Impact of weathered multi-walled carbon nanotubes on the epithelial cells of the intestinal tract in the freshwater grazers Lymnaea stagnalis and Rhithrogena semicolorata.

Freshwater grazers are suitable organisms to investigate the fate of environmental pollutants, such as weathered multi-walled carbon nanotubes (wMWCNTs). One key process is the uptake of ingested materials into digestive or absorptive cells. To address this, we investigated the localization of wMWCNTs in the intestinal tracts of the mud snail Lymnaea stagnalis (L. stagnalis) and the mayfly Rhithrogena semicolorata (R. semicolorata). In L. stagnalis, bundles of wMWCNTs could be detected in the midgut lumen, whereas only single wMWCNTs could be detected in the lumina of the digestive gland. Intracellular uptake of wMWCNTs was detected by transmission electron microscopy (TEM) but was restricted to the cells of the digestive gland. In larvae of R. semicolorata, irritations of the microvilli and damages in the apical parts of the epithelial gut cells were detected after feeding with 1 to 10 mg/L wMWCNTs. In both models, we detected fibrillar structures in close association with the epithelial cells that formed peritrophic membranes (PMs). The PM may cause a reduced transmission of wMWCNT bundles into the epithelium by forming a filter barrier and potentially protecting the cells from the wMWCNTs. As a result, the uptake of wMWCNTs into cells is rare in mud snails and may not occur at all in mayfly larvae. In addition, we monitor physiological markers such as levels of glycogen or triglycerides and the RNA/DNA ratio. This ratio was significantly affected in L. stagnalis after 24 days with 10 mg/L wMWCNTs, but not in R. semicolorata after 28 days and 10 mg/L wMWCNTs. However, significant effects on the energy status of R. semicolorata were analysed after 28 days of exposure to 1 mg/L wMWCNTs. Furthermore, we observed a significant reduction of phagosomes per enterocyte cell in mayfly larvae at a concentration of 10 mg/L wMWCNTs (p < 0.01).

Correction to: Quantitative analysis of PET microplastics in environmental model samples using quantitative 1H-NMR spectroscopy: validation of an optimized and consistent sample clean-up method.

The original version of this article contained a mistake.

Quantitative analysis of PET microplastics in environmental model samples using quantitative 1H-NMR spectroscopy: validation of an optimized and consistent sample clean-up method.

Identification and quantification of microplastics (MP) in environmental samples is crucial for understanding the risk and distribution of MP in the environment. Currently, quantification of MP particles in environmental samples and the comparability of different matrices is a major research topic. Research also focusses on sample preparation, since environmental samples must be free of inorganic and organic matrix components for the MP analysis. Therefore, we would like to propose a new method that allows the comparison of the results of MP analysis from different environmental matrices and gives a MP concentration in mass of MP particles per gram of environmental sample. This is possible by developing and validating an optimized and consistent sample preparation scheme for quantitative analysis of MP particles in environmental model samples in conjunction with quantitative 1H-NMR spectroscopy (qNMR). We evaluated for the first time the effects of different environmental matrices on identification and quantification of polyethylene terephthalate (PET) fibers using the qNMR method. Furthermore, high recovery rates were obtained from spiked environmental model samples (without matrix ~ 90%, sediment ~ 97%, freshwater ~ 94%, aquatic biofilm ~ 95%, and invertebrate matrix ~ 72%), demonstrating the high analytical potential of the method. Graphical abstract.

Metabolic activity and behavior of the invasive amphipod Dikerogammarus villosus and two common Central European gammarid species (Gammarus fossarum, Gammarus roeselii): Low metabolic rates may favor the invader.

The Ponto-Caspian amphipod Dikerogammarus villosus is one of the most successful invaders in Central European rivers. Contrary to studies on its ecology, ecophysiological studies comparing the species' physiological traits are scarce. In this context, in particular the metabolic activity of the invasive species has rarely been considered and, moreover, the few existing studies on this species report strongly deviating results. The purpose of this study was to assess the metabolic activity and behavior of D. villosus and other common European amphipod species (Gammarus fossarum, Gammarus roeselii) in relation to temperatures covering the thermal regime of the invaded habitats. Based on direct calorimetric measurements of metabolic heat dissipation at three temperature levels (5°C, 15°C and 25°C), we found the routine metabolic rate of D. villosus to be significantly lower than that of the other studied gammarid species at the medium temperature level. The estimated resting metabolic rate indicated a similar trend. At 5°C and 25°C, both routine and resting metabolic rate did not differ between species. Compared to G. fossarum and G. roeselii, D. villosus exhibited lower locomotor activity at the low and medium temperatures (5°C and 15°C). In contrast, its locomotor activity increased at the high experimental temperature (25°C). G. fossarum and G. roeselii were apparently more active than D. villosus at all studied temperatures. We conclude that D. villosus has both physiological and behavioral adaptations that lead to a reduction in metabolic energy expenditure, which is assumed to be beneficial and might contribute to its invasive success.

