Hexacoordinated tin complexes catalyse imine hydrogenation with H2

Frustrated Lewis pair (FLP) hydrogenation catalysts predominantly use alkyl- and aryl-substituted Lewis acids (LA) that offer a limited number of combinations of substituents, limiting our ability to tune their properties and, ultimately, their reactivity. Nevertheless, main-group complexes have numerous ligands available for such purposes, which could enable us to broaden the range of FLP catalysis. Supporting this hypothesis, we demonstrate here that hexacoordinated tin complexes with Schiff base ligands catalyse imine hydrogenation via activation of H2(g). As shown by hydrogen-deuterium scrambling, [Sn(tBu2Salen)(OTf)2] activated H2(g) at 25 °C and 10 bar of H2. After tuning the ligands, we found that [Sn(Salen)Cl2] was the most efficient imine hydrogenation catalyst despite having the lowest activity in H2(g) activation. Moreover, various imines were hydrogenated in yields up to 98% thereby opening up opportunities for developing novel FLP hydrogenation catalysts based on hexacoordinated LA of main-group elements.

Anthropogenic nutrient loading affects both individual species and the trophic structure of river fish communities

Although the concept of trophic interactions has been used for a long time, there are still considerable gaps in our understanding of the effect of various environmental factors on trophic interactions within river fish assemblages. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of 20 species of fish belonging to both eurytopic and rheophilic ecological groups from a large temperate rivers were used to evaluate overall trophic niche use and trophic position of species, and to find out how environmental variability associated with nutrient loading affects individual and community-wide aspects of trophic structure. The study was carried out at 11 sites along the European rivers Vltava and Elbe, representing a continuous gradient of pollution and habitat degradation. Corrected Standard Ellipse Area (SEAc) was significantly larger for the group of eurytopic ecological species than for rheophilic species. Despite narrower isotopic niche space, rheophilic fish species occupied a higher trophic position, suggesting that these species use resources more enriched in 15N. Of the 11 environmental variables tested, nutrients had a significant effect on trophic niche area of species (SEAc), indicating that eutrophication is of critical importance for fish assemblages. Isotopic niche area of species was found to be positively influenced by total phosphorus, and negatively affected by concentrations of nitrate (N-NO3−) and ammonia (N-NH4+). A negative association between oxygen demand and a measure of trophic diversity - mean distance to centroid (CD)- and a measure of density and clustering of species - mean nearest neighbor distance (MNND)- were found, indicating that the oxygen demand is a key factor influencing community trophic structure. An observed pattern where nutrient loading influenced both individual species and trophic structure of the fish assemblage provides strong support for an anthropogenic influence on riverine food webs.

Novel multi-site, multi-point biventricular pacing configuration: acute haemodynamic benefit

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Supported by the research grant of the AZV (Ministry of Health of the Czech Republic)

Background

Biventricular pacing (BVP) using multiple left ventricular (LV) sites may augment the hemodynamic effect of cardiac resynchronisation therapy (CRT) by engaging a greater mass of the myocardium.

Purpose

To evaluate the acute hemodynamic effect of a novel multi-site, multi-point BVP configuration.

Methods

The study investigated 18 patients with idiopathic dilated cardiomyopathy and left bundle-branch block during implantation of a BVP device (age: 59 ± 14 years, female gender: 7 [39%], LVEF: 27 ± 6%, native QRS: 171 ± 16 ms). Conventional leads were placed in the right atrium (RA) and ventricle (RV), one quadripolar LV lead (Quartet, Abbott, Abbott Park, IL, USA) was positioned in the posterolateral and another one in lateral or anterolateral coronary vein. Individual bipoles of all leads were connected through a splitter to separate external cardiac stimulators. Hemodynamics was evaluated using a micromanometer-tipped catheter (Micro-Cath, Millar, Tx, USA) located in the LV during RA pacing above sinus rate and five atrio-ventricular sequential pacing configurations at the same rate: 1.) RA+RV, 2.) RA + RV + distal bipole of the LV lead with greater dP/dT („conventional BVP"), 3.) RA + RV + distal and proximal bipoles of the LV lead with greater dP/dT („single-lead multi-point BVP"), 4.) RA + RV + distal bipoles of both LV leads („two-lead multi-site BVP"), and 5.) sequentional pacing RA + RV + all bipoles of both LV leads interconnected to a mesh („maximum BVP").

