| 94601. |
- Lenton, Samuel, et al.
(författare)
-
Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters.
- 2016
-
Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 1432-1017 .- 0175-7571.
-
Tidskriftsartikel (refereegranskat)abstract
- There are abundant examples of nanoclusters and inorganic microcrystals in biology. Their study under physiologically relevant conditions remains challenging due to their heterogeneity, instability, and the requirements of sample preparation. Advantages of using neutron diffraction and contrast matching to characterize biomaterials are highlighted in this article. We have applied these and complementary techniques to search for nanocrystals within clusters of calcium phosphate sequestered by bovine phosphopeptides, derived from osteopontin or casein. The neutron diffraction patterns show broad features that could be consistent with hexagonal hydroxyapatite crystallites smaller than 18.9 Å. Such nanocrystallites are, however, undetected by the complementary X-ray and FTIR data, collected on the same samples. The absence of a distinct diffraction pattern from the nanoclusters supports the generally accepted amorphous calcium phosphate structure of the mineral core.
|
|
| 94602. |
- Lenz, Annika, et al.
(författare)
-
Computational study of the catalytic effect of platinum on the decomposition of DNT
- 2012
-
Ingår i: International Journal of Quantum Chemistry. - : Wiley-Blackwell. - 0020-7608 .- 1097-461X. ; 112:7, s. 1852-1858
-
Tidskriftsartikel (refereegranskat)abstract
- The catalytic decomposition of dinitrotoluene (DNT; 3-4-DNT), a by-product of the explosive trinitrotoluene (trotyl), on a platinum surface is investigated computationally. Reaction paths have been computed for a DNT molecule interacting with a Pt-cluster under varying temperatures using quantum-chemical density functional theory. Two possible initiation steps where DNT split either into nitro-tolyl and NO2, or in nitro-tolyl-oxidanyl and NO, are considered. The energy barrier for the catalytic process is found to decrease significantly for the Pt catalyzed reaction compared with the uncatalyzed reaction.
|
|
| 94603. |
- Lenz, Annika, et al.
(författare)
-
The electronic structure and reflectivity of PEDOT:PSS from density functional theory
- 2011
-
Ingår i: Chemical Physics. - : Elsevier Science B.V., Amsterdam.. - 0301-0104 .- 1873-4421. ; 384:03-jan, s. 44-51
-
Tidskriftsartikel (refereegranskat)abstract
- The geometric and electronic structure of condensed phase organic conducting polymer PEDOT:PSS blends has been investigated by periodic density functional theory (DFT) calculations with a generalized-gradient approximation (GGA) functional, and a plane wave basis set. The influence of the degree of doping of the PEDOT polymer on structural and optical parameters such as the reflectivity, absorbance, conductivity, dielectric function, refractive index and the energy-loss function is studied. A flip from the benzoid to the quinoid structure is observed in the calculations when the neutral PEDOT is doped by negatively charged PSS. Also the optical properties are affected by the doping. In particular, the reflectivity was found to be very sensitive to the degree of doping, where higher doping implies higher reflectivity. The reflectivity is highly anisotropic, with the dominant contribution stemming from the direction parallel to the PEDOT polymer chain.
|
|
| 94604. |
- Lenz, Conny, et al.
(författare)
-
Are recent changes in sediment manganese sequestration in the euxinic basins of the Baltic Sea linked to the expansion of hypoxia?
- 2015
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 12:16, s. 4875-4894
-
Tidskriftsartikel (refereegranskat)abstract
- Expanding hypoxia in the Baltic Sea over the past century has led to the development of anoxic and sulfidic (euxinic) deep basins that are only periodically ventilated by inflows of oxygenated waters from the North Sea. In this study, we investigate the potential consequences of the expanding hypoxia for manganese (Mn) burial in the Baltic Sea using a combination of pore water and sediment analyses of dated sediment cores from eight locations. Diffusive fluxes of dissolved Mn from sediments to overlying waters at oxic, hypoxic and euxinic sites are consistent with an active release of Mn from these areas. Although the present- day fluxes are significant (ranging up to ca. 240 mu mol m(-2)d(-1)), comparison to published water column data suggests that the current benthic release of Mn is small when compared to the large pool of Mn already present in the hypoxic and anoxic water column. Our results highlight two modes of Mn carbonate formation in sediments of the deep basins. In the Gotland Deep area, Mn carbonates likely form from Mn oxides that are precipitated from the water column directly following North Sea inflows. In the Landsort Deep, in contrast, Mn carbonate and Mn sulfide layers appear to form independently of inflow events, and are possibly related to the much larger and continuous input of Mn oxides linked to sediment focusing. Whereas Mn-enriched sediments continue to accumulate in the Landsort Deep, this does not hold for the Gotland Deep area. Here, a recent increase in euxinia, as evident from measured bottom water sulfide concentrations and elevated sediment molybdenum (Mo), coincides with a decline in sediment Mn content. Sediment analyses also reveal that recent inflows of oxygenated water (since ca. 1995) are no longer consistently recorded as Mn carbonate layers. Our data suggest that eutrophication has not only led to a recent rise in sulfate reduction rates but also to a decline in reactive Fe input to these basins. We hypothesize that these factors have jointly led to higher sulfide availability near the sediment-water interface after inflow events. As a consequence, the Mn oxides may be reductively dissolved more rapidly than in the past and Mn carbonates may no longer form. Using a simple diagenetic model for Mn dynamics in the surface sediment, we demonstrate that an enhancement of the rate of reduction of Mn oxides is consistent with such a scenario. Our results have important implications for the use of Mn carbonate enrichments as a redox proxy in marine systems.
