Tara, 1980-, et al.
(författare)
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Liquid extraction of low molecular mass organic acids and hydroxamate siderophores from boreal forest soil
- 2011
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 43:12, s. 2417-2422
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Tidskriftsartikel (refereegranskat)abstract
- Low molecular mass organic acids (LMMOAs) and hydroxamate siderophores (HS) are molecules secreted by microbes and have previously been found in soil solution and in cultures. Mycorrhizal fungi are suggested to be involved in the nutrient uptake processes of trees and weathering of minerals. In this study soil samples taken from the O and E horizons of a podzol were extracted with 10 mM potassium phosphate buffer at pH 7.2. Variable parameters included addition of methanol to the extraction buffer and the use of ultrasonication or rotary shaking during extraction. LMMOAs and HS content of the soil extracts were determined. Analysis of soil extracts were carried out by liquid chromatography mass spectrometry (LC-MS) and the extraction results compared to results for soil solution samples obtained by centrifugation of the soils sampled. The extraction yields were significantly increased by addition of methanol to the extraction buffer, especially for the O horizon samples. Rotary shaking of the samples for 90 min gave slightly higher yields than ultrasonication for 15 min but the reduction in extraction time makes ultrasonication an attractive option. Of the HSs determined, ferricrocin was found in all samples. Optimal extraction conditions showed citric acid and isocitric acid to be the most abundant organic acids in the O and E horizons, respectively.
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| 2. |
- Azeem, Hafiz Abdul, et al.
(författare)
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Extending the scope of dispersive liquid–liquid microextraction for trace analysis of 3-methyl-1,2,3-butanetricarboxylic acid in atmospheric aerosols leading to the discovery of iron(III) complexes
- 2019
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Ingår i: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 411:13, s. 2937-2944
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Tidskriftsartikel (refereegranskat)abstract
- 3-Methyl-1,2,3-butanetricarboxylic acid (MBTCA) is a secondary organic aerosol and can be used as a unique emission marker of biogenic emissions of monoterpenes. Seasonal variations and differences in vegetation cover around the world may lead to low atmospheric MBTCA concentrations, in many cases too low to be measured. Hence, an important tool to quantify the contribution of terrestrial vegetation to the loading of secondary organic aerosol may be compromised. To meet this challenge, a dispersive liquid–liquid microextraction (DLLME) method, known for the extraction of hydrophobic compounds, was extended to the extraction of polar organic compounds like MBTCA without compromising the efficiency of the method. The extraction solvent was fine-tuned using tri-n-octyl phosphine oxide as additive. A multivariate experimental design was applied for deeper understanding of significant variables and interactions between them. The optimum extraction conditions included 1-octanol with 15% tri-n-octyl phosphine oxide (w/w) as extraction solvent, methanol as dispersive solvent, 25% NaCl dissolved in 5 mL sample (w/w) acidified to pH 2 using HNO 3 , and extraction time of 15 min. A limit of detection of 0.12 pg/m 3 in air was achieved. Furthermore, unique complexation behavior of MBTCA with iron(III) was found when analyzed with ultra-high-performance liquid chromatography coupled with electrospray ionization–quadrupole time-of-flight mass spectrometry (UHPLC–ESI–QToF). A comprehensive overview of this complexation behavior of MBTCA was examined with systematically designed experiments. This newly discovered behavior of MBTCA will be of interest for further research on organometallic photooxidation chemistry of atmospheric aerosols. [Figure not available: see fulltext.].
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| 3. |
- Bylund, Dan, et al.