Results

Compared to RA pacing, LV dP/dT was significantly greater during all BVP pacing configurations (RA pacing: 1940 ± 507 mmHg/s vs. conventional BVP: 2431 ± 855 mmHg/s, single-lead multi-point BVP: 2539 ± 740 mmHg/s, two-lead multisite BVP: 2517 ± 836 mmHg/s, and "maximum BVP": 2685 ± 893 mmHg/s, all p<0.001, Figure 1), but not during RA-RV pacing (2014 ± 721 mmHg/s, p=0.12). In addition, dP/dT was significantly greater during "maximum BVP" compared to conventional BVP (p=0.05).

Conclusion

Compared to RA pacing and conventional BVP, the greatest increase in LV contractility was achieved with a novel multi-site, multi-point "maximum BVP" configuration. These preliminary findings provide a rationale for designing new approaches to CRT.

The driving factors of per- and polyfluorinated alkyl substance (PFAS) accumulation in selected fish species: The influence of position in river continuum, fish feed composition, and pollutant properties

Per- and polyfluorinated alkyl substances (PFASs) represent a group of highly recalcitrant micropollutants, that continuously endanger the environment. The present work describes the geographical trends of fish contamination by individual PFASs (including new compounds, e.g., Gen-X) assessed by analyzing the muscle tissues of 5 separate freshwater fish species from 10 locations on the Czech section of the Elbe River and its largest tributary, the Vltava River. The data of this study also showed that the majority of the detected PFASs consisted of long-chain representatives (perfluorooctane sulfonate (PFOS), perfluorononanoic acid, perfluorodecanoic acid, and perfluoroundecanoic acid), whereas short-chain PFASs as well as other compounds such as Gen-X were detected in relatively small quantities. The maximum concentrations of the targeted 32 PFASs in fish were detected in the lower stretches of the Vltava and Elbe Rivers, reaching 289.9 ng/g dw, 140.5 ng/g dw, and 162.7 ng/g dw for chub, roach, and nase, respectively. Moreover, the relationships between the PFAS (PFOS) concentrations in fish muscle tissue and isotopic ratios (δ¹⁵N and δ¹³C) were studied to understand the effect of feed composition and position in the river continuum as a proxy for anthropogenic activity. Redundancy analysis and variation partitioning showed that the largest part of the data variability was explained by the interaction of position in the river continuum and δ¹⁵N (δ¹³C) of the fish. The PFAS concentrations increased downstream and were positively correlated with δ¹⁵N and negatively correlated with δ¹³C. A detailed study at one location also demonstrated the significant relationship between δ¹⁵N (estimated trophic position) and PFASs (PFOS) concentrations. From the tested physicochemical properties, the molecular mass and number of fluorine substituents seem to play crucial roles in PFAS bioaccumulation.

Dynamics of Soil Bacterial and Fungal Communities During the Secondary Succession Following Swidden Agriculture IN Lowland Forests

Elucidating dynamics of soil microbial communities after disturbance is crucial for understanding ecosystem restoration and sustainability. However, despite the widespread practice of swidden agriculture in tropical forests, knowledge about microbial community succession in this system is limited. Here, amplicon sequencing was used to investigate effects of soil ages (spanning at least 60 years) after disturbance, geographic distance (from 0.1 to 10 km) and edaphic property gradients (soil pH, conductivity, C, N, P, Ca, Mg, and K), on soil bacterial and fungal communities along a chronosequence of sites representing the spontaneous succession following swidden agriculture in lowland forests in Papua New Guinea. During succession, bacterial communities (OTU level) as well as its abundant (OTU with relative abundance > 0.5%) and rare (<0.05%) subcommunities, showed less variation but more stage-dependent patterns than those of fungi. Fungal community dynamics were significantly associated only with geographic distance, whereas bacterial community dynamics were significantly associated with edaphic factors and geographic distance. During succession, more OTUs were consistently abundant (n = 12) or rare (n = 653) for bacteria than fungi (abundant = 6, rare = 5), indicating bacteria were more tolerant than fungi to environmental gradients. Rare taxa showed higher successional dynamics than abundant taxa, and rare bacteria (mainly from Actinobacteria, Proteobacteria, Acidobacteria, and Verrucomicrobia) largely accounted for bacterial community development and niche differentiation during succession.

