Negative-ion photoelectron spectroscopy and ab initio simulations are used to study the variation in magnetic structure in Mn(x)O(y) (x = 3, 4[semicolon] y = 1, 2) clusters. The ferrimagnetic and antiferromagnetic ground-state structures of Mn(x)O(y) are 0.16-1.20 eV lower in energy than their ferromagnetic isomers. The presence of oxygen thus stabilizes low-spin isomers relative to the preferred high-spin ordering of bare Mn(3) and Mn(4). Each cluster has a preferred overall magnetic moment, and no evidence is seen of competing states with different spin multiplicities. However, non-degenerate isomags, which possess the same spin multiplicity but different arrangements of local moments, do contribute additional features and peak broadening in the photoelectron spectra. Proper accounting for all possible isomags is shown to be critical for accurate computational prediction of the spectra. 相似文献
A practical convenient conversion of oxindoles into the corresponding spirocyclopropyl oxindoles is achieved efficiently using bromoethylsulfonium salt, which is easily prepared on a large scale and is stable crystalline. This reaction of bromoethylsulfonium salt with different substituted unprotected oxindoles proceeded under mild condition and provided moderate yields. 相似文献
Using a layer‐multiplying coextrusion process to fabricate films with thousands of alternating polymer nanolayers, we report here a new crystalline morphology in confined polymer nanolayers and an abrupt transition in the crystallization habit. At higher temperatures, poly(ethylene oxide) crystallizes as large, in‐plane lamellae. A 5 °C change in the crystallization temperature produces an on‐edge lamellar orientation. The results point to a transition from heterogeneous nucleation to substrate‐assisted nucleation. This may be a general phenomenon that accounts for previously unexplained differences in the preferred chain alignment of confined polymer crystals.
A highly regioselective intramolecular cyclization of lapachol mediated by Lewis acids including NbCl5, AlCl3, and FeCl3 was developed for synthesizing β-lapachone in excellent yields without any formation of the isomer α-lapachone. This procedure was efficient, mild, and easily scalable that avoided using highly hazardous concd H2SO4. In the case of ZrCl4 the cyclization was found to give α-lapachone as the main product. A possible mechanism for the Lewis acid mediated cyclization was also discussed. 相似文献
Gambogic acid (GA, 1 ), the most prominent representative of Garcinia natural products, has been reported to be a promising anti‐tumor agent. In order to further explore the structure‐activity relationship of GA and discover novel GA derivatives as anti‐tumor agents, 17 novel C‐37 modified derivatives of GA were synthesized and evaluated for their in vitro anti‐tumor activities against A549, HCT‐116, BGC‐823, HepG2 and MCF‐7 cancer cell lines. Among them, 11 compounds were found to be more potent than GA against some cancer cell lines. Notably, compound 8 was almost 5–10 folds more active than GA against A549 and BGC‐823 cell lines with the IC50 values of 0.12 µmol·L?1 and 0.57 µmol·L?1, respectively. Chemical modification at C‐37 position of GA by introducing of hydrophilic amines could lead to increased activity and improved drug‐like properties. These findings will enhance our understanding of the structure‐activity relationship (SAR) of GA and lead to the discovery of novel GA derivatives as potential anti‐tumor agents. 相似文献
Inspired by the therapeutic potential of the simplified caged xanthones, we have developed a chemical strategy for synthesizing novel aza-caged Garcinia analogues through a regioselective Claisen/Diels-Alder cascade reaction. The origin of regioselectivity has been explained using the DFT method. We have further evaluated the cell proliferation and IKKβ inhibitory activities of these compounds and studied their binding mode with IKKβ by molecular docking. The results suggested that the aza-caged scaffold provides a suitable modification site and the introduction of a hydrophobic moiety leads to improvement in the cytotoxicity and IKKβ inhibitory activity. The aza-caged compound 6c exhibited an IC(50) value of 2.68, 2.10, 8.02 μM against the HepG2, A549 cells and IKKβ, respectively. Mechanism studies with 6c showed that the aza-caged compounds induce apoptosis and cell cycle S phase arrest in A549 cells. 相似文献