Experimental and computational studies of two new mono- and dinuclear iridium complexes containing a Buchwald biphenyl phosphine ligand

The reaction of [(η⁴-1,5-C₈H₁₂)₂Ir₂(μ-Cl)₂] with 2-di-t-butylphosphino-2′-methylbiphenyl (t-Bu₂Pbiph^Me) in the presence of AgBF₄ afforded the dichlorido-bridged Ir–Ag complex [(η⁴-1,5-C₈H₁₂)Ir(μ-Cl)₂Ag(t-Bu₂Pbiph^Me)] (1) which was fully characterized by a single crystal X-ray diffraction study. Sequential treatment of the diiridium precursor first with the silver salt and then with the phosphine yielded cyclometalated [(η⁴-1,5-C₈H₁₂)Ir(t-Bu₂Pbiph^Me–H⁺)] (2). Detailed DFT calculations gave evidence that the phosphine ligand of 2 forms a strained four-membered iridaheterocycle through orthometalation rather than a sterically congested six-membered chelate structure through C–H activation on the remote phenyl ring. The phosphonium salt [t-Bu₂P(H)biph^Me]BF₄ was isolated as a by-product of the preparations of 1 and 2; its crystal structure was determined.     

Selenoprotein P Status Correlates to Cancer-Specific Mortality in Renal Cancer Patients

Selenium (Se) is an essential trace element for selenoprotein biosynthesis. Selenoproteins have been implicated in cancer risk and tumor development. Selenoprotein P (SePP) serves as the major Se transport protein in blood and as reliable biomarker of Se status in marginally supplied individuals. Among the different malignancies, renal cancer is characterized by a high mortality rate. In this study, we aimed to analyze the Se status in renal cell cancer (RCC) patients and whether it correlates to cancer-specific mortality. To this end, serum samples of RCC patients (n = 41) and controls (n = 21) were retrospectively analyzed. Serum Se and SePP concentrations were measured by X-ray fluorescence and an immunoassay, respectively. Clinical and survival data were compared to serum Se and SePP concentrations as markers of Se status by receiver operating characteristic (ROC) curve and Kaplan-Meier and Cox regression analyses. In our patients, higher tumor grade and tumor stage at diagnosis correlated to lower SePP and Se concentrations. Kaplan-Meier analyses indicated that low Se status at diagnosis (SePP<2.4 mg/l, bottom tertile of patient group) was associated with a poor 5-year survival rate of 20% only. We conclude that SePP and Se concentrations are of prognostic value in RCC and may serve as additional diagnostic biomarkers identifying a Se deficit in kidney cancer patients potentially affecting therapy regimen. As poor Se status was indicative of high mortality odds, we speculate that an adjuvant Se supplementation of Se-deficient RCC patients might be beneficial in order to stabilize their selenoprotein expression hopefully prolonging their survival. However, this assumption needs to be rigorously tested in prospective clinical trials.     

Influence of Host Plant Genotype, Presence of a Pathogen, and Coinoculation with Pseudomonas fluorescens Strains on the Rhizosphere Expression of Hydrogen Cyanide- and 2,4-Diacetylphloroglucinol Biosynthetic Genes in P. fluorescens Biocontrol Strain CHA0

The production of hydrogen cyanide (HCN) and 2,4-diacetylphloroglucinol (DAPG) is a major factor in the control of soil-borne diseases by Pseudomonas fluorescens CHA0. We investigated the impact of different biotic factors on the expression of HCN–in comparison to DAPG biosynthetic genes in the rhizosphere. To this end, the influence of plant cultivar, pathogen infection, and coinoculation with other biocontrol strains on the expression of hcnA-lacZ and phlA-lacZ fusion in strain CHA0 was monitored on the roots of bean. Interestingly, all the tested factors influenced the expression of the two biocontrol traits in a similar way. For both genes, we observed a several-fold higher expression in the rhizosphere of cv. Derakhshan compared with cvs. Goli and Naz, although bacterial rhizosphere colonization levels were similar on all cultivars tested. Root infection by Rhizoctonia solani stimulated total phlA and hcnA gene expression in the bean rhizosphere. Coinoculation of strain CHA0 with DAPG-producing P. fluorescens biocontrol strains Pf-68 and Pf-100 did neither result in a substantial alteration of hcnA nor of phlA expression in CHA0 on bean roots. To our best knowledge, this is the first study investigating the impact of biotic factors on HCN production by a bacterial biocontrol strain in the rhizosphere.     

