黄酮类抗氧化剂的构-效关系

天然黄酮是广泛存在于自然界的酚类抗氧化剂之一,其抗氧化活性与清除自由基的能力密切相关.综述了几种研究抗氧化剂活性中常用的自由基检测方法与评价指标,并详细分析了结构因素影响黄酮类化合物抗氧化活性的机制与规律.认为黄酮类化合物的抗氧化活性主要取决于羟基的相对位置而非数目,具有色原酮结构的黄酮2-3位上不饱和双键也会在一定程度上增强其抗氧化活性,C环吸电子性质或羟基成甙则会使天然黄酮抗氧化能力降低,与金属离子的络合也是黄酮阻止自由基氧化的途径之一.对黄酮类抗氧化剂构-效关系的研究为筛选高效抗氧化剂和天然黄酮的结构修饰提供了理论依据.     

黄酮类化合物的结构-抗氧化活性关系研究进展

黄酮类化合物是一类在自然界广泛分布的多酚类抗氧化剂．由于其具有多种生物活性和药理作用，已引起了人们广泛的兴趣．笔者综述了黄酮类化合物的结构特征、生物特性。重点讨论了它的抗氧化、清除自由基的作用和其化学结构的关系．黄酮类化合物构效关系的研究对寻找高效、廉价、低毒的抗氧化剂是十分必要的手段．     

黄酮类化合物的结构—抗氧化活性关系研究进展

黄酮类化合物是一类在自然界广泛分布的多酚类抗氧化剂.由于其具有多种生物活性和药理作用,已引起了人们广泛的兴趣.笔者综述了黄酮类化合物的结构特征、生物特性,重点讨论了它的抗氧化、清除自由基的作用和其化学结构的关系.黄酮类化合物构效关系的研究对寻找高效、廉价、低毒的抗氧化剂是十分必要的手段.     

几种玉米须黄酮分子结构性质及抗氧化活性的量子化学研究

采用理论计算化学手段结合分子动力学与量子化学方法,对玉米须相关的几种黄酮类化合物槲皮素、木犀草素、芹菜素分子结构和活性进行了理论计算.从几何结构、自由基稳定性、前线轨道能等角度分析了影响黄酮类化合物抗氧化活性的因素.在分子层面上探讨了玉米须黄酮的抗氧化作用机理,预测的黄酮类化合物的抗氧化活性与实验结果一致.     

荧光光谱法研究黄酮类化合物与核酸相互作用的进展

近年来药物小分子与DNA相互作用的研究引起广泛关注并取得了重要进展.其中黄酮类化合物在自然界尤其是植物中大量存在,具有广泛的生物学作用,包括抗肿瘤、抗氧化、抗突变、抗炎症、抗菌等活性,且其结构有利于配合物的形成,亦可作为金属离子的良好配体.探讨黄酮类化合物及其金属配合物与核酸相互作用的研究进展,为开发黄酮类抗癌新药提供一些有用信息.     

天然黄酮类化合物清除自由基机理及其应用进展

黄酮类化合物在植物资源中具有广泛的分布,其清除自由基作用使其可用作天然抗氧剂.介绍了机体内自由基形成以及抗氧剂清除自由基的机理,讨论了黄酮化合物的化学结构特征和其清除自由基的构效关系.在应用方面,天然黄酮化合物具有广谱的清除自由基药理作用,还可用在食品的抗氧化领域和化妆品的清除自由基、紫外吸收等方面.     

