Rice field flora and vegetation in the provinces of Valencia and Tarragona

Twenty nine emergent and twenty floating or submerged taxa , were found in the rice fields in Valencia and Tarragona provinces. Eleven of the se taxa, all them emergent, are alien Of introduced ones. Echinochloa oryzoides and E. oryzicola are the most important in both areas, together with Cyperus difformis and Echinochloa hispidula in Valencia. The remaining thirty eight taxa belong to the native flora. There are predominantly the emergent Scirpus maritimus, Alisma plantago-aquatica. Echinochloa crus-galli and Paspalum distichum; the floating Lemna minor and L. gibba; the submersed Potamogeton nodosus; Zannichellia palustris and Najas minor; and the macroscopical algae Chara vulgaris, Cladophora glomerata, Oedogonium capilliforme, Spirogyra spp., Pithophora oedogania and Hydrodictyon reticulatum. The flora evolution during the last years is analyzed and the present weed communities are studied. The contribution of the different phytosociological classes to the rice field weed flora is presented.De los 49 táxones registrados (29 emergentes y 20 flotantes o sumergidos) 11 son exóticos introducidos, de los cuales los más importantes son Echinochloa oryzoides y E. oryzicolaen ambas zonas, además de Cyperus difformis y Echinochloa hispidula en Valencia, y el resto propios de la flora autóctona, predominando Scirpus maritimus, Alisma plantago-aquatica. Echinochloa crus-galli y Paspalum distichum como emergentes, Lemna minor y L. gibba como flotantes, Potamogeton nodosus, Zannichellia palustris y Najas minor como sumergidos y Chara vulgaris, Cladophora glomerata, Oedogonium capilliforme. Spirogyra spp., Pirhophora oedogonia e Hydrodictyon reticulatum como algas macroscópicas. Se analiza la evolución experimentada por la flora en los últimos años, además de estudiar las comunidades vegetales presentes y de indicar la importancia de las distintas clases fitosociológicas en su contribución a la flora arvense del cultivo

A Charge-Neutral Self-Assembled L₂Zn₂ Helicate as Bench-Stable Receptor for Anion Recognition at Nanomolar Concentration

The field of anion recognition chemistry is dominated by two fundamental approaches to design receptors. One relies on the formation of covalent bonds resulting in organic and often neutral host species, while the other one utilizes metal-driven self-assembly for the formation of charged receptors with well-defined nanocavities. Yet, the combination of their individual advantages in the form of charge-neutral metal-assembled bench-stable anion receptors is severely lacking. Herein, we present a fluorescent and uncharged double-stranded hydroxyquinoline-based zinc(II) helicate with the ability to bind environmentally relevant dicarboxylate anions with high fidelity in dimethyl sulfoxide (DMSO) at nanomolar concentrations. These dianions are pinned between zinc(II) centers with binding constants up to 145 000 000 M–1. The presented investigation exemplifies a pathway to bridge the two design approaches and combine their strength in one structural motif as an efficient anion receptor

First Enantioselective Total Synthesis of (+)‑(<i>R</i>)‑Pinnatolide Using an Asymmetric Domino Allylation Reaction

An efficient total synthesis of (+)-(<i>R</i>)-Pinnatolide is described. As a key step an asymmetric multicomponent domino allylation reaction of methyl levulinate is used to form the quaternary stereogenic center in a highly selective way

First Enantioselective Total Synthesis of (+)‑(<i>R</i>)‑Pinnatolide Using an Asymmetric Domino Allylation Reaction

An efficient total synthesis of (+)-(<i>R</i>)-Pinnatolide is described. As a key step an asymmetric multicomponent domino allylation reaction of methyl levulinate is used to form the quaternary stereogenic center in a highly selective way

Reactivity Studies of Heteroleptic Silylenes PhC(N<i>t</i>Bu)₂SiX (X = NPh₂, NMe₂) toward Selected Azides