Soil microbial interconnections along ecological restoration gradients of lowland forests after slash-and-burn agriculture

Microbial interconnections in soil are pivotal to ecosystem services and restoration. However, little is known about how soil microbial interconnections respond to slash-and-burn agriculture and to the subsequent ecosystem restoration after the practice. Here, we used amplicon sequencing and co-occurrence network analyses to explore the interconnections within soil bacterial and fungal communities in response to slash-and-burn practice and a spontaneous restoration (spanning ca. 60 years) of tropical forests after the practice, in Papua New Guinea. We found significantly higher complexity and greater variations in fungal networks than in those of bacteria, despite no significant changes observed in bacterial or fungal networks across successional stages. Within most successional stages, bacterial core co-occurrences (co-occurrences consistently present across all sub-networks in a stage) were more frequent than those of fungi, indicating higher stability of interconnections between bacteria along succession. The stable interconnections occurred frequently between bacterial taxa (i.e. Sporosarcina, Acidimicrobiale and Bacillaceae) and between ectomycorrhizal fungi (Boletaceae and Russula ochroleuca), implying important ecological roles of these taxa in the ecosystem restoration. Collectively, our results provide new insight into microbial interconnections in response to slash-and-burn agriculture and the subsequent ecosystem restoration, thus promoting a better understanding of microbial roles in ecosystem services and restoration.

Asymmetric response of root-associated fungal communities of an arbuscular mycorrhizal grass and an ectomycorrhizal tree to their coexistence in primary succession

The arbuscular mycorrhizal (AM) grass Calamagrostis epigejos and predominantly ectomycorrhizal (EcM) tree Salix caprea co-occur at post-mining sites spontaneously colonized by vegetation. During succession, AM herbaceous vegetation is replaced by predominantly EcM woody species. To better understand the interaction of AM and EcM plants during vegetation transition, we studied the reciprocal effects of these species' coexistence on their root-associated fungi (RAF). We collected root and soil samples from three different microenvironments: stand of C. epigejos, under S. caprea canopy, and contact zone where roots of the two species interacted. RAF communities and mycorrhizal colonization were determined in sampled roots, and the soil was tested for EcM and AM inoculation potentials. Although the microenvironment significantly affected composition of the RAF communities in both plant species, the effect was greater in the case of C. epigejos RAF communities than in that of S. caprea RAF communities. The presence of S. caprea also significantly decreased AM fungal abundance in soil as well as AM colonization and richness of AM fungi in C. epigejos roots. Changes observed in the abundance and community composition of AM fungi might constitute an important factor in transition from AM-dominated to EcM-dominated vegetation during succession.

Evaluating the potential and problems of three-dimensional computed tomography measurements of arterial stenosis

Volume visualization is gaining widespread acceptance in medical applications. As its use increases, the issue of accuracy becomes critical. There have been very few studies examining the accuracy of volume rendering techniques. We studied the accuracy of hardware-assisted volume rendering for measurement of arterial stenosis in computed tomography (CT) data. The results of our study reveal that accurate measurements can be made from volume rendered CT data. However, error is present (absolute average error from 5.1% to 13.6%) and there is some variability, even for experts (standard deviation ranged from 4.8% to 15%). The evidence suggests that the choice of volume rendering (transfer function) parameters greatly affects the accuracy of the results. Accurate transfer function parameter selection is a difficult problem. Parameters that produce realistic images often provide inaccurate measurements. As the use of volume visualization grows and more inexperienced users begin using these tools for medical diagnosis and staging, new guidelines, aids, and techniques must be developed to ensure reliable, accurate visualization results.