Emerging subject for chiral separation science: cluster boron compounds

The structural chirality is an inherent feature of fully synthetic boron cluster compounds that sometimes exhibit unique biochemical effects. HPLC studies with zwitter-ionic cluster boron compounds and electrophoretic studies with boron cluster anions reveal that the chiral separability of these species is remarkably dissimilar to that of organic species, if uncharged cyclodextrins are used as chiral selectors. Furthermore, marked differences were found between the analytical characteristics of the chiral separations of the boron cluster species and those of the organic species with uncharged cyclodextrins. The present-day experimental database indicates that the rules valid for the chiral separations of the organic species cannot be applied to the chiral separations of the boron cluster species without experimental verification. The current extent of research work devoted to the investigation of chirality and chiral separations of boron cluster species is negligibly small in comparison with that devoted to the investigation of chirality and chiral separations of organic species. This makes difficult a reliable explanation of both the particularities observed in chiral separations of boron cluster species with cyclodextrins as chiral selectors and the strange effects related to these separations at the moment.     

Morphology and molecular phylogeny of Pseudotrichonympha hertwigi and Pseudotrichonympha paulistana (Trichonymphea, parabasalia) from neotropical rhinotermitids

Pseudotrichonympha is a large hypermastigote parabasalian found in the hindgut of several species of rhinotermitid termites. The genus was discovered more than 100 years ago, and although over a dozen species have since been described, this represents only a small fraction of its likely diversity: the termite genera from which Pseudotrichonympha is known are all species rich, and in most cases their hindgut symbionts have not been examined. Even formally described species are mostly lacking in detailed microscopic data and/or sequence data. Using small subunit ribosomal RNA gene sequences and light and scanning electron microscopy we describe here the morphology and molecular phylogenetic position of two Pseudotrichonympha species: the type species for the genus, Pseudotrichonympha hertwigi from Coptotermes testaceus (described previously in line drawing only), and Pseudotrichonympha paulistana from Heterotermes tenuis (described previously based on light microscopy only).     

Synthesis and structural characterisation of the lead-platinum sulfido aggregates [Pt2(μ-S)2(PPh3)4PbX2] (X = Br, I); promotion of rare tetrahedral geometry for lead(II)

The reactions of [Pt₂(μ-S)₂(PPh₃)₄] with excess PbBr₂ or PbI₂ in methanolic suspension result in the formation of the neutral lead(II) halide adducts [Pt₂(μ-S)₂(PPh₃)₄PbX₂] (X = Br, I). The X-ray structure determination of the lead iodide adduct reveals an essentially tetrahedral lead(II) centre, which is a rare coordination geometry for lead(II), which almost invariably is hemidirected, with a stereochemically active lone pair. In contrast, the structure of the PbBr₂ adduct, although suffering from some disorder, shows a more typical, distorted arrangement of ligands; these results are discussed in terms of the tendency for soft, bulky ligands to promote symmetric, holodirected geometries. The ESI mass spectra of the adducts are reported, and yield [M−halide]⁺ ions.     

Biomphalaria tenagophila: dynamics of populations of resistant and susceptible strains to Schistosoma mansoni, with or without pressure of the parasite

Resistant (Taim, RS) and susceptible albino (Joinville, SC) Biomphalaria tenagophila populations were kept together, at different proportions, throughout a 18-month-period. Some of the snail groups were submitted to Schistosoma mansoni infection. The targets of this study were (a) to analyze the populational dynamics among resistant and susceptible individuals to S. mansoni; (b) to study the resistance phenotype in descendants of cross-breeding; (c) to observe whether the parasite could exert any kind of selection in those snail populations. Throughout the experiment it could be observed that the susceptible B. tenagophila strain (Joinville) underwent a selective pressure of the parasite that was negative, since the individuals showed a high mortality rate. Although B. tenagophila (Taim) population presented a higher mortality rate without pressure of the parasite, this event was compensated by a reproductive capacity. B. tenagophila Taim was more fecund than B. tenagophila Joinville and was able to transmit the resistance character to their descendants. F1 generation obtained by cross-breeding between resistant and susceptible lineages was completely resistant to S. mansoni infection, irrespective of the Taim proportion. Moreover, less than 5% of F2 progeny were susceptible to S. mansoni infection.     

Heterobimetallic platinum-bismuth aggregates derived from [Pt2(μ-S)2(PPh3)4]

The metalloligand [Pt₂(μ-S)₂(PPh₃)₄] reacts with Bi(S₂CNEt₂)₃ or Bi(S₂COEt)₃ in methanol to produce the orange cationic adducts [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂CNEt₂)₂]⁺ and [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂COEt)₂]⁺, respectively, isolated as their hexafluorophosphate salts. An X-ray structure determination on [Pt₂(μ-S)₂(PPh₃)₄Bi(S₂CNEt₂)₂]PF₆ reveals the presence of a six-coordinated bismuth centre with an approximately nido-pentagonal bipyramidal coordination geometry. Fragmentation pathways for both complexes have been probed using electrospray ionisation mass spectrometry; ions [Pt₂(μ-S)₂(PPh₃)₂Bi(S₂CXEt_n)₂]⁺ (X = O, n = 1, X = N, n = 2) are formed by selective loss of two PPh₃ ligands, and at higher cone voltages the species [(Ph₃P)PtS₂Bi]⁺ is observed. Ions formed by loss of CS₂ are also observed for the xanthate but not the dithiocarbamate ions.     

Contrasting trends in distribution of four major planktonic betaproteobacterial groups along a pH gradient of epilimnia of 72 freshwater habitats

The distribution and abundance of Betaproteobacteria and three of its genera - Limnohabitans (R-BT065 lineage), Polynucleobacter (including subclusters Polynucleobacter necessarius and Polynucleobacter acidiphobus/Polynucleobacter difficilis), and Methylophilus - across the epilimnia of 72 limnologically diverse freshwater habitats were investigated using fluorescence in situ hybridization. Moreover, seasonal development of Betaproteobacteria subgroups along the longitudinal axis of a reservoir was followed. Betaproteobacteria comprised on average 29.1%, Polynucleobacter 11.6%, P.?necessarius 10.1%, P.?acidiphobus/difficilis 0.5%, Limnohabitans 8.9%, and Methylophilus 0.9% of total bacterioplankton cells in the investigated habitats. Polynucleobacter necessarius and Limnohabitans coexisted in the majority of habitats but showed contrasting abundance patterns along the pH gradient of habitats (pH, 3.8-8.5). The observed distribution patterns could theoretically be explained by different preferences for substrate sources, that is, substances of humic origin in acidic waters and algal-derived substances in alkaline waters. However, substrate utilization patterns observed in laboratory experiments indicate no coherent group-specific differences in substrate preferences. Interestingly, similar distribution patterns were revealed for Limnohabitans and P.?acidiphobus/difficilis, suggesting similar ecological adaptations of these distantly related taxa. Our findings further emphasize that at least two taxa of freshwater Betaproteobacteria represent ecologically diversified groups. Investigations at higher phylogenetic resolution are required for obtaining further insights into their ecology.