类黄酮类化合物电化学研究现状

类黄酮类化合物是一类天然存在并具有抗氧化性的物质 ,由于其潜在的药用价值 ,对其研究引起了人们极大的兴趣 .本文从电化学角度综述了类黄酮类化合物抗氧化活性、抗癌作用的电化学表征及其与结构之间的关系、电化学还原及其与结构之间的关系等方面的研究进展     

抗氧剂抗氧化活性研究进展

有机体的多种疾病都与自由基对机体的氧化损伤有关,而抗氧剂具有很强的抗氧化活性和清除自由基的能力,保护机体细胞免受自由基的攻击,因此引起广泛关注并被应用于食品技术和医药学领域．抗氧剂分为内源性抗氧剂和外源性抗氧剂两类,内源性抗氧剂包括超氧化物歧化酶、谷胱甘肽过氧化物酶和过氧化氢酶等,外源性抗氧剂包括抗坏血酸、黄酮类化合物以及酚类化合物等．对上述抗氧剂抗氧化作用机理研究现状进行了综述．     

黄酮类化合物抗氧化活性理论研究

运用密度泛函理论(DFT)B3LYP方法对柯因、高良姜素、山奈酚、桑色素、槲皮素及杨梅酮这6种典型黄酮类化合物进行结构优化及单点能计算,来研究这6种化合物的抗氧化活性.本文从化合物失去最大可能活性位H原子形成半醌式自由基前后的生成热之差(⊿HOF)、失去酚羟基H原子形成的自由基的原子自旋密度、化合物分子中酚羟基数目及形成的半醌式自由基中可形成氢键数目3个方面进行分析.发现这6种黄酮类化合物的抗氧化活性顺序为:杨梅酮>槲皮素>桑色素>山奈酚>高良姜素>柯因.此外,还探讨了化合物的几何构型及最高占据轨道与抗氧化活性间是否存在关联,结果表明它们之间无相关性.     

植物黄酮类化合物功能的研究进展

黄酮类化合物广泛存在于蔬菜、水果、牧草和药用植物中,是植物在长期自然选择过程中产生的一些次级代谢产物,以游离态或与糖结合为苷的形式存在,它们不仅数量、种类繁多,而且结构类型复杂多样。大量现代研究证明,黄酮类化合物能防治呼吸系统的疾病,防治血管硬化,具有清除自由基,降低血糖,抗氧化,抗突变,抗癌,抗肿瘤以及     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

正~~     

An on-line scaling method for improving scalability of a database cluster

The explosive growth of the Internet and database applications has driven database to be more scalable and available, and able to support on-line scaling without interrupting service. To support more client's queries without downtime and degrading the response time, more nodes have to be scaled up while the database is running. This paper presents the overview of scalable and available database that satisfies the above characteristics. And we propose a novel on-line scaling method. Our method improves the existing on-line scaling method for fast response time and higher throughputs. Our proposed method reduces unnecessary network use, i.e. , we decrease the number of data copy by reusing the backup data. Also, our on-line scaling operation can be processed parallel by selecting adequate nodes as new node. Our performance study shows that our method results in significant reduction in data copy time.     

An improved R-tree based on childnode''s probability

R-Tree is a good structure for spatial searching. But in this indexing structure,either the sequence of nodes in the same level or sequence of traveling these nodes when queries are made is random. Since the possibility that the object appears in different MBR which have the same parents node is different, if we make the subnode who has the most possibility be traveled first, the time cost will be decreased in most of the cases. In some case, the possibility of a point belong to a rectangle will shows direct proportion with the size of the rectangle. But this conclusion is based on an assumption that the objects are symmetrically distributing in the area and this assumption is not always coming into existence. Now we found a more direct parameter to scale the possibility and made a little change on the structure of R-tree, to increase the possibility of founding the satisfying answer in the front sub trees. We names this structure probability based arranged R-tree (PBAR-tree).     

Integrating GIS Web services based on mediating architecture

The geographic information service is enabled by the advancements in general Web service technology and the focused efforts of the OGC in defining XML-based Web GIS service. Based on these models, this paper addresses the issue of services chaining,the process of combining or pipelining results from several interoperable GIS Web Services to create a customized solution. This paper presents a mediated chaining architecture in which a specific service takes responsibility for performing the process that describes a service chain. We designed the Spatial Information Process Language (SIPL) for dynamic modeling and describing the service chain, also a prototype of the Spatial Information Process Execution Engine (SIPEE) is implemented for executing processes written in SIPL. Discussion of measures to improve the functionality and performance of such system will be included.