The reaction of LSiX (L = PhC­(N<i>t</i>Bu)₂, X = NPh₂ (<b>1</b>), NMe₂ (<b>2</b>)) with trimethylsilyl azide (<b>3</b>) resulted in silaimines [LSi­(<i></i>NSiMe₃)­X] (X = NPh₂ (<b>5</b>), NMe₂ (<b>7</b>)). Similarly the reaction of <b>1</b> and <b>2</b> with adamantyl azide (<b>4</b>) yielded [LSi­(<i></i>NAd)­X] (X = NPh₂ (<b>6</b>), NMe₂ (<b>8</b>), Ad = adamantyl) compounds. Silaimines <b>5</b>–<b>8</b> contain tetracoordinate silicon atoms. Compounds <b>6</b> and <b>8</b> are the first tetracoordinate silicon compounds having the terminal SiNAd unit. All compounds were characterized by spectroscopic and spectrometric techniques. The molecular structures of <b>5</b>, <b>6</b>, and <b>8</b> were unequivocally established by single-crystal X-ray structure analysis

Reactivity Studies of Heteroleptic Silylenes PhC(N<i>t</i>Bu)₂SiX (X = NPh₂, NMe₂) toward Selected Azides

The reaction of LSiX (L = PhC­(N<i>t</i>Bu)₂, X = NPh₂ (<b>1</b>), NMe₂ (<b>2</b>)) with trimethylsilyl azide (<b>3</b>) resulted in silaimines [LSi­(<i></i>NSiMe₃)­X] (X = NPh₂ (<b>5</b>), NMe₂ (<b>7</b>)). Similarly the reaction of <b>1</b> and <b>2</b> with adamantyl azide (<b>4</b>) yielded [LSi­(<i></i>NAd)­X] (X = NPh₂ (<b>6</b>), NMe₂ (<b>8</b>), Ad = adamantyl) compounds. Silaimines <b>5</b>–<b>8</b> contain tetracoordinate silicon atoms. Compounds <b>6</b> and <b>8</b> are the first tetracoordinate silicon compounds having the terminal SiNAd unit. All compounds were characterized by spectroscopic and spectrometric techniques. The molecular structures of <b>5</b>, <b>6</b>, and <b>8</b> were unequivocally established by single-crystal X-ray structure analysis

Geometric Complementarity in Assembly and Guest Recognition of a Bent Heteroleptic <i>cis</i>-[Pd₂<b>L</b>^<b>A</b>₂<b>L</b>^<b>B</b>₂] Coordination Cage

Due to the inherent difficulties in achieving a defined and exclusive formation of multicomponent assemblies against entropic predisposition, we present the rational assembly of a heteroleptic [Pd₂<b>L</b>^<b>A</b>₂<b>L</b>^<b>B</b>₂]⁴⁺ coordination cage achieved through the geometric complementarity of two carefully designed ligands, <b>L</b>^<b>A</b> and <b>L</b>^<b>B</b>. With Pd­(II) cations as rigid nodes, the pure distinctly angular components readily form homoleptic cages, a [Pd₂<b>L</b>^<b>A</b>₄]⁴⁺ strained helical assembly and a [Pd₄<b>L</b>^<b>B</b>₈]⁸⁺ box-like structure, both of which were characterized by X-ray analysis. Combined, however, the two ligands could be used to cleanly assemble a <i>cis</i>-[Pd₂<b>L</b>^<b>A</b>₂<b>L</b>^<b>B</b>₂]⁴⁺ cage with a bent architecture. The same self-sorted product was also obtained by a quantitative cage-to-cage transformation upon mixing of the two homoleptic cages revealing the [Pd₂<b>L</b>^<b>A</b>₂<b>L</b>^<b>B</b>₂]⁴⁺ assembly as the thermodynamic minimum. The structure of the heteroleptic cage was examined by ESI-MS, COSY, DOSY, and NOESY methods, the latter of which pointed toward a <i>cis</i>-conformation of ligands in the assembly. Indeed, DFT calculations revealed that the angular ligands and strict Pd­(II) geometry strongly favor the <i>cis</i>-[Pd₂<b>L</b>^<b>A</b>₂<b>L</b>^<b>B</b>₂]⁴⁺ species. The robust nature of the <i>cis</i>-[Pd₂<b>L</b>^<b>A</b>₂<b>L</b>^<b>B</b>₂]⁴⁺ cage allowed us to probe the accessibility of its cavity, which could be utilized for shape recognition toward stereoisomeric guests. The ability to directly combine two different backbones in a controlled manner provides a powerful strategy for increasing complexity in the family of [Pd₂<b>L</b>₄] cages and opens up possibilities of introducing multiple functionalities into a single self-assembled architecture