Thermal Conversion of Guanylurea Dicyanamide into Graphitic Carbon Nitride via Prototype CNx Precursors

Guanylurea dicyanamide, [(H2N)C(-O)NHC(NH2)2][N(CN)2], has been synthesized by ion exchange reaction in aqueous solution and structurally characterized by single-crystal X-ray diffraction (C2/c, a = 2249.0(5) pm, b = 483.9(1) pm, c = 1382.4(3) pm, β = 99.49(3)°, V = 1483.8(5) × 106 pm3, T = 130 K). The thermal behavior of the molecular salt has been studied by thermal analysis, temperature-programmed X-ray powder diffraction, FTIR spectroscopy, and mass spectrometry between room temperature and 823 K. The results were interpreted on a molecular level in terms of a sequence of thermally induced addition, cyclization, and elimination reactions. As a consequence, melamine (2,4,6-triamino-1,3,5-triazine) is formed with concomitant loss of HNCO. Further condensation of melamine yields the prototypic CNx precursor melem (2,6,10-triamino-s-heptazine, C6N7(NH2)3), which alongside varying amounts of directly formed CNxHy material transforms into layered CNxHy phases without significant integration of oxygen into the core framework owing to the evaporation of HNCO. Thus, further evidence can be added to melamine and its condensation product melem acting as “key intermediates” in the synthetic pathway toward graphitic CNxHy materials, whose exact constitution is still a point at issue. Due to the characteristic formation process and hydrogen content a close relationship with the polymer melon is evident. In particular, the thermal transformation of guanylurea dicyanamide clearly demonstrates that the formation of volatile compounds such as HNCO during thermal decomposition may render a large variety of previously not considered molecular compounds suitable CNx precursors despite the presence of oxygen in the starting material

Intra-Genomic Ribosomal RNA Polymorphism and Morphological Variation in Elphidium macellum Suggests Inter-Specific Hybridization in Foraminifera

Elphidium macellum is a benthic foraminifer commonly found in the Patagonian fjords. To test whether its highly variable morphotypes are ecophenotypes or different genotypes, we analysed 70 sequences of the SSU rRNA gene from 25 specimens. Unexpectedly, we identified 11 distinct ribotypes, with up to 5 ribotypes co-occurring within the same specimen. The ribotypes differ by varying blocks of sequence located at the end of stem-loop motifs in the three expansion segments specific to foraminifera. These changes, distinct from typical SNPs and indels, directly affect the structure of the expansion segments. Their mosaic distribution suggests that ribotypes originated by recombination of two or more clusters of ribosomal genes. We propose that this expansion segment polymorphism (ESP) could originate from hybridization of morphologically different populations of Patagonian Elphidium. We speculate that the complex geological history of Patagonia enhanced divergence of coastal foraminiferal species and contributed to increasing genetic and morphological variation

Planktothrix populations in subalpine lakes: selection for strains with strong gas vesicles as a function of lake depth, morphometry and circulation

1. The genus Planktothrix (Cyanobacteria) usually produces concentrated populations of filaments in the summer metalimnion of thermally stratifying lakes. This has been associated with the action of gas vesicles, cellular structures providing positive buoyancy. At the end of the summer, filaments are carried by convective mixing deeper into the water column where some gas vesicles collapse as a result of high hydrostatic pressure. They then lose their buoyancy, sink and are lost from the euphotic zone. 2. The resistance of gas vesicles to hydrostatic pressures is critical for the survival of Planktothrix in deep lakes. However, comparative observations on populations from lakes of a range of depths and hydrodynamic regimes are still needed to examine the relationships between the adaptive trait (i.e. the ‘critical’ pressure at which each gas vesicle collapses) with the environmental factor (i.e. the maximum hydrostatic pressure). 3. To explore the adaptation of Planktothrix populations to the depth of winter circulation in different systems, we collected 276 strains of P. cf. rubescens from eight lakes (zmax = 24–410 m) in Northern Italy during summer 2009 and we analysed the multicopy gene gvpC coding for a protein that crucially influences the critical pressure. 4. The strains analysed clustered into two main groups having gas vesicles with a mean critical pressure of 1.1 and 0.9 MPa, respectively. The proportion of the stronger strains was generally positively related to lake depth, although the overall pattern was complicated by individual lake morphology and hydrology. The relative frequency of stronger filaments was (i) greatest in deep basins with concave slopes and (ii) least in one deep, but permanently stratified lake. 5. The simultaneous presence of ‘weaker’ and ‘stronger’ filaments could allow for a rapid adaptive response to changes in hydrostatic pressures, related to changes in the amplitude of vertical circulation characterising deep lakes