(författare)
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Analysis of low molecular mass organic acids in natural waters by ion exclusion chromatography tandem mass spectrometry
- 2007
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Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1176:1-2, s. 89-93
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Tidskriftsartikel (refereegranskat)abstract
- A sensitive and selective method for the analysis of aliphatic low molecular mass organic acids (LMMOAs) in natural waters is presented. The method is based on separation with ion exclusion chromatography and detection with electrospray ionization tandem mass spectrometry (LC-MS/MS). The extra selectivity gained by applying MS/MS allows for a minimum of sample preparation and the use of a sub-optimal mobile phase regarding chromatographic resolution. Instead the mobile phase, comprising aqueous formic acid With methanol as organic modifier, was mainly optimized for maximum sensitivity and long term MS stability. Detection limits for malonic, fumaric, maleic, succinic, citraconic, glutaric, malic, alpha-ketoglutaric, tartaric, shikimic, trans-aconitic, cis-aconitic, isocitric and citric acid were in the range 1-50 nM, while the detection limits for pyruvic, oxalic and lactic acid were around 250 nM for an injection volume of 100 mu L. Due to their metal-chelating properties, these LMMOAs are all considered to affect the bioavailability of metals and to be involved in soil forming processes. It is thus of interest to be able to monitor their presence in natural waters, and the method developed within this work was successfully applied for the analysis of LMMOAs in soil solution and stream water samples.
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| 4. |
- Chábera, Pavel, et al.
(författare)
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A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 543:7647, s. 695-699
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Tidskriftsartikel (refereegranskat)abstract
- Transition-metal complexes are used as photosensitizers1, in light-emitting diodes, for biosensing and in photocatalysis2. A key feature in these applications is excitation from the ground state to a charge-transfer state3,4; the long charge-transfer-state lifetimes typical for complexes of ruthenium5 and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron6 and copper7 being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs6,8,9,10, it remains a formidable scientific challenge11 to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered12 photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers13,14,15. Here we present the iron complex [Fe(btz)3]3+ (where btz is 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d5 complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes4,16,17. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.
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| 5. |
- Ebbevi, David, et al.
(författare)
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Value-based health care for chronic care : aligning outcomes measurement with the patient perspective
- 2016
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Ingår i: Quality Management in Health Care. - : Lippincott, Williams & Wilkins. - 1063-8628 .- 1063-8628 .- 1550-5154. ; 25:4, s. 203-212
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Tidskriftsartikel (refereegranskat)abstract
- Background: Value-based health care is increasingly used for developing health care services by relating patient outcomes to costs. A hierarchical value scorecard for creating outcome measurements has been suggested: The 3-Tier model. The objective of this study was to test the model against the patient's view of value in a chronic care setting. Methods: Semistructured interviews with 22 persons with rheumatoid arthritis were conducted, transcribed, and analyzed using qualitative content analysis. Themes were extracted, and the model was critically applied and revised. Results: The study validates existing dimensions in the model but suggests adding information, social health, predictability, and continuity to make it more useful and representative of patients' preferences. Conclusion: Although the model aims to focus on outcomes relevant to patients, it lacks dimensions important to individuals with rheumatoid arthritis. The data illustrate difficulties in finding patients' preferred outcomes and imply tactics for arriving at meaningful measurements.
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| 6. |
- Essén, Sofia
(författare)
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Hydroxamate Siderophores and Low Molecular Mass Organic Acids in Terrestrial and Aquatic Environments Determined by Liquid Chromatography Mass Spectrometry
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Siderophores are low molecular mass organic compounds with high iron(III) stability constants. They are produced by many microorganisms, often in combination with low molecular mass organic acids (LMMOAs). Both siderophores and LMMOAs accelerate mineral weathering, thereby enhancing mineral nutrient availability. Siderophore concentrations in natural environments, however, are largely unknown. In the present work, analytical methods based on liquid chromatography (LC) electrospray ionization mass spectrometry (ESI‐MS) were developed and used for concentration determination of selected hydroxamate siderophores and LMMOAs. The use of capillary LC with on‐line pre‐concentration via column switching enabled siderophore quantification with detection limits of 0.1 ‐ 5 nM. Through solid phase extraction even lower detection limits were achieved. In Swedish podzol soil solutions concentrations up to 12 nM ferricrocin and 2 nM ferrichrome were found in the upper soil layes. Additionally, in axenic pine (Pinus sylvestris) seedling cultures, the ectomycorrhizal fungus Hebeloma crustuliniforme was shown to produce ferricrocin as the main siderophore. Moreover, ferricrocin was found in enriched Baltic Sea cyanobacterial populations at concentrations up to 1 nM, while concentrations up to 0.05 nM ferrioxamine B were determined in Baltic Sea surface waters during cyanobacterial blooms. Siderophores have strong affinities for some actinides and may affect radionuclide mobilization in deep subsurface nuclear wase repositories. Two subsurface bacterial strains were shown to produce siderophores under aerobic conditions, i.e. Pseudomonas stutzeri produced mainly ferrioxamine E and Pseudomonas fluorescens produced one pyoverdin siderophore. Siderophores produced by aerobically grown P. stutzeri were not observed either in anaerobic cultures or in deep subsurface water samples.