Physiological and behavioral responses of the invasive amphipod, Dikerogammarus villosus, to ammonia.

We studied the physiological and behavioral responses of the Ponto-Caspian amphipod Dikerogammarus villosus during exposure to four total ammonia concentrations (NH3+NH4(+); TotAmm): 0.003 (control), 0.06, 1.6, and 7.0 mmol L(-1) (0.042, 0.84, 22.4, and 98.0 mg L(-1)) for a period of up to 12 h at 21 °C. During the transition period from the control to treatment concentration as well as during the first hour of exposure to 0.06 and 1.6 mmol L(-1), gammarids increased their locomotor activity, which was manifested in significantly higher routine metabolic rates compared to control conditions. At control conditions, the resting metabolic rate amounted to 0.98±0.26 mW g(-1) and significantly increased by 19 and 37% at 0.06 and 1.6 mmol L(-1), respectively. The highest examined [TotAmm] caused a rapid and significant increase in resting metabolic rate by 37% within the first 4 h of exposure before gammarids died. The exposure to elevated [TotAmm] also resulted in a significant decreased RNA:DNA ratio and significantly higher glycogen concentrations compared to the control. We conclude that even a short exposure to TotAmm of 0.06 mmol L(-1), which may occur in natural habitats, disturbs the physiology and behavior of D. villosus and leads to increased metabolic costs of the maintenance and reduced protein synthesis.

Synthesis of the carboline disaccharide domain of shishijimicin A.

A synthetic route to the carboline disaccharide domain (2) of shishijimicin A (1) has been developed. The convergent synthesis relies on a novel application of the Reetz-Müller-Starke reaction to form the central, sulfur-bearing quaternary carbon center and addition of the carboline structural motif as a dianion to a disaccharide aldehyde fragment.

Origins of regioselectivity of Diels-Alder reactions for the synthesis of bisanthraquinone antibiotic BE-43472B.

The regioselectivities of several Diels-Alder reactions utilized en route to bisanthraquinone antibiotic BE-43472B are examined using density functional theory calculations. These reactions involve highly substituted dienes and juglone dienophiles, and there is an opposite regiochemical outcome for Diels-Alder reactions with beta-aryl substituted juglones when compared to reactions of unsubstituted juglone. In this article, the effect of an aromatic conjugating group bonded to juglone is explored.

Total synthesis and biological evaluation of (+)- and (-)-bisanthraquinone antibiotic BE-43472B and related compounds.

The bisanthraquinone antibiotic BE-43472B [(+)-1] was isolated by Rowley and co-workers from a streptomycete strain found in a blue-green algae associated with the ascidian Ecteinascidia turbinata and has shown promising antibacterial activity against clinically derived isolates of methicillin-susceptible, methicillin-resistant, and tetracyclin-resistant Staphylococcus aureus (MSSA, MRSA, and TRSA, respectively) and vancomycin-resistant Enterococcus faecalis (VRE). Described herein is the first total synthesis of both enantiomers of this bisanthraquinone antibiotic, the determination of its absolute configuration, and the biological evaluation of these and related compounds. The developed synthesis relies on a highly efficient cascade sequence involving an intermolecular Diels-Alder reaction between diene (R)-61 and dienophile 55, followed by an intramolecular nucleophilic aromatic ipso substitution. Late-stage transformations included a remarkable photochemical alpha,beta-epoxyketone rearrangement [80 --> (+)-1]. Interestingly, the unnatural enantiomer [(-)-1] of antibiotic BE-43472B exhibited antibacterial properties comparable to those of the natural enantiomer [(+)-1].

Total synthesis and absolute configuration of the bisanthraquinone antibiotic BE-43472B.

An-T-biotic: The first total synthesis of the T-shaped bisanthraquinone natural product BE-43472B was accomplished and its absolute configuration assigned. Key transformations in the pivotal cascade sequence include a Diels-Alder reaction, a hemiketal formation, and a nucleophilic aromatic ipso substitution.