Authors:G. Bonanomi, G. Incerti, A. Stinca, F. Cartenì, F. Giannino, and S. Mazzoleni
Ring shaped patches of clonal plants fascinated plant ecologists since long time. In this work we review the reports on the occurrence of ring pattern in different environmental conditions, the growth forms of ring-forming plants, the mechanisms underlying ring formation, and the consequences for species diversity at community scale. Rings formed by 83 species of clonal vascular plants have been found in grasslands, deserts, bare substrates of lava flow, harvested peat lands, salt marshes, and sand dunes. Four causal hypotheses have been proposed for the emergence of ring patterns: i. occurrence of architectural constraints for ramets development; ii. induction by fire, drought, trampling or overgrazing; iii. nutrient and water depletion by competition inside the ring; and iv. onset of species-specific negative plant-soil feedback in the inner zone of the clone. Since almost all the available studies are observations of ring structure or modelling exercises, none of the putative mechanisms for ring formation emerged from the literature as either generally applicable or suitable for rejection. Therefore, long-term field experiments are needed to investigate the relative prevalence of different mechanisms in different environments. Ring formation bears important consequences at community scale, because ring forming plants often act as “nurses”, enhancing the recruitment and development of different plant species. In fact, ring establishment modifies above- and below-ground environmental conditions, providing specialized safe sites for beneficiaries in the inner zone of the clones. Such interspecific facilitation by ring forming plants, particularly in chronically stressed environments, contributes to increase plant species richness and can locally promote the successional dynamics.
Authors:S. Marković, Vera Dondur, R. Dimitrijević, and S. Macura
the present study, we performed an investigation of phase transformation of
zeolite Na-GIS in temperature interval from room temperature up to 1300C.
The collapse of S4R and S8R (secondary building units in zeolite Na-GIS) and
the forming of pure sodium nepheline phase, consists of S6R, was examined.
During the thermal transformation of Na-GIS zeolite symmetry of rings was
changed and their deformation increases. The irregularity of rings causes
the appearance of defect modes in the IR spectra of amorphous precursors.
Investigated phases were characterized by XRPD, IR, NMR and DSC methods. A
semiempirical method AM1 was used for calculation of vibrational spectrum
Authors:Frank Richter, René Dathe, Jennifer Seifert, and Klaus Banert
Conventional flash vacuum pyrolysis is the best method for the preparation of isothiocyanate-substituted allenes by [3,3]-sigmatropic rearrangement. These synthetically useful allenes undergo a variety of successive reactions; the most prominent is thiazole ring formation after nucleophilic attack at the isothiocyanate carbon. We now present the development and application of the solution spray method in flash vacuum pyrolysis of low- or nonvolatile propargyl thiocyanates. By using model reactions, the setup was optimized for a synthetic scale approach utilizing also steel nozzles (distributed for oil-fired heating furnaces) for spray generation. Selected examples emphasize advantages such as enabling gas-phase reactions of nonvolatile compounds and improvement of challenging syntheses via highly reactive species under different operating conditions (400–600 °C, 0.01–0.05 mbar).
Authors:Klára Lövei, István Greiner, János Éles, Áron Szigetvári, Miklós Dékány, Sándor Lévai, Zoltán Novák, and György István Túrós
In medicinal chemistry, the development of synthetic procedures for the access of new heterocyclic systems as potential scaffolds is elementary. Herein, we report our results on the formation of small drug-like heterocycles, utilizing flow chemistry. This approach enables the extension of the reaction parameter window, including high-pressure/high-temperature or hazardous chemistry. In our work, various novel condensed tricyclic benzothiazoles fused with furo- and thieno-rings were synthesized applying a multistep continuous-flow protocol. The process includes two ring closure steps and a nitro group reduction step. Batch and telescoped continuous-flow syntheses were also designed and performed.
Authors:Jiangang Yu, Jianguo Xu, Zhiqun Yu, Yi Jin, Jie Li, and Yanwen Lv
A continuous-flow reactor (Corning G1 reactor) was hereby introduced for Fischer indole synthesis of 3-methylindole by reaction of phenyl hydrazines and propylaldehyde. Stoichiometric Lewis acid, ZnCl2, was supplied as catalyst as well as remover of NH3 which generated during the indole ring formation. Ionic liquid ([EMIM][BF4]) was employed as solvent according to its high-temperature tolerance and good product distribution. After a straightforward extraction process, 3-methylindole could be obtained in a 95.3% yield (96.0% purity) under optimized conditions. Ionic liquid (IL) was then recovered by another extraction process, and the recovered IL acted nearly as efficiently as new IL for this Fischer indole reaction.
Temperature effect on the synergic extraction of Eu(III) by thenoyltrifluoroacetone (HTTA) in the presence of 2,2-bipyridyl(bipyr)
and 1,10-phenanthroline (phen) from sodium acetate buffer solution at pH 4.20 has been investigated. Extractions were carried
out at 15, 25, and 35°C. It was observed that the increasing temperature favours the extraction of Eu(III) by HTTA alone while
the reverse is true for synergic extractions. The extraction data indicate the formation of synergic adducts containing only
one molecule of the bidentate amine i.e. Eu(TTA)3. B where B=bipyr or phen. The synergic reaction is favoured by the enthalpy changes alone. Thermodynamic parameters suggest
a mechanism for the synergic extraction which involves complex formation with an increase or expansion of the coordination
number of the central metal atom. Larger synergic and enthalpy changes observed for phen as compared to bipyr are probably
due to the cis position of its N-atoms readily available for chelate ring formation.
Authors:Shinn-Gwo Hong, Tsung-Kai Gau, and Shih-Che Huang
degradation. As a result, the observed large Mw is from the improvement of the thermal stability of the PHB and which is resulted from the possible inhibition of six-member cyclic ringformation by the steric hindrance offered by the added long chain PVP
Authors:Mihaela Badea, Rodica Olar, Valentina Uivarosi, Dana Marinescu, and Victoria Aldea
chelate ringformation the complex stability is raised and the rate of metabolisation is slower leading thus to a lower toxicity. Having in view these requirements many vanadium compounds with a broad variety of organic derivatives have been studied and
Authors:Mayté Paredes Zaldivar, Norma Galego Fernández, Cristina Gastón Peña, Manuel Rapado Paneque, and Sonia Altanés Valentín
The first degradation stage (285–345, 315 °C) corresponds to the dehydration of PAA (water evolution associated to intra or intermolecular anhydride ringformation), which is the first degradation process of PAA [ 24 ]. A 26% of PAA mass loss occurred
Authors:Bimlesh Lochab, Indra K. Varma, and Jayashree Bijwe
, aliphatic CH 2 , >C(CH 3 ) 2 ), 4.55 (s, ArCH 2 N–), 5.28 (s, –OCH 2 N–),6.53–6.65 (s, ArH), 6.70–6.78 ( d , ArH), 6.78–6.95, 7.05–7.22 ( m , ArH).
The ring closure reaction of amino group with aldehyde group and phenolic –OH resulted in oxazine ring