|
|
| 94605. |
- Lenz, Conny, et al.
(författare)
-
Hypoxia-driven variations in iron and manganese shuttling in the Baltic Sea over the past 8 kyr
- 2015
-
Ingår i: Geochemistry Geophysics Geosystems. - 1525-2027. ; 16:10, s. 3754-3766
-
Tidskriftsartikel (refereegranskat)abstract
- The Baltic Sea has experienced three major intervals of bottom water hypoxia following the intrusion of seawater circa 8 kyr ago. These intervals occurred during the Holocene Thermal Maximum (HTM), Medieval Climate Anomaly (MCA), and during recent decades. Here we show that sequestration of both Fe and Mn in Baltic Sea sediments generally increases with water depth, and we attribute this to shelf-to-basin transfer (shuttling) of Fe and Mn. Burial of Mn in slope and basin sediments was enhanced following the lake-brackish/marine transition at the beginning of the hypoxic interval during the HTM. During hypoxic intervals, shelf-to-basin transfer of Fe was generally enhanced but that of Mn was reduced. However, intensification of hypoxia within hypoxic intervals led to decreased burial of both Mn and Fe in deep basin sediments. This implies a nonlinearity in shelf Fe release upon expanding hypoxia with initial enhanced Fe release relative to oxic conditions followed by increased retention in shelf sediments, likely in the form of iron sulfide minerals. For Mn, extended hypoxia leads to more limited sequestration as Mn carbonate in deep basin sediments, presumably because of more rapid reduction of Mn oxides formed after inflows and subsequent escape of dissolved Mn to the overlying water. Our Fe records suggest that modern Baltic Sea hypoxia is more widespread than in the past. Furthermore, hypoxia-driven variations in shelf-to-basin transfer of Fe may have impacted the dynamics of P and sulfide in the Baltic Sea thus providing potential feedbacks on the further development of hypoxia.
|
|
| 94606. |
- Lenz, Conny
(författare)
-
Manganese cycling in the Baltic Sea over the last ~8000 years: the influence of redox conditions on mineral formation and burial
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Baltic Sea is one of the largest brackish water bodies in the world and is suffering extensive environmental issues caused by eutrophication and warming climate. A halocline in the water column divides more saline bottom water fed by inflows through the narrow connection with the North Sea from the surface waters and inhibiting exchange of oxygen between the two water masses. With the nutrient input and the warmer climate primary productivity is increased and the surplus of organic matter results in higher consumptions of oxygen in the water column. As a consequence widespread oxygen deficiencies occur in the bottom waters. Although the present spreading of hypoxia is mostly caused by the influence of human activity on land surrounding the Baltic Sea hypoxia has occurred intermittently before. Since the transition from the freshwater Ancylus Lake to the brackish/marine Littorina Sea ca. 8,000 years ago, the Baltic Sea has experienced three major intervals of bottom water hypoxia. These intervals occur in relation with warmer climates during the Holocene Thermal Maximum (HTM), the Medieval Climate Anomaly (MCA) and during the last decades. This study shows that these hypoxic intervals had a major impact on redox-dependent dynamics of manganese (Mn). Previous studies link the occurrence of Mn enrichments in the high organic sediments of the deep anoxic basins to short time changes in bottom water redox conditions caused by inflows of oxygenated salt water from the North Sea. However, sediment and pore water data of the modern hypoxic interval indicate that this process can be overturned by other factors. In the near surface sediments of the Gotland Basin a clear decline in Mn sequestration can be seen although inflows of oxygenated waters occur. This decline coincides with a major expansion of hypoxia and the occurrence of anoxic, sulfidic bottom waters obvious from monitoring data and sediment geochemical proxies e.g. molybdenum contents. A rise in sulfate reduction due to eutrophication and a decline in Fe input results in higher sulfide availability at the sediment-water-interface shortly after inflows causing a more rapid reductive dissolution of Mn oxides. As a consequence, Mn carbonates may no longer form. In contrast to most deep basins in the Baltic Sea the Landsort Deep as the deepest pit shows major enrichments