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991.
1H NMR‐Guided Isolation of Formyl‐Phloroglucinol Meroterpenoids from the Leaves of Eucalyptus robusta
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Zhi‐Chun Shang Dr. Ming‐Hua Yang Kai‐Li Jian Dr. Xiao‐Bing Wang Prof. Dr. Ling‐Yi Kong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11778-11784
Nine formyl‐phloroglucinolmeroterpenoids (FPMs), namely, eucalrobusones A–I ( 1 – 9 ), were isolated from the leaves of Eucalyptus robusta by tracking the phenolic hydroxyl 1H NMR peaks. The Snatzke helicity rules for the Cotton effects of twisted benzene rings were applied to elucidate the absolute configurations of the FPMs. These findings, along with NMR spectroscopy, the circular dichroism (CD) exciton chirality method, and CD calculations, allowed complete structures for the FPMs to be assigned. Eucalrobusones A–F ( 1 – 6 ) are novel adducts formed between a formyl‐derived carbon atom on the phloroglucinol ring and monoterpene and sesquiterpene components. Eucalrobusones G–I ( 7 – 9 ) are the first examples of FPMs with cubebane part structures connected by an unusual 1‐oxaspiro[5.5]undecane subunit. Among these isolates, eucalrobusone C ( 3 ) showed significant cytotoxicity against HepG2, MCF‐7, and U2OS cancer cell lines, with IC50 values less than 10 μm . Compound 3 significantly blocks cell proliferation in MCF‐7 cells and induces MCF‐7 cell death through apoptosis. 相似文献
992.
Yin Gao Abouzar Toubaei Xianqi Kong Gang Wu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(43):11731-11735
Nitroxyl‐iron(II) (HNO‐FeII) complexes are often unstable in aqueous solution, thus making them very difficult to study. Consequently, many fundamental chemical properties of FeII‐bound HNO have remained unknown. Using a comprehensive multinuclear (1H, 15N, 17O) NMR approach, the acidity of the FeII‐bound HNO in [Fe(CN)5(HNO)]3− was investigated and its pKa value was determined to be greater than 11. Additionally, HNO undergoes rapid hydrogen exchange with water in aqueous solution and this exchange process is catalyzed by both acid and base. The hydrogen exchange dynamics for the FeII‐bound HNO have been characterized and the obtained benchmark values, when combined with the literature data on proteins, reveal that the rate of hydrogen exchange for the FeII‐bound HNO in the interior of globin proteins is reduced by a factor of 106. 相似文献
993.
Keun Man SongJong Min Kim Bong Kyun KangChan Soo Shin Chul Gi KoBo Hyun Kong Hyung Koun ChoDae Ho Yoon Hogyoung Kim Sung Min Hwang 《Applied Surface Science》2012,258(8):3565-3570
Nonpolar a-plane GaN layers grown on r-plane sapphire substrates were examined by using a two-step growth process. The higher initial growth pressure for the nucleation layer resulted in the improved crystalline quality with lower density of both threading dislocations and basal stacking faults. This was attributed to the higher degree of initial roughening and recovery time via a growth mode transition from three-dimensional (3D) to quasi two-dimensional (2D) lateral growth. Using Hall-effect measurements, the overgrown Si doped GaN layers grown with higher initial growth pressure were found to have higher mobility. The scattering mechanism due to the dislocations was dominant especially at low temperature (<200 K) for the lower initial growth pressure, which was insignificant for the higher initial growth pressure. The temperature-dependent Hall-effect measurements for the Mg doped GaN with a higher initial growth pressure yielded the activation energy and the acceptor concentration to be 128 meV and 1.2 × 1019 cm−3, respectively, corresponding to about 3.6% of activation at room temperature. Two-step growth scheme with a higher initial growth pressure is suggested as a potential method to improve the performance of nonpolar a-plane GaN based devices. 相似文献
994.
The dynamical properties of one-dimensional random transverse Ising model (RTIM) with a double-Gaussian disorder is investigated by the recursion method. Based on the first twelve recurrences derived analytically, the spin autocorrelation function (SAF) and associated spectral density at high temperature were obtained numerically. Our results indicate that when the standard deviation σg (or OrB) of the exchange couplings Ji (or the random transverse fields Bi) is small, no long-time tail appears in the SAE The spin system undergoes a crossover from a central-peak behavior to a collectivemode behavior, which is the dynamical characteristics of RTIM with the bimodal disorder. However, when σJ (or σB) is large enough, the system exhibits similar dynamics behaviors to those of the RTIM with the Gaussian disorder, i.e., the system exhibits an enhanced central-peak behavior for large σJ or a disordered behavior for large σB. In this instance, SAFs exhibit a similar long-time tail, i.e., C(t) ~ t ^-2 for large t. Similar properties are obtained when Ji (or Bi) satisfy the double-exponential distribution or the double-uniform distribution. Besides, when both the standard deviations and the mean values of the exchange couplings are small, the effects of the Gaussian random bonds may drive the system undergo two crossovers from a triplet state to a doublet state, and then to a collective-mode state. 相似文献
995.
Linlin Kong Esther Amstad Mingtan Hai Xinyou Ke Dong Chen Chun-Xia Zhao David A. Weitz 《中国化学快报》2017,28(9):1897-1900
We use single emulsions as templates to fabricate monodisperse biocompatible microcapsules with a water core. These microcapsules are fabricated using FDA-approved polymer and non-toxic solvents and are of great use in drugs, cosmetics and foods. 相似文献
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在同系物方法测定胶束迁移速度(l/tm c ) 的基础上提出了一种同时求算电渗流速率(l/t0) 的t0 和tm c 的新方法, 该法在选择同系物标记物较为适当时, 可以得到更为准确的结果。同时可以减少由t0 测定而带来的误差。 实验结果表明, 采用甲醇等标记物测定电渗流速率时, 由于其在胶束中的溶解使得实测结果较真值偏大,而由此计算得到的tm c 值偏低。t0 、tm c 皆与缓冲液的种类和浓度有关, 这可能是由于缓冲液组成的变化不仅使得离子强度改变, 也使柱管壁和胶束表面的ξ势发生变化所致。同系物标记物的选择对t0 、tmc 测定精度影响的讨论也为实际分析系统t0 、tmc 的测定和分析分离条件的优化选择提供了必要的理论依据。 相似文献
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Ionics - Manganese phosphate (Mn3(PO4)2·3H2O) nanosheets are successfully fabricated via a facile chemical precipitation method. The Mn3(PO4)2·3H2O nanosheets synthesized at... 相似文献