RESUMO
The intramolecular addition of both an alkoxy and acyl substituent across an alkene, oxyacylation of alkenes, using rhodium catalyzed C-O bond activation of an 8-quinolinyl ester is described. Our unsuccessful attempts at intramolecular carboacylation of ketones via C-C bond activation ultimately informed our choice to pursue and develop the intramolecular oxyacylation of alkenes via quinoline-directed C-O bond activation. We provide a full account of our catalyst discovery, substrate scope, and mechanistic experiments for quinoline-directed alkene oxyacylation.
RESUMO
Alkene oxyacylation is a new strategy for the preparation of ß-oxygenated ketones. Now, with Ir catalysis and low-cost salicylate esters, alkene oxyacylation can be promoted by simple and versatile hydroxyl directing groups. This paper discusses catalyst optimization, substituent effects, mechanistic experiments, and the challenges associated with asymmetric catalysis. Crossover experiments point to several key steps of the mechanism being reversible, including the most likely enantiodetermining steps. The oxyacylation products are also prone to racemization without catalyst when heated alone; however, crossover is not observed without catalyst. These observations account for the low levels of enantioinduction in alkene oxyacylation. The versatility of the hydroxyl directing group is highlighted by demonstrating further transformations of the products.
RESUMO
We propose here an electrochemical platform for multi-heavy metal ion detection in water based on MIL-88B(Fe)-NH2, an amine-functioned metal-organic framework (MOF) for modifying the surface of a glassy carbon electrode (GCE). Herein, MIL-88B(Fe)-NH2 with abundant functionalized amine groups can play the role of capture sites for the enrichment of metal ions before electrochemical oxidation sensing. MIL-88B(Fe)-NH2 was synthesized under optimized conditions through a solvothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. MIL-88B(Fe)-NH2 was then drop-casted on GCE to electrochemically determine the Cd2+, Pb2+ and Cu2+ ion concentrations by differential pulse voltammetry (DPV). The electrochemical sensor exhibits excellent electrochemical performance toward Cd2+, Pb2+ and Cu2+ ions in the large linear ranges of 0.025-1.000 µM, 0.3-10.0 µM and 0.6-10.0 µM with limits of detection that are 2.0 × 10-10 M, 1.92 × 10-7 M and 3.81 × 10-7 M, respectively. The fabricated sensor also shows high reliability and good selectivity. This MIL-88B(Fe)-NH2 application strategy is promising for the evaluation of various heavy metal ions in water.
RESUMO
In this review, we report on the recent developments made using both genetics and functional genomics approaches in the discovery of genes controlling root development in rice. QTL detection in classical biparental mapping populations initially enabled the identification of a very large number of large chromosomal segments carrying root genes. Two segments with large effects have been positionally cloned, allowing the identification of two major genes. One of these genes conferred a tolerance to low phosphate content in soil, while the other conferred a tolerance to drought by controlling root gravitropism, resulting in root system expansion deep in the soil. Findings based on the higher-resolution QTL detection offered by the development of association mapping are discussed. In parallel with genetics approaches, efforts have been made to screen mutant libraries for lines presenting alterations in root development, allowing for the identification of several genes that control different steps of root development, such as crown root and lateral root initiation and emergence, meristem patterning, and the control of root growth. Some of these genes are closely phylogenetically related to Arabidopsis genes involved in the control of lateral root initiation. This close relationship stresses the conservation among plant species of an auxin responsive core gene regulatory network involved in the control of post-embryonic root initiation. In addition, we report on several genetic regulatory pathways that have been described only in rice. The complementarities and the expected convergence of the direct and reverse genetic approaches used to decipher the genetic determinants of root development in rice are discussed in regards to the high diversity characterizing this species and to the adaptations of rice root system architecture to different edaphic environments.