Crystal structures of 3-halo-2-organochalcogenylbenzo[b]chalcogenophenes.

The structure of the title compounds 3-bromo-2-(phenyl-sulfan-yl)benzo[b]thiophene (C14H9BrS2; 1), 3-iodo-2-(phenyl-sulfan-yl)benzo[b]thio-phene (C14H9IS2; 2), 3-bromo-2-(phenyl-selan-yl)benzo[b]seleno-phene (C14H9BrSe2; 3), and 3-iodo-2-(phenyl-selan-yl)benzo[b]seleno-phene (C14H9ISe2; 4) were determined by single-crystal X-ray diffraction; all structures presented monoclinic (P21/c) symmetry. The phenyl group is distant from the halogen atom to minimize the steric hindrance repulsion for all structures. Moreover, the structures of 3 and 4 show an almost linear alignment of halogen-selenium-carbon atoms arising from the intra-molecular orbital inter-action between a lone pair of electrons on the halogen atom and the anti-bonding σ*Se-C orbital (n halogen→σ*Se-C). This inter-action leads to significant differences in the three-dimensional packing of the mol-ecules, which are assembled through π-π and C-H⋯π inter-actions. These data provide a better comprehension of the inter-molecular packing in benzo[b]chalcogenophenes, which is relevant for optoelectronic applications.

Physical and chemical characterization of natural and modified nanoclays and their ecotoxicity on a freshwater algae species (Chlamydomonas reinhardtii).

Nanoclays represent a class of natural and modified nanomaterials that have received attention from industrial and environmental fields. Studies that assess the physicochemical properties of nanoclays and compare the effects of natural and modified nanoclays are scarce. We assessed the physicochemical characteristics of a natural nanoclay (Na+ montmorillonite) and 2 modified nanoclays (Cloisite® 30B and Novaclay™) in the dry powder state and in solution, and their potential toxic effects on algal population growth (Chlamydomonas reinhardtii). All 3 nanoclays exhibited properties that are thought to cause toxic effects on organisms, but the properties varied among the nanoclays. Cloisite 30B had a low particle stability and a chemical composition that are thought to induce a greater toxic effect on organisms than either Novaclay or natural nanoclay. In contrast, Novaclay and natural nanoclay had a particle shape (nanoplate) in solution that is thought to induce a greater toxic effect on organisms than the type of particle shape (spherical) that Cloisite 30B has in solution. Cloisite 30B suppressed population growth of C. reinhardtii, an effect that increased with dosage. Neither Novaclay nor natural nanoclay affected algal population growth across a broad array of concentrations. The results show that modified nanoclays differ in their impact on algae, and careful thought must be given to their usage because some will have negative consequences if released into aquatic ecosystems. Environ Toxicol Chem 2018;37:2860-2870. © 2018 SETAC.

Pseudoreplication and the usage of biomarkers in ecotoxicological bioassays.

Pseudoreplication is a widely discussed topic in the scientific community. Its principal critique concerns the lack of independence in flawed experimental designs and the use of inferential statistics to test the hypothesis of such experiments. Thirty years after its appearance, it remains misunderstood by many researchers, including ecotoxicologists. In the present study, we try to clarify some of its concepts by filling in what seems to be a gap in the terminology of manipulative experiments. We propose the term "experimental medium" to refer strictly to the relevant spatial scale of the experiment to preserve the specificity of the experimental and observational units and to display pseudoreplication as a kind of misinterpretation and/or misanalysis of inferential statistics. A classification of the types of experimental designs in ecotoxicology is offered, and the problems in using inferential statistics in suboptimal designs are discussed. We hope to shed some light on such a classic topic for ecotoxicologists. Environ Toxicol Chem 2017;36:2868-2874. © 2017 SETAC.