of Mn to present. The steep geometry channels Mn oxides into the basin and the high alkalinity and sulfide concentration in the bottom waters at the sediment-water-interface allow frequent formation of Mn carbonate as well as sulfides at the sediment surface. With the transition to brackish/marine conditions ca. 8,000 years ago and the onset of the first hypoxic interval major amounts of Mn were buried over vast areas of the deep Baltic basins. The likely reason is a major input of dissolved Mn either from the underlying formerly oxic fresh-water sediments, where Mn oxides may have been present in the surface sediments or from land by fluvial transport or coastal erosion during a period of rather large relative sea level changes. After this first impulse, Mn burial reduced and varied with depth with no burial at the shallowest site (93 m) investigated and nearly continuous in the Fårö Deep (194 m). Although Mn sequestration occurred during intervals with hypoxic bottom waters in the deep basin, the intensification of hypoxia during the later intervals of the HTM und the MCA as observed during the last decades of the modern interval led to a reduction of Mn burial. In the Gotland Basin as well as at the Fårö Deep this decline in Mn content in the sediments coincides with indicators for enhanced hypoxia and euxinic bottom waters.
|
|
| 94607. |
- Lenz, Conny, et al.
(författare)
-
Redox-dependent changes in manganese speciation in Baltic Sea sediments from the Holocene Thermal Maximum: An EXAFS, XANES and LA-ICP-MS study
- 2014
-
Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541. ; 370, s. 49-57
-
Tidskriftsartikel (refereegranskat)abstract
- Manganese (Mn) enrichments in sediments of the deep basins of the Baltic Sea are believed to consist of Ca-Mn-carbonates that form from Mn oxides following periodic inflows of oxygen-rich North Sea waters. However, a range of Mn-bearing mineral phases, that besides Mn-carbonates (e. g. Ca-rhodochrosite), can include Mn-sulfides are known to be present in marine sediments, with formation mechanisms that are sensitive to redox conditions. In this study, we use high resolution synchrotron EXAFS and XANES combined with LA-ICP-MS and micro-XRF, to investigate the nature of the Mn enrichments in sediments from the Holocene Thermal Maximum (approx. 8000-4000 cal. yr BP) at a site in the northern Gotland Basin. Analyses were performed on epoxy-embedded sediment sequences. We specifically address the role of changes in redox conditions in bottom waters, as inferred from sediment molybdenum(Mo) contents, for Mn sequestration. We find that an up-core increase in Mo, indicating a transition into more anoxic and sulfidic (euxinic) bottom water conditions, is accompanied by a decline in total sediment Mn contents. While Mn-carbonates dominate the Mn mineral fraction in the low-Mo interval, in the more sulfidic, high Mo interval, Mn is associated with framboidal pyrite. Mn/Fe ratios in the sulfidic interval vary between the investigated sequences but reach values of up to 7.7 mol%. This exceeds ratios previously reported for sedimentary pyrite and EXAFS spectra indicate that sulfide bound Mn is predominately tetrahedrally coordinated when Mn/Fe ratios are high. This suggests that Mn is incorporated in other Fe-S phases such as mackinawite besides pyrite. There is also evidence for the presence of a low concentration of Mn associated with detrital aluminosilicates throughout the investigated intervals. Our results suggest that increased bottom water euxinia inhibited the formation of Mn-carbonate at this site during the Holocene Thermal Maximum, possibly due to a more rapid reduction of Mn oxides in more sulfidic bottom waters. (C) 2014 Elsevier B.V. All rights reserved.
|
|
| 94608. |
- Lenzing, Anke, et al.
(författare)
-
Language Transfer with Regard to Grammatical Phenomena in L1 German Learners of English
- 2022. - 1
-
Ingår i: Von integrativem zu inklusivem Englischunterricht. - Berlin : Peter Lang Publishing Group. - 1868-386X. - 9783631862032 - 9783631871393 - 9783631871386 ; , s. 291-310
-
Bokkapitel (refereegranskat)abstract
- Our chapter engages with language transfer in SLA with particular focus on the area of grammar. We argue that transfer only plays a minor role in the acquisition of grammatical structures. In order to support our claim, we present data from studies with early and intermediate learners of English.
|
|
| 94609. |
- Leo, Fredrik, et al.