G protein beta gamma subunits inhibit nongenomic progesterone-induced signaling and maturation in Xenopus laevis oocytes. Evidence for a release of inhibition mechanism for cell cycle progression

Progesterone-induced maturation of Xenopus oocytes is a well known example of nongenomic signaling by steroids; however, little is known about the early signaling events involved in this process. Previous work has suggested that G proteins and G protein-coupled receptors may be involved in progesterone-mediated oocyte maturation as well as in other nongenomic steroid-induced signaling events. To investigate the role of G proteins in nongenomic signaling by progesterone, the effects of modulating Galpha and Gbetagamma levels in Xenopus oocytes on progesterone-induced signaling and maturation were examined. Our results demonstrate that Gbetagamma subunits, rather than Galpha, are the principal mediators of progesterone action in this system. We show that overexpression of Gbetagamma inhibits both progesterone-induced maturation and activation of the MAPK pathway, whereas sequestration of endogenous Gbetagamma subunits enhances progesterone-mediated signaling and maturation. These data are consistent with a model whereby endogenous free Xenopus Gbetagamma subunits constitutively inhibit oocyte maturation. Progesterone may induce maturation by antagonizing this inhibition and therefore allowing cell cycle progression to occur. These studies offer new insight into the early signaling events mediated by progesterone and may be useful in characterizing and identifying the membrane progesterone receptor in oocytes.     

Understanding population history for conservation purposes: population genetics of Saxifraga aizoides (Saxifragaceae) in the lowlands and lower mountains north of the Alps

Several alpine species have outlying populations in the lowlands and lower mountains north of the Alps. These small, isolated populations are usually described as either (1) glacial relics, (2) descendants from populations living on forelands and moraines during the ice ages, or (3) populations founded by long-distance dispersal after glaciation. A floristic survey of the historic and present distributions and an allozyme investigation were performed on one of these relic species, Saxifraga aizoides. The species was historically more abundant and had more stations in more regions of northeastern Switzerland. The former population structures within regions, nowadays destroyed, were still reflected in distinct and high regional genetic diversity and variation. There was weak evidence of increased inbreeding in outlying populations, but populations did not deviate from Hardy-Weinberg equilibrium. No geographic pattern of genetic variation above the regional scale (>10 km) was found. Based on the spatial and genetic structures found, it was not possible to discriminate between the abovementioned hypotheses. Nevertheless, the study shows how a thorough evaluation of distribution and abundance data aids the interpretation of genetic data with respect to population history, biogeography, and conservation biology.     

Plants,microorganisms, and soil temperatures contribute to a decrease in methane fluxes on a drained Arctic floodplain

As surface temperatures are expected to rise in the future, ice‐rich permafrost may thaw, altering soil topography and hydrology and creating a mosaic of wet and dry soil surfaces in the Arctic. Arctic wetlands are large sources of CH₄, and investigating effects of soil hydrology on CH₄ fluxes is of great importance for predicting ecosystem feedback in response to climate change. In this study, we investigate how a decade‐long drying manipulation on an Arctic floodplain influences CH₄‐associated microorganisms, soil thermal regimes, and plant communities. Moreover, we examine how these drainage‐induced changes may then modify CH₄ fluxes in the growing and nongrowing seasons. This study shows that drainage substantially lowered the abundance of methanogens along with methanotrophic bacteria, which may have reduced CH₄ cycling. Soil temperatures of the drained areas were lower in deep, anoxic soil layers (below 30 cm), but higher in oxic topsoil layers (0–15 cm) compared to the control wet areas. This pattern of soil temperatures may have reduced the rates of methanogenesis while elevating those of CH₄ oxidation, thereby decreasing net CH₄ fluxes. The abundance of Eriophorum angustifolium, an aerenchymatous plant species, diminished significantly in the drained areas. Due to this decrease, a higher fraction of CH₄ was alternatively emitted to the atmosphere by diffusion, possibly increasing the potential for CH₄ oxidation and leading to a decrease in net CH₄ fluxes compared to a control site. Drainage lowered CH₄ fluxes by a factor of 20 during the growing season, with postdrainage changes in microbial communities, soil temperatures, and plant communities also contributing to this reduction. In contrast, we observed CH₄ emissions increased by 10% in the drained areas during the nongrowing season, although this difference was insignificant given the small magnitudes of fluxes. This study showed that long‐term drainage considerably reduced CH₄ fluxes through modified ecosystem properties.     

Hirsutinolides from Vernonia species

Out of the nineteen species of Vernonia studied, five contained highly oxygenated sesquiterpene lactones, while the rest contained predominantly triterpenes, especially lupane derivatives.