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| 7. |
- Essén, Sofia, et al.
(författare)
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Quantification of hydroxamate siderophores in soil solutions of podzolic soil profiles in Sweden
- 2006
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Ingår i: Biometals. - : Springer Science and Business Media LLC. - 0966-0844 .- 1572-8773. ; 19:3, s. 269-282
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations up to 2 and 12 nM of the hydroxamate siderophores ferrichrome and ferricrocin, respectively, were identified in soil solutions of podzolic forest soils at four sites in both northern and southern Sweden. No ferrichrysin was detected. As with the dissolved organic carbon and low molecular mass organic acids, the highest concentrations of the siderophores were found in the upper layers i.e. the mor layer, the eluvial and upper illuvial horizons. At the southern sites, the concentrations of ferrichrome and ferricrocin were both of similar magnitude and did not differ between the two sites. In contrast, soil solutions at the two northern sites contained more ferricrocin than ferrichrome; the ferricrocin concentrations were also higher at the northern sites than at the southern sites. Analyses were performed by high performance liquid chromatography with a porous graphitic carbon column on which ferrichrome, ferricrocin and ferrichrysin were separated. Detection by electrospray ionization mass spectrometry (ESI-MS) combined with on-line sample pre-concentration, by means of column-switching, enabled detection limits of 0.1-0.2 nM for ferrichrome, ferrichrysin and ferricrocin. The structural identities of the siderophores were further verified by MS/MS fragmentation. Fragmentation of ferrichrome, ferricrocin and ferrichrysin occured mainly via peptide cleavage. The most intense fragments were typified by the loss of one of the three iron(III) chelating hydroxamate residues, i.e N5-acyl-N5-hydroxy ornithine.
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| 8. |
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| 9. |
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| 10. |
- Ghaffarzadegan, Tannaz, et al.
(författare)
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Determination of free and conjugated bile acids in serum of Apoe(−/−) mice fed different lingonberry fractions by UHPLC-MS
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Bile acids (BAs) are known to be involved in cholesterol metabolism but interactions between the diet, BA profiles, gut microbiota and lipid metabolism have not been extensively explored. In the present study, primary and secondary BAs including their glycine and taurine-conjugated forms were quantified in serum of Apoe−/− mice by protein precipitation followed by reversed phase ultra-high-performance liquid chromatography and QTOF mass spectrometry. The mice were fed different lingonberry fractions (whole, insoluble and soluble) in a high-fat setting or cellulose in a high and low-fat setting. Serum concentrations of BAs in mice fed cellulose were higher with the high-fat diet compared to the low-fat diet (20–70%). Among the lingonberry diets, the diet containing whole lingonberries had the highest concentration of chenodeoxycholic acid (CDCA), ursodeoxycholic acid (UDCA), tauro-ursodeoxycholic acid (T-UDCA), α and ω-muricholic acids (MCA) and tauro-α-MCA (T-α-MCA), and the lowest concentration of tauro-cholic acid (T-CA), deoxycholic acid (DCA) and tauro-deoxycholic acid (T-DCA). The glycine-conjugated BAs were very similar with all diets. CDCA, UDCA and α-MCA correlated positively with Bifidobacterium and Prevotella, and T-UDCA, T-α-MCA and ω-MCA with Bacteroides and Parabacteroides.
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