(författare)
-
Characterization of a highly conserved MUC5B-degrading protease, MdpL, from Limosilactobacillus fermentum
- 2023
-
Ingår i: Frontiers in Microbiology. - : Frontiers Media S.A.. - 1664-302X. ; 14
-
Tidskriftsartikel (refereegranskat)abstract
- MUC5B is the predominant glycoprotein in saliva and is instrumental in the establishment and maintenance of multi-species eubiotic biofilms in the oral cavity. Investigations of the aciduric Lactobacillaceae family, and its role in biofilms emphasizes the diversity across different genera of the proteolytic systems involved in the nutritional utilization of mucins. We have characterized a protease from Limosilactobacillus fermentum, MdpL (Mucin degrading protease from Limosilactobacillus) with a high protein backbone similarity with commensals that exploit mucins for attachment and nutrition. MdpL was shown to be associated with the bacterial cell surface, in close proximity to MUC5B, which was sequentially degraded into low molecular weight fragments. Mapping the substrate preference revealed multiple hydrolytic sites of proteins with a high O-glycan occurrence, although hydrolysis was not dependent on the presence of O-glycans. However, since proteolysis of immunoglobulins was absent, and general protease activity was low, a preference for glycoproteins similar to MUC5B in terms of glycosylation and structure is suggested. MdpL preferentially hydrolyzed C-terminally located hydrophobic residues in peptides larger than 20 amino acids, which hinted at a limited sequence preference. To secure proper enzyme folding and optimal conditions for activity, L. fermentum incorporates a complex system that establishes a reducing environment. The importance of overall reducing conditions was confirmed by the activity boosting effect of the added reducing agents L-cysteine and DTT. High activity was retained in low to neutral pH 5.5-7.0, but the enzyme was completely inhibited in the presence of Zn2+. Here we have characterized a highly conserved mucin degrading protease from L. fermentum. MdpL, that together with the recently discovered O-glycanase and O-glycoprotease enzyme groups, increases our understanding of mucin degradation and complex biofilm dynamics.
|
|
| 94610. |
- Leo, Fredrik, et al.
(författare)
-
Characterization of MdpS: an in-depth analysis of a MUC5B-degrading protease from Streptococcus oralis
- 2024
-
Ingår i: FRONTIERS IN MICROBIOLOGY. - : Frontiers Media S.A.. - 1664-302X. ; 15
-
Tidskriftsartikel (refereegranskat)abstract
- Oral biofilms, comprising hundreds of bacteria and other microorganisms on oral mucosal and dental surfaces, play a central role in oral health and disease dynamics. Streptococcus oralis, a key constituent of these biofilms, contributes significantly to the formation of which, serving as an early colonizer and microcolony scaffold. The interaction between S. oralis and the orally predominant mucin, MUC5B, is pivotal in biofilm development, yet the mechanism underlying MUC5B degradation remains poorly understood. This study introduces MdpS (Mucin Degrading Protease from Streptococcus oralis), a protease that extensively hydrolyses MUC5B and offers an insight into its evolutionary conservation, physicochemical properties, and substrate- and amino acid specificity. MdpS exhibits high sequence conservation within the species and also explicitly among early biofilm colonizing streptococci. It is a calcium or magnesium dependent serine protease with strict physicochemical preferences, including narrow pH and temperature tolerance, and high sensitivity to increasing concentrations of sodium chloride and reducing agents. Furthermore, MdpS primarily hydrolyzes proteins with O-glycans, but also shows activity toward immunoglobulins IgA1/2 and IgM, suggesting potential immunomodulatory effects. Significantly, MdpS extensively degrades MUC5B in the N- and C-terminal domains, emphasizing its role in mucin degradation, with implications for carbon and nitrogen sequestration for S. oralis or oral biofilm cross-feeding. Moreover, depending on substrate glycosylation, the amino acids serine, threonine or cysteine triggers the enzymatic action. Understanding the interplay between S. oralis and MUC5B, facilitated by MdpS, has significant implications for the management of a healthy eubiotic oral microenvironment, offering potential targets for interventions aimed at modulating oral biofilm composition and succession. Additionally, since MdpS does not rely on O-glycan removal prior to extensive peptide backbone hydrolysis, the MdpS data challenges the current model of MUC5B degradation. These findings emphasize the necessity for further research in this field.
|
|
