Antimicrobial activity-guided identification of compounds from the deciduous leaves of Malus doumeri by HPLC-ESI-QTOF-MS/MS

This paper intends to identify the antimicrobial activity compounds from the deciduous leaves of Malus doumeri (Dong Li Tea) by HPLC-ESI-QTOF-MS/MS. The ethanol extracts of Malus doumeri were partitioned into petroleum ether, dichloromethane, ethyl acetate, n-butanol and water fraction, respectively. The antimicrobial screening experiments showed that ethyl acetate fraction has a certain antibacterial activity by inhibition zone method in vitro. And then we used the HPLC-ESI-QTOF-MS/MS method to verify the identities of bioactive compounds. Finally, 41 compounds were determined and 11 of which were firstly reported in this plant. Notably, compounds (32, 34, 38) are new dihydrochalcones, and three chlorogenic acid analogues (10, 13, 17) may be potential antimicrobial active ingredient. Which is of great significance to the isolation of novel compounds and the discovery of new natural preservative candidates from the deciduous leaves of Malus doumeri.     

Heterocyclization Strategy for Construction of Linear Conjugated Polymers: Efficient Metal‐Free Electrocatalysts for Oxygen Reduction

Exploring cost‐effective and efficient metal‐free electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the development of energy conversion and storage technologies. Reported here is a novel heterocyclization strategy to construct efficient ORR catalysts based on linear conjugated polymers (LCPs), which are composed of N‐, S‐, or Se‐heterocycles. Among these polymers, the covalently linked pyridine and thiophene molecule ( P‐T ) with reduced graphene oxide (rGO) exhibits a remarkable half‐wave potential of 0.79 V (vs. RHE) and excellent electrochemical stability, which are among the highest values for metal‐free polymers as ORR catalysts. Density‐functional theory (DFT) calculations reveal that the molecule with a phenyl unit ( P‐Ph ) is catalytically inactive, and when a thiophene unit is introduced to replace the phenyl unit in the conjugated backbone it features highly efficient electrocatalytic active sites. More importantly, the well‐defined molecular structures and controllable active sites in the pyrolysis and metal‐free polymers highlight new opportunities for the catalytic metal‐free ORR.     

Involvement of excited triplet state in the photodissociation of cyclobutane

The potential energy curves (PECs) of the ground state and the low‐lying excited states for the photodissociation of cyclobutane have been calculated at the multi‐reference configuration interaction with singlet and doublet excitation (MRCISD) and the multi‐reference second order perturbation theory (MRPT2). Firstly, the PECs are constructed following a reaction path determined by semiclassical dynamics simulation, which suggests that the lowest triplet state of tetramethylene is involved in the photodissociation of cyclobutane. Then, the adiabatic PECs are calculated for the breaking processes of C1? C3 and C2? C4 bond respectively. The singlet‐triplet PECs' intersections have been found in the two breaking C? C bond processes. During the breaking process of the second C2? C4 bond, a local minimum has been found on the PEC of the lowest triplet state, which gives us some insight to reinterpret the experimental observed diradical intermediate as being trapped in its triplet state. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

自由单元法及其在结构分析中的应用

通过吸收有限元与无网格法的优点,提出了一种新的数值方法------自由单元法.此方法在离散方面,采用有限元法中的等参单元,表征几何形状和进行物理量的插值;在算法方面,采用单元配点技术,逐点产生系统方程.主要特点是,在每个配置点只需要一个和周围自由选择的节点而形成的一个独立的等参单元,因而不需要考虑物理量在单元之间的相互连接关系与导数连续性问题. 本文介绍强形式与弱形式两种自由单元法,前者直接由控制方程和边界条件直接产生系统方程,后者通过在自由单元上建立控制方程的加权余量式产生弱形式积分式,并通过像传统有限元法中的积分过程建立系统方程组.本文提出的方法是一种单元配点法,对于域内点为了获得较高的导数精度,需要采用至少具有一个内部点的等参单元,为此除了可使用各阶次的拉格朗日四边形单元外, 还 给出了七节点三角形等参单元,用于模拟较为复杂的几何形状问题.      

Aldo‐X Bifunctional Building Blocks for the Synthesis of Heterocycles

Compounds containing oxygen, nitrogen, or sulfur atoms inside the rings are attracting much attention and interest due to their biological importance. In recent years, several methods for the synthesis of such molecules have been reported by using aldo‐X bifunctional building blocks (AXB3 s) as substrates; these are a wide class of organic molecules that contain at least two reactive sites, among them, one aldehyde, acetal, or semiacetal group was involved. Because of the multiple reactivities, AXB3 s are widely used in the one‐pot synthesis of biologically important heterocycles. This review summarizes the synthesis of important heterocycles by using AXB3 s as pivotal components in establishing multicomponent reactions, tandem reactions, and so forth. In many cases, the established reaction systems with AXB3 s were characterized by some green properties, such as easy access to the substrate, mild and environmentally benign conditions, and wide scope of the substrate.     

Synthesis of the molecular hybrid inspired by Largazole and Psammaplin A

One important class of HDAC (histone deacetylation enzymes) inhibitors is the sulfur-containing marine natural products with structural diversity. Inspired by two structurally distinguishing examples, Largazole and Psammaplin A, which possess macrocyclic depsipeptide and simple linear amide scaffold respectively, we designed one novel molecular hybrid by replacing the alkene moiety in Largazole with a semirigid amide bond. This hybrid compound has been synthesized from l-malic acid in 10 steps with an overall yield of 7%. The preliminary biological assays suggest that the replacement of trans olefin moiety with amide bond will lead to an unbeneficial effect on the inhibition against HDACs.     

Designing Silicates as Deep-UV Nonlinear Optical (NLO) Materials using Edge-Sharing Tetrahedra

Discovering new deep-ultraviolet (DUV) nonlinear optical (NLO) materials is currently a great challenge. The reported DUV NLO materials are almost exclusively borates or phosphates. Silicates—the largest constituent of the earth's crust—are excluded owing to their weak second harmonic generation (SHG) response. We report a silicate, Li₂BaSiO₄, with edge-sharing LiO₄–SiO₄ tetrahedra that achieves the balance between a short UV absorption edge, below 190 nm, and a large SHG response, 2.8×KDP. The SHG intensity is the largest for silicates without second-order Jahn–Teller cations, and exceeds that of non-isomorphic Li₂SrSiO₄ by more than an order of magnitude. As such Li₂BaSiO₄ may be seen as a promising DUV-UV NLO material. This research indicates that edge-sharing tetrahedra is a new design parameter for discovering new DUV NLO materials.